Talk:Bell's theorem

Recent reverts

I have, like, no time or energy to put into this article now, but I did want to say that I think the text removed here is a bad addition. Squeezing every possible qualification into the paragraph that is supposed to be the most broadly comprehensible is a bad idea. The intro is already overlong; if anything, it needs to be condensed (and if we are to add any more to it, it needs to be condensed significantly first). Moreover, per house style, the intro is supposed to provide a capsule summary of the main article that follows, and putting emphasis upon a point that the main article doesn't is giving that point undue weight. (The article itself doesn't even say "noncontextual" until it gets into Gleason's theorem.) No doubt the page needs improvements, but I don't think this is one of them. XOR'easter (talk) 20:56, 27 February 2024 (UTC)

Without mentioning noncontextuality, the conclusion drawn is literally incorrect. In order to describe a theorem, one must state all of the hypotheses of the theorem. As written the article is misleading. Physicalisms (talk) 18:58, 7 March 2024 (UTC)

This isn't an issue of mathematics, it's one of language and technical writing. No one disagrees as to what the theorem is or what it fundamentally requires, but we have to explain it in the format of an encyclopedia article. It's fine to have an incomplete description after the end of the first paragraph.

(This reminds me tangentially of the saga where Wikipedians came to heartache and an ArbCom decision over the ordering and treatment of explanations in the Monty Hall problem article.) Remsense诉 19:37, 7 March 2024 (UTC)

The term "noncontextual" is confusing, and does not add anything. Roger (talk) 20:11, 7 March 2024 (UTC)

Mermin-Peres magic squares.

The Mermin-Peres magic square analysis seems missing here. As a simplified "game" it might make some of this more accessible.

Mermin and Peres both worked on simplified Bell models as summarized in:

• Aravind, Padmanabhan K. "Quantum mysteries revisited again." American Journal of Physics 72.10 (2004): 1303-1307.

These models take the form of a "game" described in the common sense of a game but treated as in game theory. The wikipedia treatment of the Mermin-Peres magic square is buried inside Quantum pseudo-telepathy. Johnjbarton (talk) 17:59, 27 March 2024 (UTC)

I disagree. The rules of the game are more complicated, the proof of the local bound is more complicated, and the quantum strategy is much more complicated. The only good thing about the magic square is that the quantum probability of victory is 1. Which is rather nice but conceptually irrelevant for Bell's theorem, and in any case already covered by the GHZ game here. Tercer (talk) 19:55, 27 March 2024 (UTC)

The Copenhagen Interpretation

The section of the current article called "The Copenhagen Interpretation" seems to be WP:SYNTH to me.

For example the first part of the section covers Bohr's reply to EPR. (I'm not sure why that is even in here.) This is "Bohr's interpretation". The paragraph starts with refs to papers that are not about Bells theorem at all. Johnjbarton (talk) 15:27, 1 May 2024 (UTC)

I check some more refs then deleted the first paragraph, off topic and not useful elsewhere. Johnjbarton (talk) 15:38, 1 May 2024 (UTC)

Saying something about Bohr's reply to EPR makes sense here, in principle, as Bell '64 built on top of EPR. I don't see how the removed material qualifies as WP:SYNTH, because it didn't advance a new conclusion (e.g., "Based on what Bohr wrote in 1935, he would have responded thusly to Bell in 1964..."). Maybe it was unsuitable for other reasons (e.g., too long), but I don't think WP:SYNTH was a problem there. And the opening of the deleted paragraph performed the important role of saying what the "Copenhagen interpretation" is, or rather, what the Copenhagen interpretations are. I don't know if just providing a wiki-link is enough, but I've added one. XOR'easter (talk) 17:07, 1 May 2024 (UTC)

What I object to is the idea that Bohr's view on EPR becomes "Copenhagen" view on Bell. There is no "Copenhagen" view on Bell because there is no "Copenhagen". Half the paragraph was devoted to shoring up a definition of "Copenhagen" because it is not a thing.

There is a "standard" "conventional" or "orthodox" interpretation which is also not crisply defined but all we need are refs about Bell theorem from standard text books, not a big intro.

If we do that, which I think is wikipedia, then what happens to Bohr on EPR? Without the implicit claim that Bohr speaks on behalf of "Copenhagen" when he speaks about EPR, we need a ref to include Bohr on EPR in an article on Bell. Otherwise it is off topic.

We could make Bohr/EPR/Bell a topic as there are references that do exactly that, eg:

• Dickson, Michael. "Bohr on bell: A proposed reading of bohr and its implications for bell’s theorem." Non-locality and Modality. Dordrecht: Springer Netherlands, 2002. 19-35.

But Bohr/ERP can be discussed directly in the History without the "Copenhagen" baggage. Johnjbarton (talk) 17:36, 1 May 2024 (UTC)

I don't think a paragraph that prominently included the text There is no definitive historical statement of what is the Copenhagen interpretation. In particular, there were fundamental disagreements between the views of Bohr and Heisenberg. was "shoring up a definition" for the Copenhagen interpretation. Rather the opposite: it went out of its way to say that there is no unique definition of a single Copenhagen interpretation, only a collection of features that more-or-less distinguish this collection of separate ideas from other collections. Cutting that makes the subsection slightly worse, I think.

Bohr's reply to EPR makes sense as background to explain what "rejecting counterfactual definiteness" means. I think that qualifies it for being on-topic, but reading the subsection in its shorter form, I think we might be OK without it.

The question of how Bohr might have reacted to Bell's theorem is a matter of speculation (Dickson uses lots of language like "Bohr would presumably argue") and would of course have to be labeled as such. XOR'easter (talk) 18:07, 1 May 2024 (UTC)

Ok, my main objection here is to emphasize "Copenhagen" and exclude "orthodox" as a result. I get the sense that throughout wikipedia "Copenhagen" is a code-word for "old, incorrect". The term is not often used in textbooks or even in QM articles. Johnjbarton (talk) 18:16, 1 May 2024 (UTC)

And when the textbooks do use it, they just copy the same lazy explanation that the previous textbooks copied from the textbooks before that, ignoring everything that historians of science have been saying since the 1970s. XOR'easter (talk) 18:20, 1 May 2024 (UTC)

Alternative organization for the Interpretations section

Since I know that the many indistinguishable interpretations of QM have an equal number of ardent followers I'll suggest this reorg before editing.

I think the more effective categories for interpretations is "Hidden variables" vs "No variables". This grouping would make the implications of Bell's theorem for interpretations clearer. See for examples

• Werner, Reinhard F. "What Maudlin replied to." arXiv preprint arXiv:1411.2120 (2014).
• Żukowski, Marek. "Bell’s theorem tells us not what quantum mechanics is, but what quantum mechanics is not." Quantum [Un] Speakables II: Half a Century of Bell's Theorem (2017): 175-185.

Any "classical" interpretation must be non-local because of Bell; any non-classical interpretation is unaffected. Johnjbarton (talk) 17:41, 1 May 2024 (UTC)

I'm not sure what this reorganization would achieve. Surely organizing a section called "Interpretations" by the name of the interpretation makes sense enough? XOR'easter (talk) 18:09, 1 May 2024 (UTC)

Yes, but I don't think that is what we have. Under "Copenhagen" we have most of the modern interpretations. We have "Non-local hidden variables". And we have MWI and Superdeterminism. Johnjbarton (talk) 18:22, 1 May 2024 (UTC)

The "Copenhagen" section has one line about modern interpretations that are close to the Copenhagen collection, which sounds reasonable. Really, the odd one out is "Superdeterminism", which isn't really an interpretation but a feature that (a small number of people) have advocated for an interpretation to include. How about this: Move the line about the transactional interpretation into the next subsection, change "Superdeterminism" to "Proposals about retrocausality and superdeterminism", and change "Non-local hidden variables" to "Bohmian mechanics"? There have been other proposals to bring retrocausality into the story somehow, e.g., by Wharton and Argaman. XOR'easter (talk) 18:42, 1 May 2024 (UTC)

Yes, good. But then where do these things go?

• Fuchs, Christopher A., and Asher Peres. "Quantum theory needs no ‘interpretation’." Physics today 53.3 (2000): 70-71. "...the violation of Bell’s inequality by quantum theory is not a proof of its nonlocality. Quantum theory is essentially local. Bell’s discovery was that any realistic theory that could mimic quantum mechanics would necessarily be nonlocal."
• Bub, Jeffrey. "Why the quantum?." Studies in History and Philosophy of Science Part B: Studies in History and Philosophy of Modern Physics 35.2 (2004): 241-266. "The separability and locality conditions, formulated as constraints on probabilities, are equivalent to the assumption that correlations can be reduced to a common cause, and Bell’s derivation of an inequality (violated by certain quantum correlations) from these conditions is an elegant demonstration of a surprising implication of Einstein’s insight: the impossibility of embedding the quantum correlations in a common cause theory."

These seem like interpretation, but to classify them as "Copenhagen" seems inconsistent with any textbook or literature outside of the narrow historical discussions on "Copenhagen". Johnjbarton (talk) 22:11, 1 May 2024 (UTC)

Bub, along with Pitowsky, Brukner, and Zeilinger can be sorted into the post- or neo-Copenhagen informational interpretations. I'm not sure it's a good idea to cite the Fuchs–Peres paper; that was a slog of a compromise in order to produce something with which neither author disagreed (there's a whole chapter in Fuchs' Coming of Age with Quantum Information about the writing process!), and Fuchs later decided that a more radical position was necessary, so it's not really an essay that anyone stood by. Citing Peres' textbook or any of his solo-author papers would be a better way to represent his position. XOR'easter (talk) 02:15, 2 May 2024 (UTC)

In Interpretations of quantum mechanics there is a section "Quantum information theories" and it is backed by the (famous?) poll as a category separate from Copenhagen. I suggest a section with a name including "quantum information".

Peres' book has quite a lot about Bell, but that makes it difficult to boil down to a sentence.

This article definitely needs some content about Zeilinger's work. Johnjbarton (talk) 02:53, 2 May 2024 (UTC)

The write-up of that poll describes "information-based interpretations" as among the "intellectual offsprings" of Copenhagen. Maybe we should collect them together in a subsection called, e.g., "Copenhagen and neo-Copenhagen"? I don't have strong feelings here (though I do tend to find short subsections kind of choppy, as a matter of personal taste). XOR'easter (talk) 03:11, 2 May 2024 (UTC)

If we go strictly by the ref, we would have "information-based interpretations" and include the other (among the offspring) Copenhagen-like interpretations under their own names. To me, that matches the modern scene. While we can't find "Copenhagen" to ask how Bell works, refs on information-based interpretations will claim eg complementarity.

Also I think coining "neo-Copenhagen" as "information-based interpretations" would conflict with

• De Muynck, Willem M. "Towards a neo-Copenhagen interpretation of quantum mechanics." Foundations of Physics 34 (2004): 717-770.

Johnjbarton (talk) 03:28, 2 May 2024 (UTC)

Using neo-Copenhagen to refer to that general territory is not my coinage; see, e.g., [1][2][3][4]. But I don't think the terminology of classification is very standardized at all here. Cf. Cabello [5]. Perhaps a subsection heading like "Copenhagen-type and information-based" would be viable.

We obviously don't have a response from Bohr to Bell's theorem. We do, however, have authors like Peierls and Omnès, who tried to present what they saw as Copenhagen, and who had things to say about Bell's work. XOR'easter (talk) 12:07, 2 May 2024 (UTC)

Wow thanks for the refs!

I agree that we cannot plan to "get it right", just try to make some improvement. Cabello's 2x2 organization is worth considering for our interpretations article. In the context of this page his participatory realism (Type II) category supports a "Copenhagen-type and information-based" section. Johnjbarton (talk) 15:22, 2 May 2024 (UTC)

Just to wrap up, I think we agree:

• section name changes to "Copenhagen-type and information-based"
• Add a few sentences about information based, eg Zeilinger.

Johnjbarton (talk) 15:49, 2 May 2024 (UTC)

violation of a Bell inequality cannot be interpreted as a proof of non-locality.

The article cites:

• Brown, Harvey R.; Timpson, Christopher G. (2016). "Bell on Bell's Theorem: The Changing Face of Nonlocality". In Bell, Mary; Gao, Shan (eds.). Quantum Nonlocality and Reality: 50 years of Bell's theorem. Cambridge University Press. pp. 91–123. arXiv:1501.03521. doi:10.1017/CBO9781316219393.008. ISBN 9781316219393. S2CID 118686956.

when it says:

• "Therefore, the violation of a Bell inequality cannot be interpreted as a proof of non-locality."

The ref is a cited but unpublished arxiv article. But it does not support the current content and the current content does not make sense anyway. The question we should address is "how does Bell theorem impact MWI?"

I added a quote to the ref to support a change to the sentence. Johnjbarton (talk) 16:00, 2 May 2024 (UTC)

Well I am trying to make sense of this section but it is tough sledding. The first paragraph ends with:

• "Therefore, a violation of a Bell inequality can be interpreted as a demonstration that measurements have multiple outcomes."

citing

• Deutsch, David; Hayden, Patrick (2000). "Information flow in entangled quantum systems". Proceedings of the Royal Society A. 456 (1999): 1759–1774. arXiv:quant-ph/9906007. Bibcode:2000RSPSA.456.1759D. doi:10.1098/rspa.2000.0585. S2CID 13998168.

The paper does not claim that Bell tests demonstrate multiple outcomes as implied. Obviously that would be news. In fact the section of the cited article is called "Irrelevance of Bell’s theorem". Johnjbarton (talk) 17:21, 2 May 2024 (UTC)

In addition to these issues, the Deutsch/Hayden paper is not about Many-Worlds interpretation or any other interpretation for that matter. It does discuss locality and Bell's theorem so it may have a role in some other part of the article. Johnjbarton (talk) 20:18, 4 May 2024 (UTC)

I changed both paragraphs to match what I read in the refs. In both cases I removed concluding sentences that implied consequences beyond what the refs say. Johnjbarton (talk) 17:54, 2 May 2024 (UTC)

If you can't understand the paper then don't vandalize Wikipedia. I understood the paper and I wrote that part. Tercer (talk) 21:40, 2 May 2024 (UTC)

I understood the papers. I do not agree with the summary you wrote.

Two specific claims were made as I described above. Neither paper justifies those claims.

I'll go over the discussion I already made above, I guess in more detail.

• "Therefore, the violation of a Bell inequality cannot be interpreted as a proof of non-locality."

What is the point of this claim here? It has nothing to do with MWI. It is an assertion of a well-known issue with Bell's proof, or any proof for that matter: if your application does not include the preconditions for the proof, the results need not apply. MWI does not satisfy the separability or uniqueness of outcomes required by Bell. The point of the Brown-Timpson paper is that even MWI does not satisfy the preconditions for Bell, MWI still has something interesting to say about Bell. That is what our article should get across.

• "Therefore, a violation of a Bell inequality can be interpreted as a demonstration that measurements have multiple outcomes."

This statement is either obvious -- you can't have correlation without multiple possible outcomes -- or an extrapolation -- no one believes that Bell correlations prove MWI. So I assume that you meant something else, but what I don't know. I did not see anything like this in the ref, but maybe you did.

@Tercer I am asking you to respond to my comments above. I hope you will go back and read my version. I think it fairly represents Bell/MWI and the refs. Johnjbarton (talk) 22:04, 2 May 2024 (UTC)

I favor deleting the whole section as confusing and incorrect. Bell's theorem does not even apply to the MWI. Roger (talk) 02:26, 3 May 2024 (UTC)

I think we could have a useful section that explains why Bell's theorem does not apply to MWI and how MWI explains the observed correlations. That was the intent of my now-reverted revision. Johnjbarton (talk) 02:45, 3 May 2024 (UTC)

It just takes a sentence. Bell assumes that experiments have unique outcomes. MWI does not. There is no way to reconcile MWI with Bell's work. Roger (talk) 03:25, 3 May 2024 (UTC)

How about the following sentence-ish then:

• The results of Bell's theorem follow when a system is separable and has single outcomes, but the Multiple-worlds interpretation is not separable and has multiple outcomes. Thus the theorem does not apply.

Johnjbarton (talk) 17:51, 4 May 2024 (UTC)

That's of course unacceptable. You are removing all the interesting information, and additionally misnaming the Many-Worlds interpretation. There's also no "separability" assumption in Bell's theorem. You really should stop editing articles you don't understand. Tercer (talk) 19:34, 4 May 2024 (UTC)

Please offer a single sentence alternative if you like. Since you won't defend your content and you won't agree to mine, the only other alternative unless someone else comes along is to delete the section altogether. Johnjbarton (talk) 20:22, 4 May 2024 (UTC)

That's not how Wikipedia works. You need to get consensus for your changes, you don't get to just delete content you don't like. And I did defend my content, even provided a quotation for you. Tercer (talk) 08:03, 5 May 2024 (UTC)

Once again, this is an incorrect understanding of core Wikipedia policies, as the burden is on the person wanting to add content to establish consensus that it is verifiable, and not on the skeptics. You can escalate this further and poll for further input, but the proper state of the article sans consensus is for the passage's omission since no one agrees on any common ground. Remsense诉 08:09, 5 May 2024 (UTC)

I am not proposing to add content. It has been there for years. And yes you do need consensus for deleting content. Tercer (talk) 09:31, 5 May 2024 (UTC)

No, the core issue is verifiability. Longevity is a weak form of consensus in itself barring actual discussion, but if editors find there is an explicit lack of consensus that content is verifiable then it should likely not be retained barring further input. Unfortunately, if there's someone here who does not understand the paper it is yours truly (I gave it a shot!), do you think asking WikiProject Physics may help? Remsense诉 10:23, 5 May 2024 (UTC)

@Tercer said

• "And I did defend my content, even provided a quotation for you."

I apologize, I missed your reply because it was followed by a lot of other stuff. Johnjbarton (talk) 15:02, 5 May 2024 (UTC)

You were the one who said you didn't understand Deutsch's paper. As is clearly the case. Editing Wikipedia is not about copy-pasting sentences from the references, it's about understanding and summarizing them. The "irrelevance" of Bell's theorem is as an argument against the locality of the theory they are describing, which is a separable version of Many-Worlds. Section 7 proves that if you add the single-outcome assumption to Many-Worlds you get Bell's theorem. Try to read and understand it, it's less than three pages. Its end is rather explicit: It is hardly surprising that assigning a single-valued (albeit stochastic) variable to a physical quantity whose true descriptor is a matrix, soon leads to inconsistency.

As for the Brown-Timpson paper, they are quite explicit that they are demonstrating how a dynamically local theory can violate Bell inequalities. I find incomprehensible how you could claim that this has nothing to do with MWI, or that it doesn't belong in an article about Bell's theorem. Tercer (talk) 09:42, 3 May 2024 (UTC)

You were the one who said you didn't understand Deutsch's paper. As is clearly the case.

At no point did they say this. However, your tone so far has been unacceptable. It's also a bit puzzling to accuse someone of not understanding what they are reading or its context, and then call their actions vandalism, when it was simply not the case. Remsense诉 09:52, 3 May 2024 (UTC)

He wrote it explicitly: Well I am trying to make sense of this section but it is tough sledding. And editing an article you know you don't understand is simply vandalism. WP:CIR. Tercer (talk) 10:00, 3 May 2024 (UTC)

It it pretty clear that he was speaking about trying to understand the section of the article where the Deutsch paper was cited, not the paper itself.

Not to have a sidebar about site policy, but it's telling you've cited an essay that doesn't mention the word vandalism, while the actual vandalism policy repeats itself endlessly that exactly what you describe is not vandalism. Remsense诉 10:06, 3 May 2024 (UTC)

Fair enough, it's not "vandalism" according to the Wikipedia definition of the term. It's ill-advised, inconsiderate, arrogant, and unacceptable. Happy now? Or are you going to link more policies defining these terms in some way that excludes the intended meaning? More importantly, do you seriously think people should edit articles they don't understand?

As for his quotation, perhaps he indeed meant the Wikipedia section, I apologize if I was indeed mistaken. It doesn't change the fact that he clearly didn't understand the papers. Tercer (talk) 10:31, 3 May 2024 (UTC)

It's written there for a reason, as it is the generally-understood meaning of the term on Wikipedia, but I'm glad I could clarify in any case. Remsense诉 11:18, 3 May 2024 (UTC)

I quoted the Wikipedia section so that is obviously what I meant. Johnjbarton (talk) 15:06, 3 May 2024 (UTC)

Thank you for your comments. Please skip the personal attacks.

The Deutsch/Hayden paper is indeed short and about Bell's theorem. However it says nothing about interpretation or MWI. Consequently the claim that:

• In fact, Bell's theorem can be proven in the Many-Worlds framework from the assumption that a measurement has a single outcome.

is not supported by the ref. More important, the conclusion:

• Therefore, a violation of a Bell inequality can be interpreted as a demonstration that measurements have multiple outcomes.

is not in that ref at all. Your opinion about the its application to MWI maybe 100% correct, but that's not relevant for Wikipedia.

I agree with you on the Brown-Timpson paper but that is not what is written in the article. It says:

• At this point we can say that the Bell correlation starts existing, but it was produced by a purely local mechanism. Therefore, the violation of a Bell inequality cannot be interpreted as a proof of non-locality.

The first sentence reads as if the local mechanism occurs at the instant the "Bell correlations start existing" and that description itself is confusing. The second sentence is a strong conclusion not supported by the ref. There are plenty of other papers that discuss that conclusion, but its position here is misleading as it makes it sound like a result of MWI.

My version is not very different from yours. The most important differences are the removal of two sentences of conclusions unsupported by the refs. Johnjbarton (talk) 15:21, 5 May 2024 (UTC)

The Deutsch-Hayden paper is neither short nor about Bell's theorem. It's about developing an explicitly separable formulation of Many-Worlds. At first sight such a project should be impossible because of Bell's theorem, so they included a section showing that Bell's theorem follows from adding the assumption that measurements have single outcomes.

As for the Brown-Timpson paper, of course it supports the conclusion. You even added an appropriate quotation to the article yourself: In our discussion of locality in the Everett interpretation we have sought to provide a constructive example illustrating precisely how a theory can be dynamically local, whilst violating local causality. Tercer (talk) 17:28, 5 May 2024 (UTC)

The Deutsch-Hayden paper cited in the article is:

• Deutsch, David; Hayden, Patrick (2000). "Information flow in entangled quantum systems". Proceedings of the Royal Society A. 456 (1999): 1759–1774. arXiv:quant-ph/9906007. Bibcode:2000RSPSA.456.1759D. doi:10.1098/rspa.2000.0585. S2CID 13998168.

It says nothing about Many-Worlds.

The quote from the Brown-Timpson paper:

• In our discussion of locality in the Everett interpretation we have sought to provide a constructive example illustrating precisely how a theory can be dynamically local, whilst violating local causality.

does not support the claim in the article:

• At this point we can say that the Bell correlation starts existing, but it was produced by a purely local mechanism. Therefore, the violation of a Bell inequality cannot be interpreted as a proof of non-locality.

The quote does support MWI being dynamically local as both of our version claim.

This quote from Brown-Timpson illustrates part of complexity of concept of "locality" by using two different modified forms in the same sentence. As there are entire articles on that topic, I selected a different quote in my second revision:

• Everettian quantum mechanics exploits both non-uniqueness of outcomes and non-separability in accounting for EPR and Bell correlations without action-at-a-distance.

I think this captures the MWI-Bell Theorem relationship concisely without bring up the time when correlations "start existing" or using the complex and poorly defined words "local" and "non-local".

If I understand you, you think my version is correct but missing important content about the relationship between MWI and Bell. I don't agree that the additions are about MWI and they are not clear in their current form. Notable additions to wikipedia have multiple sources, esp including secondary refs. Here we have one primary refs not about MWI and one secondary ref. I hope you will accept my version as a reasonable summary given the limited sources. Johnjbarton (talk) 18:07, 5 May 2024 (UTC)

The entire Deutsch-Hayden paper is about Many-Worlds.

The question of when the correlations start existing is central to the question of locality, and Brown and Timpson discuss it at length. For instance: That is, we can only think of the correlations between measurement outcomes on the two sides of the experiment actually obtaining in the overlap of the future light-cones of the measurement events—they do not obtain before then and—a fortiori— they do not obtain instantaneously. And no, we're not going to avoid mentioning locality or when the correlations start existing here. The reader is supposed to actually understand what we're talking about, replacing familiar words with impenetrable jargon does not help at all.

The sources are not at all "limited", and your inability to understand them doesn't justify mutilating the article. Tercer (talk) 08:24, 6 May 2024 (UTC)

Well I suppose that someone who believes in MWI believes every paper and every observation about QM is about MWI. Of course the correlation can only be discussed when the observations are compared, but again this has nothing to do with MWI.

I'll drop my objection since the section is trivial and I don't think anyone cares about MWI anyway. Johnjbarton (talk) 15:56, 6 May 2024 (UTC)

References

I suggest deleting the whole section on many-worlds. Bell assumes single outcomes. MWI assumes the opposite. They have nothing to do with each other. Roger (talk) 01:51, 12 May 2024 (UTC)

Unverified addition to the article.

The article contains this claim:

• which is to say that somehow the two particles are able to interact instantaneously no matter how widely they ever become separated.

with two references.

• Parker, Sybil B. (1994). McGraw-Hill Encyclopaedia of Physics (2nd ed.). McGraw-Hill. p. 542. ISBN 978-0-07-051400-3.
• Mermin, N. David (July 1993). "Hidden Variables and the Two Theorems of John Bell" (PDF). Reviews of Modern Physics. 65 (3): 803–815. arXiv:1802.10119. Bibcode:1993RvMP...65..803M. doi:10.1103/RevModPhys.65.803. S2CID 119546199.

Neither reference says anything like this claim. I removed the unverified phrase but @Tercer reverted it. Johnjbarton (talk) 20:08, 4 May 2024 (UTC)

It seems in line with section 9 of Mermin's review. More generally, I'm not sure what the problem is here. Isn't that what nonlocal means in this context — influences at the level of the hidden variables that do not diminish with distance and are not limited by the speed of light? I'm not really a fan of the intro as it stands (the second paragraph seems long, in particular), but the quoted claim looks OK for an intro-level gloss on the term nonlocal. Am I missing something? XOR'easter (talk) 23:20, 4 May 2024 (UTC)

Thanks for your reply. Section 9 concerns Bohm mechanics and I assume the sentence you are referring to is:

• If two particles are in a correlated state then, because the field guiding the second particle depends on the trajectory of the first, if a field is suddenly turned on in a region where the first particle happens to be, the subsequent motion of the second particle can be drastically altered in a manner that does not diminish with the distance between the two particles.

To me this description is very different from the article. The phrase implies pairwise interaction: "two particles are able to interact", but the Bohm mechanism described by Mermin requires the guiding field.

The phrase says "interact instantaneous" but Mermin speaks of the instantaneous position of all the other particles:

• The wave function guides the particles like this: each particle obeys a first-order equation of motion specifying that its velocity is proportional to the gradient with respect to its position coordinates of the phase of the N-particle wave function, evaluated atthe instantaneous positions of all the other particles

The phrase may make sense to an expert who imagines the Bohm concept hidden behind the words and understand the many problems with that model. When I read the phrase it sounds exactly like a description of Newtonian gravity. That is what lead me to read the refs. The phrase makes it sound like the conditions imposed by Bell's theorem are not difficult to evade. I do not agree that this summarizes the Mermin article (and nothing in the other ref applies at all).

Also notice that the phrase is completely different than "Non-local hidden variables" section. That section makes the complexity of the problem much clearer. So the phrase does not summarize the article content in my opinion. Johnjbarton (talk) 02:23, 5 May 2024 (UTC)

Sorry, I'm still confused about what the problem is. For one thing, Einstein did have to modify Newtonian gravity to make it respect the speed of light. Second, whether or not a "guiding field" is involved doesn't seem relevant at this level of detail. Nor am I clear on what in the "Non-local hidden variables" subsection is not being summarized fairly. It seems about as good a summary as one can hope to do in half a sentence. XOR'easter (talk) 00:32, 6 May 2024 (UTC)

Ok then, thanks for your consideration of my complaint. Johnjbarton (talk) 02:13, 6 May 2024 (UTC)

EPR on lead

I think Nuretok has a point in the edit that XOR'easter reverted. The sentence is correct, but not helpful. But the more fundamental problem is that the lead is going into detail about a result that inspired Bell. Even if the detail was about Bell's theorem itself it wouldn't belong in the lead. Details about EPR are right out. To compound the issue the lead is already extremely long. Therefore I removed all mentions to EPR from there. It's already discussed in the History section, and that's where it belongs.

This also opens space for mentioning the variations of Bell's theorem that Ianjauslin wanted to include last year. I think that's much more relevant than historical background. Tercer (talk) 07:18, 10 June 2024 (UTC)