Re: Entanglement

[Brent Meeker]

On 5/4/2018 8:01 PM, agrayson2...@gmail.com wrote:



On Saturday, May 5, 2018 at 1:47:59 AM UTC, Brent wrote:



On 5/4/2018 5:33 PM, agrays...@gmail.com  wrote:



On Friday, May 4, 2018 at 9:44:49 PM UTC, Brent wrote:



On 5/4/2018 12:07 PM, agrays...@gmail.com wrote:


Unfortunately, it is not the case that you can implement
absolutely any unitary transformation in this way. For
instance, you cannot implement the unitary
transformation that would reverse a totally decohered
event.


*If the decoherence was unitary, why can't the process be
reversed statistically, analogous to the case of the
classical cooling gas where we imagine the hugely improbable
incoming and absorption of the previously outgoing IR
photons? AG*


It's mathematically reversible, but it's not reversible by
you or any combination of powers in this world no matter how
magical because this world is orthogonal to other worlds that
contain the information you would need to reverse it.  Which
is why I suggested this be called nomologically irreversible.

Brent


*I don't buy this argument. Since those other worlds don't exist,
one cannot speak of information lost to them. AG
*


Then you can adopt the "disappearing worlds" interpretation and
banish them.  But then you're faced with the CI problem of exactly
when and why they vanish.

Brent


Worlds which disappear must first exist, and the worlds of the MWI, 
like the "branches" of the SWE, don't exist.


Then you need some rule as to why they don't exist.  They are all the 
same in the SWE solutions.


The answer IMO must lie with decoherence, or how a measurement choice 
is made. If it's made by any describable physical process, then the 
quantum world is determinate,


You mean if it's made by some deterministic physical process.


which I think is contradicted by Bell experiments.


If it's not random then a non-local hidden variable can be used to 
signal FTL.


So the quantum world must be irreducibly random, which is the same as 
saying that measurements are irreversible in principle. AG


Well you already assumed that in the first line.  Throwing away the 
"branches" of the SWE is what CI does and that is throwing away 
information and makes it inherently irreversible.


Brent

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Re: Entanglement

[agrayson2000]

On Saturday, May 5, 2018 at 1:47:59 AM UTC, Brent wrote:
>
>
>
> On 5/4/2018 5:33 PM, agrays...@gmail.com  wrote:
>
>
>
> On Friday, May 4, 2018 at 9:44:49 PM UTC, Brent wrote: 
>>
>>
>>
>> On 5/4/2018 12:07 PM, agrays...@gmail.com wrote:
>>
>> Unfortunately, it is not the case that you can implement absolutely any 
>>> unitary transformation in this way. For instance, you cannot implement the 
>>> unitary transformation that would reverse a totally decohered event. 
>>>
>>
>> *If the decoherence was unitary, why can't the process be reversed 
>> statistically, analogous to the case of the classical cooling gas where we 
>> imagine the hugely improbable incoming and absorption of the previously 
>> outgoing IR photons? AG*
>>
>>
>> It's mathematically reversible, but it's not reversible by you or any 
>> combination of powers in this world no matter how magical because this 
>> world is orthogonal to other worlds that contain the information you would 
>> need to reverse it.  Which is why I suggested this be called nomologically 
>> irreversible.
>>
>> Brent
>>
>
>
> *I don't buy this argument. Since those other worlds don't exist, one 
> cannot speak of information lost to them. AG *
>
> Then you can adopt the "disappearing worlds" interpretation and banish 
> them.  But then you're faced with the CI problem of exactly when and why 
> they vanish.
>
> Brent
>

Worlds which disappear must first exist, and the worlds of the MWI, like 
the "branches" of the SWE, don't exist. The answer IMO must lie with 
decoherence, or how a measurement choice is made. If it's made by any 
describable physical process, then the quantum world is determinate, which 
I think is contradicted by Bell experiments. So the quantum world must be 
irreducibly random, which is the same as saying that measurements are 
irreversible in principle. AG 


 

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Re: Entanglement

[Brent Meeker]

On 5/4/2018 5:33 PM, agrayson2...@gmail.com wrote:



On Friday, May 4, 2018 at 9:44:49 PM UTC, Brent wrote:



On 5/4/2018 12:07 PM, agrays...@gmail.com  wrote:


Unfortunately, it is not the case that you can implement
absolutely any unitary transformation in this way. For
instance, you cannot implement the unitary transformation
that would reverse a totally decohered event.


*If the decoherence was unitary, why can't the process be
reversed statistically, analogous to the case of the classical
cooling gas where we imagine the hugely improbable incoming and
absorption of the previously outgoing IR photons? AG*


It's mathematically reversible, but it's not reversible by you or
any combination of powers in this world no matter how magical
because this world is orthogonal to other worlds that contain the
information you would need to reverse it. Which is why I suggested
this be called nomologically irreversible.

Brent


*I don't buy this argument. Since those other worlds don't exist, one 
cannot speak of information lost to them. AG

*

Then you can adopt the "disappearing worlds" interpretation and banish 
them.  But then you're faced with the CI problem of exactly when and why 
they vanish.


Brent

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Re: Entanglement

[agrayson2000]

On Friday, May 4, 2018 at 9:44:49 PM UTC, Brent wrote:
>
>
>
> On 5/4/2018 12:07 PM, agrays...@gmail.com  wrote:
>
> Unfortunately, it is not the case that you can implement absolutely any 
>> unitary transformation in this way. For instance, you cannot implement the 
>> unitary transformation that would reverse a totally decohered event. 
>>
>
> *If the decoherence was unitary, why can't the process be reversed 
> statistically, analogous to the case of the classical cooling gas where we 
> imagine the hugely improbable incoming and absorption of the previously 
> outgoing IR photons? AG*
>
>
> It's mathematically reversible, but it's not reversible by you or any 
> combination of powers in this world no matter how magical because this 
> world is orthogonal to other worlds that contain the information you would 
> need to reverse it.  Which is why I suggested this be called nomologically 
> irreversible.
>
> Brent
>

*I don't buy this argument. Since those other worlds don't exist, one 
cannot speak of information lost to them. AG *

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Re: Entanglement

[Brent Meeker]

On 5/4/2018 12:07 PM, agrayson2...@gmail.com wrote:


Unfortunately, it is not the case that you can implement
absolutely any unitary transformation in this way. For instance,
you cannot implement the unitary transformation that would reverse
a totally decohered event.


*If the decoherence was unitary, why can't the process be reversed 
statistically, analogous to the case of the classical cooling gas 
where we imagine the hugely improbable incoming and absorption of the 
previously outgoing IR photons? AG*


It's mathematically reversible, but it's not reversible by you or any 
combination of powers in this world no matter how magical because this 
world is orthogonal to other worlds that contain the information you 
would need to reverse it.  Which is why I suggested this be called 
nomologically irreversible.


Brent

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Re: Entanglement

[Brent Meeker]

On 5/4/2018 12:20 AM, smitra wrote:

On 03-05-2018 03:22, Brent Meeker wrote:

On 5/2/2018 6:02 PM, smitra wrote:

On 02-05-2018 03:21, Brent Meeker wrote:

On 5/1/2018 4:43 PM, smitra wrote:

On 01-05-2018 20:47, Brent Meeker wrote:

On 5/1/2018 9:01 AM, Bruno Marchal wrote:

On 29 Apr 2018, at 19:59, Brent Meeker  
wrote:



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.

I do not see why it would not been enough … in theory. You need only
a computer able to forget a memory, but not some meta-memory that it
has recorded a definite result. It isa bit like remembering we have
done a dream, without being able to remember any of its content.

In practice, that might be very difficult, if not impossible. I 
am not

sure.


Second, why should we believe the quantum computer.


In Deutsch proposal, it is a human.
 No, it's a conscious quantum computer.  It it were a human or other
(quasi-) classical instrument decoherence would happen when there 
was

a detection of welcher weg and erasure would be impossible.

 Brent
Yes, but note that you can make that quantum computing simulation 
of the observer in that thought experiment as precise as you like. 
You can in principle include a simulation of the entire Earth


And the outgoing EM and neutrino waves and their interaction with
interstellar atoms.  I'm suspicious of these fantasy thought
experiments.  But however detailed it may be doesn't answer my
question as to what it would mean to erase the welcher weg but not the
memory that the weg was detected.  I noted that this is not like a
classical erasure of a memory because in this case the coherence is
maintained, so when the welcher weg is erased there is no long any
fact-of-the-matter as to which way it went.  There is no
fact-of-the-matter that it was detected to go left or right.  So the
"memory" if it exists, is a false memory.

with billions of other people and a lot of decoherence implemented 
by qubits that simulate e.g. soft photons and other environmental 
degrees of freedom (and all that decoherence will end up getting 
reversed by the way the computation is set up ) The point is that 
if computation generates consciousness, you can in principle let 
any given person do the experimental verification of the existence 
of multiple branches by uploading the brain to a quantum computer 
and letting it be subject to such a computation.


How will the person verify it?  Reversing the computation will reverse
the person and erase their memory.

Brent


It's a simple two step measurement process where you (as a virtual 
person simulated by the QC) perform a measurement that tells you 
that the spin (represented by a qubit) has been measured without 
giving you the result. And then you perform the next measurement 
where you actually measure the value of the spin component. It can 
then be shown that there exists a unitary transform that will 
restore the original spin state that will preserve the record of the 
first measurement.


But you're speaking poetically.  I, as a classical being cannot
perform such measurements.  First, how can the simulated QC person
perform a measurement that tells you that the spin has been measured
without giving anyone the result?  In what sense is this a measurement
of the spin, not merely a measurement of some proxy that is
independent of the spin value?  Second, what is the point of the
second measurement "where you actually measure the spin component";
are you saying the first measurement did not actually measure the spin
component even though it is supposed to tell us that it was measured?
Third, all the techni

Re: Entanglement

[agrayson2000]

On Friday, May 4, 2018 at 5:49:15 PM UTC, Lawrence Crowell wrote:
>
> On Friday, May 4, 2018 at 8:21:52 AM UTC-5, Bruce wrote:
>>
>>
>> Unfortunately, it is not the case that you can implement absolutely any 
>> unitary transformation in this way. For instance, you cannot implement the 
>> unitary transformation that would reverse a totally decohered event. Your 
>> quantum computer ceases to function if there is any decoherence! For 
>> example, you cannot implement a unitary transformation that would resurrect 
>> my dead grandfather, even though his life and death were entirely unitary.  
>> So you cannot reverse a recorded measurement.
>>
>> Bruce
>>
>
> Weak measurements are or come close to being reversible. There is an 
> effort to know what the limits are on this, So far the boundary between a 
> hard and weak measurement appears flexible. This means that if one had some 
> vast master equation for all the reservior of interacting states that a 
> hard measurement might be reversible. Of course from a practical 
> perspective this becomes implausible.
>
> LC 
>

This is what I have been arguing; that CI (one world) measurements are 
possibly statistically irreversible, meaning reversible with hugely low 
probabilities; NOT irreversible in principle. AG

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Re: Entanglement

[agrayson2000]

On Friday, May 4, 2018 at 1:21:52 PM UTC, Bruce wrote:
>
> From: smitra < smi...@zonnet.nl >
>
>
> On 03-05-2018 03:22, Brent Meeker wrote:
>
>> On 5/2/2018 6:02 PM, smitra wrote:
>>
>>> On 02-05-2018 03:21, Brent Meeker wrote:
>>>
 On 5/1/2018 4:43 PM, smitra wrote:

> On 01-05-2018 20:47, Brent Meeker wrote:
>
>> On 5/1/2018 9:01 AM, Bruno Marchal wrote:
>>
>> On 29 Apr 2018, at 19:59, Brent Meeker < 
>>> meek...@verizon.net > wrote:
>>>
>>>
>>> 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.
>>
>> I do not see why it would not been enough … in theory. You need only
>> a computer able to forget a memory, but not some meta-memory that it
>> has recorded a definite result. It isa bit like remembering we have
>> done a dream, without being able to remember any of its content.
>>
>> In practice, that might be very difficult, if not impossible. I am not
>> sure.
>>
>> Second, why should we believe the quantum computer.
>>>
>>
>> In Deutsch proposal, it is a human.
>>  No, it's a conscious quantum computer.  It it were a human or other
>> (quasi-) classical instrument decoherence would happen when there was
>> a detection of welcher weg and erasure would be impossible.
>>
>>  Brent
>>
> Yes, but note that you can make that quantum computing simulation of 
> the observer in that thought experiment as precise as you like. You can 
> in 
> principle include a simulation of the entire Earth
>

 And the outgoing EM and neutrino waves and their interaction with
 interstellar atoms.  I'm suspicious of these fantasy thought
 experiments.  But however detailed it may be doesn't answer my
 question as to what it would mean to erase the welcher weg but not the
 memory that the weg was detected.  I noted that this is not like a
 classical erasure of a memory because in this case the coherence is
 maintained, so when the welcher weg is erased there is no long any
 fact-of-the-matter as to which way it went.  There is no
 fact-of-the-matter that it was detected to go left or right.  So the
 "memory" if it exists, is a false memory.

 with billions of other people and a lot of decoherence implemented by 
> qubits that simulate e.g. soft photons and other environmental degrees of 
> freedom (and all that decoherence will end up getting reversed by the way 
> the computation is set up ) The point is that if computation generates 
> consciousness, you can in principle let any given person do the 
> experimental verification of the existence of multiple branches by 
> uploading the brain to a quantum computer and letting it be subject to 
> such 
> a computation.
>

 How will the person verify it?  Reversing the computation will reverse
 the person and erase their memory.

 Brent

>>>
>>> It's a simple two step measurement process where you (as a virtual 
>>> person simulated by the QC) perform a measurement that tells you that the 
>>> spin (represented by a qubit) has been measured without giving you the 
>>> result. And then you perform the next measurement where you actually 
>>> measure the value of the spin component. It can then be shown that there 
>>> exists a unitary transform that will restore the original spin state that 
>>> wil

Re: Entanglement

[agrayson2000]

On Friday, May 4, 2018 at 1:25:19 PM UTC, Bruce wrote:
>
> From: >
>
>
> On Friday, May 4, 2018 at 5:50:04 AM UTC, Bruce wrote: 
>>
>> From: 
>>
>>
>> On Friday, May 4, 2018 at 4:22:47 AM UTC, Bruce wrote: 
>>>
>>> From: 
>>>
>>>
>>> On Thursday, May 3, 2018 at 11:52:00 PM UTC, Bruce wrote: 

 From: Brent Meeker 


 On 5/3/2018 4:03 PM, Bruce Kellett wrote:

 The problem, of course, is that this unitary operator is formed in the 
 multiverse, so to form its inverse we have to have access to the other 
 worlds of the multiverse. And this is impossible because of the linearity 
 of the SE. So although the mathematics of unitary transformations is 
 perfectly reversible, measurements are not reversible in principle in the 
 one world we find ourselves to inhabit.


 I think we need a more precise term than "in principle" which could 
 confuesed with "mathematically".  You really mean reversal is 
 *nomologically* impossible even though it's *mathematically* 
 reversible.  It's more impossible that *FAPP* or *statistically* but 
 not *logically* impossible.  :-)


 Not doable "in principle" just means that there is no conceivable way 
 in which it could be done. It is not just a matter of difficulty, or that 
 it would take longer than the lifetime of the universe. It is actually 
 impossible. Quantum mechanics does not imply that all things that are 
 logically possible are nomologically possible, or could be achieved in 
 practice.  That is why Saibal's claim that there exists a unitary operator 
 that does what he wants is rather empty -- there are an infinite number of 
 unitary operators that are not realizable in practice. And this limitation 
 is a limitation "in principle".

 Bruce

>>>
>>> *If you take the view that quantum reality is irreducibly random, it 
>>> MEANS that there is no process in nature that can explain how a random 
>>> event could occur, for if such a process existed, it would contradict 
>>> "irreducibly random". Bruce seems to take the view that all measurements 
>>> are irreversible in principle. That might not be true. For example, suppose 
>>> the temperature of a system decreases. Isn't it hypothetically possible to 
>>> imagine a time reversal of all the IR photons which caused the cooling, to 
>>> reunite with the original system and restore the previous higher 
>>> temperature? If so, the cooling process in this example is reversible 
>>> albeit hugely improbable -- which I refer to as statistically reversible, 
>>> or irreversible FAPP. I think Bruce can give an example of a measurement 
>>> which is time irreversible in principle, that is, impossible to time 
>>> reverse. AG*
>>>
>>>
>>> Classical situations involving the second law of thermodynamics 
>>> (increasing entropy) are reversible, though reversal is improbable because 
>>> the second law is statistical. The situation in quantum mechanics is 
>>> different when we have a measurement with several different possible 
>>> outcomes. In MWI these outcomes are in different branches, and we cannot 
>>> reach into these worlds to reverse things there. Decoherence in this branch 
>>> is certainly statistical, and so it is in all branches, but it is different 
>>> in each branch of the wave function, so reversing this branch does nothing 
>>> for the others, and does not restore the original superposition. Thus the 
>>> process is irreversible in principle (nomologically irreversible -- to 
>>> reverse violates the laws of physics).
>>>
>>> Bruce
>>>
>>
>> *Can you give an example of an irreversible in principle measurement 
>> using CI, not MWI? I understand your MWI analysis, but if there is only one 
>> world, and decoherence is used in an attempt to explain the measurement 
>> process, and if decoherence is statistical in this world, is there a clear 
>> example of an irreversible in principle measurement if we only have one 
>> world, this world? AG*
>>
>>
>> If there is collapse, as in the CI, then the irreversibility is even 
>> clearer: the other branches simply do not exist, so their contribution to 
>> the superposition no longer exists, so clearly cannot be reversed.all
>>
>> Bruce
>>
>
> *Don't you think that decoherence, which is a reversible statistical 
> process, is responsible for the disappearance of those other branches, and 
> thus, in principle, recoverable, allowing the entire superposition to be 
> recovered in principle in the CI, that is reversed? This where I am having 
> difficulty in arguing that all measurements in CI are in principle 
> irreversible. AG*
>
>
> Decoherence is unitary, but unitary evolution via the Schrödinger equation 
> produces a separate branch for each possible outcome.
>

*As a famous Mexican outlaw once said, "I don't need no stinkin' branches!" 
I say, what "branches"? Where does this imaginary construct come from, to 
deny? AG*
 

> The C

Re: Entanglement

[agrayson2000]

On Friday, May 4, 2018 at 1:58:04 PM UTC, Bruno Marchal wrote:
>
>
> On 4 May 2018, at 05:46, agrays...@gmail.com  wrote:
>
>
>
> On Thursday, May 3, 2018 at 4:12:31 PM UTC, Bruno Marchal wrote:
>
>
> On 2 May 2018, at 10:53, agrays...@gmail.com wrote:
>
>
>
> On Tuesday, May 1, 2018 at 3:36:31 PM UTC, Bruno Marchal wrote:
>
>
> On 29 Apr 2018, at 08:21, 'scerir' via Everything List <
> everyth...@googlegroups.com> wrote:
>
> IMO Schroedinger invented this manyworlds or manyminds or manywords 
> interpretation.
>
>
> The quote below seems to indicate that this is not the case, unless you 
> agree (with me, and Deutsch, …) that QM *is* the discovery of the many 
> superposed worlds/states/minds, and that the founder added the collapse 
> postulate ONLY to avoid the proliferation of the alternate 
> worlds/states/minds. Everett is just the guy who realise that the MW does 
> not leads to a jelly quagmire of everything, by taking the first person 
> view (what he called subjective) of the observers, as their memories get as 
> much quasi orthogonal that the results they could have attributed to a 
> collapse. The collapse, and the irreversibility is purely “subjective” 
> (first person) and irreversible in principle for *us*. To reverse the 
> entire universal wave, we would need to go outside the physical universe in 
> some practical way, which, needless to say, is rather difficult.
>
> But I do agree with you, Schroedinger and Einstein understood that the 
> collapse was a problem for the rest of physics and philosophy. They were 
> rightly skeptical that Bohr and Heisenberg got the whole thing. Would have 
> they like Everett? Bohr just threw Everett out of his home, I have read 
> somewhere. I think Einstein would have prefer it to anything involving an 
> action at a distance, like Bohm’s theory (non local hidden variable 
> theory). Indeed, as you all know, Einstein told that he would have prefered 
> to be a plumber than be involved in a theory with some action-at-a distance.
>
> Bruno
>
>
> Relativity affirms action at a distance. 
>
>
> ?
>
> Relativity is born with Einstein trying, and succeeding, to eliminate the 
> action at a distance in Newton’s theory of gravitation, and in Maxwell ’s 
> theory of electromagnetism.
>
>
> *Wrong. Completely wrong. Ever hear of the light cone in relativity? *
>
>
> Well, yes of course.
>
>
>
> *Light-like events are causally connected, which MEANS action at a 
> distance, *
>
>
> ?
>
> It means on the contrary that in the cone, we can have causal connection, 
> because they don’t need going faster than light. It means NO action at a 
> distance.
>
>
>
>
> *whereas space-like events are not.*
>
>
> Which means no action at a distance (and that is why the EPR-BELL-Aspect 
> theory and experience is astonishing. The Debate here was about the idea 
> that with the MW theory, we keep the non-locality and Bell’s violation 
> appearance in single branche, but that by looking at the entire wave, we 
> see that is a subjective phenomenon.
>
>
>
> * Relativity, and E&M after being modified by Einstein, affirm action at a 
> distance. *
>
>
> Einstein said, after EPR, that if an action at a distance was physically 
> real, he would have prefer to be a plumber instead of a physicists ever 
> related to such magic, that he qualified as spooky.
>

*You're confused. By SPOOKY action at a distance, Einstein was referring to 
INSTANTANEOUS action at a distance. In relativity and E&M, there is action 
at light speed, but not instantaneously. This is action at a distance but 
not spooky because NOT instantaneously. AG *

>
> Relativity, and I would say Everett (non collapse) saves physics from 
> action at a distance. Even Newton knew quickly that his law of gravitation 
> was dubious, because it evolves action at a distance. SR and GR don’t, nor, 
> Imo, the relative state of QM without collapse.
>
>
>
>
> *Newton's gravity theory has instantaneous action at a distance.*
>
>
> OK.
>
>
>
> * It was modified in the form of GR, which allows for action at a distance 
> at the speed of light.*
>
>
> That is not what we call “action at a distance”. If the action take the 
> speed of light or below, it is a un unproblematic propagation, at a 
> distance, only.
>
>
>
>
> * Classical E&M allowed for fields and actions to propagate at the SoL, 
> but not instantaneously. You speculate authoritatively on the nature of the 
> Cosmos but have little to no knowledge of basic physics. AG *
>
>
>
> I have no clue which speculation you are talking about, and in this case, 
> you are the one confusing action-at-a-distance with action at light speed 
> or below, which would make this entire thread spurious. 
>
> You might also try to use reason instead of showing emotion and using ad 
> hominem patronising tone which is only a sort of insult, which I take as 
> lack of argument. 
>
>
> Bruno
>
>
>
>
>
>
>
> Einstein found physical indeterminacy, and physical action at a distance 
> making no sens

Re: Entanglement

[Lawrence Crowell]

On Friday, May 4, 2018 at 8:21:52 AM UTC-5, Bruce wrote:
>
>
> Unfortunately, it is not the case that you can implement absolutely any 
> unitary transformation in this way. For instance, you cannot implement the 
> unitary transformation that would reverse a totally decohered event. Your 
> quantum computer ceases to function if there is any decoherence! For 
> example, you cannot implement a unitary transformation that would resurrect 
> my dead grandfather, even though his life and death were entirely unitary.  
> So you cannot reverse a recorded measurement.
>
> Bruce
>

Weak measurements are or come close to being reversible. There is an effort 
to know what the limits are on this, So far the boundary between a hard and 
weak measurement appears flexible. This means that if one had some vast 
master equation for all the reservior of interacting states that a hard 
measurement might be reversible. Of course from a practical perspective 
this becomes implausible.

LC 

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Re: What is a Löbian machine/number/combinator

[John Clark]

On Thu, May 3, 2018 at 7:26 PM, Quentin Anciaux  wrote:

​> ​
> Again the perfect example of I lost so I dodge...
>

After Bruno trots out the exact same argument he has 42 times before over
the last decade and I have pointed out 42 times exactly precisely why his
argument is dead wrong (and is charitable to call it a argument at all) I
figure that is quite sufficient. If an opinion is not based on logic then
logic can not destroy it and #43 is unlikely to do any good.
​

 John K Clark​

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On the reversal of time in natural law (Schroedinger)

['scerir' via Everything List]

Schroedinger wrote an interesting (little known) paper, in 1931.

It is a sort of 'Two-time symmetric interpretation' or 'Two-state vector 
quantum formalism', I mean that 'ABL rule', that Aharonov's stuff.

“Über die Umkehrung der Naturgesetze,” Sitz. preuss. Akad. Wiss., Phys.-Math. 
Klasse 9 (1931), 3-12.

You can read (download the pdf) an english version here

https://tinyurl.com/ycju6z2c

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Re: Entanglement

[Bruno Marchal]

> On 4 May 2018, at 09:20, smitra  wrote:
> 
> On 03-05-2018 03:22, Brent Meeker wrote:
>> On 5/2/2018 6:02 PM, smitra wrote:
>>> On 02-05-2018 03:21, Brent Meeker wrote:
 On 5/1/2018 4:43 PM, smitra wrote:
> On 01-05-2018 20:47, Brent Meeker wrote:
>> On 5/1/2018 9:01 AM, Bruno Marchal wrote:
>>> On 29 Apr 2018, at 19:59, Brent Meeker  wrote:
>>> 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.
>> I do not see why it would not been enough … in theory. You need only
>> a computer able to forget a memory, but not some meta-memory that it
>> has recorded a definite result. It isa bit like remembering we have
>> done a dream, without being able to remember any of its content.
>> In practice, that might be very difficult, if not impossible. I am not
>> sure.
>>> Second, why should we believe the quantum computer.
>> In Deutsch proposal, it is a human.
>>  No, it's a conscious quantum computer.  It it were a human or other
>> (quasi-) classical instrument decoherence would happen when there was
>> a detection of welcher weg and erasure would be impossible.
>>  Brent
> Yes, but note that you can make that quantum computing simulation of the 
> observer in that thought experiment as precise as you like. You can in 
> principle include a simulation of the entire Earth
 And the outgoing EM and neutrino waves and their interaction with
 interstellar atoms.  I'm suspicious of these fantasy thought
 experiments.  But however detailed it may be doesn't answer my
 question as to what it would mean to erase the welcher weg but not the
 memory that the weg was detected.  I noted that this is not like a
 classical erasure of a memory because in this case the coherence is
 maintained, so when the welcher weg is erased there is no long any
 fact-of-the-matter as to which way it went.  There is no
 fact-of-the-matter that it was detected to go left or right.  So the
 "memory" if it exists, is a false memory.
> with billions of other people and a lot of decoherence implemented by 
> qubits that simulate e.g. soft photons and other environmental degrees of 
> freedom (and all that decoherence will end up getting reversed by the way 
> the computation is set up ) The point is that if computation generates 
> consciousness, you can in principle let any given person do the 
> experimental verification of the existence of multiple branches by 
> uploading the brain to a quantum computer and letting it be subject to 
> such a computation.
 How will the person verify it?  Reversing the computation will reverse
 the person and erase their memory.
 Brent
>>> It's a simple two step measurement process where you (as a virtual person 
>>> simulated by the QC) perform a measurement that tells you that the spin 
>>> (represented by a qubit) has been measured without giving you the result. 
>>> And then you perform the next measurement where you actually measure the 
>>> value of the spin component. It can then be shown that there exists a 
>>> unitary transform that will restore the original spin state that will 
>>> preserve the record of the first measurement.
>> But you're speaking poetically.  I, as a classical being cannot
>> perform such measurements.  First, how can the simulated QC person
>> perform a measurement that tells you that the spin has been measu

Re: Entanglement

[Bruno Marchal]

> On 4 May 2018, at 05:46, agrayson2...@gmail.com wrote:
> 
> 
> 
> On Thursday, May 3, 2018 at 4:12:31 PM UTC, Bruno Marchal wrote:
> 
> On 2 May 2018, at 10:53, agrays...@gmail.com  wrote:
> 
> 
> 
> On Tuesday, May 1, 2018 at 3:36:31 PM UTC, Bruno Marchal wrote:
> 
> On 29 Apr 2018, at 08:21, 'scerir' via Everything List 
> > wrote:
> 
> IMO Schroedinger invented this manyworlds or manyminds or manywords 
> interpretation.
> 
> 
> The quote below seems to indicate that this is not the case, unless you agree 
> (with me, and Deutsch, …) that QM *is* the discovery of the many superposed 
> worlds/states/minds, and that the founder added the collapse postulate ONLY 
> to avoid the proliferation of the alternate worlds/states/minds. Everett is 
> just the guy who realise that the MW does not leads to a jelly quagmire of 
> everything, by taking the first person view (what he called subjective) of 
> the observers, as their memories get as much quasi orthogonal that the 
> results they could have attributed to a collapse. The collapse, and the 
> irreversibility is purely “subjective” (first person) and irreversible in 
> principle for *us*. To reverse the entire universal wave, we would need to go 
> outside the physical universe in some practical way, which, needless to say, 
> is rather difficult.
> 
> But I do agree with you, Schroedinger and Einstein understood that the 
> collapse was a problem for the rest of physics and philosophy. They were 
> rightly skeptical that Bohr and Heisenberg got the whole thing. Would have 
> they like Everett? Bohr just threw Everett out of his home, I have read 
> somewhere. I think Einstein would have prefer it to anything involving an 
> action at a distance, like Bohm’s theory (non local hidden variable theory). 
> Indeed, as you all know, Einstein told that he would have prefered to be a 
> plumber than be involved in a theory with some action-at-a distance.
> 
> Bruno
> 
> Relativity affirms action at a distance.
> 
> ?
> 
> Relativity is born with Einstein trying, and succeeding, to eliminate the 
> action at a distance in Newton’s theory of gravitation, and in Maxwell ’s 
> theory of electromagnetism.
> 
> Wrong. Completely wrong. Ever hear of the light cone in relativity?

Well, yes of course.



> Light-like events are causally connected, which MEANS action at a distance,

?

It means on the contrary that in the cone, we can have causal connection, 
because they don’t need going faster than light. It means NO action at a 
distance.




> whereas space-like events are not.

Which means no action at a distance (and that is why the EPR-BELL-Aspect theory 
and experience is astonishing. The Debate here was about the idea that with the 
MW theory, we keep the non-locality and Bell’s violation appearance in single 
branche, but that by looking at the entire wave, we see that is a subjective 
phenomenon.



> Relativity, and E&M after being modified by Einstein, affirm action at a 
> distance.

Einstein sais, after EPR, that if an action at a distance was physically real, 
he would have prefer to be a plumber instead of a physicists ever related to 
such magic, that he qualified as spooky.

Relativity, and I would say Everett (non collapse) saves physics from action at 
a distance. Even Newton knew quickly that his law of gravitation was dubious, 
because it evolves action at a distance. SR and GR don’t, nor, Imo, the 
relative state of QM without collapse.




> Newton's gravity theory has instantaneous action at a distance.

OK.



> It was modified in the form of GR, which allows for action at a distance at 
> the speed of light.

That is not what we call “action at a distance”. If the action take the speed 
of light or below, it is a un unproblematic propagation, at a distance, only.




> Classical E&M allowed for fields and actions to propagate at the SoL, but not 
> instantaneously. You speculate authoritatively on the nature of the Cosmos 
> but have little to no knowledge of basic physics. AG 


I have no clue which speculation you are talking about, and in this case, you 
are the one confusing action-at-a-distance with action at light speed or below, 
which would make this entire thread spurious. 

You might also try to use reason instead of showing emotion and using ad 
hominem patronising tone which is only a sort of insult, which I take as lack 
of argument. 


Bruno






> 
> Einstein found physical indeterminacy, and physical action at a distance 
> making no sense at all. But with the MW theory, neither the indeterminacy, 
> nor the “action-at-distance” are physical. They are only local appearances. 
> (Like we expect with digital mechanism).
> 
> My sense is that Einstein would have found the MWI "repellent" (to quote 
> Weinberg).
> 
> Plausiby. But I guess Einstein would have found the MW far less conceptually 
> repellent than physical action at a distance.
> 
> He would have found it excessively ornate,
> Or excessively elegant. Somehow, Everett

Re: Entanglement

[Bruce Kellett]

From: *Bruno Marchal* mailto:marc...@ulb.ac.be>>
On 4 May 2018, at 01:03, Bruce Kellett > wrote:



Actually, this is the basis of MWI -- everything in physics is based 
on unitary transformations. The Schrödinger equation can be derived 
by assuming time evolution is unitary. So, in the wider context, 
everything, even decoherence into the wider universe, is reversible, 
in the sense that there is a unitary transformation that, when 
applied to any final state, restores the initial state -- just take 
the unitary operator that describes the time evolution, say U, and 
then take its inverse, U^{-1}.


The problem, of course, is that this unitary operator is formed in 
the multiverse, so to form its inverse we have to have access to the 
other worlds of the multiverse. And this is impossible because of the 
linearity of the SE. So although the mathematics of unitary 
transformations is perfectly reversible, measurements are not 
reversible in principle in the one world we find ourselves to inhabit.


So even Deutsch's quantum brain is likely to run into difficulties, 
since it has to communicate with the real world.


OK. But that is the same with any quantum computer. Are you saying 
that quantum computing is not possible in practice?


No, quantum computing should be possible with sufficient protection 
against decoherence.


There are quantum algorithm capable of “fighting by quantum error 
procedures” the effect of decoherence. Imo, the Deutsch experiment is 
as much possible as a working quantum computer. I am pretty sure this 
is technologically possible, although plausibly not even in a near 
future, but soon after :)


The problem with Deutsch's thought experiment is that everything takes 
place within the quantum computer, so no real measurement has ever been 
made. Measurement involves decoherence and the effectively permanent 
splitting of branches. No quantum computer can work in such 
circumstances. Calling the unmeasured elements of a superposition 
"worlds" as Deutsch does, equivocates on the orthogonality inherent in 
an operational concept of a "world". If elements of a superposition can 
interfere, they are not separate worlds. Deutsch's idea is sunk by the 
"preferred basis" problem. It is only decoherence into the external 
world that can fix the basis (by einselection).


Bruce

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Re: Entanglement

[Bruno Marchal]

> On 4 May 2018, at 01:03, Bruce Kellett  wrote:
> 
> From: Bruno Marchal mailto:marc...@ulb.ac.be>>
>>> On 3 May 2018, at 04:16, Bruce Kellett < 
>>> bhkell...@optusnet.com.au 
>>> > wrote:
 From: smitra mailto:smi...@zonnet.nl>>
 
 On 02-05-2018 03:21, Brent Meeker wrote:
 
 How will the person verify it?  Reversing the computation will reverse
 the person and erase their memory.
 
 Brent
 
 It's a simple two step measurement process where you (as a virtual person 
 simulated by the QC) perform a measurement that tells you that the spin 
 (represented by a qubit) has been measured without giving you the result. 
 And then you perform the next measurement where you actually measure the 
 value of the spin component. It can then be shown that there exists a 
 unitary transform that will restore the original spin state that will 
 preserve the record of the first measurement.
 
 Saibal
>>> 
>>> You can prove anything in a simulation, because you get to choose the 
>>> physical laws that will be obeyed. How do you know that the simulation will 
>>> bear any relation to reality? A measurement is something that leaves a 
>>> permanent (un-erasable) record.
>> 
>> But for Deutsch experiments, we don’t need to erase the information, only to 
>> discard it in the vanilla ways. That seems impossible because we are used to 
>> leaking environment, but if we can do a quantum computer, we can do that, 
>> and it means we did found ways to a sort of absolute isolation, measurement 
>> without interactions, (à-la Eiltzur Vaidman), etc.
>> 
>> With a quantum brain, a human can do that experience, and come back 
>> remembering well opening the box, and saying to itself “I definiitly saw the 
>> definite result”, but after the coming back he said "now despite I remember 
>> all that, I get a blank when trying to remember that specific result, I 
>> can’t recall it (and this despite the quantum brain “knows the answer”, but 
>> is well blocked by some quantum Freudian algorithm (grin).
>> 
>> I tend to think that the laws of physics are reversible.
> 
> Actually, this is the basis of MWI -- everything in physics is based on 
> unitary transformations. The Schrödinger equation can be derived by assuming 
> time evolution is unitary. So, in the wider context, everything, even 
> decoherence into the wider universe, is reversible, in the sense that there 
> is a unitary transformation that, when applied to any final state, restores 
> the initial state -- just take the unitary operator that describes the time 
> evolution, say U, and then take its inverse, U^{-1}.
> 
> The problem, of course, is that this unitary operator is formed in the 
> multiverse, so to form its inverse we have to have access to the other worlds 
> of the multiverse. And this is impossible because of the linearity of the SE. 
> So although the mathematics of unitary transformations is perfectly 
> reversible, measurements are not reversible in principle in the one world we 
> find ourselves to inhabit.
> 
> So even Deutsch's quantum brain is likely to run into difficulties, since it 
> has to communicate with the real world.

OK. But that is the same with any quantum computer. Are you saying that quantum 
computing is not possible in practice? There are quantum algorithm capable of 
“fighting by quantum error procedures” the effect of decoherence. Imo, the 
Deutsch experiment is as much possible as a working quantum computer. I am 
pretty sure this is technologically possible, although plausibly not even in a 
near future, but soon after :)

Bruno




> 
> Bruce
> 
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Re: Entanglement

[Bruno Marchal]

> On 3 May 2018, at 17:28, 'scerir' via Everything List 
>  wrote:
> 
> 
> 
> 
>> Il 3 maggio 2018 alle 16.28 Bruno Marchal  ha scritto: 
>> 
>> 
>>> On 1 May 2018, at 18:13, 'scerir' via Everything List < 
>>> everything-list@googlegroups.com > 
>>> wrote:
>>> 
>>> 
>>> 
>>> 
 Il 1 maggio 2018 alle 17.36 Bruno Marchal < marc...@ulb.ac.be 
 > ha scritto: 
 
 
> On 29 Apr 2018, at 08:21, 'scerir' via Everything List < 
> everything-list@googlegroups.com 
> > wrote:
> 
> IMO Schroedinger invented this manyworlds or manyminds or manywords 
> interpretation.
> 
 
 The quote below seems to indicate that this is not the case, unless you 
 agree (with me, and Deutsch, …) that QM *is* the discovery of the many 
 superposed worlds/states/minds, and that the founder added the collapse 
 postulate ONLY to avoid the proliferation of the alternate 
 worlds/states/minds.
>>> 
>>> Yes, I can agree with that. But it is possible there was, in those years, 
>>> another issue too. I mean conservation of energy. It is not possible, in 
>>> general, to preserve conservation of energy in each universe during the 
>>> split-decoherence, especially in case of superposition of states of 
>>> different energy. In this special case energy increase in one universe and 
>>> decrease in another universe.  
>>> 
>> 
>> The conservation of energy seems to me to be a classical, and mainly 
>> statistical notion. I do not see why the many-universes would violate 
>> thermodynamics in any branches, given that, by linearity of evolution, each 
>> branch evolves independently of the others, and the branches can only 
>> interfere, statistically, from the first person perspective of the observer. 
>> I am not even sure how we could superpose two states with different energy. 
>> May be you could explain me this.
>> 
>> Bruno
> 
> The worlds are not autonomous during the split (decoherence process) of the 
> original unique world.
> 
> 

By linearity, I don’t see that possible. The worlds can interfere but cannot 
interact. We can’t steal the petrol in a parallel worlds. The statistical 
conservation of energy in each worlds seems to me to follow from unitary 
evolution. 



> "Now, there isn't really a story to tell about what the total energy in 
> individual universes is during that whole process [of measurement]. Because 
> the universes are not autonomous during it.
> 
I guess Deutsch alludes to the fact that they can interfere, on they non 
distinguishable parts. 


> But one thing's for sure, there is no way of construing it so that the energy 
> in each particular universe is conserved, for the simple reason that the 
> whole system starts out the same on each run of the experiment (before the 
> non-sharp state is created), and ends up different". --David Deutsch
> 
> 

Different from the observer’s point of view. That is correct; they got some bit 
of information, but that is the case for all measurement. Taken literally, what 
Deutsch says here would be a problem for the “Zurek” quantum solution of the 
Maxwell Daemon paradox, based on Landauer discovery that in a computation, only 
erasing information needs energy.

> In a superposition of states of different energy I am inclined to think 
> (naively) that  the energy of the superposition state lies in between the 
> energy of its constituents. Actually the theory only states there are 
> expectation values, that is to say what you get if you perform many 
> measurements, and then you average. Now the measurement process itself is an 
> "interaction" with the superposition state, and I do not know whether this 
> interaction, in the MWI, is unitary or not.
> 
It is unitary in the third person perspective on the “whole wave”, and it is 
not unitary from the first person view, which live (but only live, 
subjectively) the experience of the collapse.

> "In more general cases, where there are superpositions of states of different 
> energy, energy can increase in one universe at the cost of decreasing in 
> another." --David Deutsch
> 
> 

Perhaps. I am not sure. 

> But let us read Hartle here https://arxiv.org/abs/gr-qc/9410006 
> 
> http://blog.jessriedel.com/2015/08/23/how-to-think-about-quantum-mechanics-part-6-energy-conservation-and-wavefunction-branches/
> 
> 

I remember having read that paper a long time ago I might reread it, but I am 
not sure I disagree with any of it. 

Bruno



> .
> 
>> 
>> 
 Everett is just the guy who realise that the MW does not leads to a jelly 
 quagmire of everything, by taking the first person view (what he called 
 subjective) of the observers, as their memories get as much quasi 
 orthogonal that the results they could have attributed to a collapse. The 
 collapse, and the irreversibility is purely “subjective” (fi

Re: Entanglement

[Bruce Kellett]

From: mailto:agrayson2...@gmail.com>>


On Friday, May 4, 2018 at 5:50:04 AM UTC, Bruce wrote:

From: 


On Friday, May 4, 2018 at 4:22:47 AM UTC, Bruce wrote:

From: 


On Thursday, May 3, 2018 at 11:52:00 PM UTC, Bruce wrote:

From: *Brent Meeker* 


On 5/3/2018 4:03 PM, Bruce Kellett wrote:

The problem, of course, is that this unitary operator
is formed in the multiverse, so to form its inverse we
have to have access to the other worlds of the
multiverse. And this is impossible because of the
linearity of the SE. So although the mathematics of
unitary transformations is perfectly reversible,
measurements are not reversible in principle in the
one world we find ourselves to inhabit.


I think we need a more precise term than "in principle"
which could confuesed with "mathematically". You really
mean reversal is /nomologically/ impossible even though
it's /mathematically/ reversible.  It's more impossible
that /FAPP/ or /statistically/ but not /logically/
impossible.  :-)


Not doable "in principle" just means that there is no
conceivable way in which it could be done. It is not
just a matter of difficulty, or that it would take
longer than the lifetime of the universe. It is actually
impossible. Quantum mechanics does not imply that all
things that are logically possible are nomologically
possible, or could be achieved in practice.  That is why
Saibal's claim that there exists a unitary operator that
does what he wants is rather empty -- there are an
infinite number of unitary operators that are not
realizable in practice. And this limitation is a
limitation "in principle".

Bruce


*If you take the view that quantum reality is irreducibly
random, it MEANS that there is no process in nature that can
explain how a random event could occur, for if such a
process existed, it would contradict "irreducibly random".
Bruce seems to take the view that all measurements are
irreversible in principle. That might not be true. For
example, suppose the temperature of a system decreases.
Isn't it hypothetically possible to imagine a time reversal
of all the IR photons which caused the cooling, to reunite
with the original system and restore the previous higher
temperature? If so, the cooling process in this example is
reversible albeit hugely improbable -- which I refer to as
statistically reversible, or irreversible FAPP. I think
Bruce can give an example of a measurement which is time
irreversible in principle, that is, impossible to time
reverse. AG*


Classical situations involving the second law of
thermodynamics (increasing entropy) are reversible, though
reversal is improbable because the second law is statistical.
The situation in quantum mechanics is different when we have
a measurement with several different possible outcomes. In
MWI these outcomes are in different branches, and we cannot
reach into these worlds to reverse things there. Decoherence
in this branch is certainly statistical, and so it is in all
branches, but it is different in each branch of the wave
function, so reversing this branch does nothing for the
others, and does not restore the original superposition. Thus
the process is irreversible in principle (nomologically
irreversible -- to reverse violates the laws of physics).

Bruce


*Can you give an example of an irreversible in principle
measurement using CI, not MWI? I understand your MWI analysis,
but if there is only one world, and decoherence is used in an
attempt to explain the measurement process, and if decoherence is
statistical in this world, is there a clear example of an
irreversible in principle measurement if we only have one world,
this world? AG*


If there is collapse, as in the CI, then the irreversibility is
even clearer: the other branches simply do not exist, so their
contribution to the superposition no longer exists, so clearly
cannot be reversed.all

Bruce


*Don't you think that decoherence, which is a reversible statistical 
process, is responsible for the disappearance of those other branches, 
and thus, in principle, recoverable, allowing the entire superposition 
to be recovered in principle in the CI, that is reversed? This where I 
am having difficulty in arguing that all measurements in CI are in 
principle irreversible. AG*


Decoherence is unitary, but unitary evolution via the Schrödinger 
equation produces 

Re: Entanglement

[Bruce Kellett]

From: *smitra* mailto:smi...@zonnet.nl>>


On 03-05-2018 03:22, Brent Meeker wrote:

On 5/2/2018 6:02 PM, smitra wrote:

On 02-05-2018 03:21, Brent Meeker wrote:

On 5/1/2018 4:43 PM, smitra wrote:

On 01-05-2018 20:47, Brent Meeker wrote:

On 5/1/2018 9:01 AM, Bruno Marchal wrote:

On 29 Apr 2018, at 19:59, Brent Meeker
mailto:meeke...@verizon.net>> wrote:


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.

I do not see why it would not been enough … in
theory. You need only
a computer able to forget a memory, but not some
meta-memory that it
has recorded a definite result. It isa bit like
remembering we have
done a dream, without being able to remember any
of its content.

In practice, that might be very difficult, if not
impossible. I am not
sure.

Second, why should we believe the quantum
computer.


In Deutsch proposal, it is a human.
 No, it's a conscious quantum computer.  It it
were a human or other
(quasi-) classical instrument decoherence would
happen when there was
a detection of welcher weg and erasure would be
impossible.

 Brent

Yes, but note that you can make that quantum computing
simulation of the observer in that thought experiment
as precise as you like. You can in principle include a
simulation of the entire Earth


And the outgoing EM and neutrino waves and their
interaction with
interstellar atoms.  I'm suspicious of these fantasy thought
experiments.  But however detailed it may be doesn't answer my
question as to what it would mean to erase the welcher weg
but not the
memory that the weg was detected.  I noted that this is
not like a
classical erasure of a memory because in this case the
coherence is
maintained, so when the welcher weg is erased there is no
long any
fact-of-the-matter as to which way it went.  There is no
fact-of-the-matter that it was detected to go left or
right.  So the
"memory" if it exists, is a false memory.

  

Re: Entanglement

[agrayson2000]

On Friday, May 4, 2018 at 5:50:04 AM UTC, Bruce wrote:
>
> From: >
>
>
> On Friday, May 4, 2018 at 4:22:47 AM UTC, Bruce wrote: 
>>
>> From: 
>>
>>
>> On Thursday, May 3, 2018 at 11:52:00 PM UTC, Bruce wrote: 
>>>
>>> From: Brent Meeker 
>>>
>>>
>>> On 5/3/2018 4:03 PM, Bruce Kellett wrote:
>>>
>>> The problem, of course, is that this unitary operator is formed in the 
>>> multiverse, so to form its inverse we have to have access to the other 
>>> worlds of the multiverse. And this is impossible because of the linearity 
>>> of the SE. So although the mathematics of unitary transformations is 
>>> perfectly reversible, measurements are not reversible in principle in the 
>>> one world we find ourselves to inhabit.
>>>
>>>
>>> I think we need a more precise term than "in principle" which could 
>>> confuesed with "mathematically".  You really mean reversal is 
>>> *nomologically* impossible even though it's *mathematically* 
>>> reversible.  It's more impossible that *FAPP* or *statistically* but 
>>> not *logically* impossible.  :-)
>>>
>>>
>>> Not doable "in principle" just means that there is no conceivable way in 
>>> which it could be done. It is not just a matter of difficulty, or that it 
>>> would take longer than the lifetime of the universe. It is actually 
>>> impossible. Quantum mechanics does not imply that all things that are 
>>> logically possible are nomologically possible, or could be achieved in 
>>> practice.  That is why Saibal's claim that there exists a unitary operator 
>>> that does what he wants is rather empty -- there are an infinite number of 
>>> unitary operators that are not realizable in practice. And this limitation 
>>> is a limitation "in principle".
>>>
>>> Bruce
>>>
>>
>> *If you take the view that quantum reality is irreducibly random, it 
>> MEANS that there is no process in nature that can explain how a random 
>> event could occur, for if such a process existed, it would contradict 
>> "irreducibly random". Bruce seems to take the view that all measurements 
>> are irreversible in principle. That might not be true. For example, suppose 
>> the temperature of a system decreases. Isn't it hypothetically possible to 
>> imagine a time reversal of all the IR photons which caused the cooling, to 
>> reunite with the original system and restore the previous higher 
>> temperature? If so, the cooling process in this example is reversible 
>> albeit hugely improbable -- which I refer to as statistically reversible, 
>> or irreversible FAPP. I think Bruce can give an example of a measurement 
>> which is time irreversible in principle, that is, impossible to time 
>> reverse. AG*
>>
>>
>> Classical situations involving the second law of thermodynamics 
>> (increasing entropy) are reversible, though reversal is improbable because 
>> the second law is statistical. The situation in quantum mechanics is 
>> different when we have a measurement with several different possible 
>> outcomes. In MWI these outcomes are in different branches, and we cannot 
>> reach into these worlds to reverse things there. Decoherence in this branch 
>> is certainly statistical, and so it is in all branches, but it is different 
>> in each branch of the wave function, so reversing this branch does nothing 
>> for the others, and does not restore the original superposition. Thus the 
>> process is irreversible in principle (nomologically irreversible -- to 
>> reverse violates the laws of physics).
>>
>> Bruce
>>
>
> *Can you give an example of an irreversible in principle measurement using 
> CI, not MWI? I understand your MWI analysis, but if there is only one 
> world, and decoherence is used in an attempt to explain the measurement 
> process, and if decoherence is statistical in this world, is there a clear 
> example of an irreversible in principle measurement if we only have one 
> world, this world? AG*
>
>
> If there is collapse, as in the CI, then the irreversibility is even 
> clearer: the other branches simply do not exist, so their contribution to 
> the superposition no longer exists, so clearly cannot be reversed.all
>
> Bruce
>

*Don't you think that decoherence, which is a reversible statistical 
process, is responsible for the disappearance of those other branches, and 
thus, in principle, recoverable, allowing the entire superposition to be 
recovered in principle in the CI, that is reversed? This where I am having 
difficulty in arguing that all measurements in CI are in principle 
irreversible. AG *

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Re: Entanglement of macro objects

[Lawrence Crowell]

On Thursday, May 3, 2018 at 8:26:18 AM UTC-5, Bruno Marchal wrote:
>
>
> On 1 May 2018, at 13:02, Lawrence Crowell  > wrote:
>
> On Tuesday, May 1, 2018 at 3:53:19 AM UTC-5, Bruno Marchal wrote:
>>
>>
>>
>> It assumes? Or does it entail the appearance of the classical-like 
>> structure?  What you say is very interesting, but I have not yet much 
>> understanding of QM+gravity. My own non expert and non rigorous (old) 
>> attempt leads to … to much white holes: there should be almost everywhere, 
>> but … I will need to revise a bit of differential geometry (where I am not 
>> so much at ease).
>>
>
> I use the word assume to mean acquire. The system acquire more classical 
> properties and nonlocality is virtually gone.
>
>
> If “acquire” means “physically acquire”, that view could be problematic 
> with the computationalist assumption. But that would be long to explain 
> just here. With mechanism we assume a simple classical (boolean) reality 
> (arithmetic for example), and explain all non classical logics by the 
> constraints of self-referential correctness, which makes all "empirical 
> logics” non classical.
>
> Bruno
>

Classicality may simply be an approximation. It may not fundamentally 
exist, and if it does there are then deep questions on how quantum 
mechanics builds up this phenomena that appears classical. If quantum and 
classical realities are separate and equal aspects of the world, such as 
what Bohr maintained, then one must deal with objective loss of quantum 
information.

LC 

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Re: Entanglement

[smitra]

On 03-05-2018 03:22, Brent Meeker wrote:

On 5/2/2018 6:02 PM, smitra wrote:

On 02-05-2018 03:21, Brent Meeker wrote:

On 5/1/2018 4:43 PM, smitra wrote:

On 01-05-2018 20:47, Brent Meeker wrote:

On 5/1/2018 9:01 AM, Bruno Marchal wrote:

On 29 Apr 2018, at 19:59, Brent Meeker  
wrote:



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.

I do not see why it would not been enough … in theory. You need 
only
a computer able to forget a memory, but not some meta-memory that 
it

has recorded a definite result. It isa bit like remembering we have
done a dream, without being able to remember any of its content.

In practice, that might be very difficult, if not impossible. I am 
not

sure.


Second, why should we believe the quantum computer.


In Deutsch proposal, it is a human.
 No, it's a conscious quantum computer.  It it were a human or 
other
(quasi-) classical instrument decoherence would happen when there 
was

a detection of welcher weg and erasure would be impossible.

 Brent
Yes, but note that you can make that quantum computing simulation of 
the observer in that thought experiment as precise as you like. You 
can in principle include a simulation of the entire Earth


And the outgoing EM and neutrino waves and their interaction with
interstellar atoms.  I'm suspicious of these fantasy thought
experiments.  But however detailed it may be doesn't answer my
question as to what it would mean to erase the welcher weg but not 
the

memory that the weg was detected.  I noted that this is not like a
classical erasure of a memory because in this case the coherence is
maintained, so when the welcher weg is erased there is no long any
fact-of-the-matter as to which way it went.  There is no
fact-of-the-matter that it was detected to go left or right.  So the
"memory" if it exists, is a false memory.

with billions of other people and a lot of decoherence implemented 
by qubits that simulate e.g. soft photons and other environmental 
degrees of freedom (and all that decoherence will end up getting 
reversed by the way the computation is set up ) The point is that if 
computation generates consciousness, you can in principle let any 
given person do the experimental verification of the existence of 
multiple branches by uploading the brain to a quantum computer and 
letting it be subject to such a computation.


How will the person verify it?  Reversing the computation will 
reverse

the person and erase their memory.

Brent


It's a simple two step measurement process where you (as a virtual 
person simulated by the QC) perform a measurement that tells you that 
the spin (represented by a qubit) has been measured without giving you 
the result. And then you perform the next measurement where you 
actually measure the value of the spin component. It can then be shown 
that there exists a unitary transform that will restore the original 
spin state that will preserve the record of the first measurement.


But you're speaking poetically.  I, as a classical being cannot
perform such measurements.  First, how can the simulated QC person
perform a measurement that tells you that the spin has been measured
without giving anyone the result?  In what sense is this a measurement
of the spin, not merely a measurement of some proxy that is
independent of the spin value?  Second, what is the point of the
second measurement "where you actually measure the spin component";
are you saying the first measurement did not actually measure the spin
component even though it is supposed to tell us that it was measured? 
Third, all the techniques I've heard of for