- #71
zonde
Gold Member
- 2,961
- 224
Then I can't propose you anything.Boing3000 said:I am disappointed, aren't we supposed to talk about science here ?
Then I can't propose you anything.Boing3000 said:I am disappointed, aren't we supposed to talk about science here ?
And Stapp's article already contains response to Griffiths response and Griffiths response contains response to response which basically says that: "The reader will have to judge".rubi said:This is Griffiths response to it.
Can't read this article as it is behind paywall.rubi said:Read his paper. He explains that his definition of locality derived from the assumption of CFD.
I found one Griffiths article where he tries to argue that QM is non-contextual Quantum Measurements Are Noncontextualrubi said:You understand wrong. In general, it doesn't refer to measurement arrangements at all. The KS theorem just tells us that there can't be a one-to-one mapping.zonde said:But does this contextuality index describe global measurement arrangement as well? As I understand it does.
There is 0% action at a distance, independent of whether you can use it for signaling or not. I don't know what you mean by instantaneous correlation.Boing3000 said:Am I right to understand that as 0% FTL signaling, and 100% instantaneous correlation (which is on what my little code is based on) ?
He refers to [10], precisely because he has introduced the his notion of locality and explained it in that article. And he clearly explains that it implicitely assumes counterfactual definiteness. I don't know how you get the idea that he "carefully avoids counterfactual reasoning", but you are definitely in disagreement with the author.zonde said:Can't read this article as it is behind paywall.
But when I look at his definition of "local" from this article http://dx.doi.org/10.1103/PhysRevA.47.R747 it seems that he very carefully avoids any counterfactual reasoning (btw reference [10] is the paper you gave):
"For a given theory, we consider all the possible sequences of N events that can occur in each setup. N is the same for the four setups and arbitrarily large. As in [9] and [10], a theory is defined as being "local" if it predicts that, among these possible sequences of events, one can find four sequences (one for each setup) satisfying the following conditions:
It seems that you still didn't bother to understand the KS theorem. Griffiths is not talking about the KS theorem here. The KS theorem says nothing about the meaning of the ##\chi## index. It just says that a one-to-one mapping of observables to random variables is not possible. There are infinitely many ways to write down such a many-to-one correspondence. Making ##\chi## depend on non-local information is a possibility, but not a necessity. The KS theorem does not make statements about locality. Also, as I told you, it is completely irrelevant. The point is that Bell excludes contextual theories from his analysis (or do you see any contextuality index in his proof?)zonde said:Well, it seems that my understanding of common terminology (KS definition of term "contextual") is correct and you are using some private and rather uncommon terminology.
Well, then please quote his particular point.rubi said:He refers to [10], precisely because he has introduced the his notion of locality and explained it in that article. And he clearly explains that it implicitely assumes counterfactual definiteness.
I got the idea by very carefully reading his definition and doing some analysis afterwards. And please provide relevant quote from the author if you think I disagree with him.rubi said:I don't know how you get the idea that he "carefully avoids counterfactual reasoning", but you are definitely in disagreement with the author.
Wrong. I just do not jump at conclusions about things I'm not sure I understand.rubi said:It seems that you still didn't bother to understand the KS theorem.
rubi said:Griffiths is not talking about the KS theorem here.
zonde said:Well, then please quote his particular point.
(Property 3 is the locality definition from your paper)Eberhard said:Another justification of this property 3 relies on a concept which was called
(( contrafactual definiteness ~> (-m), a concept used in daily life whenever we
must make a choice. Contrafactual definiteness means that, in a given situation,
the consequence of each of the possible courses of action can be considered
even though the only sequence of events that can be known for certain is the
one produced by the tinal single choice. Thut is we can hypothesize about the
event sequences following the courses of action that will not be chosen.
Your method of carefully reading and doing some analysis doesn't seem to work very well.I got the idea by very carefully reading his definition and doing some analysis afterwards. And please provide relevant quote from the author if you think I disagree with him.
As I explained, it is totally irrelevant anyway.Wrong. I just do not jump at conclusions about things I'm not sure I understand.
So what? QM is contextual. That's what the KS theorem says. However, it doesn't force any specific form of contextuality. It just says that the mapping must be many-to-one and nothing more.This is first sentence from this paper:
"John Bell in Sec. 5 of [1] while discussing hidden variables in quantum mechanics raised the question of whether quantum theory is “contextual.”"
Reference [1] contains Bell's version of (B)KS theorem.
Thanks. Now I understand where CFD comes into Eberhards definition of "local". It's when he refers to concept of "theory".rubi said:(Property 3 is the locality definition from your paper)Eberhard said:Another justification of this property 3 relies on a concept which was called
(( contrafactual definiteness ~> (-m), a concept used in daily life whenever we
must make a choice. Contrafactual definiteness means that, in a given situation,
the consequence of each of the possible courses of action can be considered
even though the only sequence of events that can be known for certain is the
one produced by the tinal single choice. Thut is we can hypothesize about the
event sequences following the courses of action that will not be chosen.
That's a way better way to put it. And action at a distance means for me impossible (FTL) transfer of momentum/energy (as per SR)rubi said:There is 0% action at a distance, independent of whether you can use it for signaling or not.
I mean the prediction of QM and how they have been verified experimentally.rubi said:I don't know what you mean by instantaneous correlation.
I have of course anticipated an absurd response, but I couldn't imagine that it would be that absurd. What did you think? Of course, we are talking about theories. Bell's theorem is talking about theories; Eberhard is talking about theories.zonde said:Thanks. Now I understand where CFD comes into Eberhards definition of "local". It's when he refers to concept of "theory".
Hmm, so do you suggest that we should consider explanations that are not "theories"? Here ... on science forum?
Now you explain the term "instantaneous correlation" by putting the word "factual" in front of it. Anyway, nothing is instantaneous about quantum correlations.Boing3000 said:I mean the prediction of QM and how they have been verified experimentally.
That is: NO action at a distance (that means Einstein after all was right) but factual instantaneous correlation (when experimenter coerce the measurement timing of A & B to be as close to identical as possible in the labs-frame)
First, Eberhard's derivation is different as he does not use hidden variables.rubi said:The point is the following: Contrary to what you claimed, Eberhard admits that his definition of locality includes CFD, so his derivation of Bell's inequality and Bell-type inequalities does not make less assumptions than anyone elses derivations.
Ok, once again:zonde said:First, Eberhard's derivation is different as he does not use hidden variables.
Second, all his requirements can be realized in single chronological sequence of events with no parallel counterfactual sequences. So the only sense in which he is using CFD is that he requires that theory makes predictions. That's all.
From dictionary:rubi said:Eberhard's locality definition requires that the theory makes predictions about unperformed measurements.
<Mentor's note: edited for distraction>zonde said:From dictionary:
prediction - a statement made about the future
All future measurements are not (yet) performed. So any theory that makes predictions is making counterfactual statement.
Is it so hard to understand?
Sorry, sloppy language again. "Experimental/observed" is what I meant.rubi said:Now you explain the term "instantaneous correlation" by putting the word "factual" in front of it.
I feel like I am back to square one now. Do you meant that QM predict some minimal delay before Bob and Alice can make they observation about an entangled pair state ? I always though they can do them whenever they want to.rubi said:Anyway, nothing is instantaneous about quantum correlations.
Boing3000 said:I feel like I am back to square one now. Do you meant that QM predict some minimal delay before Bob and Alice can make they observation about an entangled pair state ? I always though they can do them whenever they want to.
Can you point me to this non-instantaneous computation, for example in the case of spin entangled electrons, and eventually the experimental testing of that prediction ?
But isn't quantum contextuality used when trying to understand QM deterministically?(at least that is what Wiki says:"Quantum Contextuality means that in any theory that attempts to explain quantum mechanics deterministically..."rubi said:QM is contextual. That's what the KS theorem says. However, it doesn't force any specific form of contextuality. It just says that the mapping must be many-to-one and nothing more.
No, it has nothing to do with determinism. The question is whether one can model the quantum observables one-to-one as random variables on a classical probability space. If that is not possible, then the theory is called contextual. Of course, using classical probabilities has nothing to do with determinism. I can also write down a classical probability distribution for a coin tossing experiment (##p_i=\frac 1 2##), but of course that doesn't imply that the experiment is deterministic.RockyMarciano said:But isn't quantum contextuality used when trying to understand QM deterministically?(at least that is what Wiki says:"Quantum Contextuality means that in any theory that attempts to explain quantum mechanics deterministically..."
Could you clarify why would anyone insist on explaining QM deterministically, if that's what you are doing? I thought that was precisely what Bohmian mechanics pursued, is the only basic difference between BM and CH the disagreement about locality?
But I totally agree, and I would be very happy not to use "instantaneous", in favor of "non-locality". But that is the term I see everywhere to describe that entanglement (perfect correlation) is, with no evolution with respect to time (and space) (between t1 and t2). I have always understood Bell's theorem as being a way to prove that hypothesis (by observation).DrChinese said:Time is not a factor (variable) in this case, so it is meaningless to discuss delays, instantaneous, etc. Do you recall my comment (post #64) about "when" and entanglement? That is the point I was making. There is no "when" in the normal sense of the term.
How can "nonlocal" means "long-range influences which act instantaneously over long distances", when non-local means no space-like nor time-like characteristic. How something with no-size be long, or something with no evolution in time be anything but instantaneous ?Griffiths said:The opinion is widespread that quantum mechanics is nonlocal in the sense that it implies the existence of long-range influences which act instantaneously over long distances, in apparent contradiction to special relativity
It cannot if the entanglement broke at first interaction. It can otherwise.Griffiths said:The widespread belief in the existence of such nonlocal effects seems a bit surprising in view of theorems [36, 37], whose validity does not seem to be in doubt, to the effect that these (supposed) quantum nonlocal influences cannot be used to transmit signals or information
Isn't it trivial to measure by ordinary test (after A and B get back together), that the correlation was indeed non-local ?Griffiths said:Thus they are not detectable by any ordinary experimental test.
Boing3000 said:How can "nonlocal" means "long-range influences which act instantaneously over long distances", when non-local means no space-like nor time-like characteristic. How something with no-size be long, or something with no evolution in time be anything but instantaneous ?
...
Thanks a lot for that explanation.DrChinese said:So when you "prove" there is something non-local occurring, you really aren't. You have a context which is in fact traced out by a light cone (or cones). The extent of the "non-locality" is the distance between points on a light cone and no further. QM fully qualifies as a local contextual theory, which matches what some of the theorems that Griffiths refers to would indicate.
Then I guess somebody should correct the wikipedia article.rubi said:No, it has nothing to do with determinism.
I have seen that called non-EPR realist(i.e. non-classical) instead. So it seems to me that only those that want to keep classicality recur to contextuality, why is it better to drop counterfactual definiteness(wich I'd say leads to solipsism) than classicality(EPR realism)?The question is whether one can model the quantum observables one-to-one as random variables on a classical probability space. If that is not possible, then the theory is called contextual.
Clearly classical probabilities are compatible with classical determinism, and coin tossing is usually considered deterministic with the classical 1/2 probability atributted to lack of information about the initial state.Of course, using classical probabilities has nothing to do with determinism. I can also write down a classical probability distribution for a coin tossing experiment (##p_i=\frac 1 2##), but of course that doesn't imply that the experiment is deterministic.
Solipsism and realism are philosophical terms that have no place in physics. Physics has nothing to say about these things. For the rest of your post: I'm using the terms classicality, CFD, non-contextuality interchangeably, because for the purpose of Bell's theorem, it makes no difference.RockyMarciano said:I have seen that called non-EPR realist(i.e. non-classical) instead. So it seems to me that only those that want to keep classicality recur to contextuality, why is it better to drop counterfactual definiteness(wich I'd say leads to solipsism) than classicality(EPR realism)?
Probabilities are always compatible with determinism, but they are also compatible with genuine randomness. Probabilities just don't care about such notions. Whether you can come up with a deterministic theory that underlies the coin tossing experiment is not relevant. You can also do that with QM (see Bohmian mechanics, which is in my opinion absurd).Clearly classical probabilities are compatible with classical determinism, and coin tossing is usually considered deterministic with the classical 1/2 probability atributted to lack of information about the initial state.
A paper discussing whether the assumption of classicality is made by Bell is this paper by Maudin:zonde said:Assumption is that there is physical model that can explain results of measurements that show perfect correlations. There is no assumption of hidden variables per se.
Reply to WernerWerner has made quite clear and explicit the startling claim that Bell himself did not understand what he had proved. If so, then Bell’s own pronouncements about what he did, and what it means, are not reliable. Werner thinks that Bell and Einstein and I have all tacitly made an assumption of which we are unaware, an assumption he labels C for “classicality”. When Bell, or Einstein, or I write “theory” what we really mean (although we don’t realize it) is “classical theory”. And when we draw conclusions about what a theory with certain characteristics must be like, the conclusions really only hold for classical theories. Furthermore, Operational quantum theory is not a classical theory. Therefore, according to Werner, Bell’s and Einstein’s conclusions simply do not apply to Operational quantum theory. In particular, Operational quantum theory can be local in Bell’s and Einstein’s sense and still violate Bell’s inequality because it is not classical. Werner concedes that Bell proved that any classical theory that violates his inequalities must be non-local (again, in Bell’s and Einstein’s sense of “non-local”). But deny classicality and the arguments no longer go through...Since the main contention is that Bell and Einstein and I have all been blinded by tacitly presuming classicality, the main order of business ought to be demonstrating exactly where the argument presumes classicality.
Very interesting links, thanks you. I can't help to find Maudlin straightforward and coherent, and Werner hand waving and talking at cross purpose.bohm2 said:A paper discussing whether the assumption of classicality is made by Bell is this paper by Maudin:
I don't think I'll be able either. But I also don't think that this "contextuality index", is required by the original proof.rubi said:The challange is to prove Bell's inequality with the contextuality index ##\chi## in place. You won't be able to.
Well, this is exactly the point. The original point is not concerned with contextual theories (because it tacitly suppresses the contextuality index), so a violation of Bell's inequalities says nothing about contextual theories such as QM.Boing3000 said:But I also don't think that this "contextuality index", is required by the original proof.
Well, if you attach some index to measurement results themselves then you can't get Bell inequalities. But then you are back at superpositions of Schrodinger cat states (MWI without preferred basis or something like that).Boing3000 said:But I also don't think that this "contextuality index", is required by the original proof.
Non-locality is taken just as approximation of FTL influence with very high speed. Your model of shared "variable" is just too solipsistic and too far from physics (but time to time people bring up these ideas here).Boing3000 said:I can't shake up the impression that some people don't understand why no FLT influence is a consequence of non-locality, whatever additional characteristic the candidates theories want to imbued themselves with (excluding magic of course).
I strongly disagree, on simple and straightforward logical bases. A thing that have no spatial nor temporal coordinate, cannot move nor influence nor have speed.zonde said:Non-locality is taken just as approximation of FTL influence with very high speed.
That I agree with. But that model does not pretend at all to model physical reality. It "implements" Bell's theorem logic. It is a Bell's proof "simulator", using objects made of logic(classic/not magic), stochastic(but deterministic inside, because computer cannot create true random value), classic(no complex n-dimensional space), SR compliant (no FLT influence). But then you can switch non-locality(spookiness/non-realism) on or off (uses state/value without(or with) unique "observational window").zonde said:Your model of shared "variable" is just too solipsistic and too far from physics (but time to time people bring up these ideas here).
But KS theorem already rules out any models that are non-contextual. Surely Bell's shows something further?DrChinese said:Rubi/Neumaier/Griffiths line is as follows (and I am referring to comments in concurrent threads as I do this): Bell excludes local realistic (non-contextual) theories; and QM is contextual. So a successful theory need not be non-local.
bohm2 said:But KS theorem already rules out any models that are non-contextual. Surely Bell's shows something further?
KS theorem shows that there is conflict between non-contextual HV models and QM (only theoretical argument). Bell not only shows conflict between local theories and QM but in addition opened a way how to test this conflict experimentally.bohm2 said:But KS theorem already rules out any models that are non-contextual. Surely Bell's shows something further?
How would you interpret experimental violations of Legget's inequality?DrChinese said:If you keep locality, it must be non-realistic and contextual. (I can't really envision the difference between non-realistic and contextual though.)