Local realism ruled out? (was: Photon entanglement and )

[akhmeteli]

Why don't you start a separate thread on the subject? Then we could discuss the evidence for your perspective.

Thank you for the suggestion. I should say this is the first thread I am starting since I joined physics forums four years ago.

So this thread has branched from another one -"Photon entanglement and fair sampling assumption". I noted there that, on the one hand, so far no experiments demonstrating violations of the Bell inequalities have been free from some significant loopholes, such as the detection loophole and the locality loophole, on the other hand, the proof of the Bell theorem uses two mutually contradictory results/assumptions of quantum theory: unitary evolution and the projection postulate. Therefore, I argued, the Bell theorem is on a shaky ground both on the theoretical and on the experimental level. I was not taking sides with or against local realism, but pointed out that it has not been ruled out, however prevalent the opposite point of view can be.

My posts followed in part those of nightlight, and I did not offer any original research (otherwise the posts would have been inappropriate for this forum). These issues were also discussed in some prevous threads (https://www.physicsforums.com/showthread.php?t=245242 and https://www.physicsforums.com/showthread.php?t=230461 ).

My posts were criticized by knowledgeable opponents, but I'd say until recently their factual basis was not challenged. So I'll start with replying to DrChinese's posts

Apparently not as well known as you seem to think. I probably saw 10 papers last year on that subject (measurement problems), compared to perhaps 1000 on entanglement. So I would say the problem you identify is much less of a problem for the practicing physicist than you suggest.

I was not trying to say that the measurement problem is more or less important than, say, entanglement. All I was saying it is not some problem that arose yesterday, let alone was first raised by me. In this respect it is indeed "well-known" (Google gives 184000 links for the exact phrase "measurement problem in quantum mechanics", which is, by the way, pretty much the same as the result for "quantum entanglement" - 194000).

I'll try to reply to other DrC's remarks later.

 

[ZapperZ]

I had just posted this reference in another thread, but maybe you should read it to if you're not aware of it.

M.D. Reid et al. Rev. Mod. Phys. v.81, p.1727 (2009).

If you think that none of the violation of EPR/Bell, GHZ, CHSH, Leggett, etc. inequalities constitutes a violation of local realism, then you ARE proposing something that is not already established. This means that you need to back this up with a published work to support that you are not proposing your own personal theory.

Zz.

 

[DrChinese]

My posts were criticized by knowledgeable opponents, but I'd say until recently their factual basis was not challenged. So I'll start with replying to DrChinese's posts

I was not trying to say that the measurement problem is more or less important than, say, entanglement. All I was saying it is not some problem that arose yesterday, let alone was first raised by me. In this respect it is indeed "well-known" (Google gives 184000 links for the exact phrase "measurement problem in quantum mechanics", which is, by the way, pretty much the same as the result for "quantum entanglement" - 194000).

There may be a measurement problem, but I doubt it is the problem you think it is. It is kind of like the problem of why there is more matter in the universe than anti-matter. Something it would be nice to understand, but not something that is actually in contradiction to theory.

I would say that it is NOT generally accepted that QM is inconsistent. And I would also say that it is not generally accepted that the validity (or lack thereof) of QM in any way affects the result of Bell Theorem. Generally, Bell says:

No physical theory of local Hidden Variables can ever reproduce all of the predictions of Quantum Mechanics.

So this is a direct statement that the idea left by EPR - that a local realistic explanation could mimic QM - was untenable. If you advance a local realistic theory, it WILL make predictions different than QM.

 

[akhmeteli]

I had just posted this reference in another thread, but maybe you should read it to if you're not aware of it.

M.D. Reid et al. Rev. Mod. Phys. v.81, p.1727 (2009).

If you think that none of the violation of EPR/Bell, GHZ, CHSH, Leggett, etc. inequalities constitutes a violation of local realism, then you ARE proposing something that is not already established. This means that you need to back this up with a published work to support that you are not proposing your own personal theory.

Zz.

Dear ZapperZ,

Thank you for the reference. I have read the paper. I am not sure you have read it, though. I have not found anything there ruling out local realism, and a host of quotes confirming that there have been no experimental results conclusively ruling out local realism. Maybe you could indicate some specific quote?

I won't give you all the quotes here. Let me just emphasize that EPR-type experiments typically cannot rule out local realism:

"The predictions of quantum mechanics and local hidden variable theories are shown to be incompatible in Bell’s work. This is not shown by the EPR paradox."

So the experiments reviewed in the Reid's work are, strictly speaking, not relevant, as they relate to EPR.

Let me emphasize that neither the above quote rules out local realism: Reid specifically italicizes the word "predictions". As for actual experiments, I gave the quotes by Shimony and Zeilinger, confirming that no experiments "ruling out" LR have been free from loopholes. As you want more quotes:

"a conclusive experiment falsifying in an absolutely uncontroversial way local realism is still missing" (M. Genovese, Phys. Rep. 85, 166,180 (2005).)"

So there is a consensus among experts that existing experiments do not rule out local realism (and I suspect you know that). If you state the opposite (although I am almost sure you know better than that), then you are proposing your own personal theory. But you're a mentor, so that must be OK anyway:-)

 

[DrChinese]

"The predictions of quantum mechanics and local hidden variable theories are shown to be incompatible in Bell’s work. This is not shown by the EPR paradox."

So the experiments reviewed in the Reid's work are, strictly speaking, not relevant, as they relate to EPR.

Let me emphasize that neither the above quote rules out local realism: Reid specifically italicizes the word "predictions". As for actual experiments, I gave the quotes by Shimony and Zeilinger, confirming that no experiments "ruling out" LR have been free from loopholes. As you want more quotes:

"a conclusive experiment falsifying in an absolutely uncontroversial way local realism is still missing" (M. Genovese, Phys. Rep. 85, 166,180 (2005).)"

So there is a consensus among experts that existing experiments do not rule out local realism (and I suspect you know that)...

You are misreading the quotes to your own position, there is NO SUCH CONSENSUS. Do you think there are any loophole free experiments for gravity? Or the speed of light in a vacuum? These are subjects that are in fact debated. However, the consensus is that a) we have a good theory for gravity; b) we know the speed of light in a vacuum; and c) Bell's Theorem is valid.

Read Genovese's statement again (which by the way is 5 years old), he uses 3 adjectives (conclusive, absolutely, uncontroversial) because there are some people - perhaps you are one - who cannot accept evidence that contradicts your world view. You are actually presenting NOTHING in support of your position.

In probably 500+ papers in the past year alone, there are references to Bell's Theorem and EPR. These are accepted. The work on the so-called loopholes is more in analogy to finding the 5th decimal place to a number we already know to 4 decimal places. There are only a handful of working physicists still working on local realistic theories today, and that is precisely because of the convincing nature of the evidence.

A better reference from you would show a specific case in which a quantum mechanical prediction for an entangled system was wrong, and the local realistic counterpart was right.

 

[akhmeteli]

1. QM is not considered self contradictory, although a lot of folks don't like the collapse rules. But that is 100% irrelevant to Bell's Theorem, which merely points out that the predictions of QM and LR are different in specific areas. One has nothing to do with the other, and it is plain wrong to say "Bell is inconsistent because QM is inconsistent".

DrChinese, let us try to sort it out. First, let me emphasize that my statement on the contradiction between unitary evolution (UE) and the projection postulate (PP) is not new, furthermore, it was published in peer-reviewed journals. Therefore, it’s not some independent research and thus does not break the forum’s rules. To prove this, I don’t need to prove that QM is generally considered self-contradictory, I just need to give a reference: L.E. Ballentine, Found. Phys., vol. 20, p. 1329 (1990). Of course, that does not necessarily mean Ballentine is correct. However, you don’t seem to challenge the statement that UE and PP are mutually contradictory (if you do, please advise). My reasoning was that PP introduces irreversibility, whereas UE cannot produce irreversibility.

Now, I am afraid I have to disagree that “that is 100% irrelevant to Bell's Theorem”. I explained how it is relevant: in fact, the proof of the Bell’s theorem significantly uses both UE (as the spin projections are conserved) and PP (to calculate the correlations in QM and prove that QM can indeed violate the Bell inequalities. Thus, I am not sure “it is plain wrong to say "Bell is inconsistent because QM is inconsistent"”. I gave you my reasoning, but I haven’t seen yours so far.

I’ll try to reply to your other remarks later.

 

[ZapperZ]

This is utterly confusing.

First, you argue that Bell, etc. theorem does NOT rule out local realism.

Then you argue that even if they did, the absence of loophole-free experiments would not rule out local realism anyway!

I've already address the latter in a previous post when I complaint that people like you can't seem to accept that both the locality loophole and the detection loophole have been closed separately, and that the SHEER VOLUME OF EVIDENCE alone from each one of them make for a very compelling indication for ruling out local realism.

As for the former, each time an argument is presented on the logical deduction of Bell theorem as not being able to test local realism, it has been shot down. The most recent one, from a month ago, appeared in AJP. A paper by Guy Blaylock argued that both the EPR paradox and Bell's inequality fall short in testing the issue of locality[1]. This was summarily shot down in the SAME issue[2].

THIS is what I wanted you to do, i.e. publish your argument regarding your stand that all of these quantitative tests of local realism doesn't actually test local realism or rule them out. All of the EPR-type test papers have argued for that, and yet, you haven't written either a rebuttal or any papers to counter that. The fact that such an argument still may qualify as a paper, even if it is in AJP, implies that this is a new and not generally accepted argument, and thus, should NOT be done in PF until your proposition has been published.

Zz.

[1] G. Blaylock, Am. J. Phys. v.78, p.111 (2010).
[2] T. Maudlin, Am. J., Phys. v.78 p.121 (2010).

 

[zonde]

All of the EPR-type test papers have argued for that

Either this is plain wrong or I have misunderstood the statement (all papers argue that particular experiment rule out local realism).

From G.Weihs et al paper:
"While our results confirm the quantum theoretical predictions, we admit that, however unlikely, local realistic or semi-classical interpretations are still possible. Contrary to all other statistical observations we would then have to assume that the sample of pairs registered is not a faithful representative of the whole ensemble emitted."

 

[ZapperZ]

Either this is plain wrong or I have misunderstood the statement (all papers argue that particular experiment rule out local realism).

From G.Weihs et al paper:
"While our results confirm the quantum theoretical predictions, we admit that, however unlikely, local realistic or semi-classical interpretations are still possible. Contrary to all other statistical observations we would then have to assume that the sample of pairs registered is not a faithful representative of the whole ensemble emitted."

But that paper IS trying to argue for it based on the principle that it is trying to test or demonstrate. The inability to make a slam-dunk closure on local realism in that case is not based on the intrinsic property of the inequality, as what is trying to be argued in this thread, but rather the inability to close all the loopholes. Note also that there are various classes of local realism, one of which was definitely falsified via the most recent test of the Leggett's inequality.

The point here is that this thread appears to indicate that even IF all the loopholes are closed (and I will make MY prediction here that in the near future, say within 3 years, ALL the loopholes will be closed in one single experiment), the intrinsic nature of the theory will STILL not falsify local realism.

Zz.

 

[zonde]

The inability to make a slam-dunk closure on local realism in that case is not based on the intrinsic property of the inequality, as what is trying to be argued in this thread, but rather the inability to close all the loopholes.

Basically you are saying that the problem is not in theory but rater that we have not yet done what should be possible do based on what theory says, right?

 

[ZapperZ]

Basically you are saying that the problem is not in theory but rater that we have not yet done what should be possible do based on what theory says, right?

Maybe, but I'm already quite convinced. It takes such a tremendous amount of coincidence for (i) ALL (and I mean 100%) of the experiments to violate those inequalities and (ii) different experiments that closed different loopholes all come up with the same, identical conclusions. And these experiments are being done with greater and greater precisions with ridiculous standard deviation confidence.

Zz.

 

[DrChinese]

From G.Weihs et al paper:
"While our results confirm the quantum theoretical predictions, we admit that, however unlikely, local realistic or semi-classical interpretations are still possible. Contrary to all other statistical observations we would then have to assume that the sample of pairs registered is not a faithful representative of the whole ensemble emitted."

The Unfair Sampling Assumption is that discovery of an unfair sample can save local realism. Keep in mind even that is speculative. What if the unfair sample did not trend from local realism to QM? Perhaps even larger violations of Bell's Inequality would be seen instead. Heh.

Please note the words he uses: "however unlikely". That pretty much sums it up. A lot of things are unlikely but possible. The sun could burn out tomorrow. That does not mean that scientists are unsure whether the sun will shine tomorrow. So, let's use language fairly. Bell is accepted, and so are Bell test results.

 

[yoda jedi]

why the glue ?

LOCAL REALISM ruled out?

"which concept, locality or realism, is the problem?"

 

[Dmitry67]

none.
they are just inconsistent
local non-realistic theory or non-local realistic theory (or local realistic theory with backward causality - TI)

 

[DrChinese]

why the glue ?

LOCAL REALISM ruled out?

"which concept, locality or realism, is the problem?"

Welcome to PhysicsForums, yoda jedi!

It is not clear whether it is realism, locality, or both which are ruled out. We simply know from Bell's Theorem and others, coupled with experimental verification, that at least one does not hold.

 

[Count Iblis]

The http://arxiv.org/abs/0908.3408" won't be ruled out anytime soon.

 

[Matterwave]

Welcome to PhysicsForums, yoda jedi!

It is not clear whether it is realism, locality, or both which are ruled out. We simply know from Bell's Theorem and others, coupled with experimental verification, that at least one does not hold.

It could also be that induction fails. But if we do that, we would hafta get rid of almost all of science, so let's not.

 

[akhmeteli]

This is utterly confusing.

First, you argue that Bell, etc. theorem does NOT rule out local realism.

Dear ZapperZ,
I am afraid you may have misunderstood me. That means I was not clear enough. My reasoning was quite different. I concede that the Bell theorem (BT) per se rules out local realism (LR) (assuming that all predictions of standard QT are correct, and with the standard caveat on superdeterminism). I also concede that no LR theory can reproduce ALL results of standard quantum theory (QT). However, I argued that this does not mean LR is ruled out as 1) BT proof requires using mutually contradictory assumptions, and 2) standard QT includes mutually contradictory assumptions (in both cases the contradictory assumptions are UE and PP). Indeed, you cannot reasonably argue that the failure to absorb contradictions rules out LR. I argue that it’s good for LR that it cannot absorb them, and it’s bad for standard QT that it can. Further, as we cannot have both UE and PP as precise results, I expressed my opinion that PP cannot be precise, while it looks like UE is indeed precise.

Then you argue that even if they did, the absence of loophole-free experiments would not rule out local realism anyway!

Again, this is an unfortunate misunderstanding. Looks like I was not clear enough again. In fact, I concede that if BT ruled out LR, then loophole free experiments would indeed rule out LR (I won’t repeat the caveat on determinism in the future), because I concede that the Bell inequalities cannot be violated in any LR theory.

Let me summarize. I think you’ll agree that to rule out LR you necessarily need two things together: 1) mathematical proof that some results predicted by QT cannot be reproduced by any LR; 2) experimental proof that one of such predictions is indeed correct. I argue that, on the one hand, there is no such mathematical proof, as a proper mathematical proof cannot use two mutually contradictory assumptions, and there is no such experiment. Therefore, I argue, LR has not been ruled out so far. Furthermore (and here I speculate), I suspect that loophole free experiments would have ruled out UE, so I suspect our points of view are much closer than it looks, as it seems we both swear by unitary evolution.

I've already address the latter in a previous post when I complaint that people like you can't seem to accept that both the locality loophole and the detection loophole have been closed separately, and that the SHEER VOLUME OF EVIDENCE alone from each one of them make for a very compelling indication for ruling out local realism.

ZapperZ, I further concede that the loopholes have been closed separately. This is enough for you (although I gave my reasons to believe you’re not quite happy with that), but that is not quite enough for Shimony, Zeilinger and other experts, and it’s definitely not enough for me. Recently I offered you (okay, here I am cutting some corners) to indicate the difference between your reasoning and the following one: planar Euclidian geometry is wrong because it predicts that the sum of angles of any triangle is 180 degrees, whereas experiments demonstrate with confidence of 300 sigmas or more that the sum of angles of a quadrangle and a triangle on a sphere are not equal to 180 degrees. I may have missed something, but I don’t think I’ve heard from you about that. It’s a theorem, for crying out loud! The same is true for BT: you have not even started to test it until you have made sure ALL its assumptions are fulfilled, and fulfilled simultaneously!

As for the former, each time an argument is presented on the logical deduction of Bell theorem as not being able to test local realism, it has been shot down. The most recent one, from a month ago, appeared in AJP. A paper by Guy Blaylock argued that both the EPR paradox and Bell's inequality fall short in testing the issue of locality[1]. This was summarily shot down in the SAME issue[2].

As I concede that the Bell inequalities cannot be violated in LR theories, the papers you quote do not seem relevant.

THIS is what I wanted you to do, i.e. publish your argument regarding your stand that all of these quantitative tests of local realism doesn't actually test local realism or rule them out. All of the EPR-type test papers have argued for that, and yet, you haven't written either a rebuttal or any papers to counter that. The fact that such an argument still may qualify as a paper, even if it is in AJP, implies that this is a new and not generally accepted argument, and thus, should NOT be done in PF until your proposition has been published.

Zz.

[1] G. Blaylock, Am. J. Phys. v.78, p.111 (2010).
[2] T. Maudlin, Am. J., Phys. v.78 p.121 (2010).

When you say such things, I feel somewhat confused. I had no intention to break the forum’s rules. Furthermore, to be on the safe side, I obtained a mentor’s permission to start this thread. If, however, you tell me, in your capacity of mentor, that my posts are inappropriate, I’ll certainly obey and stop discussing this topic. If, however, you, as a mentor, believe that my posts are appropriate, then the reference to the forum rules seems somewhat irrelevant.
On the other hand, I believe everything or almost everything I am saying was previously published by others in peer-reviewed journals, so I honestly don’t know what I could publish (even if I wanted to forget that I am mostly following nightlight’s reasoning).

 

[ZapperZ]

Dear ZapperZ,
I am afraid you may have misunderstood me. That means I was not clear enough. My reasoning was quite different. I concede that the Bell theorem (BT) per se rules out local realism (LR) (assuming that all predictions of standard QT are correct, and with the standard caveat on superdeterminism). I also concede that no LR theory can reproduce ALL results of standard quantum theory (QT). However, I argued that this does not mean LR is ruled out as 1) BT proof requires using mutually contradictory assumptions, and 2) standard QT includes mutually contradictory assumptions (in both cases the contradictory assumptions are UE and PP). Indeed, you cannot reasonably argue that the failure to absorb contradictions rules out LR. I argue that it’s good for LR that it cannot absorb them, and it’s bad for standard QT that it can. Further, as we cannot have both UE and PP as precise results, I expressed my opinion that PP cannot be precise, while it looks like UE is indeed precise.

This only adds to the confusion. By saying " ... 1) BT proof requires using mutually contradictory assumptions, and 2) standard QT includes mutually contradictory assumptions (in both cases the contradictory assumptions are UE and PP)... , you are explicitly stating that there's a logical inconsistency with both theories! Isn't that what I've been saying all along of YOUR position? What am I missing here?

Secondly, can you cite explicit references where the same argument has been made with regards to both Bell theorem and QM. I mean, of all the intelligent people (some of which, you cited) who are looking into this, I can't believe that this issue has been missed by them. If they did, then this would be MY argument on why you are doing this here and not pointing this "important" aspect of both theories in a journal.

Zz.

 

[DrChinese]

Let me summarize. I think you’ll agree that to rule out LR you necessarily need two things together: 1) mathematical proof that some results predicted by QT cannot be reproduced by any LR; 2) experimental proof that one of such predictions is indeed correct. I argue that, on the one hand, there is no such mathematical proof, as a proper mathematical proof cannot use two mutually contradictory assumptions, and there is no such experiment. Therefore, I argue, LR has not been ruled out so far. Furthermore (and here I speculate), I suspect that loophole free experiments would have ruled out UE, so I suspect our points of view are much closer than it looks, as it seems we both swear by unitary evolution.

Your position is fairly illogical and you should already know that from what has been said. There is no requirement that QM resolve anything for Bell to apply. And to make that even more clear, consider this:

1) Is there anything inconsistent or contradictory about Malus' Law? Obviously not. Then "presto" I have a new version of the Bell Theorem that says:

No physical theory of local Hidden Variables can ever reproduce all of the predictions of Malus' Law.

2) So now every Bell test still rules out local realism, just as before. QED.

You are quibbling in essence that QM cannot be considered a theory because it is internally inconsistent, a view which is not shared by the rest of the community. By the way, general relativity also yields inconsistent results during the very early universe. I guess by your reasoning, it should be abandoned in favor of Newtonian gravity.

Not that it matters to the application of Bell, but I would be interested in hearing a specific situation in which it is generally agreed that QM makes different predictions for the same setup. Please, make it an experiment that can be or has been performed. Then, we can ask others to judge it as to whether it makes inconsistent predictions.

 

[ThomasT]

LOCAL REALISM ruled out?

LHV theories of a particular form are ruled out. It's not clear yet whether Bell's LHV ansatz is general.

"which concept, locality or realism, is the problem?"

Neither concept is a problem. The problem is the formalization of the concept of locality. Bell's ansatz is incompatible with that of standard QM (for the joint, entangled state), and with the design of entanglement producing experiments.

 

[DrChinese]

LHV theories of a particular form are ruled out. It's not clear yet whether Bell's LHV ansatz is general.
Neither concept is a problem. The problem is the formalization of the concept of locality. Bell's ansatz is incompatible with that of standard QM (for the joint, entangled state), and with the design of entanglement producing experiments.

This gets tiring.

There is nothing wrong with the designs of the hundreds of different entanglement experiments which have been performed. These all demonstrate, using different setups and theoretical approaches, one thing: Bell Inequalities are violated wherever they are found.

There is currently NO local realistic theory in consideration - anywhere - which can reproduce all of the predictions of QM. There are a few people who are working on TRYING to create such a theory, and there is one in process I know of which is local realistic but contextual (thereby avoiding the Bell requirements). The reason there aren't any LHV candidates currently is simple: they keep getting knocked out by Bell tests. Once Bell showed us the way, scientists have been able to design new and improved ways to find and demonstrate entanglement - which BY DEFINITION does not exist in LHVs (since the correlations are thought to be spurious).

Here is one for you: model how an LHV produces entanglement for particles which have never interacted.

Non-local generation of entanglement of photons which do not meet each other

 

[MaxwellsDemon]

If I have to choose between a universe without locality or a universe without realism, I choose to get rid of locality. I was never too attached to it anyway. Good riddance. :) Would it really be such a terrible thing to abandon a local description of physical phenomena?

 

[ZapperZ]

If I have to choose between a universe without locality or a universe without realism, I choose to get rid of locality. I was never too attached to it anyway. Good riddance. :) Would it really be such a terrible thing to abandon a local description of physical phenomena?

Well then, you may have a rough time. Tony Leggett has arrived at a rather elaborate argument that, even if you relax the locality requirement, one still cannot rescue realism unless one is willing to sacrifice, among other things, the arrow of time. See this:

https://www.physicsforums.com/showpost.php?p=1599072&postcount=62

and this:

https://www.physicsforums.com/showpost.php?p=1518312&postcount=57

and one more:

https://www.physicsforums.com/showpost.php?p=1307660&postcount=40

Zz.

 

[Maaneli]

Well then, you may have a rough time. Tony Leggett has arrived at a rather elaborate argument that, even if you relax the locality requirement, one still cannot rescue realism unless one is willing to sacrifice, among other things, the arrow of time. See this:

https://www.physicsforums.com/showpost.php?p=1599072&postcount=62

and this:

https://www.physicsforums.com/showpost.php?p=1518312&postcount=57

and one more:

https://www.physicsforums.com/showpost.php?p=1307660&postcount=40

Zz.

That's not quite right. Leggett refers to "classical realism", which refers to the notions of realism in ontological (LCHV or NLCHV) theories that maintain NON-CONTEXTUALITY, and it is those such theories that are ruled out by the experiments he discusses (ignoring the detection loopholes, of course). Realism is perfectly safe however within a nonlocal, contextual, and causal HV theory (e.g. de Broglie-Bohm theories, stochastic mechanical theories, GRW and SCL theories, etc.). And yes, even Leggett acknowledges this distinction in his papers.

 

[ZapperZ]

That's not quite right. Leggett refers to "classical realism", which refers to the notions of realism in ontological (LCHV or NLCHV) theories that maintain NON-CONTEXTUALITY, and it is those such theories that are ruled out by the experiments he discusses (ignoring the detection loopholes, of course). Realism is perfectly safe however within a nonlocal, contextual, and causal HV theory (e.g. de Broglie-Bohm theories, stochastic mechanical theories, GRW and SCL theories, etc.). And yes, even Leggett acknowledges this distinction in his papers.

"Quantum realism", if you want to call it that, was never in question, nor is there any falsifiable experiment to distinguish between all the different flavors. These experiments do not contradict anything about the superposition property.

I believe the "many worlds" and "Bohm-De Broglie" followers have their own thread to play with already in this forum. The issue so far has always been classical realism or macrorealism.

Zz.

 

[Maaneli]

"Quantum realism", if you want to call it that, was never in question,

But in referring to Leggett's work, you didn't make a distinction between "classical" and "quantum" realism (which Leggett does), you just generically referred to "realism". So it was necessary for someone else to make the distinction.

nor is there any falsifiable experiment to distinguish between all the different flavors.

True, not yet, but there are proposals for such experiments in the near future.

These experiments do not contradict anything about the superposition property.

This isn't relevant to anything I said.

I believe the "many worlds" and "Bohm-De Broglie" followers have their own thread to play with already in this forum.

So? It's still relevant to mention the latter theory in the context of discussing Leggett's work, and in particular, when discussing what types of "nonlocal real" theories are and are not ruled out by current experiments.

 

[ZapperZ]

But in referring to Leggett's work, you didn't make a distinction between "classical" and "quantum" realism (which Leggett does), you just generically referred to "realism". So it was necessary for someone else to make the distinction.

Not in the context of this thread. Furthermore, using the term "realism" as applied to this particular area of study to imply classical realism is done all the time without any confusion. See a related article covering the SAME set of reports:

http://physicsworld.com/cws/article/news/27640

So I'm not the only one doing this, and various other papers dealing with "realism" have expressed the same thing. How come you didn't write a rebuttal on those?

If all we are doing here is nitpicking on semantics, I'm done, because this is a waste of time.

Zz.

 

[MaxwellsDemon]

Hmm...interesting...especially the part regarding the arrow of time... I'll have to check out those links tomorrow when I get some free time so I can let you know what I think. :)

 

[Maaneli]

Not in the context of this thread. Furthermore, using the term "realism" as applied to this particular area of study to imply classical realism is done all the time without any confusion. See a related article covering the SAME set of reports:

http://physicsworld.com/cws/article/news/27640

So I'm not the only one doing this, and various other papers dealing with "realism" have expressed the same thing.

I disagree. You replied to someone's suggestion that locality is worth sacrificing for realism, with the claim that Leggett's work shows that even "realism" (no qualifications given about contextuality or non-contextuality) is not tenable without sacrificing another intuitively plausible assumption. But that characterization of Leggett's work is simply not accurate, which anyone can see by reading those abstracts you linked to. And I don't even think that's true that everyone in this field agrees that the word realism is used to imply classical realism, and that this is done without any confusion. I know several active researchers in this field who would dispute the validity of your use of terminology. Moreover, the link you gave to try and support your claim, doesn't actually do that. If you read your own link, you'll see that everything Aspelmeyer and Zeilinger conclude about realism from their experiment is qualified in the final paragraph:

However, Alain Aspect, a physicist who performed the first Bell-type experiment in the 1980s, thinks the team's philosophical conclusions are subjective. "There are other types of non-local models that are not addressed by either Leggett's inequalities or the experiment," he said.

So Aspect is clearly indicating that Aspelmeyer and Zeilinger's use of the word "realism" is intended in a broader sense than Leggett's use of the term "classical realism".

If all we are doing here is nitpicking on semantics, I'm done, because this is a waste of time.

It's not nitpicking on semantics, it's getting the physics straight. If that's too difficult for you to do, then I'm sorry, but maybe you're just not cut out for this thread.

 

[akhmeteli]

This only adds to the confusion. By saying " ... 1) BT proof requires using mutually contradictory assumptions, and 2) standard QT includes mutually contradictory assumptions (in both cases the contradictory assumptions are UE and PP)... , you are explicitly stating that there's a logical inconsistency with both theories! Isn't that what I've been saying all along of YOUR position? What am I missing here?

Your question seems to suggest that my phrases you quote contradict something else I wrote. What is this “something else” exactly? If it is my words that “I am not sure I have problems with the Bell theorem” (I said it long ago), then I explained that I don’t see any holes in the proof, but I believe its assumptions are mutually contradictory. The theorem is just a ”messenger” of standard quantum theory (and we should not kill a messenger:-) ), it does us a great service by pushing the assumptions of SQM to the extreme and thus baring its problems. I emphasize that I fully accept unitary evolution of quantum mechanics, the only thing I have problems with is the projection postulate, which, on the one hand, has limited experimental basis (M. Schlosshauer, Annals of Physics, 321 (2006) 112-149), on the other hand, it explicitly introduces nonlocality, and last, but not least, contradicts UE.

Secondly, can you cite explicit references where the same argument has been made with regards to both Bell theorem and QM. I mean, of all the intelligent people (some of which, you cited) who are looking into this, I can't believe that this issue has been missed by them. If they did, then this would be MY argument on why you are doing this here and not pointing this "important" aspect of both theories in a journal.

I don’t have a reference “where the same argument has been made with regards to BOTH Bell theorem and QM”, though I cannot be sure it does not exist. The contradiction between UE and PP is well-known though. See e.g. http://plato.stanford.edu/entries/qt-measurement/ and references there. For example, the quote from Albert’s book there: “The dynamics and the postulate of collapse are flatly in contradiction with one another ... the postulate of collapse seems to be right about what happens when we make measurements, and the dynamics seems to be bizarrely wrong about what happens when we make measurements, and yet the dynamics seems to be right about what happens whenever we aren't making measurements. (Albert 1992, 79)”. The postulate of collapse, I believe, is pretty much the same as PP. Or, if you prefer a journal reference, see the following reference there: Bassi, A., Ghirardi, G.C., 2000, Physics Letters A, 275: 373-381 (and references there). (By the way, note that standard QT has lived happily with this contradiction for decades, and has the nerve to say that LR is untenable:-) ) So this issue "was not missed by intelligent people". The problem is, while this issue is recognized as such, people, all of a sudden, demand that LR theories faithfully reproduce this issue. This is rich!

As for what I am saying about the Bell theorem, I follow nightlight’s posts. Of course, they are no journal reference, but they were extremely useful for me, so I hope my posts can be useful for somebody else, as nightlight does not post here anymore. As for publishing, you see that I offered little if any original thinking.

Let me also quote the following work here: http://arxiv.org/PS_cache/quant-ph/pdf/0702/0702135v2.pdf (see references to their journal articles there): “The solution of our model shows that the so-called “measurement problem”, to wit, the fact that the final state … does not seem to be related unitarily to the initial state, has the same nature as the celebrated “paradox of irreversibility”, with additional quantum features. Here too, it is the large size of the apparatus which produces destructive interferences, thus generating inaccessible recurrence times; such times behave as exponentials of the level density, which itself is an exponential of the number of degrees of freedom.” This may explain how standard quantum mechanics can live with such contradiction and why PP is only an approximation. This may also explain that measurement process is relatively slow, as it requires a macroscopic system, so this may be a reason why it is both so difficult and so crucial to close all loopholes simultaneously in experiments.

 

[DrChinese]

If all we are doing here is nitpicking on semantics, I'm done, because this is a waste of time.

Zz.

I think I'm with you on that. Some people see the glass as 99.9% full. Others like to discuss the 0.1%.

akhmeteli simply ignores all experiment and theory that does not sit well, and somehow imagines that a Local Realistic theory (of which there are NONE to consider or discuss) can outperform an "inconsistent" QM. So we are arguing about the label "inconsistent" - i.e. semantics. Meanwhile, people come up with new and exciting work every day using that poor ol' inconsistent theory.

Maaneli agrees the any theory must be contextual. If someone wants to call their contextual theory "realistic" when particles clearly lack well-defined properties when not observed... I don't understand the meaning of the words the same way, which makes it an argument about semantics as well.

 

[ThomasT]

This gets tiring.

There is nothing wrong with the designs of the hundreds of different entanglement experiments which have been performed.

I didn't say there was. I said that Bell's generalized ansatz for LHV theories is incompatible with entanglement producing experimental designs. And that it's not clear yet whether his formulation is the definitively generalized form that any and all LHV theories must take.

These all demonstrate, using different setups and theoretical approaches, one thing: Bell Inequalities are violated wherever they are found.

Ok. Again, my post doesn't contradict this.

There is currently NO local realistic theory in consideration - anywhere - which can reproduce all of the predictions of QM.

Yes, this a difficult problem. And it might not have a solution. Which will mean that LHV theories of entangled states are impossible. But, establishing that definitively will require more than just Bell's Theorem, and that still wouldn't necessarily tell us anything about whether Nature is exclusively local or not.

Once Bell showed us the way, scientists have been able to design new and improved ways to find and demonstrate entanglement - which BY DEFINITION does not exist in LHVs (since the correlations are thought to be spurious).

I don't know what the last part that sentence means.

Here is one for you: model how an LHV produces entanglement for particles which have never interacted.

Same conceptual principle (and same modelling problem) as the archetypal setup -- subject the separated particles to a common torque or whatever. Spatially separated groups of many atoms have been entangled, haven't they?

And no, I can't do a viable LHV model for any of it.

Which doesn't have anything to do with what I wrote in reply to yoda jedi's question(s).

I don't see anything wrong with that reply, so I really don't know what you're on about with the this gets tiring comment. For you to reply that there's nothing wrong with the experimental designs indicates that you either misread what I wrote, or misunderstood it.

 

[akhmeteli]

2. The answer is that it doesn't convince anyone. Which explains why the LR position is completely ignored professionally except by Santos and a few others.

So going against the opponent’s weakest argument is not good enough because it does not convince anyone? So am I supposed to go against the opponent’s strongest argument, even if I agree with this argument? Strange. For example, I readily agree that LR is not popular now. But we are discussing a different issue: has it been ruled out, say, by experiments or not?

3. True, they have elevated the detection loophole to a higher status. They even published a paper with Santos on the subject. For the reasons ZapperZ explained about loopholes above, I respectfully disagree with their assessment; but I understand their position as being for the sake of bringing a final and complete end to the "loopholes" discussion. I think Santos' statement you quote is ridiculous, I have seen it before and it always makes me mad. No one is a priori ignoring hidden variables. If they existed, context free, they should be noticable and yet they never are. There is absolutely NOTHING about the setups that can be said to select a subset which is biased in any way. If such bias occurs, it must be natural and subtle (like my standard candles example). The problem with that approach is that even then, there is NO known way to get the Bell results from a biased LR sample... as we see with Santos' repeated failures. And as detection efficiency improves: the Bell result simply gets stronger in complete violation of LR predictions. And finally, there is substantial independent corroboration from other experiments.

What Santos says is: if you assume fair sampling, you pretty much rule out LHV apriori. You, however, declare fair sampling all but a ”holy cow”. You pretty much forbid me to think that a possibility of such “natural and subtle bias” has not been ruled out. I cannot accept such demand, sorry.

4. You are completely wrong again, the violations are there every time. The thing you ignore is called the scientific method. There is no requirement in the method - EVER - that all loopholes be closed simultaneously to accept the results of an experiment. I would say in fact that this almost NEVER occurs in any scientific experiment. The normal technique is to vary one variable at a time and chart relationships. That is why science accepts the Bell test results. If everyone stuck their heads in the ground until "perfect" experiments were done (as you seem to suggest), we would have no science at all.

I asked ZapperZ, let me also ask you: what’s wrong with the following reasoning: planar Euclidian geometry is wrong because it predicts that the sum of angles of any triangle is 180 degrees, whereas experiments demonstrate with confidence of 300 sigmas or more that the sums of angles of a quadrangle on a plane and a triangle on a sphere are not equal to 180 degrees. Or do you think there is nothing wrong with it? In both cases we are talking about a theorem, remember? If you have not made sure that all assumptions of the theorem are fulfilled simultaneously, you cannot demand that the statement of the theorem hold true.

While I might agree that we accept many things without “perfect experiments”, I also have to note the following. I believe you’ll agree that elimination of LR is an extremely radical idea. You may also agree that the burden of proof is much higher for extremely radical ideas. We are not talking about a 40-dollar parking ticket. This idea turns philosophy upside down. So I have the right to state that LR has not been ruled out until we have proper experimental results. OK, you are quite happy that LR has been ruled out by experiments, Shimony and Zeilinger are not quite happy, I am not happy at all. So who’s right, you or I? I think the jury is still out. And I don’t hold my breath.

5. Now you are just trying to be contradictory. You say that correlations outside of Alice and Bob's light cones are within the scope of LR? As far as I know, there has not been any attempt by a local realist to address that one. Once again, your argument circles back to "I ignore all evidence in contradiction to my viewpoint" even though this one completely contradicts every possible LR perspective.

I argue that correlations predicted using PP have not been seen without loopholes. Are you telling me that the experiments you mentioned have achieved something that experiments on Bell violations have not been able to achieve for 45 years? Then I guess I need to find out more about the experiments in question, so could you give me a reference?

6. The local realistic school, of which Einstein was a member, is virtually non-existent now. So you are wrong again. QM has more interpretations now, but they are all either non-local or non-realistic.

As I tend to think Einstein was wrong about the uncertainty principle, I am not crying for that particular school. I am not wrong about Copenhagen interpretation though. And I guess the mere coexistence of many interpretations suggests that there is no one satisfactory interpretation.

7. Of course entanglement refutes LR. That is by definition! Or more precisely, LR flatly predicts that entanglement does not exist (correlations are spurious).

I don’t know what definition you use. I thought an entangled state is anything that is not a mixture of product states. To get nonlocality from that you need the very projection postulate I am trying to offend :-) And correlations may be for real if there is any loophole:-), for example, when there is no spatial separation.

8. As with Bell, the other no-gos compare the predictions of LR with the predictions of QM. They use different techniques, and they are generally not statistical. They are instead considered "all-or-nothing" and soundly support QM. I guess you will next tell us that is even more support for LR because QM is contradictory and should not be supported.

Exactly:-) If those other no-gos use both UE and PP (or something similar to PP), any problems LR can have with those theorems are no problems at all. I should emphasize though that I fully support the unitary evolution part of QM, so if you tell me there is a no-go theorem that uses UE only and rules out LR, I am all ears.

You see, your starting premise - that QM is contradictory - flies in the face of the science of the last 100 years.

No, it does not. The quantum measurement problem is recognized as such.

While you see problems, everyone else is using the theory to make new predictions and new advances. That is because QM is useful. Now, is it also true? That is not a scientific question, it is a philosophical one. QM is a model, and should not be confused with reality. See my tag line below.

You see, I like this one about two tradesmen: one of them offered the other one raspberry jam and second-hands for watches. The other one said he would buy the jam, but is not interested in second-hands at all. The first one said: "I cannot sell you the jam without the second-hands, as the second-hands are mixed with the jam."
QM is certainly very useful, but that does not mean we cannot try to separate jam from second-hands.

 

[DrChinese]

I don't know what the last part that sentence means.

A local realist believes that the results at Alice are not dependent on the results at Bob. Therefore, any correlations between Alice and Bob must be SPURIOUS because they are both causally connected to some other (prior) event.

On the other hand, the SQM position is that the results are somehow causally connected, although there is no causality in the usual sense of the word (causes precede effects). This is simply another way of saying that there is entanglement, spooky action at a distance, etc.

Now, the reason why Bell is so important is that it gives me a way to attack ANY local realistic model. I will always know just where to look to find the Achilles Heel of any candidate theory. I simply look at how it explains entanglement. If you have read many papers on local realistic models, you know you will always find one thing: an explanation of how they (claim to) get around Bell's Theorem. And of course, they do that precisely because they know that is where they are vulnerable. Bell is the strongest argument against Local Realism.