I A new realistic stochastic interpretation of Quantum Mechanics

[PAllen]

TL;DR Summary

I attended a lecture that discussed the approach in the 3 papers listed below. It seems to be a genuinely new interpretation with some interesting features and claims.

These papers claim to present a realistic stochastic interpretation of quantum mechanics that obeys a stochastic form of local causality. (A lecture I recently attended mentioned these papers). It also claims the Born rule as a natural consequence rather than an assumption. This appears to me to be a genuinely new interpretation. I have not delved into the papers in detail, but figured some people here may be interested.

https://arxiv.org/abs/2302.10778
https://arxiv.org/abs/2309.03085
https://arxiv.org/abs/2402.16935

 

[DrChinese]

I saw the last of these papers when it was dropped into Arxiv a few days ago. The first thing I look for is their treatment of remote Entanglement Swapping* and GHZ**. These are some of the strongest experiments against all forms of local realism. If you aren't addressing these, then you really can't make any useful/serious claims in today's environment.

Of course, those seminal works aren't mentioned at all. (There is a passing GHZ reference, but it is not discussed at all.) The main idea of the paper seems to be to define local causality in a very specific manner, then deny that. Well, experiment reigns supreme. I will give this a better look once modern (last 30 years) experiments are explained in terms of the new interpretation. This paper is closer to 1980's era ideas. ***


*In these experiments, distant photons are entangled (and violate a Bell inequality) that have never existed in a common backward light cone. Pretty hard to get locality with that.

**In these experiments, each and every individual run violates realism (since he assumes locality). The quantum prediction is exactly opposite the realistic prediction, and experiment matches QM.

***Note that everyone already agrees that there is signal locality; and that the many demonstrations of quantum nonlocality are probabilistic, and therefore do not constitute evidence of what might be labeled as "causal" anyway.

 

[pines-demon]

I saw the last of these papers when it was dropped into Arxiv a few days ago. The first thing I look for is their treatment of remote Entanglement Swapping* and GHZ**. These are some of the strongest experiments against all forms of local realism. If you aren't addressing these, then you really can't make any useful/serious claims in today's environment.

Why do you have so high regard of entanglement swapping?

 

[gentzen]

Of course, those seminal works aren't mentioned at all. (There is a passing GHZ reference, but it is not discussed at all.) The main idea of the paper seems to be to define local causality in a very specific manner, then deny that. Well, experiment reigns supreme. I will give this a better look once modern (last 30 years) experiments are explained in terms of the new interpretation. This paper is closer to 1980's era ideas.

Given that those paper talk about "a new formulation of quantum theory, alongside the Hilbert-space, path-integral, and quasiprobability formulations", my guess is that this is not the most suitable metric for evaluating the usefulness of this new formulation.
The pure formalism presented in the two older papers suffered from an unclear status of causal locality. I have not studied the newest paper in any detail yet, but if it manages to overcome this problem, then it constitutes nice incremental progress for this new formulation.

 

[PeroK]

Don't we have enough interpretations already? Unless something is making testable predictions then what is the point? Mathematically I'm sure you can cook things an infinite number of ways.

 

[gentzen]

Don't we have enough interpretations already? Unless something is making testable predictions then what is the point? Mathematically I'm sure you can cook things an infinite number of ways.

Indeed, this is the point that Barandes will have to address. (Edit: Well, actually not new predictions, just new applications.) And certainly he tries, but I have no idea yet whether he came closer to an answer. Note however that most interpretations are based on the Hilbert-space formulation, so a new formulation based on a different foundation is not necessarily bad. But also the path-integral formulation had to justify itself by applications which it handles better than the simpler Hilbert-space formulation. This will be the relevant metric in the end for Barandes' new formulation.

 

[A. Neumaier]

Unless something is making testable predictions then what is the point?

How can an interpretation of an existing theory make testable predictions different from that theory?

 

[A. Neumaier]

GHZ**.
[...]
**In these experiments, each and every individual run violates realism (since he assumes locality). The quantum prediction is exactly opposite the realistic prediction, and experiment matches QM.

What do you say to the following statement, which seems contrary to your claims? (taken from p.6-7 of M. Kupczynski, Quantum Nonlocality: how does Nature do it? Entropy 26 (2024), 191.)

“Local realism, i.e., realism plus relativistic limits on causation, was debated by Einstein and Bohr using metaphysical arguments, and recently has been rejected by Bell tests” [14]. Such a conclusion is imprecise, misleading and has been a source of unfounded speculations about quantum magic.

As Wiseman correctly pointed out in [46]: “the usual philosophical meaning of “realism” is the belief that entities exist independent of the mind, a worldview one might expect to be foundational for scientists.” This point of view was also shared by Bell, who was in fact a realist [38,55,56]. The local realism should be rather called local determinism (LD) or counterfactual definiteness (CFD) [38,46] and defined as follows: results of any measurement on an individual system are predetermined by some ontic properties, which have definite values, whether they are measured or not.

 

[lodbrok]

Don't we have enough interpretations already? Unless something is making testable predictions then what is the point? Mathematically I'm sure you can cook things an infinite number of ways.

The point is Conceptual clarity. Besides, it hints at opportunities for testable predictions and new applications. I've only read the first paper, but it's solid work—a highly recommended read, in my opinion.

 

[DrChinese]

Why do you have so high regard of entanglement swapping?

Because these can be configured to demonstrate a lot of no-go's and/or correlations that defy the usual spacetime and ordering conventions while violating a Bell inequality (such as CHSH).

Here is one in which "...the resulting correlations between particles that do not share any common past are
strong enough to violate a Clauser-Horne-Shimony-Holt (CHSH) inequality". In other words, the final entangled pairs (photons 1 & 4) have never been close enough to each other for a hidden signal or other mutual rapport to be established between them at light speed or less. So this is a very unambiguous demonstration of quantum nonlocality.

High-fidelity entanglement swapping with fully independent sources
"Entanglement swapping allows to establish entanglement between independent particles that never
interacted nor share any common past."

Field test of entanglement swapping over 100-km optical fiber with independent 1-GHz-clock sequential time-bin entangled photon-pair sources
"Entanglement swapping is a unique feature of quantum physics. By entangling two independent parties that have never interacted before, entanglement swapping has been used in the study of physics foundations such as nonlocality and wave-particle duality. ... The integrity of an experimental realization of entanglement swapping is ensured only by satisfying these criteria: proper causal disconnection between relevant events, and independent quantum sources without common past."

You can even choose to entangle the target photons after the fact with these experiments. In all cases, the order of the observations and the swap make no difference to the statistical outcome.

So yes, I like these experiments a lot. I go straight to the references to check. When they are omitted from consideration, it is a sure sign - after discussing traditional (i.e. older) Bell tests - that this is where they stumble. So not much point in reading their "hand-waving". The OP references are a good example.

 

[pines-demon]

Because these can be configured to demonstrate a lot of no-go's and/or correlations that defy the usual spacetime and ordering conventions while violating a Bell inequality (such as CHSH).

Here is one in which "...the resulting correlations between particles that do not share any common past are
strong enough to violate a Clauser-Horne-Shimony-Holt (CHSH) inequality". In other words, the final entangled pairs (photons 1 & 4) have never been close enough to each other for a hidden signal or other mutual rapport to be established between them at light speed or less. So this is a very unambiguous demonstration of quantum nonlocality.

High-fidelity entanglement swapping with fully independent sources
"Entanglement swapping allows to establish entanglement between independent particles that never
interacted nor share any common past."

Field test of entanglement swapping over 100-km optical fiber with independent 1-GHz-clock sequential time-bin entangled photon-pair sources
"Entanglement swapping is a unique feature of quantum physics. By entangling two independent parties that have never interacted before, entanglement swapping has been used in the study of physics foundations such as nonlocality and wave-particle duality. ... The integrity of an experimental realization of entanglement swapping is ensured only by satisfying these criteria: proper causal disconnection between relevant events, and independent quantum sources without common past."

You can even choose to entangle the target photons after the fact with these experiments. In all cases, the order of the observations and the swap make no difference to the statistical outcome.

So yes, I like these experiments a lot. I go straight to the references to check. When they are omitted from consideration, it is a sure sign - after discussing traditional (i.e. older) Bell tests - that this is where they stumble. So not much point in reading their "hand-waving". The OP references are a good example.

I agree, It is just that I have never seen a entanglement swapping mention in an interpretation discussion. Is there any interpretation that convince you more with regard to entanglement swapping ?

 

[DrChinese]

DrChinese said:
GHZ**.
[...]
**In these experiments, each and every individual run violates realism (since he assumes locality). The quantum prediction is exactly opposite the realistic prediction, and experiment matches QM.

Neumaier asks:
What do you say to the following statement, which seems contrary to your claims? (taken from p.6-7 of M. Kupczynski, Quantum Nonlocality: how does Nature do it? Entropy 26 (2024), 191.) ...

You have actually made my point nicely.

I had read several of Kupczynski's other papers, including "Entanglement and Quantum Nonlocality Demystified" (originally 2012). This and the one you cite (cleverly and intentionally titled the same as a Gisin paper with an opposing viewpoint) also fail to mention GHZ at all*. Which was the basis for the claim we are discussing. So the rest of Kupczynski's points really don't matter to me if they can't deal with GHZ or other modern no-go's that go farther than Bell (1964).

My** claim: In GHZ, local realism predicts completely different results than quantum mechanics in each and every trial (as I'm sure you know). From "Multi-Photon Entanglement and Quantum Non-Locality":

"We conclude that the local realistic model predicts none of the terms occurring in the quantum prediction and vice versa. This implies that, whenever local realism predicts a specific result definitely to occur for a measurement on one of the photons based on the results for the other two, quantum physics definitely predicts the opposite result. For example, if two photons are both found to be H' polarized, local realism predicts the third photon to carry V' polarization while the quantum state predicts H' polarization. This is the GHZ contradiction between local realism and quantum physics."***

Once you combine the results of Entanglement Swapping (ES) experiments with GHZ experiments, many proposed "local realistic" explanations immediately fall by the wayside, including many that are simply "local". So the "preliminaries" of such explanations won't really matter; I skip to the sections on ES and GHZ. If there are any. If they aren't present, the bookmark goes into the "denier" bin.

*And skip over Entanglement Swapping with a brief mention.

**You keep referring to what I say as "my" claims. I am quoting claims verbatim from generally accepted sources and authors. I am simply repeating claims I agree with, but are basically textbook level as of 2024.

***If you have a single generally accepted reference that says the GHZ theorem is false, I'd love to see it. Note that I already have plenty of links to GHZ deniers - none of whom are generally accepted in the realm of quantum physics. So no need to present any of those.

 

[DrChinese]

I agree, It is just that I have never seen a entanglement swapping mention in an interpretation discussion. Is there any interpretation that convince you more with regard to entanglement swapping ?

Yes and no. And a fair question, by the way.

I am certainly disappointed that many "valid" interpretations claim to solve the issues present with Entanglement Swapping (and GHZ) without providing a clear picture of how that is accomplished. For example, many MWI advocates claim it is local*, but can't draw me a picture of that locality might work. Bell rules out local realism of course.

It's when a new interpretation claims to solve the outstanding quantum riddles by simply redefining the terms until their conclusion is "proven" - that's when I pull out ES. There are a surprising number of papers (and authors) I encounter each year that claim to demonstrate QM is actually local realistic. I look for novel angles, but generally the arguments tend to be similar.


*There are others here (such as myself) that believe that for MWI to make any sense, there must be a nonlocal or even a global component. It would look a lot better to me if that were explicitly factored in to match experiment.

 

[DrChinese]

These papers claim to present a realistic stochastic interpretation of quantum mechanics that obeys a stochastic form of local causality. (A lecture I recently attended mentioned these papers). It also claims the Born rule as a natural consequence rather than an assumption. This appears to me to be a genuinely new interpretation. I have not delved into the papers in detail, but figured some people here may be interested.

https://arxiv.org/abs/2302.10778
https://arxiv.org/abs/2309.03085
https://arxiv.org/abs/2402.16935

These are all by Jacob Barandes. Here is an interpretation from 2014 called the Minimal Modal Interpretation of Quantum Theory: "We introduce a realist, unextravagant interpretation of quantum theory that builds on the existing physical structure of the theory and allows experiments to have definite outcomes*..."

Of course, definite (noncontextual) outcomes are directly contradicted by GHZ - assuming locality, which they apparently do: "At the same time, we will argue that our interpretation is ultimately compatible with Lorentz invariance and is nonlocal only in the mild sense familiar from the framework of classical gauge theories."

The punchline: One of the two authors/creators of this interpretation is Barandes. (I did not search for this, I found it in my existing bookmarks of local realists.)


*Presumably independent of context.

 

[PeterDonis]

Here is an interpretation from 2014

It doesn't look to me like the actual interpretation presented in that paper fits the description in the quotes you give (which are, of course, from the paper, so the paper itself looks inconsistent to me). The actual interpretation includes entangled wave functions as "ontic states". This could be called "realist", but it is not "noncontextual", and to call it "nonlocal only in the mild sense familiar from the framework of classical gauge theories" does not strike me as a very good description.

 

[PeterDonis]

The first thing I look for is their treatment of remote Entanglement Swapping* and GHZ**...

Of course, those seminal works aren't mentioned at all.

I had a similar reaction on reading the papers linked to in the OP: I thought, ok, interesting, but when are you going to account for Bell inequality violations? I never saw that done (let alone accounting for the even more counterintuitive phenomena you describe).

 

[Vanadium 50]

How can an interpretation of an existing theory make testable predictions different from that theory?

Obviously it can't. However, it can make otherwise difficult calculations tractable.

Consider "method of images" - much like an interpretation. Some problems become very easy. If you want an actual QM examples, consider B-Bbar mixing at the B-factories. Copemhagen makes it quickly clear why you need time dependence and some of the odder features, like tagging the flavor of one B by the flavor of the 2nd one, even if it decays later. You can of course show this any way you like, but this way is intuitive and quick.

 

[PAllen]

These are all by Jacob Barandes. Here is an interpretation from 2014 called the Minimal Modal Interpretation of Quantum Theory: "We introduce a realist, unextravagant interpretation of quantum theory that builds on the existing physical structure of the theory and allows experiments to have definite outcomes*..."

Of course, definite (noncontextual) outcomes are directly contradicted by GHZ - assuming locality, which they apparently do: "At the same time, we will argue that our interpretation is ultimately compatible with Lorentz invariance and is nonlocal only in the mild sense familiar from the framework of classical gauge theories."

The punchline: One of the two authors/creators of this interpretation is Barandes. (I did not search for this, I found it in my existing bookmarks of local realists.)


*Presumably independent of context.

That appears to be a different interpretation. That paper is referenced in the first of the new ones as having developed one very specific technique which is also used in the new interpretation.

 

[bob012345]

Are all experiments that suggest non-locality theory or interpretation independent?

 

[lodbrok]

I had a similar reaction on reading the papers linked to in the OP: I thought, ok, interesting, but when are you going to account for Bell inequality violations? I never saw that done (let alone accounting for the even more counterintuitive phenomena you describe).

The third paper mentioned above specifically went into a lot of detail about EPR and Bell's theorem, concluding:

By invoking this microphysical notion of causation, one can formulate a more straightforward criterion (55) for causal locality than Bell’s principle of local causality—in either of its equivalent forms (10) or (11). As this paper has shown, quantum theory, regarded as a theory of unistochastic processes, satisfies this improved criterion, and is therefore arguably a causally local theory. Remarkably, one therefore arrives at what appears to be acausally local hidden-variables formulation of quantumtheory, despite many decades of skepticism that such atheory could exist.

 

[PeterDonis]

Are all experiments that suggest non-locality theory or interpretation independent?

It depends on what you mean by "nonlocality".

"Nonlocality" defined as "violations of the Bell inequalities and related conditions" is an experimental fact, and so is independent of any interpretation.

Other definitions of "nonlocality" might not be.

 

[PeterDonis]

The third paper mentioned above specifically went into a lot of detail about EPR and Bell's theorem

Yes, but it never explains how the claimed interpretation in the paper actually accounts for violations of the Bell inequalities. It just defines a different notion of "causal locality" and shows that QM, at least in the formulation given in the paper, satisfies it. But this notion is not at all new: it's just defining "causal locality" as "the local statistics of Bob's measurement don't depend on what Alice chooses to measure", which has been known for decades and doesn't give any help at all in understanding what does produce Bell inequality violations.

In other words, all this supposedly different notion amounts to is saying that whatever it is that produces Bell inequality violations, it's not a local property of either of the two entangled systems in isolation; it's a property of the overall system. Well, gee, thanks for pointing out the obvious.

 

[bob012345]

It depends on what you mean by "nonlocality".

"Nonlocality" defined as "violations of the Bell inequalities and related conditions" is an experimental fact, and so is independent of any interpretation.

Other definitions of "nonlocality" might not be.

Do you mean the Aspect experiment? If so, doesn't that require some framework to interpret what the data means?

 

[PeterDonis]

Do you mean the Aspect experiment?

That was one experiment that showed Bell inequality violations, yes.

If so, doesn't that require some framework to interpret what the data means?

It requires analysis of the data to take into account the fact that the photon detectors used are not perfect; they will miss some fraction of photons. But such techniques are well developed and don't depend on any particular interpretation of QM. They also have less and less impact on the results as detectors get more and more efficient.

Given the above data analysis, it requires no "framework" at all to test whether the Bell inequalities are violated. That's just straightforward math.

 

[bob012345]

That was one experiment that showed Bell inequality violations, yes.


It requires analysis of the data to take into account the fact that the photon detectors used are not perfect; they will miss some fraction of photons. But such techniques are well developed and don't depend on any particular interpretation of QM. They also have less and less impact on the results as detectors get more and more efficient.

Given the above data analysis, it requires no "framework" at all to test whether the Bell inequalities are violated. That's just straightforward math.

Ok, thanks. Just one more question. You said it doesn't depend on any particular interpretation of QM. But you have to assume QM itself right?

 

[pines-demon]

If so, doesn't that require some framework to interpret what the data means?

You can interpret it using purely classical arguments and see what happens. All the results so far on Bell tests show that Bell inequalities are violated and thus we cannot reproduce them using a purely classical theory.

 

[PeterDonis]

You said it doesn't depend on any particular interpretation of QM. But you have to assume QM itself right?

You don't have to assume any theory to look at the results of an experiment. You only have to assume a theory if you want to compare its predictions with the results of an experiment.

So you don't have to assume QM to look at the results of experiments like the Aspect experiment and see that they violate the Bell inequalities. As I've said, that's just straightforward math. (Note that the Bell inequalities themselves have nothing to do with QM. They are just inequalities that would be satisfied if the world worked a certain way. The fact that they are violated in actual experiments shows that the world doesn't work that way, but in itself it doesn't tell you how to construct a better model.) You only have to assume QM if you want to compare QM's predictions with the experimental results. (Doing that shows that the results match QM's predictions.)

 

[DrChinese]

Are all experiments that suggest non-locality theory or interpretation independent?

No, but they should be.

The theory of ordinary quantum mechanics - which predicts the experiments that suggest non-locality - has advanced over time as entanglement theory exploded. So no one really knew that Remote Entanglement Swapping was a real thing 35 years ago. Ditto with the GHZ Theorem, which was discovered about 35 years ago as well. But they knew about Bell after Aspect and other important variations. Even today, many who are familiar with the basics of Bell and entanglement are not equally familiar with recent (10-20 years) advances in experiment. So when I say there is some theory dependence, I really mean according to how up to date one is. Entanglement theory is moving very fast, as theory goes, so I would not expect everyone to be able to keep up unless this is all they do.

With interpretations, it's the wild west. Papers denying any form of nonlocality are common. Papers denying any form of contextuality (i.e. they are pushing realistic concepts) are common. And it is surprising how many papers still push local realism of a form ruled out by Bell's Theorem. Of course, you can't much publish in a peer-reviewed journal going against Bell. But in the Arxiv, they come regularly.

Of course, I would not really call a paper or two denying the existence of nonlocality a true interpretation in the first place. Most interpretations are more of a seed of an idea, rather than a full fledged interpretation featuring an interesting or useful viewpoint, basic idea, or hypothetical mechanism.

---

Are Barandes' latest works a new interpretation? He claims it "plausibly resolves the measurement problem, and deflates various exotic claims about superposition, interference, and entanglement." Big talk! The word "entanglement" appears a grand total of once in the 3rd one ("New Prospects for a Causally Local Formulation of Quantum Theory" which he names the "Unistochastic" interpretation). He says too: "...the unistochastic formulation of quantum theory reviewed in this paper lies outside the wave-function paradigm...". Maybe it's a whole new theory?

The last statement before his conclusion, which is referring to a traditional Alice/Bob Bell test is: "The only causal influences on the observer-subsystem A [source of entangled pairs] are from the two subsystems Q [Alice] and R [Bob], which both intersect the past light cone of A [the source]." This statement might* work for such a simple example; but it obviously won't apply in a Remote Entanglement Swapping example in which there is no such intersect in the past light cone. That's a huge flop.

DrChinese grade: F. Don't waste our time in 2024 giving examples from 1981. I won't be waiting for his next paper.


*I would deny it.

 

[PeterDonis]

Maybe it's a whole new theory?

As far as I can tell, it's mathematically equivalent to standard QM. I might describe it as a sort of weird variant of the Bohmian interpretation, where there are unobservable particle positions as underlying hidden variables, but stochastic dynamics for these particles, set up in just the right way to match the predictions of standard QM, takes the place of the initial distribution of particle positions in the Bohmian interpretation, which is likewise set up in just the right way to match the predictions of standard QM.

 

[A. Neumaier]

You keep referring to what I say as "my" claims. I am quoting claims verbatim from generally accepted sources and authors. I am simply repeating claims I agree with

This makes them your claims, too.

Note that by making a very selective choice, you heavily bias the quite controversial collection of claims in the literature towards your own preference. That's why I refer to your claims.

 

[PAllen]

As far as I can tell, it's mathematically equivalent to standard QM. I might describe it as a sort of weird variant of the Bohmian interpretation, where there are unobservable particle positions as underlying hidden variables, but stochastic dynamics for these particles, set up in just the right way to match the predictions of standard QM, takes the place of the initial distribution of particle positions in the Bohmian interpretation, which is likewise set up in just the right way to match the predictions of standard QM.

The comparison with Bohmian interpretation is, in fact, discussed in the first of the papers:

"Because this paper’s approach invokes hidden variables
in the form of underlying physical configurations, this
framework for quantum theory shares some aspects with
the de Broglie-Bohm formulation, or Bohmian mechan-
ics [84–86]. However, in contrast to this paper’s ap-
proach, Bohmian mechanics employs deterministic dy-
namics, and features a fundamental guiding equation
that explicitly breaks Lorentz invariance by singling out
a preferred foliation of spacetime into spacelike hyper-
surfaces. This paper instead takes seriously what exper-
iments strongly suggest—that the dynamics of quantum
theory is indeterministic, and that there is no fundamen-
tally preferred foliation of spacetime. The formulation of
quantum theory in this paper is also more flexible and
model-independent than Bohmian mechanics, and works
for all kinds of quantum systems, from particles to fields
and beyond."

Barandes also claim, in the final paper:

"Remarkably, one therefore arrives at what appears to be a
causally local hidden-variables formulation of quantum
theory, despite many decades of skepticism that such a
theory could exist"

It is here that @DrChinese comments are most relevant, because only the simplest EPR set up is actually analyzed in any of the papers.

 

[PeroK]

Barandes also claim, in the final paper:

"Remarkably, one therefore arrives at what appears to be a
causally local hidden-variables formulation of quantum
theory, despite many decades of skepticism that such a
theory could exist"

The thing that niggles me is that it the Aspect experiment testing Bell's Theorem ruled out hidden variables - or so it was assumed. It was not just "skepticism" about hidden variables. Okay, unlike pure mathematics, there is always room for manoeuvre in physics/philosophy and nothing is ever quite proven. Nevertheless, Bell's Theorem is not something to be sneezed at! And it's certaintly not just an expression of skepticism.

 

[PAllen]

The thing that niggles me is that it the Aspect experiment testing Bell's Theorem ruled out hidden variables - or so it was assumed. It was not just "skepticism" about hidden varaibles. Okay, unlike pure mathematics, there is always room for manoeuvre in physics/philosophy and nothing is ever quite proven. Nevertheless, Bell's Theorem is not something to be sneezed at! And it's certaintly not just an expression of skepticism.

According to the papers, all the hidden variable no go theorems implicitly or explicitly assume the hidden variable theories are subject to Riechenbach common cause. The third paper explains how this interpretation escapes Riechenbach. Note, Bohmian theories escape in a different way.

 

[gentzen]

The thing that niggles me is that it the Aspect experiment testing Bell's Theorem ruled out hidden variables - or so it was assumed. It was not just "skepticism" about hidden variables. Okay, unlike pure mathematics, there is always room for manoeuvre in physics/philosophy and nothing is ever quite proven. Nevertheless, Bell's Theorem is not something to be sneezed at! And it's certaintly not just an expression of skepticism.

Just like Bohmian mechanics, this new formulation initially looks extremely nonlocal. So the problem seems to be less how to overcome Bell's theorem (or DrChinese's objections), but how to get back some sort of locality into that formulation. (As I said before, I cannot yet judge how successful Barandes has been in this respect.)

 

[martinbn]

Don't we have enough interpretations already?

At what point weren't there enough interpretations? There were always too many.

 

[PeterDonis]

what appears to be a
causally local hidden-variables formulation of quantum
theory

This claim, of course, depends on using a different definition of "locality" from the one Bell, GHZ, etc. used to prove their theorems. Basically, it means something like "Alice's and Bob's measurement actions are local--they only act on the particle they are measuring". But again, we already knew this: the standard QM math tells us that the operator that describes Alice's measurement only acts on Alice's qubit, and the operator that describes Bob's measurement only acts on Bob's qubit. The nonlocality is in the wave function: acting on either qubit changes the entire entangled wave function, which includes the other qubit. In other words, there is nothing new here, just a choice of terminology that makes it seem like there's something new when there actually isn't.

 

[DrChinese]

This makes them your claims, too.

Note that by making a very selective choice, you heavily bias the quite controversial collection of claims in the literature towards your own preference. That's why I refer to your claims.

I notice that you manage to pick apart the specific words I use, without making any comments of substance about the physics. So let's see:

a. "you heavily bias the quite controversial collection of claims in the literature" Controversial? Really? You think GHZ is controversial (that was one of 2 experiments I mentioned)? GHZ says that in tests of 3 photons entanglement of GHZ states, local realism predicts 4 of 8 possible outcomes while QM predicts the other 4 outcomes - without the need for a statistical correlations. Experiments have confirmed the predictions of QM. I would say that this disproves local realism without leaving the wiggle room sometimes associated with Bell tests. But it could also be considered as disproving realism, unless you are into strange hypothetical FTL signaling mechanisms between 3 (or more) remote particles. What would you call biased or controversial?

On the other hand, your response to my reference on GHZ was to provide a reference with no mention of GHZ? Perhaps you would care to address (counter) GHZ with a relevant citation of what you consider a good experimental team/paper?

b. I also mentioned Remote Entanglement Swapping (where the final entangled pair has never existed in a common backward light cone). Is that a "biased" or "controversial" finding?

---

Yes, my references are quite selective. That's because they leave little room for doubt as to the results or related theory. In that sense, you are correct: they are "biased". And the references are selected to highlight the state of the art in entanglement as it related to the thread. In that sense, you are correct again: they are "controversial", simply because they are not known to many readers.

Something new is often considered "controversial". Hey, the Beatles were controversial when they came out too... and now they are old hat.

 

[PeroK]

Hey, the Beatles were controversial when they came out too... and now they are old hat.

Perhaps the Rolling Stones would be a better example. They were the British bad boys of the 1960's and now it's Sir Mick Jagger!

 

[PAllen]

This claim, of course, depends on using a different definition of "locality" from the one Bell, GHZ, etc. used to prove their theorems. Basically, it means something like "Alice's and Bob's measurement actions are local--they only act on the particle they are measuring". But again, we already knew this: the standard QM math tells us that the operator that describes Alice's measurement only acts on Alice's qubit, and the operator that describes Bob's measurement only acts on Bob's qubit. The nonlocality is in the wave function: acting on either qubit changes the entire entangled wave function, which includes the other qubit. In other words, there is nothing new here, just a choice of terminology that makes it seem like there's something new when there actually isn't.

Except that this formulation doesn't use wave functions at all, except as derived convenience. As I understand it so far, the correlations in measures at A and B are due to the non-factorizability of the hidden (uni-stochastic) configuration underlying Q and R, and this latter is the result of their interaction in their past. However, the part that I agree seems just playing with definitions is that the (Q,R) configuration encompasses continued influences between Q and R following the interaction. That is, while actions of A or B (Alice and Bob) are 'factored out', Q and R still seem non-locally coupled in any every-day sense of the term: the probability of a configuration change at Q remains coupled to the configuration at R, and vice versa. At least, that is my understanding based on pp. 12-13 of the third paper.

 

[PeterDonis]

this formulation doesn't use wave functions at all, except as derived convenience

But that just means the nonlocality--the whatever-you-want-to-call-it that actually enables the Bell inequality violations--is shoved somewhere else in the model. It can't be made to go away. The somewhere else might not be called a wave function in this formulation, but it has the same effect. As you note, it's just "playing with definitions".

 

[Morbert]

I saw the last of these papers when it was dropped into Arxiv a few days ago. The first thing I look for is their treatment of remote Entanglement Swapping* and GHZ**. These are some of the strongest experiments against all forms of local realism. If you aren't addressing these, then you really can't make any useful/serious claims in today's environment.

Of course, those seminal works aren't mentioned at all. (There is a passing GHZ reference, but it is not discussed at all.) The main idea of the paper seems to be to define local causality in a very specific manner, then deny that. Well, experiment reigns supreme. I will give this a better look once modern (last 30 years) experiments are explained in terms of the new interpretation. This paper is closer to 1980's era ideas. ***

The papers submit a new definition of causal locality and argue it is superior when quantum theory is understood as a theory of stochastic processes characterized by an indivisible transition matrix. GHZ etc might be an interesting homework exercise for this interpretation, but it's not clear that it poses any substantive challenge above and beyond simpler, ordinary EPRB-like experiments.

The interpretation itself might be interesting if it ends up saying something re/ intuitions about stochastic processes and the Markov property.

*In these experiments, distant photons are entangled (and violate a Bell inequality) that have never existed in a common backward light cone. Pretty hard to get locality with that.

As i have shown in this thread (you will have to ask the mods for the deleted post). That the photons have never existed in a common backward light cone does not pose any additional challenge to the question of locality beyond standard EPRB because, in the same way the EPRB system is a noncommutative generalization of a classical system, entanglement swapping experiments are are nocommutative generalization of a "correlation swapping" classical experiments where two classical systems that have never existed in a common backward light cone become correlated.

 

[WernerQH]

The interpretation itself might be interesting if it ends up saying something re/ intuitions about stochastic processes and the Markov property.

At first sight it looks more like a refurbished presentation of quantum theory's mathematical apparatus than an interpretation. The transition matrix in the form $\Gamma_{ij}(t) = \rm{tr}(\Theta^\dagger(t) P_i \Theta(t) P_j)$ (eq.26 in the first paper) reminds me of the well-known Schwinger-Keldysh formalism. Unfortunately the configuration space of the "system" is completely abstract, and it's unclear how it relates to the objects that we experience in the real world. One would also desire a clearer picture of those "division events" which permit approximating a non-Markovian process by a Markov process. In some cases the emission of a photon can be thought of as such an event, but in others the emission process cannot be considered as instantaneous and must be treated as a pair of two correlated events (two short-lived, strongly localized currents). My hunch is based on Kubo formulas, and I commented on it in an earlier post.

Yes, I do think that stochastic elements are essential for quantum theory. How could continuous and deterministic evolution according to Schrödinger's equation provide a faithful description of what happens in the real world, for example, the sudden decay of an atomic nucleus?

 

[DrChinese]

1. GHZ etc might be an interesting homework exercize for this interpretation, but it's not clear that it poses any substantive challenge above and beyond simpler, ordinary EPRB-like experiments.

2. That the photons have never existed in a common backward light cone does not pose any additional challenge to the question of locality beyond standard EPRB because, in the same way the EPRB system is a noncommutative generalization of a classical system, entanglement swapping experiments are are noncommutative generalization of a "correlation swapping" classical experiments where two classical systems that have never existed in a common backward light cone become correlated.

1. That's a quick dismissal of GHZ. It's not a homework exercise, we are talking about a major no-go theorem here. The realistic assumption ("causal locality" in "a model that consists of a set of random variables connected by a collection of conditional probabilities") leads to opposite predictions compared to experiment.

2. Whoa! Another big statement, and yet no peer-reviewed reference supporting your statement. You are basically denying the quantum nature of entanglement. Hmmm. I'll pay you $10 (I'm a cheap bettor, but I'll give you decent odds) if you can find a classical "correlation swapping" example with the following attributes, which are demonstrated in quantum experiments such as this or this.

• a. The photons (or whatever classical objects you prefer) detected by Alice and Bob never exist/interact in a common light cone. Let's call these objects 1 and 4 to match my experimental references.
• b. 1 and 4 cannot be entangled or otherwise made identical in their initial states, because the decision to entangle them (or not) will be made in a remote (FTL distant) place by Chris. So Alice, Bob and Chris are spacelike separated at the time that 1 and 4 become entangled - or correlated, or whatever you care to call it. They are also all spacelike separated when Alice and Bob perform their chosen measurements.
• c. Alice and Bob can choose to measure either i) on any same basis (in which case we must see perfect correlation); or ii) on different bases (a la CHSH, and violating a Bell inequality). I'll be impressed if you can do this for even just case i).
• d. Chris can choose to entangle - or not - the 1 and 4 objects. The observed Alice/Bob correlations must change along with this choice. No correlation if Chris chooses not to classically correlate.

This is impossible in any classical scenario, as it should be obvious - which is why the Remote Entanglement Swapping experiments are critical to interpretation analysis. I certainly have never seen a concrete example that could even remotely (pun intended) pull this off.


Note to moderators: If this is too far off the thread subject, we could split off the discussion. The relationship to the thread subject is that new interpretations should be able to explain experiments like GHZ and Remote Swapping if they are to be taken seriously. Otherwise, we are just dialing the clock back 35 years. Bell sadly passed away before the impact of these newer experiments were evident. I'm certain he would have accepted this important science, and be justifiably proud of what his groundbreaking work has given birth to.

 

[PeterDonis]

As i have shown in this thread

You were thread banned in that thread because what you claim to have "shown" there was not "shown" and you were hijacking the discussion with off topic unjustified claims. Given that, you have now been thread banned from this thread.

 

[kurt101]

2. Whoa! Another big statement, and yet no peer-reviewed reference supporting your statement. You are basically denying the quantum nature of entanglement. Hmmm. I'll pay you $10 (I'm a cheap bettor, but I'll give you decent odds) if you can find a classical "correlation swapping" example with the following attributes, which are demonstrated in quantum experiments such as this or this.

• a. The photons (or whatever classical objects you prefer) detected by Alice and Bob never exist/interact in a common light cone. Let's call these objects 1 and 4 to match my experimental references.
• b. 1 and 4 cannot be entangled or otherwise made identical in their initial states, because the decision to entangle them (or not) will be made in a remote (FTL distant) place by Chris. So Alice, Bob and Chris are spacelike separated at the time that 1 and 4 become entangled - or correlated, or whatever you care to call it. They are also all spacelike separated when Alice and Bob perform their chosen measurements.
• c. Alice and Bob can choose to measure either i) on any same basis (in which case we must see perfect correlation); or ii) on different bases (a la CHSH, and violating a Bell inequality). I'll be impressed if you can do this for even just case i).
• d. Chris can choose to entangle - or not - the 1 and 4 objects. The observed Alice/Bob correlations must change along with this choice. No correlation if Chris chooses not to classically correlate.

This is impossible in any classical scenario, as it should be obvious - which is why the Remote Entanglement Swapping experiments are critical to interpretation analysis. I certainly have never seen a concrete example that could even remotely (pun intended) pull this off.

Would you extend this bet for anyone? And would you extend it for my variant? Can I make the example myself or does it have to be something peer reviewed and published?

I don't deny entanglement. I don't deny entanglement swapping when the swap operation performed at 2 & 3 is performed before (in an absolute time sense) measuring 1 & 4. However, when the measurement on 1 & 4 is performed first (in an absolute time sense) before the swap operation at 2 & 3, I think photons 2 & 3 have all the information about 1 & 4 at the time of the swap operation to decide whether the measurements of 1 & 4 (made in the absolute past) have the property of being entangled or not. And to me this would be the part of the experiment that calls into question the classical nature, but I suppose that depends on what you mean by classical.

 

[PeterDonis]

Can I make the example myself or does it have to be something peer reviewed and published?

Any claim about what QM interpretation says about a scenario needs to be backed up by a published peer reviewed reference.

 

[DrChinese]

1. Would you extend this bet for anyone? ... Can I make the example myself or does it have to be something peer reviewed and published?

2. I don't deny entanglement. I don't deny entanglement swapping when the swap operation performed at 2 & 3 is performed before (in an absolute time sense) measuring 1 & 4. However, when the measurement on 1 & 4 is performed first (in an absolute time sense) before the swap operation at 2 & 3, I think photons 2 & 3 have all the information about 1 & 4 at the time of the swap operation to decide whether the measurements of 1 & 4 (made in the absolute past) have the property of being entangled or not. And to me this would be the part of the experiment that calls into question the classical nature, but I suppose that depends on what you mean by classical.

1. Sure! If you can keep the example simple enough, I'll give it a go. Obviously, it must follow accepted science of some kind (and if an interpretation, it should follow Peter's admonition).

2. Whew... you scared me for a moment. Your idea about order reversal (measuring 1 & 4 before 2 & 3) has one major problem. This issue is normally overlooked by those seeking some kind of traditional causal order where cause precedes effect (a very reasonable expectation, of course).

The final entangled photons are 1 & 4. They become entangled upon successful interaction (indistinguishable overlap) of photons 2 & 3. Let's specify and agree that this interaction of 2 & 3 occurs AFTER 1 & 4 are already detected (per your idea). But here are a couple of other conditions to consider:

a) The angle choices for detection of 1 & 4 are unknown to each other because they are far distant (no signal can travel between them). There are an infinite* number of combinations possible which either show perfect correlations (in each and every case when the angle choices are the same), or violate Bell inequalities via statistical averages (in many cases when the angle choices are different).

b) Likewise, at the time 1 is detected, its entangled partner 2 is far away. Ditto between 3 & 4. No signal can propagate between them. You are going to need to have some kind of remote action at a distance to have 2 "know" how 1 was measured. (But that is what we were trying to avoid!)

c) All cases - and not just some as you might imagine - in which the 2 & 3 photons overlap lead to entanglement of 1 & 4. But there are only 4 permutations of the 2 & 3 photon overlap. Those are the 4 possible Bell states. It is not possible to map those 4 cases to an infinite* number of permutations of choices for measuring 1 & 4. It's just not a wide enough channel. There are only a few variables in a pair of indistinguishable photons (2 & 3). Which is a requirement for a swap.

d) And keep in mind that the decision by Chris to overlap 2 & 3 is in fact made AFTER 1 & 4 are detected. That means that there can be no correlation at all in those cases.

Good luck! I am setting aside your future winnings aside as we speak...


*If it is not infinite, then it's a very large number.

 

[PAllen]

1. That's a quick dismissal of GHZ. It's not a homework exercise, we are talking about a major no-go theorem here. The realistic assumption ("causal locality" in "a model that consists of a set of random variables connected by a collection of conditional probabilities") leads to opposite predictions compared to experiment.

One thing here is that the author uses a new definition of causal locality which is not the same as used in any theorems (and, as @PeterDonis has noted, has arguably no content beyond established 'no messaging' results). Also, his 'hidden reality' is not equivalent to a collection of random variables. So on this question, it seems to me that existing no-go theorems are not applicable. In fact, it seems to me that properties he derives for it make it equivalent to a wave function with different mathematical representation.

 

[PAllen]

The relationship to the thread subject is that new interpretations should be able to explain experiments like GHZ and Remote Swapping if they are to be taken seriously. Otherwise, we are just dialing the clock back 35 years. Bell sadly passed away before the impact of these newer experiments were evident. I'm certain he would have accepted this important science, and be justifiably proud of what his groundbreaking work has given birth to.

This, I strongly agree with. But due to the formal mathematical equivalences demonstrated in the OP references, I think this is likely to be possible. However, the author must do it at some point to be taken seriously.

 

[DrChinese]

One thing here is that the author uses a new definition of causal locality which is not the same as used in any theorems (and, as @PeterDonis has noted, has arguably no content beyond established 'no messaging' results). Also, his 'hidden reality' is not equivalent to a collection of random variables. So on this question, it seems to me that existing no-go theorems are not applicable. In fact, it seems to me that properties he derives for it make it equivalent to a wave function with different mathematical representation.

Well, that's kinda the issue, isn't it? He says here: "one can reformulate quantum theory in terms of old-fashioned configuration spaces together with 'unistochastic' laws. These unistochastic laws take the form of directed conditional probabilities, which turn out to provide a hospitable foundation for encoding microphysical causal relationships. This unistochastic reformulation provides quantum theory with a simpler and more transparent axiomatic foundation, plausibly resolves the measurement problem, and deflates various exotic claims about superposition, interference, and entanglement."

That abstract sounds exotic to me! Superposition and interference are merely "claims? Measurement problem: solved! And entanglement... well I think it is very clear entanglement is a great big target on the back of this formulation. No, you cannot define/redefine the phrase "causal locality" to be different than "local causality", and then expect to dodge GHZ, advanced entanglement issues and the latest no-go's.

That's a far cry from agreeing with the idea that there is signal locality - which as far as I know is disputed by essentially no one. And if in fact you are correct, he has a new mathematical representation: so is it in fact exactly identical (since he drops the standard mathematical methods entirely) ? How would a reader understand that either way? His abstract contains some big claims, and I certainly missed the elements where he convinces of the abstract's claims.

Here is the last sentence of his conclusion, you tell me if he thinks he is onto something different and important. Because it certainly reads to me that the Bell conclusion* (along with GHZ etc.) is being thrown out.

"Remarkably, one therefore arrives at what appears to be a causally local hidden-variables formulation of quantum theory, despite many decades of skepticism that such a theory could exist."


*Which is: "No physical theory of local Hidden Variables can ever reproduce all of the predictions of Quantum Mechanics."-DrC