Do Bell and PBR together point toward nonlocal reality?

[DrChinese]

I can let Dr. Chinese answer for himself, but I thought the point of quantum mechanics is that causality isn't fundamental. There is no causality at the level of microscopic physical laws, so the appearance of causality at the macroscopic is some kind of emergent phenomenon.

Well said. I do not think any notion of causal influences is really necessary for orthodox QM. Does a unique set of initial (quantum) conditions always produce a unique outcome? No, and certainly not as far as anyone knows.

So I guess that the appearance of causality is much like the appearance of a thermodynamic arrow of time.

 

[bohm2]

What is the status of measurement problem in the light of PBR theorem?

PBR has no effect on the measurement problem but, since you brought it up, others do argue that the issue of causality/probability/randomness/time direction discussed in above threads do depend on how the quantum measurement problem is resolved:

In quantum theory, the statistical move plays no particular role: the results of quantum statistical mechanics arise from the quantum dynamics of individual states and do not depend on any additional probabilistic postulate. As a consequence, debates about the nature of classical statistical-mechanical probability are not of direct relevance to our understanding of the actual world as described by contemporary physics. Probability in contemporary physics arises from the probabilistic nature of quantum theory itself, not from any additional posit.

That `probabilistic nature' depends on how the quantum measurement problem is resolved. According to dynamical-collapse theories, it is a fundamental stochasticity, analogous to pre-quantum stochastic mechanics. According to (deterministic) hidden-variable theories, it is a consequence of a probability distribution over the hidden variables, analogous to pre-quantum statistical mechanics. According to the Everett interpretation, it is something new, not analogous to either; it is controversial whether this means that Everettian probability is more or less well understood than pre-quantum probability.

The direction of time in the probabilistic macrodynamics of quantum theory is also dependent on the resolution of the measurement problem. In dynamical collapse theories, it is a consequence of the fundamental time-asymmetry of the dynamics. In the Everett interpretation, and in hidden-variable theories, it is a consequence of a non-probabilistic constraint on the initial quantum state.

Probability in physics: stochastic, statistical, quantum
http://philsci-archive.pitt.edu/9815/1/wilson.pdf

 

[Ilja]

But how does the theory predict that a correlation is actual a causal relationship? I'm not convinced that the word "cause" plays any role in physics that can't be played by "correlation".

There is a correlation between IQ and race. A lot of people care about explanations for such a correlation. Genes? Environment? Which environmental influence?

Of course, this example may be an unfortunate choice, because the various causal theories used to explain this correlation have a strong ideological background, so one may doubt that they are scientific theories. At least in some completely objective, idealized science, one may argue, these theories should be rejected as unscientific.

But even if these theories may be attractive to people with certain ideological backgrounds, they remain scientific. Because they allow to make predictions. The theory that some C is the cause of the correlation can be tested by considering various constellations where C is absent or present. Ok, this part is reducible to correlations: The theory leads to predictions about other correlations.

But this is not the only way to decide if C is a reasonable cause. There should be, in this case, a reasonable causal explanation, that means, a mechanism which explains why C, say more books at home, can lead to a higher IQ.

And, sorry, this part is much more interesting at least for me. If I find a way to replace a claim about A correlates with B by C correlates with A as well as with B, this does not really sound like a scientific progress. But if we find a causal explanation for something where initially there was only a strange correlation, we have a different situation.

It is, of course, not an accident that I have chosen an example from everyday life and not from fundamental physics. The point is that the everyday life example makes the difference more clear. Instead, the interpretations of fundamental physics I consider as distorted by the influence of positivism.

 

[stevendaryl]

There is a correlation between IQ and race. A lot of people care about explanations for such a correlation. Genes? Environment? Which environmental influence?

But isn't it true that what we're really worried about is how robust the correlation is? Here's an example that's a little less controversial. Suppose we notice a correlation between the length of a tree's shadow and the position of the sun in the sky: In the morning and evening, the shadow is very long, and the sun is low in the sky. At noon, the shadow is very short, and the sun is high in the sky. So can we control the sun by manipulating the length of the shadow? Of course not, but the failure to be able to do that doesn't actually require causality, but can be seen through correlations alone. If you make the shadow shorter by cutting off the top of the tree, the position of the sun doesn't change. The correlation disappears.

It seems to me that most of the time that we are interested in causality, we can re-express our interests in terms of correlations.

 

[Ilja]

It seems to me that most of the time that we are interested in causality, we can re-express our interests in terms of correlations.

This may be indeed possible, but is it helpful?

There is, so to say, a subtype of correlations we can name "causal correlations". These causal correlations have, first, a particular sequence in time, A->B means t(A)<t(B) in a fundamental notion of time. Second, they have realistic explanations, some mechanism which explains it, which, in terms of correlations, may be described as a sequence of other causal correlations, such that A->C₁->C₂->C₃...->C_n->B. Is that all? No, there is also that the smallest causal connections C_k->C_k+1 in this sequence which we are able to find out have more elementary character, they are usually of an especially simple type, say, some bodies simply moving inertially or so, and usually much more universal.

Note also that this explanatory sequence requires that all of these correlations are of the special causal type, thus, t(C_k)<t(C_k+1). And than there is the additional hypothesis that for every intermediate t t(A)<t<t(B), there has to be yet another C_t between them, A->C_t->B. And that this explanation has to be complete, that means, after controlling for the correlations which are explained by this sequence, there is no remaining correlation between A and B, else the explanation is not complete and one has to look for other causal explanations.

Thus, looking for causal connections means looking for especially simple correlations with some special properties. It is, so to say, a guidance for our research, which of the correlations are really interesting and helpful and which are more of less accidental, like all those correlations studied by astrology.

 

[audioloop]

I can let Dr. Chinese answer for himself, but I thought the point of quantum mechanics is that causality isn't fundamental. There is no causality at the level of microscopic physical laws, so the appearance of causality at the macroscopic is some kind of emergent phenomenon.

or the inverse randomness from determinism.

 

[audioloop]

@audioloop: non-signalling is different, and weaker. Violations of Einstein causality may be hidden, associated with a hidden preferred frame. One choice of a preferred frame allows an explanation with superluminal A->B, another choice with superluminal B->A. There is no explanation without superluminal influence. But you cannot use this for superluminal signalling. Because signalling A->B would be impossible, incompatible with the explanation B->A, and signalling B->A incompatible with the explanation A->B. So there is no superluminal signalling, but nonetheless no Einstein causality.
.

well not to Pawłowski:
he recently gave a quantum key distribution protocols based non-local correlations, which is a strictly weaker assumption than the assumption of no-signalling.

http://arxiv.org/abs/0907.3778
http://pra.aps.org/abstract/PRA/v82/i3/e032313

 

[bohm2]

Not sure if this was posted previously but a recent, neat, non-technical summary of the implications of PBR at physicsworld:

That makes four views in total: that realism is nonsense and the wavefunction is simply a good, workaday description of observations (Bohr); that reality exists and the wavefunction represents incomplete knowledge about it (Einstein); that the wavefunction corresponds to part of reality (Bohm); and that the wavefunction corresponds to all of reality (Everett). So far, so good – except for the second and third options, which appear somewhat similar. What is the difference between Einstein's wavefunction, which represents partial knowledge about reality, and Bohm's wavefunction, which is part (but not all) of reality? Roughly speaking, the latter wavefunction corresponds to something physical, whereas the former wavefunction does not...

Last year physicists Terry Rudolph and Matthew Pusey at Imperial College London, together with mathematician Jonathan Barrett at Royal Holloway, University of London, took up the challenge. They developed a theorem to determine which realist view, epistemic or ontic, is compatible with the predictions of quantum mechanics...

Pusey, Barrett and Rudolph's theorem, which has come to be known as the PBR theorem, essentially offers an ultimatum. If quantum mechanics is right, then the wavefunction cannot be epistemic – it cannot merely represent an experimentalist's partial knowledge about reality. It must instead be ontic and directly correspond either to part of reality (as Bohm said) or to reality in full (as Everett said).

The life of psi
http://physicsworld.com/cws/article/indepth/2013/may/02/the-life-of-psi

 

[audioloop]

Not sure if this was posted previously but a recent, neat, non-technical summary of the implications of PBR at physicsworld:


The life of psi
http://physicsworld.com/cws/article/indepth/2013/may/02/the-life-of-psi

or exist a Epistemic-Epistemic State.


.

 

[DrChinese]

Not sure if this was posted previously but a recent, neat, non-technical summary of the implications of PBR at physicsworld:


The life of psi
http://physicsworld.com/cws/article/indepth/2013/may/02/the-life-of-psi

Well, this is saying that the Bohmian and MWI interpretations are the big winners. Hmmm.

 

[bohm2]

Well, this is saying that the Bohmian and MWI interpretations are the big winners. Hmmm.

It has no effect on non-realist interpetations e.g. Bohr's. It just rules out certain realist interpretations (e.g. Einstein's). The diagram attached below from the article nicely summarizes the 4 major positions:

 

[Ilja]

It has no effect on non-realist interpetations e.g. Bohr's. It just rules out certain realist interpretations (e.g. Einstein's).

But in fact it is much weaker, because it is possible to preserve a Bayesian interpretation of the wave function if one follows the Bohmian way by introducing the position (configuration) q(t) into reality. In this case, the wave function of a complete system can be interpreted in purely Bayesian terms.

The point is the Bohmian formula for the effective wave function of a subsystem: ψ_{sub}(q)=ψ_{full}(q,q_{env}). So, even if the ψ_{full} is purely Bayesian or nomological, what we consider in PBR is only ψ_{sub}, which depends on q_{env}, which is ontological.

 

[bohm2]

But in fact it is much weaker, because it is possible to preserve a Bayesian interpretation of the wave function if one follows the Bohmian way by introducing the position (configuration) q(t) into reality. In this case, the wave function of a complete system can be interpreted in purely Bayesian terms.

The point is the Bohmian formula for the effective wave function of a subsystem: ψ_{sub}(q)=ψ_{full}(q,q_{env}). So, even if the ψ_{full} is purely Bayesian or nomological, what we consider in PBR is only ψ_{sub}, which depends on q_{env}, which is ontological.

I'm having trouble understanding this part on Bayesian interpretation, so let me summarize how I interpreted the stuff from what I've read. Epistemic interpretations of the quantum state can be divided into 2 types:

1. those that are epistemic with respect to underlying ontic states
2. those that are epistemic with respect to measurement outcomes

The PBR theorem would place serious constraints on 1. but not 2. A quantum Bayesian approach (at least as favored by Caves, Fuchs, etc.) would not be undermined by the PBR theorem, as far as I understand, because Fuchs and that group would deny that quantum states have ontic states. Would you agree with this part?

 

[Ilja]

I would agree that Fuchs and Caves, as far as they are completely anti-realistic, do not have to bother about PBR.

But, wait, I'm not completely sure. Bayesian probability theory is derived. We start with a few common sense principles and obtain all the rules of classical probability theory. Classical probability theory? What does this mean? Probability theory as defined by the Kolmogorov axioms?

If yes: Kolmogorovian probability theory is a probability density defined on a space of elementary events. What are these "elementary states"? Another, mathematical word for the underlying ontic states? Or only for the measurement outcomes? But measurement outcomes are described in classical Kolmogorovian probability theory by stochastic functions, that means, functions on the space of elementary states, not by elementary states.

Something worth to think about. But I tend to think that it shold be at least possible to follow a purely positivistic, anti-realistic direction, without any underlying reality, with measurement results as the only replacement for reality, and probability distributions on them as Bayesian probabilities. For such a Bayesian direction, PBR would be unproblematic.

The other problem is if such a subdivision is that clear. In the Bayesian variant of dBB the effective wave function depends on a purely Bayesian wave function of the universe and the real ontic state of the environment.
The first question - the Bayesian wave function of the universe is expistemic with respect to what? The very question does not make sense, I think.

The second question: The q_env(t) of the environment is an ontic state, but contains also all the macroscopic measurement results of the preparation procedure. And these measurement results are usually sufficient to define ψ_eff completely.

 

[audioloop]

I would agree that Fuchs and Caves, as far as they are completely anti-realistic, do not have to bother about PBR.

But, wait, I'm not completely sure. Bayesian probability theory is derived. We start with a few common sense principles and obtain all the rules of classical probability theory. Classical probability theory? What does this mean? Probability theory as defined by the Kolmogorov axioms?

If yes: Kolmogorovian probability theory is a probability density defined on a space of elementary events. What are these "elementary states"? Another, mathematical word for the underlying ontic states? Or only for the measurement outcomes? But measurement outcomes are described in classical Kolmogorovian probability theory by stochastic functions, that means, functions on the space of elementary states, not by elementary states.

Something worth to think about. But I tend to think that it shold be at least possible to follow a purely positivistic, anti-realistic direction, without any underlying reality, with measurement results as the only replacement for reality, and probability distributions on them as Bayesian probabilities. For such a Bayesian direction, PBR would be unproblematic.

The other problem is if such a subdivision is that clear. In the Bayesian variant of dBB the effective wave function depends on a purely Bayesian wave function of the universe and the real ontic state of the environment.
The first question - the Bayesian wave function of the universe is expistemic with respect to what? The very question does not make sense, I think.

The second question: The q_env(t) of the environment is an ontic state, but contains also all the macroscopic measurement results of the preparation procedure. And these measurement results are usually sufficient to define ψ_eff completely.

measurements from who or what ? no reality; no who - no what...



.

 

[Ilja]

measurements from who or what ? no reality; no who - no what...

Ask this the anti-realist camp. Its not my problem.

 

[mitchell porter]

I missed this earlier...

I don't think that this theory escapes PBR. True, the wave function psi(x,t) is not a part of its formulation. But the theory is formulated in terms of another function p(x,t), which is essentially a logarithm of psi(x,t). Thus, the reality of p is equivalent to the reality of psi.

Or perhaps your point is that psi is not real in Bohmian mechanics? If that is the case, then I have to say that most Bohmians (including myself) disagree.

If you focus on a particular physical system, psi doesn't have to be a "thing", it can just be a function appearing in the equations of motion of the "classical" beables. As I'm sure you know, this is the point of "nomological" Bohmian mechanics: wavefunction as "law" (or as part of a law), rather than as "thing".

Raykin is interesting because he has actually taken a step beyond Bohmian mechanics, by focusing on the trajectories and beginning to rewrite the equations of motion. Okay, he still has log-psi rather than psi, but it's a start.

 

[Demystifier]

If you focus on a particular physical system, psi doesn't have to be a "thing", it can just be a function appearing in the equations of motion of the "classical" beables. As I'm sure you know, this is the point of "nomological" Bohmian mechanics: wavefunction as "law" (or as part of a law), rather than as "thing".

Let me repeat that Bohmian "nomological" also belongs to the PBR "ontological" class.

 

[mitchell porter]

Let me repeat that Bohmian "nomological" also belongs to the PBR "ontological" class.

I'm not entirely sure what you're saying... but let me repeat :-) that neither psi-ontic Bohmian mechanics nor nomological Bohmian mechanics (nor Raykin's theory) falls within the scope of the PBR theorem, because of PBR's assumption of ontic overlap between the epistemic states.

 

[halfrealist]

New arXiv posting on PBR theorem http://arxiv.org/abs/1306.5805.

 

[audioloop]

New arXiv posting on PBR theorem http://arxiv.org/abs/1306.5805.

"leads to a very general nogo theorem that rules out not only the epistemic models
targeted by PBR but also ontic models"

"This blunts the PBR argument for the reality of the quantum state, even for the ontological hidden-variables models to which the argument applies."

"This is an important lesson about modeling quantum mechanics, but one that leaves open the question of "whether quantum states are real.
---------
ontic, epistemic... any model is ruled out...

Fuchs stands

 

[bohm2]

"leads to a very general nogo theorem that rules out not only the epistemic models targeted by PBR but also ontic models"

That doesn't make sense to me. If PBR ruled out both models then what's left? Non-realism? Assuming the implications of PBR are accurate as assessed by most authors (e.g. it rules out only a certain class of realist interpretations), I can sort of sympathize why a nomological Bohmian interpretation may not initially jive with one's naive notion of "ontic" (e.g. an entity existing in space-time). I mean, if the wave function is a law of motion, then it seems it is just a mathematical object, instead of a "physical" object existing in space-time in addition to the particles. I have read others (e.g. Belot, Esfeld) arguing that the law might be grounded in the nature or essence of the properties that the entities in space and time instantiate. I suppose one can argue that such "dispositions" are ontic? For example, Esfeld et al write:

A law of motion tells us what happens, or can happen or would happen in four-dimensional space-time (given the specification of initial conditions), but it is not itself an entity existing in space and time. By the same token, the wave-function, insofar as it figures in the law of motion, is a mathematical object defined on configuration space, instead of a physical object existing in addition to the particles. This is to say nothing more than that the formulation of a law of motion for the primitive ontology may contain mathematical objects that do not themselves correspond to physical objects...

The other possibility is to admit more in the ontology than just particles’ positions and to take the law, including the universal wave-function, to be grounded in what there thus is added to the ontology. In other words, the law is grounded in the nature or essence of the properties that the entities in space and time instantiate. These properties then are conceived as dispositions (in the sense of what one may call “law-making properties”, that is, properties for which it is essential to exercize a certain nomological role).

The ontology of Bohmian mechanics
http://philsci-archive.pitt.edu/9381/1/Bohm-ont1012.pdf

 

[Quantumental]

Aren't they saying "ontological hidden variable interpretations" ? Meaning that GRW and Many Worlds are still left on the table?

 

[bohm2]

Aren't they saying "ontological hidden variable interpretations" ? Meaning that GRW and Many Worlds are still left on the table?

Yes, so if the author's claims are accurate, then Bohmian would be ruled out, I think, but not realist interpretations like GRW and MWI. But I think those are the only authors making that claim wrt PBR. I don't understand their idea of tracking They write:

Examination of the no-go result reveals, however, that it does not require overlap. It requires only a weaker condition that we call tracking. While overlap entails tracking, the converse is not true. Hence if the demonstration rules out hidden-variables models where the quantum state can be understood epistemically, the same strategy may rule out a host of nonepistemic (“ontic”) models of the ontological type as well.

Their definition of tracking:

Definition. (Tracking) A hidden variable λ tracks |ψ⧽ with respect to a discrete observable M just in case whenever Pr(M = k | |ψ⧽ ) = 0, then pr(M = k |λ ) = 0.

 

[Demystifier]

New arXiv posting on PBR theorem http://arxiv.org/abs/1306.5805.

In the last paragraph they conclude:
"Just as the no-go result of the Bell–Kochen–Specker theorem [6, 7] has taught us about the failure of noncontextuality for quantum measurements, we suggest one can learn an important lesson from the PBR theorem about the failure of separability in ontological models. Namely, even for a quantum tensor-product state, physical states” sufficient to model measurements on a composite system may not be determined just by “real physical states” associated with the separate components."

This is remarkably similar to my own conclusions presented at early days after the first version of the PBR paper:
https://www.physicsforums.com/showpost.php?p=3627144&postcount=95
https://www.physicsforums.com/showpost.php?p=3628836&postcount=123
https://www.physicsforums.com/showpost.php?p=3628847&postcount=124

 

[Demystifier]

Yes, so if the author's claims are accurate, then Bohmian would be ruled out, I think, but not realist interpretations like GRW and MWI.

No. If the authors claims are accurate, then what is ruled out is the idea that the act of measurement is merely a passive determination of preexisting ontic properties. Instead, the act of measurement is an active part of the story as well. A complete description must involve not only lambda of the measured system, but also lambda of the measuring apparatus. Bohmian, MWI, GRW, Copenhagen, etc. are still compatible with it.

 

[audioloop]

not realist interpretations like GRW and MWI.

not realist, GRW ? MWI ?

 

[audioloop]

"Our results suggest that rather than demonstrating the reality of the quantum state, the
PBR theorem highlights quantum nonseparability in ontological hidden-variables models"

We could with concepts, understand reality?

 

[bohm2]

If the authors claims are accurate, then what is ruled out is the idea that the act of measurement is merely a passive determination of preexisting ontic properties. Instead, the act of measurement is an active part of the story as well. A complete description must involve not only lambda of the measured system, but also lambda of the measuring apparatus. Bohmian, MWI, GRW, Copenhagen, etc. are still compatible with it.

Do you or anyone else know which ontological hidden variable interpretations are ruled out that the authors are referring to? And this is assuming that their assessment of implications of PBR is correct. Kochen-Specker already ruled out non-contextual models and Bell's non-local ontic models. So I don't understand which ontological hidden variable models Maximilian Schlosshauer and Arthur Fine believe are ruled out by PBR?

 

[audioloop]

http://arxiv.org/pdf/0706.2661v1.pdf
"For instance, in deBroglie-Bohm, a system is not separable from the experimental apparatus"


http://arxiv.org/pdf/1306.5805v1.pdf
"we suggest one can learn an important lesson from the PBR theorem about the failure of separability in ontological models"


http://arxiv.org/pdf/quant-ph/0406166v3.pdf
"The resolution of this puzzle is that one can distinguish two sorts of locality [30], and it is only the failureof one of these that implies measurement contextuality.The first notion of locality, which we call separability, is the assumption that the ontic state of the universe is defined in terms of the ontic states at each point of space-time. The other sort of locality assumption, which presumes separability, we call local causality. It is the assumption that the probability distribution over values for a variable in a space-time region are determined by the values of all the variables in the backward light-cone of this region (see footnote in section III). A failure of local causality within the framework of a separable model does indeed imply measurement contextuality. However, a model can be nonlocal by virtue of failing to be separable, and in this case it does not follow that the model is measurement contextual. This is precisely what occurs
in the Beltrametti-Bugajski model"


.

 

[bohm2]

http://arxiv.org/pdf/0706.2661v1.pdf
"For instance, in deBroglie-Bohm, a system is not separable from the experimental apparatus"

That paper is interesting because it is those author's definitions of ψ-ontic and ψ-epistemic that are used in the PBR theorem. What is interesting is the latter part os that quote:

For instance, in deBroglie-Bohm, a system is not separable from the experimental apparatus and consequently it is unclear whether one misrepresents the interpretation by casting it in our current framework ...

Does this support Schlosshauer/Fine and Demystifier's original criticism of PBR assumption? See Demystifier's letter to one of the co-authors (Barrett) of the PBR paper and that author's response. Another interesting part of the paper was the point discussed above regarding the ontic nature of the different Bohmian interpretations. Harrigan and Spekken write:

Inspired by this pattern, Valentini has wondered whether the pilot-wave (and hence ontic) nature of the wave function in the deBroglie-Bohm approach might be unavoidable. On the other hand, it has been suggested by Wiseman that there exists an unconventional reading of the deBroglie-Bohm approach which is not ψ-ontic. A distinction is made between the quantum state of the universe and the conditional quantum state of a subsystem, defined in Ref. [79]. The latter is argued to be epistemic while the former is deemed to be nomic, that is, law-like, following the lines of Ref. [80] (in which case it is presumably a category mistake to try to characterize the universal wave function as ontic or epistemic). We shall not provide a detailed analysis of this claim here, but highlight it as an interesting possibility that is deserving of further scrutiny.

Einstein, incompleteness, and the epistemic view of quantum states
http://arxiv.org/pdf/0706.2661v1.pdf

 

[Demystifier]

Do you or anyone else know which ontological hidden variable interpretations are ruled out that the authors are referring to? And this is assuming that their assessment of implications of PBR is correct. Kochen-Specker already ruled out non-contextual models and Bell's non-local ontic models. So I don't understand which ontological hidden variable models Maximilian Schlosshauer and Arthur Fine believe are ruled out by PBR?

That's a good question. If I understood Schlosshauer and Fine correctly, they seem to think that the PBR result does not teach as anything new, i.e., it does not exclude anything which has not already been excluded by Kochen-Specker.

 

[bhobba]

That's a good question. If I understood Schlosshauer and Fine correctly, they seem to think that the PBR result does not teach as anything new, i.e., it does not exclude anything which has not already been excluded by Kochen-Specker.

Its only some fringe ones that I had never really heard of before - but evidently some held to them. Matt Leifer for example held to one it affected and he mentions a few it did:
http://mattleifer.info/2011/11/20/can-the-quantum-state-be-interpreted-statistically/

He also thinks Einsten held to it as well. Not so sure about that. He believed QM was incomplete and an approximation to some deeper theory that was real. He would have welcomed PBR as showing the Ensemble interpretation he favored could not be the whole story.

Thanks
Bill

 

[Quantumental]

Einstein never believed in any "Ensemble interpretation" wtf.
The ensemble interpretation is indeterministic and really a agnostic non-interpretation who doesn't say anything about the reality

 

[DrChinese]

Einstein never believed in any "Ensemble interpretation" wtf.
The ensemble interpretation is indeterministic and really a agnostic non-interpretation who doesn't say anything about the reality

I agree, Einstein was more a local realist who accepted the predictions of QM. I have seen a lot of recent work* attempting to try to cast Einstein's positions in a different light, but I have yet to see any statement since EPR where Einstein disavows traditional notions of locality or realism. I personally like to believe (and this is speculation) that if he had lived to see Bell, he would have changed his position.


*eg Norsen.

 

[bhobba]

Einstein never believed in any "Ensemble interpretation" wtf.
The ensemble interpretation is indeterministic and really a agnostic non-interpretation who doesn't say anything about the reality

That's just plain wrong:
http://en.wikipedia.org/wiki/Ensemble_interpretation
Probably the most notable supporter of such an interpretation was Albert Einstein:
'The attempt to conceive the quantum-theoretical description as the complete description of the individual systems leads to unnatural theoretical interpretations, which become immediately unnecessary if one accepts the interpretation that the description refers to ensembles of systems and not to individual systems.'

Read Ballentines 1970 paper on it and his book where he examines it in more detail.

Calling it a non interpretation is just plain silly - it most definitely is one. And to say something about reality first requires agreement on what reality is - good luck with that.

Thanks
Bill

 

[bhobba]

I agree, Einstein was more a local realist who accepted the predictions of QM. I have seen a lot of recent work* attempting to try to cast Einstein's positions in a different light, but I have yet to see any statement since EPR where Einstein disavows traditional notions of locality or realism. I personally like to believe (and this is speculation) that if he had lived to see Bell, he would have changed his position.

Of course Einstein was a local realist but the actual interpretation he held to was the Ensemble interpretation. That's one reason he believed it incomplete - the ensemble interpretation is about a conceptual ensemble of similarly prepared systems like statistical mechanics. To him it strongly suggested, along with other considerations like EPR, but probably the most important thing of all his strongly felt conviction about how the world operates, that it was just an approximation to a more fundamental theory.

I also believe if Einstein was alive today he likely would have changed his mind. My comment had to do if he knew of the PBR result not the myriad of new stuff we now know.

Thanks
Bill

 

[audioloop]

Harrigan and Spekken write:

Einstein, incompleteness, and the epistemic view of quantum states
http://arxiv.org/pdf/0706.2661v1.pdf

and
Einstein, incompleteness, and the epistemic view of quantum states
http://arxiv.org/pdf/0706.2661v1.pdfFuchs has previously argued in favor of this conclusion. In his words, “[Einstein] was the first person to say in absolutely unambiguous terms why the quantum state should be viewed as information [...]. His argument was simply that a quantum-state assignment for a system can
be forced to go one way or the other by interacting with a part of the world that should have no causal connection with the system of interest.” [13]. One of the main goals of the present article is to lend further support to this thesis by clarifying the relevant concepts and by undertaking a more detailed exploration of Einstein’s writings.
We also investigate the implications of our analysis for the history of incompleteness and nonlocality arguments in quantum theory. In particular, our analysis helps to shed light on an
interesting puzzle regarding the evolution of Einstein’s arguments for incompleteness.
The argument Einstein gave at the 1927 Solvay conference requires only a single measurement to be performed, whereas from 1935 onwards he adopted an argument requiring a measurement to be chosen from two possibilities. Why did Einstein complicate the argument in this way? Indeed, as has been noted by many authors, this complication was actually detrimental to the effectiveness of the argument, given that most of the criticisms directed against the two-measurement form of the argument (Bohr’s included) focus upon his use of counterfactual reasoning, an avenue that is not available in the 1927 version [14, 15, 16, 17, 18].
The notion that Einstein introduced this two measurement complication in order to simultaneously beat the uncertainty principle, though plausible, is not supported by textual evidence. Although the EinsteinPodolsky Rosen (EPR) paper does take aim at the uncertainty principle, it was written by Podolsky and, by Einstein’s own admission, did not provide an accurate synopsis of his (Einstein’s) views. This has been emphasized by Fine [12] and Howard [19]. In the versions of the argument that were authored by Einstein, such as those appearing in his correspondence with Schrodinger, the uncertainty principle is explicitly de-emphasized. Moreover, to the authors’ knowledge, whenever Einstein summarizes his views on incompleteness in publications or in his correspondence after 1935, it is the argument appearing in his correspondence with Schrodinger, rather than the EPR argument, to which he appeals.
We suggest a different answer to the puzzle. Einstein consistently used his more complicated 1935 argument in favor of his simpler 1927 one because the extra complication bought a stronger conclusion, namely, that the quantum state is not just incomplete, but epistemic.
We suggest that Einstein implicitly recognized this fact, even though he failed to emphasize it adequately.

 

[audioloop]

Was Einstein Really a Realist ?
https://www3.nd.edu/~dhoward1/Was Einstein Really a Realist.pdf

...satisfying a principle of separability...

in concise terms:
Einstein`s criterion of reality.


more in:

The Shaky Game: Einstein, Realism, and the Quantum Theory
Arthur Fine.
Einstein to Schrödinger, June 17:
From the point of view of principles, I absolutely do not believe in a statistical basis for physics in the sense of quantum mechanics, despite the singular success of the formalism of which I am well aware. I do not believe such a theory can be made general relativistic. Aside from that, I consider the renunciation of the spatio-temporal setting for real events to be idealistic-spiritualistic. This epistemology-soaked orgy ought to come to an end. No doubt, however, you smile at me and think that, after all, many a young whore turns into an old praying sister, and many a young revolutionary becomes an old reactionary.


-------
Space-Time and Separability: Problems of Identity and Individuation in Fundamental Physics
Don Howard.

.

 

[Jolb]

Why does it even matter what Einstein believed? Though he was a great physicist, he couldn't see the future, so he was bound to have some erroneous ideas. He has many famous mistakes, e.g. he died believing his introduction of the cosmological constant was a mistake (we now know it probably does have a nonzero value), and he also died believing that GR successfully reflects Mach's principle (He believed that the Lense-Thirring effect supported Mach's principle, but the actual Lense-Thirring effect is the negative of what a conventional Machian principle would imply. Ref: Wolfgang Rindler: "The Lense-Thirring effect exposed as anti-Machian").

Either way, I think it's clear that Einstein believed the universe actually obeyed local realism, since in his development of GR he often invoked philosophical principles such as "the principle of locality" and "the principle of causality". On the other hand, it's pretty clear that he thought QM was "wrong"--not that it gave the wrong predictions, but to Einstein it was definitely incomplete because it made suggestions that would fly in the face of SR and GR which he was so deeply invested in. He is famous for pointing out "paradoxes" in quantum mechanics--perhaps he was trying to poke holes in it.

In other words, Einstein's personal beliefs on the universe were local realism, while his views on QM were that it was manifestly unphysical in the "model" it used and therefore incomplete. However, he realized that QM somehow made correct predictions--maybe because QM was just modeling our "knowledge" of the system such as in an "ensemble" interpretation, or maybe for some other reason, such as in a "shut up and calculate" interpretation. But he certainly didn't believe that the ensemble interpretation was "the correct interpretation"--who cares about the interpretation of something that's plain wrong? It's much more likely he believed that QM is an emergent phenomenon of a deeper underlying locally realistic theory.

This view is basically what is reflected in the EPR paper, and I don't think Einstein would have put his name on the paper if it directly contradicted what his real beliefs were. What Harrigan-Spekken, Fine, and Howard are pointing out are his specific views on how QM manages to make right predictions; Harrigan et al. do NOT argue that Einstein believed in QM over the locally realistic hidden variable theories that EPR proposes as the fundamental theory.

 

[bohm2]

This is the part that is still confusing me and relates to one the major assumptions of the PBR theorem and the issue of non-separability brought up by a few papers/authors. This summary contrasting the implications of PBR theorem versus Bell's theorem is taken from one of the author's slide presentations:

Bell’s theorem: Systems have an objective physical state + Experimenter free will + QM → Non-locality

PBR theorem: Systems have an objective physical state + Preparation independence + QM → ψ-ontic

What is the quantum state?
http://www.cs.ox.ac.uk/qisw2012/slides/barrett.pdf

From that slide presentation, it seems that there is a difference between the 2 theorems with respect to the assumptions made (hi-lited in red above) and yet one of the authors in a blog suggests that both Bell's and PBR make the same and seemingly reasonable assumption:

Preparation independence is simply the assumption that we have the ability to build independent, uncorrelated experimental apparatuses to act as preparation devices of microscopic systems, and that any deeper theory of nature than quantum theory will not overthrow this principle by virtue of “hidden super-correlations” where to date scientists have always successfully assumed there are none...We are in a similar position with Bell’s theorem...that theorem relies on a presumed ability to make independent choices of measurements at separated locations. Denial of such is the “super-determinism” loophole, and while intelligent people can and do consider its plausibility, and while it is an important insight into Bell’s theorem that this assumption is necessary, the jury is still out (‘t Hoofts efforts notwithstanding) as to whether a super-deterministic theory agreeing with all experiments to date can even be constructed, never mind be a plausible theory of nature.

Guest Post: Terry Rudolph on Nature versus Nurture
http://www.preposterousuniverse.com...-post-terry-rudolph-on-nature-versus-nurture/

It seems to me that there is a difference between Experimenter free will vs. Preparation independence or am I mistaken?

 

[Demystifier]

It seems to me that there is a difference between Experimenter free will vs. Preparation independence or am I mistaken?

That's a very good and very subtle question!

It seems to me that the relevant aspects of those two assumptions are essentially the same. Namely, when in the Bell theorem we require that "experimenters have free will", all what we really need is that the choice made by one experimenter is INDEPENDENT on the choice made by another experimenter. These two experimenters choose the directions in which the spins will be measured, so we can say that they PREPARE the measuring devices.

From this point of view, the difference between PBR and Bell lies in the fact that the former requires preparation independence of the two PARTICLES which will be measured, while the latter requires preparation independence of the MEASURING DEVICES for the two particles. Both require preparation independence, but for different objects - the measured system for PBR, or the measuring device for Bell.

Now, if we assume that there is no fundamental difference between measured systems and measuring devices (e.g., that both are ultimately described by quantum mechanics), then these two kinds of preparation independence are actually the same.

 

[Jolb]

These last two posts are very interesting. The superdeterminism loophole is a deep one and often gets overlooked (to the point that most objections to Bell's theorem actually rely on sneakily incorporating superdeterminism), and what Bartlett says in his slides demonstrates a very interesting parallel between PBR and Bell with regards to superdeterminism.