View Poll Results: What do observed violation of Bell's inequality tell us about nature?  
Nature is nonlocal  11  32.35%  
Antirealism (quantum measurement results do not preexist)  15  44.12%  
Other: Superdeterminism, backward causation, many worlds, etc.  8  23.53%  
Voters: 34. You may not vote on this poll 
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What do violations of Bell's inequalities tell us about nature? 
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#37
Feb1213, 09:19 AM

PF Gold
P: 691

http://arxiv.org/pdf/0808.2178v1.pdf With respect to a discussion of Bell's concept of local causality see this paper with this interesting quote: http://arxiv.org/pdf/0707.0401.pdf 


#38
Feb1213, 10:57 PM

P: 380

And from both these papers it seems that Bell presupposes that completeness holds. While at the same time Bell limits and qualifies completeness of λ to properties of candidate theories. So this is a conflict on completeness. And I cannot agree that because no local casual theory agrees with experiment that nature is nonlocal, conclusion. Rather it is that the description of λ the hidden variable that is not complete . And when it is the violations of the inequalities can be understood. And I voted to reject realism, in its limited definition 


#39
Feb1313, 09:01 AM

P: 733

Hi folks. I voted for "nonlocality". And so, incidentally, did Bell  though, being dead, he is unable to vote in this particular poll. But here are his words (from the classic paper "Bertlmann's socks and the nature of reality"):
"Let us summarize once again the logic that leads to the impasse. The EPRB correlations are such that the result of the experiment on one side immediately foretells that on the other, whenever the analyzers happen to be parallel. If we do not accept the intervention on one side as a causal influence on the other, we seem obliged to admit that the results on both sides are determined in advance anyway, independently of the intervention on the other side, by signals from the source and by the local magnet setting. But this has implications for nonparallel settings which conflict with those of quantum mechanics. So we cannot dismiss intervention on one side as a causal influence on the other." For the convenience of the people who are confused here (i.e., the people who voted that we should conclude, from Bell's theorem, that "realism" is wrong) I have bolded the relevant part of the argument above. Note that it is just the EPR argument. The point is that "realism" just means the existence of variables which determine, in advance, what the result on each side will be. What Bell points out here  and what EPR already pointed out long ago  is that such variables are (i.e., "realism" is) the *only* way to account *locally* for the perfect correlations that are observed "whenever the analyzers happen to be parallel". So the idea that we can still account for the QM predictions with a model that respects locality but denies "realism" is simply wrong. It will not, does not, and can not work. Still don't agree? Still think that one can have a local explanation of even this small subset of the quantum predictions  namely, the perfect correlations that are observed "whenever the analyzers happen to be parallel"? Let's see the model. (Note: the model should also respect the "free choice" aka "no conspiracies" assumption, if it is to be taken seriously.) This is a serious challenge. Anybody who voted for (b) in the poll evidently thinks (or at least is unwittingly committed to thinking) that these perfect correlations can be explained by a local, nonrealist model. Let's see it. 


#40
Feb1313, 09:28 AM

P: 79

@ bohm2, re your post #38
I agree with Norsen, and Bell, that it's Bell's locality condition that causes Bell's LHV formulation to be incompatible with QM and experiments, and that realism (hidden variable models) is not ruled out. Bell locality is necessarily realistic, but a realistic model need not be Bell local. We know from deBB that realism isn't ruled out. Which leaves only locality. I disagree with Norsen, and Bell, that violations of Bell's inequalities tells us anything about nature. I think that the incompatibility with QM and experiment is determined by some feature of Bell's locality condition other than the assumption of locality. 


#41
Feb1313, 09:40 AM

P: 79

On the other hand, some quantum phenomena (the physical, instrumental stuff, not the theory) do seem weird, but I wouldn't include entanglement correlations in there. [... snip nice discussion ...] So, I would change your last sentence to read: the perfect anticorrelation of paired (entangled) particles is a matter of a repeatable relationship between, and deterministic evolution of, certain motional properties of the entangled particles subsequent to their creation via a common source, their interaction, or their being altered by identical stimulii. Which doesn't seem weird to me. 


#42
Feb1313, 11:28 AM

P: 733




#43
Feb1313, 11:50 AM

Sci Advisor
P: 2,108

It's weird that distant particles would be connected in any way other than shared state information. 


#44
Feb1313, 01:36 PM

P: 79

My understanding of Bell locality is that the denotation of Bell locality in a Bell test model requires some such hidden variable, whether the definition of that hidden variable includes a denotation about precisely how the hidden variable affects individual detection or not. In other words, I would consider your example to be realistic in the same sense that Bell's λ is realistic, and therefore not a counterexample to my statement. Since Bell tests are prepared to produce outcome dependence, and since this does not necessarily inform regarding locality or nonlocality in nature, and since this might be the effective cause of the incompatibility between Bell LHVs and QM, and between Bell LHVs and experimental results, then violations of Bell inequalities don't inform regarding locality/nonlocality in nature. There is another aspect to the form that Bell locality imposes on LHV models of quantum entanglement to consider. Any Bell LHV model of quantum entanglement must necessarily denote coincidental detection as a function of the product of the independent functions for individual detection at A and B. So the relevant underlying parameter determining coincidental detection is the same underlying parameter determining individual detection. I think the underlying parameter determining coincidental detection can be viewed as an invariant (per any specific run in any specific Bell test preparation) relationship between the motional properties of the entangled particles, and therefore a nonvariable underlying parameter. I'm not sure how to think about this. Is it significant? If so, how do we get from a randomly varying underlying parameter to a nonvarying underlying parameter? 


#45
Feb1313, 02:09 PM

P: 79

Consider, for example, the polarization entangled photons created via atomic cascades. Entangled photons are assumed to be emitted from the same atom (albeit a different atom for each entangled pair). Is it surprising (weird) that their spins and therefore their polarizations would be related in a predictable way via the application of the law of conservation of angular momentum? Is it surprising that each entangled pair would be related in the same way? After all, the emission process is presumably the same for each pair, and the selection process is the same for each pair. 


#46
Feb1313, 03:19 PM

P: 733




#47
Feb1313, 03:21 PM

P: 733




#48
Feb1313, 03:44 PM

Sci Advisor
Thanks
P: 3,728

That's a trick question, of course. If you do come up with such an example I'll use it instead of Norsen's coin in his example to produce a local but not realistic model. If you can't, then I'll argue that something is wrong with your definition of realism because it includes everything. 


#49
Feb1313, 05:52 PM

P: 79

Ok, you could write A(a) = ±1 and B(b) = ±1, but then your formulation has already deviated from one of the primary requirements of the exercise aimed at finding an answer to the suggestion that QM might be made a more complete theory, perhaps a more accurate (or at least a more heuristic) description of the physical reality with the addition of supplementary 'hidden' variables. To further clarify how I'm using the terms underlying and hidden variable, underlying refers to the subinstrumental 'quantum realm' where the evolution of the 'system' being instrumentally analyzed is assumed to be occuring. Hidden variable refers to unknown variable parameter(s) or property(ies) of the quantum system being instrumentally analyzed that are assumed to exist 'out there' in the 'quantum realm' in the predetection evolution of the system. But, as I mentioned, I still have this feeling that I don't fully understand your argument against Jarrett ... but will say that if your argument is correct, then there wouldn't seem to be anything left but to conclude that nonlocality must be present in nature. (Unless the idea that this nonlocality must refer to instantaneous action at a distance is also correct, and then I have no idea what it could possibly mean.) 


#50
Feb1313, 06:11 PM

P: 733

So... anybody who talks about "realism" (and in particular, anybody who says that Bell's theorem leaves us the choice of abandoning "realism" to save locality) better say really really carefully exactly what they mean. Incidentally, equivocation on the word "realism" is exactly how muddleheaded people manage to infer, from something like the KochenSpecker theorem (which shows that you cannot consistently assign preexisting definite values to a certain set of "observables"), that the moon isn't there when nobody looks. 


#51
Feb1313, 06:12 PM

P: 79

If you think that there's something wrong with λ including anything and everything, then your argument is with Bell's formulation ... I think. 


#52
Feb1313, 06:32 PM

P: 733

http://www.scholarpedia.org/article/Bell%27s_theorem or (for more detail) this paper of mine: http://arxiv.org/abs/0707.0401 Incidentally, I think you have the wrong idea about how deBB actually works. The "quantum potential" is a kind of pointless and weird way of formulating the theory that Bohm of course used, but basically nobody in the last 2030 years who works on the theory thinks of it in those terms anymore. See this recent paper of mine (intended as an accessible introduction to the theory for physics students) to get a sense of how the theory should actually be understood: http://arxiv.org/abs/1210.7265 


#53
Feb1313, 07:20 PM

P: 733




#54
Feb1313, 07:34 PM

Sci Advisor
P: 2,108




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