Bell's Inequality: Must we ditch locality, realism or something else?

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Discussion Overview

The discussion centers on Bell's theorem and its implications for locality and realism in quantum mechanics. Participants explore whether violations of Bell-type inequalities necessitate the rejection of locality or realism, and they examine a paper that claims to present a counterexample to this assumption.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Exploratory

Main Points Raised

  • Some participants assert that Bell's theorem suggests a conflict between locality and realism, as violations of Bell's inequality have been observed in experiments.
  • Others introduce a paper claiming to provide a scenario where both locality and realism hold, yet still violate Bell-type inequalities, prompting questions about the validity of Bell's conclusions.
  • Concerns are raised regarding the credibility of the paper, with some participants noting it is a conference proceedings paper and expressing skepticism about its findings.
  • One participant mentions that the authors may be attempting to create a new characterization of local realism that could coexist with quantum mechanics, distinguishing between naive local realism and a more sophisticated version.
  • Another participant discusses the implications of time coincidence windows in experiments, suggesting that they may be crucial for understanding violations of Bell's inequalities and the relationship between classical and quantum predictions.
  • Some participants argue that previous claims of disproving Bell's theorem may not hold, emphasizing that local realism could still be valid in light of new interpretations and findings.
  • Questions arise about the nature of local realism and whether current interpretations of quantum mechanics are flawed or simply incomplete.

Areas of Agreement / Disagreement

Participants express a range of views on the implications of Bell's theorem, with no consensus reached on the validity of the paper discussed or the status of locality and realism in light of quantum mechanics. Disagreement persists regarding the interpretation of experimental results and the potential for new insights into local realism.

Contextual Notes

Participants note that the discussion involves complex interpretations of experimental setups, particularly regarding time coincidence windows, and the implications these have for understanding local realism and quantum mechanics. There is an acknowledgment of the limitations in current experimental designs and interpretations.

moving-finger
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Bell's theorem is generally thought to show that the world cannot be both local and real.

http://en.wikipedia.org/wiki/Bell's_theorem

In simplistic terms, Bell derives an inequality which allegedly must be satisfied if the world is both local and real. In practice, it is found in numerous experiments that Bell's inequality is actually violated - leading to the conclusion that either the locality assumption, or the reality assumption, (or both) must be rejected.

But the following paper allegedly provides a counterexample - a hypothetical situation which involves assumptions that are most definitely both local and real, and yet the scenario described would also violate Bell-type inequalities if analysed in a manner similar to that used for Bell's theorem.

http://rugth30.phys.rug.nl/pdf/aipqo0-KRM.pdf

Conclusion: Violation of Bell-type inequalities does not necessarily always imply that either locality or realism assumptions are incorrect?

Comments?
 
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Please provide the exact citation on where this paper was published.

Zz.
 
Appears to be a conference proceedings paper, http://rugth30.phys.rug.nl/dlm/Down7535load.htm , which is typically at best barely referreed - however the authors have published papers on related topics in journals. I would have to spend far too much time wading through the paper to understand it, never mind formulate an opinion, but I personally would be amazed if the authors have uncovered something profound that has not already been considered and discarded.
 
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ZapperZ said:
Please provide the exact citation on where this paper was published.

Zz.

ADVANCES IN QUANTUM THEORY: Proceedings of the International Conference on Advances in Quantum Theory, edited by G. Jaeger, A. Khrennikov, M. Schlosshauer, G. Weihs, (AIP Conference Proceedings, Melville and New York, 2011), vol. 1327, p. 429 - 433

Similar but much more detailed paper published here:

J. Comp. Theor. Nanosci. 8, 1011 - 1039 (2011); http://arxiv.org/abs/0901.2546
 
If anyone has time to wade through it and explain it to the rest of us, that would be great. They seem to be saying that they have a different scheme for generating Bell-type inequalities that do work for quantum mechanics, so understanding the differences between the assumptions that work and those that don't would be an interesting insight.
 
JeffKoch said:
I personally would be amazed if the authors have uncovered something profound that has not already been considered and discarded.
With respect, this reminds me of the alleged Lord Kelvin statement over 100 years ago:

"There is nothing new to be discovered in physics now, All that remains is more and more precise measurement"
 
moving-finger said:
With respect, this reminds me of the alleged Lord Kelvin statement over 100 years ago:

"There is nothing new to be discovered in physics now, All that remains is more and more precise measurement"

Yes, but more and more precise measurements drive advances in theoretical physics - and there are a lot more physicists in the world than there were in his time, armed with sophisticated experimental and computational tools. It's simply highly unlikely that they have uncovered anything that someone else hasn't already considered and discarded, and that would explain experimental results that I am not aware of - that does not make it impossible, just highly unlikely, though I would love to see a cool person in the armor of QM that might lead to something more likely to be fully correct.
 
I don't think these authors are looking for a cool person in QM with this work, I think they are looking for a better way to characterize the pedagogies that QM allows. They seem to be saying that right now all we have is a particular brand of local realism (ruled out by Bell), versus "anything else." They want to find a new version of the inequality that still holds, so they can create a third category, fully consistent with QM, that distinguishes something like "naive local realism" from "our more sophisticated version" from "what QM cannot do." If they've pulled it off, it's a valuable accomplishment, I just don't know how long, or if ever, it would take me to figure out if they did pull it off, but maybe someone can.
 
I have studied the De Raedt et al, papers extensively. We had a big discussion of them on the sci.physics.foundations newsgroup. It appears that they have successfully invalidated the EPRB type experiments with photons. If the time coincidence window is taken out of the experiments, then the experiments do not produce the QM results. They produce Bell's results. They also have a successful computer simulation that does produce QM results when a time coincidence window is used and produces Bell's results when it is not used; it is not supposed to be possible for a computer simulation to produce QM results. IMHO, they have shown that Bell's theorem does not and can not match physical reality. Not surprising since Joy Christian has also "disproved" Bell's theorem. Disproved is in quotes because you can't really disprove a mathematical theorem but what he has disproved is that Bell's theorem doesn't match physical reality same as De Raedt et al. Basically, Bell and its variants missed that you have to match pairs up in time.

Fred
 
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  • #10
So are you saying that there is a more sophisticated version of local realism, taking account of some sort of ambiguity in coincidence matching, that reality obeys, or that reality obeys the garden variety local realism and it was simply an error in interpretation of the experimental correlations that said local realism was violated? Also, are you saying that quantum mechanics is making incorrect predictions, or that it is making correct predictions but the entangled wave function is not breaking locally real constraints?
 
  • #11
QM makes the correct predictions and are backed up by Joy Christian's geometric algebra presentation. I am only saying that the experiments are probably flawed and Bell's theorem doesn't match physical reality since we have two classical examples (possibly more) that violate the inequalities. So local realism is still quite alive contrary to what has been said for a few decades now. :-) As far as EPRB type scenarios go.

Fred
 
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  • #12
QM makes the correct predictions and are backed up by Joy Christian's geometric algebra presentation. I am only saying that the experiments are probably flawed and Bell's theorem doesn't match physical reality since we have two classical examples (possibly more) that violate the inequalities. So local realism is still quite alive contrary to what has been said for a few decades now. :-) As far as EPRB type scenarios go.

Fred
 
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  • #13
OK, I'm getting that the presence of a time coincidence window is needed to get violations of Bell's inequality, and so that distinction is crucial for understanding the ability of real and computed systems to violate or not violate that inequality. What I'm not getting is how having a time coincidence window is still a version of local realism. Same with the computer codes with it-- why does such a code have to exhibit local realism? Are you saying that if we allow ourselves magical powers to match up coincidences in ways we can't actually know, then we can give ourselves the impression we have violated Bell, even when in fact we have not violated either Bell or local realism? If I have this right, does this mean QM predictions are themselves consistent with LR, or does it mean that our experiments have simply not yet probed the domain of departure?
 
  • #15
Ken G,

Yes, a time coincidence window is necessary to get violations of Bell's inequalities for the EPRB type experiments IMHO. This is what Bell and its variants missed and why they are just mathematical theorems that have not much to do with actual physical reality. QM predictions do violate Bell; but it doesn't matter because Bell doesn't really apply physically. That is what De Raedt et al, and Joy Christian have shown.

See the link that billschnieder provided plus there is a bunch more here on Physics Forums and at sci.physics.foundations if you search.

Fred
 
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  • #16
Thank you for this information. The issue seems controversial, but in an interesting way.
 
  • #17
FrediFizzx said:
It appears that they have successfully invalidated the EPRB type experiments with photons. If the time coincidence window is taken out of the experiments, then the experiments do not produce the QM results. They produce Bell's results. They also have a successful computer simulation that does produce QM results when a time coincidence window is used and produces Bell's results when it is not used; it is not supposed to be possible for a computer simulation to produce QM results.
Thanks for this, Fred.

I'm struggling to understand their work. It seems to me the time coincidence window cannot be taken out of the experiments (all work to date has relied on time coincidence to identify entangled pairs?), so their algorithms (based on local reality) can be made to match the experimental data - but I'm struggling to understand what implications their algorithms have for the kind of local reality we would have to accept. It seems their model entails a dependency on the time-separation of the measurements on entangled pairs, which seems just a little weird if its correct?
 
  • #18
FrediFizzx said:
I have studied the De Raedt et al, papers extensively. We had a big discussion of them on the sci.physics.foundations newsgroup. It appears that they have successfully invalidated the EPRB type experiments with photons. If the time coincidence window is taken out of the experiments, then the experiments do not produce the QM results. They produce Bell's results. They also have a successful computer simulation that does produce QM results when a time coincidence window is used and produces Bell's results when it is not used; it is not supposed to be possible for a computer simulation to produce QM results. IMHO, they have shown that Bell's theorem does not and can not match physical reality. Not surprising since Joy Christian has also "disproved" Bell's theorem. Disproved is in quotes because you can't really disprove a mathematical theorem but what he has disproved is that Bell's theorem doesn't match physical reality same as De Raedt et al. Basically, Bell and its variants missed that you have to match pairs up in time.

Fred
moderator sci.physics.foundations

This is an extremely complex issue, and it is going to be hard to discuss here. First, it is not at all generally accepted that Bell is anything other than rock solid. That considers the attacks by de Raedt, Christian, etc. These show up quite frequently.

Second, I have studied the de Raedt et al simulation, and in fact it does as you describe. However, it does not follow QM in that the basic Malus rule is not followed. The coincidence time window "loophole" has been closed in other experiments so I would not call this a viable model.
 
  • #19
FrediFizzx said:
...but nobody really saw Bell's mistake until now except for Jaynes. Einstein was correct after all.

Well, I will withhold judgement on this until it becomes widely accepted in the community. Even if I read and fully understood the cited references, chances are I would miss something, and the same is true for everyone else; hence, the value of consensus.
 
  • #20
JeffKoch said:
Well, I will withhold judgement on this until it becomes widely accepted in the community.

Don't hold your breath... :smile:
 
  • #21
No need for anyone to hold their breath. Bell is finished since it is only a mathematical theorem and doesn't / can't match physical reality. Jaynes saw this quite a few years ago but I suppose Bell was such a nice guy that no one sided with Jaynes. Now we have at least two classical local realistic models that produce the results of QM. What more is there to say?
 
  • #22
It would certainly help this issue with loopholes if there would be results from photon polarization Bell test with detection loophole closed.
I wonder how long it might take considering that nearly 100% efficient photon detectors where developed around one and half years ago.
http://www.nist.gov/pml/optoelectronics/detector_041310.cfm"

Even more - how long it might take if results are hmm ... not exactly those that where expected?
 
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  • #23
FrediFizzx said:
No need for anyone to hold their breath. Bell is finished since it is only a mathematical theorem and doesn't / can't match physical reality. Jaynes saw this quite a few years ago but I suppose Bell was such a nice guy that no one sided with Jaynes. Now we have at least two classical local realistic models that produce the results of QM. What more is there to say?

There's plenty to say. What you are claiming isn't a widely-held view and appears to be more of your own personal preference. Variations to the Bell-type formulation, both the multipartite GHZ model and the more extensive test of CHSH and Leggett inequality are well-tested.

Falsifying Bell's formulation should be BIG news. Something like this gets published in PRL, Nature, or Science. It is of that caliber. Where are they?

Zz.
 
  • #24
DrChinese said:
First, it is not at all generally accepted that Bell is anything other than rock solid.
Agreed. But its also true that 110 years ago, it was not at all generally accepted that Newton was anything other than rock solid.
 
  • #25
moving-finger said:
Agreed. But its also true that 110 years ago, it was not at all generally accepted that Newton was anything other than rock solid.

So this is supposed to be an attack on Bell? Sounds like an across the board attack on science to me.

Besides, I would say that Newton should rightly be offended. There is nothing "wrong" per se with Newton's work. :smile:
 
  • #26
FrediFizzx said:
No need for anyone to hold their breath. Bell is finished since it is only a mathematical theorem and doesn't / can't match physical reality. Jaynes saw this quite a few years ago but I suppose Bell was such a nice guy that no one sided with Jaynes. Now we have at least two classical local realistic models that produce the results of QM. What more is there to say?

As ZapperZ says, there is a lot more to say.

The Christian model is not realistic (despite claims to the contrary) because it cannot provide results for counterfactual observations - the DrChinese challenge.

The de Raedt et al computer simulation is "local realistic" (i.e it passed my challenge) but does not match all of the predictions of QM.
 
  • #27
zonde said:
It would certainly help this issue with loopholes if there would be results from photon polarization Bell test with detection loophole closed.
I wonder how long it might take considering that nearly 100% efficient photon detectors where developed around one and half years ago.
http://www.nist.gov/pml/optoelectronics/detector_041310.cfm"

Even more - how long it might take if results are hmm ... not exactly those that where expected?

It won't help the time coincidence problem. See De Raedt et al's, model and computer simulation.

http://rugth30.phys.rug.nl/dlm/
 
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  • #28
DrChinese said:
As ZapperZ says, there is a lot more to say.

The de Raedt et al computer simulation is "local realistic" (i.e it passed my challenge) but does not match all of the predictions of QM.

And specifically what QM predictions does it not match and why would the De Raedt et al, simulation need to match *all* of the predictions of QM? It is a classical model. One matching prediction should suffice.

Fred
 
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  • #29
DrChinese said:
The coincidence time window "loophole" has been closed in other experiments so I would not call this a viable model.
Do you have any good (read: non-crackpot) references that explain this loophole and how it was closed? Because all I can find is a bunch of fringe papers claiming to refute QM.
 
  • #30
Originally Posted by DrChinese
"The coincidence time window "loophole" has been closed in other experiments so I would not call this a viable model."

lugita15 said:
Do you have any good (read: non-crackpot) references that explain this loophole and how it was closed? Because all I can find is a bunch of fringe papers claiming to refute QM.

Probably referring to the ion trap experiment,

http://www.nature.com/nature/journal/v409/n6822/abs/409791a0.html

But I believe it had a time window of 7 ns.

However, the time coincidence problem is not a "loophole". It is one of the reasons why Bell's theorem can't make contact with physical reality. De Raedt et al, have a classical local realistic model that gives a prediction of quantum theory. So Bell is out. This however does not invalidate QM. It just means that local realism is still alive and well contrary to many that have claimed its death. As far as the EPRB type scenarios go.

Fred
 
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