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

[DrChinese]

What Santos says is: if you assume fair sampling, you pretty much rule out LHV apriori.

That's funny! You should really re-read what you are writing first. Poor Santos, God picks unfair samples just to ruin him personally.

The humor here has gone far enough. You already know about the evidence - over and above Bell - which independently rules out LR (GHZ, Hardy, Leggett, etc.). That doesn't matter to you though. There are no candidate local realistic theories in existence at this time. You don't even care about that.

If God came down and told you LR is wrong, you would still be looking for another loophole. I am interested in science rather than listening to you nitpicking. My discussion with you on this point has ended.

 

[yoda jedi]

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.

thanks !
answer on the right track, to alain aspect is locality.

but i think for example, the electron spin have just 2 possible values, spin-up and spin-down,
right ? then emitting a pair of electron at once, you measure first one value, right ? and then is spin down, then the other electron "have to be" spin up, they can have their values from the beginning.

excuse my english please.

 

[DrChinese]

thanks !
answer on the right track, to alain aspect is locality.

but i think for example, the electron spin have just 2 possible values, spin-up and spin-down,
right ? then emitting a pair of electron at once, you measure first one value, right ? and then is spin down, then the other electron "have to be" spin up, they can have their values from the beginning.

excuse my english please.

That was the thinking of the EPR paper, and it is very reasonable. But it turns out that the cos^2(theta) rule throws a link into things. That is what we learned from Bell's Theorem. It is a little easier to discuss photon spin than electron spin (used by Bell) because that is how most experiments are formed today.

Specifically, the problem comes at various angle settings other than 0 and 90 degrees, although you also have some problems there. Try to imagine entangled photons measured at 45 degrees apart. You would expect them, according to the cos^2(theta) rule, to be completely randomly correlated - and they are (cos^2(45 degrees) is .5). However, if you look at correlations at 22.5 degrees - half way between 0 and 45 degrees, you get something like 85% correlation. That is way too high. There is no dataset of values that is random at 0 and 45 degrees and yet has 85% correlation at 22.5 degrees. The QM answer is that there is only reality for the angles actually measured, not for hypothetical (counterfactual) cases.

I realize my example is probably not clear. But the overall ooint is, you are looking at the most simple case only, so it is no surprise that the result works for your model. But almost any other case does not work when fully analyzed.

 

[akhmeteli]

Sorry, it has taken me quite some time to reply.

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.

Sorry, there is a contradiction between UE and collapse– see references in my post 31 in this thread. It’s something that has been known since von Neumann (I was not born then, so don’t blame me).

I would say that it is NOT generally accepted that QM is inconsistent.

I gave you the reasoning, I gave you the references, it’s not my independent research or something, you don’t seem to challenge my statement that there is indeed a contradiction (if you do, please advise), so does it really matter if it is generally accepted? I tend to believe it is generally accepted, you tend to believe it is not, but do we have to waste our time deciding if it is or isn’t, unless you personally dispute it?

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.

I concede that it is not generally accepted.

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.

I prefer your original wording: “the Bell Theorem states that no LHV theory can reproduce ALL of the predictions of quantum theory”. However, as I said, this is good for LR, not bad, that it cannot reproduce contradictory statements of QM.

 

[akhmeteli]

You are misreading the quotes to your own position, there is NO SUCH CONSENSUS.

There is, sorry. I gave you the quotes by Shimony, Zeilinger, Genovese. You are just telling me that “there are hundreds of articles ruling out LR.” I am not sure you can offer a serious quote actually confirming that. The only thing that is controversial is how probable or improbable can be LR. This thread is about whether LR has or has not been ruled out. Probability is an important, but secondary issue.

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.

Again, ruling out LR is extremely radical, so the burden of proof is extremely high.

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.

He could have used seven adjectives, depending on his temperament, this does not change the essence of his statement: LR has not been ruled out (as for Genovese’s article being 5 year old, that could only matter if a loophole-free experiment had been performed since then). And I did present enough evidence to support my position. Indeed, you do not dispute that there have been no experiments without loopholes. You don’t seem to dispute that there is a contradiction between UE and PP (if you do, please give your reasoning). What else do I need to prove? Again, you can say LR is improbable, and I dispute that, but you cannot say it has been ruled out.

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.

I already offered this question: why experiments attempting to close loopholes are published in the best journals, if the evidence is overwhelming as it is? Again, your evidence is as good or as bad as my evidence that planar Euclidian geometry is wrong.

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.

I can only offer a hint. As UE and PP contradict each other, there should be possible in principle to offer an experiment where they give different results. That would be the experiment where LR would give a different prediction from that of PP as well. I speculate that the predictions of LR and UE will coincide in such an experiment.

 

[akhmeteli]

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.

How come? In your wording, the Bell theorem states that no LR theory can mimic ALL predictions of QT. Until QT is free of contradictions, this cannot rule out LR: indeed, you just cannot demand with a straight face that a theory faithfully reproduce mutually contradictory predictions. So QT better sort out its own problems first, otherwise it’s a pot calling a kettle black.

And to make that even more clear, consider this:

1) Is there anything inconsistent or contradictory about Malus' Law? Obviously not.

Not so fast, please. Neither is PP per se inconsistent or contradictory. However, PP is inconsistent with UE, and PP and UE are mutually contradictory. Actually, as far as I understand, in the context of the Bell experiment, the Malus law and PP give the same result, therefore, strictly speaking, the Malus law is in contradiction with UE. Indeed, UE cannot turn a superposition into a mixture of states. Therefore, the rewording you offer does not change anything

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.

I did not use quite that wording, I said that standard QT contains mutually contradictory assumptions. Maybe this is pretty much the same, but I still prefer this wording. As for incompatibility between UE and PP, I believe it is recognized. I gave you the references to work on quantum measurement problem. As I said, it is not a question of this being generally accepted or not. Do you personally agree with that or not? In essence, I guess you appreciate that a superposition cannot “unitarily evolve” into a mixture of states. Do you challenge that? Do you challenge my reversibility reasoning? Do you challenge the Bassi article? Please advise, and then we’ll either consider your objections, or agree on this issue.

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.

You see, I know next to nothing about gravity, but if general relativity is indeed inconsistent, it will eventually be replaced by a better theory. However, as far as Newtonian gravity is concerned, there is a difference between the situation you describe and the situation with LR and QT. Indeed, Newtonian gravity is a reasonably well-defined theory, and experiments demonstrate deviations from its predictions. However, it is really difficult to rule out the incredibly wide class of LR theories.

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.

As I said, the contradiction between UE and PP suggests that it will be possible in principle to perform an experiment for which UE and PP give differing predictions. I cannot offer any specifics right now. I can even imagine that this can be as difficult as proving reversibility, which, however, is a direct consequence of UE. Do you really think that UE does not always hold? I guess the Schlosshauer article is relevant (I gave the reference in post 31 in this thread). His conclusions are:
(i) the universal validity of unitary dynamics and the superposition principle has been confirmed far into the mesoscopic and macroscopic realm in all experiments conducted thus far;
(ii) all observed ‘‘restrictions’’ can be correctly and completely accounted for by taking into account environmental decoherence effects;
(iii) no positive experimental evidence exists for physical state-vector
collapse;
(iv) the perception of single ‘‘outcomes’’ is likely to be explainable through decoherence effects in the neuronal apparatus.

Another thing. I speculate that there will be no violations of the Bell inequalities in loophole-free experiments.

 

[MaxwellsDemon]

So our conclusion here is either locality or realism or both must be abandoned or quantum mechanics is just plain wrong. (Its highly unlikely quantum physics is just plain wrong since it makes so many verified testable predictions) I wonder if entaglement would be a "problem" in general relativistic quantum mechanics. I mean our current theory must be wrong in some ways since it doesn't take general relativity into account. Still, if it is, I say we abandon locality. That might be a problem for reductionism though. If you can't describe basic physics in terms of local things, then it might be tough to describe the universe in terms of the sum of its parts interacting. Getting rid of locality might give us some deeper insight into the way our universe works though...specifically I'm thinking of something like Mach's principle where mass here is somehow dependent and defined by the existence of other objects out there.

 

[PTM19]

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.

I just want to clarify that the above is true when locality is defined in terms of the speed of light. This may be the common usage but in general the concept of locality is independent of any particular speed limit it only requires that some limit does exist.

In the general sense local realistic hidden variable theories which reproduce QM are still possible. Experiments can never rule out this kind of locality, they can only place lower bounds on maximum signal propagation speed required to maintain locality.

 

[DrChinese]

I just want to clarify that the above is true when locality is defined in terms of the speed of light. This may be the common usage but in general the concept of locality is independent of any particular speed limit it only requires that some limit does exist.

In the general sense local realistic hidden variable theories which reproduce QM are still possible. Experiments can never rule out this kind of locality, they can only place lower bounds on maximum signal propagation speed required to maintain locality.

Just to put this argument in perspective: the current experimental lower bound is somewhere between 10,000 and 10,000,000 times the speed of light. The difference has to do with assumptions about the movement of the Earth through space. Either way, it far exceeds c.

Since c more or less defines relativistic constraints and defines what locality is, I would not call such a solution a local realistic one. It is a non-local one, such as Bohmian Mechanics. There are also true local solutions in which there is causal time symmetry (such as Relational BlockWorld, Cramer's, etc.). These are contextual so I would say they are not Bell realistic.

 

[Dmitry67]

I believe that Transactional Interpretation is an example of LR theory. But as it is explicitly retrocasual it does not help to recover a dream of local realists - to restore some Newtonian-like theory, just with different formulas.

Am I right? How could one explain these desperate attempts to find a loophole, over and over again?

 

[akhmeteli]

That's funny! You should really re-read what you are writing first. Poor Santos, God picks unfair samples just to ruin him personally.

Do you think I misrepresented Santos' position?

Again, for you the fair sampling assumption is a holy cow, but it isn't for me.

The humor here has gone far enough. You already know about the evidence - over and above Bell - which independently rules out LR (GHZ, Hardy, Leggett, etc.). That doesn't matter to you though.

Again, I admit that I don't know much about GHZ, Hardy, Legget. I know two things though. First, as far as I know, nobody stated that these newer developments are different from Bell IN PRINCIPLE. If you tell me, for example, that their proof does not use PP or something similar, that will matter to me, but you are not saying anything like this, so I’m not sure about “INDEPENDENTLY rules out”. Second, as far as I know, the number of experiments testing these newer statements is very limited so far compared to the number of experiments testing Bell.

There are no candidate local realistic theories in existence at this time. You don't even care about that.

I admit, this is an important consideration. However, some remarks may be appropriate here.
First, strictly speaking, in this thread I was not trying to convince anybody that QT will be eventually replaced by an LR theory. I was discussing a somewhat different question: has LR been ruled out by recent developments, both theoretical and experimental? You did not seem to challenge the factual basis of my reasoning (the mutually contradicting assumptions of Bell and no loophole-free experiments). Well, to be more precise, your objections to the statement on the mutually contradicting assumptions of Bell were half-hearted at best. If, however, you do want to challenge this statement head-on, please advise. Basically, you just argued that my point of view is not generally accepted, and LR is improbable. But “improbable” and “ruled out” are quite different expressions.
Second, let us imagine something improbable for a second: that we bought two sixpacks on a weekend and decided to find an LR replacement (LRR) to QT :-). The first question we’ll need to answer would be: is it possible in principle? Let us imagine something even more improbable: that you agreed with me that there are no no-go theorems or no-go experiments eliminating such a possibility. Then we’ll have to proceed with the next phase of our “brainstorming session”: what are the technical requirements to such LRR (specifications)? I think we’ll agree without any further fuss that our LRR does not need to mimic all predictions of QT, as they are mutually contradictory (so no LRR would be able to mimic them anyway). And I’d like to emphasize that this may be a crucial issue: finding LRR may be extremely difficult because it is not clear what requirements such LRR must meet.
Suppose, however, that we agree that if our LRR mimics “just” unitary evolution of QT, that would be enough for us. Is it possible to find such LRR? I don’t know. However, the following nightlight’s observation may be of great interest here: QTP-like unitary evolution in Hilbert space (which, by the way, seems to describe entanglement as well) may be just a disguise for nonlinear partial differential equations (you may wish to look at the very brief outline of the relevant published results of other people in my post https://www.physicsforums.com/showpost.php?p=1825523&postcount=90 – it may be worth a glance).

If God came down and told you LR is wrong, you would still be looking for another loophole.

I don’t know, I guess I should wonder what you would do if god “came down and told you LR is” right? :-)
However, I guess yours is a good question (or is it a statement ? :-) ). Let me explain my position. I don’t think there is any credible evidence of god’s existence. However, I cannot be sure that there will be no such evidence tomorrow (indeed, I could imagine that human race can produce some tiny rational creatures in the future (using biological, chemical, or physical methods). For such creatures, we would be pretty much the same as gods).
I take a similar position with respect to LR. Right now I don’t think there is any credible evidence ruling out LR. But I cannot be sure that there will be no such evidence tomorrow. When there is such evidence, I will have to change my point of view.

I am interested in science rather than listening to you nitpicking.

Look, I gave you an example with planar Euclidian geometry. You don’t like it? You believe the sum of angles of a quadrangle is not quite relevant to the sum of angles of a triangle? C’mon, you’re nitpicking. You think the sum of angles of a triangle on a sphere is not quite relevant to the sum of angles of a planar triangle? C’mon, you’re nitpicking.

My discussion with you on this point has ended.

I do appreciate your time and input.

 

[DrChinese]

I believe that Transactional Interpretation is an example of LR theory. But as it is explicitly retrocasual it does not help to recover a dream of local realists - to restore some Newtonian-like theory, just with different formulas.

Am I right? How could one explain these desperate attempts to find a loophole, over and over again?

I don't think of retrocausal as being realistic, although I can see how some might. I think such interpretations are viable, certainly as viable as Bohmian types. I think there are particular theoretical reasons why you might be drawn to them: for example, relativity is respected as is T symmetry. I can also see where it might be too weird for some to accept. It certainly makes it easy to explain delayed choice quantum eraser experiments!

 

[DrChinese]

...Again, I admit that I don't know much about GHZ, Hardy, Legget. I know two things though. First, as far as I know, nobody stated that these newer developments are different from Bell IN PRINCIPLE...

...the mutually contradicting assumptions of Bell and no loophole-free experiments). Well, to be more precise, your objections to the statement on the mutually contradicting assumptions of Bell were half-hearted at best...

This is why discussion with you is fruitless. I have said any number of times, in any number of ways, quite the opposite of what you portray here. There are NO contradictory elements of Bell. Period. And I HAVE said that these are fully independent of Bell. The only similarity to Bell is as follows:

The predictions of QM are set against the predictions of LR, and experiments support the predictions of QM.

You don't accept that QM can be considered as a valid theory, a position which is patently absurd. So you throw the baby out with the bathwater. I can't help in this matter, as it is strictly a matter of your personal opinion and has no element of science associated with it. Good luck with your next experiment, I want to see you do one without "contradictory" QM as your basis.



P.S. You REALLY ought to re-read what you are saying BEFORE you say it. I am sure you are impressing yourself with your brilliant logic, but it isn't working for others. Trying asking yourself: Why would someone who has spent a lot of time studying an area have a different opinion than I do? (Not talking about myself there.) There might be a strong reason that has nothing to do with their unreasonable, pigheaded stubbornness and blind following of orthodoxy. Maybe others use words differently than I do. Maybe addressing the substance of an argument is more important than semantics. Maybe others are actually open to useful ideas when they are accompanied by sound scientific reasoning. Maybe useful citations, rather than out-of-context quotes, go farther in making my points. Maybe there is a reason why my personal opinions are frowned upon on a physics board followed by lay readers.

 

[akhmeteli]

This is why discussion with you is fruitless. I have said any number of times, in any number of ways, quite the opposite of what you portray here.

Evidently, I misrepresented your position, and I apologize. However, you’ll notice that I immediately asked you to clarify your position, and I am glad you did just that. When you reproached me, I tried to understand why your position did not seem clear to me. I found only three places in this and previous threads where you directly touched upon contradictions in Bell assumptions, here they are (in no particular order):

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.

As to Bell using mutually contradictory assumptions: all Bell is saying is that LR predictions can never match QM. If you think QM itself is based on mutually contradictory assumptions (which some claim is the case), that is NOT equivalent to saying Bell itself is based on those assumptions. If QM is shown to be experimentally wrong tomorrow, then so be it. But the predictions of QM are still the predictions of QM, and I don't know anyone who sees any confusion (or contradiction) in the cos^2(theta) rule.

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".

In the first quote you just do not express your personal opinion. In the second one you don’t state that there are no contradictions in Bell assumptions. The third one is indeed categorical, but it was said rather early in the game, and after that I explained that the mutually contradictory assumptions of QT are used in the proof of the Bell theorem. So I guess there were some reasons why I was not quite clear about your position. Anyway, I’m glad your position is clear now, so I may discuss it:

There are NO contradictory elements of Bell. Period.

Let me ask you for a favor. Could you please tell me which one (or more) of the following three statements you personally disagree with, so that we could pinpoint the source of our disagreement?

1. A typical Bell theorem proof assumes unitary evolution of QT (as it assumes, for example, that projections of spin of the two-particle system are conserved).

2. A typical Bell theorem proof assumes projection postulate of QT (or something similar) (when the QT correlations are calculated to prove that the inequalities can indeed be violated in QT).

3. Unitary evolution and projection postulate are, strictly speaking, mutually contradictory, as, for example, the latter introduces irreversibility, whereas UE, strictly speaking, is not compatible with irreversibility (for example, due to the quantum recurrence theorem).

And I HAVE said that these are fully independent of Bell.

But I did not state that you had not “said that these are fully independent of Bell”. I just expressed my doubts that they are independent, as, I suspect, they use pretty much the same assumptions as Bell. What I did state was that “as far as I know, nobody stated that these newer developments are different from Bell IN PRINCIPLE”. Do you disagree with that? If you do, then do you state that PP or something similar is not used to prove Leggett, GHZ, Hardy?

You don't accept that QM can be considered as a valid theory, a position which is patently absurd. So you throw the baby out with the bathwater. I can't help in this matter, as it is strictly a matter of your personal opinion and has no element of science associated with it. Good luck with your next experiment, I want to see you do one without "contradictory" QM as your basis.

No, I did not say that I “don't accept that QM can be considered as a valid theory”. I just did not say that. I have greatest respect for QT. I did say that standard QT contains mutually contradictory assumptions. This is quite different. And this is not just my personal opinion. The measurement problem in quantum mechanics had existed long before I was born. Don’t kill the messenger. Kill Albert, kill Bassi, even von Neumann.

P.S. You REALLY ought to re-read what you are saying BEFORE you say it. I am sure you are impressing yourself with your brilliant logic, but it isn't working for others. Trying asking yourself: Why would someone who has spent a lot of time studying an area have a different opinion than I do? There might be a strong reason that has nothing to do with their unreasonable, pigheaded stubbornness and blind following of orthodoxy.

DrChinese, If you believe I used personal attacks in my posts, please tell me where, and I’ll be happy to apologize. If I was not sensitive enough in my posts, I regret that and I can assure you that I meant no offence or disrespect. I do sincerely respect you as a knowledgeable and eloquent person, and I sincerely respect your opinion, even when I disagree. If my logic is faulty, it means I err in good faith, but I am not trying to sell you something I don’t believe myself using some court-room rhetoric. And I will certainly appreciate if you show where my logic is faulty.

Maybe others use words differently than I do. Maybe addressing the substance of an argument is more important than semantics. Maybe others are actually open to useful ideas when they are accompanied by sound scientific reasoning. Maybe useful citations, rather than out-of-context quotes, go farther in making my points. Maybe there is a reason why my personal opinions are frowned upon on a physics board followed by lay readers.

I believe I generally used sound scientific reasoning, but you may disagree, and I certainly appreciate your critique. As for “out-of-context quotes”, I don’t think I misrepresented Shimony, Zeilinger, and Genovese’s opinions. I was not trying to say that they believe in LR, they don’t. I said that they believe LR has not been ruled out by experiments so far. Therefore I strongly disagree that this is just my “personal opinion” (“LR has not been ruled out yet”), which may confuse “lay readers” of this forum. Again, don’t kill the messenger.

 

[zonde]

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

Seems similar to double slit experiment in a sense that photon's context wave splits over two paths with exception that paths do not end at the same place.
At polarization independent beam splitter photon goes down one path but photon's context wave (pilot wave if you like) goes down by both paths. At PBS photon's context wave interacts with other photon's (empty) context wave and creates entanglement. Only requirement is that both photons come from common source and polarization of one of photons is rotated by 90deg (polarizer + HWP at 45deg relative to polarization axis of polarizer).

That seems to be common recipe for creating polarization entangled photons.

 

[DrChinese]

Seems similar to double slit experiment in a sense that photon's context wave splits over two paths with exception that paths do not end at the same place.
At polarization independent beam splitter photon goes down one path but photon's context wave (pilot wave if you like) goes down by both paths. At PBS photon's context wave interacts with other photon's (empty) context wave and creates entanglement. Only requirement is that both photons come from common source and polarization of one of photons is rotated by 90deg (polarizer + HWP at 45deg relative to polarization axis of polarizer).

That seems to be common recipe for creating polarization entangled photons.

I don't think it is actually a requirement that they come from a common source (there does need to be phase matching). I think that it the easier way by far to create the pairs. They are no longer polarization entangled when they start their independent processes.

 

[yoda jedi]

You don't accept that QM can be considered as a valid theory

and/or maybe a transitory one.

quantum mechanics is just plain wrong.

or inconsistent or incomplete.

many interpretations suggests that there is no one satisfactory interpretation.

and are "INTERPRETATIONS"....

That was the thinking of the EPR paper, and it is very reasonable.

thanks !
but i think for example, the electron spin have just 2 possible values, spin-up and spin-down,
right ? then emitting a pair of electron at once, you measure first one value, right ? and then is spin down, then the other electron "have to be" spin up, they can have their values from the beginning.

excuse my english please.

a spin can be up and the other down, or both up ? or both down ?
but that it can be argued in any case, that results are predetermined (from the beginning).







-------------------------------------------

Proceedings Vol. 7421
Andrei Khrennikov

The main aim of this review is to show that the common conclusion that Bell's argument implies that any attempt to proceed beyond quantum mechanics induces a nonlocal model was not totally justified. Our analysis of Bell's argument demonstrates that violation of Bell's inequality implies neither "death of realism" nor nonlocality. This violation is just a sign of non-Kolmogorovness of statistical data - impossibility to put statistical data collected in a few different experiments (corresponding to incompatible settings of polarization beam splitters) in one probability space.



.

 

[DrChinese]

1. and maybe a transitory one.

2. or just incomplete.

...

3. not 100 %, respect to ?
to non-contextuality ? contextuality ?
or independence ?

a spin can be up and the other down, or both up ? or both down ?
but that it can be argued in any case, that results are predetermined (from the beginning).


4. Proceedings Vol. 7421
Andrei Khrennikov

The main aim of this review is to show that the common conclusion that Bell's argument implies that any attempt to proceed beyond quantum mechanics induces a nonlocal model was not totally justified. Our analysis of Bell's argument demonstrates that violation of Bell's inequality implies neither "death of realism" nor nonlocality. This violation is just a sign of non-Kolmogorovness of statistical data - impossibility to put statistical data collected in a few different experiments (corresponding to incompatible settings of polarization beam splitters) in one probability space.

1. Sure, a better (more useful) theory could come along any day. In fact, I hope one does.

2. The incompleteness argument was made in EPR and is now soundly rejected.

3. The correlation is 85% when Alice measures at 0 degrees and Bob measures at 22.5 degrees. So not 100%.

4. A fair example of his thinking is from his paper: "Complete account of randomness in the
EPR-Bohm-Bell experiment" which is at: http://arxiv.org/PS_cache/arxiv/pdf/0806/0806.0445v1.pdf"

He derives the usually CHSH inequality but ends up with result CHSH<=8 when the accepted result is CHSH<=2. See his (2) on page 6. So he concludes that experiment does not rule out local reality, since a typical experimental result is aboout 2.4. The point is that makes no sense. If you know how CHSH is derived, that is like proving that 1=3. It really isn't worth time to dispute the logic here, as no one really accepts it as useful in the first place.

In the paper you reference, he attacks the Kolmogorov axioms - this has been raised previously as an objection and it basically defeats the local realistic agenda if accepted. So not much there.

Suffice it to say, publication is not equivalent to general acceptance per se, especially with pure theoretical work. Just ask anyone who publishes if they expect their work to end up in a textbook. In sum: Khrennikov's work is not generally accepted, and I don't see any merit to his argument as it stands.

He does have some interesting papers, though:

"A Conclusive Experimentation Evidences that Mental States Follow Quantum Mechanics." (I actually like this, strange as it seems.)

"Quantum-like Representation of Extensive Form Games: Wine Testing Game" (I am a fan of reds.)

He also has some interesting papers about random fields, including: "Demystification of quantum entanglement".

 

[Dmitry67]

Can I ask my question again.
Why people are attacking that tiny partucular area?
There are no people who are trying to bring flogiston or either. Whats so special with LR?

 

[DrChinese]

Can I ask my question again.
Why people are attacking that tiny partucular area?
There are no people who are trying to bring flogiston or either. Whats so special with LR?

If someone asserts something on this board that is not generally accepted as if it is traditional science (i.e. they label it as fact, not an opinion)... that is the invitation.

On the other hand, generally accepted science is not "proven" so much as "supported". It usually makes useful predictions which can be used to rule out that theory. When folks make predictions which are contradicted by experiment, then it is time to change their theories. QM does not make any predictions at this time which are inconsistent with entanglement experiments. LR does. QM is supported and LR is not.

That is a generally accepted statement within the physics community, like it or not.

 

[yoda jedi]

2. The incompleteness argument was made in EPR and is now soundly rejected.

i refer to the "information loss problem" not to epr.



(and other details).

 

[DrChinese]

i refer to the "information loss problem" not to epr.
(and other details).

Not sure I follow. Can you be more specific? Are you talking about with black holes? If so I don't see the issue as being relevant.

 

[ThomasT]

A local realist believes that the results at Alice are not dependent on the results at Bob.

If a local realist is one who believes that LHV theories of entangled states haven't been definitively ruled out, then I'm a local realist. If a local realist is one who believes that such a theory is likely to be forthcoming, then I'm not a local realist.

Either way, I believe that in order to produce entangled states experimentally, then it's necessary that the results at Alice and Bob be statistically interdependent (which is accomplished entirely via local interactions/transmissions during the pairing process), which will also ensure that any associated Bell-type inequality will be violated.

Therefore, any correlations between Alice and Bob must be SPURIOUS because they are both causally connected to some other (prior) event.

Why would a common causal connection to some other (prior) event make them spurious? In fact we only see predictable correlations between results at Alice and Bob for two settings.

 

[DrChinese]

Why would a common causal connection to some other (prior) event make them spurious? In fact we only see predictable correlations between results at Alice and Bob for two settings.

Because the results at Alice are not causally related to the results at Bob. They are instead both causally related to some other prior event.

On the other hand, entanglement acts "as if" there is a causal connection.

 

[ThomasT]

Because the results at Alice are not causally related to the results at Bob. They are instead both causally related to some other prior event.

On the other hand, entanglement acts "as if" there is a causal connection.

Thanks for the replies. My latest was hurried and I had to cut it short. I had a couple more comments/questions which it looks like will have to wait until later, or tomorrow.

 

[yoda jedi]

why the glue ?

LOCAL REALISM ruled out?

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

i understand, is a type of realism (are jointly false).
a realism that is local.

cos the real, observed or not, exist.









-------------------
Bell inequalities are based on poincare relativity, have to be seen what happen in a sitter relativity.

 

[Demystifier]

Generally, Bell says:
No physical theory of local Hidden Variables can ever reproduce all of the predictions of Quantum Mechanics.

It is important to understand the assumptions under which the Bell theorem is obtained. As stressed, e.g., in
http://xxx.lanl.gov/pdf/quant-ph/0702225 [Rev. Mod. Phys. Vol. 81, No. 2, pp. 865-942 (2009)]
page 3, the assumptions are:
(i) realism
(ii) locality
(iii) free will
The theorem says that QM violates at least one of these 3 assumptions.

In particular, it is possible to retain both realism and locality if you give up free will. That's the idea of superdeterminism. The problem with that option is that it is very difficult to construct an explicit local-realistic model that has the same predictions as QM. ('t Hooft has attempts in this direction, but I don't think that these attempts are very successfull.)

On the other hand, if you give up locality, then it is easy to construct a nonlocal-realistic model consistent with QM. The simplest known model of that sort is Bohmian mechanics, which also turns out to be a superdeterministic model (no free will).

 

[Demystifier]

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

Indeed. In fact, probably it will never be ruled out.

 

[Demystifier]

I agree with Akhmeteli that there exist experimental loopholes which do not allow us to say WITH ABSOLUTE CERTAINTY that nature is nonlocal.
However, what I don't understand is - why does it matter?

I mean, the above is true for ANY property of nature, we are not absolutely certain about anything. So why it is nonlocality, and not some other property of nature, that is questioned so frequently by serious physicists? Why nonlocality seems so difficult or weird to them?

 

[DrChinese]

Indeed. In fact, probably it will never be ruled out.

And indeed, it is a loophole for all physical theories, not just quantum mechanics. Relativity, evolution, big bang... all can be equally well explained by superdeterminism. With a mere wave of the hand, at that!

 

[ThomasT]

It is important to understand the assumptions under which the Bell theorem is obtained. As stressed, e.g., in
http://xxx.lanl.gov/pdf/quant-ph/0702225 [Rev. Mod. Phys. Vol. 81, No. 2, pp. 865-942 (2009)]
page 3, the assumptions are:
(i) realism
(ii) locality
(iii) free will
The theorem says that QM violates at least one of these 3 assumptions.

I don't think this is the clearest (read: correct) way to talk about what Bell's theorem means.

In particular, it is possible to retain both realism and locality if you give up free will. That's the idea of superdeterminism.

Superdeterminism and free will have nothing to do with it. It just has to do with the formal expression of locality.

The problem with that option is that it is very difficult to construct an explicit local-realistic model that has the same predictions as QM. ('t Hooft has attempts in this direction, but I don't think that these attempts are very successfull.)

Bell advanced a certain generic formulation for LHV models of quantum entangled states whose salient formal characteristic was assumed to be necessary for any LHV model of a quantum entangled state.

But that has by no means been proven to be the case.

The current state of affairs is that there's no formal expression of locality that is compatible with entanglement experimental designs and the salient feature of SQM formalization of entangled states (nonseparability or nonfactorability). Does 't Hooft's match all the precictions of SQM? Is it explicitly local?

A successful LHV model of entangled states can't be rendered in the straightforward factorable form proffered by Bell, because this alone contradicts a necessary condition of entanglement experiments which is the statistical interdependency of Alice's and Bob's results (outcome dependence) -- ie., Bell's locality condition is ambiguous.

On the other hand, if you give up locality, then it is easy to construct a nonlocal-realistic model consistent with QM. The simplest known model of that sort is Bohmian mechanics, which also turns out to be a superdeterministic model (no free will).

What's so realistic about the quantum potential and instantaneous action-at-a-distance?

Besides, there's no reason to give up locality.

So why it is nonlocality, and not some other property of nature, that is questioned so frequently by serious physicists?

Because of Bell?

Why nonlocality seems so difficult or weird to them?

It has no empirical foundation. Just an easy explanation for entanglement corrolations.

 

[MaxwellsDemon]

I agree with Akhmeteli that there exist experimental loopholes which do not allow us to say WITH ABSOLUTE CERTAINTY that nature is nonlocal.
However, what I don't understand is - why does it matter?

I mean, the above is true for ANY property of nature, we are not absolutely certain about anything. So why it is nonlocality, and not some other property of nature, that is questioned so frequently by serious physicists? Why nonlocality seems so difficult or weird to them?

I think locality is valued for a couple different reasons:

1. Simplicity, the assumption of locality makes calculations easier. For example, you can describe the physics of a game of billiards without having to worry about whether the planet Jupiter is moving through the constellation Gemini. You don't have to consider the effect of some ancient dinosaur's sneeze in your calculation when figuring out what force you should hit the 8 ball with.

2. Reductionism. Reductionism is the idea that you can completely describe the whole in terms of its parts and their interactions. Non-locality would be bad news for reductionism I think. (I can elaborate on why I suspect that if you would like...) Since reductionism seems to be the paradigm favored in modern science, an abandonment of locality would be distasteful to most.

 

[akhmeteli]

I agree with Akhmeteli that there exist experimental loopholes which do not allow us to say WITH ABSOLUTE CERTAINTY that nature is nonlocal.
However, what I don't understand is - why does it matter?

I mean, the above is true for ANY property of nature, we are not absolutely certain about anything. So why it is nonlocality, and not some other property of nature, that is questioned so frequently by serious physicists? Why nonlocality seems so difficult or weird to them?

I have been trying to avoid answering this question, but I guess your post was the last straw:-)

First, why was I reluctant to answer (of course, I cannot answer for other people)? Because, as long as there are no clear-cut theoretical or experimental reasons to reject locality (and I don't believe there are such reasons), this is a matter of personal preferences, maybe philosophical views, which a) take a long time to outline and b) are not very appropriate for this forum. So I'll try to stick to physical reasoning. I believe relativity strongly favors locality, and partial differential equations, which are all-pervading in physics, also favor locality. The absense of faster-than-light signaling also tends to suggest locality.

However, this is still a matter of preferences, so let me ask you, all other things equal, would you prefer a local theory, or a nonlocal one?

 

[DrChinese]

I think locality is valued for a couple different reasons:

1. Simplicity, the assumption of locality makes calculations easier. For example, you can describe the physics of a game of billiards without having to worry about whether the planet Jupiter is moving through the constellation Gemini. You don't have to consider the effect of some ancient dinosaur's sneeze in your calculation when figuring out what force you should hit the 8 ball with.

2. Reductionism. Reductionism is the idea that you can completely describe the whole in terms of its parts and their interactions. Non-locality would be bad news for reductionism I think. (I can elaborate on why I suspect that if you would like...) Since reductionism seems to be the paradigm favored in modern science, an abandonment of locality would be distasteful to most.

You don't need to change your calculations as is, Demystifier has tried to show this on many occasions. So that doesn't seem a fair critique. And if you did need to change them, that would actually be a near-proof of non-locality.

As to reductionism, the alternative is to abandon realism (which I am personally OK with). So that is probably equally distasteful if it comes down to taste.

 

[RUTA]

However, this is still a matter of preferences, so let me ask you, all other things equal, would you prefer a local theory, or a nonlocal one?

Causally local, constitutively non-local, i.e., non-separable.