Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Wednesday, December 5, 2018 at 9:46:08 PM UTC, Bruce wrote:
>
> On Wed, Dec 5, 2018 at 11:01 PM > wrote:
>
>> On Wednesday, December 5, 2018 at 5:39:43 AM UTC, Bruce wrote:
>>>
>>> On Wed, Dec 5, 2018 at 3:53 PM Philip Thrift  wrote:
>>>
 On Tuesday, December 4, 2018 at 10:28:39 PM UTC-6, Philip Thrift wrote:
>
> On Tuesday, December 4, 2018 at 3:45:32 PM UTC-6, Bruce wrote:
>>
>> On Wed, Dec 5, 2018 at 6:58 AM Philip Thrift  
>> wrote:
>>
>>>
>>> On Tuesday, December 4, 2018 at 1:53:15 PM UTC-6, Brent wrote:


 On 12/4/2018 12:25 AM, Philip Thrift wrote:


 1. Histories originate at an emitter e and end at screen locations 
 s on a screen S.
 2. At each s there is a history bundle histories(s). A weight w(s) 
 is computed from the bundle by summing the unit complex numbers of the 
 histories and taking the modulus. 
 3. The weight w(s) is sent back in time over a single history h*(s) 
 selected at random (uniformly) from histories(s).
 4. At e, the weights w(s) on backchannel of h*(s) are received (in 
 the "present" time)
 5. A single history h*(s*) is then selected from the distribution 
 in 4.


 How is it selected?  Above you said "at random".  But that implies 
 there is already a probability measure defined on the histories.  How 
 is 
 this probability measure determined?  Or put another way how do you 
 determine what histories to consider to form the bundles in step 2?

 Brent

>>>
>>> Selection happens via quantum Darwinism. 
>>>
>>
>>
>> Do you have even the faintest understanding of Quantum Darwinism?
>>
>> Bruce 
>>
>
> How is *sum over histories with Darwinian selection*  (as defined) 
> not quantum Darwinism?
>
> Operationally, what is different?
>
> - pt
>

 *Sum over histories with Darwinian selection* is consistent with *Quantum 
 Darwinism as a Darwinian process*  [ https://arxiv.org/abs/1001.0745 ].

>>>
>>> No, you clearly don't understand Quantum Darwinism! Zurek's Darwinism is 
>>> selection of pointer states, not one history from a bundle.
>>>
>>> Bruce
>>>
>>
>> Wiki isn't clear in its definition of pointer states. WRT the double slit 
>> experiment, would it be correct to say the impacts with very high 
>> probability are "pointer states" and those with a low or zero probability 
>> are respectively less, or not at all pointer states? TIA, AG 
>>
>
> No. Pointer states are those corresponding to the basis that is stable 
> against environmental decoherence. In the double slit experiment, the 
> pointer states are positions on the screen -- some are occupied and some 
> not, but that is not a distinction that is relevant to the formation of the 
> pointer states.
>
> Bruce
>

An illustrative example might suffice to explain the concept; what are the 
pointer states for the double slit experiment? AG 

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Re: Measuring a system in a superposition of states vs in a mixed state

[Bruce Kellett]

On Wed, Dec 5, 2018 at 11:01 PM  wrote:

> On Wednesday, December 5, 2018 at 5:39:43 AM UTC, Bruce wrote:
>>
>> On Wed, Dec 5, 2018 at 3:53 PM Philip Thrift  wrote:
>>
>>> On Tuesday, December 4, 2018 at 10:28:39 PM UTC-6, Philip Thrift wrote:

 On Tuesday, December 4, 2018 at 3:45:32 PM UTC-6, Bruce wrote:
>
> On Wed, Dec 5, 2018 at 6:58 AM Philip Thrift 
> wrote:
>
>>
>> On Tuesday, December 4, 2018 at 1:53:15 PM UTC-6, Brent wrote:
>>>
>>>
>>> On 12/4/2018 12:25 AM, Philip Thrift wrote:
>>>
>>>
>>> 1. Histories originate at an emitter e and end at screen locations s
>>> on a screen S.
>>> 2. At each s there is a history bundle histories(s). A weight w(s)
>>> is computed from the bundle by summing the unit complex numbers of the
>>> histories and taking the modulus.
>>> 3. The weight w(s) is sent back in time over a single history h*(s)
>>> selected at random (uniformly) from histories(s).
>>> 4. At e, the weights w(s) on backchannel of h*(s) are received (in
>>> the "present" time)
>>> 5. A single history h*(s*) is then selected from the distribution in
>>> 4.
>>>
>>>
>>> How is it selected?  Above you said "at random".  But that implies
>>> there is already a probability measure defined on the histories.  How is
>>> this probability measure determined?  Or put another way how do you
>>> determine what histories to consider to form the bundles in step 2?
>>>
>>> Brent
>>>
>>
>> Selection happens via quantum Darwinism.
>>
>
>
> Do you have even the faintest understanding of Quantum Darwinism?
>
> Bruce
>

 How is *sum over histories with Darwinian selection*  (as defined) not
 quantum Darwinism?

 Operationally, what is different?

 - pt

>>>
>>> *Sum over histories with Darwinian selection* is consistent with *Quantum
>>> Darwinism as a Darwinian process*  [ https://arxiv.org/abs/1001.0745 ].
>>>
>>
>> No, you clearly don't understand Quantum Darwinism! Zurek's Darwinism is
>> selection of pointer states, not one history from a bundle.
>>
>> Bruce
>>
>
> Wiki isn't clear in its definition of pointer states. WRT the double slit
> experiment, would it be correct to say the impacts with very high
> probability are "pointer states" and those with a low or zero probability
> are respectively less, or not at all pointer states? TIA, AG
>

No. Pointer states are those corresponding to the basis that is stable
against environmental decoherence. In the double slit experiment, the
pointer states are positions on the screen -- some are occupied and some
not, but that is not a distinction that is relevant to the formation of the
pointer states.

Bruce

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Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Wednesday, December 5, 2018 at 5:39:43 AM UTC, Bruce wrote:
>
> On Wed, Dec 5, 2018 at 3:53 PM Philip Thrift  > wrote:
>
>> On Tuesday, December 4, 2018 at 10:28:39 PM UTC-6, Philip Thrift wrote:
>>>
>>> On Tuesday, December 4, 2018 at 3:45:32 PM UTC-6, Bruce wrote:

 On Wed, Dec 5, 2018 at 6:58 AM Philip Thrift  
 wrote:

>
> On Tuesday, December 4, 2018 at 1:53:15 PM UTC-6, Brent wrote:
>>
>>
>> On 12/4/2018 12:25 AM, Philip Thrift wrote:
>>
>>
>> 1. Histories originate at an emitter e and end at screen locations s 
>> on a screen S.
>> 2. At each s there is a history bundle histories(s). A weight w(s) is 
>> computed from the bundle by summing the unit complex numbers of the 
>> histories and taking the modulus. 
>> 3. The weight w(s) is sent back in time over a single history h*(s) 
>> selected at random (uniformly) from histories(s).
>> 4. At e, the weights w(s) on backchannel of h*(s) are received (in 
>> the "present" time)
>> 5. A single history h*(s*) is then selected from the distribution in 
>> 4.
>>
>>
>> How is it selected?  Above you said "at random".  But that implies 
>> there is already a probability measure defined on the histories.  How is 
>> this probability measure determined?  Or put another way how do you 
>> determine what histories to consider to form the bundles in step 2?
>>
>> Brent
>>
>
> Selection happens via quantum Darwinism. 
>


 Do you have even the faintest understanding of Quantum Darwinism?

 Bruce 

>>>
>>> How is *sum over histories with Darwinian selection*  (as defined) not 
>>> quantum Darwinism?
>>>
>>> Operationally, what is different?
>>>
>>> - pt
>>>
>>
>> *Sum over histories with Darwinian selection* is consistent with *Quantum 
>> Darwinism as a Darwinian process*  [ https://arxiv.org/abs/1001.0745 ].
>>
>
> No, you clearly don't understand Quantum Darwinism! Zurek's Darwinism is 
> selection of pointer states, not one history from a bundle.
>
> Bruce
>

Wiki isn't clear in its definition of pointer states. WRT the double slit 
experiment, would it be correct to say the impacts with very high 
probability are "pointer states" and those with a low or zero probability 
are respectively less, or not at all pointer states? TIA, AG 

>  
>

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Re: Measuring a system in a superposition of states vs in a mixed state

[Philip Thrift]

On Wednesday, December 5, 2018 at 1:55:22 AM UTC-6, Bruce wrote:
>
> On Wed, Dec 5, 2018 at 6:08 PM Philip Thrift  > wrote:
>
>>
>>> As has been pointed out, path integrals are a calculational tool, not an 
>>> interpretation.
>>>
>>
>>
>> Oh,* that* again. It's like Groundhog Day (the movie).
>>
>
> Given your repetitive harping on half-baked path integral ideas, I thought 
> repetition was the way forward. 
>
> Bruce
>
>

Just harping on the misguided Platonism of belief in the wave function. 

- pt

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Re: Measuring a system in a superposition of states vs in a mixed state

[Bruce Kellett]

On Wed, Dec 5, 2018 at 6:08 PM Philip Thrift  wrote:

> On Wednesday, December 5, 2018 at 12:53:45 AM UTC-6, Bruce wrote:
>>
>> On Wed, Dec 5, 2018 at 5:43 PM Philip Thrift  wrote:
>>
>>> On Wednesday, December 5, 2018 at 12:28:19 AM UTC-6, Bruce wrote:

 On Wed, Dec 5, 2018 at 5:19 PM Philip Thrift 
 wrote:

> On Wednesday, December 5, 2018 at 12:00:18 AM UTC-6, Bruce wrote:
>>
>> On Wed, Dec 5, 2018 at 4:51 PM Philip Thrift 
>> wrote:
>>
>>> On Tuesday, December 4, 2018 at 11:39:43 PM UTC-6, Bruce wrote:

 On Wed, Dec 5, 2018 at 3:53 PM Philip Thrift 
 wrote:

> On Tuesday, December 4, 2018 at 10:28:39 PM UTC-6, Philip Thrift
> wrote:
>>
>> On Tuesday, December 4, 2018 at 3:45:32 PM UTC-6, Bruce wrote:
>>>
>>> On Wed, Dec 5, 2018 at 6:58 AM Philip Thrift 
>>> wrote:
>>>

 On Tuesday, December 4, 2018 at 1:53:15 PM UTC-6, Brent wrote:
>
>
> On 12/4/2018 12:25 AM, Philip Thrift wrote:
>
>
> 1. Histories originate at an emitter e and end at screen
> locations s on a screen S.
> 2. At each s there is a history bundle histories(s). A weight
> w(s) is computed from the bundle by summing the unit complex 
> numbers of the
> histories and taking the modulus.
> 3. The weight w(s) is sent back in time over a single history
> h*(s) selected at random (uniformly) from histories(s).
> 4. At e, the weights w(s) on backchannel of h*(s) are received
> (in the "present" time)
> 5. A single history h*(s*) is then selected from the
> distribution in 4.
>
>
> How is it selected?  Above you said "at random".  But that
> implies there is already a probability measure defined on the 
> histories.
> How is this probability measure determined?  Or put another way 
> how do you
> determine what histories to consider to form the bundles in step 
> 2?
>
> Brent
>

 Selection happens via quantum Darwinism.

>>>
>>>
>>> Do you have even the faintest understanding of Quantum Darwinism?
>>>
>>> Bruce
>>>
>>
>> How is *sum over histories with Darwinian selection*  (as
>> defined) not quantum Darwinism?
>>
>> Operationally, what is different?
>>
>> - pt
>>
>
> *Sum over histories with Darwinian selection* is consistent with 
> *Quantum
> Darwinism as a Darwinian process*  [
> https://arxiv.org/abs/1001.0745 ].
>

 No, you clearly don't understand Quantum Darwinism! Zurek's
 Darwinism is selection of pointer states, not one history from a 
 bundle.

 Bruce

>>>
>>>  Histories are (hidden) states.
>>>
>>
>> It becomes obvious that you don't really understand consistent
>> histories, either.
>>
>> Bruce
>>
>
> I've never once mentioned *consistent histories*, only *sum over
> histories*.
>

 Inconsistent histories?


> (Did you watch the lecture by Fay Dowker?)
>

 No, I don't watch utube videos.

 Pointer states [ https://arxiv.org/abs/1508.04101 ] can best be
> understood as related to histories via the *Reflective Path Integral*
> interpretation of the EPR experiment.
>

 Your arxiv references do not support your case. Reverse causation, as
 it seems to be required in your account, is simply a nonsense. Huw Price
 lost the plot a long time ago.

 There is no competition between the different paths between the initial
 and final state -- which is what is used to calculate probabilities in the
 path integral approach. So there is no Darwinian (or other) selection of
 one such path over others. Quantum Darwinism is about something quite
 different. Even Wikipedia agrees! Read Zurek's papers on this.

 Bruce

>>>
>>>
>>> OK. As Kay Dowker stated in her presentation: The path integral
>>> interpretation is still under development.
>>>
>>
>> As has been pointed out, path integrals are a calculational tool, not an
>> interpretation.
>>
>
>
> Oh,* that* again. It's like Groundhog Day (the movie).
>

Given your repetitive harping on half-baked path integral ideas, I thought
repetition was the way forward.

Bruce



>> My (retrocausal) version of Darwinian selection w.r.t. multiple histories
>>>  *is* *the next
>>> development.*
>>>
>>
>> I see, it is not actually a coherent proposition at the 

Re: Measuring a system in a superposition of states vs in a mixed state

[Philip Thrift]

On Wednesday, December 5, 2018 at 12:53:45 AM UTC-6, Bruce wrote:
>
> On Wed, Dec 5, 2018 at 5:43 PM Philip Thrift  > wrote:
>
>> On Wednesday, December 5, 2018 at 12:28:19 AM UTC-6, Bruce wrote:
>>>
>>> On Wed, Dec 5, 2018 at 5:19 PM Philip Thrift  wrote:
>>>
 On Wednesday, December 5, 2018 at 12:00:18 AM UTC-6, Bruce wrote:
>
> On Wed, Dec 5, 2018 at 4:51 PM Philip Thrift  
> wrote:
>
>> On Tuesday, December 4, 2018 at 11:39:43 PM UTC-6, Bruce wrote:
>>>
>>> On Wed, Dec 5, 2018 at 3:53 PM Philip Thrift  
>>> wrote:
>>>
 On Tuesday, December 4, 2018 at 10:28:39 PM UTC-6, Philip Thrift 
 wrote:
>
> On Tuesday, December 4, 2018 at 3:45:32 PM UTC-6, Bruce wrote:
>>
>> On Wed, Dec 5, 2018 at 6:58 AM Philip Thrift  
>> wrote:
>>
>>>
>>> On Tuesday, December 4, 2018 at 1:53:15 PM UTC-6, Brent wrote:


 On 12/4/2018 12:25 AM, Philip Thrift wrote:


 1. Histories originate at an emitter e and end at screen 
 locations s on a screen S.
 2. At each s there is a history bundle histories(s). A weight 
 w(s) is computed from the bundle by summing the unit complex 
 numbers of the 
 histories and taking the modulus. 
 3. The weight w(s) is sent back in time over a single history 
 h*(s) selected at random (uniformly) from histories(s).
 4. At e, the weights w(s) on backchannel of h*(s) are received 
 (in the "present" time)
 5. A single history h*(s*) is then selected from the 
 distribution in 4.


 How is it selected?  Above you said "at random".  But that 
 implies there is already a probability measure defined on the 
 histories.  
 How is this probability measure determined?  Or put another way 
 how do you 
 determine what histories to consider to form the bundles in step 2?

 Brent

>>>
>>> Selection happens via quantum Darwinism. 
>>>
>>
>>
>> Do you have even the faintest understanding of Quantum Darwinism?
>>
>> Bruce 
>>
>
> How is *sum over histories with Darwinian selection*  (as 
> defined) not quantum Darwinism?
>
> Operationally, what is different?
>
> - pt
>

 *Sum over histories with Darwinian selection* is consistent with 
 *Quantum 
 Darwinism as a Darwinian process*  [ 
 https://arxiv.org/abs/1001.0745 ].

>>>
>>> No, you clearly don't understand Quantum Darwinism! Zurek's 
>>> Darwinism is selection of pointer states, not one history from a bundle.
>>>
>>> Bruce
>>>
>>
>>  Histories are (hidden) states. 
>>
>
> It becomes obvious that you don't really understand consistent 
> histories, either.
>
> Bruce 
>

 I've never once mentioned *consistent histories*, only *sum over 
 histories*.

>>>
>>> Inconsistent histories?
>>>  
>>>
 (Did you watch the lecture by Fay Dowker?)

>>>
>>> No, I don't watch utube videos. 
>>>
>>> Pointer states [ https://arxiv.org/abs/1508.04101 ] can best be 
 understood as related to histories via the *Reflective Path Integral* 
 interpretation of the EPR experiment.

>>>
>>> Your arxiv references do not support your case. Reverse causation, as it 
>>> seems to be required in your account, is simply a nonsense. Huw Price lost 
>>> the plot a long time ago.
>>>
>>> There is no competition between the different paths between the initial 
>>> and final state -- which is what is used to calculate probabilities in the 
>>> path integral approach. So there is no Darwinian (or other) selection of 
>>> one such path over others. Quantum Darwinism is about something quite 
>>> different. Even Wikipedia agrees! Read Zurek's papers on this.
>>>
>>> Bruce
>>>
>>  
>>
>> OK. As Kay Dowker stated in her presentation: The path integral 
>> interpretation is still under development.
>>
>
> As has been pointed out, path integrals are a calculational tool, not an 
> interpretation.
>



Oh,* that* again. It's like Groundhog Day (the movie).




 
>
>> My (retrocausal) version of Darwinian selection w.r.t. multiple histories 
>>  *is* *the next 
>> development.*
>>
>
> I see, it is not actually a coherent proposition at the moment...
>
> Bruce
>



Coherency is overrated.

- pt 

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To 

Re: Measuring a system in a superposition of states vs in a mixed state

[Bruce Kellett]

On Wed, Dec 5, 2018 at 5:43 PM Philip Thrift  wrote:

> On Wednesday, December 5, 2018 at 12:28:19 AM UTC-6, Bruce wrote:
>>
>> On Wed, Dec 5, 2018 at 5:19 PM Philip Thrift  wrote:
>>
>>> On Wednesday, December 5, 2018 at 12:00:18 AM UTC-6, Bruce wrote:

 On Wed, Dec 5, 2018 at 4:51 PM Philip Thrift 
 wrote:

> On Tuesday, December 4, 2018 at 11:39:43 PM UTC-6, Bruce wrote:
>>
>> On Wed, Dec 5, 2018 at 3:53 PM Philip Thrift 
>> wrote:
>>
>>> On Tuesday, December 4, 2018 at 10:28:39 PM UTC-6, Philip Thrift
>>> wrote:

 On Tuesday, December 4, 2018 at 3:45:32 PM UTC-6, Bruce wrote:
>
> On Wed, Dec 5, 2018 at 6:58 AM Philip Thrift 
> wrote:
>
>>
>> On Tuesday, December 4, 2018 at 1:53:15 PM UTC-6, Brent wrote:
>>>
>>>
>>> On 12/4/2018 12:25 AM, Philip Thrift wrote:
>>>
>>>
>>> 1. Histories originate at an emitter e and end at screen
>>> locations s on a screen S.
>>> 2. At each s there is a history bundle histories(s). A weight
>>> w(s) is computed from the bundle by summing the unit complex 
>>> numbers of the
>>> histories and taking the modulus.
>>> 3. The weight w(s) is sent back in time over a single history
>>> h*(s) selected at random (uniformly) from histories(s).
>>> 4. At e, the weights w(s) on backchannel of h*(s) are received
>>> (in the "present" time)
>>> 5. A single history h*(s*) is then selected from the
>>> distribution in 4.
>>>
>>>
>>> How is it selected?  Above you said "at random".  But that
>>> implies there is already a probability measure defined on the 
>>> histories.
>>> How is this probability measure determined?  Or put another way how 
>>> do you
>>> determine what histories to consider to form the bundles in step 2?
>>>
>>> Brent
>>>
>>
>> Selection happens via quantum Darwinism.
>>
>
>
> Do you have even the faintest understanding of Quantum Darwinism?
>
> Bruce
>

 How is *sum over histories with Darwinian selection*  (as defined)
 not quantum Darwinism?

 Operationally, what is different?

 - pt

>>>
>>> *Sum over histories with Darwinian selection* is consistent with 
>>> *Quantum
>>> Darwinism as a Darwinian process*  [ https://arxiv.org/abs/1001.0745
>>> ].
>>>
>>
>> No, you clearly don't understand Quantum Darwinism! Zurek's Darwinism
>> is selection of pointer states, not one history from a bundle.
>>
>> Bruce
>>
>
>  Histories are (hidden) states.
>

 It becomes obvious that you don't really understand consistent
 histories, either.

 Bruce

>>>
>>> I've never once mentioned *consistent histories*, only *sum over
>>> histories*.
>>>
>>
>> Inconsistent histories?
>>
>>
>>> (Did you watch the lecture by Fay Dowker?)
>>>
>>
>> No, I don't watch utube videos.
>>
>> Pointer states [ https://arxiv.org/abs/1508.04101 ] can best be
>>> understood as related to histories via the *Reflective Path Integral*
>>> interpretation of the EPR experiment.
>>>
>>
>> Your arxiv references do not support your case. Reverse causation, as it
>> seems to be required in your account, is simply a nonsense. Huw Price lost
>> the plot a long time ago.
>>
>> There is no competition between the different paths between the initial
>> and final state -- which is what is used to calculate probabilities in the
>> path integral approach. So there is no Darwinian (or other) selection of
>> one such path over others. Quantum Darwinism is about something quite
>> different. Even Wikipedia agrees! Read Zurek's papers on this.
>>
>> Bruce
>>
>
>
> OK. As Kay Dowker stated in her presentation: The path integral
> interpretation is still under development.
>

As has been pointed out, path integrals are a calculational tool, not an
interpretation.


> My (retrocausal) version of Darwinian selection w.r.t. multiple histories
>  *is* *the next
> development.*
>

I see, it is not actually a coherent proposition at the moment...

Bruce

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Re: Measuring a system in a superposition of states vs in a mixed state

[Philip Thrift]

On Wednesday, December 5, 2018 at 12:28:19 AM UTC-6, Bruce wrote:
>
> On Wed, Dec 5, 2018 at 5:19 PM Philip Thrift  > wrote:
>
>> On Wednesday, December 5, 2018 at 12:00:18 AM UTC-6, Bruce wrote:
>>>
>>> On Wed, Dec 5, 2018 at 4:51 PM Philip Thrift  wrote:
>>>
 On Tuesday, December 4, 2018 at 11:39:43 PM UTC-6, Bruce wrote:
>
> On Wed, Dec 5, 2018 at 3:53 PM Philip Thrift  
> wrote:
>
>> On Tuesday, December 4, 2018 at 10:28:39 PM UTC-6, Philip Thrift 
>> wrote:
>>>
>>> On Tuesday, December 4, 2018 at 3:45:32 PM UTC-6, Bruce wrote:

 On Wed, Dec 5, 2018 at 6:58 AM Philip Thrift  
 wrote:

>
> On Tuesday, December 4, 2018 at 1:53:15 PM UTC-6, Brent wrote:
>>
>>
>> On 12/4/2018 12:25 AM, Philip Thrift wrote:
>>
>>
>> 1. Histories originate at an emitter e and end at screen 
>> locations s on a screen S.
>> 2. At each s there is a history bundle histories(s). A weight 
>> w(s) is computed from the bundle by summing the unit complex numbers 
>> of the 
>> histories and taking the modulus. 
>> 3. The weight w(s) is sent back in time over a single history 
>> h*(s) selected at random (uniformly) from histories(s).
>> 4. At e, the weights w(s) on backchannel of h*(s) are received 
>> (in the "present" time)
>> 5. A single history h*(s*) is then selected from the distribution 
>> in 4.
>>
>>
>> How is it selected?  Above you said "at random".  But that 
>> implies there is already a probability measure defined on the 
>> histories.  
>> How is this probability measure determined?  Or put another way how 
>> do you 
>> determine what histories to consider to form the bundles in step 2?
>>
>> Brent
>>
>
> Selection happens via quantum Darwinism. 
>


 Do you have even the faintest understanding of Quantum Darwinism?

 Bruce 

>>>
>>> How is *sum over histories with Darwinian selection*  (as defined) 
>>> not quantum Darwinism?
>>>
>>> Operationally, what is different?
>>>
>>> - pt
>>>
>>
>> *Sum over histories with Darwinian selection* is consistent with 
>> *Quantum 
>> Darwinism as a Darwinian process*  [ https://arxiv.org/abs/1001.0745 
>> ].
>>
>
> No, you clearly don't understand Quantum Darwinism! Zurek's Darwinism 
> is selection of pointer states, not one history from a bundle.
>
> Bruce
>


  Histories are (hidden) states. 

>>>
>>> It becomes obvious that you don't really understand consistent 
>>> histories, either.
>>>
>>> Bruce 
>>>
>>
>> I've never once mentioned *consistent histories*, only *sum over 
>> histories*.
>>
>
> Inconsistent histories?
>  
>
>> (Did you watch the lecture by Fay Dowker?)
>>
>
> No, I don't watch utube videos. 
>
> Pointer states [ https://arxiv.org/abs/1508.04101 ] can best be 
>> understood as related to histories via the *Reflective Path Integral* 
>> interpretation of the EPR experiment.
>>
>
> Your arxiv references do not support your case. Reverse causation, as it 
> seems to be required in your account, is simply a nonsense. Huw Price lost 
> the plot a long time ago.
>
> There is no competition between the different paths between the initial 
> and final state -- which is what is used to calculate probabilities in the 
> path integral approach. So there is no Darwinian (or other) selection of 
> one such path over others. Quantum Darwinism is about something quite 
> different. Even Wikipedia agrees! Read Zurek's papers on this.
>
> Bruce
>
 


OK. As Kay Dowker stated in her presentation: The path integral 
interpretation is still under development.

My (retrocausal) version of Darwinian selection w.r.t. multiple histories 
 *is* *the next 
development.*

- pt

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Re: Measuring a system in a superposition of states vs in a mixed state

[Bruce Kellett]

On Wed, Dec 5, 2018 at 5:19 PM Philip Thrift  wrote:

> On Wednesday, December 5, 2018 at 12:00:18 AM UTC-6, Bruce wrote:
>>
>> On Wed, Dec 5, 2018 at 4:51 PM Philip Thrift  wrote:
>>
>>> On Tuesday, December 4, 2018 at 11:39:43 PM UTC-6, Bruce wrote:

 On Wed, Dec 5, 2018 at 3:53 PM Philip Thrift 
 wrote:

> On Tuesday, December 4, 2018 at 10:28:39 PM UTC-6, Philip Thrift wrote:
>>
>> On Tuesday, December 4, 2018 at 3:45:32 PM UTC-6, Bruce wrote:
>>>
>>> On Wed, Dec 5, 2018 at 6:58 AM Philip Thrift 
>>> wrote:
>>>

 On Tuesday, December 4, 2018 at 1:53:15 PM UTC-6, Brent wrote:
>
>
> On 12/4/2018 12:25 AM, Philip Thrift wrote:
>
>
> 1. Histories originate at an emitter e and end at screen locations
> s on a screen S.
> 2. At each s there is a history bundle histories(s). A weight w(s)
> is computed from the bundle by summing the unit complex numbers of the
> histories and taking the modulus.
> 3. The weight w(s) is sent back in time over a single history
> h*(s) selected at random (uniformly) from histories(s).
> 4. At e, the weights w(s) on backchannel of h*(s) are received (in
> the "present" time)
> 5. A single history h*(s*) is then selected from the distribution
> in 4.
>
>
> How is it selected?  Above you said "at random".  But that implies
> there is already a probability measure defined on the histories.  How 
> is
> this probability measure determined?  Or put another way how do you
> determine what histories to consider to form the bundles in step 2?
>
> Brent
>

 Selection happens via quantum Darwinism.

>>>
>>>
>>> Do you have even the faintest understanding of Quantum Darwinism?
>>>
>>> Bruce
>>>
>>
>> How is *sum over histories with Darwinian selection*  (as defined)
>> not quantum Darwinism?
>>
>> Operationally, what is different?
>>
>> - pt
>>
>
> *Sum over histories with Darwinian selection* is consistent with *Quantum
> Darwinism as a Darwinian process*  [ https://arxiv.org/abs/1001.0745
> ].
>

 No, you clearly don't understand Quantum Darwinism! Zurek's Darwinism
 is selection of pointer states, not one history from a bundle.

 Bruce

>>>
>>>
>>>  Histories are (hidden) states.
>>>
>>
>> It becomes obvious that you don't really understand consistent histories,
>> either.
>>
>> Bruce
>>
>
> I've never once mentioned *consistent histories*, only *sum over
> histories*.
>

Inconsistent histories?


> (Did you watch the lecture by Fay Dowker?)
>

No, I don't watch utube videos.

Pointer states [ https://arxiv.org/abs/1508.04101 ] can best be understood
> as related to histories via the *Reflective Path Integral* interpretation
> of the EPR experiment.
>

Your arxiv references do not support your case. Reverse causation, as it
seems to be required in your account, is simply a nonsense. Huw Price lost
the plot a long time ago.

There is no competition between the different paths between the initial and
final state -- which is what is used to calculate probabilities in the path
integral approach. So there is no Darwinian (or other) selection of one
such path over others. Quantum Darwinism is about something quite
different. Even Wikipedia agrees! Read Zurek's papers on this.

Bruce

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Re: Measuring a system in a superposition of states vs in a mixed state

[Philip Thrift]

On Wednesday, December 5, 2018 at 12:00:18 AM UTC-6, Bruce wrote:
>
> On Wed, Dec 5, 2018 at 4:51 PM Philip Thrift  > wrote:
>
>> On Tuesday, December 4, 2018 at 11:39:43 PM UTC-6, Bruce wrote:
>>>
>>> On Wed, Dec 5, 2018 at 3:53 PM Philip Thrift  wrote:
>>>
 On Tuesday, December 4, 2018 at 10:28:39 PM UTC-6, Philip Thrift wrote:
>
> On Tuesday, December 4, 2018 at 3:45:32 PM UTC-6, Bruce wrote:
>>
>> On Wed, Dec 5, 2018 at 6:58 AM Philip Thrift  
>> wrote:
>>
>>>
>>> On Tuesday, December 4, 2018 at 1:53:15 PM UTC-6, Brent wrote:


 On 12/4/2018 12:25 AM, Philip Thrift wrote:


 1. Histories originate at an emitter e and end at screen locations 
 s on a screen S.
 2. At each s there is a history bundle histories(s). A weight w(s) 
 is computed from the bundle by summing the unit complex numbers of the 
 histories and taking the modulus. 
 3. The weight w(s) is sent back in time over a single history h*(s) 
 selected at random (uniformly) from histories(s).
 4. At e, the weights w(s) on backchannel of h*(s) are received (in 
 the "present" time)
 5. A single history h*(s*) is then selected from the distribution 
 in 4.


 How is it selected?  Above you said "at random".  But that implies 
 there is already a probability measure defined on the histories.  How 
 is 
 this probability measure determined?  Or put another way how do you 
 determine what histories to consider to form the bundles in step 2?

 Brent

>>>
>>> Selection happens via quantum Darwinism. 
>>>
>>
>>
>> Do you have even the faintest understanding of Quantum Darwinism?
>>
>> Bruce 
>>
>
> How is *sum over histories with Darwinian selection*  (as defined) 
> not quantum Darwinism?
>
> Operationally, what is different?
>
> - pt
>

 *Sum over histories with Darwinian selection* is consistent with *Quantum 
 Darwinism as a Darwinian process*  [ https://arxiv.org/abs/1001.0745 ].

>>>
>>> No, you clearly don't understand Quantum Darwinism! Zurek's Darwinism is 
>>> selection of pointer states, not one history from a bundle.
>>>
>>> Bruce
>>>
>>
>>
>>  Histories are (hidden) states. 
>>
>
> It becomes obvious that you don't really understand consistent histories, 
> either.
>
> Bruce 
>




I've never once mentioned *consistent histories*, only *sum over histories*.

(Did you watch the lecture by Fay Dowker?)

Pointer states [ https://arxiv.org/abs/1508.04101 ] can best be understood 
as related to histories via the *Reflective Path Integral* interpretation 
of the EPR experiment.

- pt


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Re: Measuring a system in a superposition of states vs in a mixed state

[Bruce Kellett]

On Wed, Dec 5, 2018 at 4:51 PM Philip Thrift  wrote:

> On Tuesday, December 4, 2018 at 11:39:43 PM UTC-6, Bruce wrote:
>>
>> On Wed, Dec 5, 2018 at 3:53 PM Philip Thrift  wrote:
>>
>>> On Tuesday, December 4, 2018 at 10:28:39 PM UTC-6, Philip Thrift wrote:

 On Tuesday, December 4, 2018 at 3:45:32 PM UTC-6, Bruce wrote:
>
> On Wed, Dec 5, 2018 at 6:58 AM Philip Thrift 
> wrote:
>
>>
>> On Tuesday, December 4, 2018 at 1:53:15 PM UTC-6, Brent wrote:
>>>
>>>
>>> On 12/4/2018 12:25 AM, Philip Thrift wrote:
>>>
>>>
>>> 1. Histories originate at an emitter e and end at screen locations s
>>> on a screen S.
>>> 2. At each s there is a history bundle histories(s). A weight w(s)
>>> is computed from the bundle by summing the unit complex numbers of the
>>> histories and taking the modulus.
>>> 3. The weight w(s) is sent back in time over a single history h*(s)
>>> selected at random (uniformly) from histories(s).
>>> 4. At e, the weights w(s) on backchannel of h*(s) are received (in
>>> the "present" time)
>>> 5. A single history h*(s*) is then selected from the distribution in
>>> 4.
>>>
>>>
>>> How is it selected?  Above you said "at random".  But that implies
>>> there is already a probability measure defined on the histories.  How is
>>> this probability measure determined?  Or put another way how do you
>>> determine what histories to consider to form the bundles in step 2?
>>>
>>> Brent
>>>
>>
>> Selection happens via quantum Darwinism.
>>
>
>
> Do you have even the faintest understanding of Quantum Darwinism?
>
> Bruce
>

 How is *sum over histories with Darwinian selection*  (as defined) not
 quantum Darwinism?

 Operationally, what is different?

 - pt

>>>
>>> *Sum over histories with Darwinian selection* is consistent with *Quantum
>>> Darwinism as a Darwinian process*  [ https://arxiv.org/abs/1001.0745 ].
>>>
>>
>> No, you clearly don't understand Quantum Darwinism! Zurek's Darwinism is
>> selection of pointer states, not one history from a bundle.
>>
>> Bruce
>>
>
>
>  Histories are (hidden) states.
>

It becomes obvious that you don't really understand consistent histories,
either.

Bruce

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Re: Measuring a system in a superposition of states vs in a mixed state

[Philip Thrift]

On Tuesday, December 4, 2018 at 11:39:43 PM UTC-6, Bruce wrote:
>
> On Wed, Dec 5, 2018 at 3:53 PM Philip Thrift  > wrote:
>
>> On Tuesday, December 4, 2018 at 10:28:39 PM UTC-6, Philip Thrift wrote:
>>>
>>> On Tuesday, December 4, 2018 at 3:45:32 PM UTC-6, Bruce wrote:

 On Wed, Dec 5, 2018 at 6:58 AM Philip Thrift  
 wrote:

>
> On Tuesday, December 4, 2018 at 1:53:15 PM UTC-6, Brent wrote:
>>
>>
>> On 12/4/2018 12:25 AM, Philip Thrift wrote:
>>
>>
>> 1. Histories originate at an emitter e and end at screen locations s 
>> on a screen S.
>> 2. At each s there is a history bundle histories(s). A weight w(s) is 
>> computed from the bundle by summing the unit complex numbers of the 
>> histories and taking the modulus. 
>> 3. The weight w(s) is sent back in time over a single history h*(s) 
>> selected at random (uniformly) from histories(s).
>> 4. At e, the weights w(s) on backchannel of h*(s) are received (in 
>> the "present" time)
>> 5. A single history h*(s*) is then selected from the distribution in 
>> 4.
>>
>>
>> How is it selected?  Above you said "at random".  But that implies 
>> there is already a probability measure defined on the histories.  How is 
>> this probability measure determined?  Or put another way how do you 
>> determine what histories to consider to form the bundles in step 2?
>>
>> Brent
>>
>
> Selection happens via quantum Darwinism. 
>


 Do you have even the faintest understanding of Quantum Darwinism?

 Bruce 

>>>
>>> How is *sum over histories with Darwinian selection*  (as defined) not 
>>> quantum Darwinism?
>>>
>>> Operationally, what is different?
>>>
>>> - pt
>>>
>>
>> *Sum over histories with Darwinian selection* is consistent with *Quantum 
>> Darwinism as a Darwinian process*  [ https://arxiv.org/abs/1001.0745 ].
>>
>
> No, you clearly don't understand Quantum Darwinism! Zurek's Darwinism is 
> selection of pointer states, not one history from a bundle.
>
> Bruce
>



 Histories are (hidden) states. 

- pt

>  
>

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Re: Measuring a system in a superposition of states vs in a mixed state

[Bruce Kellett]

On Wed, Dec 5, 2018 at 3:53 PM Philip Thrift  wrote:

> On Tuesday, December 4, 2018 at 10:28:39 PM UTC-6, Philip Thrift wrote:
>>
>> On Tuesday, December 4, 2018 at 3:45:32 PM UTC-6, Bruce wrote:
>>>
>>> On Wed, Dec 5, 2018 at 6:58 AM Philip Thrift  wrote:
>>>

 On Tuesday, December 4, 2018 at 1:53:15 PM UTC-6, Brent wrote:
>
>
> On 12/4/2018 12:25 AM, Philip Thrift wrote:
>
>
> 1. Histories originate at an emitter e and end at screen locations s
> on a screen S.
> 2. At each s there is a history bundle histories(s). A weight w(s) is
> computed from the bundle by summing the unit complex numbers of the
> histories and taking the modulus.
> 3. The weight w(s) is sent back in time over a single history h*(s)
> selected at random (uniformly) from histories(s).
> 4. At e, the weights w(s) on backchannel of h*(s) are received (in the
> "present" time)
> 5. A single history h*(s*) is then selected from the distribution in 4.
>
>
> How is it selected?  Above you said "at random".  But that implies
> there is already a probability measure defined on the histories.  How is
> this probability measure determined?  Or put another way how do you
> determine what histories to consider to form the bundles in step 2?
>
> Brent
>

 Selection happens via quantum Darwinism.

>>>
>>>
>>> Do you have even the faintest understanding of Quantum Darwinism?
>>>
>>> Bruce
>>>
>>
>> How is *sum over histories with Darwinian selection*  (as defined) not
>> quantum Darwinism?
>>
>> Operationally, what is different?
>>
>> - pt
>>
>
> *Sum over histories with Darwinian selection* is consistent with *Quantum
> Darwinism as a Darwinian process*  [ https://arxiv.org/abs/1001.0745 ].
>

No, you clearly don't understand Quantum Darwinism! Zurek's Darwinism is
selection of pointer states, not one history from a bundle.

Bruce

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Re: Measuring a system in a superposition of states vs in a mixed state

[Philip Thrift]

On Tuesday, December 4, 2018 at 10:28:39 PM UTC-6, Philip Thrift wrote:
>
>
>
> On Tuesday, December 4, 2018 at 3:45:32 PM UTC-6, Bruce wrote:
>>
>> On Wed, Dec 5, 2018 at 6:58 AM Philip Thrift  wrote:
>>
>>>
>>> On Tuesday, December 4, 2018 at 1:53:15 PM UTC-6, Brent wrote:


 On 12/4/2018 12:25 AM, Philip Thrift wrote:


 1. Histories originate at an emitter e and end at screen locations s on 
 a screen S.
 2. At each s there is a history bundle histories(s). A weight w(s) is 
 computed from the bundle by summing the unit complex numbers of the 
 histories and taking the modulus. 
 3. The weight w(s) is sent back in time over a single history h*(s) 
 selected at random (uniformly) from histories(s).
 4. At e, the weights w(s) on backchannel of h*(s) are received (in the 
 "present" time)
 5. A single history h*(s*) is then selected from the distribution in 4.


 How is it selected?  Above you said "at random".  But that implies 
 there is already a probability measure defined on the histories.  How is 
 this probability measure determined?  Or put another way how do you 
 determine what histories to consider to form the bundles in step 2?

 Brent

>>>
>>> Selection happens via quantum Darwinism. 
>>>
>>
>>
>> Do you have even the faintest understanding of Quantum Darwinism?
>>
>> Bruce 
>>
>
>
>
>
> How is *sum over histories with Darwinian selection*  (as defined) not 
> quantum Darwinism?
>
> Operationally, what is different?
>
> - pt
>

*Sum over histories with Darwinian selection* is consistent with *Quantum 
Darwinism as a Darwinian process*  [ https://arxiv.org/abs/1001.0745 ].

- pt

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Re: Measuring a system in a superposition of states vs in a mixed state

[Philip Thrift]

On Tuesday, December 4, 2018 at 3:45:32 PM UTC-6, Bruce wrote:
>
> On Wed, Dec 5, 2018 at 6:58 AM Philip Thrift  > wrote:
>
>>
>> On Tuesday, December 4, 2018 at 1:53:15 PM UTC-6, Brent wrote:
>>>
>>>
>>> On 12/4/2018 12:25 AM, Philip Thrift wrote:
>>>
>>>
>>> 1. Histories originate at an emitter e and end at screen locations s on 
>>> a screen S.
>>> 2. At each s there is a history bundle histories(s). A weight w(s) is 
>>> computed from the bundle by summing the unit complex numbers of the 
>>> histories and taking the modulus. 
>>> 3. The weight w(s) is sent back in time over a single history h*(s) 
>>> selected at random (uniformly) from histories(s).
>>> 4. At e, the weights w(s) on backchannel of h*(s) are received (in the 
>>> "present" time)
>>> 5. A single history h*(s*) is then selected from the distribution in 4.
>>>
>>>
>>> How is it selected?  Above you said "at random".  But that implies there 
>>> is already a probability measure defined on the histories.  How is this 
>>> probability measure determined?  Or put another way how do you determine 
>>> what histories to consider to form the bundles in step 2?
>>>
>>> Brent
>>>
>>
>> Selection happens via quantum Darwinism. 
>>
>
>
> Do you have even the faintest understanding of Quantum Darwinism?
>
> Bruce 
>




How is *sum over histories with Darwinian selection*  (as defined) not 
quantum Darwinism?

Operationally, what is different?

- pt

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Re: Measuring a system in a superposition of states vs in a mixed state

[Bruce Kellett]

On Wed, Dec 5, 2018 at 6:58 AM Philip Thrift  wrote:

>
> On Tuesday, December 4, 2018 at 1:53:15 PM UTC-6, Brent wrote:
>>
>>
>> On 12/4/2018 12:25 AM, Philip Thrift wrote:
>>
>>
>> 1. Histories originate at an emitter e and end at screen locations s on a
>> screen S.
>> 2. At each s there is a history bundle histories(s). A weight w(s) is
>> computed from the bundle by summing the unit complex numbers of the
>> histories and taking the modulus.
>> 3. The weight w(s) is sent back in time over a single history h*(s)
>> selected at random (uniformly) from histories(s).
>> 4. At e, the weights w(s) on backchannel of h*(s) are received (in the
>> "present" time)
>> 5. A single history h*(s*) is then selected from the distribution in 4.
>>
>>
>> How is it selected?  Above you said "at random".  But that implies there
>> is already a probability measure defined on the histories.  How is this
>> probability measure determined?  Or put another way how do you determine
>> what histories to consider to form the bundles in step 2?
>>
>> Brent
>>
>
> Selection happens via quantum Darwinism.
>


Do you have even the faintest understanding of Quantum Darwinism?

Bruce

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Re: Measuring a system in a superposition of states vs in a mixed state

[Brent Meeker]

On 12/4/2018 3:05 AM, Bruno Marchal wrote:

… where Omnès added “time to be irrational” ...





1. Histories originate at an emitter e and end at screen locations s 
on a screen S.
2. At each s there is a history bundle histories(s). A weight w(s) is 
computed from the bundle by summing the unit complex numbers of the 
histories and taking the modulus.
3. The weight w(s) is sent back in time over a single history h*(s) 
selected at random (uniformly) from histories(s).
4. At e, the weights w(s) on backchannel of h*(s) are received (in 
the "present" time)

5. A single history h*(s*) is then selected from the distribution in 4.


"5.”  follows from mechanism as a first person view. No need of Omnès 
mysterious selection.


The first person view is a view of the result of the sum over the 
bundle; not of a single history. How would one perceive a history?


Brent

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Re: Measuring a system in a superposition of states vs in a mixed state

[Philip Thrift]

On Tuesday, December 4, 2018 at 1:53:15 PM UTC-6, Brent wrote:
>
>
>
> On 12/4/2018 12:25 AM, Philip Thrift wrote:
>
>
>
> On Monday, December 3, 2018 at 9:00:26 PM UTC-6, Brent wrote: 
>>
>>
>>
>> On 12/3/2018 8:50 AM, Bruno Marchal wrote:
>>
>>
>> On 3 Dec 2018, at 10:35, Philip Thrift  wrote:
>>
>>
>>
>> On Sunday, December 2, 2018 at 8:17:54 PM UTC-6, Brent wrote: 
>>>
>>>
>>>
>>> On 12/2/2018 5:14 PM, Philip Thrift wrote:
>>>
>>>
>>>
>>> On Sunday, December 2, 2018 at 4:25:04 PM UTC-6, Brent wrote: 



 On 12/2/2018 11:42 AM, Philip Thrift wrote:



 On Sunday, December 2, 2018 at 8:13:48 AM UTC-6, agrays...@gmail.com 
 wrote: 
>
>
> *Obviously, from a one-world perspective, only one history survives 
> for a single trial. But to even grossly approach anything describable as 
> "Darwinian", you have to identify characteristics of histories which 
> contribute positively or negatively wrt surviving but I don't see an 
> inkling of that. IMO, Quantum Darwinism is at best a vacuous restatement 
> of 
> the measurement problemt; that we don't know why we get what we get. AG*
>
>>
>>
>>

 In the *sum over histories* interpretation - of the double-slit 
 experiment, for example - each history carries a unit complex number - 
 like 
 a gene - and this gene reenforces (positively) or interferes (negatively) 
 with other history's genes in the sum.


 But I thought you said the ontology was that only one history "popped 
 out of the Lottery machine"?  Here you seem to contemplate an ensemble of 
 histories, all those ending at the given spot, as being real.

 Brent

>>>
>>>
>>>
>>>
>>> All are real until all but one dies.
>>> RIP: All those losing histories.
>>>
>>>
>>> The trouble with that is the Born probability doesn't apply to 
>>> histories, it applies to results.  So your theory says nothing about the 
>>> probability of the fundamental ontologies.
>>>
>>> Brent
>>>
>>
>>
>>
>>
>>
>> The probability distribution on the space of histories is provided by the 
>> path integral. 
>>
>>
>> Except that isn't true. A probability (or probability density) is 
>> provided for a bundle of histories joining two events.  It doesn't not 
>> provide a probability of a single history.
>>
>> Brent
>>
>>
> That's why you add to that "pick any history at random from the bundle":
>
>
> But the probability didn't apply to that history.  The Born rule gave the 
> probability of the bundle.  To it is false that, "The probability 
> distribution on the space of histories is provided by the path integral." 
>
>
> 1. Histories originate at an emitter e and end at screen locations s on a 
> screen S.
> 2. At each s there is a history bundle histories(s). A weight w(s) is 
> computed from the bundle by summing the unit complex numbers of the 
> histories and taking the modulus. 
> 3. The weight w(s) is sent back in time over a single history h*(s) 
> selected at random (uniformly) from histories(s).
> 4. At e, the weights w(s) on backchannel of h*(s) are received (in the 
> "present" time)
> 5. A single history h*(s*) is then selected from the distribution in 4.
>
>
> How is it selected?  Above you said "at random".  But that implies there 
> is already a probability measure defined on the histories.  How is this 
> probability measure determined?  Or put another way how do you determine 
> what histories to consider to form the bundles in step 2?
>
> Brent
>
>
> See the *Wheeler-Feynman computer*:
> [ 
> https://codicalist.wordpress.com/2018/09/25/retrosignaling-in-the-quantum-substrate/
>  
> ]
>
> - p
>
>
>
 

Selection happens via quantum Darwinism. 

- pt 

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Re: Measuring a system in a superposition of states vs in a mixed state

[Brent Meeker]

On 12/4/2018 12:25 AM, Philip Thrift wrote:



On Monday, December 3, 2018 at 9:00:26 PM UTC-6, Brent wrote:



On 12/3/2018 8:50 AM, Bruno Marchal wrote:



On 3 Dec 2018, at 10:35, Philip Thrift > wrote:



On Sunday, December 2, 2018 at 8:17:54 PM UTC-6, Brent wrote:



On 12/2/2018 5:14 PM, Philip Thrift wrote:



On Sunday, December 2, 2018 at 4:25:04 PM UTC-6, Brent wrote:



On 12/2/2018 11:42 AM, Philip Thrift wrote:



On Sunday, December 2, 2018 at 8:13:48 AM UTC-6,
agrays...@gmail.com wrote:

*
*
*Obviously, from a one-world perspective, only one
history survives for a single trial. But to even
grossly approach anything describable as
"Darwinian", you have to identify characteristics
of histories which contribute positively or
negatively wrt surviving but I don't see an
inkling of that. IMO, Quantum Darwinism is at best
a vacuous restatement of the measurement problemt;
that we don't know why we get what we get. AG*





In the *sum over histories* interpretation - of the
double-slit experiment, for example - each history
carries a unit complex number - like a gene - and this
gene reenforces (positively) or interferes
(negatively) with other history's genes in the sum.


But I thought you said the ontology was that only one
history "popped out of the Lottery machine"?  Here you
seem to contemplate an ensemble of histories, all those
ending at the given spot, as being real.

Brent





All are real until all but one dies.
RIP: All those losing histories.


The trouble with that is the Born probability doesn't apply
to histories, it applies to results.  So your theory says
nothing about the probability of the fundamental ontologies.

Brent






The probability distribution on the space of histories is
provided by the path integral.


Except that isn't true. A probability (or probability density) is
provided for a bundle of histories joining two events.  It doesn't
not provide a probability of a single history.

Brent


That's why you add to that "pick any history at random from the bundle":


But the probability didn't apply to that history.  The Born rule gave 
the probability of the bundle.  To it is false that, "The probability 
distribution on the space of histories is provided by the path integral."




1. Histories originate at an emitter e and end at screen locations s 
on a screen S.
2. At each s there is a history bundle histories(s). A weight w(s) is 
computed from the bundle by summing the unit complex numbers of the 
histories and taking the modulus.
3. The weight w(s) is sent back in time over a single history h*(s) 
selected at random (uniformly) from histories(s).
4. At e, the weights w(s) on backchannel of h*(s) are received (in the 
"present" time)

5. A single history h*(s*) is then selected from the distribution in 4.


How is it selected?  Above you said "at random".  But that implies there 
is already a probability measure defined on the histories. How is this 
probability measure determined?  Or put another way how do you determine 
what histories to consider to form the bundles in step 2?


Brent



See the *Wheeler-Feynman computer*:
[ https://codicalist.wordpress.com/2018/09/25/retrosignaling-in-the-quantum-substrate/ 
]


- pt
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Re: Measuring a system in a superposition of states vs in a mixed state

[Bruno Marchal]

> On 4 Dec 2018, at 09:25, Philip Thrift  wrote:
> 
> 
> 
> On Monday, December 3, 2018 at 9:00:26 PM UTC-6, Brent wrote:
> 
> 
> On 12/3/2018 8:50 AM, Bruno Marchal wrote:
>> 
>>> On 3 Dec 2018, at 10:35, Philip Thrift > 
>>> wrote:
>>> 
>>> 
>>> 
>>> On Sunday, December 2, 2018 at 8:17:54 PM UTC-6, Brent wrote:
>>> 
>>> 
>>> On 12/2/2018 5:14 PM, Philip Thrift wrote:
 
 
 On Sunday, December 2, 2018 at 4:25:04 PM UTC-6, Brent wrote:
 
 
 On 12/2/2018 11:42 AM, Philip Thrift wrote:
> 
> 
> On Sunday, December 2, 2018 at 8:13:48 AM UTC-6, agrays...@gmail.com <> 
> wrote:
> 
> Obviously, from a one-world perspective, only one history survives for a 
> single trial. But to even grossly approach anything describable as 
> "Darwinian", you have to identify characteristics of histories which 
> contribute positively or negatively wrt surviving but I don't see an 
> inkling of that. IMO, Quantum Darwinism is at best a vacuous restatement 
> of the measurement problemt; that we don't know why we get what we get. AG
> 
> 
> 
> 
> In the sum over histories interpretation - of the double-slit experiment, 
> for example - each history carries a unit complex number - like a gene - 
> and this gene reenforces (positively) or interferes (negatively) with 
> other history's genes in the sum.
 
 But I thought you said the ontology was that only one history "popped out 
 of the Lottery machine"?  Here you seem to contemplate an ensemble of 
 histories, all those ending at the given spot, as being real.
 
 Brent
 
 
 
 
 All are real until all but one dies.
 RIP: All those losing histories.
>>> 
>>> The trouble with that is the Born probability doesn't apply to histories, 
>>> it applies to results.  So your theory says nothing about the probability 
>>> of the fundamental ontologies.
>>> 
>>> Brent
>>> 
>>> 
>>> 
>>> 
>>> 
>>> The probability distribution on the space of histories is provided by the 
>>> path integral. 
> 
> Except that isn't true. A probability (or probability density) is provided 
> for a bundle of histories joining two events.  It doesn't not provide a 
> probability of a single history.
> 
> Brent
> 
> 
> That's why you add to that "pick any history at random from the bundle”:

… where Omnès added “time to be irrational” ...



> 
> 1. Histories originate at an emitter e and end at screen locations s on a 
> screen S.
> 2. At each s there is a history bundle histories(s). A weight w(s) is 
> computed from the bundle by summing the unit complex numbers of the histories 
> and taking the modulus. 
> 3. The weight w(s) is sent back in time over a single history h*(s) selected 
> at random (uniformly) from histories(s).
> 4. At e, the weights w(s) on backchannel of h*(s) are received (in the 
> "present" time)
> 5. A single history h*(s*) is then selected from the distribution in 4.

"5.”  follows from mechanism as a first person view. No need of Omnès 
mysterious selection.

Bruno



> 
> See the Wheeler-Feynman computer:
> [ 
> https://codicalist.wordpress.com/2018/09/25/retrosignaling-in-the-quantum-substrate/
>  ]
> 
> - pt
> 
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Re: Measuring a system in a superposition of states vs in a mixed state

[Philip Thrift]

On Monday, December 3, 2018 at 9:00:26 PM UTC-6, Brent wrote:
>
>
>
> On 12/3/2018 8:50 AM, Bruno Marchal wrote:
>
>
> On 3 Dec 2018, at 10:35, Philip Thrift > 
> wrote:
>
>
>
> On Sunday, December 2, 2018 at 8:17:54 PM UTC-6, Brent wrote: 
>>
>>
>>
>> On 12/2/2018 5:14 PM, Philip Thrift wrote:
>>
>>
>>
>> On Sunday, December 2, 2018 at 4:25:04 PM UTC-6, Brent wrote: 
>>>
>>>
>>>
>>> On 12/2/2018 11:42 AM, Philip Thrift wrote:
>>>
>>>
>>>
>>> On Sunday, December 2, 2018 at 8:13:48 AM UTC-6, agrays...@gmail.com 
>>> wrote: 


 *Obviously, from a one-world perspective, only one history survives for 
 a single trial. But to even grossly approach anything describable as 
 "Darwinian", you have to identify characteristics of histories which 
 contribute positively or negatively wrt surviving but I don't see an 
 inkling of that. IMO, Quantum Darwinism is at best a vacuous restatement 
 of 
 the measurement problemt; that we don't know why we get what we get. AG*

>
>
>
>>>
>>> In the *sum over histories* interpretation - of the double-slit 
>>> experiment, for example - each history carries a unit complex number - like 
>>> a gene - and this gene reenforces (positively) or interferes (negatively) 
>>> with other history's genes in the sum.
>>>
>>>
>>> But I thought you said the ontology was that only one history "popped 
>>> out of the Lottery machine"?  Here you seem to contemplate an ensemble of 
>>> histories, all those ending at the given spot, as being real.
>>>
>>> Brent
>>>
>>
>>
>>
>>
>> All are real until all but one dies.
>> RIP: All those losing histories.
>>
>>
>> The trouble with that is the Born probability doesn't apply to histories, 
>> it applies to results.  So your theory says nothing about the probability 
>> of the fundamental ontologies.
>>
>> Brent
>>
>
>
>
>
>
> The probability distribution on the space of histories is provided by the 
> path integral. 
>
>
> Except that isn't true. A probability (or probability density) is provided 
> for a bundle of histories joining two events.  It doesn't not provide a 
> probability of a single history.
>
> Brent
>
>
That's why you add to that "pick any history at random from the bundle":

1. Histories originate at an emitter e and end at screen locations s on a 
screen S.
2. At each s there is a history bundle histories(s). A weight w(s) is 
computed from the bundle by summing the unit complex numbers of the 
histories and taking the modulus. 
3. The weight w(s) is sent back in time over a single history h*(s) 
selected at random (uniformly) from histories(s).
4. At e, the weights w(s) on backchannel of h*(s) are received (in the 
"present" time)
5. A single history h*(s*) is then selected from the distribution in 4.

See the *Wheeler-Feynman computer*:
[ 
https://codicalist.wordpress.com/2018/09/25/retrosignaling-in-the-quantum-substrate/
 
]

- pt

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Re: Measuring a system in a superposition of states vs in a mixed state

[Brent Meeker]

On 12/3/2018 8:50 AM, Bruno Marchal wrote:


On 3 Dec 2018, at 10:35, Philip Thrift > wrote:




On Sunday, December 2, 2018 at 8:17:54 PM UTC-6, Brent wrote:



On 12/2/2018 5:14 PM, Philip Thrift wrote:



On Sunday, December 2, 2018 at 4:25:04 PM UTC-6, Brent wrote:



On 12/2/2018 11:42 AM, Philip Thrift wrote:



On Sunday, December 2, 2018 at 8:13:48 AM UTC-6,
agrays...@gmail.com wrote:

*
*
*Obviously, from a one-world perspective, only one
history survives for a single trial. But to even
grossly approach anything describable as "Darwinian",
you have to identify characteristics of histories which
contribute positively or negatively wrt surviving but I
don't see an inkling of that. IMO, Quantum Darwinism is
at best a vacuous restatement of the measurement
problemt; that we don't know why we get what we get. AG*





In the *sum over histories* interpretation - of the
double-slit experiment, for example - each history carries
a unit complex number - like a gene - and this gene
reenforces (positively) or interferes (negatively) with
other history's genes in the sum.


But I thought you said the ontology was that only one
history "popped out of the Lottery machine"?  Here you seem
to contemplate an ensemble of histories, all those ending at
the given spot, as being real.

Brent





All are real until all but one dies.
RIP: All those losing histories.


The trouble with that is the Born probability doesn't apply to
histories, it applies to results.  So your theory says nothing
about the probability of the fundamental ontologies.

Brent






The probability distribution on the space of histories is provided by 
the path integral.


Except that isn't true. A probability (or probability density) is 
provided for a bundle of histories joining two events.  It doesn't not 
provide a probability of a single history.


Brent



I agree, and this statement can be made rather rigorously in the 
approach of Griffith and Omnes, except that Omnes eventually add an 
axiom of irrationality to extract a unique physical reality from the 
formalism. He said it, at least, explicitly: like saying “and now 
there is a miracle”. He says that at this stage, we need 
irrationalism. But that appears in the last ten sentences of a rather 
quite rational book.
Well, the point is that we can generalise the Born rule for making 
sense on some probabilities on "consistent histories”.
(But I am in trouble (now) on how to handle the GHZ state in term of 
(Griffith and Omnes)-histories (3-particle-GHZ = 1/sqrt(2)(up up up + 
down down down)).






*Backward causation, hidden variables and the meaning of completenes*s
[ https://www.ias.ac.in/article/fulltext/pram/056/02-03/0199-0209 ]

/Feynman’s path integral approach, calculation of the probability of 
the outcome in question depends on an integration over the possible 
individual paths between the given initial state and the given final 
state, each weighted by a complex number. The fact that the weights 
associated with individual paths are complex makes it impossible to 
interpret them as real valued probabilities, associated with a 
classical statistical distribution of possibilities./

/
/
/However, there is no such difficulty at the level of the entire 
‘bundle’ of paths which comprise the path integral. If we think of 
the hidden reality as the instantiation not of one path rather than 
another but of one entire bundle rather than another, then the 
quantum mechanical probabilities can be thought of as classical 
probability distributions over such elements of reality. (For 
example, suppose we specify the boundary conditions in terms of the 
electron source, the fact that two slits are open, and the fact that 
a detector screen is present at a certain distance on the opposite 
side of the central screen. We then partition the detector screen, so 
as to define possible outcomes for the experiment. For each element 
O_i of this partition, there is a bundle B_i of Feynman paths, 
constituting the path integral used in calculating the probability of 
outcome O_i . We have a classical probability distribution/

/over the set of such B_i ./

One could stop at /history bundles/ as the sample space, or the 
"hidden reality" could be that /one history/ is selected at random 
from the history bundle. That could occur with t*ime symmetry* 
(retrocausality): The one path is chosen at random from a history 
bundle at the source in the present from the distribution determined 
on the history bundles in the future.



With mechanism, the randomness and the unicity is a first person 
(plural) experience only, and seems to me no more astonishing than in 
the amoeba duplication, or than in the Helsinki—> 

Re: Measuring a system in a superposition of states vs in a mixed state

[Bruno Marchal]

> On 3 Dec 2018, at 10:35, Philip Thrift  wrote:
> 
> 
> 
> On Sunday, December 2, 2018 at 8:17:54 PM UTC-6, Brent wrote:
> 
> 
> On 12/2/2018 5:14 PM, Philip Thrift wrote:
>> 
>> 
>> On Sunday, December 2, 2018 at 4:25:04 PM UTC-6, Brent wrote:
>> 
>> 
>> On 12/2/2018 11:42 AM, Philip Thrift wrote:
>>> 
>>> 
>>> On Sunday, December 2, 2018 at 8:13:48 AM UTC-6, agrays...@gmail.com <> 
>>> wrote:
>>> 
>>> Obviously, from a one-world perspective, only one history survives for a 
>>> single trial. But to even grossly approach anything describable as 
>>> "Darwinian", you have to identify characteristics of histories which 
>>> contribute positively or negatively wrt surviving but I don't see an 
>>> inkling of that. IMO, Quantum Darwinism is at best a vacuous restatement of 
>>> the measurement problemt; that we don't know why we get what we get. AG
>>> 
>>> 
>>> 
>>> 
>>> In the sum over histories interpretation - of the double-slit experiment, 
>>> for example - each history carries a unit complex number - like a gene - 
>>> and this gene reenforces (positively) or interferes (negatively) with other 
>>> history's genes in the sum.
>> 
>> But I thought you said the ontology was that only one history "popped out of 
>> the Lottery machine"?  Here you seem to contemplate an ensemble of 
>> histories, all those ending at the given spot, as being real.
>> 
>> Brent
>> 
>> 
>> 
>> 
>> All are real until all but one dies.
>> RIP: All those losing histories.
> 
> The trouble with that is the Born probability doesn't apply to histories, it 
> applies to results.  So your theory says nothing about the probability of the 
> fundamental ontologies.
> 
> Brent
> 
> 
> 
> 
> 
> The probability distribution on the space of histories is provided by the 
> path integral. 

I agree, and this statement can be made rather rigorously in the approach of 
Griffith and Omnes, except that Omnes eventually add an axiom of irrationality 
to extract a unique physical reality from the formalism. He said it, at least, 
explicitly: like saying “and now there is a miracle”. He says that at this 
stage, we need irrationalism. But that appears in the last ten sentences of a 
rather quite rational book. 
Well, the point is that we can generalise the Born rule for making sense on 
some probabilities on "consistent histories”.
(But I am in trouble (now) on how to handle the GHZ state in term of (Griffith 
and Omnes)-histories (3-particle-GHZ = 1/sqrt(2)(up up up + down down down)).



> 
> Backward causation, hidden variables and the meaning of completeness 
> [ https://www.ias.ac.in/article/fulltext/pram/056/02-03/0199-0209 ]
> 
> Feynman’s path integral approach, calculation of the probability of the 
> outcome in question depends on an integration over the possible individual 
> paths between the given initial state and the given final state, each 
> weighted by a complex number. The fact that the weights associated with 
> individual paths are complex makes it impossible to interpret them as real 
> valued probabilities, associated with a classical statistical distribution of 
> possibilities.
> 
> However, there is no such difficulty at the level of the entire ‘bundle’ of 
> paths which comprise the path integral. If we think of the hidden reality as 
> the instantiation not of one path rather than another but of one entire 
> bundle rather than another, then the quantum mechanical probabilities can be 
> thought of as classical probability distributions over such elements of 
> reality. (For example, suppose we specify the boundary conditions in terms of 
> the electron source, the fact that two slits are open, and the fact that a 
> detector screen is present at a certain distance on the opposite side of the 
> central screen. We then partition the detector screen, so as to define 
> possible outcomes for the experiment. For each element O_i of this partition, 
> there is a bundle B_i of Feynman paths, constituting the path integral used 
> in calculating the probability of outcome O_i . We have a classical 
> probability distribution
> over the set of such B_i .
> 
> One could stop at history bundles as the sample space, or the "hidden 
> reality" could be that one history is selected at random from the history 
> bundle. That could occur with time symmetry (retrocausality): The one path is 
> chosen at random from a history bundle at the source in the present from the 
> distribution determined on the history bundles in the future.


With mechanism, the randomness and the unicity is a first person (plural) 
experience only, and seems to me no more astonishing than in the amoeba 
duplication, or than in the Helsinki—> Washington/Moscow duplication, as seen 
from the first person ways.

Bruno



> 
> - pt
> 
> 
> 
> 
> -- 
> You received this message because you are subscribed to the Google Groups 
> "Everything List" group.
> To unsubscribe from this group and stop receiving emails from it, send an 
> email to 

Re: Measuring a system in a superposition of states vs in a mixed state

[Philip Thrift]

On Sunday, December 2, 2018 at 8:17:54 PM UTC-6, Brent wrote:
>
>
>
> On 12/2/2018 5:14 PM, Philip Thrift wrote:
>
>
>
> On Sunday, December 2, 2018 at 4:25:04 PM UTC-6, Brent wrote: 
>>
>>
>>
>> On 12/2/2018 11:42 AM, Philip Thrift wrote:
>>
>>
>>
>> On Sunday, December 2, 2018 at 8:13:48 AM UTC-6, agrays...@gmail.com 
>> wrote: 
>>>
>>>
>>> *Obviously, from a one-world perspective, only one history survives for 
>>> a single trial. But to even grossly approach anything describable as 
>>> "Darwinian", you have to identify characteristics of histories which 
>>> contribute positively or negatively wrt surviving but I don't see an 
>>> inkling of that. IMO, Quantum Darwinism is at best a vacuous restatement of 
>>> the measurement problemt; that we don't know why we get what we get. AG*
>>>



>>
>> In the *sum over histories* interpretation - of the double-slit 
>> experiment, for example - each history carries a unit complex number - like 
>> a gene - and this gene reenforces (positively) or interferes (negatively) 
>> with other history's genes in the sum.
>>
>>
>> But I thought you said the ontology was that only one history "popped out 
>> of the Lottery machine"?  Here you seem to contemplate an ensemble of 
>> histories, all those ending at the given spot, as being real.
>>
>> Brent
>>
>
>
>
>
> All are real until all but one dies.
> RIP: All those losing histories.
>
>
> The trouble with that is the Born probability doesn't apply to histories, 
> it applies to results.  So your theory says nothing about the probability 
> of the fundamental ontologies.
>
> Brent
>





The probability distribution on the space of histories is provided by the 
path integral. 

*Backward causation, hidden variables and the meaning of completenes*s 
[ https://www.ias.ac.in/article/fulltext/pram/056/02-03/0199-0209 ]

*Feynman’s path integral approach, calculation of the probability of the 
outcome in question depends on an integration over the possible individual 
paths between the given initial state and the given final state, each 
weighted by a complex number. The fact that the weights associated with 
individual paths are complex makes it impossible to interpret them as real 
valued probabilities, associated with a classical statistical distribution 
of possibilities.*

*However, there is no such difficulty at the level of the entire ‘bundle’ 
of paths which comprise the path integral. If we think of the hidden 
reality as the instantiation not of one path rather than another but of one 
entire bundle rather than another, then the quantum mechanical 
probabilities can be thought of as classical probability distributions over 
such elements of reality. (For example, suppose we specify the boundary 
conditions in terms of the electron source, the fact that two slits are 
open, and the fact that a detector screen is present at a certain distance 
on the opposite side of the central screen. We then partition the detector 
screen, so as to define possible outcomes for the experiment. For each 
element O_i of this partition, there is a bundle B_i of Feynman paths, 
constituting the path integral used in calculating the probability of 
outcome O_i . We have a classical probability distribution*
*over the set of such B_i .*

One could stop at *history bundles* as the sample space, or the "hidden 
reality" could be that *one history* is selected at random from the history 
bundle. That could occur with t*ime symmetry* (retrocausality): The one 
path is chosen at random from a history bundle at the source in the present 
from the distribution determined on the history bundles in the future.

- pt



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Re: Measuring a system in a superposition of states vs in a mixed state

[Brent Meeker]

On 12/2/2018 5:14 PM, Philip Thrift wrote:



On Sunday, December 2, 2018 at 4:25:04 PM UTC-6, Brent wrote:



On 12/2/2018 11:42 AM, Philip Thrift wrote:



On Sunday, December 2, 2018 at 8:13:48 AM UTC-6,
agrays...@gmail.com wrote:

*
*
*Obviously, from a one-world perspective, only one history
survives for a single trial. But to even grossly approach
anything describable as "Darwinian", you have to identify
characteristics of histories which contribute positively or
negatively wrt surviving but I don't see an inkling of that.
IMO, Quantum Darwinism is at best a vacuous restatement of
the measurement problemt; that we don't know why we get what
we get. AG*





In the *sum over histories* interpretation - of the double-slit
experiment, for example - each history carries a unit complex
number - like a gene - and this gene reenforces (positively) or
interferes (negatively) with other history's genes in the sum.


But I thought you said the ontology was that only one history
"popped out of the Lottery machine"?  Here you seem to contemplate
an ensemble of histories, all those ending at the given spot, as
being real.

Brent





All are real until all but one dies.
RIP: All those losing histories.


The trouble with that is the Born probability doesn't apply to 
histories, it applies to results.  So your theory says nothing about the 
probability of the fundamental ontologies.


Brent

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Re: Measuring a system in a superposition of states vs in a mixed state

[Philip Thrift]

On Sunday, December 2, 2018 at 4:25:04 PM UTC-6, Brent wrote:
>
>
>
> On 12/2/2018 11:42 AM, Philip Thrift wrote:
>
>
>
> On Sunday, December 2, 2018 at 8:13:48 AM UTC-6, agrays...@gmail.com 
> wrote: 
>>
>>
>> *Obviously, from a one-world perspective, only one history survives for a 
>> single trial. But to even grossly approach anything describable as 
>> "Darwinian", you have to identify characteristics of histories which 
>> contribute positively or negatively wrt surviving but I don't see an 
>> inkling of that. IMO, Quantum Darwinism is at best a vacuous restatement of 
>> the measurement problemt; that we don't know why we get what we get. AG*
>>
>>>
>>>
>>>
>
> In the *sum over histories* interpretation - of the double-slit 
> experiment, for example - each history carries a unit complex number - like 
> a gene - and this gene reenforces (positively) or interferes (negatively) 
> with other history's genes in the sum.
>
>
> But I thought you said the ontology was that only one history "popped out 
> of the Lottery machine"?  Here you seem to contemplate an ensemble of 
> histories, all those ending at the given spot, as being real.
>
> Brent
>




All are real until all but one dies.
RIP: All those losing histories.

- pt 

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Re: Measuring a system in a superposition of states vs in a mixed state

[Brent Meeker]

On 12/2/2018 11:42 AM, Philip Thrift wrote:



On Sunday, December 2, 2018 at 8:13:48 AM UTC-6, agrays...@gmail.com 
wrote:


*
*
*Obviously, from a one-world perspective, only one history
survives for a single trial. But to even grossly approach anything
describable as "Darwinian", you have to identify characteristics
of histories which contribute positively or negatively wrt
surviving but I don't see an inkling of that. IMO, Quantum
Darwinism is at best a vacuous restatement of the measurement
problemt; that we don't know why we get what we get. AG*





In the *sum over histories* interpretation - of the double-slit 
experiment, for example - each history carries a unit complex number - 
like a gene - and this gene reenforces (positively) or interferes 
(negatively) with other history's genes in the sum.


But I thought you said the ontology was that only one history "popped 
out of the Lottery machine"?  Here you seem to contemplate an ensemble 
of histories, all those ending at the given spot, as being real.


Brent

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Re: Measuring a system in a superposition of states vs in a mixed state

[Philip Thrift]

On Sunday, December 2, 2018 at 8:13:48 AM UTC-6, agrays...@gmail.com wrote:
>
>
> *Obviously, from a one-world perspective, only one history survives for a 
> single trial. But to even grossly approach anything describable as 
> "Darwinian", you have to identify characteristics of histories which 
> contribute positively or negatively wrt surviving but I don't see an 
> inkling of that. IMO, Quantum Darwinism is at best a vacuous restatement of 
> the measurement problemt; that we don't know why we get what we get. AG*
>
>>
>>
>>

In the *sum over histories* interpretation - of the double-slit experiment, 
for example - each history carries a unit complex number - like a gene - 
and this gene reenforces (positively) or interferes (negatively) with other 
history's genes in the sum.

- pt

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Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Sunday, December 2, 2018 at 1:27:05 PM UTC, Bruno Marchal wrote:
>
>
> On 1 Dec 2018, at 17:12, agrays...@gmail.com  wrote:
>
>
>
> On Friday, November 30, 2018 at 8:53:43 AM UTC, Bruno Marchal wrote:
>>
>>
>> On 27 Nov 2018, at 22:55, agrays...@gmail.com wrote:
>>
>>
>>
>> On Tuesday, November 27, 2018 at 8:43:55 PM UTC, Philip Thrift wrote:
>>>
>>>
>>>
>>> On Tuesday, November 27, 2018 at 2:05:04 PM UTC-6, agrays...@gmail.com 
>>> wrote:



 On Tuesday, November 27, 2018 at 6:49:51 PM UTC, Philip Thrift wrote:
>
>
>
> On Tuesday, November 27, 2018 at 12:17:08 PM UTC-6, 
> agrays...@gmail.com wrote:
>>
>>
>>
>> On Tuesday, November 27, 2018 at 6:00:50 PM UTC, Philip Thrift wrote:
>>>
>>>
>>>
>>> On Tuesday, November 27, 2018 at 8:43:35 AM UTC-6, 
>>> agrays...@gmail.com wrote:



 On Tuesday, November 27, 2018 at 9:27:46 AM UTC, Philip Thrift 
 wrote:
>
>
>
> On Monday, November 26, 2018 at 3:43:14 PM UTC-6, 
> agrays...@gmail.com wrote:
>>
>>
>> *I checked the postulates in Feynman's Sums Over Histories (in 
>> link provided by Phil) and I see nothing related to waves, as 
>> expected, and 
>> thus nothing about collapse of anything. I would suppose the same 
>> applies 
>> to Heisenberg's Matrix Mechanics; no waves, no collapse. I suppose 
>> you 
>> could say they just produce correct probabilities, and imply nothing 
>> about 
>> relative states other than their probabilities (which wave mechanics 
>> does), 
>> but certainly nothing about consciousness. To summarize: you're 
>> right that 
>> they are "no collapse" theories, but IMO they say nothing about 
>> consciousness. AG*
>>
>>>
>>>
>
>
> In terms of the path-integral (PI) interpretation [ interesting 
> lecture: 
> https://www.perimeterinstitute.ca/videos/path-integral-interpretation-quantum-mechanics
>  
> ], there is in effect no waves or wave function, just paths, or 
> histories, 
> in the sum-over-histories (SOH) terminology.
>
> There is still "decoherence" in the SOH (a single history is 
> ultimately "realized"), but it could be called "selection": a single 
> history is selected from the total ensemble of multiple and 
> interfering 
> histories. E.g. a single point on a screen is "hit" by a photon in 
> the 
> double-slit experiment.
>

 *Does "selection" add any insight to the measurement problem; that 
 is, why do we get what we get? And if not, what is its value? TIA, AG *

>
>
>
>>> If you look at it as a "selection of the fittest" (one history 
>>> surviving from an ensemble of histories), then it's like a form of 
>>> quantum 
>>> Darwinism. The quantum substrate is a cruel world where all histories 
>>> (but 
>>> one) die.
>>>
>>
>> That's not an explanation; rather, a vacuous statement of the result. 
>> AG 
>>
>>>
>>>
> But that is a criticism of Darwinism (*natural selection*) in general.
>

 *Ridiculous comparison IMO. Darwinism posits a changing environment and 
 competition among species for niches. Nothing comparable in Quantum 
 Darwinism other than all outcomes fail except for one which succeeds in 
 each single trial, which we knew from the get-go. AG*

>
> *Quantum Darwinism* is a theory claiming to explain the emergence of 
> the classical world from 
> the quantum world  as 
> due to *a process of **Darwinian 
>  natural selection 
> *; where the many 
> possible quantum states  
> are 
> selected against in favor of a stable pointer state 
> .
> [ https://en.wikipedia.org/wiki/Quantum_Darwinism ]
>
> - pt
>  
>

>>>
>>>
>>> As for "competition for niches", the histories are in a sense competing. 
>>> Perhaps there is some conservation principle at work, so only one history 
>>> can win. 
>>>
>>> I don't know. Physicists don't know. We're even. :)
>>>
>>
>> *Darwin had a theory or proposal to explain why some changes occur and 
>> persist, but Quantum Darwinism doesn't, as far as I can tell. AG *
>>
>>
>> I think that the comparison with Darwin makes sense, and in both case, 
>> there are many “fittest” entities.
>>
>
> *IMO, it's a ridiculous comparison. If you affirm the MWI, 

Re: Measuring a system in a superposition of states vs in a mixed state

[Bruno Marchal]

> On 1 Dec 2018, at 17:12, agrayson2...@gmail.com wrote:
> 
> 
> 
> On Friday, November 30, 2018 at 8:53:43 AM UTC, Bruno Marchal wrote:
> 
>> On 27 Nov 2018, at 22:55, agrays...@gmail.com  wrote:
>> 
>> 
>> 
>> On Tuesday, November 27, 2018 at 8:43:55 PM UTC, Philip Thrift wrote:
>> 
>> 
>> On Tuesday, November 27, 2018 at 2:05:04 PM UTC-6, agrays...@gmail.com <> 
>> wrote:
>> 
>> 
>> On Tuesday, November 27, 2018 at 6:49:51 PM UTC, Philip Thrift wrote:
>> 
>> 
>> On Tuesday, November 27, 2018 at 12:17:08 PM UTC-6, agrays...@gmail.com <> 
>> wrote:
>> 
>> 
>> On Tuesday, November 27, 2018 at 6:00:50 PM UTC, Philip Thrift wrote:
>> 
>> 
>> On Tuesday, November 27, 2018 at 8:43:35 AM UTC-6, agrays...@gmail.com <> 
>> wrote:
>> 
>> 
>> On Tuesday, November 27, 2018 at 9:27:46 AM UTC, Philip Thrift wrote:
>> 
>> 
>> On Monday, November 26, 2018 at 3:43:14 PM UTC-6, agrays...@gmail.com <> 
>> wrote:
>> 
>> I checked the postulates in Feynman's Sums Over Histories (in link provided 
>> by Phil) and I see nothing related to waves, as expected, and thus nothing 
>> about collapse of anything. I would suppose the same applies to Heisenberg's 
>> Matrix Mechanics; no waves, no collapse. I suppose you could say they just 
>> produce correct probabilities, and imply nothing about relative states other 
>> than their probabilities (which wave mechanics does), but certainly nothing 
>> about consciousness. To summarize: you're right that they are "no collapse" 
>> theories, but IMO they say nothing about consciousness. AG
>> 
>> 
>> 
>> 
>> In terms of the path-integral (PI) interpretation [ interesting lecture: 
>> https://www.perimeterinstitute.ca/videos/path-integral-interpretation-quantum-mechanics
>>  
>> 
>>  ], there is in effect no waves or wave function, just paths, or histories, 
>> in the sum-over-histories (SOH) terminology.
>> 
>> There is still "decoherence" in the SOH (a single history is ultimately 
>> "realized"), but it could be called "selection": a single history is 
>> selected from the total ensemble of multiple and interfering histories. E.g. 
>> a single point on a screen is "hit" by a photon in the double-slit 
>> experiment.
>> 
>> Does "selection" add any insight to the measurement problem; that is, why do 
>> we get what we get? And if not, what is its value? TIA, AG 
>> 
>> 
>> 
>> If you look at it as a "selection of the fittest" (one history surviving 
>> from an ensemble of histories), then it's like a form of quantum Darwinism. 
>> The quantum substrate is a cruel world where all histories (but one) die.
>> 
>> That's not an explanation; rather, a vacuous statement of the result. AG 
>> 
>> 
>> But that is a criticism of Darwinism (natural selection) in general.
>> 
>> Ridiculous comparison IMO. Darwinism posits a changing environment and 
>> competition among species for niches. Nothing comparable in Quantum 
>> Darwinism other than all outcomes fail except for one which succeeds in each 
>> single trial, which we knew from the get-go. AG
>> 
>> Quantum Darwinism is a theory claiming to explain the emergence of the 
>> classical world from the 
>> quantum world  as due to a 
>> process of Darwinian  natural 
>> selection ; where the many 
>> possible quantum states  are 
>> selected against in favor of a stable pointer state 
>> .
>> [ https://en.wikipedia.org/wiki/Quantum_Darwinism 
>>  ]
>> 
>> - pt
>>  
>> 
>> 
>> 
>> As for "competition for niches", the histories are in a sense competing. 
>> Perhaps there is some conservation principle at work, so only one history 
>> can win. 
>> 
>> I don't know. Physicists don't know. We're even. :)
>> 
>> Darwin had a theory or proposal to explain why some changes occur and 
>> persist, but Quantum Darwinism doesn't, as far as I can tell. AG 
> 
> I think that the comparison with Darwin makes sense, and in both case, there 
> are many “fittest” entities.
> 
> IMO, it's a ridiculous comparison. If you affirm the MWI, then ALL histories 
> survive.

Only the relatively consistent one, and then with very different relative 
measure. If you go through the windows instead of taking the lift, you will 
survive in both case, but in the normal/Gaussian worlds (measure close to 1), 
you are severely injured in the first case, and not so in the second case.

Bruno


> If you deny the MWI, there's no model whatever of "fittest" to explain why 
> all histories cease to exist except the one measured for a single trial. The 
> only thing remarkable here is that I have to explain this. AG 
> 
> Evolution gives a tree, with many branches, and 

Re: Measuring a system in a superposition of states vs in a mixed state

[Bruno Marchal]

> On 30 Nov 2018, at 12:29, agrayson2...@gmail.com wrote:
> 
> 
> 
> On Friday, November 30, 2018 at 9:03:51 AM UTC, Bruno Marchal wrote:
> 
>> On 28 Nov 2018, at 15:02, agrays...@gmail.com  wrote:
>> 
>> 
>> 
>> On Wednesday, November 28, 2018 at 1:41:03 PM UTC, Bruno Marchal wrote:
>> 
>>> On 26 Nov 2018, at 22:43, agrays...@gmail.com <> wrote:
>>> 
>>> 
>>> 
>>> On Monday, November 26, 2018 at 4:41:42 PM UTC, agrays...@gmail.com 
>>>  wrote:
>>> 
>>> 
>>> On Monday, November 26, 2018 at 12:01:05 PM UTC, Bruno Marchal wrote:
>>> 
 On 23 Nov 2018, at 13:30, agrays...@gmail.com <> wrote:
 
 
 
 On Friday, November 23, 2018 at 11:29:14 AM UTC, Bruno Marchal wrote:
 
> On 21 Nov 2018, at 18:03, agrays...@gmail.com <> wrote:
> 
> 
> 
> On Monday, November 19, 2018 at 3:52:37 PM UTC, Bruno Marchal wrote:
> 
>> On 18 Nov 2018, at 14:00, agrays...@gmail.com <> wrote:
>> 
>> 
>> 
>> On Sunday, November 18, 2018 at 12:19:20 PM UTC, Bruno Marchal wrote:
>> 
>>> On 16 Nov 2018, at 15:38, agrays...@gmail.com <> wrote:
>>> 
>>> 
>>> 
>>> On Friday, November 16, 2018 at 10:14:32 AM UTC, scerir wrote:
>>> 
>>> 
 Il 16 novembre 2018 alle 10.19 agrays...@gmail.com <> ha scritto: 
 
 
 
 On Thursday, November 15, 2018 at 2:14:48 PM UTC, scerir wrote:
 
 
> Il 15 novembre 2018 alle 14.29 agrays...@gmail.com <> ha scritto: 
> 
> 
> 
> On Thursday, November 15, 2018 at 8:04:53 AM UTC, scerir wrote:
> Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) 
> [(s+)_z + (s-)_z] .
> 
> If the x-component of spin is measured by passing the spin-1/2 
> particle through a Stern-Gerlach with its field oriented along the 
> x-axis, the particle will ALWAYS emerge 'up'.
> 
> 
> Why?  Won't the measured value be along the x axis in both 
> directions, in effect Up or Dn? AG
 "Hence we must conclude that the system described by the |+>x state is 
 not the
 same as a mixture of atoms in the |+> and !-> states. This means that 
 each atom in the
 beam is in a state that itself is a combination of the |+> and |-> 
 states. A superposition
 state is often called a coherent superposition since the relative 
 phase of the two terms is
 important."
 
 .see pages 18-19 here https://tinyurl.com/ybm56whu 
 
 
 Try answering in your own words. When the SG device is oriented along 
 the x axis, now effectively the z-axix IIUC, and we're dealing with 
 superpositions, the outcomes will be 50-50 plus and minus. Therefore, 
 unless I am making some error, what you stated above is incorrect. AG
>>> sqrt(1/2) [(s+)_z +(s-)_z]  is a superposition, but since sqrt(1/2) 
>>> [(s+)_z +(s-)_z]  =  (s+)_x the particle will always emerge 'up'
>>> 
>>> 
>>> I'll probably get back to on the foregoing. In the meantime, consider 
>>> this; I claim one can never MEASURE Up + Dn or Up - Dn with a SG 
>>> apparatus regardless of how many other instruments one uses to create a 
>>> composite measuring apparatus (Bruno's claim IIUC). The reason is 
>>> simple. We know that the spin operator
>> 
>> Which one?
>> 
>> Good question. AG
>> 
>> There are spin operator for each direction in space. The superposition 
>> of up and down is a precise pure state, with precise eigenvalues, when 
>> measuring state in the complementary directions.
>> 
>> As I wrote earlier, based on scerir's superpositions on different axes, 
>> and simulation, I now think that Up + Dn and Up - Dn can be measured 
>> along the x axis but not along the z axis (which I was focused on).
> 
> All you need to do is a change of base. The operator will be defined 
> clearly by the Eigen value on the diagonal in the corresponding base. You 
> can prepare any state, and measure them “in any base”. 
> 
> I'll get back to this issue in my next post. AG 
>> You were probably correct about x axis measurements, but perhaps were 
>> not clear enough. You were not explicit that measurements along the x 
>> axis is a different SG experiment from along z axis.
> 
> OK. Sorry. 
>> I thought you meant do them in succession, not as separate experiments.
> 
> Ah? OK.
>> Also introducing an infinity of universes seems extraneous and confusing 
>> for a solution to this problem. AG 
> I are probably different on this. I don’t take the word “universe” too 
> much seriously, as with mechanism we know at the start that there is 
> “physical universe” at all, just the natural numbers with the laws of 

Re: Measuring a system in a superposition of states vs in a mixed state

[Philip Thrift]

On Saturday, December 1, 2018 at 10:12:53 AM UTC-6, agrays...@gmail.com 
wrote:
>
>
>
> On Friday, November 30, 2018 at 8:53:43 AM UTC, Bruno Marchal wrote:
>>
>>
>>
>> I think that the comparison with Darwin makes sense, and in both case, 
>> there are many “fittest” entities.
>>
>
>
> *IMO, it's a ridiculous comparison. If you affirm the MWI, then ALL 
> histories survive. If you deny the MWI, there's no model whatever of 
> "fittest" to explain why all histories cease to exist except the one 
> measured for a single trial. The only thing remarkable here is that I have 
> to explain this. AG *
>
>
>>
With some tweaking, this could be a picture of "histories" competing for 
survival:

*Lottery Machine*
https://www.youtube.com/watch?v=Aw2aKhoD7_U

- pt

 

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Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Friday, November 30, 2018 at 8:53:43 AM UTC, Bruno Marchal wrote:
>
>
> On 27 Nov 2018, at 22:55, agrays...@gmail.com  wrote:
>
>
>
> On Tuesday, November 27, 2018 at 8:43:55 PM UTC, Philip Thrift wrote:
>>
>>
>>
>> On Tuesday, November 27, 2018 at 2:05:04 PM UTC-6, agrays...@gmail.com 
>> wrote:
>>>
>>>
>>>
>>> On Tuesday, November 27, 2018 at 6:49:51 PM UTC, Philip Thrift wrote:



 On Tuesday, November 27, 2018 at 12:17:08 PM UTC-6, agrays...@gmail.com 
 wrote:
>
>
>
> On Tuesday, November 27, 2018 at 6:00:50 PM UTC, Philip Thrift wrote:
>>
>>
>>
>> On Tuesday, November 27, 2018 at 8:43:35 AM UTC-6, 
>> agrays...@gmail.com wrote:
>>>
>>>
>>>
>>> On Tuesday, November 27, 2018 at 9:27:46 AM UTC, Philip Thrift wrote:



 On Monday, November 26, 2018 at 3:43:14 PM UTC-6, 
 agrays...@gmail.com wrote:
>
>
> *I checked the postulates in Feynman's Sums Over Histories (in 
> link provided by Phil) and I see nothing related to waves, as 
> expected, and 
> thus nothing about collapse of anything. I would suppose the same 
> applies 
> to Heisenberg's Matrix Mechanics; no waves, no collapse. I suppose 
> you 
> could say they just produce correct probabilities, and imply nothing 
> about 
> relative states other than their probabilities (which wave mechanics 
> does), 
> but certainly nothing about consciousness. To summarize: you're right 
> that 
> they are "no collapse" theories, but IMO they say nothing about 
> consciousness. AG*
>
>>
>>


 In terms of the path-integral (PI) interpretation [ interesting 
 lecture: 
 https://www.perimeterinstitute.ca/videos/path-integral-interpretation-quantum-mechanics
  
 ], there is in effect no waves or wave function, just paths, or 
 histories, 
 in the sum-over-histories (SOH) terminology.

 There is still "decoherence" in the SOH (a single history is 
 ultimately "realized"), but it could be called "selection": a single 
 history is selected from the total ensemble of multiple and 
 interfering 
 histories. E.g. a single point on a screen is "hit" by a photon in the 
 double-slit experiment.

>>>
>>> *Does "selection" add any insight to the measurement problem; that 
>>> is, why do we get what we get? And if not, what is its value? TIA, AG *
>>>



>> If you look at it as a "selection of the fittest" (one history 
>> surviving from an ensemble of histories), then it's like a form of 
>> quantum 
>> Darwinism. The quantum substrate is a cruel world where all histories 
>> (but 
>> one) die.
>>
>
> That's not an explanation; rather, a vacuous statement of the result. 
> AG 
>
>>
>>
 But that is a criticism of Darwinism (*natural selection*) in general.

>>>
>>> *Ridiculous comparison IMO. Darwinism posits a changing environment and 
>>> competition among species for niches. Nothing comparable in Quantum 
>>> Darwinism other than all outcomes fail except for one which succeeds in 
>>> each single trial, which we knew from the get-go. AG*
>>>

 *Quantum Darwinism* is a theory claiming to explain the emergence of 
 the classical world from 
 the quantum world  as 
 due to *a process of **Darwinian 
  natural selection 
 *; where the many 
 possible quantum states  are 
 selected against in favor of a stable pointer state 
 .
 [ https://en.wikipedia.org/wiki/Quantum_Darwinism ]

 - pt
  

>>>
>>
>>
>> As for "competition for niches", the histories are in a sense competing. 
>> Perhaps there is some conservation principle at work, so only one history 
>> can win. 
>>
>> I don't know. Physicists don't know. We're even. :)
>>
>
> *Darwin had a theory or proposal to explain why some changes occur and 
> persist, but Quantum Darwinism doesn't, as far as I can tell. AG *
>
>
> I think that the comparison with Darwin makes sense, and in both case, 
> there are many “fittest” entities.
>


*IMO, it's a ridiculous comparison. If you affirm the MWI, then ALL 
histories survive. If you deny the MWI, there's no model whatever of 
"fittest" to explain why all histories cease to exist except the one 
measured for a single trial. The only thing remarkable here is that I have 
to explain this. AG *

Evolution gives a tree, with many branches, and 

Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Friday, November 30, 2018 at 9:03:51 AM UTC, Bruno Marchal wrote:
>
>
> On 28 Nov 2018, at 15:02, agrays...@gmail.com  wrote:
>
>
>
> On Wednesday, November 28, 2018 at 1:41:03 PM UTC, Bruno Marchal wrote:
>>
>>
>> On 26 Nov 2018, at 22:43, agrays...@gmail.com wrote:
>>
>>
>>
>> On Monday, November 26, 2018 at 4:41:42 PM UTC, agrays...@gmail.com 
>> wrote:
>>>
>>>
>>>
>>> On Monday, November 26, 2018 at 12:01:05 PM UTC, Bruno Marchal wrote:


 On 23 Nov 2018, at 13:30, agrays...@gmail.com wrote:



 On Friday, November 23, 2018 at 11:29:14 AM UTC, Bruno Marchal wrote:
>
>
> On 21 Nov 2018, at 18:03, agrays...@gmail.com wrote:
>
>
>
> On Monday, November 19, 2018 at 3:52:37 PM UTC, Bruno Marchal wrote:
>>
>>
>> On 18 Nov 2018, at 14:00, agrays...@gmail.com wrote:
>>
>>
>>
>> On Sunday, November 18, 2018 at 12:19:20 PM UTC, Bruno Marchal wrote:
>>>
>>>
>>> On 16 Nov 2018, at 15:38, agrays...@gmail.com wrote:
>>>
>>>
>>>
>>> On Friday, November 16, 2018 at 10:14:32 AM UTC, scerir wrote:


 Il 16 novembre 2018 alle 10.19 agrays...@gmail.com ha scritto: 



 On Thursday, November 15, 2018 at 2:14:48 PM UTC, scerir wrote:


 Il 15 novembre 2018 alle 14.29 agrays...@gmail.com ha scritto: 



 On Thursday, November 15, 2018 at 8:04:53 AM UTC, scerir wrote:

 Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) 
 [(s+)_z + (s-)_z] .

 If the x-component of spin is measured by passing the spin-1/2 
 particle through a Stern-Gerlach with its field oriented along the 
 x-axis, 
 the particle will ALWAYS emerge 'up'.


 *Why?  Won't the measured value be along the x axis in both 
 directions, in effect Up or Dn? AG*

 "Hence we must conclude that the system described by the |+>x state 
 is not the
 same as a mixture of atoms in the |+> and !-> states. This means 
 that each atom in the
 beam is in a state that itself is a combination of the |+> and |-> 
 states. A superposition
 state is often called a coherent superposition since the relative 
 phase of the two terms is
 important."

 .see pages 18-19 here *https://tinyurl.com/ybm56whu 
 *


 *Try answering in your own words. When the SG device is oriented 
 along the x axis, now effectively the z-axix IIUC, and we're dealing 
 with 
 superpositions, the outcomes will be 50-50 plus and minus. Therefore, 
 unless I am making some error, what you stated above is incorrect. AG *

 sqrt(1/2) [(s+)_z +(s-)_z]  is a superposition, but since sqrt(1/2) 
 [(s+)_z +(s-)_z]  =  (s+)_x the particle will always emerge 'up'

>>>
>>> I'll probably get back to on the foregoing. In the meantime, 
>>> consider this; I claim one can never MEASURE Up + Dn or Up - Dn with a 
>>> SG 
>>> apparatus regardless of how many other instruments one uses to create a 
>>> composite measuring apparatus (Bruno's claim IIUC). The reason is 
>>> simple. 
>>> We know that the spin operator 
>>>
>>>
>>> Which one? 
>>>
>>
>> *Good question. AG*
>>
>> There are spin operator for each direction in space. The 
>>> superposition of up and down is a precise pure state, with precise 
>>> eigenvalues, when measuring state in the complementary directions.
>>>
>>
>> *As I wrote earlier, based on scerir's superpositions on different 
>> axes, and simulation, I now think that Up + Dn and Up - Dn can be 
>> measured 
>> along the x axis but not along the z axis (which I was focused on). *
>>
>>
>> All you need to do is a change of base. The operator will be defined 
>> clearly by the Eigen value on the diagonal in the corresponding base. 
>> You 
>> can prepare any state, and measure them “in any base”. 
>>
>
>
> *I'll get back to this issue in my next post. AG *
>
>> *You were probably correct about x axis measurements, but perhaps 
>> were not clear enough. You were not explicit that measurements along the 
>> x 
>> axis is a different SG experiment from along z axis.*
>>
>>
>> OK. Sorry. 
>>
>> * I thought you meant do them in succession, not as separate 
>> experiments.*
>>
>>
>> Ah? OK.
>>
>>
>> * Also introducing an infinity of universes seems extraneous and 
>> confusing for a solution to this problem. AG *
>>
>> I are probably different on this. I don’t take the word “universe” 
>> too much seriously, as with mechanism we know at the start 

Re: Measuring a system in a superposition of states vs in a mixed state

[Bruno Marchal]

> On 28 Nov 2018, at 16:37, agrayson2...@gmail.com wrote:
> 
> 
> 
> On Wednesday, November 28, 2018 at 1:46:28 PM UTC, Bruno Marchal wrote:
> 
>> On 26 Nov 2018, at 22:49, agrays...@gmail.com  wrote:
>> 
>> 
>> 
>> On Monday, November 26, 2018 at 9:43:14 PM UTC, agrays...@gmail.com 
>>  wrote:
>> 
>> 
>> On Monday, November 26, 2018 at 4:41:42 PM UTC, agrays...@gmail.com <> wrote:
>> 
>> 
>> On Monday, November 26, 2018 at 12:01:05 PM UTC, Bruno Marchal wrote:
>> 
>>> On 23 Nov 2018, at 13:30, agrays...@gmail.com <> wrote:
>>> 
>>> 
>>> 
>>> On Friday, November 23, 2018 at 11:29:14 AM UTC, Bruno Marchal wrote:
>>> 
 On 21 Nov 2018, at 18:03, agrays...@gmail.com <> wrote:
 
 
 
 On Monday, November 19, 2018 at 3:52:37 PM UTC, Bruno Marchal wrote:
 
> On 18 Nov 2018, at 14:00, agrays...@gmail.com <> wrote:
> 
> 
> 
> On Sunday, November 18, 2018 at 12:19:20 PM UTC, Bruno Marchal wrote:
> 
>> On 16 Nov 2018, at 15:38, agrays...@gmail.com <> wrote:
>> 
>> 
>> 
>> On Friday, November 16, 2018 at 10:14:32 AM UTC, scerir wrote:
>> 
>> 
>>> Il 16 novembre 2018 alle 10.19 agrays...@gmail.com <> ha scritto: 
>>> 
>>> 
>>> 
>>> On Thursday, November 15, 2018 at 2:14:48 PM UTC, scerir wrote:
>>> 
>>> 
 Il 15 novembre 2018 alle 14.29 agrays...@gmail.com <> ha scritto: 
 
 
 
 On Thursday, November 15, 2018 at 8:04:53 AM UTC, scerir wrote:
 Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) 
 [(s+)_z + (s-)_z] .
 
 If the x-component of spin is measured by passing the spin-1/2 
 particle through a Stern-Gerlach with its field oriented along the 
 x-axis, the particle will ALWAYS emerge 'up'.
 
 
 Why?  Won't the measured value be along the x axis in both directions, 
 in effect Up or Dn? AG
>>> "Hence we must conclude that the system described by the |+>x state is 
>>> not the
>>> same as a mixture of atoms in the |+> and !-> states. This means that 
>>> each atom in the
>>> beam is in a state that itself is a combination of the |+> and |-> 
>>> states. A superposition
>>> state is often called a coherent superposition since the relative phase 
>>> of the two terms is
>>> important."
>>> 
>>> .see pages 18-19 here https://tinyurl.com/ybm56whu 
>>> 
>>> 
>>> Try answering in your own words. When the SG device is oriented along 
>>> the x axis, now effectively the z-axix IIUC, and we're dealing with 
>>> superpositions, the outcomes will be 50-50 plus and minus. Therefore, 
>>> unless I am making some error, what you stated above is incorrect. AG
>> sqrt(1/2) [(s+)_z +(s-)_z]  is a superposition, but since sqrt(1/2) 
>> [(s+)_z +(s-)_z]  =  (s+)_x the particle will always emerge 'up'
>> 
>> 
>> I'll probably get back to on the foregoing. In the meantime, consider 
>> this; I claim one can never MEASURE Up + Dn or Up - Dn with a SG 
>> apparatus regardless of how many other instruments one uses to create a 
>> composite measuring apparatus (Bruno's claim IIUC). The reason is 
>> simple. We know that the spin operator
> 
> Which one?
> 
> Good question. AG
> 
> There are spin operator for each direction in space. The superposition of 
> up and down is a precise pure state, with precise eigenvalues, when 
> measuring state in the complementary directions.
> 
> As I wrote earlier, based on scerir's superpositions on different axes, 
> and simulation, I now think that Up + Dn and Up - Dn can be measured 
> along the x axis but not along the z axis (which I was focused on).
 
 All you need to do is a change of base. The operator will be defined 
 clearly by the Eigen value on the diagonal in the corresponding base. You 
 can prepare any state, and measure them “in any base”. 
 
 I'll get back to this issue in my next post. AG 
> You were probably correct about x axis measurements, but perhaps were not 
> clear enough. You were not explicit that measurements along the x axis is 
> a different SG experiment from along z axis.
 
 OK. Sorry. 
> I thought you meant do them in succession, not as separate experiments.
 
 Ah? OK.
> Also introducing an infinity of universes seems extraneous and confusing 
> for a solution to this problem. AG 
 I are probably different on this. I don’t take the word “universe” too 
 much seriously, as with mechanism we know at the start that there is 
 “physical universe” at all, just the natural numbers with the laws of 
 addition and multiplication. Both the computational and the quantum state 
 are relative, and high level, pertaining to what is “observable” for some 
 the point 

Re: Measuring a system in a superposition of states vs in a mixed state

[Bruno Marchal]

> On 28 Nov 2018, at 15:02, agrayson2...@gmail.com wrote:
> 
> 
> 
> On Wednesday, November 28, 2018 at 1:41:03 PM UTC, Bruno Marchal wrote:
> 
>> On 26 Nov 2018, at 22:43, agrays...@gmail.com  wrote:
>> 
>> 
>> 
>> On Monday, November 26, 2018 at 4:41:42 PM UTC, agrays...@gmail.com 
>>  wrote:
>> 
>> 
>> On Monday, November 26, 2018 at 12:01:05 PM UTC, Bruno Marchal wrote:
>> 
>>> On 23 Nov 2018, at 13:30, agrays...@gmail.com <> wrote:
>>> 
>>> 
>>> 
>>> On Friday, November 23, 2018 at 11:29:14 AM UTC, Bruno Marchal wrote:
>>> 
 On 21 Nov 2018, at 18:03, agrays...@gmail.com <> wrote:
 
 
 
 On Monday, November 19, 2018 at 3:52:37 PM UTC, Bruno Marchal wrote:
 
> On 18 Nov 2018, at 14:00, agrays...@gmail.com <> wrote:
> 
> 
> 
> On Sunday, November 18, 2018 at 12:19:20 PM UTC, Bruno Marchal wrote:
> 
>> On 16 Nov 2018, at 15:38, agrays...@gmail.com <> wrote:
>> 
>> 
>> 
>> On Friday, November 16, 2018 at 10:14:32 AM UTC, scerir wrote:
>> 
>> 
>>> Il 16 novembre 2018 alle 10.19 agrays...@gmail.com <> ha scritto: 
>>> 
>>> 
>>> 
>>> On Thursday, November 15, 2018 at 2:14:48 PM UTC, scerir wrote:
>>> 
>>> 
 Il 15 novembre 2018 alle 14.29 agrays...@gmail.com <> ha scritto: 
 
 
 
 On Thursday, November 15, 2018 at 8:04:53 AM UTC, scerir wrote:
 Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) 
 [(s+)_z + (s-)_z] .
 
 If the x-component of spin is measured by passing the spin-1/2 
 particle through a Stern-Gerlach with its field oriented along the 
 x-axis, the particle will ALWAYS emerge 'up'.
 
 
 Why?  Won't the measured value be along the x axis in both directions, 
 in effect Up or Dn? AG
>>> "Hence we must conclude that the system described by the |+>x state is 
>>> not the
>>> same as a mixture of atoms in the |+> and !-> states. This means that 
>>> each atom in the
>>> beam is in a state that itself is a combination of the |+> and |-> 
>>> states. A superposition
>>> state is often called a coherent superposition since the relative phase 
>>> of the two terms is
>>> important."
>>> 
>>> .see pages 18-19 here https://tinyurl.com/ybm56whu 
>>> 
>>> 
>>> Try answering in your own words. When the SG device is oriented along 
>>> the x axis, now effectively the z-axix IIUC, and we're dealing with 
>>> superpositions, the outcomes will be 50-50 plus and minus. Therefore, 
>>> unless I am making some error, what you stated above is incorrect. AG
>> sqrt(1/2) [(s+)_z +(s-)_z]  is a superposition, but since sqrt(1/2) 
>> [(s+)_z +(s-)_z]  =  (s+)_x the particle will always emerge 'up'
>> 
>> 
>> I'll probably get back to on the foregoing. In the meantime, consider 
>> this; I claim one can never MEASURE Up + Dn or Up - Dn with a SG 
>> apparatus regardless of how many other instruments one uses to create a 
>> composite measuring apparatus (Bruno's claim IIUC). The reason is 
>> simple. We know that the spin operator
> 
> Which one?
> 
> Good question. AG
> 
> There are spin operator for each direction in space. The superposition of 
> up and down is a precise pure state, with precise eigenvalues, when 
> measuring state in the complementary directions.
> 
> As I wrote earlier, based on scerir's superpositions on different axes, 
> and simulation, I now think that Up + Dn and Up - Dn can be measured 
> along the x axis but not along the z axis (which I was focused on).
 
 All you need to do is a change of base. The operator will be defined 
 clearly by the Eigen value on the diagonal in the corresponding base. You 
 can prepare any state, and measure them “in any base”. 
 
 I'll get back to this issue in my next post. AG 
> You were probably correct about x axis measurements, but perhaps were not 
> clear enough. You were not explicit that measurements along the x axis is 
> a different SG experiment from along z axis.
 
 OK. Sorry. 
> I thought you meant do them in succession, not as separate experiments.
 
 Ah? OK.
> Also introducing an infinity of universes seems extraneous and confusing 
> for a solution to this problem. AG 
 I are probably different on this. I don’t take the word “universe” too 
 much seriously, as with mechanism we know at the start that there is 
 “physical universe” at all, just the natural numbers with the laws of 
 addition and multiplication. Both the computational and the quantum state 
 are relative, and high level, pertaining to what is “observable” for some 
 the point of view of some locally finite subject, run by some computation.
 
 The empirical 

Re: Measuring a system in a superposition of states vs in a mixed state

[Bruno Marchal]

> On 27 Nov 2018, at 22:55, agrayson2...@gmail.com wrote:
> 
> 
> 
> On Tuesday, November 27, 2018 at 8:43:55 PM UTC, Philip Thrift wrote:
> 
> 
> On Tuesday, November 27, 2018 at 2:05:04 PM UTC-6, agrays...@gmail.com <> 
> wrote:
> 
> 
> On Tuesday, November 27, 2018 at 6:49:51 PM UTC, Philip Thrift wrote:
> 
> 
> On Tuesday, November 27, 2018 at 12:17:08 PM UTC-6, agrays...@gmail.com <> 
> wrote:
> 
> 
> On Tuesday, November 27, 2018 at 6:00:50 PM UTC, Philip Thrift wrote:
> 
> 
> On Tuesday, November 27, 2018 at 8:43:35 AM UTC-6, agrays...@gmail.com <> 
> wrote:
> 
> 
> On Tuesday, November 27, 2018 at 9:27:46 AM UTC, Philip Thrift wrote:
> 
> 
> On Monday, November 26, 2018 at 3:43:14 PM UTC-6, agrays...@gmail.com <> 
> wrote:
> 
> I checked the postulates in Feynman's Sums Over Histories (in link provided 
> by Phil) and I see nothing related to waves, as expected, and thus nothing 
> about collapse of anything. I would suppose the same applies to Heisenberg's 
> Matrix Mechanics; no waves, no collapse. I suppose you could say they just 
> produce correct probabilities, and imply nothing about relative states other 
> than their probabilities (which wave mechanics does), but certainly nothing 
> about consciousness. To summarize: you're right that they are "no collapse" 
> theories, but IMO they say nothing about consciousness. AG
> 
> 
> 
> 
> In terms of the path-integral (PI) interpretation [ interesting lecture: 
> https://www.perimeterinstitute.ca/videos/path-integral-interpretation-quantum-mechanics
>  
> 
>  ], there is in effect no waves or wave function, just paths, or histories, 
> in the sum-over-histories (SOH) terminology.
> 
> There is still "decoherence" in the SOH (a single history is ultimately 
> "realized"), but it could be called "selection": a single history is selected 
> from the total ensemble of multiple and interfering histories. E.g. a single 
> point on a screen is "hit" by a photon in the double-slit experiment.
> 
> Does "selection" add any insight to the measurement problem; that is, why do 
> we get what we get? And if not, what is its value? TIA, AG 
> 
> 
> 
> If you look at it as a "selection of the fittest" (one history surviving from 
> an ensemble of histories), then it's like a form of quantum Darwinism. The 
> quantum substrate is a cruel world where all histories (but one) die.
> 
> That's not an explanation; rather, a vacuous statement of the result. AG 
> 
> 
> But that is a criticism of Darwinism (natural selection) in general.
> 
> Ridiculous comparison IMO. Darwinism posits a changing environment and 
> competition among species for niches. Nothing comparable in Quantum Darwinism 
> other than all outcomes fail except for one which succeeds in each single 
> trial, which we knew from the get-go. AG
> 
> Quantum Darwinism is a theory claiming to explain the emergence of the 
> classical world from the 
> quantum world  as due to a 
> process of Darwinian  natural 
> selection ; where the many 
> possible quantum states  are 
> selected against in favor of a stable pointer state 
> .
> [ https://en.wikipedia.org/wiki/Quantum_Darwinism 
>  ]
> 
> - pt
>  
> 
> 
> 
> As for "competition for niches", the histories are in a sense competing. 
> Perhaps there is some conservation principle at work, so only one history can 
> win. 
> 
> I don't know. Physicists don't know. We're even. :)
> 
> Darwin had a theory or proposal to explain why some changes occur and 
> persist, but Quantum Darwinism doesn't, as far as I can tell. AG 

I think that the comparison with Darwin makes sense, and in both case, there 
are many “fittest” entities. Evolution gives a tree, with many branches, and 
"quantum Darwinism” gives rise too too many locally consistent histories. None 
select one individual branche, ISTM.

Bruno



> 
> - pt
> 
> -- 
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Re: Measuring a system in a superposition of states vs in a mixed state

[Philip Thrift]

On Wednesday, November 28, 2018 at 7:41:03 AM UTC-6, Bruno Marchal wrote:
>
>
> You can derive Schroedinger's equation (even Dirac’s equation) from 
> Feynman’s formulation. This should be intuitively obvious if you read 
> Feynman popular book on the Nature of Light. The waves are there. But yes: 
> the collapse does not make sense in Feynman’s formulation (or it looks even 
> more ad hoc and non covariant). That is a reason to disbelieve in the 
> collapse, but then you get some version of the many-world view (which you 
> dislike apparently).
>
>
>


With Feynman (path integral, or sum over histories), instead of Many 
Worlds, you get Multiple Histories. 
- https://en.wikipedia.org/wiki/Multiple_histories

Spoiler alert: Only one history makes it out alive!

Some physicists who can't believe in probabilities (stochasticity) - which 
they avoid like vampires avoid running water - like Many Worlds.

- pt

-- 
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To unsubscribe from this group and stop receiving emails from it, send an email 
to everything-list+unsubscr...@googlegroups.com.
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Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Wednesday, November 28, 2018 at 1:46:28 PM UTC, Bruno Marchal wrote:
>
>
> On 26 Nov 2018, at 22:49, agrays...@gmail.com  wrote:
>
>
>
> On Monday, November 26, 2018 at 9:43:14 PM UTC, agrays...@gmail.com wrote:
>>
>>
>>
>> On Monday, November 26, 2018 at 4:41:42 PM UTC, agrays...@gmail.com 
>> wrote:
>>>
>>>
>>>
>>> On Monday, November 26, 2018 at 12:01:05 PM UTC, Bruno Marchal wrote:


 On 23 Nov 2018, at 13:30, agrays...@gmail.com wrote:



 On Friday, November 23, 2018 at 11:29:14 AM UTC, Bruno Marchal wrote:
>
>
> On 21 Nov 2018, at 18:03, agrays...@gmail.com wrote:
>
>
>
> On Monday, November 19, 2018 at 3:52:37 PM UTC, Bruno Marchal wrote:
>>
>>
>> On 18 Nov 2018, at 14:00, agrays...@gmail.com wrote:
>>
>>
>>
>> On Sunday, November 18, 2018 at 12:19:20 PM UTC, Bruno Marchal wrote:
>>>
>>>
>>> On 16 Nov 2018, at 15:38, agrays...@gmail.com wrote:
>>>
>>>
>>>
>>> On Friday, November 16, 2018 at 10:14:32 AM UTC, scerir wrote:


 Il 16 novembre 2018 alle 10.19 agrays...@gmail.com ha scritto: 



 On Thursday, November 15, 2018 at 2:14:48 PM UTC, scerir wrote:


 Il 15 novembre 2018 alle 14.29 agrays...@gmail.com ha scritto: 



 On Thursday, November 15, 2018 at 8:04:53 AM UTC, scerir wrote:

 Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) 
 [(s+)_z + (s-)_z] .

 If the x-component of spin is measured by passing the spin-1/2 
 particle through a Stern-Gerlach with its field oriented along the 
 x-axis, 
 the particle will ALWAYS emerge 'up'.


 *Why?  Won't the measured value be along the x axis in both 
 directions, in effect Up or Dn? AG*

 "Hence we must conclude that the system described by the |+>x state 
 is not the
 same as a mixture of atoms in the |+> and !-> states. This means 
 that each atom in the
 beam is in a state that itself is a combination of the |+> and |-> 
 states. A superposition
 state is often called a coherent superposition since the relative 
 phase of the two terms is
 important."

 .see pages 18-19 here *https://tinyurl.com/ybm56whu 
 *


 *Try answering in your own words. When the SG device is oriented 
 along the x axis, now effectively the z-axix IIUC, and we're dealing 
 with 
 superpositions, the outcomes will be 50-50 plus and minus. Therefore, 
 unless I am making some error, what you stated above is incorrect. AG *

 sqrt(1/2) [(s+)_z +(s-)_z]  is a superposition, but since sqrt(1/2) 
 [(s+)_z +(s-)_z]  =  (s+)_x the particle will always emerge 'up'

>>>
>>> I'll probably get back to on the foregoing. In the meantime, 
>>> consider this; I claim one can never MEASURE Up + Dn or Up - Dn with a 
>>> SG 
>>> apparatus regardless of how many other instruments one uses to create a 
>>> composite measuring apparatus (Bruno's claim IIUC). The reason is 
>>> simple. 
>>> We know that the spin operator 
>>>
>>>
>>> Which one? 
>>>
>>
>> *Good question. AG*
>>
>> There are spin operator for each direction in space. The 
>>> superposition of up and down is a precise pure state, with precise 
>>> eigenvalues, when measuring state in the complementary directions.
>>>
>>
>> *As I wrote earlier, based on scerir's superpositions on different 
>> axes, and simulation, I now think that Up + Dn and Up - Dn can be 
>> measured 
>> along the x axis but not along the z axis (which I was focused on). *
>>
>>
>> All you need to do is a change of base. The operator will be defined 
>> clearly by the Eigen value on the diagonal in the corresponding base. 
>> You 
>> can prepare any state, and measure them “in any base”. 
>>
>
>
> *I'll get back to this issue in my next post. AG *
>
>> *You were probably correct about x axis measurements, but perhaps 
>> were not clear enough. You were not explicit that measurements along the 
>> x 
>> axis is a different SG experiment from along z axis.*
>>
>>
>> OK. Sorry. 
>>
>> * I thought you meant do them in succession, not as separate 
>> experiments.*
>>
>>
>> Ah? OK.
>>
>>
>> * Also introducing an infinity of universes seems extraneous and 
>> confusing for a solution to this problem. AG *
>>
>> I are probably different on this. I don’t take the word “universe” 
>> too much seriously, as with mechanism we know at the start that there is 
>> “physical universe” at all, just 

Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Wednesday, November 28, 2018 at 1:41:03 PM UTC, Bruno Marchal wrote:
>
>
> On 26 Nov 2018, at 22:43, agrays...@gmail.com  wrote:
>
>
>
> On Monday, November 26, 2018 at 4:41:42 PM UTC, agrays...@gmail.com wrote:
>>
>>
>>
>> On Monday, November 26, 2018 at 12:01:05 PM UTC, Bruno Marchal wrote:
>>>
>>>
>>> On 23 Nov 2018, at 13:30, agrays...@gmail.com wrote:
>>>
>>>
>>>
>>> On Friday, November 23, 2018 at 11:29:14 AM UTC, Bruno Marchal wrote:


 On 21 Nov 2018, at 18:03, agrays...@gmail.com wrote:



 On Monday, November 19, 2018 at 3:52:37 PM UTC, Bruno Marchal wrote:
>
>
> On 18 Nov 2018, at 14:00, agrays...@gmail.com wrote:
>
>
>
> On Sunday, November 18, 2018 at 12:19:20 PM UTC, Bruno Marchal wrote:
>>
>>
>> On 16 Nov 2018, at 15:38, agrays...@gmail.com wrote:
>>
>>
>>
>> On Friday, November 16, 2018 at 10:14:32 AM UTC, scerir wrote:
>>>
>>>
>>> Il 16 novembre 2018 alle 10.19 agrays...@gmail.com ha scritto: 
>>>
>>>
>>>
>>> On Thursday, November 15, 2018 at 2:14:48 PM UTC, scerir wrote:
>>>
>>>
>>> Il 15 novembre 2018 alle 14.29 agrays...@gmail.com ha scritto: 
>>>
>>>
>>>
>>> On Thursday, November 15, 2018 at 8:04:53 AM UTC, scerir wrote:
>>>
>>> Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) 
>>> [(s+)_z + (s-)_z] .
>>>
>>> If the x-component of spin is measured by passing the spin-1/2 
>>> particle through a Stern-Gerlach with its field oriented along the 
>>> x-axis, 
>>> the particle will ALWAYS emerge 'up'.
>>>
>>>
>>> *Why?  Won't the measured value be along the x axis in both 
>>> directions, in effect Up or Dn? AG*
>>>
>>> "Hence we must conclude that the system described by the |+>x state 
>>> is not the
>>> same as a mixture of atoms in the |+> and !-> states. This means 
>>> that each atom in the
>>> beam is in a state that itself is a combination of the |+> and |-> 
>>> states. A superposition
>>> state is often called a coherent superposition since the relative 
>>> phase of the two terms is
>>> important."
>>>
>>> .see pages 18-19 here *https://tinyurl.com/ybm56whu 
>>> *
>>>
>>>
>>> *Try answering in your own words. When the SG device is oriented 
>>> along the x axis, now effectively the z-axix IIUC, and we're dealing 
>>> with 
>>> superpositions, the outcomes will be 50-50 plus and minus. Therefore, 
>>> unless I am making some error, what you stated above is incorrect. AG *
>>>
>>> sqrt(1/2) [(s+)_z +(s-)_z]  is a superposition, but since sqrt(1/2) 
>>> [(s+)_z +(s-)_z]  =  (s+)_x the particle will always emerge 'up'
>>>
>>
>> I'll probably get back to on the foregoing. In the meantime, consider 
>> this; I claim one can never MEASURE Up + Dn or Up - Dn with a SG 
>> apparatus 
>> regardless of how many other instruments one uses to create a composite 
>> measuring apparatus (Bruno's claim IIUC). The reason is simple. We know 
>> that the spin operator 
>>
>>
>> Which one? 
>>
>
> *Good question. AG*
>
> There are spin operator for each direction in space. The superposition 
>> of up and down is a precise pure state, with precise eigenvalues, when 
>> measuring state in the complementary directions.
>>
>
> *As I wrote earlier, based on scerir's superpositions on different 
> axes, and simulation, I now think that Up + Dn and Up - Dn can be 
> measured 
> along the x axis but not along the z axis (which I was focused on). *
>
>
> All you need to do is a change of base. The operator will be defined 
> clearly by the Eigen value on the diagonal in the corresponding base. You 
> can prepare any state, and measure them “in any base”. 
>


 *I'll get back to this issue in my next post. AG *

> *You were probably correct about x axis measurements, but perhaps were 
> not clear enough. You were not explicit that measurements along the x 
> axis 
> is a different SG experiment from along z axis.*
>
>
> OK. Sorry. 
>
> * I thought you meant do them in succession, not as separate 
> experiments.*
>
>
> Ah? OK.
>
>
> * Also introducing an infinity of universes seems extraneous and 
> confusing for a solution to this problem. AG *
>
> I are probably different on this. I don’t take the word “universe” too 
> much seriously, as with mechanism we know at the start that there is 
> “physical universe” at all, just the natural numbers with the laws of 
> addition and multiplication. Both the computational and the quantum state 
> are relative, and high level, pertaining to what is “observable” for some 
> the point of view of some locally finite 

Re: Measuring a system in a superposition of states vs in a mixed state

[Bruno Marchal]

> On 26 Nov 2018, at 22:49, agrayson2...@gmail.com wrote:
> 
> 
> 
> On Monday, November 26, 2018 at 9:43:14 PM UTC, agrays...@gmail.com wrote:
> 
> 
> On Monday, November 26, 2018 at 4:41:42 PM UTC, agrays...@gmail.com <> wrote:
> 
> 
> On Monday, November 26, 2018 at 12:01:05 PM UTC, Bruno Marchal wrote:
> 
>> On 23 Nov 2018, at 13:30, agrays...@gmail.com <> wrote:
>> 
>> 
>> 
>> On Friday, November 23, 2018 at 11:29:14 AM UTC, Bruno Marchal wrote:
>> 
>>> On 21 Nov 2018, at 18:03, agrays...@gmail.com <> wrote:
>>> 
>>> 
>>> 
>>> On Monday, November 19, 2018 at 3:52:37 PM UTC, Bruno Marchal wrote:
>>> 
 On 18 Nov 2018, at 14:00, agrays...@gmail.com <> wrote:
 
 
 
 On Sunday, November 18, 2018 at 12:19:20 PM UTC, Bruno Marchal wrote:
 
> On 16 Nov 2018, at 15:38, agrays...@gmail.com <> wrote:
> 
> 
> 
> On Friday, November 16, 2018 at 10:14:32 AM UTC, scerir wrote:
> 
> 
>> Il 16 novembre 2018 alle 10.19 agrays...@gmail.com <> ha scritto: 
>> 
>> 
>> 
>> On Thursday, November 15, 2018 at 2:14:48 PM UTC, scerir wrote:
>> 
>> 
>>> Il 15 novembre 2018 alle 14.29 agrays...@gmail.com <> ha scritto: 
>>> 
>>> 
>>> 
>>> On Thursday, November 15, 2018 at 8:04:53 AM UTC, scerir wrote:
>>> Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) 
>>> [(s+)_z + (s-)_z] .
>>> 
>>> If the x-component of spin is measured by passing the spin-1/2 particle 
>>> through a Stern-Gerlach with its field oriented along the x-axis, the 
>>> particle will ALWAYS emerge 'up'.
>>> 
>>> 
>>> Why?  Won't the measured value be along the x axis in both directions, 
>>> in effect Up or Dn? AG
>> "Hence we must conclude that the system described by the |+>x state is 
>> not the
>> same as a mixture of atoms in the |+> and !-> states. This means that 
>> each atom in the
>> beam is in a state that itself is a combination of the |+> and |-> 
>> states. A superposition
>> state is often called a coherent superposition since the relative phase 
>> of the two terms is
>> important."
>> 
>> .see pages 18-19 here https://tinyurl.com/ybm56whu 
>> 
>> 
>> Try answering in your own words. When the SG device is oriented along 
>> the x axis, now effectively the z-axix IIUC, and we're dealing with 
>> superpositions, the outcomes will be 50-50 plus and minus. Therefore, 
>> unless I am making some error, what you stated above is incorrect. AG
> sqrt(1/2) [(s+)_z +(s-)_z]  is a superposition, but since sqrt(1/2) 
> [(s+)_z +(s-)_z]  =  (s+)_x the particle will always emerge 'up'
> 
> 
> I'll probably get back to on the foregoing. In the meantime, consider 
> this; I claim one can never MEASURE Up + Dn or Up - Dn with a SG 
> apparatus regardless of how many other instruments one uses to create a 
> composite measuring apparatus (Bruno's claim IIUC). The reason is simple. 
> We know that the spin operator
 
 Which one?
 
 Good question. AG
 
 There are spin operator for each direction in space. The superposition of 
 up and down is a precise pure state, with precise eigenvalues, when 
 measuring state in the complementary directions.
 
 As I wrote earlier, based on scerir's superpositions on different axes, 
 and simulation, I now think that Up + Dn and Up - Dn can be measured along 
 the x axis but not along the z axis (which I was focused on).
>>> 
>>> All you need to do is a change of base. The operator will be defined 
>>> clearly by the Eigen value on the diagonal in the corresponding base. You 
>>> can prepare any state, and measure them “in any base”. 
>>> 
>>> I'll get back to this issue in my next post. AG 
 You were probably correct about x axis measurements, but perhaps were not 
 clear enough. You were not explicit that measurements along the x axis is 
 a different SG experiment from along z axis.
>>> 
>>> OK. Sorry. 
 I thought you meant do them in succession, not as separate experiments.
>>> 
>>> Ah? OK.
 Also introducing an infinity of universes seems extraneous and confusing 
 for a solution to this problem. AG 
>>> I are probably different on this. I don’t take the word “universe” too much 
>>> seriously, as with mechanism we know at the start that there is “physical 
>>> universe” at all, just the natural numbers with the laws of addition and 
>>> multiplication. Both the computational and the quantum state are relative, 
>>> and high level, pertaining to what is “observable” for some the point of 
>>> view of some locally finite subject, run by some computation.
>>> 
>>> The empirical point, though, is that to predict correctly an event in 
>>> quantum mechanics, we have to take into account may simultaneous 
>>> “incompatible path”, like going through each hole in a plane. 

Re: Measuring a system in a superposition of states vs in a mixed state

[Bruno Marchal]

> On 26 Nov 2018, at 22:43, agrayson2...@gmail.com wrote:
> 
> 
> 
> On Monday, November 26, 2018 at 4:41:42 PM UTC, agrays...@gmail.com wrote:
> 
> 
> On Monday, November 26, 2018 at 12:01:05 PM UTC, Bruno Marchal wrote:
> 
>> On 23 Nov 2018, at 13:30, agrays...@gmail.com <> wrote:
>> 
>> 
>> 
>> On Friday, November 23, 2018 at 11:29:14 AM UTC, Bruno Marchal wrote:
>> 
>>> On 21 Nov 2018, at 18:03, agrays...@gmail.com <> wrote:
>>> 
>>> 
>>> 
>>> On Monday, November 19, 2018 at 3:52:37 PM UTC, Bruno Marchal wrote:
>>> 
 On 18 Nov 2018, at 14:00, agrays...@gmail.com <> wrote:
 
 
 
 On Sunday, November 18, 2018 at 12:19:20 PM UTC, Bruno Marchal wrote:
 
> On 16 Nov 2018, at 15:38, agrays...@gmail.com <> wrote:
> 
> 
> 
> On Friday, November 16, 2018 at 10:14:32 AM UTC, scerir wrote:
> 
> 
>> Il 16 novembre 2018 alle 10.19 agrays...@gmail.com <> ha scritto: 
>> 
>> 
>> 
>> On Thursday, November 15, 2018 at 2:14:48 PM UTC, scerir wrote:
>> 
>> 
>>> Il 15 novembre 2018 alle 14.29 agrays...@gmail.com <> ha scritto: 
>>> 
>>> 
>>> 
>>> On Thursday, November 15, 2018 at 8:04:53 AM UTC, scerir wrote:
>>> Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) 
>>> [(s+)_z + (s-)_z] .
>>> 
>>> If the x-component of spin is measured by passing the spin-1/2 particle 
>>> through a Stern-Gerlach with its field oriented along the x-axis, the 
>>> particle will ALWAYS emerge 'up'.
>>> 
>>> 
>>> Why?  Won't the measured value be along the x axis in both directions, 
>>> in effect Up or Dn? AG
>> "Hence we must conclude that the system described by the |+>x state is 
>> not the
>> same as a mixture of atoms in the |+> and !-> states. This means that 
>> each atom in the
>> beam is in a state that itself is a combination of the |+> and |-> 
>> states. A superposition
>> state is often called a coherent superposition since the relative phase 
>> of the two terms is
>> important."
>> 
>> .see pages 18-19 here https://tinyurl.com/ybm56whu 
>> 
>> 
>> Try answering in your own words. When the SG device is oriented along 
>> the x axis, now effectively the z-axix IIUC, and we're dealing with 
>> superpositions, the outcomes will be 50-50 plus and minus. Therefore, 
>> unless I am making some error, what you stated above is incorrect. AG
> sqrt(1/2) [(s+)_z +(s-)_z]  is a superposition, but since sqrt(1/2) 
> [(s+)_z +(s-)_z]  =  (s+)_x the particle will always emerge 'up'
> 
> 
> I'll probably get back to on the foregoing. In the meantime, consider 
> this; I claim one can never MEASURE Up + Dn or Up - Dn with a SG 
> apparatus regardless of how many other instruments one uses to create a 
> composite measuring apparatus (Bruno's claim IIUC). The reason is simple. 
> We know that the spin operator
 
 Which one?
 
 Good question. AG
 
 There are spin operator for each direction in space. The superposition of 
 up and down is a precise pure state, with precise eigenvalues, when 
 measuring state in the complementary directions.
 
 As I wrote earlier, based on scerir's superpositions on different axes, 
 and simulation, I now think that Up + Dn and Up - Dn can be measured along 
 the x axis but not along the z axis (which I was focused on).
>>> 
>>> All you need to do is a change of base. The operator will be defined 
>>> clearly by the Eigen value on the diagonal in the corresponding base. You 
>>> can prepare any state, and measure them “in any base”. 
>>> 
>>> I'll get back to this issue in my next post. AG 
 You were probably correct about x axis measurements, but perhaps were not 
 clear enough. You were not explicit that measurements along the x axis is 
 a different SG experiment from along z axis.
>>> 
>>> OK. Sorry. 
 I thought you meant do them in succession, not as separate experiments.
>>> 
>>> Ah? OK.
 Also introducing an infinity of universes seems extraneous and confusing 
 for a solution to this problem. AG 
>>> I are probably different on this. I don’t take the word “universe” too much 
>>> seriously, as with mechanism we know at the start that there is “physical 
>>> universe” at all, just the natural numbers with the laws of addition and 
>>> multiplication. Both the computational and the quantum state are relative, 
>>> and high level, pertaining to what is “observable” for some the point of 
>>> view of some locally finite subject, run by some computation.
>>> 
>>> The empirical point, though, is that to predict correctly an event in 
>>> quantum mechanics, we have to take into account may simultaneous 
>>> “incompatible path”, like going through each hole in a plane. Quantum 
>>> computations, for example, exploits that seemingly parallelism. 
>>> 
>>> I 

Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Wednesday, November 28, 2018 at 8:13:21 AM UTC, Philip Thrift wrote:
>
>
>
> On Tuesday, November 27, 2018 at 6:07:41 PM UTC-6, agrays...@gmail.com 
> wrote:
>>
>>
>>
>> On Tuesday, November 27, 2018 at 10:47:08 PM UTC, Philip Thrift wrote:
>>>
>>>
>>>
>>> On Tuesday, November 27, 2018 at 3:55:16 PM UTC-6, agrays...@gmail.com 
>>> wrote:



 On Tuesday, November 27, 2018 at 8:43:55 PM UTC, Philip Thrift wrote:
>
>
>
> On Tuesday, November 27, 2018 at 2:05:04 PM UTC-6, agrays...@gmail.com 
> wrote:
>>
>>
>>
>> On Tuesday, November 27, 2018 at 6:49:51 PM UTC, Philip Thrift wrote:
>>>
>>>
>>>
>>> On Tuesday, November 27, 2018 at 12:17:08 PM UTC-6, 
>>> agrays...@gmail.com wrote:



 On Tuesday, November 27, 2018 at 6:00:50 PM UTC, Philip Thrift 
 wrote:
>
>
>
> On Tuesday, November 27, 2018 at 8:43:35 AM UTC-6, 
> agrays...@gmail.com wrote:
>>
>>
>>
>> On Tuesday, November 27, 2018 at 9:27:46 AM UTC, Philip Thrift 
>> wrote:
>>>
>>>
>>>
>>> On Monday, November 26, 2018 at 3:43:14 PM UTC-6, 
>>> agrays...@gmail.com wrote:


 *I checked the postulates in Feynman's Sums Over Histories (in 
 link provided by Phil) and I see nothing related to waves, as 
 expected, and 
 thus nothing about collapse of anything. I would suppose the same 
 applies 
 to Heisenberg's Matrix Mechanics; no waves, no collapse. I suppose 
 you 
 could say they just produce correct probabilities, and imply 
 nothing about 
 relative states other than their probabilities (which wave 
 mechanics does), 
 but certainly nothing about consciousness. To summarize: you're 
 right that 
 they are "no collapse" theories, but IMO they say nothing about 
 consciousness. AG*

>
>
>>>
>>>
>>> In terms of the path-integral (PI) interpretation [ interesting 
>>> lecture: 
>>> https://www.perimeterinstitute.ca/videos/path-integral-interpretation-quantum-mechanics
>>>  
>>> ], there is in effect no waves or wave function, just paths, or 
>>> histories, 
>>> in the sum-over-histories (SOH) terminology.
>>>
>>> There is still "decoherence" in the SOH (a single history is 
>>> ultimately "realized"), but it could be called "selection": a 
>>> single 
>>> history is selected from the total ensemble of multiple and 
>>> interfering 
>>> histories. E.g. a single point on a screen is "hit" by a photon in 
>>> the 
>>> double-slit experiment.
>>>
>>
>> *Does "selection" add any insight to the measurement problem; 
>> that is, why do we get what we get? And if not, what is its value? 
>> TIA, AG *
>>
>>>
>>>
>>>
> If you look at it as a "selection of the fittest" (one history 
> surviving from an ensemble of histories), then it's like a form of 
> quantum 
> Darwinism. The quantum substrate is a cruel world where all histories 
> (but 
> one) die.
>

 That's not an explanation; rather, a vacuous statement of the 
 result. AG 

>
>
>>> But that is a criticism of Darwinism (*natural selection*) in 
>>> general.
>>>
>>
>> *Ridiculous comparison IMO. Darwinism posits a changing environment 
>> and competition among species for niches. Nothing comparable in Quantum 
>> Darwinism other than all outcomes fail except for one which succeeds in 
>> each single trial, which we knew from the get-go. AG*
>>
>>>
>>> *Quantum Darwinism* is a theory claiming to explain the emergence 
>>> of the classical world 
>>> from the quantum 
>>> world  as due to *a 
>>> process of **Darwinian 
>>>  natural selection 
>>> *; where the many 
>>> possible quantum states 
>>>  are selected against 
>>> in favor of a stable pointer state 
>>> .
>>> [ https://en.wikipedia.org/wiki/Quantum_Darwinism ]
>>>
>>> - pt
>>>  
>>>
>>
>
>
> As for "competition for niches", the histories are in a sense 
> competing. Perhaps there is some conservation principle at work, so only 
> one history can win. 
>
> I 

Re: Measuring a system in a superposition of states vs in a mixed state

[Philip Thrift]

On Tuesday, November 27, 2018 at 6:07:41 PM UTC-6, agrays...@gmail.com 
wrote:
>
>
>
> On Tuesday, November 27, 2018 at 10:47:08 PM UTC, Philip Thrift wrote:
>>
>>
>>
>> On Tuesday, November 27, 2018 at 3:55:16 PM UTC-6, agrays...@gmail.com 
>> wrote:
>>>
>>>
>>>
>>> On Tuesday, November 27, 2018 at 8:43:55 PM UTC, Philip Thrift wrote:



 On Tuesday, November 27, 2018 at 2:05:04 PM UTC-6, agrays...@gmail.com 
 wrote:
>
>
>
> On Tuesday, November 27, 2018 at 6:49:51 PM UTC, Philip Thrift wrote:
>>
>>
>>
>> On Tuesday, November 27, 2018 at 12:17:08 PM UTC-6, 
>> agrays...@gmail.com wrote:
>>>
>>>
>>>
>>> On Tuesday, November 27, 2018 at 6:00:50 PM UTC, Philip Thrift wrote:



 On Tuesday, November 27, 2018 at 8:43:35 AM UTC-6, 
 agrays...@gmail.com wrote:
>
>
>
> On Tuesday, November 27, 2018 at 9:27:46 AM UTC, Philip Thrift 
> wrote:
>>
>>
>>
>> On Monday, November 26, 2018 at 3:43:14 PM UTC-6, 
>> agrays...@gmail.com wrote:
>>>
>>>
>>> *I checked the postulates in Feynman's Sums Over Histories (in 
>>> link provided by Phil) and I see nothing related to waves, as 
>>> expected, and 
>>> thus nothing about collapse of anything. I would suppose the same 
>>> applies 
>>> to Heisenberg's Matrix Mechanics; no waves, no collapse. I suppose 
>>> you 
>>> could say they just produce correct probabilities, and imply 
>>> nothing about 
>>> relative states other than their probabilities (which wave 
>>> mechanics does), 
>>> but certainly nothing about consciousness. To summarize: you're 
>>> right that 
>>> they are "no collapse" theories, but IMO they say nothing about 
>>> consciousness. AG*
>>>


>>
>>
>> In terms of the path-integral (PI) interpretation [ interesting 
>> lecture: 
>> https://www.perimeterinstitute.ca/videos/path-integral-interpretation-quantum-mechanics
>>  
>> ], there is in effect no waves or wave function, just paths, or 
>> histories, 
>> in the sum-over-histories (SOH) terminology.
>>
>> There is still "decoherence" in the SOH (a single history is 
>> ultimately "realized"), but it could be called "selection": a single 
>> history is selected from the total ensemble of multiple and 
>> interfering 
>> histories. E.g. a single point on a screen is "hit" by a photon in 
>> the 
>> double-slit experiment.
>>
>
> *Does "selection" add any insight to the measurement problem; that 
> is, why do we get what we get? And if not, what is its value? TIA, AG 
> *
>
>>
>>
>>
 If you look at it as a "selection of the fittest" (one history 
 surviving from an ensemble of histories), then it's like a form of 
 quantum 
 Darwinism. The quantum substrate is a cruel world where all histories 
 (but 
 one) die.

>>>
>>> That's not an explanation; rather, a vacuous statement of the 
>>> result. AG 
>>>


>> But that is a criticism of Darwinism (*natural selection*) in 
>> general.
>>
>
> *Ridiculous comparison IMO. Darwinism posits a changing environment 
> and competition among species for niches. Nothing comparable in Quantum 
> Darwinism other than all outcomes fail except for one which succeeds in 
> each single trial, which we knew from the get-go. AG*
>
>>
>> *Quantum Darwinism* is a theory claiming to explain the emergence of 
>> the classical world 
>> from 
>> the quantum world  as 
>> due to *a process of **Darwinian 
>>  natural selection 
>> *; where the many 
>> possible quantum states 
>>  are selected against 
>> in favor of a stable pointer state 
>> .
>> [ https://en.wikipedia.org/wiki/Quantum_Darwinism ]
>>
>> - pt
>>  
>>
>


 As for "competition for niches", the histories are in a sense 
 competing. Perhaps there is some conservation principle at work, so only 
 one history can win. 

 I don't know. Physicists don't know. We're even. :)

>>>
>>> *Darwin had a theory or proposal to explain why some changes occur and 
>>> persist, but Quantum Darwinism doesn't, as far as I can tell. AG *
>>>

 -

>>>
>> What was the 

Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Tuesday, November 27, 2018 at 10:47:08 PM UTC, Philip Thrift wrote:
>
>
>
> On Tuesday, November 27, 2018 at 3:55:16 PM UTC-6, agrays...@gmail.com 
> wrote:
>>
>>
>>
>> On Tuesday, November 27, 2018 at 8:43:55 PM UTC, Philip Thrift wrote:
>>>
>>>
>>>
>>> On Tuesday, November 27, 2018 at 2:05:04 PM UTC-6, agrays...@gmail.com 
>>> wrote:



 On Tuesday, November 27, 2018 at 6:49:51 PM UTC, Philip Thrift wrote:
>
>
>
> On Tuesday, November 27, 2018 at 12:17:08 PM UTC-6, 
> agrays...@gmail.com wrote:
>>
>>
>>
>> On Tuesday, November 27, 2018 at 6:00:50 PM UTC, Philip Thrift wrote:
>>>
>>>
>>>
>>> On Tuesday, November 27, 2018 at 8:43:35 AM UTC-6, 
>>> agrays...@gmail.com wrote:



 On Tuesday, November 27, 2018 at 9:27:46 AM UTC, Philip Thrift 
 wrote:
>
>
>
> On Monday, November 26, 2018 at 3:43:14 PM UTC-6, 
> agrays...@gmail.com wrote:
>>
>>
>> *I checked the postulates in Feynman's Sums Over Histories (in 
>> link provided by Phil) and I see nothing related to waves, as 
>> expected, and 
>> thus nothing about collapse of anything. I would suppose the same 
>> applies 
>> to Heisenberg's Matrix Mechanics; no waves, no collapse. I suppose 
>> you 
>> could say they just produce correct probabilities, and imply nothing 
>> about 
>> relative states other than their probabilities (which wave mechanics 
>> does), 
>> but certainly nothing about consciousness. To summarize: you're 
>> right that 
>> they are "no collapse" theories, but IMO they say nothing about 
>> consciousness. AG*
>>
>>>
>>>
>
>
> In terms of the path-integral (PI) interpretation [ interesting 
> lecture: 
> https://www.perimeterinstitute.ca/videos/path-integral-interpretation-quantum-mechanics
>  
> ], there is in effect no waves or wave function, just paths, or 
> histories, 
> in the sum-over-histories (SOH) terminology.
>
> There is still "decoherence" in the SOH (a single history is 
> ultimately "realized"), but it could be called "selection": a single 
> history is selected from the total ensemble of multiple and 
> interfering 
> histories. E.g. a single point on a screen is "hit" by a photon in 
> the 
> double-slit experiment.
>

 *Does "selection" add any insight to the measurement problem; that 
 is, why do we get what we get? And if not, what is its value? TIA, AG *

>
>
>
>>> If you look at it as a "selection of the fittest" (one history 
>>> surviving from an ensemble of histories), then it's like a form of 
>>> quantum 
>>> Darwinism. The quantum substrate is a cruel world where all histories 
>>> (but 
>>> one) die.
>>>
>>
>> That's not an explanation; rather, a vacuous statement of the result. 
>> AG 
>>
>>>
>>>
> But that is a criticism of Darwinism (*natural selection*) in general.
>

 *Ridiculous comparison IMO. Darwinism posits a changing environment and 
 competition among species for niches. Nothing comparable in Quantum 
 Darwinism other than all outcomes fail except for one which succeeds in 
 each single trial, which we knew from the get-go. AG*

>
> *Quantum Darwinism* is a theory claiming to explain the emergence of 
> the classical world from 
> the quantum world  as 
> due to *a process of **Darwinian 
>  natural selection 
> *; where the many 
> possible quantum states  
> are 
> selected against in favor of a stable pointer state 
> .
> [ https://en.wikipedia.org/wiki/Quantum_Darwinism ]
>
> - pt
>  
>

>>>
>>>
>>> As for "competition for niches", the histories are in a sense competing. 
>>> Perhaps there is some conservation principle at work, so only one history 
>>> can win. 
>>>
>>> I don't know. Physicists don't know. We're even. :)
>>>
>>
>> *Darwin had a theory or proposal to explain why some changes occur and 
>> persist, but Quantum Darwinism doesn't, as far as I can tell. AG *
>>
>>>
>>> -
>>>
>>
> What was the "why" of Darwin's theory?
>

*Darwin didn't know about DNA, but he hypothesized that specie could change 
in time, and he could explain the persistence of some traits and 
non-persistence of others by the process of natural selection. In Quantum 

Re: Measuring a system in a superposition of states vs in a mixed state

[Philip Thrift]

On Tuesday, November 27, 2018 at 3:55:16 PM UTC-6, agrays...@gmail.com 
wrote:
>
>
>
> On Tuesday, November 27, 2018 at 8:43:55 PM UTC, Philip Thrift wrote:
>>
>>
>>
>> On Tuesday, November 27, 2018 at 2:05:04 PM UTC-6, agrays...@gmail.com 
>> wrote:
>>>
>>>
>>>
>>> On Tuesday, November 27, 2018 at 6:49:51 PM UTC, Philip Thrift wrote:



 On Tuesday, November 27, 2018 at 12:17:08 PM UTC-6, agrays...@gmail.com 
 wrote:
>
>
>
> On Tuesday, November 27, 2018 at 6:00:50 PM UTC, Philip Thrift wrote:
>>
>>
>>
>> On Tuesday, November 27, 2018 at 8:43:35 AM UTC-6, 
>> agrays...@gmail.com wrote:
>>>
>>>
>>>
>>> On Tuesday, November 27, 2018 at 9:27:46 AM UTC, Philip Thrift wrote:



 On Monday, November 26, 2018 at 3:43:14 PM UTC-6, 
 agrays...@gmail.com wrote:
>
>
> *I checked the postulates in Feynman's Sums Over Histories (in 
> link provided by Phil) and I see nothing related to waves, as 
> expected, and 
> thus nothing about collapse of anything. I would suppose the same 
> applies 
> to Heisenberg's Matrix Mechanics; no waves, no collapse. I suppose 
> you 
> could say they just produce correct probabilities, and imply nothing 
> about 
> relative states other than their probabilities (which wave mechanics 
> does), 
> but certainly nothing about consciousness. To summarize: you're right 
> that 
> they are "no collapse" theories, but IMO they say nothing about 
> consciousness. AG*
>
>>
>>


 In terms of the path-integral (PI) interpretation [ interesting 
 lecture: 
 https://www.perimeterinstitute.ca/videos/path-integral-interpretation-quantum-mechanics
  
 ], there is in effect no waves or wave function, just paths, or 
 histories, 
 in the sum-over-histories (SOH) terminology.

 There is still "decoherence" in the SOH (a single history is 
 ultimately "realized"), but it could be called "selection": a single 
 history is selected from the total ensemble of multiple and 
 interfering 
 histories. E.g. a single point on a screen is "hit" by a photon in the 
 double-slit experiment.

>>>
>>> *Does "selection" add any insight to the measurement problem; that 
>>> is, why do we get what we get? And if not, what is its value? TIA, AG *
>>>



>> If you look at it as a "selection of the fittest" (one history 
>> surviving from an ensemble of histories), then it's like a form of 
>> quantum 
>> Darwinism. The quantum substrate is a cruel world where all histories 
>> (but 
>> one) die.
>>
>
> That's not an explanation; rather, a vacuous statement of the result. 
> AG 
>
>>
>>
 But that is a criticism of Darwinism (*natural selection*) in general.

>>>
>>> *Ridiculous comparison IMO. Darwinism posits a changing environment and 
>>> competition among species for niches. Nothing comparable in Quantum 
>>> Darwinism other than all outcomes fail except for one which succeeds in 
>>> each single trial, which we knew from the get-go. AG*
>>>

 *Quantum Darwinism* is a theory claiming to explain the emergence of 
 the classical world from 
 the quantum world  as 
 due to *a process of **Darwinian 
  natural selection 
 *; where the many 
 possible quantum states  are 
 selected against in favor of a stable pointer state 
 .
 [ https://en.wikipedia.org/wiki/Quantum_Darwinism ]

 - pt
  

>>>
>>
>>
>> As for "competition for niches", the histories are in a sense competing. 
>> Perhaps there is some conservation principle at work, so only one history 
>> can win. 
>>
>> I don't know. Physicists don't know. We're even. :)
>>
>
> *Darwin had a theory or proposal to explain why some changes occur and 
> persist, but Quantum Darwinism doesn't, as far as I can tell. AG *
>
>>
>> -
>>
>
What was the "why" of Darwin's theory?

- pt 

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Re: Measuring a system in a superposition of states vs in a mixed state

[Philip Thrift]

On Tuesday, November 27, 2018 at 2:56:36 PM UTC-6, Brent wrote:
>
>
>
> On 11/27/2018 12:43 PM, Philip Thrift wrote:
>
>
>
> On Tuesday, November 27, 2018 at 2:05:04 PM UTC-6, agrays...@gmail.com 
> wrote: 
>>
>>
>>
>> On Tuesday, November 27, 2018 at 6:49:51 PM UTC, Philip Thrift wrote: 
>>>
>>>
>>>
>>> On Tuesday, November 27, 2018 at 12:17:08 PM UTC-6, agrays...@gmail.com 
>>> wrote: 



 On Tuesday, November 27, 2018 at 6:00:50 PM UTC, Philip Thrift wrote: 
>
>
>
> On Tuesday, November 27, 2018 at 8:43:35 AM UTC-6, agrays...@gmail.com 
> wrote: 
>>
>>
>>
>> On Tuesday, November 27, 2018 at 9:27:46 AM UTC, Philip Thrift wrote: 
>>>
>>>
>>>
>>> On Monday, November 26, 2018 at 3:43:14 PM UTC-6, 
>>> agrays...@gmail.com wrote: 


 *I checked the postulates in Feynman's Sums Over Histories (in link 
 provided by Phil) and I see nothing related to waves, as expected, and 
 thus 
 nothing about collapse of anything. I would suppose the same applies 
 to 
 Heisenberg's Matrix Mechanics; no waves, no collapse. I suppose you 
 could 
 say they just produce correct probabilities, and imply nothing about 
 relative states other than their probabilities (which wave mechanics 
 does), 
 but certainly nothing about consciousness. To summarize: you're right 
 that 
 they are "no collapse" theories, but IMO they say nothing about 
 consciousness. AG*

>
>
>>>
>>>
>>> In terms of the path-integral (PI) interpretation [ interesting 
>>> lecture: 
>>> https://www.perimeterinstitute.ca/videos/path-integral-interpretation-quantum-mechanics
>>>  
>>> ], there is in effect no waves or wave function, just paths, or 
>>> histories, 
>>> in the sum-over-histories (SOH) terminology.
>>>
>>> There is still "decoherence" in the SOH (a single history is 
>>> ultimately "realized"), but it could be called "selection": a single 
>>> history is selected from the total ensemble of multiple and interfering 
>>> histories. E.g. a single point on a screen is "hit" by a photon in the 
>>> double-slit experiment.
>>>
>>
>> *Does "selection" add any insight to the measurement problem; that 
>> is, why do we get what we get? And if not, what is its value? TIA, AG *
>>
>>>
>>>
>>>
> If you look at it as a "selection of the fittest" (one history 
> surviving from an ensemble of histories), then it's like a form of 
> quantum 
> Darwinism. The quantum substrate is a cruel world where all histories 
> (but 
> one) die.
>

 That's not an explanation; rather, a vacuous statement of the result. 
 AG 

>
>
>>> But that is a criticism of Darwinism (*natural selection*) in general.
>>>
>>
>> *Ridiculous comparison IMO. Darwinism posits a changing environment and 
>> competition among species for niches. Nothing comparable in Quantum 
>> Darwinism other than all outcomes fail except for one which succeeds in 
>> each single trial, which we knew from the get-go. AG*
>>
>>>
>>> *Quantum Darwinism* is a theory claiming to explain the emergence of 
>>> the classical world from 
>>> the quantum world  as 
>>> due to *a process of **Darwinian 
>>>  natural selection 
>>> *; where the many 
>>> possible quantum states  are 
>>> selected against in favor of a stable pointer state 
>>> .
>>> [ https://en.wikipedia.org/wiki/Quantum_Darwinism ]
>>>
>>> - pt
>>>  
>>>
>>
>
>
> As for "competition for niches", the histories are in a sense competing. 
> Perhaps there is some conservation principle at work, so only one history 
> can win. 
>
> I don't know. Physicists don't know. We're even. :)
>
>
> In a delayed quantum erasure experiment I wonder if you would be possible 
> to make a weak measurement on the photon to be erased?  Would you get an 
> intermediate result in the interference pattern?
>
> Brent
>

I don't know about this or other attempts to show the reality of 
"alternative" histories.

https://physicsworld.com/a/exotic-non-classical-paths-affect-quantum-interference-experiment-confirms/

- pt

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Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Tuesday, November 27, 2018 at 8:43:55 PM UTC, Philip Thrift wrote:
>
>
>
> On Tuesday, November 27, 2018 at 2:05:04 PM UTC-6, agrays...@gmail.com 
> wrote:
>>
>>
>>
>> On Tuesday, November 27, 2018 at 6:49:51 PM UTC, Philip Thrift wrote:
>>>
>>>
>>>
>>> On Tuesday, November 27, 2018 at 12:17:08 PM UTC-6, agrays...@gmail.com 
>>> wrote:



 On Tuesday, November 27, 2018 at 6:00:50 PM UTC, Philip Thrift wrote:
>
>
>
> On Tuesday, November 27, 2018 at 8:43:35 AM UTC-6, agrays...@gmail.com 
> wrote:
>>
>>
>>
>> On Tuesday, November 27, 2018 at 9:27:46 AM UTC, Philip Thrift wrote:
>>>
>>>
>>>
>>> On Monday, November 26, 2018 at 3:43:14 PM UTC-6, 
>>> agrays...@gmail.com wrote:


 *I checked the postulates in Feynman's Sums Over Histories (in link 
 provided by Phil) and I see nothing related to waves, as expected, and 
 thus 
 nothing about collapse of anything. I would suppose the same applies 
 to 
 Heisenberg's Matrix Mechanics; no waves, no collapse. I suppose you 
 could 
 say they just produce correct probabilities, and imply nothing about 
 relative states other than their probabilities (which wave mechanics 
 does), 
 but certainly nothing about consciousness. To summarize: you're right 
 that 
 they are "no collapse" theories, but IMO they say nothing about 
 consciousness. AG*

>
>
>>>
>>>
>>> In terms of the path-integral (PI) interpretation [ interesting 
>>> lecture: 
>>> https://www.perimeterinstitute.ca/videos/path-integral-interpretation-quantum-mechanics
>>>  
>>> ], there is in effect no waves or wave function, just paths, or 
>>> histories, 
>>> in the sum-over-histories (SOH) terminology.
>>>
>>> There is still "decoherence" in the SOH (a single history is 
>>> ultimately "realized"), but it could be called "selection": a single 
>>> history is selected from the total ensemble of multiple and interfering 
>>> histories. E.g. a single point on a screen is "hit" by a photon in the 
>>> double-slit experiment.
>>>
>>
>> *Does "selection" add any insight to the measurement problem; that 
>> is, why do we get what we get? And if not, what is its value? TIA, AG *
>>
>>>
>>>
>>>
> If you look at it as a "selection of the fittest" (one history 
> surviving from an ensemble of histories), then it's like a form of 
> quantum 
> Darwinism. The quantum substrate is a cruel world where all histories 
> (but 
> one) die.
>

 That's not an explanation; rather, a vacuous statement of the result. 
 AG 

>
>
>>> But that is a criticism of Darwinism (*natural selection*) in general.
>>>
>>
>> *Ridiculous comparison IMO. Darwinism posits a changing environment and 
>> competition among species for niches. Nothing comparable in Quantum 
>> Darwinism other than all outcomes fail except for one which succeeds in 
>> each single trial, which we knew from the get-go. AG*
>>
>>>
>>> *Quantum Darwinism* is a theory claiming to explain the emergence of 
>>> the classical world from 
>>> the quantum world  as 
>>> due to *a process of **Darwinian 
>>>  natural selection 
>>> *; where the many 
>>> possible quantum states  are 
>>> selected against in favor of a stable pointer state 
>>> .
>>> [ https://en.wikipedia.org/wiki/Quantum_Darwinism ]
>>>
>>> - pt
>>>  
>>>
>>
>
>
> As for "competition for niches", the histories are in a sense competing. 
> Perhaps there is some conservation principle at work, so only one history 
> can win. 
>
> I don't know. Physicists don't know. We're even. :)
>

*Darwin had a theory or proposal to explain why some changes occur and 
persist, but Quantum Darwinism doesn't, as far as I can tell. AG *

>
> - pt
>

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Re: Measuring a system in a superposition of states vs in a mixed state

[Brent Meeker]

On 11/27/2018 12:43 PM, Philip Thrift wrote:



On Tuesday, November 27, 2018 at 2:05:04 PM UTC-6, agrays...@gmail.com 
wrote:




On Tuesday, November 27, 2018 at 6:49:51 PM UTC, Philip Thrift wrote:



On Tuesday, November 27, 2018 at 12:17:08 PM UTC-6,
agrays...@gmail.com wrote:



On Tuesday, November 27, 2018 at 6:00:50 PM UTC, Philip
Thrift wrote:



On Tuesday, November 27, 2018 at 8:43:35 AM UTC-6,
agrays...@gmail.com wrote:



On Tuesday, November 27, 2018 at 9:27:46 AM UTC,
Philip Thrift wrote:



On Monday, November 26, 2018 at 3:43:14 PM
UTC-6, agrays...@gmail.com wrote:

*
*
*I checked the postulates in Feynman's
Sums Over Histories (in link provided by
Phil) and I see nothing related to waves,
as expected, and thus nothing about
collapse of anything. I would suppose the
same applies to Heisenberg's Matrix
Mechanics; no waves, no collapse. I
suppose you could say they just produce
correct probabilities, and imply nothing
about relative states other than their
probabilities (which wave mechanics does),
but certainly nothing about consciousness.
To summarize: you're right that they are
"no collapse" theories, but IMO they say
nothing about consciousness. AG*





In terms of the path-integral (PI)
interpretation [ interesting lecture:

https://www.perimeterinstitute.ca/videos/path-integral-interpretation-quantum-mechanics


], there is in effect no waves or wave
function, just paths, or histories, in the
sum-over-histories (SOH) terminology.

There is still "decoherence" in the SOH (a
single history is ultimately "realized"), but
it could be called "selection": a single
history is selected from the total ensemble of
multiple and interfering histories. E.g. a
single point on a screen is "hit" by a photon
in the double-slit experiment.


*Does "selection" add any insight to the
measurement problem; that is, why do we get what
we get? And if not, what is its value? TIA, AG *




If you look at it as a "selection of the fittest" (one
history surviving from an ensemble of histories), then
it's like a form of quantum Darwinism. The quantum
substrate is a cruel world where all histories (but
one) die.


That's not an explanation; rather, a vacuous statement of
the result. AG



But that is a criticism of Darwinism (*natural selection*) in
general.

*
*
*Ridiculous comparison IMO. Darwinism posits a changing
environment and competition among species for niches. Nothing
comparable in Quantum Darwinism other than all outcomes fail
except for one which succeeds in each single trial, which we knew
from the get-go. AG*


*Quantum Darwinism* is a theory claiming to explain the
emergence of the classical world
from the
quantum world
 as due to *a
process of **Darwinian
natural
selection *;
where the many possible quantum states
 are selected
against in favor of a stable pointer state
.
[ https://en.wikipedia.org/wiki/Quantum_Darwinism
 ]

- pt




As for "competition for niches", the histories are in a sense 
competing. Perhaps there is some conservation principle at work, so 
only one history can win.


I don't know. Physicists don't know. We're even. :)


In a delayed quantum erasure experiment I wonder if you would be 
possible to make a weak measurement on the photon to be erased? Would 
you get an 

Re: Measuring a system in a superposition of states vs in a mixed state

[Philip Thrift]

On Tuesday, November 27, 2018 at 2:05:04 PM UTC-6, agrays...@gmail.com 
wrote:
>
>
>
> On Tuesday, November 27, 2018 at 6:49:51 PM UTC, Philip Thrift wrote:
>>
>>
>>
>> On Tuesday, November 27, 2018 at 12:17:08 PM UTC-6, agrays...@gmail.com 
>> wrote:
>>>
>>>
>>>
>>> On Tuesday, November 27, 2018 at 6:00:50 PM UTC, Philip Thrift wrote:



 On Tuesday, November 27, 2018 at 8:43:35 AM UTC-6, agrays...@gmail.com 
 wrote:
>
>
>
> On Tuesday, November 27, 2018 at 9:27:46 AM UTC, Philip Thrift wrote:
>>
>>
>>
>> On Monday, November 26, 2018 at 3:43:14 PM UTC-6, agrays...@gmail.com 
>> wrote:
>>>
>>>
>>> *I checked the postulates in Feynman's Sums Over Histories (in link 
>>> provided by Phil) and I see nothing related to waves, as expected, and 
>>> thus 
>>> nothing about collapse of anything. I would suppose the same applies to 
>>> Heisenberg's Matrix Mechanics; no waves, no collapse. I suppose you 
>>> could 
>>> say they just produce correct probabilities, and imply nothing about 
>>> relative states other than their probabilities (which wave mechanics 
>>> does), 
>>> but certainly nothing about consciousness. To summarize: you're right 
>>> that 
>>> they are "no collapse" theories, but IMO they say nothing about 
>>> consciousness. AG*
>>>


>>
>>
>> In terms of the path-integral (PI) interpretation [ interesting 
>> lecture: 
>> https://www.perimeterinstitute.ca/videos/path-integral-interpretation-quantum-mechanics
>>  
>> ], there is in effect no waves or wave function, just paths, or 
>> histories, 
>> in the sum-over-histories (SOH) terminology.
>>
>> There is still "decoherence" in the SOH (a single history is 
>> ultimately "realized"), but it could be called "selection": a single 
>> history is selected from the total ensemble of multiple and interfering 
>> histories. E.g. a single point on a screen is "hit" by a photon in the 
>> double-slit experiment.
>>
>
> *Does "selection" add any insight to the measurement problem; that is, 
> why do we get what we get? And if not, what is its value? TIA, AG *
>
>>
>>
>>
 If you look at it as a "selection of the fittest" (one history 
 surviving from an ensemble of histories), then it's like a form of quantum 
 Darwinism. The quantum substrate is a cruel world where all histories (but 
 one) die.

>>>
>>> That's not an explanation; rather, a vacuous statement of the result. AG 
>>>


>> But that is a criticism of Darwinism (*natural selection*) in general.
>>
>
> *Ridiculous comparison IMO. Darwinism posits a changing environment and 
> competition among species for niches. Nothing comparable in Quantum 
> Darwinism other than all outcomes fail except for one which succeeds in 
> each single trial, which we knew from the get-go. AG*
>
>>
>> *Quantum Darwinism* is a theory claiming to explain the emergence of the 
>> classical 
>> world from the quantum 
>> world  as due to *a 
>> process of **Darwinian 
>>  natural selection 
>> *; where the many 
>> possible quantum states  are 
>> selected against in favor of a stable pointer state 
>> .
>> [ https://en.wikipedia.org/wiki/Quantum_Darwinism ]
>>
>> - pt
>>  
>>
>


As for "competition for niches", the histories are in a sense competing. 
Perhaps there is some conservation principle at work, so only one history 
can win. 

I don't know. Physicists don't know. We're even. :)

- pt

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Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Tuesday, November 27, 2018 at 6:49:51 PM UTC, Philip Thrift wrote:
>
>
>
> On Tuesday, November 27, 2018 at 12:17:08 PM UTC-6, agrays...@gmail.com 
> wrote:
>>
>>
>>
>> On Tuesday, November 27, 2018 at 6:00:50 PM UTC, Philip Thrift wrote:
>>>
>>>
>>>
>>> On Tuesday, November 27, 2018 at 8:43:35 AM UTC-6, agrays...@gmail.com 
>>> wrote:



 On Tuesday, November 27, 2018 at 9:27:46 AM UTC, Philip Thrift wrote:
>
>
>
> On Monday, November 26, 2018 at 3:43:14 PM UTC-6, agrays...@gmail.com 
> wrote:
>>
>>
>> *I checked the postulates in Feynman's Sums Over Histories (in link 
>> provided by Phil) and I see nothing related to waves, as expected, and 
>> thus 
>> nothing about collapse of anything. I would suppose the same applies to 
>> Heisenberg's Matrix Mechanics; no waves, no collapse. I suppose you 
>> could 
>> say they just produce correct probabilities, and imply nothing about 
>> relative states other than their probabilities (which wave mechanics 
>> does), 
>> but certainly nothing about consciousness. To summarize: you're right 
>> that 
>> they are "no collapse" theories, but IMO they say nothing about 
>> consciousness. AG*
>>
>>>
>>>
>
>
> In terms of the path-integral (PI) interpretation [ interesting 
> lecture: 
> https://www.perimeterinstitute.ca/videos/path-integral-interpretation-quantum-mechanics
>  
> ], there is in effect no waves or wave function, just paths, or 
> histories, 
> in the sum-over-histories (SOH) terminology.
>
> There is still "decoherence" in the SOH (a single history is 
> ultimately "realized"), but it could be called "selection": a single 
> history is selected from the total ensemble of multiple and interfering 
> histories. E.g. a single point on a screen is "hit" by a photon in the 
> double-slit experiment.
>

 *Does "selection" add any insight to the measurement problem; that is, 
 why do we get what we get? And if not, what is its value? TIA, AG *

>
>
>
>>> If you look at it as a "selection of the fittest" (one history surviving 
>>> from an ensemble of histories), then it's like a form of quantum Darwinism. 
>>> The quantum substrate is a cruel world where all histories (but one) die.
>>>
>>
>> That's not an explanation; rather, a vacuous statement of the result. AG 
>>
>>>
>>>
> But that is a criticism of Darwinism (*natural selection*) in general.
>

*Ridiculous comparison IMO. Darwinism posits a changing environment and 
competition among species for niches. Nothing comparable in Quantum 
Darwinism other than all outcomes fail except for one which succeeds in 
each single trial, which we knew from the get-go. AG*

>
> *Quantum Darwinism* is a theory claiming to explain the emergence of the 
> classical 
> world from the quantum 
> world  as due to *a 
> process of **Darwinian 
>  natural selection 
> *; where the many 
> possible quantum states  are 
> selected against in favor of a stable pointer state 
> .
> [ https://en.wikipedia.org/wiki/Quantum_Darwinism ]
>
> - pt
>  
>

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Re: Measuring a system in a superposition of states vs in a mixed state

[Philip Thrift]

On Tuesday, November 27, 2018 at 12:17:08 PM UTC-6, agrays...@gmail.com 
wrote:
>
>
>
> On Tuesday, November 27, 2018 at 6:00:50 PM UTC, Philip Thrift wrote:
>>
>>
>>
>> On Tuesday, November 27, 2018 at 8:43:35 AM UTC-6, agrays...@gmail.com 
>> wrote:
>>>
>>>
>>>
>>> On Tuesday, November 27, 2018 at 9:27:46 AM UTC, Philip Thrift wrote:



 On Monday, November 26, 2018 at 3:43:14 PM UTC-6, agrays...@gmail.com 
 wrote:
>
>
> *I checked the postulates in Feynman's Sums Over Histories (in link 
> provided by Phil) and I see nothing related to waves, as expected, and 
> thus 
> nothing about collapse of anything. I would suppose the same applies to 
> Heisenberg's Matrix Mechanics; no waves, no collapse. I suppose you could 
> say they just produce correct probabilities, and imply nothing about 
> relative states other than their probabilities (which wave mechanics 
> does), 
> but certainly nothing about consciousness. To summarize: you're right 
> that 
> they are "no collapse" theories, but IMO they say nothing about 
> consciousness. AG*
>
>>
>>


 In terms of the path-integral (PI) interpretation [ interesting 
 lecture: 
 https://www.perimeterinstitute.ca/videos/path-integral-interpretation-quantum-mechanics
  
 ], there is in effect no waves or wave function, just paths, or histories, 
 in the sum-over-histories (SOH) terminology.

 There is still "decoherence" in the SOH (a single history is ultimately 
 "realized"), but it could be called "selection": a single history is 
 selected from the total ensemble of multiple and interfering histories. 
 E.g. a single point on a screen is "hit" by a photon in the double-slit 
 experiment.

>>>
>>> *Does "selection" add any insight to the measurement problem; that is, 
>>> why do we get what we get? And if not, what is its value? TIA, AG *
>>>



>> If you look at it as a "selection of the fittest" (one history surviving 
>> from an ensemble of histories), then it's like a form of quantum Darwinism. 
>> The quantum substrate is a cruel world where all histories (but one) die.
>>
>
> That's not an explanation; rather, a vacuous statement of the result. AG 
>
>>
>>
But that is a criticism of Darwinism (*natural selection*) in general.

*Quantum Darwinism* is a theory claiming to explain the emergence of the 
classical 
world from the quantum 
world  as due to *a 
process of **Darwinian 
 natural selection 
*; where the many possible 
quantum 
states  are selected against 
in favor of a stable pointer state 
.
[ https://en.wikipedia.org/wiki/Quantum_Darwinism ]

- pt
 

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Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Tuesday, November 27, 2018 at 6:00:50 PM UTC, Philip Thrift wrote:
>
>
>
> On Tuesday, November 27, 2018 at 8:43:35 AM UTC-6, agrays...@gmail.com 
> wrote:
>>
>>
>>
>> On Tuesday, November 27, 2018 at 9:27:46 AM UTC, Philip Thrift wrote:
>>>
>>>
>>>
>>> On Monday, November 26, 2018 at 3:43:14 PM UTC-6, agrays...@gmail.com 
>>> wrote:


 *I checked the postulates in Feynman's Sums Over Histories (in link 
 provided by Phil) and I see nothing related to waves, as expected, and 
 thus 
 nothing about collapse of anything. I would suppose the same applies to 
 Heisenberg's Matrix Mechanics; no waves, no collapse. I suppose you could 
 say they just produce correct probabilities, and imply nothing about 
 relative states other than their probabilities (which wave mechanics 
 does), 
 but certainly nothing about consciousness. To summarize: you're right that 
 they are "no collapse" theories, but IMO they say nothing about 
 consciousness. AG*

>
>
>>>
>>>
>>> In terms of the path-integral (PI) interpretation [ interesting lecture: 
>>> https://www.perimeterinstitute.ca/videos/path-integral-interpretation-quantum-mechanics
>>>  
>>> ], there is in effect no waves or wave function, just paths, or histories, 
>>> in the sum-over-histories (SOH) terminology.
>>>
>>> There is still "decoherence" in the SOH (a single history is ultimately 
>>> "realized"), but it could be called "selection": a single history is 
>>> selected from the total ensemble of multiple and interfering histories. 
>>> E.g. a single point on a screen is "hit" by a photon in the double-slit 
>>> experiment.
>>>
>>
>> *Does "selection" add any insight to the measurement problem; that is, 
>> why do we get what we get? And if not, what is its value? TIA, AG *
>>
>>>
>>>
>>>
> If you look at it as a "selection of the fittest" (one history surviving 
> from an ensemble of histories), then it's like a form of quantum Darwinism. 
> The quantum substrate is a cruel world where all histories (but one) die.
>

That's not an explanation; rather, a vacuous statement of the result. AG 

>
> - pt
>
>
>  
>

-- 
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Re: Measuring a system in a superposition of states vs in a mixed state

[Philip Thrift]

On Tuesday, November 27, 2018 at 8:43:35 AM UTC-6, agrays...@gmail.com 
wrote:
>
>
>
> On Tuesday, November 27, 2018 at 9:27:46 AM UTC, Philip Thrift wrote:
>>
>>
>>
>> On Monday, November 26, 2018 at 3:43:14 PM UTC-6, agrays...@gmail.com 
>> wrote:
>>>
>>>
>>> *I checked the postulates in Feynman's Sums Over Histories (in link 
>>> provided by Phil) and I see nothing related to waves, as expected, and thus 
>>> nothing about collapse of anything. I would suppose the same applies to 
>>> Heisenberg's Matrix Mechanics; no waves, no collapse. I suppose you could 
>>> say they just produce correct probabilities, and imply nothing about 
>>> relative states other than their probabilities (which wave mechanics does), 
>>> but certainly nothing about consciousness. To summarize: you're right that 
>>> they are "no collapse" theories, but IMO they say nothing about 
>>> consciousness. AG*
>>>


>>
>>
>> In terms of the path-integral (PI) interpretation [ interesting lecture: 
>> https://www.perimeterinstitute.ca/videos/path-integral-interpretation-quantum-mechanics
>>  
>> ], there is in effect no waves or wave function, just paths, or histories, 
>> in the sum-over-histories (SOH) terminology.
>>
>> There is still "decoherence" in the SOH (a single history is ultimately 
>> "realized"), but it could be called "selection": a single history is 
>> selected from the total ensemble of multiple and interfering histories. 
>> E.g. a single point on a screen is "hit" by a photon in the double-slit 
>> experiment.
>>
>
> *Does "selection" add any insight to the measurement problem; that is, why 
> do we get what we get? And if not, what is its value? TIA, AG *
>
>>
>>
>>
If you look at it as a "selection of the fittest" (one history surviving 
from an ensemble of histories), then it's like a form of quantum Darwinism. 
The quantum substrate is a cruel world where all histories (but one) die.

- pt


 

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Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Tuesday, November 27, 2018 at 9:27:46 AM UTC, Philip Thrift wrote:
>
>
>
> On Monday, November 26, 2018 at 3:43:14 PM UTC-6, agrays...@gmail.com 
> wrote:
>>
>>
>> *I checked the postulates in Feynman's Sums Over Histories (in link 
>> provided by Phil) and I see nothing related to waves, as expected, and thus 
>> nothing about collapse of anything. I would suppose the same applies to 
>> Heisenberg's Matrix Mechanics; no waves, no collapse. I suppose you could 
>> say they just produce correct probabilities, and imply nothing about 
>> relative states other than their probabilities (which wave mechanics does), 
>> but certainly nothing about consciousness. To summarize: you're right that 
>> they are "no collapse" theories, but IMO they say nothing about 
>> consciousness. AG*
>>
>>>
>>>
>
>
> In terms of the path-integral (PI) interpretation [ interesting lecture: 
> https://www.perimeterinstitute.ca/videos/path-integral-interpretation-quantum-mechanics
>  
> ], there is in effect no waves or wave function, just paths, or histories, 
> in the sum-over-histories (SOH) terminology.
>
> There is still "decoherence" in the SOH (a single history is ultimately 
> "realized"), but it could be called "selection": a single history is 
> selected from the total ensemble of multiple and interfering histories. 
> E.g. a single point on a screen is "hit" by a photon in the double-slit 
> experiment.
>

*Does "selection" add any insight to the measurement problem; that is, why 
do we get what we get? And if not, what is its value? TIA, AG *

>
> - pt
>

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Re: Measuring a system in a superposition of states vs in a mixed state

[Philip Thrift]

On Monday, November 26, 2018 at 3:43:14 PM UTC-6, agrays...@gmail.com wrote:
>
>
> *I checked the postulates in Feynman's Sums Over Histories (in link 
> provided by Phil) and I see nothing related to waves, as expected, and thus 
> nothing about collapse of anything. I would suppose the same applies to 
> Heisenberg's Matrix Mechanics; no waves, no collapse. I suppose you could 
> say they just produce correct probabilities, and imply nothing about 
> relative states other than their probabilities (which wave mechanics does), 
> but certainly nothing about consciousness. To summarize: you're right that 
> they are "no collapse" theories, but IMO they say nothing about 
> consciousness. AG*
>
>>
>>


In terms of the path-integral (PI) interpretation [ interesting 
lecture: 
https://www.perimeterinstitute.ca/videos/path-integral-interpretation-quantum-mechanics
 
], there is in effect no waves or wave function, just paths, or histories, 
in the sum-over-histories (SOH) terminology.

There is still "decoherence" in the SOH (a single history is ultimately 
"realized"), but it could be called "selection": a single history is 
selected from the total ensemble of multiple and interfering histories. 
E.g. a single point on a screen is "hit" by a photon in the double-slit 
experiment.

- pt

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Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Monday, November 26, 2018 at 9:43:14 PM UTC, agrays...@gmail.com wrote:
>
>
>
> On Monday, November 26, 2018 at 4:41:42 PM UTC, agrays...@gmail.com wrote:
>>
>>
>>
>> On Monday, November 26, 2018 at 12:01:05 PM UTC, Bruno Marchal wrote:
>>>
>>>
>>> On 23 Nov 2018, at 13:30, agrays...@gmail.com wrote:
>>>
>>>
>>>
>>> On Friday, November 23, 2018 at 11:29:14 AM UTC, Bruno Marchal wrote:


 On 21 Nov 2018, at 18:03, agrays...@gmail.com wrote:



 On Monday, November 19, 2018 at 3:52:37 PM UTC, Bruno Marchal wrote:
>
>
> On 18 Nov 2018, at 14:00, agrays...@gmail.com wrote:
>
>
>
> On Sunday, November 18, 2018 at 12:19:20 PM UTC, Bruno Marchal wrote:
>>
>>
>> On 16 Nov 2018, at 15:38, agrays...@gmail.com wrote:
>>
>>
>>
>> On Friday, November 16, 2018 at 10:14:32 AM UTC, scerir wrote:
>>>
>>>
>>> Il 16 novembre 2018 alle 10.19 agrays...@gmail.com ha scritto: 
>>>
>>>
>>>
>>> On Thursday, November 15, 2018 at 2:14:48 PM UTC, scerir wrote:
>>>
>>>
>>> Il 15 novembre 2018 alle 14.29 agrays...@gmail.com ha scritto: 
>>>
>>>
>>>
>>> On Thursday, November 15, 2018 at 8:04:53 AM UTC, scerir wrote:
>>>
>>> Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) 
>>> [(s+)_z + (s-)_z] .
>>>
>>> If the x-component of spin is measured by passing the spin-1/2 
>>> particle through a Stern-Gerlach with its field oriented along the 
>>> x-axis, 
>>> the particle will ALWAYS emerge 'up'.
>>>
>>>
>>> *Why?  Won't the measured value be along the x axis in both 
>>> directions, in effect Up or Dn? AG*
>>>
>>> "Hence we must conclude that the system described by the |+>x state 
>>> is not the
>>> same as a mixture of atoms in the |+> and !-> states. This means 
>>> that each atom in the
>>> beam is in a state that itself is a combination of the |+> and |-> 
>>> states. A superposition
>>> state is often called a coherent superposition since the relative 
>>> phase of the two terms is
>>> important."
>>>
>>> .see pages 18-19 here *https://tinyurl.com/ybm56whu 
>>> *
>>>
>>>
>>> *Try answering in your own words. When the SG device is oriented 
>>> along the x axis, now effectively the z-axix IIUC, and we're dealing 
>>> with 
>>> superpositions, the outcomes will be 50-50 plus and minus. Therefore, 
>>> unless I am making some error, what you stated above is incorrect. AG *
>>>
>>> sqrt(1/2) [(s+)_z +(s-)_z]  is a superposition, but since sqrt(1/2) 
>>> [(s+)_z +(s-)_z]  =  (s+)_x the particle will always emerge 'up'
>>>
>>
>> I'll probably get back to on the foregoing. In the meantime, consider 
>> this; I claim one can never MEASURE Up + Dn or Up - Dn with a SG 
>> apparatus 
>> regardless of how many other instruments one uses to create a composite 
>> measuring apparatus (Bruno's claim IIUC). The reason is simple. We know 
>> that the spin operator 
>>
>>
>> Which one? 
>>
>
> *Good question. AG*
>
> There are spin operator for each direction in space. The superposition 
>> of up and down is a precise pure state, with precise eigenvalues, when 
>> measuring state in the complementary directions.
>>
>
> *As I wrote earlier, based on scerir's superpositions on different 
> axes, and simulation, I now think that Up + Dn and Up - Dn can be 
> measured 
> along the x axis but not along the z axis (which I was focused on). *
>
>
> All you need to do is a change of base. The operator will be defined 
> clearly by the Eigen value on the diagonal in the corresponding base. You 
> can prepare any state, and measure them “in any base”. 
>


 *I'll get back to this issue in my next post. AG *

> *You were probably correct about x axis measurements, but perhaps were 
> not clear enough. You were not explicit that measurements along the x 
> axis 
> is a different SG experiment from along z axis.*
>
>
> OK. Sorry. 
>
> * I thought you meant do them in succession, not as separate 
> experiments.*
>
>
> Ah? OK.
>
>
> * Also introducing an infinity of universes seems extraneous and 
> confusing for a solution to this problem. AG *
>
> I are probably different on this. I don’t take the word “universe” too 
> much seriously, as with mechanism we know at the start that there is 
> “physical universe” at all, just the natural numbers with the laws of 
> addition and multiplication. Both the computational and the quantum state 
> are relative, and high level, pertaining to what is “observable” for some 
> the point of view of some locally finite subject, run by some computation.
>
> The 

Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Monday, November 26, 2018 at 4:41:42 PM UTC, agrays...@gmail.com wrote:
>
>
>
> On Monday, November 26, 2018 at 12:01:05 PM UTC, Bruno Marchal wrote:
>>
>>
>> On 23 Nov 2018, at 13:30, agrays...@gmail.com wrote:
>>
>>
>>
>> On Friday, November 23, 2018 at 11:29:14 AM UTC, Bruno Marchal wrote:
>>>
>>>
>>> On 21 Nov 2018, at 18:03, agrays...@gmail.com wrote:
>>>
>>>
>>>
>>> On Monday, November 19, 2018 at 3:52:37 PM UTC, Bruno Marchal wrote:


 On 18 Nov 2018, at 14:00, agrays...@gmail.com wrote:



 On Sunday, November 18, 2018 at 12:19:20 PM UTC, Bruno Marchal wrote:
>
>
> On 16 Nov 2018, at 15:38, agrays...@gmail.com wrote:
>
>
>
> On Friday, November 16, 2018 at 10:14:32 AM UTC, scerir wrote:
>>
>>
>> Il 16 novembre 2018 alle 10.19 agrays...@gmail.com ha scritto: 
>>
>>
>>
>> On Thursday, November 15, 2018 at 2:14:48 PM UTC, scerir wrote:
>>
>>
>> Il 15 novembre 2018 alle 14.29 agrays...@gmail.com ha scritto: 
>>
>>
>>
>> On Thursday, November 15, 2018 at 8:04:53 AM UTC, scerir wrote:
>>
>> Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) 
>> [(s+)_z + (s-)_z] .
>>
>> If the x-component of spin is measured by passing the spin-1/2 
>> particle through a Stern-Gerlach with its field oriented along the 
>> x-axis, 
>> the particle will ALWAYS emerge 'up'.
>>
>>
>> *Why?  Won't the measured value be along the x axis in both 
>> directions, in effect Up or Dn? AG*
>>
>> "Hence we must conclude that the system described by the |+>x state 
>> is not the
>> same as a mixture of atoms in the |+> and !-> states. This means that 
>> each atom in the
>> beam is in a state that itself is a combination of the |+> and |-> 
>> states. A superposition
>> state is often called a coherent superposition since the relative 
>> phase of the two terms is
>> important."
>>
>> .see pages 18-19 here *https://tinyurl.com/ybm56whu 
>> *
>>
>>
>> *Try answering in your own words. When the SG device is oriented 
>> along the x axis, now effectively the z-axix IIUC, and we're dealing 
>> with 
>> superpositions, the outcomes will be 50-50 plus and minus. Therefore, 
>> unless I am making some error, what you stated above is incorrect. AG *
>>
>> sqrt(1/2) [(s+)_z +(s-)_z]  is a superposition, but since sqrt(1/2) 
>> [(s+)_z +(s-)_z]  =  (s+)_x the particle will always emerge 'up'
>>
>
> I'll probably get back to on the foregoing. In the meantime, consider 
> this; I claim one can never MEASURE Up + Dn or Up - Dn with a SG 
> apparatus 
> regardless of how many other instruments one uses to create a composite 
> measuring apparatus (Bruno's claim IIUC). The reason is simple. We know 
> that the spin operator 
>
>
> Which one? 
>

 *Good question. AG*

 There are spin operator for each direction in space. The superposition 
> of up and down is a precise pure state, with precise eigenvalues, when 
> measuring state in the complementary directions.
>

 *As I wrote earlier, based on scerir's superpositions on different 
 axes, and simulation, I now think that Up + Dn and Up - Dn can be measured 
 along the x axis but not along the z axis (which I was focused on). *


 All you need to do is a change of base. The operator will be defined 
 clearly by the Eigen value on the diagonal in the corresponding base. You 
 can prepare any state, and measure them “in any base”. 

>>>
>>>
>>> *I'll get back to this issue in my next post. AG *
>>>
 *You were probably correct about x axis measurements, but perhaps were 
 not clear enough. You were not explicit that measurements along the x axis 
 is a different SG experiment from along z axis.*


 OK. Sorry. 

 * I thought you meant do them in succession, not as separate 
 experiments.*


 Ah? OK.


 * Also introducing an infinity of universes seems extraneous and 
 confusing for a solution to this problem. AG *

 I are probably different on this. I don’t take the word “universe” too 
 much seriously, as with mechanism we know at the start that there is 
 “physical universe” at all, just the natural numbers with the laws of 
 addition and multiplication. Both the computational and the quantum state 
 are relative, and high level, pertaining to what is “observable” for some 
 the point of view of some locally finite subject, run by some computation.

 The empirical point, though, is that to predict correctly an event in 
 quantum mechanics, we have to take into account may simultaneous 
 “incompatible path”, like going through each hole in a plane. Quantum 
 computations, for 

Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Monday, November 26, 2018 at 12:01:05 PM UTC, Bruno Marchal wrote:
>
>
> On 23 Nov 2018, at 13:30, agrays...@gmail.com  wrote:
>
>
>
> On Friday, November 23, 2018 at 11:29:14 AM UTC, Bruno Marchal wrote:
>>
>>
>> On 21 Nov 2018, at 18:03, agrays...@gmail.com wrote:
>>
>>
>>
>> On Monday, November 19, 2018 at 3:52:37 PM UTC, Bruno Marchal wrote:
>>>
>>>
>>> On 18 Nov 2018, at 14:00, agrays...@gmail.com wrote:
>>>
>>>
>>>
>>> On Sunday, November 18, 2018 at 12:19:20 PM UTC, Bruno Marchal wrote:


 On 16 Nov 2018, at 15:38, agrays...@gmail.com wrote:



 On Friday, November 16, 2018 at 10:14:32 AM UTC, scerir wrote:
>
>
> Il 16 novembre 2018 alle 10.19 agrays...@gmail.com ha scritto: 
>
>
>
> On Thursday, November 15, 2018 at 2:14:48 PM UTC, scerir wrote:
>
>
> Il 15 novembre 2018 alle 14.29 agrays...@gmail.com ha scritto: 
>
>
>
> On Thursday, November 15, 2018 at 8:04:53 AM UTC, scerir wrote:
>
> Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) 
> [(s+)_z + (s-)_z] .
>
> If the x-component of spin is measured by passing the spin-1/2 
> particle through a Stern-Gerlach with its field oriented along the 
> x-axis, 
> the particle will ALWAYS emerge 'up'.
>
>
> *Why?  Won't the measured value be along the x axis in both 
> directions, in effect Up or Dn? AG*
>
> "Hence we must conclude that the system described by the |+>x state is 
> not the
> same as a mixture of atoms in the |+> and !-> states. This means that 
> each atom in the
> beam is in a state that itself is a combination of the |+> and |-> 
> states. A superposition
> state is often called a coherent superposition since the relative 
> phase of the two terms is
> important."
>
> .see pages 18-19 here *https://tinyurl.com/ybm56whu 
> *
>
>
> *Try answering in your own words. When the SG device is oriented along 
> the x axis, now effectively the z-axix IIUC, and we're dealing with 
> superpositions, the outcomes will be 50-50 plus and minus. Therefore, 
> unless I am making some error, what you stated above is incorrect. AG *
>
> sqrt(1/2) [(s+)_z +(s-)_z]  is a superposition, but since sqrt(1/2) 
> [(s+)_z +(s-)_z]  =  (s+)_x the particle will always emerge 'up'
>

 I'll probably get back to on the foregoing. In the meantime, consider 
 this; I claim one can never MEASURE Up + Dn or Up - Dn with a SG apparatus 
 regardless of how many other instruments one uses to create a composite 
 measuring apparatus (Bruno's claim IIUC). The reason is simple. We know 
 that the spin operator 


 Which one? 

>>>
>>> *Good question. AG*
>>>
>>> There are spin operator for each direction in space. The superposition 
 of up and down is a precise pure state, with precise eigenvalues, when 
 measuring state in the complementary directions.

>>>
>>> *As I wrote earlier, based on scerir's superpositions on different axes, 
>>> and simulation, I now think that Up + Dn and Up - Dn can be measured along 
>>> the x axis but not along the z axis (which I was focused on). *
>>>
>>>
>>> All you need to do is a change of base. The operator will be defined 
>>> clearly by the Eigen value on the diagonal in the corresponding base. You 
>>> can prepare any state, and measure them “in any base”. 
>>>
>>
>>
>> *I'll get back to this issue in my next post. AG *
>>
>>> *You were probably correct about x axis measurements, but perhaps were 
>>> not clear enough. You were not explicit that measurements along the x axis 
>>> is a different SG experiment from along z axis.*
>>>
>>>
>>> OK. Sorry. 
>>>
>>> * I thought you meant do them in succession, not as separate 
>>> experiments.*
>>>
>>>
>>> Ah? OK.
>>>
>>>
>>> * Also introducing an infinity of universes seems extraneous and 
>>> confusing for a solution to this problem. AG *
>>>
>>> I are probably different on this. I don’t take the word “universe” too 
>>> much seriously, as with mechanism we know at the start that there is 
>>> “physical universe” at all, just the natural numbers with the laws of 
>>> addition and multiplication. Both the computational and the quantum state 
>>> are relative, and high level, pertaining to what is “observable” for some 
>>> the point of view of some locally finite subject, run by some computation.
>>>
>>> The empirical point, though, is that to predict correctly an event in 
>>> quantum mechanics, we have to take into account may simultaneous 
>>> “incompatible path”, like going through each hole in a plane. Quantum 
>>> computations, for example, exploits that seemingly parallelism. 
>>>
>>
>> *I don't like this approach -- in fact I abhor it -- since it implies 
>> simultaneous interference among a multitude of paths to the same point on 
>> the detection screen. This 

Re: Measuring a system in a superposition of states vs in a mixed state

[Bruno Marchal]

> On 23 Nov 2018, at 13:30, agrayson2...@gmail.com wrote:
> 
> 
> 
> On Friday, November 23, 2018 at 11:29:14 AM UTC, Bruno Marchal wrote:
> 
>> On 21 Nov 2018, at 18:03, agrays...@gmail.com  wrote:
>> 
>> 
>> 
>> On Monday, November 19, 2018 at 3:52:37 PM UTC, Bruno Marchal wrote:
>> 
>>> On 18 Nov 2018, at 14:00, agrays...@gmail.com <> wrote:
>>> 
>>> 
>>> 
>>> On Sunday, November 18, 2018 at 12:19:20 PM UTC, Bruno Marchal wrote:
>>> 
 On 16 Nov 2018, at 15:38, agrays...@gmail.com <> wrote:
 
 
 
 On Friday, November 16, 2018 at 10:14:32 AM UTC, scerir wrote:
 
 
> Il 16 novembre 2018 alle 10.19 agrays...@gmail.com <> ha scritto: 
> 
> 
> 
> On Thursday, November 15, 2018 at 2:14:48 PM UTC, scerir wrote:
> 
> 
>> Il 15 novembre 2018 alle 14.29 agrays...@gmail.com <> ha scritto: 
>> 
>> 
>> 
>> On Thursday, November 15, 2018 at 8:04:53 AM UTC, scerir wrote:
>> Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) 
>> [(s+)_z + (s-)_z] .
>> 
>> If the x-component of spin is measured by passing the spin-1/2 particle 
>> through a Stern-Gerlach with its field oriented along the x-axis, the 
>> particle will ALWAYS emerge 'up'.
>> 
>> 
>> Why?  Won't the measured value be along the x axis in both directions, 
>> in effect Up or Dn? AG
> "Hence we must conclude that the system described by the |+>x state is 
> not the
> same as a mixture of atoms in the |+> and !-> states. This means that 
> each atom in the
> beam is in a state that itself is a combination of the |+> and |-> 
> states. A superposition
> state is often called a coherent superposition since the relative phase 
> of the two terms is
> important."
> 
> .see pages 18-19 here https://tinyurl.com/ybm56whu 
> 
> 
> Try answering in your own words. When the SG device is oriented along the 
> x axis, now effectively the z-axix IIUC, and we're dealing with 
> superpositions, the outcomes will be 50-50 plus and minus. Therefore, 
> unless I am making some error, what you stated above is incorrect. AG
 sqrt(1/2) [(s+)_z +(s-)_z]  is a superposition, but since sqrt(1/2) 
 [(s+)_z +(s-)_z]  =  (s+)_x the particle will always emerge 'up'
 
 
 I'll probably get back to on the foregoing. In the meantime, consider 
 this; I claim one can never MEASURE Up + Dn or Up - Dn with a SG apparatus 
 regardless of how many other instruments one uses to create a composite 
 measuring apparatus (Bruno's claim IIUC). The reason is simple. We know 
 that the spin operator
>>> 
>>> Which one?
>>> 
>>> Good question. AG
>>> 
>>> There are spin operator for each direction in space. The superposition of 
>>> up and down is a precise pure state, with precise eigenvalues, when 
>>> measuring state in the complementary directions.
>>> 
>>> As I wrote earlier, based on scerir's superpositions on different axes, and 
>>> simulation, I now think that Up + Dn and Up - Dn can be measured along the 
>>> x axis but not along the z axis (which I was focused on).
>> 
>> All you need to do is a change of base. The operator will be defined clearly 
>> by the Eigen value on the diagonal in the corresponding base. You can 
>> prepare any state, and measure them “in any base”. 
>> 
>> I'll get back to this issue in my next post. AG 
>>> You were probably correct about x axis measurements, but perhaps were not 
>>> clear enough. You were not explicit that measurements along the x axis is a 
>>> different SG experiment from along z axis.
>> 
>> OK. Sorry. 
>>> I thought you meant do them in succession, not as separate experiments.
>> 
>> Ah? OK.
>>> Also introducing an infinity of universes seems extraneous and confusing 
>>> for a solution to this problem. AG 
>> I are probably different on this. I don’t take the word “universe” too much 
>> seriously, as with mechanism we know at the start that there is “physical 
>> universe” at all, just the natural numbers with the laws of addition and 
>> multiplication. Both the computational and the quantum state are relative, 
>> and high level, pertaining to what is “observable” for some the point of 
>> view of some locally finite subject, run by some computation.
>> 
>> The empirical point, though, is that to predict correctly an event in 
>> quantum mechanics, we have to take into account may simultaneous 
>> “incompatible path”, like going through each hole in a plane. Quantum 
>> computations, for example, exploits that seemingly parallelism. 
>> 
>> I don't like this approach -- in fact I abhor it -- since it implies 
>> simultaneous interference among a multitude of paths to the same point on 
>> the detection screen. This adds an unnecessary mystery to QM. In the Hilbert 
>> Space representation, the wf is what it is, but can be represented in a 
>> multitude of different bases. It is 

Re: Measuring a system in a superposition of states vs in a mixed state.

[John Clark]

On Sat, Nov 24, 2018 at 8:08 AM  wrote:

*> Why do you make this gratuitous point. and on a regular basis, when you
> habitually indicate which theories you like or don't like?*


As I've said before I have no loyalty, if I find a idea doesn't fit the
facts then regardless of my previous infatuation I abandon it, and if it
does fit the facts then I learn to like it and continue to like it until I
find an idea that fits the facts even better.

 John K Clark

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Re: Measuring a system in a superposition of states vs in a mixed state.

[agrayson2000]

On Friday, November 23, 2018 at 5:29:05 PM UTC, John Clark wrote:
>
>
> agrays...@gmail.com 
>
> *>** So Feynman adds this additional hypothesis to QM. Is this kosher?*
>
>  
> It had better be kosher because it works!
>
> *> ** introducing an infinity of universes seems extraneous and confusing 
>> for a solution to this problem. AG*
>
>  
> Far from being extraneous Feynman's method is the easiest way to make a 
> calculation in Quantum Electrodynamics, a calculation that would take weeks 
> or months using other methods can be done with pencil and paper in just a 
> few hours doing it Feynman's way. Feynman said the magnetic moment of an 
> electron can't be exactly 1 as had been previously thought, he calculated 
> it to be 1.00115965246, while the best experimental value that was found 
> much later is   1.00115965221. That's like measuring the distance between 
> Los Angeles and New York to the thickness of a human hair.  This is the 
> most accurate prediction in all of science, Feynman must have been doing 
> something right
>
> *> I don't like this approach -- in fact I abhor it*
>
>
> The Universe likes it, and it's likes and dislikes are far more important 
> than yours.
>

*Why do you make this gratuitous point. and on a regular basis, when you 
habitually indicate which theories you like or don't like? Does the 
universe care what theories you like? I doubt it cares, or can care. Some 
interpretations are more useful than others for calculating purposes. 
Doesn't imply they have greater ontological value. AG *

>
>  John K Clark 
>
>
>  
>

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Re: Measuring a system in a superposition of states vs in a mixed state.

[agrayson2000]

On Friday, November 23, 2018 at 5:29:05 PM UTC, John Clark wrote:
>
>
> agrays...@gmail.com 
>
> *>** So Feynman adds this additional hypothesis to QM. Is this kosher?*
>
>  
> It had better be kosher because it works!
>
> *> ** introducing an infinity of universes seems extraneous and confusing 
>> for a solution to this problem. AG*
>
>  
> Far from being extraneous Feynman's method is the easiest way to make a 
> calculation in Quantum Electrodynamics, a calculation that would take weeks 
> or months using other methods can be done with pencil and paper in just a 
> few hours doing it Feynman's way. Feynman said the magnetic moment of an 
> electron can't be exactly 1 as had been previously thought, he calculated 
> it to be 1.00115965246, while the best experimental value that was found 
> much later is   1.00115965221. That's like measuring the distance between 
> Los Angeles and New York to the thickness of a human hair.  This is the 
> most accurate prediction in all of science, Feynman must have been doing 
> something right
>
> *> I don't like this approach -- in fact I abhor it*
>
>
> The Universe likes it, and it's likes and dislikes are far more important 
> than yours.
>


*Quantum theory is replete with mathematics that works, that we don't 
understand why it works. What is different about this case? Incidentally, 
can you shed any light on my question about coherent states of a 
superposition? TIA, AG *

>
>  John K Clark 
>
>
>  
>

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Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Friday, November 23, 2018 at 11:29:14 AM UTC, Bruno Marchal wrote:
>
>
> On 21 Nov 2018, at 18:03, agrays...@gmail.com  wrote:
>
>
>
> On Monday, November 19, 2018 at 3:52:37 PM UTC, Bruno Marchal wrote:
>>
>>
>> On 18 Nov 2018, at 14:00, agrays...@gmail.com wrote:
>>
>>
>>
>> On Sunday, November 18, 2018 at 12:19:20 PM UTC, Bruno Marchal wrote:
>>>
>>>
>>> On 16 Nov 2018, at 15:38, agrays...@gmail.com wrote:
>>>
>>>
>>>
>>> On Friday, November 16, 2018 at 10:14:32 AM UTC, scerir wrote:


 Il 16 novembre 2018 alle 10.19 agrays...@gmail.com ha scritto: 



 On Thursday, November 15, 2018 at 2:14:48 PM UTC, scerir wrote:


 Il 15 novembre 2018 alle 14.29 agrays...@gmail.com ha scritto: 



 On Thursday, November 15, 2018 at 8:04:53 AM UTC, scerir wrote:

 Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) 
 [(s+)_z + (s-)_z] .

 If the x-component of spin is measured by passing the spin-1/2 particle 
 through a Stern-Gerlach with its field oriented along the x-axis, the 
 particle will ALWAYS emerge 'up'.


 *Why?  Won't the measured value be along the x axis in both directions, 
 in effect Up or Dn? AG*

 "Hence we must conclude that the system described by the |+>x state is 
 not the
 same as a mixture of atoms in the |+> and !-> states. This means that 
 each atom in the
 beam is in a state that itself is a combination of the |+> and |-> 
 states. A superposition
 state is often called a coherent superposition since the relative phase 
 of the two terms is
 important."

 .see pages 18-19 here *https://tinyurl.com/ybm56whu 
 *


 *Try answering in your own words. When the SG device is oriented along 
 the x axis, now effectively the z-axix IIUC, and we're dealing with 
 superpositions, the outcomes will be 50-50 plus and minus. Therefore, 
 unless I am making some error, what you stated above is incorrect. AG *

 sqrt(1/2) [(s+)_z +(s-)_z]  is a superposition, but since sqrt(1/2) 
 [(s+)_z +(s-)_z]  =  (s+)_x the particle will always emerge 'up'

>>>
>>> I'll probably get back to on the foregoing. In the meantime, consider 
>>> this; I claim one can never MEASURE Up + Dn or Up - Dn with a SG apparatus 
>>> regardless of how many other instruments one uses to create a composite 
>>> measuring apparatus (Bruno's claim IIUC). The reason is simple. We know 
>>> that the spin operator 
>>>
>>>
>>> Which one? 
>>>
>>
>> *Good question. AG*
>>
>> There are spin operator for each direction in space. The superposition of 
>>> up and down is a precise pure state, with precise eigenvalues, when 
>>> measuring state in the complementary directions.
>>>
>>
>> *As I wrote earlier, based on scerir's superpositions on different axes, 
>> and simulation, I now think that Up + Dn and Up - Dn can be measured along 
>> the x axis but not along the z axis (which I was focused on). *
>>
>>
>> All you need to do is a change of base. The operator will be defined 
>> clearly by the Eigen value on the diagonal in the corresponding base. You 
>> can prepare any state, and measure them “in any base”. 
>>
>
>
> *I'll get back to this issue in my next post. AG *
>
>> *You were probably correct about x axis measurements, but perhaps were 
>> not clear enough. You were not explicit that measurements along the x axis 
>> is a different SG experiment from along z axis.*
>>
>>
>> OK. Sorry. 
>>
>> * I thought you meant do them in succession, not as separate experiments.*
>>
>>
>> Ah? OK.
>>
>>
>> * Also introducing an infinity of universes seems extraneous and 
>> confusing for a solution to this problem. AG *
>>
>> I are probably different on this. I don’t take the word “universe” too 
>> much seriously, as with mechanism we know at the start that there is 
>> “physical universe” at all, just the natural numbers with the laws of 
>> addition and multiplication. Both the computational and the quantum state 
>> are relative, and high level, pertaining to what is “observable” for some 
>> the point of view of some locally finite subject, run by some computation.
>>
>> The empirical point, though, is that to predict correctly an event in 
>> quantum mechanics, we have to take into account may simultaneous 
>> “incompatible path”, like going through each hole in a plane. Quantum 
>> computations, for example, exploits that seemingly parallelism. 
>>
>
> *I don't like this approach -- in fact I abhor it -- since it implies 
> simultaneous interference among a multitude of paths to the same point on 
> the detection screen. This adds an unnecessary mystery to QM. In the 
> Hilbert Space representation, the wf is what it is, but can be represented 
> in a multitude of different bases. It is therefore misleading to claim the 
> system being analyzed is in a multitude of states; rather it is in one 
> state, 

Re: Measuring a system in a superposition of states vs in a mixed state

[Bruno Marchal]

> On 21 Nov 2018, at 18:03, agrayson2...@gmail.com wrote:
> 
> 
> 
> On Monday, November 19, 2018 at 3:52:37 PM UTC, Bruno Marchal wrote:
> 
>> On 18 Nov 2018, at 14:00, agrays...@gmail.com  wrote:
>> 
>> 
>> 
>> On Sunday, November 18, 2018 at 12:19:20 PM UTC, Bruno Marchal wrote:
>> 
>>> On 16 Nov 2018, at 15:38, agrays...@gmail.com <> wrote:
>>> 
>>> 
>>> 
>>> On Friday, November 16, 2018 at 10:14:32 AM UTC, scerir wrote:
>>> 
>>> 
 Il 16 novembre 2018 alle 10.19 agrays...@gmail.com <> ha scritto: 
 
 
 
 On Thursday, November 15, 2018 at 2:14:48 PM UTC, scerir wrote:
 
 
> Il 15 novembre 2018 alle 14.29 agrays...@gmail.com <> ha scritto: 
> 
> 
> 
> On Thursday, November 15, 2018 at 8:04:53 AM UTC, scerir wrote:
> Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) 
> [(s+)_z + (s-)_z] .
> 
> If the x-component of spin is measured by passing the spin-1/2 particle 
> through a Stern-Gerlach with its field oriented along the x-axis, the 
> particle will ALWAYS emerge 'up'.
> 
> 
> Why?  Won't the measured value be along the x axis in both directions, in 
> effect Up or Dn? AG
 "Hence we must conclude that the system described by the |+>x state is not 
 the
 same as a mixture of atoms in the |+> and !-> states. This means that each 
 atom in the
 beam is in a state that itself is a combination of the |+> and |-> states. 
 A superposition
 state is often called a coherent superposition since the relative phase of 
 the two terms is
 important."
 
 .see pages 18-19 here https://tinyurl.com/ybm56whu 
 
 
 Try answering in your own words. When the SG device is oriented along the 
 x axis, now effectively the z-axix IIUC, and we're dealing with 
 superpositions, the outcomes will be 50-50 plus and minus. Therefore, 
 unless I am making some error, what you stated above is incorrect. AG
>>> sqrt(1/2) [(s+)_z +(s-)_z]  is a superposition, but since sqrt(1/2) [(s+)_z 
>>> +(s-)_z]  =  (s+)_x the particle will always emerge 'up'
>>> 
>>> 
>>> I'll probably get back to on the foregoing. In the meantime, consider this; 
>>> I claim one can never MEASURE Up + Dn or Up - Dn with a SG apparatus 
>>> regardless of how many other instruments one uses to create a composite 
>>> measuring apparatus (Bruno's claim IIUC). The reason is simple. We know 
>>> that the spin operator
>> 
>> Which one?
>> 
>> Good question. AG
>> 
>> There are spin operator for each direction in space. The superposition of up 
>> and down is a precise pure state, with precise eigenvalues, when measuring 
>> state in the complementary directions.
>> 
>> As I wrote earlier, based on scerir's superpositions on different axes, and 
>> simulation, I now think that Up + Dn and Up - Dn can be measured along the x 
>> axis but not along the z axis (which I was focused on).
> 
> All you need to do is a change of base. The operator will be defined clearly 
> by the Eigen value on the diagonal in the corresponding base. You can prepare 
> any state, and measure them “in any base”. 
> 
> I'll get back to this issue in my next post. AG 
>> You were probably correct about x axis measurements, but perhaps were not 
>> clear enough. You were not explicit that measurements along the x axis is a 
>> different SG experiment from along z axis.
> 
> OK. Sorry. 
>> I thought you meant do them in succession, not as separate experiments.
> 
> Ah? OK.
>> Also introducing an infinity of universes seems extraneous and confusing for 
>> a solution to this problem. AG 
> I are probably different on this. I don’t take the word “universe” too much 
> seriously, as with mechanism we know at the start that there is “physical 
> universe” at all, just the natural numbers with the laws of addition and 
> multiplication. Both the computational and the quantum state are relative, 
> and high level, pertaining to what is “observable” for some the point of view 
> of some locally finite subject, run by some computation.
> 
> The empirical point, though, is that to predict correctly an event in quantum 
> mechanics, we have to take into account may simultaneous “incompatible path”, 
> like going through each hole in a plane. Quantum computations, for example, 
> exploits that seemingly parallelism. 
> 
> I don't like this approach -- in fact I abhor it -- since it implies 
> simultaneous interference among a multitude of paths to the same point on the 
> detection screen. This adds an unnecessary mystery to QM. In the Hilbert 
> Space representation, the wf is what it is, but can be represented in a 
> multitude of different bases. It is therefore misleading to claim the system 
> being analyzed is in a multitude of states; rather it is in one state, which 
> due to linear algebra, has many representations. AG


I can be OK with this, if you agree that the consciousness of the observer 

Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Monday, November 19, 2018 at 3:52:37 PM UTC, Bruno Marchal wrote:
>
>
> On 18 Nov 2018, at 14:00, agrays...@gmail.com  wrote:
>
>
>
> On Sunday, November 18, 2018 at 12:19:20 PM UTC, Bruno Marchal wrote:
>>
>>
>> On 16 Nov 2018, at 15:38, agrays...@gmail.com wrote:
>>
>>
>>
>> On Friday, November 16, 2018 at 10:14:32 AM UTC, scerir wrote:
>>>
>>>
>>> Il 16 novembre 2018 alle 10.19 agrays...@gmail.com ha scritto: 
>>>
>>>
>>>
>>> On Thursday, November 15, 2018 at 2:14:48 PM UTC, scerir wrote:
>>>
>>>
>>> Il 15 novembre 2018 alle 14.29 agrays...@gmail.com ha scritto: 
>>>
>>>
>>>
>>> On Thursday, November 15, 2018 at 8:04:53 AM UTC, scerir wrote:
>>>
>>> Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) 
>>> [(s+)_z + (s-)_z] .
>>>
>>> If the x-component of spin is measured by passing the spin-1/2 particle 
>>> through a Stern-Gerlach with its field oriented along the x-axis, the 
>>> particle will ALWAYS emerge 'up'.
>>>
>>>
>>> *Why?  Won't the measured value be along the x axis in both directions, 
>>> in effect Up or Dn? AG*
>>>
>>> "Hence we must conclude that the system described by the |+>x state is 
>>> not the
>>> same as a mixture of atoms in the |+> and !-> states. This means that 
>>> each atom in the
>>> beam is in a state that itself is a combination of the |+> and |-> 
>>> states. A superposition
>>> state is often called a coherent superposition since the relative phase 
>>> of the two terms is
>>> important."
>>>
>>> .see pages 18-19 here *https://tinyurl.com/ybm56whu 
>>> *
>>>
>>>
>>> *Try answering in your own words. When the SG device is oriented along 
>>> the x axis, now effectively the z-axix IIUC, and we're dealing with 
>>> superpositions, the outcomes will be 50-50 plus and minus. Therefore, 
>>> unless I am making some error, what you stated above is incorrect. AG *
>>>
>>> sqrt(1/2) [(s+)_z +(s-)_z]  is a superposition, but since sqrt(1/2) 
>>> [(s+)_z +(s-)_z]  =  (s+)_x the particle will always emerge 'up'
>>>
>>
>> I'll probably get back to on the foregoing. In the meantime, consider 
>> this; I claim one can never MEASURE Up + Dn or Up - Dn with a SG apparatus 
>> regardless of how many other instruments one uses to create a composite 
>> measuring apparatus (Bruno's claim IIUC). The reason is simple. We know 
>> that the spin operator 
>>
>>
>> Which one? 
>>
>
> *Good question. AG*
>
> There are spin operator for each direction in space. The superposition of 
>> up and down is a precise pure state, with precise eigenvalues, when 
>> measuring state in the complementary directions.
>>
>
> *As I wrote earlier, based on scerir's superpositions on different axes, 
> and simulation, I now think that Up + Dn and Up - Dn can be measured along 
> the x axis but not along the z axis (which I was focused on). *
>
>
> All you need to do is a change of base. The operator will be defined 
> clearly by the Eigen value on the diagonal in the corresponding base. You 
> can prepare any state, and measure them “in any base”. 
>


*I'll get back to this issue in my next post. AG *

> *You were probably correct about x axis measurements, but perhaps were not 
> clear enough. You were not explicit that measurements along the x axis is a 
> different SG experiment from along z axis.*
>
>
> OK. Sorry. 
>
> * I thought you meant do them in succession, not as separate experiments.*
>
>
> Ah? OK.
>
>
> * Also introducing an infinity of universes seems extraneous and confusing 
> for a solution to this problem. AG *
>
> I are probably different on this. I don’t take the word “universe” too 
> much seriously, as with mechanism we know at the start that there is 
> “physical universe” at all, just the natural numbers with the laws of 
> addition and multiplication. Both the computational and the quantum state 
> are relative, and high level, pertaining to what is “observable” for some 
> the point of view of some locally finite subject, run by some computation.
>
> The empirical point, though, is that to predict correctly an event in 
> quantum mechanics, we have to take into account may simultaneous 
> “incompatible path”, like going through each hole in a plane. Quantum 
> computations, for example, exploits that seemingly parallelism. 
>

*I don't like this approach -- in fact I abhor it -- since it implies 
simultaneous interference among a multitude of paths to the same point on 
the detection screen. This adds an unnecessary mystery to QM. In the 
Hilbert Space representation, the wf is what it is, but can be represented 
in a multitude of different bases. It is therefore misleading to claim the 
system being analyzed is in a multitude of states; rather it is in one 
state, which due to linear algebra, has many representations. AG *

> has exactly two eigenstates, each with probability of .5. We can write 
>> them down. We also know that every quantum measurement gives up an 
>> eigenvalue of some eigenstate. Therefore, if there existed an Up + 

Re: Measuring a system in a superposition of states vs in a mixed state

[Bruno Marchal]

> On 18 Nov 2018, at 14:00, agrayson2...@gmail.com wrote:
> 
> 
> 
> On Sunday, November 18, 2018 at 12:19:20 PM UTC, Bruno Marchal wrote:
> 
>> On 16 Nov 2018, at 15:38, agrays...@gmail.com  wrote:
>> 
>> 
>> 
>> On Friday, November 16, 2018 at 10:14:32 AM UTC, scerir wrote:
>> 
>> 
>>> Il 16 novembre 2018 alle 10.19 agrays...@gmail.com <> ha scritto: 
>>> 
>>> 
>>> 
>>> On Thursday, November 15, 2018 at 2:14:48 PM UTC, scerir wrote:
>>> 
>>> 
 Il 15 novembre 2018 alle 14.29 agrays...@gmail.com <> ha scritto: 
 
 
 
 On Thursday, November 15, 2018 at 8:04:53 AM UTC, scerir wrote:
 Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) [(s+)_z 
 + (s-)_z] .
 
 If the x-component of spin is measured by passing the spin-1/2 particle 
 through a Stern-Gerlach with its field oriented along the x-axis, the 
 particle will ALWAYS emerge 'up'.
 
 
 Why?  Won't the measured value be along the x axis in both directions, in 
 effect Up or Dn? AG
>>> "Hence we must conclude that the system described by the |+>x state is not 
>>> the
>>> same as a mixture of atoms in the |+> and !-> states. This means that each 
>>> atom in the
>>> beam is in a state that itself is a combination of the |+> and |-> states. 
>>> A superposition
>>> state is often called a coherent superposition since the relative phase of 
>>> the two terms is
>>> important."
>>> 
>>> .see pages 18-19 here https://tinyurl.com/ybm56whu 
>>> 
>>> 
>>> Try answering in your own words. When the SG device is oriented along the x 
>>> axis, now effectively the z-axix IIUC, and we're dealing with 
>>> superpositions, the outcomes will be 50-50 plus and minus. Therefore, 
>>> unless I am making some error, what you stated above is incorrect. AG
>> sqrt(1/2) [(s+)_z +(s-)_z]  is a superposition, but since sqrt(1/2) [(s+)_z 
>> +(s-)_z]  =  (s+)_x the particle will always emerge 'up'
>> 
>> 
>> I'll probably get back to on the foregoing. In the meantime, consider this; 
>> I claim one can never MEASURE Up + Dn or Up - Dn with a SG apparatus 
>> regardless of how many other instruments one uses to create a composite 
>> measuring apparatus (Bruno's claim IIUC). The reason is simple. We know that 
>> the spin operator
> 
> Which one?
> 
> Good question. AG
> 
> There are spin operator for each direction in space. The superposition of up 
> and down is a precise pure state, with precise eigenvalues, when measuring 
> state in the complementary directions.
> 
> As I wrote earlier, based on scerir's superpositions on different axes, and 
> simulation, I now think that Up + Dn and Up - Dn can be measured along the x 
> axis but not along the z axis (which I was focused on).

All you need to do is a change of base. The operator will be defined clearly by 
the Eigen value on the diagonal in the corresponding base. You can prepare any 
state, and measure them “in any base”. 



> You were probably correct about x axis measurements, but perhaps were not 
> clear enough. You were not explicit that measurements along the x axis is a 
> different SG experiment from along z axis.

OK. Sorry. 



> I thought you meant do them in succession, not as separate experiments.

Ah? OK.




> Also introducing an infinity of universes seems extraneous and confusing for 
> a solution to this problem. AG 


I are probably different on this. I don’t take the word “universe” too much 
seriously, as with mechanism we know at the start that there is “physical 
universe” at all, just the natural numbers with the laws of addition and 
multiplication. Both the computational and the quantum state are relative, and 
high level, pertaining to what is “observable” for some the point of view of 
some locally finite subject, run by some computation.

The empirical point, though, is that to predict correctly an event in quantum 
mechanics, we have to take into account may simultaneous “incompatible path”, 
like going through each hole in a plane. Quantum computations, for example, 
exploits that seemingly parallelism. 




> 
>> has exactly two eigenstates, each with probability of .5. We can write them 
>> down. We also know that every quantum measurement gives up an eigenvalue of 
>> some eigenstate. Therefore, if there existed an Up + Dn or Up - Dn 
>> eigenstate, it would have to have probability ZERO since the Up and Dn 
>> eigenstates have probabilities which sum to unity. Do you agree or not, and 
>> if not, why? TIA, AG 
> 
> You add the probabilities, but you need to add the amplitudes of 
> probabilities instead, and then take their square. You simply dismiss the 
> quantum formalism, it seems to me.
> 
> I did not; an incorrect inference on your part.

All right. (I was just trying to figure out what you did, to be sure).



> I never mentioned Born's rule (it wasn't necessary),

You did use the probability 1/2 at some place, with the particle in a state 
1/sqrt(2)(up + down). We use all 

Re: Measuring a system in a superposition of states vs in a mixed state

[Philip Thrift]

On Sunday, November 18, 2018 at 3:20:47 PM UTC-6, agrays...@gmail.com wrote:
>
>
>
> On Sunday, November 18, 2018 at 9:14:25 PM UTC, Philip Thrift wrote:
>>
>>
>>
>> On Sunday, November 18, 2018 at 11:49:57 AM UTC-6, agrays...@gmail.com 
>> wrote:
>>>
>>>
>>> *For the simple case of two histories, presumably of particles, how does 
>>> Feynman introduce interference? What's the conceptual framework for 
>>> interference among or between histories? TIA, AG *
>>>


>> Attached to each history is an "evolving" *unit complex number* [ 
>> https://en.wikipedia.org/wiki/Circle_group ], or UCN (the complex 
>> numbers of modulus 1). When histories are "summed" (the sum of UCNs at the 
>> end of the histories that go to the same end point)  there is 
>> "interference" (just in the way complex numbers add up, since you can have 
>> a UCN pointing in one direction and another 180 plus or minus x degrees 
>> opposite). The modulus of that sum is then the "weight" for that end point.
>>
>> - pt
>>
>
> *So Feynman adds this additional hypothesis to QM. Is this kosher? Also, 
> doesn't he used forward and backward in time histories? Finally, how does 
> he choose the histories and presumably eliminate forward and backward 
> spatial loops, or doesn't this matter? AG *
>



His Sum Over Histories (Path Integral) is based on a set of postulates 
listed here:

  
 http://muchomas.lassp.cornell.edu/8.04/Lecs/lec_FeynmanDiagrams/node3.html

It gives the same numerical results as the Hilbert space formulation.

My Reflective Path integral has histories and futures (backwards-in-time 
histories). It puts multiple histories and time symmetry together. Feynman 
didn't do that. I did.

- pt


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Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Sunday, November 18, 2018 at 9:14:25 PM UTC, Philip Thrift wrote:
>
>
>
> On Sunday, November 18, 2018 at 11:49:57 AM UTC-6, agrays...@gmail.com 
> wrote:
>>
>>
>> *For the simple case of two histories, presumably of particles, how does 
>> Feynman introduce interference? What's the conceptual framework for 
>> interference among or between histories? TIA, AG *
>>
>>>
>>>
> Attached to each history is an "evolving" *unit complex number* [ 
> https://en.wikipedia.org/wiki/Circle_group ], or UCN (the complex numbers 
> of modulus 1). When histories are "summed" (the sum of UCNs at the end of 
> the histories that go to the same end point)  there is "interference" (just 
> in the way complex numbers add up, since you can have a UCN pointing in one 
> direction and another 180 plus or minus x degrees opposite). The modulus of 
> that sum is then the "weight" for that end point.
>
> - pt
>

*So Feynman adds this additional hypothesis to QM. Is this kosher? Also, 
doesn't he used forward and backward in time histories? Finally, how does 
he choose the histories and presumably eliminate forward and backward 
spatial loops, or doesn't this matter? AG *

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Re: Measuring a system in a superposition of states vs in a mixed state

[Philip Thrift]

On Sunday, November 18, 2018 at 11:49:57 AM UTC-6, agrays...@gmail.com 
wrote:
>
>
> *For the simple case of two histories, presumably of particles, how does 
> Feynman introduce interference? What's the conceptual framework for 
> interference among or between histories? TIA, AG *
>
>>
>>
Attached to each history is an "evolving" *unit complex number* 
[ https://en.wikipedia.org/wiki/Circle_group ], or UCN (the complex numbers 
of modulus 1). When histories are "summed" (the sum of UCNs at the end of 
the histories that go to the same end point)  there is "interference" (just 
in the way complex numbers add up, since you can have a UCN pointing in one 
direction and another 180 plus or minus x degrees opposite). The modulus of 
that sum is then the "weight" for that end point.

- pt

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Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Thursday, November 15, 2018 at 7:37:58 PM UTC, Brent wrote:
>
>
>
> On 11/14/2018 11:23 PM, Philip Thrift wrote:
>
>
>
> On Wednesday, November 14, 2018 at 6:55:36 PM UTC-6, agrays...@gmail.com 
> wrote: 
>>
>>
>>
>> On Wednesday, November 14, 2018 at 10:20:09 PM UTC, Pierz wrote: 
>>>
>>> Obviously you can't measure the particle simultaneously in the up and 
>>> down state. Nobody believes that. Nobody is arguing it. 
>>
>>
>> *Haven't you ever heard of physicists, some prominent who write books 
>> about QM for the lay public, who assert that one of the mysteries of QM is 
>> that a particle can be in two places at the same time, or cats can be alive 
>> and dead simultaneously, or spin can be Up and Dn simultaneously? If you 
>> haven't, you're not paying attention. AG*
>>
>>
>>>
> *"a particle can be in two places at the same time"*
>
>
> A path-integral realist (one who is "starting from a framework in which 
> *histories* are fundamental")* might formulate it this way:
>
> "a particle can have multiple histories — only one of which survives 
> measurement"
>
>
> Don't you need multiple histories to account for interference effects?
>

*For the simple case of two histories, presumably of particles, how does 
Feynman introduce interference? What's the conceptual framework for 
interference among or between histories? TIA, AG *

>
> Brent
>
>
>
> * *Hilbert Spaces from Path Integrals*
> https://arxiv.org/abs/1002.0589
>
> - pt 
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> .
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>
>
>

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Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Sunday, November 18, 2018 at 12:19:20 PM UTC, Bruno Marchal wrote:
>
>
> On 16 Nov 2018, at 15:38, agrays...@gmail.com  wrote:
>
>
>
> On Friday, November 16, 2018 at 10:14:32 AM UTC, scerir wrote:
>>
>>
>> Il 16 novembre 2018 alle 10.19 agrays...@gmail.com ha scritto: 
>>
>>
>>
>> On Thursday, November 15, 2018 at 2:14:48 PM UTC, scerir wrote:
>>
>>
>> Il 15 novembre 2018 alle 14.29 agrays...@gmail.com ha scritto: 
>>
>>
>>
>> On Thursday, November 15, 2018 at 8:04:53 AM UTC, scerir wrote:
>>
>> Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) 
>> [(s+)_z + (s-)_z] .
>>
>> If the x-component of spin is measured by passing the spin-1/2 particle 
>> through a Stern-Gerlach with its field oriented along the x-axis, the 
>> particle will ALWAYS emerge 'up'.
>>
>>
>> *Why?  Won't the measured value be along the x axis in both directions, 
>> in effect Up or Dn? AG*
>>
>> "Hence we must conclude that the system described by the |+>x state is 
>> not the
>> same as a mixture of atoms in the |+> and !-> states. This means that 
>> each atom in the
>> beam is in a state that itself is a combination of the |+> and |-> 
>> states. A superposition
>> state is often called a coherent superposition since the relative phase 
>> of the two terms is
>> important."
>>
>> .see pages 18-19 here *https://tinyurl.com/ybm56whu 
>> *
>>
>>
>> *Try answering in your own words. When the SG device is oriented along 
>> the x axis, now effectively the z-axix IIUC, and we're dealing with 
>> superpositions, the outcomes will be 50-50 plus and minus. Therefore, 
>> unless I am making some error, what you stated above is incorrect. AG *
>>
>> sqrt(1/2) [(s+)_z +(s-)_z]  is a superposition, but since sqrt(1/2) 
>> [(s+)_z +(s-)_z]  =  (s+)_x the particle will always emerge 'up'
>>
>
> I'll probably get back to on the foregoing. In the meantime, consider 
> this; I claim one can never MEASURE Up + Dn or Up - Dn with a SG apparatus 
> regardless of how many other instruments one uses to create a composite 
> measuring apparatus (Bruno's claim IIUC). The reason is simple. We know 
> that the spin operator 
>
>
> Which one? 
>

*Good question. AG*

There are spin operator for each direction in space. The superposition of 
> up and down is a precise pure state, with precise eigenvalues, when 
> measuring state in the complementary directions.
>

*As I wrote earlier, based on scerir's superpositions on different axes, 
and simulation, I now think that Up + Dn and Up - Dn can be measured along 
the x axis but not along the z axis (which I was focused on). You were 
probably correct about x axis measurements, but perhaps were not clear 
enough. You were not explicit that measurements along the x axis is a 
different SG experiment from along z axis. I thought you meant do them in 
succession, not as separate experiments. Also introducing an infinity of 
universes seems extraneous and confusing for a solution to this problem. AG 
*

>
> has exactly two eigenstates, each with probability of .5. We can write 
> them down. We also know that every quantum measurement gives up an 
> eigenvalue of some eigenstate. Therefore, if there existed an Up + Dn or Up 
> - Dn eigenstate, it would have to have probability ZERO since the Up and Dn 
> eigenstates have probabilities which sum to unity. Do you agree or not, and 
> if not, why? TIA, AG 
>
>
> You add the probabilities, but you need to add the amplitudes of 
> probabilities instead, and then take their square. You simply dismiss the 
> quantum formalism, it seems to me. 
>

*I did not; an incorrect inference on your part. I*
* never mentioned Born's rule (it wasn't necessary), from which one cannot 
infer I am criticizing QM itself. AG *

The states constituted a vector space: the sum (superposition) of 
> orthogonal states are pure state, after a change of base, and I did give 
> you the corresponding operator. You are not criticising an interpretation 
> of QM, but QM itself.
>


> Bruno
>
>
>
>
>
>>
>>   
>>
>> In fact (s+)_z = sqrt(1/2) [(s+)_x + (s-)_x]
>>
>> and (s-)_z = sqrt(1/2) [(s+)_x - (s-)_x]
>>
>> (where _z, _x, are the z-component and the x-component of spin)
>>
>> so that psi = sqrt(1/2)[(s+)_z +(s-)_z] = (s+)_x.   (pure state, not 
>> mixture state)..
>>
>> AGrayson2000 asked "If a system is in a superposition of states, whatever 
>> value measured, will be repeated if the same system is repeatedly 
>> measured.  But what happens if the system is in a mixed state?"
>>
>> Does Everett's "relative state interpretation" show how to interpret a 
>> real superposition (like the above, in which the particle will always 
>> emerge 'up') and how to interpret a mixture (in which the particle will 
>> emerge 50% 'up' or 50% 'down')?
>>
>>  
>> -- 
>> You received this message because you are subscribed to the Google Groups 
>> "Everything List" group. 
>> To unsubscribe from this group and stop receiving emails from it, send an 
>> email to 

Re: Measuring a system in a superposition of states vs in a mixed state

[Bruno Marchal]

> On 16 Nov 2018, at 15:38, agrayson2...@gmail.com wrote:
> 
> 
> 
> On Friday, November 16, 2018 at 10:14:32 AM UTC, scerir wrote:
> 
> 
>> Il 16 novembre 2018 alle 10.19 agrays...@gmail.com  ha scritto: 
>> 
>> 
>> 
>> On Thursday, November 15, 2018 at 2:14:48 PM UTC, scerir wrote:
>> 
>> 
>>> Il 15 novembre 2018 alle 14.29 agrays...@gmail.com <> ha scritto: 
>>> 
>>> 
>>> 
>>> On Thursday, November 15, 2018 at 8:04:53 AM UTC, scerir wrote:
>>> Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) [(s+)_z 
>>> + (s-)_z] .
>>> 
>>> If the x-component of spin is measured by passing the spin-1/2 particle 
>>> through a Stern-Gerlach with its field oriented along the x-axis, the 
>>> particle will ALWAYS emerge 'up'.
>>> 
>>> 
>>> Why?  Won't the measured value be along the x axis in both directions, in 
>>> effect Up or Dn? AG
>> "Hence we must conclude that the system described by the |+>x state is not 
>> the
>> same as a mixture of atoms in the |+> and !-> states. This means that each 
>> atom in the
>> beam is in a state that itself is a combination of the |+> and |-> states. A 
>> superposition
>> state is often called a coherent superposition since the relative phase of 
>> the two terms is
>> important."
>> 
>> .see pages 18-19 here https://tinyurl.com/ybm56whu 
>> 
>> 
>> Try answering in your own words. When the SG device is oriented along the x 
>> axis, now effectively the z-axix IIUC, and we're dealing with 
>> superpositions, the outcomes will be 50-50 plus and minus. Therefore, unless 
>> I am making some error, what you stated above is incorrect. AG
> sqrt(1/2) [(s+)_z +(s-)_z]  is a superposition, but since sqrt(1/2) [(s+)_z 
> +(s-)_z]  =  (s+)_x the particle will always emerge 'up'
> 
> 
> I'll probably get back to on the foregoing. In the meantime, consider this; I 
> claim one can never MEASURE Up + Dn or Up - Dn with a SG apparatus regardless 
> of how many other instruments one uses to create a composite measuring 
> apparatus (Bruno's claim IIUC). The reason is simple. We know that the spin 
> operator

Which one? There are spin operator for each direction in space. The 
superposition of up and down is a precise pure state, with precise eigenvalues, 
when measuring state in the complementary directions.



> has exactly two eigenstates, each with probability of .5. We can write them 
> down. We also know that every quantum measurement gives up an eigenvalue of 
> some eigenstate. Therefore, if there existed an Up + Dn or Up - Dn 
> eigenstate, it would have to have probability ZERO since the Up and Dn 
> eigenstates have probabilities which sum to unity. Do you agree or not, and 
> if not, why? TIA, AG 

You add the probabilities, but you need to add the amplitudes of probabilities 
instead, and then take their square. You simply dismiss the quantum formalism, 
it seems to me. The states constituted a vector space: the sum (superposition) 
of orthogonal states are pure state, after a change of base, and I did give you 
the corresponding operator. You are not criticising an interpretation of QM, 
but QM itself.

Bruno




> 
>> 
>>>   
>>> In fact (s+)_z = sqrt(1/2) [(s+)_x + (s-)_x]
>>> 
>>> and (s-)_z = sqrt(1/2) [(s+)_x - (s-)_x]
>>> 
>>> (where _z, _x, are the z-component and the x-component of spin)
>>> 
>>> so that psi = sqrt(1/2)[(s+)_z +(s-)_z] = (s+)_x.   (pure state, not 
>>> mixture state)..
>>> 
>>> AGrayson2000 asked "If a system is in a superposition of states, whatever 
>>> value measured, will be repeated if the same system is repeatedly measured. 
>>>  But what happens if the system is in a mixed state?"
>>> 
>>> Does Everett's "relative state interpretation" show how to interpret a real 
>>> superposition (like the above, in which the particle will always emerge 
>>> 'up') and how to interpret a mixture (in which the particle will emerge 50% 
>>> 'up' or 50% 'down')?
>>> 
>>>  
>>> 
>>> -- 
>>> You received this message because you are subscribed to the Google Groups 
>>> "Everything List" group. 
>>> To unsubscribe from this group and stop receiving emails from it, send an 
>>> email to everything-li...@googlegroups.com <>. 
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>>> Visit this group at https://groups.google.com/group/everything-list 
>>> . 
>>> For more options, visit https://groups.google.com/d/optout 
>>> . 
>> 
>>  
>> 
>> -- 
>> You received this message because you are subscribed to the Google Groups 
>> "Everything List" group. 
>> To unsubscribe from this group and stop receiving emails from it, send an 
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>> . 
>> Visit this group at https://groups.google.com/group/everything-list 
>> . 
>> For more options, visit 

Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Saturday, November 17, 2018 at 4:39:08 PM UTC, agrays...@gmail.com wrote:
>
>
>
> On Saturday, November 17, 2018 at 4:22:35 PM UTC, agrays...@gmail.com 
> wrote:
>>
>>
>>
>> On Friday, November 16, 2018 at 4:39:42 PM UTC, scerir wrote:
>>>
>>>
>>> Il 16 novembre 2018 alle 15.38 agrays...@gmail.com ha scritto: 
>>>
>>>
>>>
>>> On Friday, November 16, 2018 at 10:14:32 AM UTC, scerir wrote:
>>>
>>>
>>> Il 16 novembre 2018 alle 10.19 agrays...@gmail.com ha scritto: 
>>>
>>>
>>>
>>> On Thursday, November 15, 2018 at 2:14:48 PM UTC, scerir wrote:
>>>
>>>
>>> Il 15 novembre 2018 alle 14.29 agrays...@gmail.com ha scritto: 
>>>
>>>
>>>
>>> On Thursday, November 15, 2018 at 8:04:53 AM UTC, scerir wrote:
>>>
>>> Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) 
>>> [(s+)_z + (s-)_z] .
>>>
>>> If the x-component of spin is measured by passing the spin-1/2 particle 
>>> through a Stern-Gerlach with its field oriented along the x-axis, the 
>>> particle will ALWAYS emerge 'up'.
>>>
>>>
>>> *Why?  Won't the measured value be along the x axis in both directions, 
>>> in effect Up or Dn? AG*
>>>
>>> "Hence we must conclude that the system described by the |+>x state is 
>>> not the
>>> same as a mixture of atoms in the |+> and !-> states. This means that 
>>> each atom in the
>>> beam is in a state that itself is a combination of the |+> and |-> 
>>> states. A superposition
>>> state is often called a coherent superposition since the relative phase 
>>> of the two terms is
>>> important."
>>>
>>> .see pages 18-19 here *https://tinyurl.com/ybm56whu 
>>> *
>>>
>>>
>>> *Try answering in your own words. When the SG device is oriented along 
>>> the x axis, now effectively the z-axix IIUC, and we're dealing with 
>>> superpositions, the outcomes will be 50-50 plus and minus. Therefore, 
>>> unless I am making some error, what you stated above is incorrect. AG *
>>>
>>> sqrt(1/2) [(s+)_z +(s-)_z]  is a superposition, but since sqrt(1/2) 
>>> [(s+)_z +(s-)_z]  =  (s+)_x the particle will always emerge 'up'
>>>
>>>
>>> I'll probably get back to on the foregoing. In the meantime, consider 
>>> this; I claim one can never MEASURE Up + Dn or Up - Dn with a SG apparatus 
>>> regardless of how many other instruments one uses to create a composite 
>>> measuring apparatus (Bruno's claim IIUC). The reason is simple. We know 
>>> that the spin operator has exactly two eigenstates, each with probability 
>>> of .5. We can write them down. We also know that every quantum measurement 
>>> gives up an eigenvalue of some eigenstate. Therefore, if there existed an 
>>> Up + Dn or Up - Dn eigenstate, it would have to have probability ZERO since 
>>> the Up and Dn eigenstates have probabilities which sum to unity. Do you 
>>> agree or not, and if not, why? TIA, AG 
>>>
>>> I think the question should rather be how to prepare a superposition 
>>> state like  sqrt(1/2) [(s+)_z +(s-)_z] . But when you have this specific 
>>> state, and when you orient the SG along "x", you always get "up". 
>>>
>>
>> *If the SG field is oriented perpendicular to z axis, the usual situation 
>> for a measurement along z, you get Up or Dn along z axis. If field is along 
>> x axis, which is perpendicular to z axis, the device blocks the stream of 
>> electrons, so no measurement is possible.*
>>
>
>
> *Correction; the SG device doesn't block stream of elections when its 
> field is oriented along x axis. But what has this to do with whether one 
> can measure Up + Dn, or Up - Dn along z axis, or any axis? Does it show Up 
> + Dn can be measured along x axis? AG*
>

*I still have to check your math. I think you've shown that Up + Dn can be 
measured along x axis, and presumably Up - Dn can also also be measured 
when a negative sign is used between elements of the above superposition. I 
suppose this is what Bruno was trying to say, whereas I was focused on 
measurements along z axis with the SG device in the standard orientation. 
Nonetheless, I don't see that this result has anything to do with Bruno's 
introduction of an infinity of universes, a concept I find totally 
extraneous (and for my aesthetics, abhorrent) to this issue. AG *

>
>  
>
>>
>> *Also, note that your simulation uses only Up or Dn, as I did above, to 
>> show it's impossible to measure Up + Dn, or Up - Dn. Can you respond to my 
>> comments above? AG *
>>
>>>  
>>>
>>>   
>>>
>>> In fact (s+)_z = sqrt(1/2) [(s+)_x + (s-)_x]
>>>
>>> and (s-)_z = sqrt(1/2) [(s+)_x - (s-)_x]
>>>
>>> (where _z, _x, are the z-component and the x-component of spin)
>>>
>>> so that psi = sqrt(1/2)[(s+)_z +(s-)_z] = (s+)_x.   (pure state, not 
>>> mixture state)..
>>>
>>> AGrayson2000 asked "If a system is in a superposition of states, 
>>> whatever value measured, will be repeated if the same system is repeatedly 
>>> measured.  But what happens if the system is in a mixed state?"
>>>
>>> Does Everett's "relative state interpretation" show how to interpret a 
>>> real 

Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Saturday, November 17, 2018 at 4:22:35 PM UTC, agrays...@gmail.com wrote:
>
>
>
> On Friday, November 16, 2018 at 4:39:42 PM UTC, scerir wrote:
>>
>>
>> Il 16 novembre 2018 alle 15.38 agrays...@gmail.com ha scritto: 
>>
>>
>>
>> On Friday, November 16, 2018 at 10:14:32 AM UTC, scerir wrote:
>>
>>
>> Il 16 novembre 2018 alle 10.19 agrays...@gmail.com ha scritto: 
>>
>>
>>
>> On Thursday, November 15, 2018 at 2:14:48 PM UTC, scerir wrote:
>>
>>
>> Il 15 novembre 2018 alle 14.29 agrays...@gmail.com ha scritto: 
>>
>>
>>
>> On Thursday, November 15, 2018 at 8:04:53 AM UTC, scerir wrote:
>>
>> Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) 
>> [(s+)_z + (s-)_z] .
>>
>> If the x-component of spin is measured by passing the spin-1/2 particle 
>> through a Stern-Gerlach with its field oriented along the x-axis, the 
>> particle will ALWAYS emerge 'up'.
>>
>>
>> *Why?  Won't the measured value be along the x axis in both directions, 
>> in effect Up or Dn? AG*
>>
>> "Hence we must conclude that the system described by the |+>x state is 
>> not the
>> same as a mixture of atoms in the |+> and !-> states. This means that 
>> each atom in the
>> beam is in a state that itself is a combination of the |+> and |-> 
>> states. A superposition
>> state is often called a coherent superposition since the relative phase 
>> of the two terms is
>> important."
>>
>> .see pages 18-19 here *https://tinyurl.com/ybm56whu 
>> *
>>
>>
>> *Try answering in your own words. When the SG device is oriented along 
>> the x axis, now effectively the z-axix IIUC, and we're dealing with 
>> superpositions, the outcomes will be 50-50 plus and minus. Therefore, 
>> unless I am making some error, what you stated above is incorrect. AG *
>>
>> sqrt(1/2) [(s+)_z +(s-)_z]  is a superposition, but since sqrt(1/2) 
>> [(s+)_z +(s-)_z]  =  (s+)_x the particle will always emerge 'up'
>>
>>
>> I'll probably get back to on the foregoing. In the meantime, consider 
>> this; I claim one can never MEASURE Up + Dn or Up - Dn with a SG apparatus 
>> regardless of how many other instruments one uses to create a composite 
>> measuring apparatus (Bruno's claim IIUC). The reason is simple. We know 
>> that the spin operator has exactly two eigenstates, each with probability 
>> of .5. We can write them down. We also know that every quantum measurement 
>> gives up an eigenvalue of some eigenstate. Therefore, if there existed an 
>> Up + Dn or Up - Dn eigenstate, it would have to have probability ZERO since 
>> the Up and Dn eigenstates have probabilities which sum to unity. Do you 
>> agree or not, and if not, why? TIA, AG 
>>
>> I think the question should rather be how to prepare a superposition 
>> state like  sqrt(1/2) [(s+)_z +(s-)_z] . But when you have this specific 
>> state, and when you orient the SG along "x", you always get "up". 
>>
>
> *If the SG field is oriented perpendicular to z axis, the usual situation 
> for a measurement along z, you get Up or Dn along z axis. If field is along 
> x axis, which is perpendicular to z axis, the device blocks the stream of 
> electrons, so no measurement is possible.*
>


*Correction; the SG device doesn't block stream of elections when its field 
is oriented along x axis. But what has this to do with whether one can 
measure Up + Dn, or Up - Dn along z axis, or any axis? Does it show Up + Dn 
can be measured along x axis? AG*

 

>
> *Also, note that your simulation uses only Up or Dn, as I did above, to 
> show it's impossible to measure Up + Dn, or Up - Dn. Can you respond to my 
> comments above? AG *
>
>>  
>>
>>   
>>
>> In fact (s+)_z = sqrt(1/2) [(s+)_x + (s-)_x]
>>
>> and (s-)_z = sqrt(1/2) [(s+)_x - (s-)_x]
>>
>> (where _z, _x, are the z-component and the x-component of spin)
>>
>> so that psi = sqrt(1/2)[(s+)_z +(s-)_z] = (s+)_x.   (pure state, not 
>> mixture state)..
>>
>> AGrayson2000 asked "If a system is in a superposition of states, whatever 
>> value measured, will be repeated if the same system is repeatedly 
>> measured.  But what happens if the system is in a mixed state?"
>>
>> Does Everett's "relative state interpretation" show how to interpret a 
>> real superposition (like the above, in which the particle will always 
>> emerge 'up') and how to interpret a mixture (in which the particle will 
>> emerge 50% 'up' or 50% 'down')?
>>
>>  
>> -- 
>> You received this message because you are subscribed to the Google Groups 
>> "Everything List" group. 
>> To unsubscribe from this group and stop receiving emails from it, send an 
>> email to everything-li...@googlegroups.com. 
>> To post to this group, send email to everyth...@googlegroups.com. 
>> Visit this group at https://groups.google.com/group/everything-list. 
>> For more options, visit https://groups.google.com/d/optout. 
>>
>>  
>> -- 
>> You received this message because you are subscribed to the Google Groups 
>> "Everything List" group. 
>> To unsubscribe from this group and 

Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Friday, November 16, 2018 at 4:39:42 PM UTC, scerir wrote:
>
>
> Il 16 novembre 2018 alle 15.38 agrays...@gmail.com  ha 
> scritto: 
>
>
>
> On Friday, November 16, 2018 at 10:14:32 AM UTC, scerir wrote:
>
>
> Il 16 novembre 2018 alle 10.19 agrays...@gmail.com ha scritto: 
>
>
>
> On Thursday, November 15, 2018 at 2:14:48 PM UTC, scerir wrote:
>
>
> Il 15 novembre 2018 alle 14.29 agrays...@gmail.com ha scritto: 
>
>
>
> On Thursday, November 15, 2018 at 8:04:53 AM UTC, scerir wrote:
>
> Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) [(s+)_z 
> + (s-)_z] .
>
> If the x-component of spin is measured by passing the spin-1/2 particle 
> through a Stern-Gerlach with its field oriented along the x-axis, the 
> particle will ALWAYS emerge 'up'.
>
>
> *Why?  Won't the measured value be along the x axis in both directions, in 
> effect Up or Dn? AG*
>
> "Hence we must conclude that the system described by the |+>x state is not 
> the
> same as a mixture of atoms in the |+> and !-> states. This means that each 
> atom in the
> beam is in a state that itself is a combination of the |+> and |-> states. 
> A superposition
> state is often called a coherent superposition since the relative phase of 
> the two terms is
> important."
>
> .see pages 18-19 here *https://tinyurl.com/ybm56whu 
> *
>
>
> *Try answering in your own words. When the SG device is oriented along the 
> x axis, now effectively the z-axix IIUC, and we're dealing with 
> superpositions, the outcomes will be 50-50 plus and minus. Therefore, 
> unless I am making some error, what you stated above is incorrect. AG *
>
> sqrt(1/2) [(s+)_z +(s-)_z]  is a superposition, but since sqrt(1/2) 
> [(s+)_z +(s-)_z]  =  (s+)_x the particle will always emerge 'up'
>
>
> I'll probably get back to on the foregoing. In the meantime, consider 
> this; I claim one can never MEASURE Up + Dn or Up - Dn with a SG apparatus 
> regardless of how many other instruments one uses to create a composite 
> measuring apparatus (Bruno's claim IIUC). The reason is simple. We know 
> that the spin operator has exactly two eigenstates, each with probability 
> of .5. We can write them down. We also know that every quantum measurement 
> gives up an eigenvalue of some eigenstate. Therefore, if there existed an 
> Up + Dn or Up - Dn eigenstate, it would have to have probability ZERO since 
> the Up and Dn eigenstates have probabilities which sum to unity. Do you 
> agree or not, and if not, why? TIA, AG 
>
> I think the question should rather be how to prepare a superposition state 
> like  sqrt(1/2) [(s+)_z +(s-)_z] . But when you have this specific state, 
> and when you orient the SG along "x", you always get "up". 
>


*If the SG field is oriented perpendicular to z axis, the usual situation 
for a measurement along z, you get Up or Dn along z axis. If field is along 
x axis, which is perpendicular to z axis, the device blocks the stream of 
electrons, so no measurement is possible. Also, note that your simulation 
uses only Up or Dn, as I did above, to show it's impossible to measure Up + 
Dn, or Up - Dn. Can you respond to my comments above? AG *

>  
>
>   
>
> In fact (s+)_z = sqrt(1/2) [(s+)_x + (s-)_x]
>
> and (s-)_z = sqrt(1/2) [(s+)_x - (s-)_x]
>
> (where _z, _x, are the z-component and the x-component of spin)
>
> so that psi = sqrt(1/2)[(s+)_z +(s-)_z] = (s+)_x.   (pure state, not 
> mixture state)..
>
> AGrayson2000 asked "If a system is in a superposition of states, whatever 
> value measured, will be repeated if the same system is repeatedly 
> measured.  But what happens if the system is in a mixed state?"
>
> Does Everett's "relative state interpretation" show how to interpret a 
> real superposition (like the above, in which the particle will always 
> emerge 'up') and how to interpret a mixture (in which the particle will 
> emerge 50% 'up' or 50% 'down')?
>
>  
> -- 
> You received this message because you are subscribed to the Google Groups 
> "Everything List" group. 
> To unsubscribe from this group and stop receiving emails from it, send an 
> email to everything-li...@googlegroups.com. 
> To post to this group, send email to everyth...@googlegroups.com. 
> Visit this group at https://groups.google.com/group/everything-list. 
> For more options, visit https://groups.google.com/d/optout. 
>
>  
> -- 
> You received this message because you are subscribed to the Google Groups 
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> To unsubscribe from this group and stop receiving emails from it, send an 
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> To post to this group, send email to everyth...@googlegroups.com. 
> Visit this group at https://groups.google.com/group/everything-list. 
> For more options, visit https://groups.google.com/d/optout. 
>
>  
> -- 
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> "Everything List" group. 
> To unsubscribe from this group and stop receiving emails from it, 

Re: Measuring a system in a superposition of states vs in a mixed state

['scerir' via Everything List]

> Il 16 novembre 2018 alle 18.20 agrayson2...@gmail.com ha scritto:
> 
> 
> 
> On Friday, November 16, 2018 at 4:39:42 PM UTC, scerir wrote:
> 
> > > 
> > 
> > > > > Il 16 novembre 2018 alle 15.38 agrays...@gmail.com ha 
> > scritto:
> > > 
> > > 
> > > 
> > > On Friday, November 16, 2018 at 10:14:32 AM UTC, scerir wrote:
> > > 
> > > > > > > 
> > > > 
> > > > > > > > > Il 16 novembre 2018 alle 10.19 
> > > > agrays...@gmail.com ha scritto:
> > > > > 
> > > > > 
> > > > > 
> > > > > On Thursday, November 15, 2018 at 2:14:48 PM UTC, 
> > > > > scerir wrote:
> > > > > 
> > > > > > > > > > > 
> > > > > > 
> > > > > > > > > > > > > Il 15 novembre 2018 alle 
> > > > > > 14.29 agrays...@gmail.com ha scritto:
> > > > > > > 
> > > > > > > 
> > > > > > > 
> > > > > > > On Thursday, November 15, 2018 at 
> > > > > > > 8:04:53 AM UTC, scerir wrote:
> > > > > > > 
> > > > > > > > > > > > > > > 
> > > > > > > > Imagine a spin-1/2 particle 
> > > > > > > > described by the state psi = sqrt(1/2) [(s+)_z + (s-)_z] .
> > > > > > > > 
> > > > > > > > If the x-component of spin is 
> > > > > > > > measured by passing the spin-1/2 particle through a 
> > > > > > > > Stern-Gerlach with its field oriented along the x-axis, the 
> > > > > > > > particle will ALWAYS emerge 'up'.
> > > > > > > > 
> > > > > > > > > > > > > > > 
> > > > > > > Why?  Won't the measured value be 
> > > > > > > along the x axis in both directions, in effect Up or Dn? AG
> > > > > > > 
> > > > > > > > > > > > > 
> > > > > > "Hence we must conclude that the system 
> > > > > > described by the |+>x state is not the
> > > > > > same as a mixture of atoms in the |+> and 
> > > > > > !-> states. This means that each atom in the
> > > > > > beam is in a state that itself is a 
> > > > > > combination of the |+> and |-> states. A superposition
> > > > > > state is often called a coherent 
> > > > > > superposition since the relative phase of the two terms is
> > > > > > important."
> > > > > > 
> > > > > > .see pages 18-19 here 
> > > > > > https://tinyurl.com/ybm56whu
> > > > > > 
> > > > > > > > > > > 
> > > > > Try answering in your own words. When the SG 
> > > > > device is oriented along the x axis, now effectively the z-axix IIUC, 
> > > > > and we're dealing with superpositions, the outcomes will be 50-50 
> > > > > plus and minus. Therefore, unless I am making some error, what you 
> > > > > stated above is incorrect. AG
> > > > > 
> > > > > > > > > 
> > > > sqrt(1/2) [(s+)_z +(s-)_z]  is a superposition, but 
> > > > since sqrt(1/2) [(s+)_z +(s-)_z]  =  (s+)_x the particle will always 
> > > > emerge 'up'
> > > > 
> > > > > > > 
> > > I'll probably get back to on the foregoing. In the meantime, 
> > > consider this; I claim one can never MEASURE Up + Dn or Up - Dn with a SG 
> > > apparatus regardless of how many other instruments one uses to create a 
> > > composite measuring apparatus (Bruno's claim IIUC). The reason is simple. 
> > > We know that the spin operator has exactly two eigenstates, each with 
> > > probability of .5 . We can write them down. We also know that every 
> > > quantum measurement gives up an eigenvalue of some eigenstate. Therefore, 
> > > if there existed an Up + Dn or Up - Dn eigenstate, it would have to have 
> > > probability ZERO since the Up and Dn eigenstates have probabilities which 
> > > sum to unity. Do you agree or not, and if not, why? TIA, AG
> > > 
> > > > > 
> > I think the question should rather be how to prepare a 
> > superposition state like  sqrt(1/2) [(s+)_z +(s-)_z] . But when you have 
> > this specific state, and when you orient the SG along "x", you always get 
> > "up".
> > 
> > > 
> I'm still not sure I understand your comment. I will think about it some 
> more.  But back to my original question; Is there any circumstance where the 
> result could be an eigenvalue of Up + Dn  or Up - Dn? Alternately, can Up + 
> Dn or Up - Dn ever be an eigenstate of the spin vector? TIA, AG
> 

Try this 
https://www.st-andrews.ac.uk/~www_pa/quvis/simulations_html5/sims/superposition/superposition-mixed-states.html

at "step-by-step explanation" page.

At the bottom of that page you can choose 5 options (1-2-3-4-5) and read the 
explanation (and look at the "orientation of SGA")

> 
> > > 
> >  
> > 
> > > > > 
> > > > > > > 
> > > > > > > > > 
> 

Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Friday, November 16, 2018 at 4:39:42 PM UTC, scerir wrote:
>
>
> Il 16 novembre 2018 alle 15.38 agrays...@gmail.com  ha 
> scritto: 
>
>
>
> On Friday, November 16, 2018 at 10:14:32 AM UTC, scerir wrote:
>
>
> Il 16 novembre 2018 alle 10.19 agrays...@gmail.com ha scritto: 
>
>
>
> On Thursday, November 15, 2018 at 2:14:48 PM UTC, scerir wrote:
>
>
> Il 15 novembre 2018 alle 14.29 agrays...@gmail.com ha scritto: 
>
>
>
> On Thursday, November 15, 2018 at 8:04:53 AM UTC, scerir wrote:
>
> Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) [(s+)_z 
> + (s-)_z] .
>
> If the x-component of spin is measured by passing the spin-1/2 particle 
> through a Stern-Gerlach with its field oriented along the x-axis, the 
> particle will ALWAYS emerge 'up'.
>
>
> *Why?  Won't the measured value be along the x axis in both directions, in 
> effect Up or Dn? AG*
>
> "Hence we must conclude that the system described by the |+>x state is not 
> the
> same as a mixture of atoms in the |+> and !-> states. This means that each 
> atom in the
> beam is in a state that itself is a combination of the |+> and |-> states. 
> A superposition
> state is often called a coherent superposition since the relative phase of 
> the two terms is
> important."
>
> .see pages 18-19 here *https://tinyurl.com/ybm56whu 
> *
>
>
> *Try answering in your own words. When the SG device is oriented along the 
> x axis, now effectively the z-axix IIUC, and we're dealing with 
> superpositions, the outcomes will be 50-50 plus and minus. Therefore, 
> unless I am making some error, what you stated above is incorrect. AG *
>
> sqrt(1/2) [(s+)_z +(s-)_z]  is a superposition, but since sqrt(1/2) 
> [(s+)_z +(s-)_z]  =  (s+)_x the particle will always emerge 'up'
>
>
> I'll probably get back to on the foregoing. In the meantime, consider 
> this; I claim one can never MEASURE Up + Dn or Up - Dn with a SG apparatus 
> regardless of how many other instruments one uses to create a composite 
> measuring apparatus (Bruno's claim IIUC). The reason is simple. We know 
> that the spin operator has exactly two eigenstates, each with probability 
> of .5*. We can write *them down. We also know that every quantum 
> measurement gives up an eigenvalue of some eigenstate. Therefore, if there 
> existed an Up + Dn or Up - Dn eigenstate, it would have to have probability 
> ZERO since the Up and Dn eigenstates have probabilities which sum to unity. 
> Do you agree or not, and if not, why? TIA, AG 
>
> I think the question should rather be how to prepare a superposition state 
> like  sqrt(1/2) [(s+)_z +(s-)_z] . But when you have this specific state, 
> and when you orient the SG along "x", you always get "up". 
>

*I'm still not sure I understand your comment. I will think about it some 
more.  But back to my original question; Is there any circumstance where 
the result could be an eigenvalue of Up + Dn  or Up - Dn? Alternately, can 
Up + Dn or Up - Dn ever be an eigenstate of the spin vector? TIA, AG*

>  
>
>   
>
> In fact (s+)_z = sqrt(1/2) [(s+)_x + (s-)_x]
>
> and (s-)_z = sqrt(1/2) [(s+)_x - (s-)_x]
>
> (where _z, _x, are the z-component and the x-component of spin)
>
> so that psi = sqrt(1/2)[(s+)_z +(s-)_z] = (s+)_x.   (pure state, not 
> mixture state)..
>
> AGrayson2000 asked "If a system is in a superposition of states, whatever 
> value measured, will be repeated if the same system is repeatedly 
> measured.  But what happens if the system is in a mixed state?"
>
> Does Everett's "relative state interpretation" show how to interpret a 
> real superposition (like the above, in which the particle will always 
> emerge 'up') and how to interpret a mixture (in which the particle will 
> emerge 50% 'up' or 50% 'down')?
>
>  
> -- 
> You received this message because you are subscribed to the Google Groups 
> "Everything List" group. 
> To unsubscribe from this group and stop receiving emails from it, send an 
> email to everything-li...@googlegroups.com. 
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>
>  
> -- 
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>
>  
> -- 
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> . 
> Visit this 

Re: Measuring a system in a superposition of states vs in a mixed state

['scerir' via Everything List]

> Il 16 novembre 2018 alle 15.38 agrayson2...@gmail.com ha scritto:
> 
> 
> 
> On Friday, November 16, 2018 at 10:14:32 AM UTC, scerir wrote:
> 
> > > 
> > 
> > > > > Il 16 novembre 2018 alle 10.19 agrays...@gmail.com ha 
> > scritto:
> > > 
> > > 
> > > 
> > > On Thursday, November 15, 2018 at 2:14:48 PM UTC, scerir 
> > > wrote:
> > > 
> > > > > > > 
> > > > 
> > > > > > > > > Il 15 novembre 2018 alle 14.29 
> > > > agrays...@gmail.com ha scritto:
> > > > > 
> > > > > 
> > > > > 
> > > > > On Thursday, November 15, 2018 at 8:04:53 AM UTC, 
> > > > > scerir wrote:
> > > > > 
> > > > > > > > > > > 
> > > > > > Imagine a spin-1/2 particle described by 
> > > > > > the state psi = sqrt(1/2) [(s+)_z + (s-)_z] .
> > > > > > 
> > > > > > If the x-component of spin is measured by 
> > > > > > passing the spin-1/2 particle through a Stern-Gerlach with its 
> > > > > > field oriented along the x-axis, the particle will ALWAYS emerge 
> > > > > > 'up'.
> > > > > > 
> > > > > > > > > > > 
> > > > > Why?  Won't the measured value be along the x 
> > > > > axis in both directions, in effect Up or Dn? AG
> > > > > 
> > > > > > > > > 
> > > > "Hence we must conclude that the system described by 
> > > > the |+>x state is not the
> > > > same as a mixture of atoms in the |+> and !-> states. 
> > > > This means that each atom in the
> > > > beam is in a state that itself is a combination of the 
> > > > |+> and |-> states. A superposition
> > > > state is often called a coherent superposition since 
> > > > the relative phase of the two terms is
> > > > important."
> > > > 
> > > > .see pages 18-19 here https://tinyurl.com/ybm56whu
> > > > 
> > > > > > > 
> > > Try answering in your own words. When the SG device is 
> > > oriented along the x axis, now effectively the z-axix IIUC, and we're 
> > > dealing with superpositions, the outcomes will be 50-50 plus and minus. 
> > > Therefore, unless I am making some error, what you stated above is 
> > > incorrect. AG
> > > 
> > > > > 
> > sqrt(1/2) [(s+)_z +(s-)_z]  is a superposition, but since sqrt(1/2) 
> > [(s+)_z +(s-)_z]  =  (s+)_x the particle will always emerge 'up'
> > 
> > > 
> I'll probably get back to on the foregoing. In the meantime, consider 
> this; I claim one can never MEASURE Up + Dn or Up - Dn with a SG apparatus 
> regardless of how many other instruments one uses to create a composite 
> measuring apparatus (Bruno's claim IIUC). The reason is simple. We know that 
> the spin operator has exactly two eigenstates, each with probability of .5. 
> We can write them down. We also know that every quantum measurement gives up 
> an eigenvalue of some eigenstate. Therefore, if there existed an Up + Dn or 
> Up - Dn eigenstate, it would have to have probability ZERO since the Up and 
> Dn eigenstates have probabilities which sum to unity. Do you agree or not, 
> and if not, why? TIA, AG
> 

I think the question should rather be how to prepare a superposition state like 
 sqrt(1/2) [(s+)_z +(s-)_z] . But when you have this specific state, and when 
you orient the SG along "x", you always get "up".

> 
> > > 
> > > > > 
> > > > > > > 
> > > >  
> > > > 
> > > > > > > > >  
> > > > > 
> > > > > > > > > > > 
> > > > > > In fact (s+)_z = sqrt(1/2) [(s+)_x + (s-)_x]
> > > > > > 
> > > > > > and (s-)_z = sqrt(1/2) [(s+)_x - (s-)_x]
> > > > > > 
> > > > > > (where _z, _x, are the z-component and the 
> > > > > > x-component of spin)
> > > > > > 
> > > > > > so that psi = sqrt(1/2)[(s+)_z +(s-)_z] = 
> > > > > > (s+)_x.   (pure state, not mixture state)..
> > > > > > 
> > > > > > AGrayson2000 asked "If a system is in a 
> > > > > > superposition of states, whatever value measured, will be repeated 
> > > > > > if the same system is repeatedly measured.  But what happens if the 
> > > > > > system is in a mixed state?"
> > > > > > 
> > > > > > Does Everett's "relative state 
> > > > > > interpretation" show how to interpret a real superposition (like 
> > > > > > the above, in which the particle will always emerge 'up') and how 
> > > > > > to interpret a mixture (in which the particle will emerge 50% 'up' 
> > > > > > or 50% 'down')?
> > > > > > 
> > > > > > > > > > > 
> > > > >  
> > > > > 
> > > > > --
> > > > > You received this message because you are 
> > > > > subscribed to 

Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Friday, November 16, 2018 at 10:14:32 AM UTC, scerir wrote:
>
>
> Il 16 novembre 2018 alle 10.19 agrays...@gmail.com  ha 
> scritto: 
>
>
>
> On Thursday, November 15, 2018 at 2:14:48 PM UTC, scerir wrote:
>
>
> Il 15 novembre 2018 alle 14.29 agrays...@gmail.com ha scritto: 
>
>
>
> On Thursday, November 15, 2018 at 8:04:53 AM UTC, scerir wrote:
>
> Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) [(s+)_z 
> + (s-)_z] .
>
> If the x-component of spin is measured by passing the spin-1/2 particle 
> through a Stern-Gerlach with its field oriented along the x-axis, the 
> particle will ALWAYS emerge 'up'.
>
>
> *Why?  Won't the measured value be along the x axis in both directions, in 
> effect Up or Dn? AG*
>
> "Hence we must conclude that the system described by the |+>x state is not 
> the
> same as a mixture of atoms in the |+> and !-> states. This means that each 
> atom in the
> beam is in a state that itself is a combination of the |+> and |-> states. 
> A superposition
> state is often called a coherent superposition since the relative phase of 
> the two terms is
> important."
>
> .see pages 18-19 here *https://tinyurl.com/ybm56whu 
> *
>
>
> *Try answering in your own words. When the SG device is oriented along the 
> x axis, now effectively the z-axix IIUC, and we're dealing with 
> superpositions, the outcomes will be 50-50 plus and minus. Therefore, 
> unless I am making some error, what you stated above is incorrect. AG *
>
> sqrt(1/2) [(s+)_z +(s-)_z]  is a superposition, but since sqrt(1/2) 
> [(s+)_z +(s-)_z]  =  (s+)_x the particle will always emerge 'up'
>

I'll probably get back to on the foregoing. In the meantime, consider this; 
I claim one can never MEASURE Up + Dn or Up - Dn with a SG apparatus 
regardless of how many other instruments one uses to create a composite 
measuring apparatus (Bruno's claim IIUC). The reason is simple. We know 
that the spin operator has exactly two eigenstates, each with probability 
of .5. We can write them down. We also know that every quantum measurement 
gives up an eigenvalue of some eigenstate. Therefore, if there existed an 
Up + Dn or Up - Dn eigenstate, it would have to have probability ZERO since 
the Up and Dn eigenstates have probabilities which sum to unity. Do you 
agree or not, and if not, why? TIA, AG 

>   
>
> In fact (s+)_z = sqrt(1/2) [(s+)_x + (s-)_x]
>
> and (s-)_z = sqrt(1/2) [(s+)_x - (s-)_x]
>
> (where _z, _x, are the z-component and the x-component of spin)
>
> so that psi = sqrt(1/2)[(s+)_z +(s-)_z] = (s+)_x.   (pure state, not 
> mixture state)..
>
> AGrayson2000 asked "If a system is in a superposition of states, whatever 
> value measured, will be repeated if the same system is repeatedly 
> measured.  But what happens if the system is in a mixed state?"
>
> Does Everett's "relative state interpretation" show how to interpret a 
> real superposition (like the above, in which the particle will always 
> emerge 'up') and how to interpret a mixture (in which the particle will 
> emerge 50% 'up' or 50% 'down')?
>
>  
> -- 
> You received this message because you are subscribed to the Google Groups 
> "Everything List" group. 
> To unsubscribe from this group and stop receiving emails from it, send an 
> email to everything-li...@googlegroups.com. 
> To post to this group, send email to everyth...@googlegroups.com. 
> Visit this group at https://groups.google.com/group/everything-list. 
> For more options, visit https://groups.google.com/d/optout. 
>
>  
> -- 
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> . 
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> For more options, visit https://groups.google.com/d/optout. 
>
>

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Re: Measuring a system in a superposition of states vs in a mixed state

['scerir' via Everything List]

https://www.st-andrews.ac.uk/~www_pa/quvis/simulations_html5/sims/superposition/superposition-mixed-states.html

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Re: Measuring a system in a superposition of states vs in a mixed state

['scerir' via Everything List]

> Il 16 novembre 2018 alle 10.19 agrayson2...@gmail.com ha scritto:
> 
> 
> 
> On Thursday, November 15, 2018 at 2:14:48 PM UTC, scerir wrote:
> 
> > > 
> > 
> > > > > Il 15 novembre 2018 alle 14.29 agrays...@gmail.com ha 
> > scritto:
> > > 
> > > 
> > > 
> > > On Thursday, November 15, 2018 at 8:04:53 AM UTC, scerir 
> > > wrote:
> > > 
> > > > > > > 
> > > > Imagine a spin-1/2 particle described by the state psi 
> > > > = sqrt(1/2) [(s+)_z + (s-)_z] .
> > > > 
> > > > If the x-component of spin is measured by passing the 
> > > > spin-1/2 particle through a Stern-Gerlach with its field oriented along 
> > > > the x-axis, the particle will ALWAYS emerge 'up'.
> > > > 
> > > > > > > 
> > > Why?  Won't the measured value be along the x axis in both 
> > > directions, in effect Up or Dn? AG
> > > 
> > > > > 
> > "Hence we must conclude that the system described by the |+>x state 
> > is not the
> > same as a mixture of atoms in the |+> and !-> states. This means 
> > that each atom in the
> > beam is in a state that itself is a combination of the |+> and |-> 
> > states. A superposition
> > state is often called a coherent superposition since the relative 
> > phase of the two terms is
> > important."
> > 
> > .see pages 18-19 here https://tinyurl.com/ybm56whu
> > 
> > > 
> Try answering in your own words. When the SG device is oriented along the 
> x axis, now effectively the z-axix IIUC, and we're dealing with 
> superpositions, the outcomes will be 50-50 plus and minus. Therefore, unless 
> I am making some error, what you stated above is incorrect. AG
> 

sqrt(1/2) [(s+)_z +(s-)_z]  is a superposition, but since sqrt(1/2) [(s+)_z 
+(s-)_z]  =  (s+)_x the particle will always emerge 'up'

> 
> > > 
> > > > >  
> > > 
> > > > > > > 
> > > > In fact (s+)_z = sqrt(1/2) [(s+)_x + (s-)_x]
> > > > 
> > > > and (s-)_z = sqrt(1/2) [(s+)_x - (s-)_x]
> > > > 
> > > > (where _z, _x, are the z-component and the x-component 
> > > > of spin)
> > > > 
> > > > so that psi = sqrt(1/2)[(s+)_z +(s-)_z] = (s+)_x.   
> > > > (pure state, not mixture state)..
> > > > 
> > > > AGrayson2000 asked "If a system is in a superposition 
> > > > of states, whatever value measured, will be repeated if the same system 
> > > > is repeatedly measured.  But what happens if the system is in a mixed 
> > > > state?"
> > > > 
> > > > Does Everett's "relative state interpretation" show how 
> > > > to interpret a real superposition (like the above, in which the 
> > > > particle will always emerge 'up') and how to interpret a mixture (in 
> > > > which the particle will emerge 50% 'up' or 50% 'down')?
> > > > 
> > > > > > > 
> > >  
> > > 
> > > --
> > > You received this message because you are subscribed to the 
> > > Google Groups "Everything List" group.
> > > To unsubscribe from this group and stop receiving emails from 
> > > it, send an email to everything-li...@googlegroups.com.
> > > To post to this group, send email to 
> > > everyth...@googlegroups.com.
> > > Visit this group at 
> > > https://groups.google.com/group/everything-list 
> > > https://groups.google.com/group/everything-list .
> > > For more options, visit https://groups.google.com/d/optout 
> > > https://groups.google.com/d/optout .
> > > 
> > > > > 
> > > 
>  
> 
> --
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Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Thursday, November 15, 2018 at 2:14:48 PM UTC, scerir wrote:
>
>
> Il 15 novembre 2018 alle 14.29 agrays...@gmail.com  ha 
> scritto: 
>
>
>
> On Thursday, November 15, 2018 at 8:04:53 AM UTC, scerir wrote:
>
> Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) [(s+)_z 
> + (s-)_z] .
>
> If the x-component of spin is measured by passing the spin-1/2 particle 
> through a Stern-Gerlach with its field oriented along the x-axis, the 
> particle will ALWAYS emerge 'up'.
>
>
> *Why?  Won't the measured value be along the x axis in both directions, in 
> effect Up or Dn? AG*
>
> "Hence we must conclude that the system described by the |+>x state is not 
> the
> same as a mixture of atoms in the |+> and !-> states. This means that each 
> atom in the
> beam is in a state that itself is a combination of the |+> and |-> states. 
> A superposition
> state is often called a coherent superposition since the relative phase of 
> the two terms is
> important."
>
> .see pages 18-19 here *https://tinyurl.com/ybm56whu 
> *
>


*Try answering in your own words. When the SG device is oriented along the 
x axis, now effectively the z-axix IIUC, and we're dealing with 
superpositions, the outcomes will be 50-50 plus and minus. Therefore, 
unless I am making some error, what you stated above is incorrect. AG *

>
>  
>
> In fact (s+)_z = sqrt(1/2) [(s+)_x + (s-)_x]
>
> and (s-)_z = sqrt(1/2) [(s+)_x - (s-)_x]
>
> (where _z, _x, are the z-component and the x-component of spin)
>
> so that psi = sqrt(1/2)[(s+)_z +(s-)_z] = (s+)_x.   (pure state, not 
> mixture state)..
>
> AGrayson2000 asked "If a system is in a superposition of states, whatever 
> value measured, will be repeated if the same system is repeatedly 
> measured.  But what happens if the system is in a mixed state?"
>
> Does Everett's "relative state interpretation" show how to interpret a 
> real superposition (like the above, in which the particle will always 
> emerge 'up') and how to interpret a mixture (in which the particle will 
> emerge 50% 'up' or 50% 'down')?
>
>  
> -- 
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Re: Measuring a system in a superposition of states vs in a mixed state

[Philip Thrift]

On Thursday, November 15, 2018 at 1:37:58 PM UTC-6, Brent wrote:
>
>
>
> On 11/14/2018 11:23 PM, Philip Thrift wrote:
>
>
>
> On Wednesday, November 14, 2018 at 6:55:36 PM UTC-6, agrays...@gmail.com 
> wrote: 
>>
>>
>>
>> On Wednesday, November 14, 2018 at 10:20:09 PM UTC, Pierz wrote: 
>>>
>>> Obviously you can't measure the particle simultaneously in the up and 
>>> down state. Nobody believes that. Nobody is arguing it. 
>>
>>
>> *Haven't you ever heard of physicists, some prominent who write books 
>> about QM for the lay public, who assert that one of the mysteries of QM is 
>> that a particle can be in two places at the same time, or cats can be alive 
>> and dead simultaneously, or spin can be Up and Dn simultaneously? If you 
>> haven't, you're not paying attention. AG*
>>
>>
>>>
> *"a particle can be in two places at the same time"*
>
>
> A path-integral realist (one who is "starting from a framework in which 
> *histories* are fundamental")* might formulate it this way:
>
> "a particle can have multiple histories — only one of which survives 
> measurement"
>
>
> Don't you need multiple histories to account for interference effects?
>
> Brent
>
>
>
Of course:


 
https://codicalist.wordpress.com/2018/09/25/retrosignaling-in-the-quantum-substrate/

But only one history of a  "history bundle" is selected (survives). The 
others die into the quantum substrate. :(




> * *Hilbert Spaces from Path Integrals*
> https://arxiv.org/abs/1002.0589
>
>


- pt 
>
>
>

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Re: Measuring a system in a superposition of states vs in a mixed state

[Brent Meeker]

On 11/14/2018 11:23 PM, Philip Thrift wrote:



On Wednesday, November 14, 2018 at 6:55:36 PM UTC-6, 
agrays...@gmail.com wrote:




On Wednesday, November 14, 2018 at 10:20:09 PM UTC, Pierz wrote:

Obviously you can't measure the particle simultaneously in the
up and down state. Nobody believes that. Nobody is arguing it. 



*Haven't you ever heard of physicists, some prominent who write
books about QM for the lay public, who assert that one of the
mysteries of QM is that a particle can be in two places at the
same time, or cats can be alive and dead simultaneously, or spin
can be Up and Dn simultaneously? If you haven't, you're not paying
attention. AG*


*
*
*"a particle can be in two places at the same time"*


A path-integral realist (one who is "starting from a framework in 
which /histories/ are fundamental")* might formulate it this way:


"a particle can have multiple histories — only one of which survives 
measurement"


Don't you need multiple histories to account for interference effects?

Brent




* *Hilbert Spaces from Path Integrals*
https://arxiv.org/abs/1002.0589

- pt
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Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Thursday, November 15, 2018 at 3:03:09 PM UTC, Bruno Marchal wrote:
>
>
> On 15 Nov 2018, at 09:04, 'scerir' via Everything List <
> everyth...@googlegroups.com > wrote:
>
> Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) [(s+)_z 
> + (s-)_z] .
>
> If the x-component of spin is measured by passing the spin-1/2 particle 
> through a Stern-Gerlach with its field oriented along the x-axis, the 
> particle will ALWAYS emerge 'up'..
>
> In fact (s+)_z = sqrt(1/2) [(s+)_x + (s-)_x]
>
> and (s-)_z = sqrt(1/2) [(s+)_x - (s-)_x]
>
> (where _z, _x, are the z-component and the x-component of spin)
>
> so that psi = sqrt(1/2)[(s+)_z +(s-)_z] = (s+)_x.   (pure state, not 
> mixture state)..
>
> AGrayson2000 asked "If a system is in a superposition of states, whatever 
> value measured, will be repeated if the same system is repeatedly 
> measured.  But what happens if the system is in a mixed state?"
>
> Does Everett's "relative state interpretation" show how to interpret a 
> real superposition (like the above, in which the particle will always 
> emerge 'up') and how to interpret a mixture (in which the particle will 
> emerge 50% 'up' or 50% 'down’)?
>
> With a lot of difficulties, no doubt. But with much less difficulties than 
> with a “physical collapse”, I would say.
>
> What is hard with up’ = up + down (renormalised) is that the physical 
> state up’ *is* the same as two (times infinity) particles in the state up 
> and down, with me being in both universe, without any means to distinguish 
> which one before I do the measurement. It is weird, but that is QM. 
> Similarly a particle with a definite position *is* that particles with an 
> indefinite momentum, and in the many-world, that is an infinity of 
> universes/histories possibles, with each momentum being definite in each 
> universe. Measuring a position is the same as putting myself in *all* those 
> universe where the momentum is unknown.
>
> Bruno
>

Let's forget it. This discussion has degenerated into gobblygook and now 
with the introduction of an infinity of universes it's gotten infinitely 
worse. I say FORGET IT! I AM NOT INTERESTED!!  AG

>
>
>
>
>
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>
>

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Re: Measuring a system in a superposition of states vs in a mixed state

[Bruno Marchal]

> On 15 Nov 2018, at 09:04, 'scerir' via Everything List 
>  wrote:
> 
> Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) [(s+)_z + 
> (s-)_z] .
> 
> If the x-component of spin is measured by passing the spin-1/2 particle 
> through a Stern-Gerlach with its field oriented along the x-axis, the 
> particle will ALWAYS emerge 'up'..
> 
> In fact (s+)_z = sqrt(1/2) [(s+)_x + (s-)_x]
> 
> and (s-)_z = sqrt(1/2) [(s+)_x - (s-)_x]
> 
> (where _z, _x, are the z-component and the x-component of spin)
> 
> so that psi = sqrt(1/2)[(s+)_z +(s-)_z] = (s+)_x.   (pure state, not mixture 
> state)..
> 
> AGrayson2000 asked "If a system is in a superposition of states, whatever 
> value measured, will be repeated if the same system is repeatedly measured.  
> But what happens if the system is in a mixed state?"
> 
> Does Everett's "relative state interpretation" show how to interpret a real 
> superposition (like the above, in which the particle will always emerge 'up') 
> and how to interpret a mixture (in which the particle will emerge 50% 'up' or 
> 50% 'down’)?
> 
With a lot of difficulties, no doubt. But with much less difficulties than with 
a “physical collapse”, I would say.

What is hard with up’ = up + down (renormalised) is that the physical state up’ 
*is* the same as two (times infinity) particles in the state up and down, with 
me being in both universe, without any means to distinguish which one before I 
do the measurement. It is weird, but that is QM. Similarly a particle with a 
definite position *is* that particles with an indefinite momentum, and in the 
many-world, that is an infinity of universes/histories possibles, with each 
momentum being definite in each universe. Measuring a position is the same as 
putting myself in *all* those universe where the momentum is unknown.

Bruno




> 
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Re: Measuring a system in a superposition of states vs in a mixed state

[Bruno Marchal]

> On 13 Nov 2018, at 19:38, agrayson2...@gmail.com wrote:
> 
> 
> 
> On Monday, November 12, 2018 at 2:32:53 AM UTC, agrays...@gmail.com wrote:
> 
> 
> On Sunday, November 11, 2018 at 5:43:00 PM UTC, agrays...@gmail.com <> wrote:
> 
> 
> On Sunday, November 11, 2018 at 7:52:00 AM UTC, Bruno Marchal wrote:
> 
>> On 10 Nov 2018, at 01:27, agrays...@gmail.com <> wrote:
>> 
>> 
>> 
>> On Friday, November 9, 2018 at 12:26:52 PM UTC, Bruno Marchal wrote:
>> 
>>> On 8 Nov 2018, at 18:25, agrays...@gmail.com <> wrote:
>>> 
>>> 
>>> 
>>> On Thursday, November 8, 2018 at 11:04:20 AM UTC, Bruno Marchal wrote:
>>> 
 On 6 Nov 2018, at 12:22, agrays...@gmail.com <> wrote:
 
 
 
 On Tuesday, November 6, 2018 at 9:27:31 AM UTC, Bruno Marchal wrote:
 
> On 4 Nov 2018, at 22:02, agrays...@gmail.com <> wrote:
> 
> 
> 
> On Sunday, November 4, 2018 at 8:33:10 PM UTC, jessem wrote:
> 
> 
> On Wed, Oct 31, 2018 at 7:30 AM Bruno Marchal > wrote:
> 
>> On 30 Oct 2018, at 14:21, agrays...@gmail.com <> wrote:
>> 
>> 
>> 
>> On Tuesday, October 30, 2018 at 8:58:30 AM UTC, Bruno Marchal wrote:
>> 
>>> On 29 Oct 2018, at 13:55, agrays...@gmail.com <> wrote:
>>> 
>>> 
>>> 
>>> On Monday, October 29, 2018 at 10:22:02 AM UTC, Bruno Marchal wrote:
>>> 
 On 28 Oct 2018, at 13:21, agrays...@gmail.com <> wrote:
 
 
 
 On Sunday, October 28, 2018 at 9:27:56 AM UTC, Bruno Marchal wrote:
 
> On 25 Oct 2018, at 17:12, agrays...@gmail.com <> wrote:
> 
> 
> 
> On Tuesday, October 23, 2018 at 10:39:11 PM UTC, agrays...@gmail.com 
>  wrote:
> If a system is in a superposition of states, whatever value measured, 
> will be repeated if the same system is repeatedly measured.  But what 
> happens if the system is in a mixed state? TIA, AG
> 
> If you think about it, whatever value you get on a single trial for a 
> mixed state, repeated on the same system, will result in the same 
> value measured repeatedly. If this is true, how does measurement 
> distinguish superposition of states, with mixed states? AG
 
 That is not correct. You can distinguish a mixture of particles in the 
 up or down states with a set of 1/sqrt(2)(up+down) by measuring them 
 with the {1/sqrt(2)(up+down), 1/sqrt(2)(up-down}) discriminating 
 apparatus. With the mixture, half the particles will be defected in 
 one direction, with the pure state, they will all pass in the same 
 direction. Superposition would not have been discovered if that was 
 not the case.
 
 And someone will supply the apparatus measuring (up + down), and (up - 
 down)? No such apparatuses are possible since those states are 
 inherently contradictory. We can only measure up / down. AG
>>> 
>>> You can do the experience by yourself using a simple crystal of calcium 
>>> (CaCO3, Island Spath), or with polarising glass. Or with Stern-Gerlach 
>>> devices and electron spin. Just rotating (90° or 180°) an app/down 
>>> apparatus, gives you an (up + down)/(up - down) apparatus. 
>>> 
>>> I don't understand. With SG one can change the up/down axis by 
>>> rotation, but that doesn't result in an (up + down), or (up - down) 
>>> measurement. If that were the case, what is the operator for which 
>>> those states are eigenstates? Which book by Albert? AG
>> 
>> David Z Albert, Quantum Mechanics and Experience, Harvard University 
>> Press, 1992.
>> https://www.amazon.com/Quantum-Mechanics-Experience-David-Albert/dp/0674741137
>>  
>> 
>> 
>> Another very good books is
>> 
>> D’Espagnat B. Conceptual foundations of Quantum mechanics,  I see there 
>> is a new edition here:
>> https://www.amazon.com/Conceptual-Foundations-Quantum-Mechanics-Advanced/dp/0738201049/ref=sr_1_1?s=books=UTF8=1540889778=1-1=d%27espagnat+conceptual+foundation+of+quantum+mechanics=41NcluHD6fL=_SY291_BO1,204,203,200_QL40_=srch
>>  
>> 
>> 
>> It explains very well the difference between mixtures and pure states.
>> 
>> Bruno
>> 
>> Thanks for the references. I think I have a reasonable decent 
>> understanding of mixed states. Say a system is in a mixed state of phi1 
>> and phi2 with some probability for each. IIUC, a measurement will always 
>> result in an eigenstate of either phi1 or phi2 (with relative 
>> probabilities 

Re: Measuring a system in a superposition of states vs in a mixed state

[Bruno Marchal]

> On 12 Nov 2018, at 03:32, agrayson2...@gmail.com wrote:
> 
> 
> 
> On Sunday, November 11, 2018 at 5:43:00 PM UTC, agrays...@gmail.com wrote:
> 
> 
> On Sunday, November 11, 2018 at 7:52:00 AM UTC, Bruno Marchal wrote:
> 
>> On 10 Nov 2018, at 01:27, agrays...@gmail.com <> wrote:
>> 
>> 
>> 
>> On Friday, November 9, 2018 at 12:26:52 PM UTC, Bruno Marchal wrote:
>> 
>>> On 8 Nov 2018, at 18:25, agrays...@gmail.com <> wrote:
>>> 
>>> 
>>> 
>>> On Thursday, November 8, 2018 at 11:04:20 AM UTC, Bruno Marchal wrote:
>>> 
 On 6 Nov 2018, at 12:22, agrays...@gmail.com <> wrote:
 
 
 
 On Tuesday, November 6, 2018 at 9:27:31 AM UTC, Bruno Marchal wrote:
 
> On 4 Nov 2018, at 22:02, agrays...@gmail.com <> wrote:
> 
> 
> 
> On Sunday, November 4, 2018 at 8:33:10 PM UTC, jessem wrote:
> 
> 
> On Wed, Oct 31, 2018 at 7:30 AM Bruno Marchal > wrote:
> 
>> On 30 Oct 2018, at 14:21, agrays...@gmail.com <> wrote:
>> 
>> 
>> 
>> On Tuesday, October 30, 2018 at 8:58:30 AM UTC, Bruno Marchal wrote:
>> 
>>> On 29 Oct 2018, at 13:55, agrays...@gmail.com <> wrote:
>>> 
>>> 
>>> 
>>> On Monday, October 29, 2018 at 10:22:02 AM UTC, Bruno Marchal wrote:
>>> 
 On 28 Oct 2018, at 13:21, agrays...@gmail.com <> wrote:
 
 
 
 On Sunday, October 28, 2018 at 9:27:56 AM UTC, Bruno Marchal wrote:
 
> On 25 Oct 2018, at 17:12, agrays...@gmail.com <> wrote:
> 
> 
> 
> On Tuesday, October 23, 2018 at 10:39:11 PM UTC, agrays...@gmail.com 
>  wrote:
> If a system is in a superposition of states, whatever value measured, 
> will be repeated if the same system is repeatedly measured.  But what 
> happens if the system is in a mixed state? TIA, AG
> 
> If you think about it, whatever value you get on a single trial for a 
> mixed state, repeated on the same system, will result in the same 
> value measured repeatedly. If this is true, how does measurement 
> distinguish superposition of states, with mixed states? AG
 
 That is not correct. You can distinguish a mixture of particles in the 
 up or down states with a set of 1/sqrt(2)(up+down) by measuring them 
 with the {1/sqrt(2)(up+down), 1/sqrt(2)(up-down}) discriminating 
 apparatus. With the mixture, half the particles will be defected in 
 one direction, with the pure state, they will all pass in the same 
 direction. Superposition would not have been discovered if that was 
 not the case.
 
 And someone will supply the apparatus measuring (up + down), and (up - 
 down)? No such apparatuses are possible since those states are 
 inherently contradictory. We can only measure up / down. AG
>>> 
>>> You can do the experience by yourself using a simple crystal of calcium 
>>> (CaCO3, Island Spath), or with polarising glass. Or with Stern-Gerlach 
>>> devices and electron spin. Just rotating (90° or 180°) an app/down 
>>> apparatus, gives you an (up + down)/(up - down) apparatus. 
>>> 
>>> I don't understand. With SG one can change the up/down axis by 
>>> rotation, but that doesn't result in an (up + down), or (up - down) 
>>> measurement. If that were the case, what is the operator for which 
>>> those states are eigenstates? Which book by Albert? AG
>> 
>> David Z Albert, Quantum Mechanics and Experience, Harvard University 
>> Press, 1992.
>> https://www.amazon.com/Quantum-Mechanics-Experience-David-Albert/dp/0674741137
>>  
>> 
>> 
>> Another very good books is
>> 
>> D’Espagnat B. Conceptual foundations of Quantum mechanics,  I see there 
>> is a new edition here:
>> https://www.amazon.com/Conceptual-Foundations-Quantum-Mechanics-Advanced/dp/0738201049/ref=sr_1_1?s=books=UTF8=1540889778=1-1=d%27espagnat+conceptual+foundation+of+quantum+mechanics=41NcluHD6fL=_SY291_BO1,204,203,200_QL40_=srch
>>  
>> 
>> 
>> It explains very well the difference between mixtures and pure states.
>> 
>> Bruno
>> 
>> Thanks for the references. I think I have a reasonable decent 
>> understanding of mixed states. Say a system is in a mixed state of phi1 
>> and phi2 with some probability for each. IIUC, a measurement will always 
>> result in an eigenstate of either phi1 or phi2 (with relative 
>> probabilities applying).
> 
> If the measurement is done with a phi1/phi2 discriminating 

Re: Measuring a system in a superposition of states vs in a mixed state

[Bruno Marchal]

> On 11 Nov 2018, at 18:43, agrayson2...@gmail.com wrote:
> 
> 
> 
> On Sunday, November 11, 2018 at 7:52:00 AM UTC, Bruno Marchal wrote:
> 
>> On 10 Nov 2018, at 01:27, agrays...@gmail.com  wrote:
>> 
>> 
>> 
>> On Friday, November 9, 2018 at 12:26:52 PM UTC, Bruno Marchal wrote:
>> 
>>> On 8 Nov 2018, at 18:25, agrays...@gmail.com <> wrote:
>>> 
>>> 
>>> 
>>> On Thursday, November 8, 2018 at 11:04:20 AM UTC, Bruno Marchal wrote:
>>> 
 On 6 Nov 2018, at 12:22, agrays...@gmail.com <> wrote:
 
 
 
 On Tuesday, November 6, 2018 at 9:27:31 AM UTC, Bruno Marchal wrote:
 
> On 4 Nov 2018, at 22:02, agrays...@gmail.com <> wrote:
> 
> 
> 
> On Sunday, November 4, 2018 at 8:33:10 PM UTC, jessem wrote:
> 
> 
> On Wed, Oct 31, 2018 at 7:30 AM Bruno Marchal > wrote:
> 
>> On 30 Oct 2018, at 14:21, agrays...@gmail.com <> wrote:
>> 
>> 
>> 
>> On Tuesday, October 30, 2018 at 8:58:30 AM UTC, Bruno Marchal wrote:
>> 
>>> On 29 Oct 2018, at 13:55, agrays...@gmail.com <> wrote:
>>> 
>>> 
>>> 
>>> On Monday, October 29, 2018 at 10:22:02 AM UTC, Bruno Marchal wrote:
>>> 
 On 28 Oct 2018, at 13:21, agrays...@gmail.com <> wrote:
 
 
 
 On Sunday, October 28, 2018 at 9:27:56 AM UTC, Bruno Marchal wrote:
 
> On 25 Oct 2018, at 17:12, agrays...@gmail.com <> wrote:
> 
> 
> 
> On Tuesday, October 23, 2018 at 10:39:11 PM UTC, agrays...@gmail.com 
>  wrote:
> If a system is in a superposition of states, whatever value measured, 
> will be repeated if the same system is repeatedly measured.  But what 
> happens if the system is in a mixed state? TIA, AG
> 
> If you think about it, whatever value you get on a single trial for a 
> mixed state, repeated on the same system, will result in the same 
> value measured repeatedly. If this is true, how does measurement 
> distinguish superposition of states, with mixed states? AG
 
 That is not correct. You can distinguish a mixture of particles in the 
 up or down states with a set of 1/sqrt(2)(up+down) by measuring them 
 with the {1/sqrt(2)(up+down), 1/sqrt(2)(up-down}) discriminating 
 apparatus. With the mixture, half the particles will be defected in 
 one direction, with the pure state, they will all pass in the same 
 direction. Superposition would not have been discovered if that was 
 not the case.
 
 And someone will supply the apparatus measuring (up + down), and (up - 
 down)? No such apparatuses are possible since those states are 
 inherently contradictory. We can only measure up / down. AG
>>> 
>>> You can do the experience by yourself using a simple crystal of calcium 
>>> (CaCO3, Island Spath), or with polarising glass. Or with Stern-Gerlach 
>>> devices and electron spin. Just rotating (90° or 180°) an app/down 
>>> apparatus, gives you an (up + down)/(up - down) apparatus. 
>>> 
>>> I don't understand. With SG one can change the up/down axis by 
>>> rotation,  but that doesn't result in an (up + down), or (up - down) 
>>> measurement. If that were the case, what is the operator for which 
>>> those states are eigenstates? Which book by Albert? AG
>> 
>> David Z Albert, Quantum Mechanics and Experience, Harvard University 
>> Press, 1992.
>> https://www.amazon.com/Quantum-Mechanics-Experience-David-Albert/dp/0674741137
>>  
>> 
>> 
>> Another very good books is
>> 
>> D’Espagnat B. Conceptual foundations of Quantum mechanics,  I see there 
>> is a new edition here:
>> https://www.amazon.com/Conceptual-Foundations-Quantum-Mechanics-Advanced/dp/0738201049/ref=sr_1_1?s=books=UTF8=1540889778=1-1=d%27espagnat+conceptual+foundation+of+quantum+mechanics=41NcluHD6fL=_SY291_BO1,204,203,200_QL40_=srch
>>  
>> 
>> 
>> It explains very well the difference between mixtures and pure states.
>> 
>> Bruno
>> 
>> Thanks for the references. I think I have a reasonable decent 
>> understanding of mixed states. Say a system is in a mixed state of phi1 
>> and phi2 with some probability for each. IIUC, a measurement will always 
>> result in an eigenstate of either phi1 or phi2 (with relative 
>> probabilities applying).
> 
> If the measurement is done with a phi1/phi2 discriminating apparatus. 
> Keep in mind that any state can be seen as a superposition of other 

Re: Measuring a system in a superposition of states vs in a mixed state

[Bruno Marchal]

> On 11 Nov 2018, at 10:56, agrayson2...@gmail.com wrote:
> 
> 
> 
> On Sunday, November 11, 2018 at 7:52:00 AM UTC, Bruno Marchal wrote:
> 
>> On 10 Nov 2018, at 01:27, agrays...@gmail.com  wrote:
>> 
>> 
>> 
>> On Friday, November 9, 2018 at 12:26:52 PM UTC, Bruno Marchal wrote:
>> 
>>> On 8 Nov 2018, at 18:25, agrays...@gmail.com <> wrote:
>>> 
>>> 
>>> 
>>> On Thursday, November 8, 2018 at 11:04:20 AM UTC, Bruno Marchal wrote:
>>> 
 On 6 Nov 2018, at 12:22, agrays...@gmail.com <> wrote:
 
 
 
 On Tuesday, November 6, 2018 at 9:27:31 AM UTC, Bruno Marchal wrote:
 
> On 4 Nov 2018, at 22:02, agrays...@gmail.com <> wrote:
> 
> 
> 
> On Sunday, November 4, 2018 at 8:33:10 PM UTC, jessem wrote:
> 
> 
> On Wed, Oct 31, 2018 at 7:30 AM Bruno Marchal > wrote:
> 
>> On 30 Oct 2018, at 14:21, agrays...@gmail.com <> wrote:
>> 
>> 
>> 
>> On Tuesday, October 30, 2018 at 8:58:30 AM UTC, Bruno Marchal wrote:
>> 
>>> On 29 Oct 2018, at 13:55, agrays...@gmail.com <> wrote:
>>> 
>>> 
>>> 
>>> On Monday, October 29, 2018 at 10:22:02 AM UTC, Bruno Marchal wrote:
>>> 
 On 28 Oct 2018, at 13:21, agrays...@gmail.com <> wrote:
 
 
 
 On Sunday, October 28, 2018 at 9:27:56 AM UTC, Bruno Marchal wrote:
 
> On 25 Oct 2018, at 17:12, agrays...@gmail.com <> wrote:
> 
> 
> 
> On Tuesday, October 23, 2018 at 10:39:11 PM UTC, agrays...@gmail.com 
>  wrote:
> If a system is in a superposition of states, whatever value measured, 
> will be repeated if the same system is repeatedly measured.  But what 
> happens if the system is in a mixed state? TIA, AG
> 
> If you think about it, whatever value you get on a single trial for a 
> mixed state, repeated on the same system, will result in the same 
> value measured repeatedly. If this is true, how does measurement 
> distinguish superposition of states, with mixed states? AG
 
 That is not correct. You can distinguish a mixture of particles in the 
 up or down states with a set of 1/sqrt(2)(up+down) by measuring them 
 with the {1/sqrt(2)(up+down), 1/sqrt(2)(up-down}) discriminating 
 apparatus. With the mixture, half the particles will be defected in 
 one direction, with the pure state, they will all pass in the same 
 direction. Superposition would not have been discovered if that was 
 not the case.
 
 And someone will supply the apparatus measuring (up + down), and (up - 
 down)? No such apparatuses are possible since those states are 
 inherently contradictory. We can only measure up / down. AG
>>> 
>>> You can do the experience by yourself using a simple crystal of calcium 
>>> (CaCO3, Island Spath), or with polarising glass. Or with Stern-Gerlach 
>>> devices and electron spin. Just rotating (90° or 180°) an app/down 
>>> apparatus, gives you an (up + down)/(up - down) apparatus. 
>>> 
>>> I don't understand. With SG one can change the up/down axis by 
>>> rotation,  but that doesn't result in an (up + down), or (up - down) 
>>> measurement. If that were the case, what is the operator for which 
>>> those states are eigenstates? Which book by Albert? AG
>> 
>> David Z Albert, Quantum Mechanics and Experience, Harvard University 
>> Press, 1992.
>> https://www.amazon.com/Quantum-Mechanics-Experience-David-Albert/dp/0674741137
>>  
>> 
>> 
>> Another very good books is
>> 
>> D’Espagnat B. Conceptual foundations of Quantum mechanics,  I see there 
>> is a new edition here:
>> https://www.amazon.com/Conceptual-Foundations-Quantum-Mechanics-Advanced/dp/0738201049/ref=sr_1_1?s=books=UTF8=1540889778=1-1=d%27espagnat+conceptual+foundation+of+quantum+mechanics=41NcluHD6fL=_SY291_BO1,204,203,200_QL40_=srch
>>  
>> 
>> 
>> It explains very well the difference between mixtures and pure states.
>> 
>> Bruno
>> 
>> Thanks for the references. I think I have a reasonable decent 
>> understanding of mixed states. Say a system is in a mixed state of phi1 
>> and phi2 with some probability for each. IIUC, a measurement will always 
>> result in an eigenstate of either phi1 or phi2 (with relative 
>> probabilities applying).
> 
> If the measurement is done with a phi1/phi2 discriminating apparatus. 
> Keep in mind that any state can be seen as a superposition of other 

Re: Measuring a system in a superposition of states vs in a mixed state

['scerir' via Everything List]

> Il 15 novembre 2018 alle 14.29 agrayson2...@gmail.com ha scritto:
> 
> 
> 
> On Thursday, November 15, 2018 at 8:04:53 AM UTC, scerir wrote:
> 
> > > 
> > Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) 
> > [(s+)_z + (s-)_z] .
> > 
> > If the x-component of spin is measured by passing the spin-1/2 
> > particle through a Stern-Gerlach with its field oriented along the x-axis, 
> > the particle will ALWAYS emerge 'up'.
> > 
> > > 
> Why?  Won't the measured value be along the x axis in both directions, in 
> effect Up or Dn? AG
> 

"Hence we must conclude that the system described by the |+>x state is not the
same as a mixture of atoms in the |+> and !-> states. This means that each atom 
in the
beam is in a state that itself is a combination of the |+> and |-> states. A 
superposition
state is often called a coherent superposition since the relative phase of the 
two terms is
important."

.see pages 18-19 here https://tinyurl.com/ybm56whu

>  
> 
> > > 
> > In fact (s+)_z = sqrt(1/2) [(s+)_x + (s-)_x]
> > 
> > and (s-)_z = sqrt(1/2) [(s+)_x - (s-)_x]
> > 
> > (where _z, _x, are the z-component and the x-component of spin)
> > 
> > so that psi = sqrt(1/2)[(s+)_z +(s-)_z] = (s+)_x.   (pure state, 
> > not mixture state)..
> > 
> > AGrayson2000 asked "If a system is in a superposition of states, 
> > whatever value measured, will be repeated if the same system is repeatedly 
> > measured.  But what happens if the system is in a mixed state?"
> > 
> > Does Everett's "relative state interpretation" show how to 
> > interpret a real superposition (like the above, in which the particle will 
> > always emerge 'up') and how to interpret a mixture (in which the particle 
> > will emerge 50% 'up' or 50% 'down')?
> > 
> > > 
>  
> 
> --
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Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Thursday, November 15, 2018 at 8:04:53 AM UTC, scerir wrote:
>
> Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) [(s+)_z 
> + (s-)_z] .
>
> If the x-component of spin is measured by passing the spin-1/2 particle 
> through a Stern-Gerlach with its field oriented along the x-axis, the 
> particle will ALWAYS emerge 'up'.
>

*Why?  Won't the measured value be along the x axis in both directions, in 
effect Up or Dn? AG*

In fact (s+)_z = sqrt(1/2) [(s+)_x + (s-)_x]
>
> and (s-)_z = sqrt(1/2) [(s+)_x - (s-)_x]
>
> (where _z, _x, are the z-component and the x-component of spin)
>
> so that psi = sqrt(1/2)[(s+)_z +(s-)_z] = (s+)_x.   (pure state, not 
> mixture state)..
>
> AGrayson2000 asked "If a system is in a superposition of states, whatever 
> value measured, will be repeated if the same system is repeatedly 
> measured.  But what happens if the system is in a mixed state?"
>
> Does Everett's "relative state interpretation" show how to interpret a 
> real superposition (like the above, in which the particle will always 
> emerge 'up') and how to interpret a mixture (in which the particle will 
> emerge 50% 'up' or 50% 'down')?
>

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Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Monday, October 29, 2018 at 10:22:02 AM UTC, Bruno Marchal wrote:
>
>
> On 28 Oct 2018, at 13:21, agrays...@gmail.com  wrote:
>
>
>
> On Sunday, October 28, 2018 at 9:27:56 AM UTC, Bruno Marchal wrote:
>>
>>
>> On 25 Oct 2018, at 17:12, agrays...@gmail.com wrote:
>>
>>
>>
>> On Tuesday, October 23, 2018 at 10:39:11 PM UTC, agrays...@gmail.com 
>> wrote:
>>>
>>> If a system is in a superposition of states, whatever value measured, 
>>> will be repeated if the same system is repeatedly measured.  But what 
>>> happens if the system is in a mixed state? TIA, AG
>>>
>>
>> If you think about it, whatever value you get on a single trial for a 
>> mixed state, repeated on the same system, will result in the same value 
>> measured repeatedly. If this is true, how does measurement distinguish 
>> superposition of states, with mixed states? AG
>>
>>
>> That is not correct. You can distinguish a mixture of particles in the up 
>> or down states with a set of 1/sqrt(2)(up+down) by measuring them with the 
>> {1/sqrt(2)(up+down), 1/sqrt(2)(up-down}) discriminating apparatus. With the 
>> mixture, half the particles will be defected in one direction, with the 
>> pure state, they will all pass in the same direction. Superposition would 
>> not have been discovered if that was not the case.
>>
>
>
> *And someone will supply the apparatus measuring (up + down), and (up - 
> down)? No such apparatuses are possible since those states are inherently 
> contradictory. We can only measure up / down. AG*
>
>
> You can do the experience by yourself using a simple crystal of calcium 
> (CaCO3, Island Spath), or with polarising glass. Or with Stern-Gerlach 
> devices and electron spin. Just rotating (90° or 180°) an app/down 
> apparatus, gives you an (up + down)/(up - down) apparatus. 
>

*I gave you several ways to show you're completely mistaken. You just don't 
understand eigenstates and the measurement postulates of QM. AG *

>
> Buy the book by David Albert. It will help you a lot, I think.
>
> Bruno
>
>
>
>
>
>
>> Bruno
>>
>>
>>
>>
>>
>>
>> -- 
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>>
>>
>>
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>
>

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Re: Measuring a system in a superposition of states vs in a mixed state

['scerir' via Everything List]

Imagine a spin-1/2 particle described by the state psi = sqrt(1/2) [(s+)_z + 
(s-)_z] .

If the x-component of spin is measured by passing the spin-1/2 particle through 
a Stern-Gerlach with its field oriented along the x-axis, the particle will 
ALWAYS emerge 'up'..

In fact (s+)_z = sqrt(1/2) [(s+)_x + (s-)_x]

and (s-)_z = sqrt(1/2) [(s+)_x - (s-)_x]

(where _z, _x, are the z-component and the x-component of spin)

so that psi = sqrt(1/2)[(s+)_z +(s-)_z] = (s+)_x.   (pure state, not mixture 
state)..

AGrayson2000 asked "If a system is in a superposition of states, whatever value 
measured, will be repeated if the same system is repeatedly measured.  But what 
happens if the system is in a mixed state?"

Does Everett's "relative state interpretation" show how to interpret a real 
superposition (like the above, in which the particle will always emerge 'up') 
and how to interpret a mixture (in which the particle will emerge 50% 'up' or 
50% 'down')?

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Re: Measuring a system in a superposition of states vs in a mixed state

[Philip Thrift]

On Wednesday, November 14, 2018 at 6:55:36 PM UTC-6, agrays...@gmail.com 
wrote:
>
>
>
> On Wednesday, November 14, 2018 at 10:20:09 PM UTC, Pierz wrote:
>>
>> Obviously you can't measure the particle simultaneously in the up and 
>> down state. Nobody believes that. Nobody is arguing it. 
>
>
> *Haven't you ever heard of physicists, some prominent who write books 
> about QM for the lay public, who assert that one of the mysteries of QM is 
> that a particle can be in two places at the same time, or cats can be alive 
> and dead simultaneously, or spin can be Up and Dn simultaneously? If you 
> haven't, you're not paying attention. AG*
>
>
>>
*"a particle can be in two places at the same time"*


A path-integral realist (one who is "starting from a framework in which 
*histories* are fundamental")* might formulate it this way:

"a particle can have multiple histories — only one of which survives 
measurement"


* *Hilbert Spaces from Path Integrals*
https://arxiv.org/abs/1002.0589

- pt 

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Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Wednesday, November 14, 2018 at 10:20:09 PM UTC, Pierz wrote:
>
> Obviously you can't measure the particle simultaneously in the up and down 
> state. Nobody believes that. Nobody is arguing it. 


*Haven't you ever heard of physicists, some prominent who write books about 
QM for the lay public, who assert that one of the mysteries of QM is that a 
particle can be in two places at the same time, or cats can be alive and 
dead simultaneously, or spin can be Up and Dn simultaneously? If you 
haven't, you're not paying attention. AG*

Honestly it's hard to understand why you have such an agitated bee in your 
> bonnet about superpositions. The mathematical expression of the photon 
> polarised at 45 degrees to the measurement apparatus is a normalised vector 
> spanning the space of both up and down. I guess what you interpret that to 
> mean is up to you since the mathematical predictions that arise from it are 
> the same: 50% chance of up or down. Once again, you're simply arguing at 
> cross purposes with Bruno, who clearly understands QM perfectly well. He's 
> not saying the photon can be measured as up and down at the same time. He's 
> just saying that any superposition of up and down is an eigenvector in some 
> other orientation of the apparatus.

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Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Wednesday, November 14, 2018 at 10:20:09 PM UTC, Pierz wrote:
>
> Obviously you can't measure the particle simultaneously in the up and down 
> state. Nobody believes that.


Bruno does. 

Nobody is arguing it.


Bruno argues it.

Honestly it's hard to understand why you have such an agitated bee in your 
> bonnet about superpositions. 


I don't like misleading ideas. 

The mathematical expression of the photon polarised at 45 degrees to the 
> measurement apparatus is a normalised vector spanning the space of both up 
> and down. I guess what you interpret that to mean is up to you since the 
> mathematical predictions that arise from it are the same: 50% chance of up 
> or down. Once again, you're simply arguing at cross purposes with Bruno, 
> who clearly understands QM perfectly well.


Not in my opinion. He thinks that an Up or Dn measurement is the same as 
measuring Up + Dn or Up - Dn because the wf can be written that way in some 
basis.  

He's not saying the photon can be measured as up and down at the same time. 
> He's just saying that any superposition of up and down is an eigenvector in 
> some other orientation of the apparatus.


It's not. My last post proved this with utmost clarity. Up + Dn or Up - Dn 
is never an eigenfunction regardless of the orientation of the apparatus. 
How could it be if measuring Up and Dn separately exhausts the total 
probability of unity? I think you need to rethink this issue. 

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Re: Measuring a system in a superposition of states vs in a mixed state

[Pierz]

Obviously you can't measure the particle simultaneously in the up and down 
state. Nobody believes that. Nobody is arguing it. Honestly it's hard to 
understand why you have such an agitated bee in your bonnet about 
superpositions. The mathematical expression of the photon polarised at 45 
degrees to the measurement apparatus is a normalised vector spanning the space 
of both up and down. I guess what you interpret that to mean is up to you since 
the mathematical predictions that arise from it are the same: 50% chance of up 
or down. Once again, you're simply arguing at cross purposes with Bruno, who 
clearly understands QM perfectly well. He's not saying the photon can be 
measured as up and down at the same time. He's just saying that any 
superposition of up and down is an eigenvector in some other orientation of the 
apparatus.

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Re: Measuring a system in a superposition of states vs in a mixed state

[agrayson2000]

On Monday, November 12, 2018 at 2:32:53 AM UTC, agrays...@gmail.com wrote:
>
>
>
> On Sunday, November 11, 2018 at 5:43:00 PM UTC, agrays...@gmail.com wrote:
>>
>>
>>
>> On Sunday, November 11, 2018 at 7:52:00 AM UTC, Bruno Marchal wrote:
>>>
>>>
>>> On 10 Nov 2018, at 01:27, agrays...@gmail.com wrote:
>>>
>>>
>>>
>>> On Friday, November 9, 2018 at 12:26:52 PM UTC, Bruno Marchal wrote:


 On 8 Nov 2018, at 18:25, agrays...@gmail.com wrote:



 On Thursday, November 8, 2018 at 11:04:20 AM UTC, Bruno Marchal wrote:
>
>
> On 6 Nov 2018, at 12:22, agrays...@gmail.com wrote:
>
>
>
> On Tuesday, November 6, 2018 at 9:27:31 AM UTC, Bruno Marchal wrote:
>>
>>
>> On 4 Nov 2018, at 22:02, agrays...@gmail.com wrote:
>>
>>
>>
>> On Sunday, November 4, 2018 at 8:33:10 PM UTC, jessem wrote:
>>>
>>>
>>>
>>> On Wed, Oct 31, 2018 at 7:30 AM Bruno Marchal  
>>> wrote:
>>>

 On 30 Oct 2018, at 14:21, agrays...@gmail.com wrote:



 On Tuesday, October 30, 2018 at 8:58:30 AM UTC, Bruno Marchal wrote:
>
>
> On 29 Oct 2018, at 13:55, agrays...@gmail.com wrote:
>
>
>
> On Monday, October 29, 2018 at 10:22:02 AM UTC, Bruno Marchal 
> wrote:
>>
>>
>> On 28 Oct 2018, at 13:21, agrays...@gmail.com wrote:
>>
>>
>>
>> On Sunday, October 28, 2018 at 9:27:56 AM UTC, Bruno Marchal 
>> wrote:
>>>
>>>
>>> On 25 Oct 2018, at 17:12, agrays...@gmail.com wrote:
>>>
>>>
>>>
>>> On Tuesday, October 23, 2018 at 10:39:11 PM UTC, agrays...@
>>> gmail.com wrote:

 If a system is in a superposition of states, whatever value 
 measured, will be repeated if the same system is repeatedly 
 measured.  But 
 what happens if the system is in a mixed state? TIA, AG

>>>
>>> If you think about it, whatever value you get on a single trial 
>>> for a mixed state, repeated on the same system, will result in the 
>>> same 
>>> value measured repeatedly. If this is true, how does measurement 
>>> distinguish superposition of states, with mixed states? AG
>>>
>>>
>>> That is not correct. You can distinguish a mixture of particles 
>>> in the up or down states with a set of 1/sqrt(2)(up+down) by 
>>> measuring them 
>>> with the {1/sqrt(2)(up+down), 1/sqrt(2)(up-down}) discriminating 
>>> apparatus. 
>>> With the mixture, half the particles will be defected in one 
>>> direction, 
>>> with the pure state, they will all pass in the same direction. 
>>> Superposition would not have been discovered if that was not the 
>>> case.
>>>
>>
>>
>> *And someone will supply the apparatus measuring (up + down), and 
>> (up - down)? No such apparatuses are possible since those states are 
>> inherently contradictory. We can only measure up / down. AG*
>>
>>
>> You can do the experience by yourself using a simple crystal of 
>> calcium (CaCO3, Island Spath), or with polarising glass. Or with 
>> Stern-Gerlach devices and electron spin. Just rotating (90° or 180°) 
>> an 
>> app/down apparatus, gives you an (up + down)/(up - down) apparatus. 
>>
>
> *I don't understand. With SG one can change the up/down axis by 
> rotation, but that doesn't result in an (up + down), or (up - down) 
> measurement. If that were the case, what is the operator for which 
> those 
> states are eigenstates? Which book by Albert? AG *
>
>
> David Z Albert, Quantum Mechanics and Experience, Harvard 
> University Press, 1992.
>
> https://www.amazon.com/Quantum-Mechanics-Experience-David-Albert/dp/0674741137
>
> Another very good books is
>
> D’Espagnat B. Conceptual foundations of Quantum mechanics,  I see 
> there is a new edition here:
>
> https://www.amazon.com/Conceptual-Foundations-Quantum-Mechanics-Advanced/dp/0738201049/ref=sr_1_1?s=books=UTF8=1540889778=1-1=d%27espagnat+conceptual+foundation+of+quantum+mechanics=41NcluHD6fL=_SY291_BO1,204,203,200_QL40_=srch
>
> It explains very well the difference between mixtures and pure 
> states.
>
> Bruno
>

 *Thanks for the references. I think I have a reasonable decent 
 understanding of mixed states. Say a system is in a mixed state of 
 phi1 and 
 phi2 with some probability for each. IIUC, a measurement will always 
 result 
 in an