Talk:Principle of locality

New outline?

I have new material for quantum locality issues, but it is hard to work into the current chronological outline. An alternative outline:

Principle of Locality

• History
  • current pre-quantum
  • EPR,
  • Bell,
  • Modern (one paragraph summaries, no tech)
• Models of locality
  • Action at a distance
  • Bell screening
  • Quantum wavefunction
    • Bell local hidden variables proof and consequences
  • Field theory
    • Maxwell
    • QFT
  • Local realism definitional issues.

The History section would contain most of the current article; action at a distance could be merged in there. This section would have no discussion of current issues beyond mentioning "ongoing research". A causal reader might drop off here.

The later section would be more technical and mention unsettled aspects of locality and issues of definitions. Johnjbarton (talk) 14:42, 9 October 2023 (UTC)

Works for me.--ReyHahn (talk) 22:03, 9 October 2023 (UTC)

New version of QM section in place.

I re-wrote and expanded the QM section. I tried to focus on "locality" and not on eg QM, realism, photons etc.

The new version does not mention "counterfactual definiteness", which is not a difficult concept but is a very challenging pair of words to encounter. I feel if it is included it needs a full (short) paragraph to avoid being confusing jargon.

The new version does not mention non-communications. Worth adding, but the old version had no reference.

The new version cut the experimental section. We could say more, but I'm not keen on a mini-history of loophole-reduction. That info is not about locality but about Bell experiments and details. To say more I think we could outline one modern experiment with some kilometer bits to emphasize the locality test.

The realism bits are smaller; I'm kinda thinking about whether we should have Realism (physics) instead. The QFT section needs work.

Before these kinds of additions I think the best thing is to edit the new text to ensure it does the basic job adequately. And I would like to bring more from action at a distance over for eventual merge.

Please review. Johnjbarton (talk) 18:48, 16 October 2023 (UTC)

On a first read it is a great job! You manage to avoid most of my concerns. I'll be checking on it and editing a thing or two in the next couple days. Some quick answers:

• It is ok that realism does not appear as such in the article, maybe it is not needed and thus conterfactual definiteness neither. As long as local realism is there I'm good with it. For the moment, I do not think realism deserves its own article is a mess and the article on counterfactual definiteness might be enough.
• I still think that experiments could have a place here. The point is not to explain them but to provide insight on how well tested this is. Quantum mechanics has been experimentally shown to violate local realism. Pleople reading the article might benefit from this point being clear. Many people referenced this article after the 2022 Nobel Prize in Physics.
• The same thing as the above point with non communication. This is an important point. Many people on the web, after hearing about entanglement, try to figure a way to use entanglement as a way to send information faster than light. This should be clear.
• I am favorable with a merge with action at a distance.

Thanks again.--ReyHahn (talk) 19:14, 16 October 2023 (UTC)

Comment 2: I see that the "Models of locality for quantum mechanics" subsection do not need any quantum mechanics, can they be discussed in a preliminary section (before quantum mechanics sections)? Maybe just called "models of locality".--ReyHahn (talk) 20:59, 16 October 2023 (UTC)

We could try that. This would give the article a bit less of a historical slant. Johnjbarton (talk) 23:21, 16 October 2023 (UTC)

Also pinging a user with whom I had had previous discussions on the subtlety of the terms used in related wikipages. @Tercer: you might want to give the new version of the article a read (if you are interested).--ReyHahn (talk) 22:11, 16 October 2023 (UTC)

Thanks for the ping. The new version is a definite improvement over the previous one. I did fix a couple of mistakes. I'm unhappy with the subsections "Action at a distance" and "No future-input dependence". They are making a tempest in a tea pot, and the illustrations are unhelpful. Moreover, they are using jargon that is only really used by Wharton and Argaman.

More generally, I'm a bit worried that this article is becoming rather redundant with Bell's theorem and Local hidden-variable theory. Tercer (talk) 09:21, 17 October 2023 (UTC)

There does seem to be a considerable amount of redundancy in this corner of the encyclopedia, but I'm not sure what to do about that. XOR'easter (talk) 22:48, 17 October 2023 (UTC)

Thank for both of your feedback. I realize there is a huge overlap, throw also in quantum nonlocality and EPR paradox (probably there are more). This calls for an global article but the effort would be huge. As for the diagrams and models of locality, I am neutral, I'm fine with keeping them for illustrative purpose but I am fine with removing them per concerns of their lack of notability.--ReyHahn (talk) 23:00, 17 October 2023 (UTC)

In addition to those, we also have Aspect's experiment, Bell test, CHSH inequality, counterfactual definiteness, and probably others. The one that sticks out to me the most is local hidden-variable theory, because the title doesn't match the content. It's supposed to be about local hidden-variable theories, but it's actually a worse version of the Bell's theorem article. It would make more sense to rip out most of the text and replace it with material on LHV models, like the ones in section 3 of Bell's 1964 paper. XOR'easter (talk) 20:58, 25 October 2023 (UTC)

My quick assessment for the articles discussed above:

• Local hidden-variable theory is missing material and the first 2/3 is off base.
• quantum nonlocality I don't have patience enough to wade through this one. Seems like it is at least 3 articles pasted together.
• CHSH inequality 50% too long.
• Counterfactual definiteness needs a little work but not bloated with Bell.
• Aspect's experiment too long, a couple of section should be deleted to start.
• Einstein–Podolsky–Rosen paradox just needs a little work.
• Bell test Kinda listy but I think it gives the character of the subject. Could be trimmed a bit.

I think an article about the principle of locality must discuss Bell; I think don't think this article overly long or detailed for that goal.

The only question I have in my mind about the current article is whether it is the correct place for the discussion of "local-realism". We could move that topic to Bell's theorem but that article covers a lot of topics unrelated to locality.

In my opinion we should declare victory here and move on to articles with more problems. Johnjbarton (talk) 21:45, 25 October 2023 (UTC)

The explanation for Local hidden-variable theory is simple: it was written by Caroline Thompson, a crackpot that was very active in the articles about Bell in the early Wikipedia. That's why it's mostly about loopholes, she was a firm believer that loopholes would allow one to evade Bell's theorem. She died before the loophole-free experiments were performed. Tercer (talk) 07:31, 26 October 2023 (UTC)

Thanks.

• Realism: good let's leave it as now. (The physical concept of "realism" is messy and philosophical, but the only danger is fixing on one definition; I think we could present multiple perspectives. But another time).
• I agree that the results of experiments need more emphasis. I will take a try.
• Non-communications is strictly speaking orthogonal to locality. It's really only an issue after you discover that QM gives correlations. I think it can be mentioned in connection with experimental-results-show-correlations additions.

Johnjbarton (talk) 23:32, 16 October 2023 (UTC)

Would this order work for you? See User:ReyHahn/locality.--ReyHahn (talk) 07:39, 17 October 2023 (UTC)

There is something wrong with the following passage: In the 1935 EPR paper, Albert Einstein, Boris Podolsky and Nathan Rosen imagined such an experiment. They observed that quantum mechanics predicts "two spatially separated particles which have both perfectly correlated positions and momenta." Some comparison in missing. In classical physics any two particles that interact are correlated due to conservation of energy, momentum, angular momentum and so on. The problem of the EPR paradox is not that the two are correlated, but that the correlation seem to go against quantum mechanics uncertainty or more specifically against the incompatibility of observables. One could think that if we have two entangled particles with "perfect correlations" if Alice measures first the position of her particle and then Bob (who is far away) measures the momentum of his particle then we have all the information of the system. Thus we know position and momentum of both particles (this is not possible e.g. Heisenberg uncertainty principle). This is what is wrong, and in order for quantum mechanics to solve this, some nonlocal effect has to update what Bob will measure (instantaneously) right after Alice's measurement.--ReyHahn (talk) 07:59, 17 October 2023 (UTC)

Maybe we can write They observed that quantum mechanics predicts "two spatially separated particles which have both perfectly correlated positions and momenta." This seemed to be contradiction with the indeterminacy of quantum states. (if not we need more words).--ReyHahn (talk) 08:04, 17 October 2023 (UTC)

Sorry, I hadn't seen that you were already arguing about the problematic part of the EPR section. I hope you're happy with what I wrote. Tercer (talk) 09:22, 17 October 2023 (UTC)

Thanks, yes I prefer your new version.--ReyHahn (talk) 09:37, 17 October 2023 (UTC)

@Johnjbarton: could you chip in on the comments we have made about the locality diagrams. I suggest to split them as in User:ReyHahn/locality. Tercer suggested to remove them entirely, concerned that it might no be a very conventional way to describe the issue.--ReyHahn (talk) 15:52, 21 October 2023 (UTC)

Bell's local causality can be described using math, words, or diagrams, to varying degrees and effect. For the Wikipedia reader, I think diagrams should be tried when possible. Words are especially ineffective here, judging by the number of papers which seem to consider "locality" definitions as much as physics. Bell used a diagram similar to the last on in the article; it seemed clear and effective to me.

For a reader familiar with the topic, the last diagram in the article is all that is needed. But I thought it would help to break the diagram down in stages (Bell has one intro stage diagram similar to "Alice and Bob in spacetime").

If this were an article about Bell, then the two intermediate diagrams, action at a distance and no-future, are not needed. But this an article on locality and these two broaden the section, directing the readers attention to "locality models", of which Bell's is one.

Your reordering looks fine to me. Johnjbarton (talk) 20:51, 21 October 2023 (UTC)

Glove analogy

On this section Imagine that rather than quantum systems, Alice ad Bob are studying gloves. When Alice sees a right handed glove, she expects Bob will find a left handed glove. This type of explanation for the experimentally-confirmed quantum correlations is not valid': the hidden handedness variable does not exist in quantum mechanics is misleading. As long as Alice and Bob are measuring the same observable (handedness of gloves, or let's say spin component in the z-axis), then the glove analogy is fine. I wonder if we can avoid this analogy altogether as it is the one bringing confusion to the subject. A better analogy would be Mermin's device, but that would be a hassle to introduce.--ReyHahn (talk) 10:26, 17 October 2023 (UTC)

I don't think it's misleading. The point is only to introduce the usual hidden-variable explanation that is valid in classical cases, and claim that it doesn't work in the quantum case. Now you're worrying about *proving* that it doesn't work in the quantum case, but I don't think we need yet another proof of Bell's theorem.

Your edit, on the other hand, I find misleading. You replaced "is not valid" with "is not always valid". This implies that it is sometimes valid, but this is false. It's not as if Nature uses hidden variables when you're not violating a Bell inequality, and switches them off as soon as you do a Bell test. No. The correlations of an entangled state are not mere ignorance of an underlying value, even when you're just measuring it in a fixed basis. Tercer (talk) 16:07, 18 October 2023 (UTC)

I understand what you mean (hidden variables do not pop into existence at certain angles) but I am not sure that it is what most people get out of the analogies. I decided to drop the analogy. Popular culture and introductory discussions are repeating the fallacy that the glove experiment is different than entanglement because the "state is not defined until measurement" or whatever. That's not true but the real difference is so subtle that the glove analogy cannot provide the right image. That's why I want to avoid associating entanglement to that analogy. It is clear that if we did the experiments with the same angle for both detectors, we cannot violate Bell's inequalities (and hidden variables could be at work, in principle). In that sense when the angles are the same, the glove box analogy is on the contrary not that bad, but in the opposite sense that we want to use it here. The glove example shows that these correlations are not helpful for communication (when Alice gets her glove out of the box, she knows the handedness of Bob's glove, instantaneously!). --ReyHahn (talk) 18:44, 18 October 2023 (UTC)

The difference is not subtle. The handedness of the glove is determined before the measurement. The spin of the particle is not. Tercer (talk) 07:45, 19 October 2023 (UTC)

Again that is right but my point is that we have to convince people that just think in terms of classical mechanics that there is something different between entanglement and classical experiments. We can tell them that the difference is that handedness is not determined before measurement. Let me argue along those lines (not my position): Ok, let us think that the handedness of the gloves is undefined through some very complex chaotic chemical reaction (add some quantumness if you like) that finishes when you open the box. So what? How is that different from entanglement experiments? Bell test (with same angle detectors) or chaotic gloves there is nothing unusual about it. There is nothing different in terms of physical predictions. How do we even know that quantumness is just not another chaotic system? Only if we consider more observables (more than just handedness of gloves) then we can notice that something is different, but then the whole glove analogy breaks down. That's why Mermin's device is a better analogy because the detectors can measure more than one thing. Note that EPR authors were clever too, they did not argue in terms of gloves, they had to introduce relations between momentum and position (incompatible observables). The glove analogy is distracting from the issue, we should really consider saying something more about the incompatibility of observables. Sidenote: All this conversation remind me that there is another bad article that we should revise at some point quantum indeterminacy.--ReyHahn (talk) 08:25, 19 October 2023 (UTC)

Convincing people that quantum mechanics is different is important, but that's a different point. Here the goal is simply to say: "in the classical case there's obviously no nonlocality, because there's a hidden variable explaining it. In the quantum case this explanation does not hold." Explaining what does hold in the quantum case is another subject entirely. Tercer (talk) 10:10, 21 October 2023 (UTC)

Can we address that with a simple phrase without falling for the glove analogy? I mean Bell and co. argue that (aside from superdeterministic loopholes) the problem here is on locality not on the undeterminacy of the variables previous to measurement (I think that you would agree that this is not about "realism" as defined in the article).--ReyHahn (talk) 16:20, 21 October 2023 (UTC)

Yes, Bell is arguing that there is nonlocality, that's why it is important for him to emphasize that the quantum correlations are not of the glove sort, that can be easily explained by local hidden variables.

I don't see how avoiding a concrete example would help any reader. I mean, we have just shown the general abstract case with the factorizability equation. The gloves show what this explanation via factorizability means. Tercer (talk) 17:58, 21 October 2023 (UTC)

I say that there are examples but the glove one is not a good one. The section read This type of explanation for the experimentally-confirmed quantum correlations is not valid: the hidden handedness variable does not exist in quantum mechanics. My problem with this is that it sort of implies that realism (pre-existence of some values before measurement) is why quantum is different from classical. That is not what Bell says. What he seems to imply is that the difference is not on the hidden values but on the locality condition.--ReyHahn (talk) 18:09, 21 October 2023 (UTC)

No, it doesn't at all imply that "realism" is why quantum is different than classical. I advise you to read Bell's paper (La Nouvelle Cuisine), but other than that I give up. Tercer (talk) 19:12, 21 October 2023 (UTC)

I apologize if this went far for too long, but I think you are misreading what I have said. Maybe I am misreading you too. For the third time, Bell has never implied that realism is why quantum is different from classical. The glove analogy as stated so carelessly is.--ReyHahn (talk) 19:20, 21 October 2023 (UTC)

Bell himself wrote the glove analogy. Tercer (talk) 20:45, 21 October 2023 (UTC)

He was more careful. Please let us try to focus on how to word it you insist in keeping it there. Bell's discussed this in a clear context related to his theorem, he did not just simply say that gloves are different from quantum entanglement, he argued that it was unhelpful. In the words of Bell The analogy of the gloves is not a good one. Common sense does not work here. --ReyHahn (talk) 21:04, 21 October 2023 (UTC)

Just to add my opinion, I find analogies like the glove distracting and not instructive. Similarly in an introductory quantum class an instructor began: "Imagine that one of the emitted particles is red, and the other blue..." My reaction is always "Why can't we use the actual property, whether it is spin or whatever? That's one less abstraction to worry about." --Chetvorno^TALK 08:01, 9 November 2023 (UTC)

The purpose of the glove analogy is to discuss a property intrinsic to a an object which then "obviously" accounts for the classical correlations. You can't use spin or any other quantum property because these are not intrinsic to the object, but rather, according to quantum mechanics, emerge during the measurement. It is exactly this difference which makes the glove analogy useful and the quantum correlations not at all obvious. Johnjbarton (talk) 15:46, 9 November 2023 (UTC)

"property intrinsic to a an object" makes me think of realism (predefined properties before measurement) I hope that you agree that this is not the point of Bell's theorem. It seems misleading--ReyHahn (talk) 22:51, 9 November 2023 (UTC)

Yes, exactly: the glove analogy is about realism. Whether it's the point of Bell's theorem depends upon ones view of the point. The glove analogy tells us what classical realism predicts; Bell's theorem tells us that QM makes a different prediction.

I have to say that the first time I read the whole socks/gloves bit I was confused by what the point was. My sense is that Bell went out of his way to avoid discussing the ontology (glove-like) vs epistemic (no intrinsic properties) view. Bohm's pilot wave work shows that the opposite of glove-like is not simple, not so the black and white. Disproving the gloves (local causality) as does not prove any particular alternative. Johnjbarton (talk) 00:15, 10 November 2023 (UTC)

Realism

@Tercer: Why is this [1] controversial? It is clearly the usual definition and below we explain that it is complicated.--ReyHahn (talk) 09:55, 19 October 2023 (UTC)

As I wrote in the edit summary, this "realism" boils down to simply determinism. The usual definition of realism is the existence of an observer-independent world. This "realism" was not even invented by Bell or CHSH, it was invented by d'Espagnat and was always controversial even in the quantum nonlocality community. Most authors (including me) avoid "realism" completely and adopt less misleading expressions.

The phrasing before was more careful about it, in your version it sounded like the definition of "realism" is straightforward. Tercer (talk) 10:08, 21 October 2023 (UTC)

If you want to add something about determinism that can be added but that does not change that it is a common definition. I am not equating it with anything and the text afterwards says it is not used by Bell.--ReyHahn (talk) 10:17, 21 October 2023 (UTC)

Numerous papers physics papers refer to "local realism" and two review articles discuss this specific combination in detail. The review articles call out the special meaning of the combination in contrast to individual meanings of the words. Our article here needs just enough of the "realism" issue to surface these two points (to be clear: 1) "local realism" is a compound synonym for Bell's "local causality" 2) it is not a synonym for "realism").

"Realism" is certainly controversial and any particular definition won't satisfy everyone. We could consider a separate article on "Realism (physics)" to (attempt to) report the many sides of that issue. Here the short quote from the review is presented as just one simplistic definition, not to explore realism but to make the point that "local realism" is now a technical term. Johnjbarton (talk) 15:32, 21 October 2023 (UTC)

I think we all agree on that. I was just trying to make the phrase "A review of papers using this phrase suggests that a common (classical) physics definition of realism is" into "One common (classical) physics definition of realism is" just because that definition is common enough. Do we agree that it is one common definition? Even if vague and not necessarily tied to Bell's theorem.--ReyHahn (talk) 15:49, 21 October 2023 (UTC)

Ok thanks, I was unsure of the context. The "A review..." bit was just to head off "that's not what realism really means" kinds of edits and to avoid the appearance of editorializing. Johnjbarton (talk) 15:56, 21 October 2023 (UTC)

No spookiness project

Several of you have indicated problems with a series of "entangled" articles about Bell's theorem. Here is the full list of the spooky 10 (alphabetical order):

1. Action at a distance (AaaD)
2. Aspect's experiment
3. Bell's theorem
4. CHSH inequality
5. Counterfactual definiteness
6. Einstein–Podolsky–Rosen paradox
7. Hidden-variable theory
8. Local hidden-variable theory (LHVT)
9. Principle of locality
10. Quantum nonlocality

Leaving aside Bell test and superdeterminism. I was wondering (I) can we make a category or a template to navigate between them (there might be more later)? (II) can we discuss which of them should be merged? There is already an effort by Johnjbarton to improve on 1 (AaaD) and merge with 9 (locality). (III) If I understood it correctly, Tercer suggested that Caroline added some conflicting information in 8 (LHVT), and similar concerns were raised in other article (maybe 4 (CHSH) ?). Do we know all the articles were this might be an issue? (IV) Trimming: if we can find some consensus of what is wrong with this articles, I suggest that we trim with the sharpest razor. Efforts to rebuild them will come later either naturally by other users or by people interested like you and me. (Edited)--ReyHahn (talk) 12:55, 26 October 2023 (UTC)ReyHahn (talk) 09:44, 26 October 2023 (UTC)

What I said is that she mostly wrote it. I don't see why you're being so oblique about it, this is not a conspiracy theory or an attempt at outing, her authorship is clearly attributed. She also had written most of Loopholes in Bell tests (now redirecting to Bell test), but I removed all of the nonsense from there. Indeed she also wrote a lot of CHSH inequality, and I haven't dealt with it.

As for your question, I think Aspect's experiment is rather problematic. It does include some content about Aspect's experiment specifically, but most of it is rambling about Bell and EPR. After trimming down the the good parts I'm not sure if it's enough material for a standalone article or it should be merged to Bell test. Hidden variable theory could be a good article, but as it stands it mostly repeats Bell and EPR, with very little material about hidden variables themselves. As for the good articles, I think they are Bell's theorem, EPR paradox, and Quantum nonlocality. The last one is also guilty of repetition, but it does focus mostly on nonlocality itself and has a lot of good content from a more technical point of view. Tercer (talk) 10:54, 26 October 2023 (UTC)

I am sorry if I quickly misjudged Caroline's participation to Wikipedia, I saw some critics in articles were she participated (I hope I am not confusing her with somebody else). As you referred to her as "crackpot" [2] I taught that we were critizicing her contribution. Nobody is calling for a conspiracy but if there is some content that any user has propagated throughout this article list and that does not reflect the modern consensus on the topic then it should be removed.

I think Aspect experiment can still be kept as a standalone article, it just needs more historical and tehcnical details about the actual experiment and less discussions on its implications.

I agree with the three articles that you suggest as good. --ReyHahn (talk) 12:15, 26 October 2023 (UTC)

Just to set expectations for my WP:TNT of action at a distance: after reading references I'm focusing on placing it in the context of force rather than merging with locality. For the the no-spookiness purposes the effect should be the same: if I even mention Bell it will be in one sentence. Johnjbarton (talk) 13:16, 26 October 2023 (UTC)

I just applied the razor to Local hidden-variable theory. XOR'easter (talk) 01:25, 27 October 2023 (UTC)

Further thoughts: Aspect's experiment should be trimmed down to be about Aspect's experiment specifically, with a much more concise background and less about its "implications" (both of which apply to the topic more widely and not to Aspect's experiment in particular). CHSH inequality needs more checking for weird statements, attempts to downplay the violation of Bell inequalities, etc. It also has a big chunk that is written in a blow-by-blow textbook style and should probably be replaced with a more encyclopedic treatment of a different proof. XOR'easter (talk) 19:44, 29 October 2023 (UTC)

Agreed. I will take a look at Aspect's experiment, later this week.--ReyHahn (talk) 09:38, 30 October 2023 (UTC)

I condensed the historical background material by replacing it with text from Bell's theorem and EPR paradox, which (as noted above) have been vetted more thoroughly. I'm tempted to delete the whole "Relativistic causality" subsection as opinionated WP:SYNTH, but maybe you'd like to take a crack at the article first. XOR'easter (talk) 19:07, 4 November 2023 (UTC)

OK, I looked at that section again and was even less happy with it (what wasn't WP:SYNTH was uncited), so I brought out the machete again. I think that "Later experiments" might be salvageable, if we can talk about later experiments specifically in relation to Aspect's. XOR'easter (talk) 22:26, 4 November 2023 (UTC)

Thanks for tackling the Aspect's experiment page, ReyHahn. XOR'easter (talk) 17:18, 8 November 2023 (UTC)

Fixing an issue in the QM section.

The Quantum mechanics section of this article discusses very complex topic in a few paragraphs. The second paragraph starts with two sentences introducing the EPR paper and then these two sentences:

In their view, the classical principle of locality implied that "no real change can take place" at Bob's site as a result of whatever measurements Alice was doing. Since quantum mechanics does predict a wavefunction collapse that depends on Bob's choice of measurement, they concluded that this was a form of action-at-distance and that the wavefunction could not be a complete description of reality.

This content has multiple problems:

• Undue Neither the EPR paper nor the Clauser/Shimony papers mention collapse. The Reid review paper has one sentence on collapse:

Despite the apparently acausal nature of state collapse (Herbert, 1982), the linearity or “no-cloning” property of quantum mechanics rules out superluminal communication (Dieks, 1982; Wootters and Zurek, 1982)

The phrase "Despite the apparently acausal nature of state collapse" means collapse arguments were used in the now disproven claim by Herbert and this indicates that state collapse is problematic in the EPR context. To backup this claim, consider this from another review:

... some authors to speculate on the possibility of superluminal communication (actually, instantaneous communication). One of these proposals (Herbert, 1981) looked reasonably serious and aroused enough interest to lead to investigations disproving its possibility (Glauber, 1986) and in particular to the discovery of the no-cloning theorem (Dieks, 1982; Wootters and Zurek, 1982)

The Reid review also discusses the math of the EPR paper where they say: The puzzling issue is that different choices of measurements $\phi$ at B will cause reduction of the wave packet at A in more than one possible way. This resembles the current content but this sentence is about detail in EPR's reasoning and not about about their core reasoning. None of these sources mention action at a distance.

• Incorrect. Quantum mechanics does not "predict a wavefunction collapse that depends on Bob's choice of measurement". The wavefunction collapse is a postulate, not a prediction. See for example

...von Neumann postulated a second kind of time evolution: when a measurement is complete, the superposition of positions collapses to a definite position..

• Confusing Dropping the word "collapse" into the paragraph distracts from the topic because the concept is complex. For example, in their brief section 4.14 on collapse, Susskind and Friedman describe it as: This strange fact–that the system evolves one way between measurements and another way during measurements–has been the source of contention and confusion for decades.

Furthermore, "collapse that depends upon Bob's choice" is confusing. In the previous sentence "Alice was doing" now suddenly Bob is choosing.

• Jargon. Wikipedia avoids unnecessary technical language. Since none of the sources make significant use of "collapse", neither should we. For non-technical readers the word sounds like an event, but it is not: Collapse is something that happens in our description of the system, not to the system itself. The concept of collapse is limited to nonrelativistic QM. Aharnov and Rohrlich discuss the EPR-like scenarios starting with: The paradox is that there seems to be no way to make collapse Lorentz invariant. The paradox concerns the collapse, not the correlations, of entangled states. General readers will not know that the time sequence of casual discussions of EPR scenarios are not correct in QM.

The fix is not difficult. The cited Reid reference does provide a summary of the relationship between the topic of the article -- principle of locality -- and the EPR papers. The second sentence of the third paragraph of the Reid review is: The EPR conclusion was based on the assumption of local realism, and thus the EPR argument pinpoints a contradiction between local realism and the completeness of quantum mechanics. A few paragraphs later they write The EPR paper therefore provides a way to distinguish quantum mechanics as a complete theory from classical reality, in a quantitative sense. My summary of this content is:

• They conclude that this violation of principle of locality implies that the wavefunction could not be a complete description of reality.

Note that in our article the sentence immediately preceding this one uses the phrase "the classical principle of locality", implying the realism stated explicitly in the reference. The issues of "local realism" are discussed elsewhere in our article.

I applied my fix, but it was reverted by @Tercer. I am hoping that this more extensive explanation of my change will be sufficient to convince Tercer to restore my changes.

I am not against discussing the relationship between the principle of locality and wavefunction collapse if we can find good sources that address these two directly.

References

Johnjbarton (talk) 02:20, 10 December 2024 (UTC)

Collapse is not strictly necessary in that paragraph so to keep it minimal I just replaced it with "results". Hope that's not controversial. The problem with entanglement articles is that people disagree very heavily on what words to use, EPR did not use collapse because his authors were against that but any other Copenhagener would have used it.--ReyHahn (talk) 08:46, 10 December 2024 (UTC)

EPR did use collapse. Read the paper. They call it "reduction of the wave packet", but that's just a synonym.

And it is necessary in that paragraph, otherwise the very next sentence doesn't make sense. Tercer (talk) 11:27, 10 December 2024 (UTC)

I assume by "the very next sentence" you mean

• Other physicists did not agree: they accepted the quantum wavefunction as complete and questioned the nature of locality and reality assumed in the EPR paper.

But this sentence has nothing to do with state reduction and thus does not require any preceding discussion of it. This sentence simply follows up on the conclusion I summarized from Reid. Johnjbarton (talk) 15:56, 10 December 2024 (UTC)

No, the very next sentence is they concluded that this was a form of action-at-distance and that the wavefunction could not be a complete description of reality. The argument is rather simple: the wavefunction cannot be a complete description of reality because the wavefunction collapse is obviously not physical. You are removing the first part of the argument and making it impossible to understand. Tercer (talk) 17:15, 10 December 2024 (UTC)

Your claim sounds like what Everett says. It is not what EPR, Reid et al, or Clauser/Shimony say. Again there may be sources which connect the topic of locality to Everett's work, but that is not the topic of this paragraph. Johnjbarton (talk) 18:07, 10 December 2024 (UTC)

This has nothing to do with Everett. Frankly it's not my job to teach you EPR. Tercer (talk) 18:28, 10 December 2024 (UTC)

Please focus on the article content per WP:UNCIVIL. Johnjbarton (talk) 23:41, 10 December 2024 (UTC)

ReyHahn's edit is good. It avoids the problems I listed. Of course I think the paragraph could be better. Johnjbarton (talk) 16:08, 10 December 2024 (UTC)