Entanglement and Bell's theorem. Is the non-locality real?

by Sylvia Else
Tags: bell, entanglement, nonlocality, real, theorem
P: 29
 Quote by Greg-ulate If you set up bells experiment then you are making a cut on a statistical sample of photons which average out to be polarized in the direction of polarizer A and asking how many identical ones make it through polarizer B and its .707. Why is this surprising? How could it be any different? I feel like I'm taking crazy pills! I really can't see any reason anyone comes to the conclusion that there is something superluminal going on, especially since the correlation between A and B is not known until Alice walks over to where Bob is and they compare notes.
Did you look at this link, posting earlier by bohm2?

http://lanl.arxiv.org/pdf/1212.5214.pdf

In Bell's theorem we're not just concerned with the measurements that are actually made. We're also considering the other measurements that could have been made instead, and how nature balances its books with entangled particles so that the numbers come out right in the end regardless of which measurements we choose to make.

Bell's theorem says in essence that there is no way in which nature can achieve this if the result of a given measurement depends only on that measurement and not on the other measurement. Since measurements can be space-like separated, this means that whatever nature is doing, it cannot be mediated by light-speed influences, and thus that whatever it is must be non-local.

Sylvia.
P: 1,574
 Quote by Greg-ulate I dont understand what bells inequality is refuting. Why does local realism predict a different outcome?
I think this easy-to-understand explanation of Bell's theorem should help:
http://quantumtantra.com/bell2.html
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P: 5,055
 Quote by mbd Or, through a simple, deterministic, arguably classical, mechanism using only speed-of-light interactions as described and linked to above, but here again for convenience: https://docs.google.com/open?id=0BxB...XR2R3ExTlEyNm8 Per Occam's Razor, would you turn first to speed-of-light interactions from E to A and E to B that operate for an interval of time, or an instantaneous interaction between A and B? The former, of course. Unless you have a grant application pending for yet another EPR experiment? I've most certainly shown that the former can achieve the same results as QT and I have (you can too) tweaked the simulation to match any EPR experiment performed thus far. The simulation I provide in the paper can even be implemented in circuitry with space-like separation between A and B. It will certainly result in CHSH > 2, over a broad range of random walk step sizes of the signal from E to A and E to B as well as over a broad range of coincidence windows. In other words, I believe the game has been changed, pending experimental confirmation that nature actually works this way. But, Occam clearly suggests what experiment to do next (hint: not another traditional CHSH). Michael B Devine
Ah, you are treading into some deep water here!

If you are ready to take the DrChinese challenge, we will find out what your code is made of. To make your claim successfully, you MUST present results at a third angle other than for Alice and Bob. So we will need to see some results for Chris as well. Otherwise you fail the realism requirement.

Let me know if you are ready to go down this road. Else you will be forced to move this line of discussion elsewhere. In fact that may be necessary anyway.
 P: 53 DrChinese, you are moving the goal line! I have shown that CHSH experiments, as performed thus far, cannot rule out the mechanism I've proposed. And, I have proposed an experimental modification to CHSH to confirm or rule out this mechanism. The mechanism is most certainly local realistic. That said, I am NOT claiming that it is capable of performing everything that nature can. Further, the reason I have shared it is that I figure others may find it compelling and may want to test it, theoretically, against other phenomena. Regarding a third angle, note there are four angles in the code. Can you be more specific as to your challenge? Are you asking whether the mechanism honors Malus' Law? (it does) Lastly, your last paragraph is thoroughy rude and inappropriate. Perhaps you're reacting to my careless reference to EPR exerpiments when I meant CHSH EPR experiments?
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P: 5,055
 Quote by Greg-ulate I dont understand what bells inequality is refuting. Why does local realism predict a different outcome? The probability for a photon to pass through a polarizer is the Cos of the angle between it and the polarizer. So if you put a source of linearly polarized photons through a polarizer oriented at 45° to the axis of polarization and .707 of them go through it. If you set up bells experiment then you are making a cut on a statistical sample of photons which average out to be polarized in the direction of polarizer A and asking how many identical ones make it through polarizer B and its .707. Why is this surprising? How could it be any different? I feel like I'm taking crazy pills! I really can't see any reason anyone comes to the conclusion that there is something superluminal going on, especially since the correlation between A and B is not known until Alice walks over to where Bob is and they compare notes. About your paper, it doesn't seem to matter that E is updated in the iteration of the loop that comes before its comparison with A and B. So how does this make a comment on the speed of information travel? The simulation could be interpreted as a model of two detectors, A and B, at the same location as past E. I recreated your code in LabVIEW and I get .678 for the correlation. Is this emmitt += (2 * rand.Next(2) - 1) * Math.PI / 4; the same as emmitt += (rand.Next(4) - 1) * Math.PI / 4; which would tend to increase emmitt instead of maintaining equal probability to be negative? This seems like its measuring the probability of your random number generator to generate numbers within a certain range. Edit: Oh I see rand.Next(2) returns an integer, I get .707 now
The issue relates to values for other angles than A and B. for example, when A, B ,C are 0, 120, 240 respectively, you cannot have a data set in which the cos^2 relationship is maintained independently of selecting which 2 are being actually observed. That means the outcome is observer dependent, which violates the premise of realism. Try it with about 10 sets of triple values and you will quickly see the problem.

A. B. c.
Y n y
Y n n
N y n
Etc

Then compare ab, bc and ac. You want each to match 25% of the time as cos^2(120 degrees) is .25.
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P: 5,055
 Quote by mbd DrChinese, you are moving the goal line! I have shown that CHSH experiments, as performed thus far, cannot rule out the mechanism I've proposed. And, I have proposed an experimental modification to CHSH to confirm or rule out this mechanism. The mechanism is most certainly local realistic. That said, I am NOT claiming that it is capable of performing everything that nature can. Further, the reason I have shared it is that I figure others may find it compelling and may want to test it, theoretically, against other phenomena. Regarding a third angle, note there are four angles in the code. Can you be more specific as to your challenge? Are you asking whether the mechanism honors Malus' Law? (it does) Lastly, your last paragraph is thoroughy rude and inappropriate. Perhaps you're reacting to my careless reference to EPR exerpiments when I meant CHSH EPR experiments?
Rude, not I my friend. Forum rules are at issue, just trying to point that out. I am not an admin, so I am not the decision maker on this point. Posting unpublished assertions going against the mainstream can bring a thread to a halt. So please be careful how you say it. There are no accepted local realistic explanation for observed results of experiments. Yours does not qualify as such. And I am not the one moving the goal posts, you are. Realism implies observer independence, a key element of the Bell proof.
 P: 53 DrChinese, the model I've proposed is local realistic. It only involves speed-of-light interaction, albeit direct particle-to-particle. Physics already accepts that particles are affecting each other through fields at the speed of light. Regarding appropriateness, two participants in this thread have already run the simulation code I provided, one of them being the person who asked the original question, "is the non-locality real?", and both achieved the same results. So, I think this thread is proving to be well within the spirit of the forum. If nothing else, it serves as an illumination of the significant potential of one of the loopholes to Bell's Theorem. That alone goes well toward answering the question.
P: 713
 Quote by Sylvia Else If influences are travelling at some FTL but finite speed then it will necessarily by possible to arrange that some measurements on entangled particles are made so close together that the influence cannot arrive in time. The results would then have to respect Bell's inequality. So if entanglement is actually mediated by FTL finite speed influences, then QM is capable of being falsified, with the required experiment simply not having been done yet.
You might find this paper interesting: http://www.gap-optique.unige.ch/wiki...nal_signalling
P: 1,401
 Quote by mbd DrChinese, the model I've proposed is local realistic. It only involves speed-of-light interaction, albeit direct particle-to-particle. Physics already accepts that particles are affecting each other through fields at the speed of light.
I do not see any good proof that the model is indeed realistic. The method DrChinese proposed is the standard way of checking whether it is. This is not moving the goal line by any means. We have seen like 50 to 60 proposals for local realistic models in these forums over the past few years which could reproduce Bell experiments or CHSH experiments for two angles. Some of these proposals contained simple errors in the code, but most of them indeed could not give results when picking three different angles and turned out to be not realistic. So unless you can indeed show that your code works for three arbitrary angles, you have not shown anything interesting so far. It is just a fact that many models, which seem realistic, are in fact not. So you need to rule that out.

Even so, these forums are not the right place for pushing personal theories.
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P: 5,055
 Quote by mbd DrChinese, the model I've proposed is local realistic. It only involves speed-of-light interaction, albeit direct particle-to-particle. Physics already accepts that particles are affecting each other through fields at the speed of light. Regarding appropriateness, two participants in this thread have already run the simulation code I provided, one of them being the person who asked the original question, "is the non-locality real?", and both achieved the same results. So, I think this thread is proving to be well within the spirit of the forum. If nothing else, it serves as an illumination of the significant potential of one of the loopholes to Bell's Theorem. That alone goes well toward answering the question.
It is local, not realistic.

So: Loophole in Bell's Theorem is what you just said. Please indicate a suitable place your theory has been published or some other indication your ideas are generally accepted. Barring that, your ideas are inappropriate here.
 P: 53 DrChinese, I will stipulate to the fact that there may have been a slight breach of forum rules if you will accept that the consequence has been a lively discussion from which we all, including myself, have learned something? That said, it is patently unfair to single out my postings when this forum is chock full of posts with links to unreviewed, unpublished, articles on arxiv. In fact, another active thread today has multiple instances of that. Will you please inform the participants in that thread too of your objections to their behavior? http://www.physicsforums.com/showthread.php?t=482657
P: 713
 Quote by mbd DrChinese, I will stipulate to the fact that there may have been a slight breach of forum rules if you will accept that the consequence has been a lively discussion from which we all, including myself, have learned something? That said, it is patently unfair to single out my postings when this forum is chock full of posts with links to unreviewed, unpublished, articles on arxiv. In fact, another active thread today has multiple instances of that. Will you please inform the participants in that thread too of your objections to their behavior? http://www.physicsforums.com/showthread.php?t=482657
I must state that I was surprised that I was given infraction points for asking questions pertinent to an article on arxiv, to which ZapperZ and I exchanged private messages on whether peer-review is more superior to unpublished articles.
P: 53
According to definitions in Zeilinger (2010), http://www.pnas.org/content/107/46/19708.full.pdf, the mechanism I described is local and realistic:

 Realism is a world view “according to which external reality is assumed to exist and have definite properties, whether or not they are observed by someone” (22). Locality is the concept that, if “two systems no longer interact, no real change can take place in the second system in consequence of anything that may be done to the first system” (1) .
The mechanism I proposed, however, is not "local realistic" as defined in the same paper. But, "local and realistic" is not the same as "local realistic", hence the confusion here.

Zeilinger is a good example to use too because the mechanism I described can operate through the experiment - it is NOT ruled out by Zeilinger - because, in Zeilinger, the optical pathways are open, albeit changing, for the duration of the experiment.

The Zeilinger paper also contains an excellent explanation of conditional probability and bayes rule and how it leads to the necessity of closing the "freedom of choice" loophole.
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P: 5,055
 Quote by mbd DrChinese, I will stipulate to the fact that there may have been a slight breach of forum rules if you will accept that the consequence has been a lively discussion from which we all, including myself, have learned something? That said, it is patently unfair to single out my postings when this forum is chock full of posts with links to unreviewed, unpublished, articles on arxiv. In fact, another active thread today has multiple instances of that. Will you please inform the participants in that thread too of your objections to their behavior? http://www.physicsforums.com/showthread.php?t=482657
No, the issue is whether the concepts are consistent with generally accepted science. I am an advisor here, not a mentor or admin. You are discussing an issue that I follow closely, and frequently debate with folks who are still learning the the nuances of the area. For those who are asking, there is rarely an issue. For those who are telling others, you should follow established protocol.

If you will simply stop pushing your theory, defending it, explaining it, etc, all is fine. Otherwise I will report it. I, unlike you, bear no burden of proof. As I have already told you, your idea is not realistic. I have also defined, for your example, what realism would require. And you have already been told by a second advisor who is knowledgeable that this is standard science.

The OP asked is nonlocality real. It may be. Otherwise, locality is not realistic. This is Bell.
 P: 53 The December issue of Physics Today demonstrates that there is no prevailing view on many of these issues. In particular, see the responses to Mermin's excellent commentary on conditional probability that appeared in the July issue. In any case, it is most definitely NOT a consensus viewpoint to say that a realistic system is one in which outcomes of a measurement are observer-independent. To say so conflates the measurement problem with realism. A system can be realistic whether or not you are able to glean perfect, or no, information from it, and whether or not doing so impacts or does not impact the system.
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