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

[ThomasT]

I still completely fail to understand your point of view. You are simultaneously accepting and denying entanglement in separate points of your argument. You say that the experiment is designed to produce entanglement, and therefore the A and B sets are statistically dependent.

Yes, without statistical dependency between A and B you can't demonstrate entanglement. It's the successful matching of the separate data sets wrt certain criteria that makes the difference between seeing the QM-predicted correlations or not.

Then you go on to say that there are no correlations between the A and B measurements except when the angle between the detector setting is 0 or pi, and that this can be explained by a purely local mechanism. Huh? That seems contradictory and non-sensical ... you can't have it both ways.

The correlation that the experiment is designed to produce, and that QM and proposed LHV models are making predictions about is the correlation between θ (the angular difference between the analyzer settings) and the rate of joint detection.

There's no correlation between individual detections at A and B except for θ=0 and θ=90 degrees. Wrt these two settings a simple LHV model (producing a linear correlation function between θ and rate of joint detection) predicts the same thing as QM for θ=0 and θ=90 degrees (as well as θ=45 degrees).

So, there is an LHV account of any correlation between A and B. What there's no complete LHV account of is the correlation between θ and rate of joint detection for values of θ between 0 and 90 degrees.

But there is a more basic issue with your arguments in my view. Consider the following:

The detectors and coincidence circuitry are controlled by Alice, who has no knowledge of the source conditions ... all she has is a definition of what a coincidence is in the context of the experiment. Bob has two experimental setups P and Q, both produce oppositely polarized pairs of counter-propagating photons, but in the case of P, they are entangled, and in Q they are not. From your previous statements, you appear to agree that for source P, the sets A and B will show a statistical dependence, and for source Q they will not. Therefore, simply from her observations, and without communicating with Bob, Alice can determine which source is being used, based on her measured coincidence statistics.

Statistical dependence between A and B means that a detection at A changes the sample space at B, and vice versa, in a nonrandom way. Setup P is designed to produce related counter-propagating photons via the emission process. Setup Q isn't.

The criterion for data matching has to do with the relationship between the counter-propagating photons.

So, yes Alice should observe that the P and Q results are different and that the P correlations closely resemble those predicted for certain entangled states.

My point here is that it doesn't matter what the experimenters are *trying* to do with the source, because the detection scheme allows for the possibility that their design would fail, as I argued above.

I don't follow what you're saying here. The criterion for data matching has to do with the relationship between the counter-propagating photons. Setup P is designed to produce related counter-propagating photons via the emission process. Setup Q isn't.

 

[yoda jedi]

4) Therefore, I do believe that SQM is, strictly speaking wrong.

not wrong, rather incomplete or aproximate...

read:

Quantum Theory: Exact or Approximate?
http://arxiv.org/PS_cache/arxiv/pdf/0912/0912.2211v1.pdf

...There are two distinct approaches. One is to assume that quantum theory is exact, but that the interpretive postulates need modification, to eliminate apparent contradictions. Many worlds, decoherent histories, Bohmian mechanics, and quantum theory as information, all fall in this category. Although their underlying mathematical formulations differ, empirically they are indistinguishable, since they predict the same experimental results as does standard quantum theory.
The second approach is to assume that quantum mechanics is not exact, but instead is
a very accurate approximation to a deeper level theory, which reconciles the deterministic
and probabilistic aspects. This may seem radical, even heretical, but looking back in the
history of physics, there are precedents. Newtonian mechanics was considered to be exact
for several centuries, before being supplanted by relativity and quantum theory, to which
classical physics is an approximation. But apart from this history, there is another important
motivation for considering modifications of quantum theory. This is to give a quantitative
meaning to experiments testing quantum theory, by having an alternative theory, making
predictions that differ from those of standard quantum theory, to which these experiments
can be compared...




http://arxiv.org/PS_cache/arxiv/pdf/1001/1001.3964v1.pdf

...quantum phenomena possibly emerge only at larger scales than LP (planck sclae) , the scale of spacetime discreteness...




http://arxiv.org/PS_cache/arxiv/pdf/0912/0912.2845v2.pdf

....The outcome of the second measurement will evidently be different from what quantum mechanics predicts for a pair of successive measurements...

Please see my reply to Demystifier, which can be summarized as follows: I don't know enough about non-collapse interpretations.

rather, objective collapse ?
Continuous Spontaneous Localization (Dynamical Reduction Models).



http://arxiv.org/PS_cache/quant-ph/pdf/0701/0701014v2.pdf

...This idea, that the environment somehow naturally guarantees the emergence of definite properties when moving from the micro to the macro, by destroying coherence among different terms of a superposition, is very appealing. But wrong...

...I note here that the division between a system and its environment is not
a division dictated by Nature. Such a division is arbitrarily set by the Physicist because he or
she is not able to solve the Schrodinger equation for the global system; he or she then decides to select some degrees of freedom as the relevant ones, and to trace over all other degrees. This is a very legitimate division, but not compelling at all. Such a division is more or less equivalent to the division between a quantum system and a measuring device: it’s artificial, just a matter of practical convenience. But if the physicist were able to analyze exactly the microscopic quantum system, the macroscopic apparatus and the surrounding environment together, i.e. if he or she used the Schr¨odinger equation to study the global system, he or she would get a very simple result: once more, because of linearity, all terms of the superposition would be present at the same time in the wave function, no one of them being singled out as that which really occurs when the measurement is performed in the laboratory.
The so called measurement problem of Quantum Mechanics is an open problem still waiting
for a solution. Dynamical reduction models, together with Bohmian Mechanics, up to now are,
in my opinion, the most serious candidates for a resolution of this problem...

...He (S. Adler) assumes precisely that quantum mechanics is not a fundamental theory of nature but an emergent phenomenon arising from the statistical mechanics of matrix models with a global unitary invariance...

 

[akhmeteli]

Yes they do. For example, they all predict violation of Bell inequalities for the (ideal) case of detectors with perfect efficiency.


Many-world and Bohmian interpretations do not use a projection postulate or anything like that.

Thank you very much for this information. However, another question is in order in such case. Let me ask it using the example of the de Broglie - Bohm interpretation (dBB) (as, on the one hand, you are an expert in it, and on the other hand, because I know more about it than about other non-standard interpretations).

It is my understanding that dBB fully accepts unitary evolution (UE) of standard quantum mechanics (at least, in some of its versions).

If I am wrong, please advise. However, if I am indeed wrong (or for those versions that do not accept UE unconditionally), that means that dBB predicts deviations from UE and thus experimental results differing from those of SQM (at least in principle). How do we know that these predictions of dBB are indeed correct? I think you'll agree that we cannot know that until we have experimental confirmation. So anything that dBB has to say on nonlocality beyond what SQM says has no experimental basis.

If, however, I am right (or for those versions of dBB that fully accept UE), my question is as follows. Is UE enough to prove nonlocality in dBB? If it is enough, then the relevant proof can be translated into a proof for SQM, and that means that nonlocality in SQM can be proven without the projection postulate (PP) or something like that. That would mean that I was terribly wrong from the very beginning of this thread, and I would certainly want to know if this is indeed the case.

If, however, dBB adds something extra to UE to prove nonlocality, then this extra is either correct in SQM, or it's wrong there. If it's correct in SQM, then again we can translate the dBB proof of nonlocality into a proof for SQM, and it is possible to prove nonlocality in SQM without PP or something like that. Again, I would want to know if this is so.

If, however, this extra is wrong in SQM, that means that it has no experimental basis.

So the above reasoning has several branches generated by several ifs, and I would very much appreciate if you could tell me which branch is correct. Or maybe the entire reasoning is wrong for some other reason that I cannot see right now.

That's fair to say. Anyway, if you did know more about them, it would probably much easier for you to accept quantum nonlocality, at least in the sense of violation of Bell inequalities for the (ideal) case of detectors with perfect efficiency.

That may be so. Right now, however, the above reasoning makes me doubt it.

Well, I would advise you to give up of searching for a variant of QM that does not predict violation of Bell inequalities for the (ideal) case of detectors with perfect efficiency.

Thank you for your advice.

 

[akhmeteli]

not wrong, rather incomplete or aproximate...

I could agree with you for practical purposes (indeed, one can say that PP is not wrong, but it's approximate), but this thread is not about practical purposes. Indeed, SQM implies nonlocality. If I use your wording ("approximate" instead of "wrong"), then am I supposed to talk about "approximate nonlocality"? Then what, am I supposed to say that this "approximate nonlocality" rules out locality or does not rule out locality? Does not make much sense either way, if you ask me. So for the purpose of this thread I prefer the following wording: "strictly speaking, wrong".

As for work of Adler and others, their theories may be correct, but it is my understanding that they deny precise unitary evolution, and there is no experimental basis for that. Maybe there will be such experimental basis in the future, but I am not sure I can meaningfully discuss these theories now.

Actually, I have problems with the motivation of their work. They seem to believe that measurements have definite outcomes, and I doubt that. I quoted the articles by Allahverdyan a.o., where they rigorously study a model of measurement. In the process of measurement of a spin projection, the particle interacts with a paramagnetic system. This paramagnetic system evolves into some macroscopic state, and this seems to decide the outcome of the measurement. However, according to the quantum recurrence theorem, after an incredibly long period of time this macroscopic state will inevitably flip, if UE is correct, thus reversing the outcome of the measurement.

 

[Demystifier]

If, however, I am right (or for those versions of dBB that fully accept UE), my question is as follows. Is UE enough to prove nonlocality in dBB? If it is enough, then the relevant proof can be translated into a proof for SQM, and that means that nonlocality in SQM can be proven without the projection postulate (PP) or something like that. That would mean that I was terribly wrong from the very beginning of this thread, and I would certainly want to know if this is indeed the case.

Yes, that seems to be the case. QM is nonlocal even without the PP. Essentially, QM is nonlocal because the basic entity is the wave function, which is a single quantity attributed to all particles, even when they are spatially separated. For more elaborated argumentation that QM is nonlocal in ANY interpretation see
http://xxx.lanl.gov/abs/quant-ph/0703071

 

[akhmeteli]

Yes, that seems to be the case. QM is nonlocal even without the PP. Essentially, QM is nonlocal because the basic entity is the wave function, which is a single quantity attributed to all particles, even when they are spatially separated. For more elaborated argumentation that QM is nonlocal in ANY interpretation see
http://xxx.lanl.gov/abs/quant-ph/0703071

"Seems to be the case" is not the same as "is nonlocal". Neither is your article categorical ("strongly supports" is not the same as "proves"). You don't state that "nonlocality in SQM can be proven without the projection postulate (PP) or something like that", so while I certainly can be wrong saying it cannot, so far I stand by what I said. I certainly respect your opinion, but opinion is not a proof.

So I'd like to ask you again: is nonlocality proven in dBB using just UE?

As for "QM is nonlocal because the basic entity is the wave function, which is a single quantity attributed to all particles, even when they are spatially separated." - I mentioned a mathematical mechanism suggesting that a QFT-like theory can be a disguise for a local theory. Or, reversing the argument, a local theory can have a seemingly nonlocal form.

 

[akhmeteli]

Unfortunately I can't understand the details of that post, as I already mentioned. However, even if I accepted its content, I am not sure why it is relevant to this discussion ... and earlier you said "nonlinear" PDE's, only here do you mention that they are local. Can you please break down the physical significance of this statement in the current context, or link to a post where you described it previously?.

So let me try to explain. You see, in general, time evolution can be described by partial differential equations in 3+1 dimensions, such as the Maxwell equations, and they are typically local. There are also linear equations in the Fock space, such as in quantum electrodynamics (QED), and the Bell theorem seems to imply that, e.g., QED is nonlocal. So it seems that these two kinds of evolution are worlds apart. However, the formulae from Kowalski's book that I posted show that nonlinear equations in (3+1)D can be embedded in linear equations in the Fock space, and they look pretty much like unitary evolution in quantum field theory, and even the relevant Hamiltonian is expressed in terms of operators of creation and annihilation (I am hypothesizing now, but I think that similar results for fermions can be obtained using the fermionic coherent states (Cahill, Glauber, 1999)). So a local theory may be disguised as a nonlocal one.

Later I'll try to give a simple example of Carleman linearization to illustrate how a low-dimensional nonlinear differential equation can be embedded into a linear equation in infinitely many dimensions.

 

[Demystifier]

So I'd like to ask you again: is nonlocality proven in dBB using just UE?

Yes, it is proven. Moreover, it is proven within any known formulation/interpretation of quantum theory.

As for "QM is nonlocal because the basic entity is the wave function, which is a single quantity attributed to all particles, even when they are spatially separated." - I mentioned a mathematical mechanism suggesting that a QFT-like theory can be a disguise for a local theory. Or, reversing the argument, a local theory can have a seemingly nonlocal form.

As QFT is also a known formulation of quantum theory, my assertion above refers also to QFT. QFT also contains nonlocal objects - quantum states (represented by a sort of wave functions or something equivalent).

 

[Demystifier]

"Seems to be the case" is not the same as "is nonlocal". Neither is your article categorical ("strongly supports" is not the same as "proves"). You don't state that "nonlocality in SQM can be proven without the projection postulate (PP) or something like that", so while I certainly can be wrong saying it cannot, so far I stand by what I said. I certainly respect your opinion, but opinion is not a proof.

Have you read my paper completely? I have an impression that you read the abstract only.

 

[akhmeteli]

Yes, it is proven. Moreover, it is proven within any known formulation/interpretation of quantum theory.

This is strange. My understanding was nonlocality was not proven, e.g., in SQM, using just UE, and you have not stated the opposite before (your article is not at all categorical on this point, moreover, you are saying there that you don't have (yet) a proof of your conjecture). Maybe you misread my question? Or maybe you could give me a reference to such proof (using just UE) for SQM or dBB?

 

[Demystifier]

This is strange. My understanding was nonlocality was not proven, e.g., in SQM, using just UE, and you have not stated the opposite before (your article is not at all categorical on this point, moreover, you are saying there that you don't have (yet) a proof of your conjecture). Maybe you misread my question? Or maybe you could give me a reference to such proof (using just UE) for SQM or dBB?

Or maybe you have not read my paper? Nonlocality (where the word "nonlocality" is defined in the algorithmic sense explained in the paper) is proven in any definite formulation/interpretation of QM. When I say that nonlocality is not proven, I mean that it is not proven that there does not exist another (yet unknown) formulation/interpretation which can avoid algorithmic nonlocality. All that is explained in the paper, for those who want to read it.

Furthermore, independent on my conjecture on "algorithmic" nonlocality that I haven't proven, Bell has already proven "realistic" nonlocality. My unproven "algorithmic" nonlocality is a generalization of the Bell's proven "realistic" nonlocality.

 

[Frame Dragger]

@Akhmeteli: Did you even skim the paper? They address EXACTLY your concerns, and lay them to rest in all but a rhetorical sense. They begin in the last portion of page 3 and conclude with:

However, we emphasize that this is true
only if these hidden-variable formulations really are observationally
equivalent to the local formulation. In this
regard, we note that some variants of the Bohmian interpretation
may, under certain circumstances, observationally
differ from other formulations. The examples of
such circumstances are the early universe [26] and certain
relativistic conditions [27].

If you didn't read it, or can't grasp it then just say that. There's nothing wrong with that on an educational website, with a science advisor (Demystifier) who's bending over backwards trying to help you.
And yes... now I'm having a field day.

 

[akhmeteli]

Or maybe you have not read my paper? Nonlocality (where the word "nonlocality" is defined in the algorithmic sense explained in the paper) is proven in any definite formulation/interpretation of QM. When I say that nonlocality is not proven, I mean that it is not proven that there does not exist another (yet unknown) formulation/interpretation which can avoid algorithmic nonlocality. All that is explained in the paper, for those who want to read it.

Furthermore, independent on my conjecture on "algorithmic" nonlocality that I haven't proven, Bell has already proven "realistic" nonlocality. My unproven "algorithmic" nonlocality is a generalization of the Bell's proven "realistic" nonlocality.

Demystifier,

To be frank, I am completely confused...

I asked you about nonlocality of non-standard interpretations of QM, such as dBB. You told me: yeah, sure, their nonlocality can be proven using UE only. Now you're telling me you had in mind YOUR VERY OWN definition of locality... And what definition it is!

My take on your article is as follows. Actually, you implicitly introduce at least two definitions.

One of them is as follows: "A theory is local if and only if there exists an FI [formulation/interpretation] of the theory in which all irreducible elements are local." Actually, I could live with such a definition. But you do not have a proof of nonlocality under such definition for QM, it's just your conjecture.

The other (implicit) definition is actually for FI, not theories, and it requires that all its irreducible elements are local. Under this definition you do prove that all known FI of quantum theory are not local (say, because they contain such elements as psi(x,y)). However, under this definition even the Hamilton-Jacobi formulation of classical mechanics is not local, as far as I can see. Some definition indeed...

As for Bell's proof, it requires something beyond UE, such as PP.

 

[Demystifier]

I don't understand what exactly you are confused about. That there are different inequivalent definitions of nonlocality? It's often the case in discussions on various stuff that the source of disagreement lies in the unrecognized fact that people have in mind different definitions of the same word. Thus, saying explicitly that there are different definitions is often the first and sometimes crucial step towards achieving agreement.

So, when you say that you believe in locality, what exactly your definition of that word is?

 

[DrChinese]

As for Bell's proof, it requires something beyond UE, such as PP.

As we keep telling you, it does NOT require such. You do NOT need to accept QM to rule out local realism. You only need to accept the cos^2(theta) experimental prediction. Which of course is incompatible with LR.

Please quit repeating what has already been pointed out as false. Whether you accept the experimental results of Bell tests or not, there is no sense in which Bell depends on one's acceptance of QM itself. And as such, your (also ridiculous) assessment of QM as "wrong" is completely meaningless.

P.S. All theories are "wrong" in some sense. A model is not reality. Please see my tag line.

 

[Frame Dragger]

As we keep telling you, it does NOT require such. You do NOT need to accept QM to rule out local realism. You only need to accept the cos^2(theta) experimental prediction. Which of course is incompatible with LR.

Please quit repeating what has already been pointed out as false. Whether you accept the experimental results of Bell tests or not, there is no sense in which Bell depends on one's acceptance of QM itself. And as such, your (also ridiculous) assessment of QM as "wrong" is completely meaningless.

P.S. All theories are "wrong" in some sense. A model is not reality. Please see my tag line.

Why do I think that akhmeteli would not be familiar with GS? Someone that enamoured with words in a physical discipline is obviously not concerned about GIGO in relation to their brain.

To follow that semantic thread... would it be better to say that all theories are incomplete representations of reality, and potentially misleading if taken as more? To me the terms "right and wrong" are polar opposites, not open to degrees. I'm open to correction on this point.

To Ahkmeteli: If you do reject the results of the Bell tests, I would be very interested to hear your defense of that unenviable position.

 

[akhmeteli]

I don't understand what exactly you are confused about. That there are different inequivalent definitions of nonlocality? It's often the case in discussions on various stuff that the source of disagreement lies in the unrecognized fact that people have in mind different definitions of the same word. Thus, saying explicitly that there are different definitions is often the first and sometimes crucial step towards achieving agreement.

So, when you say that you believe in locality, what exactly your definition of that word is?

This thread is about the assumptions of the Bell theorem and experimental tests of the theorem, at least that’s how the thread started. Of course, the topic can change with time, but, on the one hand, I asked you the following questions about non-standard variants of QM:

"Do they predict any experimental results incompatible with any LR models, as is the case for standard quantum mechanics? If you say they do (for example, I am not even sure if this is the case for dBB), then my second question is: Does the relevant proof (an analog of the proof of the Bell theorem in SQM) uses the projection postulate or something like that?",

and you yourself mentioned that non-standard versions of QM "predict violation of Bell inequalities for the (ideal) case of detectors with perfect efficiency", so I had all reasons to assume that you also had in mind the nonlocality as it is defined in the Bell theorem. Then you told me that nonlocality can be proven in, say, dBB using UE only. If you had in mind a new definition of nonlocality, would not it have been appropriate to warn me and other readers of your posts, the more so as you did not use some generally recognized definition, but your own one? That was one source of my confusion.

The other source of confusion was that the specific definition of nonlocality you used was downright unreasonable, as even the Hamilton-Jacobi formulation of classical mechanics satisfies it. You reproached me for not reading your article carefully enough, but I just could not imagine you took that definition seriously (let alone the fact that I was under no obligations to learn the article by heart).

As for your question on the definition of locality that I believe in, it would be more precise to talk about the definition of nonlocality that I don't believe in - existence of violation of the Bell inequalities.

So my question again is: can violations of the Bell inequalities be proven in dBB using UE only, and if yes, I wonder if you could possibly give a reference.

 

[akhmeteli]

As for Bell's proof, it requires something beyond UE, such as PP.

As we keep telling you, it does NOT require such. You do NOT need to accept QM to rule out local realism. You only need to accept the cos^2(theta) experimental prediction. Which of course is incompatible with LR.

You seem to be reproaching me for not listening to what you're saying, but it looks like you're not listening. Indeed, you mentioned the Malus law before in this thread, and I replied that "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." I have not seen any critique of this statement from you (and I repeated that statement replying to SpectraCat). Therefore I stand by what I said: "As for Bell's proof, it requires something beyond UE, such as PP."

You see, the Malus law may be a great approximation, but it's just an approximation. The Coulomb law is a great approximation, but it breaks exactly where it predicts nonlocality.

Please quit repeating what has already been pointed out as false.

If you pointed out that something is false, that does not necessarily mean it is indeed false. I believe I answered your critique, so I guess we just disagree on what is false and what is correct.

Whether you accept the experimental results of Bell tests or not, there is no sense in which Bell depends on one's acceptance of QM itself.

I emphasized that the proof of the Bell theorem uses as assumptions the mutually contradictory elements of standard quantum mechanics - UE and PP, so the problem of QM does indeed become a problem for the Bell theorem.

And as such, your (also ridiculous) assessment of QM as "wrong" is completely meaningless.

OK, so you think this assessment is ridiculous. The problem is I substantiated this assessment: UE and PP are mutually contradictory, because the former cannot destroy a superposition or introduce irreversibility, and PP does that. And this makes the assessment meaningful.

P.S. All theories are "wrong" in some sense. A model is not reality. Please see my tag line.

That does not mean theories cannot be improved.

 

[Demystifier]

As for your question on the definition of locality that I believe in, it would be more precise to talk about the definition of nonlocality that I don't believe in - existence of violation of the Bell inequalities.

Good! Let's then talk only about this definition of locality and ignore other definitions.

So my question again is: can violations of the Bell inequalities be proven in dBB using UE only, and if yes, I wonder if you could possibly give a reference.

Yes it can.

The reference is the classic 1952 Bohm paper (part II, section entitled "Theory of quantum measurements" or something like that). There it is shown that ALL probabilistic predictions are the same as those of standard QM with a collapse, even though there is no collapse in dBB. In fact, the role of this quantum theory of measurements is to explain why we can, for all practical purposes, use collapse as an effective description of measurements, despite the fact that, in dBB, the collapse does not really exist.

This is the classic reference, but even a better explanation of the same stuff can be found in many reviews of dBB. My favored one is the Holland book, chapter "Quantum theory of measurements".

 

[Frame Dragger]

Good! Let's then talk only about this definition of locality and ignore other definitions.


Yes it can.

The reference is the classic 1952 Bohm paper (part II, section entitled "Theory of quantum measurements" or something like that). There it is shown that ALL probabilistic predictions are the same as those of standard QM with a collapse, even though there is no collapse in dBB. In fact, the role of this quantum theory of measurements is to explain why we can, for all practical purposes, use collapse as an effective description of measurements, despite the fact that, in dBB, the collapse does not really exist.

This is the classic reference, but even a better explanation of the same stuff can be found in many reviews of dBB. My favored one is the Holland book, chapter "Quantum theory of measurements".

Demystifier is a kind individual. It goes without SAYING that dBB satisfies the predictions of QM; this is why it's around when all of the LHV theories died; because dBB is NON-Local HV Theory. It's not a matter of reference, but a matter of the very definition of why dBB isn't dead, but rather no longer a shooting offense to teach.

Akhmeteli: You do realize you now have pages of your writing that boils down to, "I'M the sane one, it is all of THEM who are are mad *insane laughter"? No need to respond, I know you think you have your pride.

Edit @ Akhmeteli: I do believe you've annoyed DrChinese... which is a first I've seen. Why the insistance on rhetoric and not just a stand for what you believe? Do you even KNOW what it is you believe? I get the sense that maybe you're just blowing smoke here, and don't believe anything in particular, which you should also come out and say clearly.

 

[DrChinese]

You seem to be reproaching me for not listening to what you're saying, but it looks like you're not listening. Indeed, you mentioned the Malus law before in this thread, and I replied that "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." I have not seen any critique of this statement from you (and I repeated that statement replying to SpectraCat). Therefore I stand by what I said: "As for Bell's proof, it requires something beyond UE, such as PP."

2. That does not mean theories cannot be improved.

1. Arrgh! Bell does NOT require you to believe ANYTHING other than the idea that QM predicts (rightly or wrongly) that there is a cos^2(theta) relationship. It does NOT matter how QM gets that prediction or whether it is observed in experiments (which it is). There is NO other prediction from QM other than the cos^2(theta) relationship (despite your absurd claims that QM is "wrong" whatever that means in this context). So WHAT ARE YOU TALKING ABOUT? Bell is not dependent on the correctness of QM in any way. That was Bell's point actually, that QM and LR are mutually incompatible.

There is no controversery to what I am saying. What you are saying not only makes NO SENSE, but is not accepted by anyone I have ever talked to or read. Forum rules require that you identify personal theories which are not generally accepted as such, and to back up your statements with references when challenged - and you are being challenged. Or better, acknowledge that it is a personal theory with no support other than your belief and stick to discussion points that are appropriate. In this forum, continuing to push points that have been discredited - as yours have - is poor etiquette. We have already covered this ground before in this thread!

2. I couldn't agree more - you can improve on theories. But theories should NOT be judged according to whether they are "right" or "wrong", but rather according to their utility. For example, Newtonian gravity is actually a better theory than General Relativity for many applications (it has fewer variables). You will see that the next time you calculate the velocity an apple drops from a tree.

 

[akhmeteli]

Good! Let's then talk only about this definition of locality and ignore other definitions.

Very well, thank you.

So my question again is: can violations of the Bell inequalities be proven in dBB using UE only, and if yes, I wonder if you could possibly give a reference.

Yes it can.

The reference is the classic 1952 Bohm paper (part II, section entitled "Theory of quantum measurements" or something like that). There it is shown that ALL probabilistic predictions are the same as those of standard QM with a collapse, even though there is no collapse in dBB. In fact, the role of this quantum theory of measurements is to explain why we can, for all practical purposes, use collapse as an effective description of measurements, despite the fact that, in dBB, the collapse does not really exist.

This is the classic reference, but even a better explanation of the same stuff can be found in many reviews of dBB. My favored one is the Holland book, chapter "Quantum theory of measurements".

I am afraid we've run into one of the problems that I anticipated in my post 273 in this thread. If your following statement were precise: "ALL probabilistic predictions are the same as those of standard QM with a collapse", then dBB would have inherited the internal contradictions of standard quantum mechanics and would have been, strictly speaking, wrong. However, this statement is not a precise result in dBB. How do I know that? Just because you told me in another thread that the projection postulate is an approximation in dBB (https://www.physicsforums.com/showpost.php?p=2167542&postcount=19 ).

Therefore, I suspect that violations of the Bell inequalities cannot be proven in dBB using UE only, you need some additional assumptions (or approximations, if you like).

 

[ThomasT]

SpectraCat, to revisit your last comments:

From your previous statements, you appear to agree that for source P, the sets A and B will show a statistical dependence, and for source Q they will not.

The data sets A and B don't, by themselves, show anything. They're just random sequences of detection attributes.

Therefore, simply from her observations, and without communicating with Bob, Alice can determine which source is being used, based on her measured coincidence statistics.

The matched data wrt Q won't show entanglement correlations no matter how you match it, while appropriately matched data wrt P will. P(A,B) can deviate from P(A)P(B) if there's some common cause connection between paired photons produced by Q. But only wrt setup P will rate of coincidental detection be cos²Θ .

My point here is that it doesn't matter what the experimenters are *trying* to do with the source, because the detection scheme allows for the possibility that their design would fail, as I argued above.

How the counter-propagating optical disturbances are produced, how they're filtered, how they're detected and how the resulting data is processed all matters.

Am I missing your point?

 

[ThomasT]

I really don't get what you are saying.

Just that:

1. The factorability of the LHV form for Bell test joint probabilities is what makes this form incompatible with QM and entanglement experiments.
2. This factorability represents statistical dependence between A and B.
3. Statistical dependence between A and B doesn't require flt propagation between them.
4. Therefore, violation of Bell inequality doesn"t imply nonlocality.

The fact is, local realists deny that entanglement is a state.

A state is just a mathematical representation of an experimental setup.

If you mean that they deny that the QM representation is the correct one, then, while this might be a fitting characterization in general, such a denial isn't required in order to be a local realist.

They say it is all coincidence, and there is a common cause.

Of course. And because there's a common cause the rate of coincidental detection wrt angular difference is predictable.

So it is true that Bell tests - which demonstrate entanglement as a state - will always violate LR.

I don't think this is why LHV formulations have so far been incompatible with Bell tests.

Bell tests show that entangled photons operate in a different spacetime view than the local realist would envision.

Not necessarily, In fact the QM prediction, P(A,B) = cos2Θ , is what a local realist might expect for experiments in which counter-propagating optical disturbances emitted by the same atom are analyzed by crossed polarizers.

 

[SpectraCat]

SpectraCat, to revisit your last comments:
The data sets A and B don't, by themselves, show anything. They're just random sequences of detection attributes.

The matched data wrt Q won't show entanglement correlations no matter how you match it, while appropriately matched data wrt P will. P(A,B) can deviate from P(A)P(B) if there's some common cause connection between paired photons produced by Q. But only wrt setup P will rate of coincidental detection be cos²Θ .

How the counter-propagating optical disturbances are produced, how they're filtered, how they're detected and how the resulting data is processed all matters.

Am I missing your point?

Yes, because without knowing about the source, and by applying a consistent treatment to the data, based only on a consistent definition of what construes a coincident detection event, Alice can use the data sets A and B to determine empirically if Bob is using the entangled source P, or the unentangled source Q. That is why the results of Bell tests are valid, because the measurement and data analysis *can distinguish* between entangled and unentangled pairs based on the coincidence counting. Note that the results will not necessarily be random if Bob uses an unentangled source, they will just fail to violate a Bell inequality, because the two measurement sets will not show a statistical dependence.

Finally, your assertion that the data sets are only correlated at the two relative measurement angles of 0 and pi/2 seems false to me. The fact is that more coincidences are observed when the angle is closer to pi/2 and fewer are observed when it is closer to 0. So yes, the correlation of any particular pair of measurements is fundamentally unknowable, but the probability of observing a coincindence will be given by Malus's law based on the *difference between the measurement angles at A and B* when an entangled source is used. If an unentangled source is used, then the results at detector B will be independent of the measurement angle choice at A, and vice versa. So the correlation between sets A and B for the entangled case is not "perfectly random" except for the two cases of theta=0 and theta=pi/2 as you are claiming, and certainly differs in a measurable way from the correlation in the unentangled case.

I know that the above is somewhat repetitive, but I don't know how else to explain it. I hope this makes it clearer

 

[DrChinese]

If you mean that they deny that the QM representation is the correct one, then, while this might be a fitting characterization in general, such a denial isn't required in order to be a local realist.

Of course. And because there's a common cause the rate of coincidental detection wrt angular difference is predictable.

...

Not necessarily, In fact the QM prediction, P(A,B) = cos2Θ , is what a local realist might expect for experiments in which counter-propagating optical disturbances emitted by the same atom are analyzed by crossed polarizers.

Now, if you are a local realist, you say there is a common cause. And yet you cannot construct a dataset in which the cos^2 relationship holds. So what is all the deal about separability? Just show me the dataset for 0, 120 and 240 degrees and we will have something meaningful to discuss. I don't follow all your comments about Bell tests being biased from inception when you cannot do something this simple (because it is impossible).

And entanglement is not so easy to explain these days with some of the newer experiments. EPR is completely lost on these. Please explain, for example, how photons become entangled when they are not in each other's light cones - and never have been - and originate from different lasers. Meanwhile, QM can.

I just do not understand technical objections against Bell when it seems as if the entire point of Bell is lost. Bell is a road map to understanding that local realism is incompatible with the predictions of QM. No matter what the local realistic theory looks like, I can use the Bell thinking to disprove it when compared to experiment. Now, it matters not at all if my map has a small misprint or other minor issue as long as I can get where I need to go.

 

[ThomasT]

Yes, because without knowing about the source, and by applying a consistent treatment to the data, based only on a consistent definition of what construes a coincident detection event, Alice can use the data sets A and B to determine empirically if Bob is using the entangled source P, or the unentangled source Q. That is why the results of Bell tests are valid, because the measurement and data analysis *can distinguish* between entangled and unentangled pairs based on the coincidence counting.

Ok ...

Note that the results will not necessarily be random if Bob uses an unentangled source, ...

Right, but P(A,B) won't be cos2Θ.

... they will just fail to violate a Bell inequality, because the two measurement sets will not show a statistical dependence.

There will still be a statistical dependence between A and B if the (unentangled) counter-propagating disturbances have a common cause and the data are matched wrt this criterion. For example, where setup Q has (emitter - polarizer 1 - polarizer 2 - detector) on both sides, and polarizers 1 are aligned and the setting is changing rapidly and randomly so as to produce identical random polarization for each counter-propagating pair.

Finally, your assertion that the data sets are only correlated at the two relative measurement angles of 0 and pi/2 seems false to me.

These are the only two settings wrt which you can predict B given A, and vice versa.

The fact is that more coincidences are observed when the angle is closer to pi/2 and fewer are observed when it is closer to 0.

In the ideal, when Θ = 0 then P(A,B) = 1 (detection attributes for A and B are always identical), and when Θ = 90 degrees then P(A,B) = 0 (detection attributes for A and B are always opposite).

If an unentangled source is used, then the results at detector B will be independent of the measurement angle choice at A, and vice versa.

This is true even wrt an entangling source.

So the correlation between sets A and B for the entangled case is not "perfectly random" except for the two cases of theta=0 and theta=pi/2 as you are claiming ...

Actually, it is. To illustrate:

The polarizers at A and B are misaligned but not by 90 degrees. A has just registered a detection. Will B also register a detection wrt this pair or not?

 

[ThomasT]

Now, if you are a local realist, you say there is a common cause. And yet you cannot construct a dataset in which the cos^2 relationship holds.

Right, not if the LHV joint probability has to be expressed in factorable form.

So what is all the deal about separability?

It entails that local realist models can be formulated as nonseparable states.

I don't follow all your comments about Bell tests being biased from inception when you cannot do something this simple (because it is impossible).

I agree that it's impossible. That's the point of departure for the argument. The question, then, is why is it impossible. One answer is that it has to do with the factorability of the LHV representation of the joint probability.

Assuming that it has to do with this factorability, then the argument goes ... this factorability was meant to represent locality. Instead it merely represents statistical independence.

However, one might notice, Bell tests are designed to produce statistically dependent data sets, and this statistical dependence doesn't require nonlocal interactions/transmissions.

Hence, violation of Bell inequality doesn't mean that locality or realism has been contradicted, because the violation is simply due to a formal misapplication.

Please explain, for example, how photons become entangled when they are not in each other's light cones - and never have been - and originate from different lasers.

Different lasers can produce the same light, indistinguishable photons.

 

[akhmeteli]

1. Arrgh! Bell does NOT require you to believe ANYTHING other than the idea that QM predicts (rightly or wrongly) that there is a cos^2(theta) relationship.

I respectfully disagree. I think this is factually incorrect. Indeed, you need SOMETHING else to prove the Bell theorem, namely, conservation of angular momentum (otherwise how can you be sure that after you measured polarization of one photon of the entangled pair you definitively know polarization of the other one?) And conservation of angular momentum is a consequence of unitary evolution of QM. That is why I repeat that the proof of the Bell theorem requires both UE and PP, which contradict each other.

It does NOT matter how QM gets that prediction or whether it is observed in experiments (which it is). There is NO other prediction from QM other than the cos^2(theta) relationship (despite your absurd claims that QM is "wrong" whatever that means in this context). So WHAT ARE YOU TALKING ABOUT?

Again, I respectfully disagree. The cos^2(theta) relationship is not the only prediction from QM. Indeed, if the system was initially in a superposition, there is no way you can get destruction of this superposition or irreversibility, unless you reject unitary evolution for the entire system, including the instrument (and an observer, if you wish). So, if there is no irreversibility, that means that no measurement is ever final, in the first place. You want to know what this prediction is exactly? I cannot write the exact prediction, not within a reasonable time frame, but this is not just my opinion. Other people took the trouble to study the process of quantum measurement using a rigorously solved model and showed how the standard results we all are accustomed to arise as approximations, not as precise results, how the projection postulate evolves as a result of irreversibility, which irreversibility, strictly speaking, does not exist, e.g. due to the quantum recurrence theorem. I quoted this published work several times: arXiv:quant-ph/0702135 (Phys. Rev. A 64, 032108 (2001), Europhys. Lett. 61, 452 (2003), Physica E 29, 261 (2005)). Again, you don't need to believe me or Allahverdyan and coauthors. You are a knowledgeable person with profound understanding of quantum mechanics, you are fully aware of the measurement problem in quantum mechanics (and I gave you all the references), so I suspect you fully understand that UE and destruction of superposition are incompatible. Nevertheless, you keep saying something like "C'mon, you're nit-picking, nobody's perfect, so why pick at QM? Be a sport". Sorry, DrChinese, a spade is a spade.

Bell is not dependent on the correctness of QM in any way.

Yes, it is, as the Bell theorem proof requires both elements of QM as assumptions - UE and PP, which are mutually contradictory.

That was Bell's point actually, that QM and LR are mutually incompatible.

I agree. However, as I said, standard quantum mechanics is also incompatible with standard quantum mechanics, so if you believe your (or Bell's) statement rules out LR, it also means it rules out standard QM.

There is no controversery to what I am saying. What you are saying not only makes NO SENSE, but is not accepted by anyone I have ever talked to or read.

I am not sure this is technically correct:-), as I mostly follow nightlight's reasoning, and you criticized nightlight's opinions many times, so I guess you read them:-). Of course, that does not mean that nightlight's opinions or my opinions are correct, but that means that you have been exposed to such opinions.

Forum rules require that you identify personal theories which are not generally accepted as such, and to back up your statements with references when challenged - and you are being challenged. Or better, acknowledge that it is a personal theory with no support other than your belief and stick to discussion points that are appropriate. In this forum, continuing to push points that have been discredited - as yours have - is poor etiquette. We have already covered this ground before in this thread!

Again, what is it that I state? It's actually three statements:

1. There have been no loophole-less experimental demonstration of violations of the Bell inequalities.
2. The proof of the Bell theorem requires both unitary evolution (UE) and the projection postulate (PP) as assumptions.
3. UE and PP, strictly speaking, contradict each other.

and a conclusion:

The Bell theorem is on shaky grounds both experimentally and theoretically.

Statement 1 is the mainstream, and I gave all the references to Shimony, Zeilinger, Genovese.

For statement 2 I indicated where UE and PP are used in the proof of the Bell theorem (to use conservation of angular momentum and to calculate the QM correlations, respectively).

I gave the references to statement 3 (in the form of the problem of measurement in QM) - to von Neumann, Albert, Bassi.

So where is my personal theory? In the conclusion? I believe this conclusion immediately follows from Statements 1-3.

You state that my points were discredited. I reject your statement. I believe I gave adequate answers to the objections. You disagree. That does not mean you're correct and I am wrong or vice versa.

2. I couldn't agree more - you can improve on theories. But theories should NOT be judged according to whether they are "right" or "wrong", but rather according to their utility. For example, Newtonian gravity is actually a better theory than General Relativity for many applications (it has fewer variables). You will see that the next time you calculate the velocity an apple drops from a tree.

This is an excellent example. The problem is it proves my point, not yours. Indeed, Newtonian gravity is very useful. However, it is nonlocal (same as the Coulomb law), whereas general relativity is local, and wherever predictions of these theories differ, the predictions of the latter are correct. I highly respect Newtonian gravity, let alone quantum theory, which is a monumental achievement. But useful theories are not always sufficient to prove such notions as locality or nonlocality, which are important not just for physics, but also for philosophy.

Another example of this kind is thermodynamics. It's an extremely successful and useful theory, but more fundamental theories, such as mechanics or quantum mechanics, strictly speaking, do not allow any irreversibility, which is an integral part of thermodynamics.

 

[Frame Dragger]

You state that my points were discredited. I reject your statement. I believe I gave adequate answers to the objections. You disagree. That does not mean you're correct and I am wrong or vice versa.

True, that's for staff to decide, but since "what naturally follows..." is that you reject Bell Theorem and that, believe me, is YOUR theory. Your view that UE and PP are contradictory have been addressed, and I suppose, "rejected" by you.

So, you've finally made yourself (mostly) clear. Now it's time for you to cite like crazy to support such an ATM view here.