The Arrow of Time

[agrayson2000]

Implied by standard QM insofar as the theory is inherently irreversible, 
that is, irreversible in principle at the quantum level since the wf cannot 
be recovered by time reversal. AG

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Re: Entanglement

[Russell Standish]

On Sat, Apr 28, 2018 at 01:56:51PM -0700, agrayson2...@gmail.com wrote:
> > I would add this; even assuming that consciousness is ultimately based on 
> quantum processes, where's the argument that consciousness is responsible 
> for the collapse?. As I've told Clark 43 times, Feynman showed that a 
> device can record the output on the screen (interference, collapse, not the 
> which-way situation) without any intervention by a conscious being. AG  

The key process, I think is digitisation of a continuum. Think
measuring a particle spin, which is indeterminate both in magnitude
and direction. After measurement, it has a particular half integral or
integral value in a particular direction.

When performing a computation, ultimately a voltage is converted (or
interpreted) as a either a 0 or 1 according to which side of a
threshold it lies on. The closer to the threshold you are, the more
error prone this is, which is why there is an inverse relationship
between clock speeds and voltage (and hence the amount of heat that
the computation generates). 

The thing is that the threshold value is a subjective thing - there's
nothing in the physics to say that a given voltage is a 1 or a 0. The
same can be said of the gradation marks on a d'Arsenval meter that are
interpreted as the result of a more classical experiment.

The nice thing about all of this is that the tension between the
discrete and continua can be studied as a theoretical computer science
or pure maths problem, there's nothing woo about it. However, it is a
field still in its infancy IMHO - traditionally mathematicians study
continuous things (call analysis), and those that study discrete
things call themselves computer scientists, and ne'er the twain shall
meet.

Cheer
-- 


Dr Russell StandishPhone 0425 253119 (mobile)
Principal, High Performance Coders
Visiting Senior Research Fellowhpco...@hpcoders.com.au
Economics, Kingston University http://www.hpcoders.com.au


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Re: Entanglement

[Brent Meeker]

On 4/29/2018 8:53 AM, Bruno Marchal wrote:
But that's my question: Why isn't it the same?  And even if it's not 
how would be know?  The "conscious" quantum computer assures us that 
it not only detected that there was a welcher weg photon but that 
it's weg was known to the "consciousness" of the quantum computer, 
before it was erased.  But why would we believe it?  We already have 
these experiments in which we know the weg was available and could 
have been recorded, but was erased.  So what is the "consciousness" 
that adds a secret-sauce to the experiment?


Good question. I doubt that you can fool quantum mechanics by calling 
it "consciousness". I think in this case the interaction with the 
welcher weg photon would amount to sufficient decoherence -- 
basically information was extracted that was not restored. Also, of 
course, if the QC "forgets" what it did, how can it report on the 
fact that it did anything. How can we believe that it actually knew 
which slit at some point?


Because in Deutsch experiment, not everything has been erased, notably 
the memory that he has known the result. He would say something like: 
I remember doing the measurement and writing it in the enveloppe. Now 
the envelop has been erased, and I can’t remember its content, but I 
definitely remember having known the content.


But two questions remain.  First, the empirical question of whether this 
erasure is enough to restore interference.  Second, why should we 
believe the quantum computer.  It is not like the classical case in 
which there is a fact-of-them-matter about which slit I observed and 
I've simply forgotten it.  But by quantum erasing the information, there 
is no fact-of-the-matter as to welcher weg, so what can it mean that the 
quantum consciousness once knew it and now remembers something that 
didn't happen.


Brent

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Re: Entanglement

[Brent Meeker]

On 4/29/2018 8:35 AM, Bruno Marchal wrote:
All computations can be done in a reversible way. The basic idea is 
that we can discard memories instead of erasing them, and that idea is 
coherent with physics and mechanism.


Because it is theoretically possible to do computations reversibly, 
doesn't mean that they are done that way.  It is very difficult in 
practice, as the developers quantum computers have found.  And even 
computations that are done reversibly in a quantum computer then do not 
come to definite results.  We are not conscious of superpositions.  So I 
stand by my point that consciousness is a classical phenomenon.


Brent

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Re: Measurements in QM

[Lawrence Crowell]

On Saturday, April 28, 2018 at 8:43:43 PM UTC-5, agrays...@gmail.com wrote:
>
>
>
> On Sunday, April 29, 2018 at 1:16:37 AM UTC, Lawrence Crowell wrote:
>>
>> On Saturday, April 28, 2018 at 6:04:31 PM UTC-5, Bruce wrote:
>>>
>>> From: 
>>>
>>> On Saturday, April 28, 2018 at 9:33:58 PM UTC, Brent wrote: 



 On 4/28/2018 9:39 AM, agrays...@gmail.com wrote: 
 > Is it a settled issue whether measurements in QM are strictly 
 > irreversible, 

 There are interactions that, if you did not arrange that they be 
 erased, 
 would constitute measurements.  Whether you say they were measurements 
 and then got erased or they are not measurments because they didn't 
 produce an irreversible record is a phlosophical or semantic question. 

 > that is irreversible in principle, or just statistically 
 irreversible, 
 > that is, reversible but with infinitesimal probability? TIA, 

 The equations are all reversible so you might say they are reversible 
 with infinitesimal probability...but in most cases that reversal would 
 mean catching and reversing photons that are already on their way 
 outbound beyond the orbit of the Moon. 

 Brent 

>>>
>>> Are there any measurements that can't be reversed regardless of the 
>>> fact that the equations of physics are time reversible? I could swear, 
>>> and I DO, that Bruce demonstrated such a case for spin 1/2 particles 
>>> measured by SG device.  AG
>>>
>>>
>>> I vaguely remember that from several years ago. As I recall, it was in 
>>> response to a claim by Vic that time reversibility of the equations meant 
>>> that if you measured the x-spin of a silver atom, the you could reverse the 
>>> result, say spin-up, and recover the initial state. That is certainly 
>>> impossible, since that does not take into account the phases associated 
>>> with the alternative result -- MWI is reversible only if you reverse all 
>>> the worlds.
>>>
>>> Besides, decoherence means that measurement resulting in classical 
>>> pointer-state outcomes are not reversible, even in principle, because of 
>>> the loss of IR photons which are never recoverable. Time reversal 
>>> invariance of the equations does not necessarily mean that you can actually 
>>> reverse things in practice.
>>>
>>> Bruce
>>>
>>
>> In order to reverse a quantum system you must have the entire wave 
>> function. After a measurement the states are in decoherent sets, and you 
>> the observer "pull the marble out of the bag" and get your result. You 
>> would have to have access to the entire decoherent set and the prior 
>> superposition or entanglement phases of these states. Without that you 
>> can't back out squat. In fact if you have computed knowledge of the 
>> decoherent sets of states you still can't do anything without knowing their 
>> pre-measurement phases. This is the sort of thing soft measurements allow 
>> you to do, at least up to a point. The Schrodinger equation with time 
>> reversal invariance, with Wigner's requirement of complex conjugation of 
>> the energy operator 
>>
>> iħ∂/∂t → i^*ħ∂/∂(-t) = iħ∂/∂t,
>>
>> which gives time reversal  invariance. Entanglement phases evolve through 
>> systems accordingly, but if the reservoir of states is extremely large the 
>> Poincare recurrence time may be longer than the duration of the universe. 
>> In effect if this phase is lost the practical situation is there is a 
>> collapse or loss of quantum information in decoherence sets.
>>
>> LC
>>
>
>
>
> *Aren't you describing what I've referred to as "statistical 
> irreversibiity", or the PRACTICAL inability to reverse a measurement, in 
> contrast to "irreversible in principle", by which I mean the absolute 
> impossibility of reversal? AGConcerning the pre-measurement phases of the 
> states comprising the superposition, aren't they irrelevant for calculating 
> probabilities? If so, why are they needed to reverse any measurement? That 
> is, if you can only recover the original wf up to phase angles and get the 
> same probabilities, why are the phases important for reversal of 
> measurements? AG *
>

It is more than statistical. Nonquantum physics has probabilities, while 
quantum physics is about amplitudes that have a modulus square that is a 
probability. You must have control over not just probabilities, but 
amplitudes and by the same measure phases. 

LC
 

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Re: Measurements in QM

[John Clark]

On Sat, Apr 28, 2018 at 8:16 PM, Bruce Kellett 
wrote:

​
>> ​>> ​
>> Although the other universe is only slightly different from ours and only
>> exists for a short time before it merges back into ours I think we do have
>> access to another universe every time we perform the 2 slit experiment.  ​
>
>
>
> ​>* ​*
> *Not once you take account of decoherence. You are equivocating on the
> meaning of "world". Separate "worlds" only emerge after decoherence.*
>

Separate worlds only emerge if there is a difference between them, if the
worlds evolve in such a way that the difference
disappears then re-coherence occurs. A photon goes through slot X in one
world and slot Y in another and that is a difference. When the photon hits
the photographic plate, or even just a brick wall, the photon no longer
exists in either world so there is no longer a difference, but there once
was and those incompatible histories cause the interference bands. If you
had no photographic plate or brick wall and just let the photons go onto
infinite space after passing the slits the 2 worlds would remain separate
forever. For obvious reasons re-coherence can only occur if the 2 worlds
are only very slightly different and have only been separated for a short
time, and that is why experiment of this sort are difficult but they are
not impossible.


> ​> *​*
> *Your "relative state" does not permit access to other "worlds".*
>

​
The truth or falsehood o
​f​
that statement can only be determined by experiment, and I think most on
this list will live long enough to see the answer.

​ John K Clark​

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Re: Entanglement

[Bruno Marchal]

> On 27 Apr 2018, at 08:23, Brent Meeker  wrote:
> 
> 
> 
> On 4/26/2018 10:38 PM, agrayson2...@gmail.com  
> wrote:
>> 
>> 
>> On Friday, April 27, 2018 at 5:10:46 AM UTC, Brent wrote:
>> 
>> 
>> On 4/26/2018 9:24 PM, agrays...@gmail.com  wrote:
>>> 
>>> 
>>> On Friday, April 27, 2018 at 1:43:30 AM UTC, Brent wrote:
>>> 
>>> 
>>> On 4/26/2018 6:21 PM, agrays...@gmail.com <> wrote:
 
 
 On Friday, April 27, 2018 at 1:10:25 AM UTC, Brent wrote:
 
 
 On 4/26/2018 4:14 PM, agrays...@gmail.com <> wrote:
> 
> 
> On Thursday, April 26, 2018 at 10:25:29 PM UTC, Brent wrote:
> 
> 
> On 4/26/2018 2:33 PM, agrays...@gmail.com <> wrote:
>> 
>> 
>> On Thursday, April 26, 2018 at 9:09:48 PM UTC, Brent wrote:
>> 
>> 
>> On 4/26/2018 7:23 AM, agrays...@gmail.com <> wrote:
>>> 
>>> 
>>> On Thursday, April 26, 2018 at 4:12:41 AM UTC, Brent wrote:
>>> 
>>> 
>>> On 4/25/2018 7:44 PM, agrays...@gmail.com <> wrote:
 
 
 On Thursday, April 26, 2018 at 2:17:31 AM UTC, Brent wrote:
 
 
 On 4/25/2018 6:39 PM, agrays...@gmail.com <> wrote:
> 
> On its face it's absurd to think the SoL is invariant for all 
> observers regardless of the relative motion of source and recipient, 
> but it has testable consequences. The MWI has no testable 
> consequences, so it makes no sense to omit this key difference in 
> your historical comparisons with other apparent absurdities in 
> physics. Moreover when you factor into consideration that non 
> locality persists in the many worlds postulated -- assuming you 
> accept Bruce's analysis -- what exactly has been gained by asserting 
> the MWI? Nothing as far as I can tell. And the loss is significant as 
> any false path would be. AG
 
 It's one possible answer to the question of where the Heisenberg cut 
 is located (the other is QBism).  It led to the theory of decoherence 
 and Zurek's theory of quantum Darwinism which may explain Born's rule.
 
 Brent
 
 I've always found the Heisenberg Cut to be a nebulous concept, a kind 
 of hypothetical demarcation between the quantum and classical worlds.
>>> 
>>> That's the problem with it; it doesn't have an objective physical 
>>> definition.  Bohr regarded it as a choice in analyzing an experiment; 
>>> you put it where ever was convenient.
>>> 
 What kind of boundary are we talking about, and how could the MWI shed 
 any light on it, whatever it is? AG 
>>> 
>>> In MWI there is no Heisenberg cut; instead there's a splitting of 
>>> worlds which has some objective location in terms of decoherence.
>>> 
>>> Brent
>>> 
>>> The Heisenberg Cut is too vague and ill-defined to shed light on 
>>> anything, and to say the MWI is helpful is adding another layer of 
>>> confusion. AG
>> 
>> Decoherence is a specific well-defined physical process and it describes 
>> the splitting of worlds.  There is still some question whether it 
>> entails the Born rule, but at worst the Born rule remains as a separate 
>> axiom.
>> 
>> Brent
>> 
>> Let's say an electron goes through an SG device. IIUC, its spin state 
>> becomes entangled with the spin wf's of the device. How do you infer 
>> splitting of worlds from this? AG
> 
> I don't.  Why should I?
> 
> Brent
> 
> I could swear that you wrote above that decoherence describes the 
> splitting of worlds, so I gave you an example of decoherence
 
 You didn't give an example of decoherence.  Where's the decoherence in an 
 electron flying through a divergent magnetic field?
 
 Brent
 
 That's what I figured you would write and maybe you're correct. I thought 
 decoherence means that the wf of the system being measured, gets entangled 
 with the wf's of the environment, in this case the SG device. Why is this 
 not decoherence, and if it isn't, what is?  TIA, AG
>>> 
>>> Decoherence happens when the particle is detected in one path or the other, 
>>> not when going thru the SG.  It's a classic experiment to show that 
>>> particle wf can be coherently recombined after going through SGs.  So if 
>>> you set up a detector on one leg of the SG then the world splits when there 
>>> is a detection vs no detection.
>>> 
>>> Brent
>>> 
>>> I am not considering a singlet state; just an electron passing through a SG 
>>> device and being measured, spin up or down. Are you saying no decoherence 
>>> in this case?
>> 
>> No.  I just saying when you posed the problem you didn't say anything about 
>> detection.  You just said an electron went through an SG apparatus.
>> 
>>> From what I gather from 

Re: Entanglement

[Bruno Marchal]

> On 27 Apr 2018, at 05:02, Bruce Kellett  wrote:
> 
> From: Brent Meeker < meeke...@verizon.net 
> >
>> On 4/26/2018 7:16 PM, Bruce Kellett wrote:
>>> On 4/26/2018 5:55 PM, Bruce Kellett wrote:
> From: Brent Meeker < meeke...@verizon.net 
> >
>> 
>> On 4/26/2018 3:41 PM, Bruce Kellett wrote:
>> 
> My point was that if there is a record that a measurement was made, 
> something irreversible has been extracted from the
>  experiment. If the QC is "conscious", then it has to interact with 
> something to make this irreversible record, so its quantum state is 
> irreversibly changed. But you are probably right: if there is no 
> decoherence, then there is no consciousness, since consciousness involves 
> irreversible memory.
 
 There are experiments already performed in which the welcher weg is 
 available but is erased, even spacelike relative to detection
>>> 
>>> I know. But no information was extracted from the welcher weg photons 
>>> before they were erased. I.e., no consciousness "recorded" which way and 
>>> then forgot the result. I think the act of recording the result, by a 
>>> consciousness or anything else, is inherently irreversible. If no record is 
>>> made, then erasure is perfectly possible. Just knowing that there were 
>>> welcher weg photons that have been erased is not quite the same thing.
>> 
>> But that's my question: Why isn't it the same?  And even if it's not how 
>> would be know?  The "conscious" quantum computer assures us that it not only 
>> detected that there was a welcher weg photon but that it's weg was known to 
>> the "consciousness" of the quantum computer, before it was erased.  But why 
>> would we believe it?  We already have these experiments in which we know the 
>> weg was available and could have been recorded, but was erased.  So what is 
>> the "consciousness" that adds a secret-sauce to the experiment?
> 
> Good question. I doubt that you can fool quantum mechanics by calling it 
> "consciousness". I think in this case the interaction with the welcher weg 
> photon would amount to sufficient decoherence -- basically information was 
> extracted that was not restored. Also, of course, if the QC "forgets" what it 
> did, how can it report on the fact that it did anything. How can we believe 
> that it actually knew which slit at some point?

Because in Deutsch experiment, not everything has been erased, notably the 
memory that he has known the result. He would say something like: I remember 
doing the measurement and writing it in the enveloppe. Now the envelop has been 
erased, and I can’t remember its content, but I definitely remember having 
known the content. 

Bruno


> 
> Bruce
> 
> 
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Re: Entanglement

[Bruno Marchal]

> On 27 Apr 2018, at 05:25, Brent Meeker  wrote:
> 
> 
> 
> On 4/26/2018 8:02 PM, Bruce Kellett wrote:
>> From: Brent Meeker >
>>> On 4/26/2018 7:16 PM, Bruce Kellett wrote:
 On 4/26/2018 5:55 PM, Bruce Kellett wrote:
>> From: Brent Meeker >
>>> 
>>> On 4/26/2018 3:41 PM, Bruce Kellett wrote:
>>> 
>> My point was that if there is a record that a measurement was made, 
>> something irreversible has been extracted from the experiment. If the QC 
>> is "conscious", then it has to interact with something to make this 
>> irreversible record, so its quantum state is irreversibly changed. But 
>> you are probably right: if there is no decoherence, then there is no 
>> consciousness, since consciousness involves irreversible memory.
> 
> There are experiments already performed in which the welcher weg is 
> available but is erased, even spacelike relative to detection
 
 I know. But no information was extracted from the welcher weg photons 
 before they were erased. I.e., no consciousness "recorded" which way and 
 then forgot the result. I think the act of recording the result, by a 
 consciousness or anything else, is inherently irreversible. If no record 
 is made, then erasure is perfectly possible. Just knowing that there were 
 welcher weg photons that have been erased is not quite the same thing.
>>> 
>>> But that's my question: Why isn't it the same?  And even if it's not how 
>>> would be know?  The "conscious" quantum computer assures us that it not 
>>> only detected that there was a welcher weg photon but that it's weg was 
>>> known to the "consciousness" of the quantum computer, before it was erased. 
>>>  But why would we believe it?  We already have these experiments in which 
>>> we know the weg was available and could have been recorded, but was erased. 
>>>  So what is the "consciousness" that adds a secret-sauce to the experiment?
>> 
>> Good question. I doubt that you can fool quantum mechanics by calling it 
>> "consciousness". I think in this case the interaction with the welcher weg 
>> photon would amount to sufficient decoherence -- basically information was 
>> extracted that was not restored. Also, of course, if the QC "forgets" what 
>> it did, how can it report on the fact that it did anything. How can we 
>> believe that it actually knew which slit at some point?
> 
> This is actually an example of the kind of experiment I've suggested Bruno 
> should analyze using his "comp" theory.  It seems sufficiently fundamental 
> and dependent on a theory of consciousness and quantum mechanics that Bruno's 
> theory should have something to say about it.  One successful prediction and 
> his Nobel prize will be assured.

I got already a price, but it has been erased (!).

Yes, as I just said, the comp analysis sustains Deutsch analysis, like it 
sustains the MW. 

Bruno



> 
> Brent
> 
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Re: Entanglement

[Bruno Marchal]

> On 27 Apr 2018, at 04:26, Brent Meeker  wrote:
> 
> 
> 
> On 4/26/2018 7:16 PM, Bruce Kellett wrote:
>> On 4/26/2018 5:55 PM, Bruce Kellett wrote:
 From: Brent Meeker >
> 
> On 4/26/2018 3:41 PM, Bruce Kellett wrote:
> 
 My point was that if there is a record that a measurement was made, 
 something irreversible has been extracted from the experiment. If the QC 
 is "conscious", then it has to interact with something to make this 
 irreversible record, so its quantum state is irreversibly changed. But you 
 are probably right: if there is no decoherence, then there is no 
 consciousness, since consciousness involves irreversible memory.
>>> 
>>> There are experiments already performed in which the welcher weg is 
>>> available but is erased, even spacelike relative to detection
>> 
>> I know. But no information was extracted from the welcher weg photons before 
>> they were erased. I.e., no consciousness "recorded" which way and then 
>> forgot the result. I think the act of recording the result, by a 
>> consciousness or anything else, is inherently irreversible. If no record is 
>> made, then erasure is perfectly possible. Just knowing that there were 
>> welcher weg photons that have been erased is not quite the same thing.
> 
> But that's my question: Why isn't it the same?  And even if it's not how 
> would be know?  The "conscious" quantum computer assures us that it not only 
> detected that there was a welcher weg photon but that it's weg was known to 
> the "consciousness" of the quantum computer, before it was erased.  But why 
> would we believe it?  We already have these experiments in which we know the 
> weg was available and could have been recorded, but was erased.  So what is 
> the "consciousness" that adds a secret-sauce to the experiment?

With mechanism, it is the usual consciousness, and here, the consciousness of 
having got a result + amnesia of the particular results. Why would he becomes a 
zombie on this? (Here I agree with Deutch that such a report would sustain the 
MW (and mechanism).

Bruno


> 
> Brent
> 
>> 
>> Bruce
>> 
>>> 
>>> https://arxiv.org/pdf/1206.4348.pdf 
>>> 
>>> (I wonder if the French appreciated the labeling of their apparatus BS-in 
>>> and BS-out?)
>>> 
>>> Brent
>> 
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Re: Entanglement

[Bruno Marchal]

> On 27 Apr 2018, at 03:36, Brent Meeker  wrote:
> 
> 
> 
> On 4/26/2018 5:55 PM, Bruce Kellett wrote:
>> From: Brent Meeker >
>>> 
>>> On 4/26/2018 3:41 PM, Bruce Kellett wrote:
 From: John Clark >
> 
> On Thu, Apr 26, 2018 at 2:02 PM,  > wrote:
> 
> ​ > ​  How many times must I remind you that Feynman explained that very 
> clearly.
> 
> ​ 42.​  
> 
> ​ > ​ Please repeat it. AG
>  
> I originally sent this on December 14 2017: 
> 
> David Deutsch proposed a test of Many Worlds about 30 years ago in his 
> book "The Ghost In The Atom", but  it would be very difficult to perform. 
> The reason it's so difficult to test is not  the Many World's theory 
> fault, the reason is that the conventional view says that conscious 
> observers obey different laws of physics, many worlds says they do not, 
> so to test who's right we need a mind that uses quantum properties. 
> Quantum Computers have advanced enormously over the last 30 years so I 
> wouldn't be surprised if it or something very much like it  is actually 
> performed in the decade or two.
> 
> An intelligent quantum computer shoots photons at a metal plate one at a 
> time that has 2 small slits in it, and then the photons hit a 
> photographic plate. Nobody looks at the photographic plate till the very 
> end of the experiment.  The quantum mind has detectors near each slit so 
> it knows which slit the various electrons went through. After each photon 
> passes the slits but before they hit the photographic plate the quantum 
> mind signs a document saying that it has observed each and every photon  
> and knows  which slit each photon went through. It is very important that 
> the document does not say which slit any photon went through, it only 
> says that they went through one slit and one slit only and the mind has 
> knowledge of which one. There is a signed document to this effect for 
> every photon it shot.
> 
> Now the mind uses quantum erasure to completely destroy its memory of 
> which slit any of the photons went through; the only part remaining is 
> the document which states that each photon went through one and only one 
> slit and the mind (at the time) knew which one. Now develop the 
> photographic plate and look at it.  If you see interference bands then 
> the many world interpretation is correct. If you do not see interference 
> bands then there are no worlds but this one and the conventional quantum  
> interpretation is correct. 
> 
> This works because in the Copenhagen interpretation when the results of a 
> measurement enters the consciousness of an observer the wave function 
> collapses, in effect all the universes except one disappear without a 
> trace so you get no interference. In the many worlds model all the other 
> worlds will converge back into one universe because information on which 
> slit the various photons went through was the only thing that made one 
> universe different from another, so when that was erased they became 
> identical again and merged, but their influence will still be felt, 
> you'll see indications that the photon went through slot A only and 
> indications it went through slot B only, and that's what causes 
> interference.
 
 Quantum erasure involves more than just forgetting what happened. What 
 about Zurek's "many records in the environment". If you know what 
 happened, many traces of that result remain -- even if your memory is 
 erased. Deutsch on the wrong track, yet again!
>>> 
>>> Deutsch knows the difference, and he specifies quantum erasure, which 
>>> implies that the detection of welcher weg  is never classical, i.e. it is 
>>> not decohered into the environment since if it were it could not be quantum 
>>> erased.  Which is the point of my remark that maybe all that would be 
>>> proved is that quantum "detection" can't be conscious.  I'm pretty sure 
>>> consciousness is a purely classical phenomenon.  So Deutsch's scheme to 
>>> detecting welcher-weg but erasing the knowledge may retain the interference 
>>> pattern but just prove that quantum knowledge is not conscious...something 
>>> Borh might well say.
>> 
>> My point was that if there is a record that a measurement was made, 
>> something irreversible has been extracted from the experiment. If the QC is 
>> "conscious", then it has to interact with something to make this 
>> irreversible record, so its quantum state is irreversibly changed. But you 
>> are probably right: if there is no decoherence, then there is no 
>> consciousness, since consciousness involves irreversible memory.
> 
> 

Re: Entanglement

[Bruno Marchal]

> On 27 Apr 2018, at 02:55, Bruce Kellett  wrote:
> 
> From: Brent Meeker < meeke...@verizon.net 
> >
>> 
>> On 4/26/2018 3:41 PM, Bruce Kellett wrote:
>>> From: John Clark >
 
 On Thu, Apr 26, 2018 at 2:02 PM, < 
 agrayson2...@gmail.com 
 > wrote:
 
 ​ > ​  How many times must I remind you that Feynman explained that very 
 clearly.
 
 ​ 42.​  
 
 ​ > ​ Please repeat it. AG
  
 I originally sent this on December 14 2017: 
 
 David Deutsch proposed a test of Many Worlds about 30 years ago in his 
 book "The Ghost In The Atom", but  it would be very difficult to perform. 
 The reason it's so difficult to test is not  the Many World's theory 
 fault, the reason is that the conventional view says that conscious 
 observers obey different laws of physics, many worlds says they do not, so 
 to test who's right we need a mind that uses quantum properties. Quantum 
 Computers have advanced enormously over the last 30 years so I wouldn't be 
 surprised if it or something very much like it  is actually performed in 
 the decade or two.
 
 An intelligent quantum computer shoots photons at a metal plate one at a 
 time that has 2 small slits in it, and then the photons hit a photographic 
 plate. Nobody looks at the photographic plate till the very end of the 
 experiment.  The quantum mind has detectors near each slit so it knows 
 which slit the various electrons went through. After each photon passes 
 the slits but before they hit the photographic plate the quantum mind 
 signs a document saying that it has observed each and every photon  and 
 knows  which slit each photon went through. It is very important that the 
 document does not say which slit any photon went through, it only says 
 that they went through one slit and one slit only and the mind has 
 knowledge of which one. There is a signed document to this effect for 
 every photon it shot.
 
 Now the mind uses quantum erasure to completely destroy its memory of 
 which slit any of the photons went through; the only part remaining is the 
 document which states that each photon went through one and only one slit 
 and the mind (at the time) knew which one. Now develop the photographic 
 plate and look at it.  If you see interference bands then the many world 
 interpretation is correct. If you do not see interference bands then there 
 are no worlds but this one and the conventional quantum  interpretation is 
 correct. 
 
 This works because in the Copenhagen interpretation when the results of a 
 measurement enters the consciousness of an observer the wave function 
 collapses, in effect all the universes except one disappear without a 
 trace so you get no interference. In the many worlds model all the other 
 worlds will converge back into one universe because information on which 
 slit the various photons went through was the only thing that made one 
 universe different from another, so when that was erased they became 
 identical again and merged, but their influence will still be felt, you'll 
 see indications that the photon went through slot A only and indications 
 it went through slot B only, and that's what causes interference.
>>> 
>>> Quantum erasure involves more than just forgetting what happened. What 
>>> about Zurek's "many records in the environment". If you know what happened, 
>>> many traces of that result remain -- even if your memory is erased. Deutsch 
>>> on the wrong track, yet again!
>> 
>> Deutsch knows the difference, and he specifies quantum erasure, which 
>> implies that the detection of welcher weg  is never classical, i.e. it is 
>> not decohered into the environment since if it were it could not be quantum 
>> erased.  Which is the point of my remark that maybe all that would be proved 
>> is that quantum "detection" can't be conscious.  I'm pretty sure 
>> consciousness is a purely classical phenomenon.  So Deutsch's scheme to 
>> detecting welcher-weg but erasing the knowledge may retain the interference 
>> pattern but just prove that quantum knowledge is not conscious...something 
>> Borh might well say.
> 
> My point was that if there is a record that a measurement was made, something 
> irreversible has been extracted from the experiment. If the QC is 
> "conscious", then it has to interact with something to make this irreversible 
> record, so its quantum state is irreversibly changed. But you are probably 
> right: if there is no decoherence, then there is no consciousness, since 
> consciousness involves irreversible memory.

All computations can be done in a reversible way. The basic idea 

Re: Entanglement

[Bruno Marchal]

> On 26 Apr 2018, at 16:23, agrayson2...@gmail.com wrote:
> 
> 
> 
> On Thursday, April 26, 2018 at 4:12:41 AM UTC, Brent wrote:
> 
> 
> On 4/25/2018 7:44 PM, agrays...@gmail.com  wrote:
>> 
>> 
>> On Thursday, April 26, 2018 at 2:17:31 AM UTC, Brent wrote:
>> 
>> 
>> On 4/25/2018 6:39 PM, agrays...@gmail.com <> wrote:
>>> 
>>> On its face it's absurd to think the SoL is invariant for all observers 
>>> regardless of the relative motion of source and recipient, but it has 
>>> testable consequences. The MWI has no testable consequences, so it makes no 
>>> sense to omit this key difference in your historical comparisons with other 
>>> apparent absurdities in physics. Moreover when you factor into 
>>> consideration that non locality persists in the many worlds postulated -- 
>>> assuming you accept Bruce's analysis -- what exactly has been gained by 
>>> asserting the MWI? Nothing as far as I can tell. And the 
>>> loss is significant as any false path would be. AG
>> 
>> It's one possible answer to the question of where the Heisenberg cut is 
>> located (the other is QBism).  It led to the theory of decoherence and 
>> Zurek's theory of quantum Darwinism which may explain Born's rule.
>> 
>> Brent
>> 
>> I've always found the Heisenberg Cut to be a nebulous concept, a kind of 
>> hypothetical demarcation between the quantum and classical worlds.
> 
> That's the problem with it; it doesn't have an objective physical definition. 
>  Bohr regarded it as a choice in analyzing an experiment; you put it where 
> ever was convenient.
> 
>> What kind of boundary are we talking about, and how could the MWI shed any 
>> light on it, whatever it is? AG 
> 
> In MWI there is no Heisenberg cut; instead there's a splitting of worlds 
> which has some objective location in terms of decoherence.
> 
> Brent
> 
> The Heisenberg Cut is too vague and ill-defined to shed light on anything, 
> and to say the MWI is helpful is adding another layer of confusion. AG 

Either the cut is in consciousness (Wigner, von Neumann, London & Bauer, 
Walker, etc.). That is a quite dualist theory which, Imo, has been refuted by 
Shimony.

Or the cut is in between the observer and the particle (say).

Or there is no cut, but then there is no collapse, and this leads to 
many-things theories, where the things are worlds, minds, or histories (debate 
on this remains possible, but with digital mechanism, they are computations, or 
quotient of equivalence on the set of all computations).

Bruno



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Re: Entanglement

[Bruno Marchal]

> On 25 Apr 2018, at 20:21, Brent Meeker  wrote:
> 
> 
> 
> On 4/25/2018 1:31 AM, Bruno Marchal wrote:
>> See my papers. We get a quantum logic for the observable.
> 
> How do you define an observable such that everyone can agree on the observed 
> value?

That is a complex problem, not yet solved. But if you can show that there is no 
solution, you refute Mechanism.

Yet the basic idea is simple: people can share histories when they are 
collectively multiplied, which is what QM provides, so the problem is that we 
don’t have a tensor product yet. I got an idea to extract it, buying 
Temperley-Lieb algebra related to formal Reidemester moves (cf knot theory) 
which appears in the graded quantum logics []^n p & <>^m t, with n < m. The 
self-referential arithmetic physical reality might be an immense braid, 
apparently. But this asks for many generations of mathematicians to solve.

Bruno



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Re: Entanglement

[Bruno Marchal]

> On 25 Apr 2018, at 20:19, Brent Meeker  wrote:
> 
> 
> 
> On 4/25/2018 1:31 AM, Bruno Marchal wrote:
>> 
>> Obviates action at a distance, but not the quantum inseparability, which is 
>> simply linearity, which should be derived from Mechanism, and steps have 
>> been done in that direction, as physics must be given by self-reference 
>> statistics on semi-computable predicate
> 
> How is that going to guarantee intersubjective agreement... or does it lead 
> to many solipistic worlds with one consciousness in each?

The solipsist world are the souls, and they can share it with other souls by 
having the same physics, and plausibly deep histories.

Bruno 



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Re: Entanglement

[Bruno Marchal]

> On 25 Apr 2018, at 20:16, Brent Meeker  wrote:
> 
> 
> 
> On 4/25/2018 1:18 AM, Bruno Marchal wrote:
>> Exactly like in arithmetic. But the interaction of Bob and Alice, does not 
>> make any worlds less probable, only some worlds get less accessible from 
>> where they have made the measurement. Cf RSSA … the probabilities are always 
>> relative.
> 
> ?? How do you calculate the probabilities; relative or not.

Constructively and mathematically, by the logic of "measure one” on the 
“intelligible matter hypostase” (the nuance []p & <>t, p sigma_1) which put a 
quantum logical structure on the sigma_1 (semi-computable) propositions (the 
computations). That is the arithmetical way to put it. Intuitively, but non 
constructively, by the limiting measure on the set of computations going 
through my mind state and going to some result, divided by the set of all 
computations. Of course, this is an image, and that is why I gave a 
mathematical treatment of it.

Bruno



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Re: Entanglement

[Bruno Marchal]

> On 25 Apr 2018, at 12:51, Bruce Kellett  wrote:
> 
> From: Bruno Marchal >
>>> On 22 Apr 2018, at 01:47, Bruce Kellett < 
>>> bhkell...@optusnet.com.au 
>>> > wrote:
>>> 
>>> From: smitra >
 
 On 22-04-2018 00:18, Brent Meeker wrote:
 On 4/21/2018 12:42 PM, smitra wrote:
 
 That's then an artifact of invoking an effective collapse of the 
 wavefunction due to introducing the observer. The correlated two particle 
 state is either put in by hand or one has shown how it was created. In the 
 former case one is introducing non-local effects in an ad-hoc way in a 
 theory that only has local interactions, so there is then nothing to 
 explain in that case. In the latter case, the entangled state itself 
 results from the local dynamics, one can put ALice and Bob at far away 
 locations there and wait until the two particles arrive at their 
 locations. The way the state vectors of the entire system that now also 
 includes the state vectors of Alice and Bob themselves evolve, has no 
 nontrivial non-local effects in them at all.
 
 Sure it does.  The state vector itself is a function of spacelike
 separate events, which cause it to evolve into orthogonal
 components...whose statistics violated Bell's inequality.
 
 Brent
 
 There is no non-locality implied here unless you assume that the dynamics 
 as predicted by QM is the result of a local hidden variables theory.
 
 Saibal
>>> 
>>> There is no need to suggest local (or non-local) hidden variables. The 
>>> non-locality we are talking about is implied by the quantum state itself -- 
>>> nothing to do with the dynamics.
>> 
>> 
>> But that type of non-locality has never been questioned, neither in the MWI, 
>> or a fortiori in QM+collapse. But the MWI explains without the need of 
>> “mysterious” influence-at-a-distance, which would be the case in the 
>> mono-universe theory, or in Bohm-De Broglie pilot wave theory. Without 
>> dynamic we have “only” d’Espagnat type of inseparability.
>> 
>> Bruno
> 
> It seems that you are starting to see it from my perspective.

We have already conclude that we agree. I have never doubt inseparability. The 
problem is perhaps just the term “non-locality”, which sometimes is claimed to 
mean “physical action at a distance in one branch of the multiverse”. 


> Non-locality is just another way of emphasizing the non-separablity of the 
> quantum singlet state. As you say, this is true in MWI as in collapse 
> theories. In my extended development of the mathematics in another recent 
> post, I demonstrated that there is actually no difference between MWI and CI 
> in this regard.

In the prediction? I agree. But if there is a collapse, inseparability do 
entails some action at a distance, even it it cannot be used to send signal. 


> All that we have is the non-separability of the state, which means that a 
> measurement on one particle affects the result of measurements on the other 
> -- they are inseparable.

“Affects” is ambiguous. Do you follow Bohr in saying that the action at a 
distance is not physical? But what could that mean? In the one-world 
assumption, it has to be as physical as the wave. In the MWI, it is only 
branch-self-localisation.


> This is all that non-locality means, and this is not changed by MWI.

In the MWI, we keep clearly d'espagant inseparability. But there is physical 
action at a distance, only the amoeba 1p-indeterminacy on which branch we 
belong.



> An awful lot of nonsense has been talked about this -- people trying to find 
> a "mechanism" for the inseparability -- but that is not necessary.

OK. (But assuming a bit of physical realism, you need the MW, it seems to me).


> Quantum theory requires it, and it has been totally vindicated by experiment. 
> That is the way things are, in one world or many.

In one world, I do not see how inseparability could not lead to action-at-a 
distance. In MW, I do not see why we would need a physical of mechanical action 
at a distance.

Bruno




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Re: Entanglement

[Bruno Marchal]

> On 24 Apr 2018, at 21:59, Brent Meeker  wrote:
> 
> 
> 
> On 4/24/2018 11:48 AM, agrayson2...@gmail.com  
> wrote:
>> 
>> 
>> On Tuesday, April 24, 2018 at 6:26:59 PM UTC, agrays...@gmail.com 
>>  wrote:
>> 
>> 
>> On Tuesday, April 24, 2018 at 6:14:49 PM UTC, Brent wrote:
>> 
>> 
>> On 4/24/2018 9:24 AM, agrays...@gmail.com <> wrote:
>>> 
>>> 
>>> On Tuesday, April 24, 2018 at 4:10:30 PM UTC, Brent wrote:
>>> 
>>> 
>>> On 4/24/2018 12:03 AM, agrays...@gmail.com <> wrote:
 
 
 On Tuesday, April 24, 2018 at 5:14:25 AM UTC, scerir wrote:
 According to Kennedy tensor product (in QM) has a very interesting story. 
 https://philpapers.org/rec/KENOTE 
 
 
 
 On the empirical foundations of the quantum no-signalling proofs 
 
 J. B. Kennedy 
 Philosophy of Science  62 
 (4):543-560 (1995)
 Abstract   
 I analyze a number of the quantum no-signalling proofs (Ghirardi et al. 
 1980, Bussey 1982, Jordan 1983, Shimony 1985, Redhead 1987, Eberhard and 
 Ross 1989, Sherer and Busch 1993). These purport to show that the EPR 
 correlations cannot be exploited for transmitting signals, i.e., are not 
 causal. First, I show that these proofs can be mathematically unified; 
 they are disguised versions of a single theorem. Second, I argue that 
 these proofs are circular. The essential theorem relies upon the tensor 
 product representation for combined systems, which has no physical basis 
 in the von Neumann axioms. Historically, the construction of this 
 representation scheme by von Neumann and Weyl built no-signalling 
 assumptions into the quantum theory. Signalling between the wings of the 
 EPR-Bell experiments is unlikely but is not ruled out empirically by the 
 class of proofs considered
  
 Wow! Thank you. It costs $10 to get a copy for a non-member, but very 
 likely well worth it IMO. AG
>>> 
>>> I wouldn't pay $0.01 for a paper written by a guy who says something is not 
>>> ruled out empirically by some mathematical proofs, and says something has 
>>> no physical basis in axioms.   He seems very confused about the difference 
>>> between mathematics and empiricism.
>>> 
>>> Brent
>>> 
>>> I'll pay the money and see what he has to say. He's saying the tensor 
>>> product states do not follow from the axioms of QM. Seems pretty clear even 
>>> if wrong. But you can save me the fee if you can clearly state how the 
>>> tensor product states follow from First Principles, that is, from the 
>>> postulates of QM. AG
>> 
>> Physics isn't mathematics.  It's not required to derive everything from a 
>> few axioms.  The mathematics is invented to describe the physics, no the 
>> other way around.  If you want to understand the use of the tensor product 
>> in quantum mechanics read this: 
>> 
>> https://ocw.mit.edu/courses/physics/8-05-quantum-physics-ii-fall-2013/lecture-notes/MIT8_05F13_Chap_08.pdf
>>  
>> 
>> 
>> Equation 1.20 answers your question about singlets.
>> 
>> Brent
>> 
>> Thanks. This looks good. AG 
>>  
>> I can't copy and paste some pertinent paragraphs of the pdf scerir sent me, 
>> but from reading some of Kennedy's claims, he seem to be saying that 
>> although he doesn't dispute the validity and usefulness of tensor products 
>> in quantum mechanics, unlike other quantum axioms which ARE empirically 
>> based, tensor products are NOT empirically based. Perhaps your link says 
>> otherwise. AG
> 
> Read this and then tell me what "empirically based" means
> 
> https://pdfs.semanticscholar.org/2fb0/4475228ff385a44a16e3ba42b432d3bf5b17.pdf
>  
> 
> 
> As far as I know the only empirical basis for a theory is that it always 
> gives the right answer when empirically tested.  Kennedy seems to have a 
> strange concept of circular reasoning.  He says that adopting an equation 
> that implies no-signaling and then using it to prove quantum theory avoids 
> FTL signaling is circular.  He misses the point that the reason for adopting 
> the no-signaling is the empirical success of special relativity, which would 
> be violated by FTL signaling.


I agree. Kennedy does not seems serious. Also, it is the first time I hear 
people criticising the tenor axiom axiom in Quantum mechanics, which is a 
fundamental postulate, but seems obvious in the old “de Broglie” “wave 
mechanics”. That motivation does not work well for the spin and discrete 
observable, but that is why von Neumann, in his famous treatise, makes it into 

Re: Measurements in QM

[agrayson2000]

On Sunday, April 29, 2018 at 7:17:48 AM UTC, agrays...@gmail.com wrote:
>
>
>
> On Saturday, April 28, 2018 at 11:33:58 PM UTC, Bruce wrote:
>>
>> From: >
>> On Saturday, April 28, 2018 at 11:17:54 PM UTC, Bruce wrote: 
>>>
>>> From: >>
>>> On Saturday, April 28, 2018 at 10:55:13 PM UTC, agrays...@gmail.com 
>>> wrote: 



 On Saturday, April 28, 2018 at 9:33:58 PM UTC, Brent wrote: 
>
>
>
> On 4/28/2018 9:39 AM, agrays...@gmail.com wrote: 
> > Is it a settled issue whether measurements in QM are strictly 
> > irreversible, 
>
> There are interactions that, if you did not arrange that they be 
> erased, 
> would constitute measurements.  Whether you say they were measurements 
> and then got erased or they are not measurments because they didn't 
> produce an irreversible record is a phlosophical or semantic question. 
>
> > that is irreversible in principle, or just statistically 
> irreversible, 
> > that is, reversible but with infinitesimal probability? TIA, 
>
> The equations are all reversible so you might say they are reversible 
> with infinitesimal probability...but in most cases that reversal would 
> mean catching and reversing photons that are already on their way 
> outbound beyond the orbit of the Moon. 
>
> Brent 
>

 Are there any measurements that can't be reversed regardless of the 
 fact that the equations of physics are time reversible? I could swear, 
 and I DO, that Bruce demonstrated such a case for spin 1/2 particles 
 measured by SG device.  AG 

>>>
>>> You can always take a movie of the measurement and play it backward.  
>>> Does this say anything about reversal in principle; that every 
>>> measurement
>>> is in principle reversible? AG
>>>
>>>
>>> That was the trap Vic fell into. Playing the movie backwards is not 
>>> generally equivalent to time reversal. It is in classical physics, but in 
>>> the quantum case, the movie is taken in only one world after the decoherent 
>>> splitting of the MWI , so playing it backwards does not reverse the other 
>>> worlds.
>>>
>>> Bruce
>>>
>>
>> Can't we analyze this problem without bringing the MWI?
>>
>>
>> The short answer is, No. Reversible means unitary evolution. Schrödinger 
>> evolution is unitary only with MWI. So reversible implies MWI. And since we 
>> don't have access to other MWI worlds, reversiblity is impossible for us 
>> "*in principle*.
>>
>> Bruce
>>
>
> I'm in Cali, Colombia, on a Saturday night, music late at night and I 
> can't sleep. Then it hit me. In a one world analysis using standard QM, 
> there is no process for going from the SWE to a definite measurement; that 
> is, there is no process for the transition of the system being measured to 
> the eigenfunction for which the measured value is an eigenvalue. So 
> although the SWE is time symmetric, the measuring process is NOT. Standard 
> QM does not tell us how we transition from the SWE to a particular 
> measurement and eigenstate. So, if it doesn't tell us how we get TO the 
> measured value and the final eigenstate, it surely can't tell us how to go 
> in the opposite direction, back to the original state, which would be the 
> reversed process. IOW, after a measurement occurs, there is no way to 
> recover the original wf. This means that standard one world QM is 
> irreversible "in principle". Playing the movie backward is totally 
> misleading. AG
>

Further, since I am in the Weinberg camp of finding the MWI "repellant", I 
conclude that irreducible randomness at the quantum level implies the arrow 
of time, insofar as quantum processes are strictly, in principle, 
irreversible. AG 

>
>> If we play the movie backward, and the movie is good enough to include 
>> all IR photons involved in the process, won't the movie played backward 
>> indicate the every measurement, indeed every physical process, is in 
>> PRINCIPLE reversible? AG
>>
>>

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Re: Entanglement

['scerir' via Everything List]

-scerir: IMO Schroedinger invented this manyworlds or manyminds or manywords 
interpretation.

-AG: I disagree. He's clearly criticizing the idea that all possible 
measurements are manifested in reality, which surely suggests other people were 
advancing a theory he strongly disliked.
. https://groups.google.com/d/optout
### G Bacciagaluppi writes, in  philsci-archive.pitt.edu/8876/1/beable3.pdf
The picture of the two cats, while surely an overinterpretation o f 
Schroedinger’s own views, may resonate with modern Everettians. In fact, if the 
above remarks on mass density as the three-dimensional manifestation ofthe 
Hilbert-space wave function are correct, then this picture just is the Everett 
interpretation.

The difference to the usual presentations in terms of Hilbert-space components 
of the wave function that constitute “worlds”, is
merely that here the emphasis is on the three-dimensional manifestation of the 
different components of the wave function.

As remarked by Bitbol (Schroedinger 1995, p. 17), it also resonates with some 
of Schroedinger’s own words (with the appropriate qualifications and warnings 
about overinterpretation):

'Nearly every result [a quantum theorist] pronounces is about the
probability of this or that or that... happening — with usually a
great many alternatives. The idea that they be not alternatives
but all really happen simultaneously seems lunatic to him, just
impossible. He thinks that if the laws of nature took this form for,
let us say, a quarter of an hour, we should find our surroundings
rapidly turning into a quagmire, or sort of a featureless jelly or
plasma, all contours becoming blurred, we ourselves probably
becoming jelly fish. It is strange that he should believe this.'
(Schroedinger 1995, p. 19)

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Re: Entanglement

[agrayson2000]

On Sunday, April 29, 2018 at 6:21:13 AM UTC, scerir wrote:
>
> IMO Schroedinger invented this manyworlds or manyminds or manywords 
> interpretation.
>

I disagree. He's clearly criticizing the idea that all possible 
measurements are manifested in reality, which surely suggests other people 
were advancing a theory he strongly disliked. AG 

> Il 28 aprile 2018 alle 23.01 agrays...@gmail.com  ha 
> scritto: 
>
>
>
> On Saturday, April 28, 2018 at 5:55:16 AM UTC, scerir wrote:
>
>
>
> I think Schroedinger and his cat bear some responsibility.  In trying to 
> debunk Born's probabilistic interpretation he appealed to the absurdity of 
> observation changing the physical state...even though no one had actually 
> proposed that.  
>
> Brent 
>
>
> “The idea that the alternate measurement outcomes be not alternatives but 
> *all 
> *really happening simultaneously seems lunatic to the quantum theorist, 
> just *impossible. *He thinks that if the laws of nature took *this *form 
> for, let me say, a quarter of an hour, we should find our surroundings 
> rapidly turning into a quagmire, a sort of a featureless jelly or plasma, 
> all contours becoming blurred, we ourselves probably becoming jelly fish. 
> It is strange that he should believe this. For I understand he grants that 
> unobserved nature does behave this way – namely according to the wave 
> equation. . . . according to the quantum theorist, nature is prevented from 
> rapid jellification only by our perceiving or observing it.”
>
> -Erwin Schroedinger, *The Interpretation of Quantum Mechanics. Dublin 
> Seminars (1949-1955) and Other Unpublished Assays *(Ox Bow Press, 
> Woodbridge, Connecticut, 1995).
>
>
> Who is Schrodinger referring to? This was written before 1957, when 
> Everett published his MWI.? Were other theorists advancing the idea that 
> all alternatives are physically manifested in reality? AG 
>
>  
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Re: Measurements in QM

['scerir' via Everything List]

I have two questions, on a personal note and curiosity.

1) Generally speaking, at what level do you understand the content
of your links, on a scale of 0 to 100, 100 being full comprehension?
I find them difficult and think I should start my study of QM from
the beginning, using the link Brent gave me about tensors, which
is part of an excellent course at MIT.

### It depends on the specific paper. Sometimes 100 on that scale. I would say, 
in general, that I understand the papers FAPP.

2) Is your life as a farmer in Italy finished?

### Unfortunately no!

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Re: Measurements in QM

[agrayson2000]

On Saturday, April 28, 2018 at 11:33:58 PM UTC, Bruce wrote:
>
> From: 
> On Saturday, April 28, 2018 at 11:17:54 PM UTC, Bruce wrote: 
>>
>> From: >
>> On Saturday, April 28, 2018 at 10:55:13 PM UTC, agrays...@gmail.com 
>> wrote: 
>>>
>>>
>>>
>>> On Saturday, April 28, 2018 at 9:33:58 PM UTC, Brent wrote: 



 On 4/28/2018 9:39 AM, agrays...@gmail.com wrote: 
 > Is it a settled issue whether measurements in QM are strictly 
 > irreversible, 

 There are interactions that, if you did not arrange that they be 
 erased, 
 would constitute measurements.  Whether you say they were measurements 
 and then got erased or they are not measurments because they didn't 
 produce an irreversible record is a phlosophical or semantic question. 

 > that is irreversible in principle, or just statistically 
 irreversible, 
 > that is, reversible but with infinitesimal probability? TIA, 

 The equations are all reversible so you might say they are reversible 
 with infinitesimal probability...but in most cases that reversal would 
 mean catching and reversing photons that are already on their way 
 outbound beyond the orbit of the Moon. 

 Brent 

>>>
>>> Are there any measurements that can't be reversed regardless of the 
>>> fact that the equations of physics are time reversible? I could swear, 
>>> and I DO, that Bruce demonstrated such a case for spin 1/2 particles 
>>> measured by SG device.  AG 
>>>
>>
>> You can always take a movie of the measurement and play it backward.  
>> Does this say anything about reversal in principle; that every measurement
>> is in principle reversible? AG
>>
>>
>> That was the trap Vic fell into. Playing the movie backwards is not 
>> generally equivalent to time reversal. It is in classical physics, but in 
>> the quantum case, the movie is taken in only one world after the decoherent 
>> splitting of the MWI , so playing it backwards does not reverse the other 
>> worlds.
>>
>> Bruce
>>
>
> Can't we analyze this problem without bringing the MWI?
>
>
> The short answer is, No. Reversible means unitary evolution. Schrödinger 
> evolution is unitary only with MWI. So reversible implies MWI. And since we 
> don't have access to other MWI worlds, reversiblity is impossible for us 
> "*in principle*.
>
> Bruce
>

I'm in Cali, Colombia, on a Saturday night, music late at night and I can't 
sleep. Then it hit me. In a one world analysis using standard QM, there is 
no process for going from the SWE to a definite measurement; that is, there 
is no process for the transition of the system being measured to the 
eigenfunction for which the measured value is an eigenvalue. So although 
the SWE is time symmetric, the measuring process is NOT. Standard QM does 
not tell us how we transition from the SWE to a particular measurement and 
eigenstate. So, if it doesn't tell us how we get TO the measured value and 
the final eigenstate, it surely can't tell us how to go in the opposite 
direction, back to the original state, which would be the reversed process. 
IOW, after a measurement occurs, there is no way to recover the original 
wf. This means that standard one world QM is irreversible "in principle". 
Playing the movie backward is totally misleading. AG

>
> If we play the movie backward, and the movie is good enough to include all 
> IR photons involved in the process, won't the movie played backward 
> indicate the every measurement, indeed every physical process, is in 
> PRINCIPLE reversible? AG
>
>

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Re: Measurements in QM

['scerir' via Everything List]

The short answer is, No. Reversible means unitary evolution. Schrödinger 
evolution is unitary only with MWI. So reversible implies MWI. And since we 
don't have access to other MWI worlds, reversiblity is impossible for us "*in 
principle*.

Bruce

It seems interesting to point out that Vaidman (manyworlder) has something to 
say about that here (see page 11 of pdf, point 10)
https://arxiv.org/abs/quant-ph/9609006
It seems that reversibility has different consequences following MWI vs 
following CI.
 

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Re: Entanglement

['scerir' via Everything List]

IMO Schroedinger invented this manyworlds or manyminds or manywords 
interpretation.

> Il 28 aprile 2018 alle 23.01 agrayson2...@gmail.com ha scritto:
> 
> 
> 
> On Saturday, April 28, 2018 at 5:55:16 AM UTC, scerir wrote:
> 
> > > 
> > 
> > 
> > > > > I think Schroedinger and his cat bear some 
> > responsibility.  In trying to debunk Born's probabilistic interpretation he 
> > appealed to the absurdity of observation changing the physical state...even 
> > though no one had actually proposed that. 
> > > 
> > > Brent
> > > 
> > > 
> > > > > 
> > “The idea that the alternate measurement outcomes be not 
> > alternatives but all really happening simultaneously seems lunatic to the 
> > quantum theorist, just impossible. He thinks that if the laws of nature 
> > took this form for, let me say, a quarter of an hour, we should find our 
> > surroundings rapidly turning into a quagmire, a sort of a featureless jelly 
> > or plasma, all contours becoming blurred, we ourselves probably becoming 
> > jelly fish. It is strange that he should believe this. For I understand he 
> > grants that unobserved nature does behave this way – namely according to 
> > the wave equation. . . . according to the quantum theorist, nature is 
> > prevented from rapid jellification only by our perceiving or observing it.”
> > 
> > -Erwin Schroedinger, The Interpretation of Quantum Mechanics. 
> > Dublin Seminars (1949-1955) and Other Unpublished Assays (Ox Bow Press, 
> > Woodbridge, Connecticut, 1995).
> > 
> > > 
> Who is Schrodinger referring to? This was written before 1957, when 
> Everett published his MWI.? Were other theorists advancing the idea that all 
> alternatives are physically manifested in reality? AG
> 
>  
> 
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