Talk:Principle of locality/Archive 1

Bad syntax "of in" -- please correct
Last sentence reads: This interpretation of the word "locality" is closely related to the relativistic version of in physics.

Someone please correct this - I don't know if it should be "relativistic version of physics" or if there is a word missing. --Smithfarm 20:09, 23 January 2006 (UTC)

Obscure phrasing
Our Einstein quote mentions "quasienclosed systems" but this phrase only appears in two Google results (or another, different two if a hyphen is inserted). I'm guessing it means 'systems where the behaviour can be described without reference to anything external' but if anyone knows differently, perhaps they could add a clarification. Ben Zealley 20:31, 4 May 2007 (UTC)

Definition
"In another use of the term, if we have two observables, each localized within two distinct spacetime regions which happen to be at a spacelike separation from each other, both observables would commute and we have locality." "both observables would commute and we have locality" Unclear what you're trying to say. GangofOne 01:43, 21 July 2005 (UTC)

Regarding the "conventional interpretations" which state that "the actual definite properties of a physical system do not exist prior to the measurement", what does "measurement" mean? Because if it has the standard physical definition of "being bombarded with radiation" then this would not really violate realism in our universe, would it? Since, you know, there is no perfect and energy-free vacuum in our universe. In that case this interpretation really only stipulates that such a system "does not exist" until it is first hit with a photon, which anywhere in the universe should be nigh-instantaneous. Measurement doesn't actually require a consciousness to notice the bombardment. That is simple anthropic arrogance, and it would also be ridiculous metaphysics. --68.251.41.72 12:28, 26 November 2005 (UTC)

Although many people believe it and there is no proof to the contrary. Keith Bowden, Birkbeck Physics. Keithbowden (talk) 14:57, 5 February 2008 (UTC)

Fixed the final paragraph. There is only one sense of "locality," though it is formalized in different ways for different physical theories. Locality is axiomatic to all quantum field theories.

Also, the vast majority of physicists accept that local realism is violated in experiment. At this point, the only way to avoid this conclusion is to invoke previously unknown physical mechanisms that are not supported by other experiments. I changed the wording of a sentence earlier in the article to make this clear. Dave Kielpinski 21:49, 17 December 2005 (UTC)

Following two paragraphs edited
WAS:

"In most of the conventional interpretations, such as the version of the Copenhagen interpretation in which the wavefunction is not real, the many-worlds interpretation, and the interpretation based on Consistent Histories, it is realism that is rejected. The actual definite properties of a physical system "do not exist" prior to the measurement and the wavefunction is only interpreted as a mathematical tool used to calculate the probabilities of the outcome of the experiments, which is, in agreement with positivism in philosophy, the only topic that science should discuss."

"In the version of the Copenhagen interpretation where the wavefunction is real, it is the principle of locality that is violated. The wavefunction is a real object that exists prior to the measurement, but the measurement causes the wavefunction collapse which is a non-local process."

IS:

"In most of the conventional interpretations, such as the Copenhagen interpretation wherein the wavefunction has no direct physical interpretation, the many-worlds interpretation, and the interpretation based on Consistent Histories, it is realism that is rejected. The actual definite properties of a physical system "do not exist" prior to the measurement and the wavefunction is only interpreted as a mathematical tool used to calculate the probabilities of the outcome of the experiments, which is, in agreement with positivism in philosophy, the only topic that science should discuss."

"In the Copenhagen interpretation the only physical interpretation of the wavefunction is via the application of Born's Rule that yields a probability density for all regions of space and time. The principle of locality is violated in the measurement process via wavefunction collapse. This is a non-local process since the probability density vanishes everywhere instantaneously, except where (and when) the measured entity is found to exist."

Note: I don't believe there are two Copenhagen interpretations; one where the wave function is real and another were it is not real. Also, the word 'real' is misleading here since the wave function exists in the complex plane and has both 'real' and imaginary parts. The issue is whether the wave function has a direct physical interpretation, and as far as I know, within the CI, it does not. green 65.88.65.217 06:05, 3 February 2006 (UTC)


 * Note: After further consideration, I agree that two CI's exist wrt the wf, but referring to them as 'real' versus 'not real' is unclear. I believe I have improved the text in this regard. See most recent edit below. green 65.88.65.217 20:56, 3 February 2006 (UTC)

Note it is common folk lore in the Physics community that there are "as many versions of the CI as there are people who have written about it". There is certainly the pure Bohrian positivist version versus the "consensus interpretation" which to me never seems to be consistent. Keithbowden (talk) 15:02, 5 February 2008 (UTC)

I edited these two paragraphs again, as follows.

"In most of the conventional interpretations, such as the version of the Copenhagen interpretation where the wavefunction has no direct physical interpretation, the many-worlds interpretation, and the interpretation based on Consistent Histories, it is realism that is rejected. The actual definite properties of a physical system "do not exist" prior to the measurement and the wavefunction is only interpreted as a mathematical tool used to calculate the probabilities of the outcome of the experiments, which is, in agreement with positivism in philosophy, the only topic that science should discuss."

"In the version of the Copenhagen interpretation where the wavefunction is considered to have an unspecified physical interpretation, the principle of locality is violated during the measurement process via wavefunction collapse. This is a non-local process because Born's Rule, when applied to the system's wave function, yields a probability density for all regions of space and time. Upon measurement of the physical system, the probability density vanishes everywhere instantaneously, except where (and when) the measured entity is found to exist. This "vanishing" would be a real physical process, and clearly non-local (faster-than-lightspeed) if the wave function is considered physically real and the probability density converged to zero at infinite distances during the finite time required for the measurement process."

green 65.88.65.217 07:56, 3 February 2006 (UTC)

---

And again! Here is the latest/current version.

"In most of the conventional interpretations, such as the version of the Copenhagen interpretation where the wavefunction is assumed to have no direct physical interpretation or reality, the many-worlds interpretation, and the interpretation based on Consistent Histories, it is realism that is rejected. The actual definite properties of a physical system "do not exist" prior to the measurement and the wavefunction has a restricted interpretation as nothing more than a mathematical tool used to calculate the probabilities of experimental outcomes, in agreement with positivism in philosophy as the only topic that science should discuss."

"In the version of the Copenhagen interpretation where the wavefunction is assumed to have a physical interpretation or reality (the nature of which is unspecified), the principle of locality is violated during the measurement process via wavefunction collapse. This is a non-local process because Born's Rule, when applied to the system's wave function, yields a probability density for all regions of space and time. Upon measurement of the physical system, the probability density vanishes everywhere instantaneously, except where (and when) the measured entity is found to exist. This "vanishing" would be a real physical process, and clearly non-local (faster-than-lightspeed), if the wave function is considered physically real and the probability density converged to zero at arbitrarily far distances during the finite time required for the measurement process."

green 65.88.65.217 20:39, 3 February 2006 (UTC)

Relevance of quantum entanglement
There is a link at the bottom pointing to quantum entanglement, which seems highly relevant to this topic, but entanglement is not mentioned in the article at all. Someone please explain how the principle of locality holds up in regards to entanglement.
 * Explanation added to article --Michael C. Price talk 22:01, 21 June 2006 (UTC)
 * It's gone again -- Why? --87.178.11.33 (talk) 20:33, 27 December 2008 (UTC)

Quantum mechanic
Quantum mechanic in the top of article is offtopic. --Камень (talk) 22:07, 2 April 2009 (UTC)

add the link please
and maybe even steal an article or two off of that page because they talk about thought experiments. http://en.wikipedia.org/wiki/Action_at_a_distance_%28physics%29 Bobthefishmonger (talk) 06:00, 5 July 2010 (UTC)

Einstein's view
Einstein's view was not that QM was nonlocal, but that it was incomplete. If you don't believe me, read the EPR paper! I accordingly edited the corresponding passage in this article. To be sure, he also did not believe in "spooky action at a distance". Therefore he did not believe in the "reality" of the wave function. This is a completely different issue from what is raised by the EPR paradox. Richard Gill (talk) 18:02, 1 June 2012 (UTC)

Copenhagen interpretation
The Copenhagen interpretation does not assert the physical reality (in real space-time) of the wave function. I accordingly corrected the passages in the article referring to two different Copenhagen interpretations, one with and one without this feature. Richard Gill (talk) 18:16, 1 June 2012 (UTC)

Redirect?
I suggest that a redirect from locality (physics) might be helpful. 70.247.162.84 (talk) 15:00, 8 September 2012 (UTC)

'Spacetime'
According to Einstein who coined the term, the correct spelling is spacetime with no hyphen. This emphasizes their interconnectedness. - 71.206.87.9 (talk) 22:03, 3 May 2013 (UTC) Ben Franklin
 * It is possible that “spacetime” should be preferred, but arguments of Ben Franklin are invalid.
 * Albert Einstein can rightfully dictate that de:Raumzeit is a correct spelling (in his native German), but he was not a native English speaker to become a great authority in this question. Spelling rules differ between languages. For example, in Russian the correct spelling is “пространство-время”, whereas “пространствовремя” or “времяпространство” are thought to be incorrect.
 * The rôle of a hyphen is namely to “emphasize the interconnectedness”: compare space-time (with hyphen) and space–time code, spelled with dash, where space and time are contrasted.
 * Albert Einstein is not a supreme authority for modern physics, by no means.
 * Albert Einstein was not the discoverer of the space-time, which was already known no later than in the age of d'Alembert and Lagrange.
 * Incnis Mrsi (talk) 08:16, 4 May 2013 (UTC)

Misleading summary
"Experiments have shown that quantum mechanically entangled particles must either violate the principle of locality or engage in superluminal communication.[1]"

I think this is a misinterpretation of the article being referenced, and improperly suggests that entanglement allows superluminal communication, which is a distressingly common misconception. I believe the sentence would be technically correct if it said "the principle of local realism" but even so I think would be misleading. I think the referenced article is too advanced a topic for Wikipedia and should be removed, but at least should be moved to a subsection rather than being in the header.

If we need a summary of the relationship between QM and locality, it should represent the scientific consensus that it is realism, rather than locality or causality, that should be dropped in QM. (Does anyone have a suitable reference?) Harryjohnston (talk) 03:58, 4 June 2013 (UTC)

Lack of clarity
Locality means several different things; in quantum field theory it means observables in spacelike separated regions commute, but this sense is utterly different from the sense used in discussions of "local realism", Bell's inequality and the like. So, the article starts by saying that locality breaks down in quantum mechanics (true in one sense), and concludes by saying it's an axiom in quantum field theory (true in the other sense). That must be really confusing to nonexperts. I'm too tired to fix this now. John Baez (talk) 05:30, 16 June 2013 (UTC)

Introduction has a problem common to technical articles
The introduction to this article has a disease which is very common in WP technical articles: it is brief, cryptic, jargon-laden, and incomprehensible to nontechnical readers. The introduction is supposed to be understandable by general readers (WP:EXPLAINLEAD) and be an adequate summary of the article (WP:SUMMARY). As it stands the intro has only 3 sentences:
 * In physics, the principle of locality states that an object is only directly influenced by its immediate surroundings. A physical theory is said to be a local theory if it is consistent with the principle of locality. To date, no test has simultaneously closed all loopholes to the idea that entangled particles violate the principle of locality or engage in superluminal communication.

The first two are an excellent start, they define the property well. But the 3rd is full of jargon, and readers are going to require a course in quantum physics to understand its relation to the first two; it looks like a nonsequitur. And it is nowhere near an adequate summary.

I don't mean to be critical of the obviously expert and conscientious editors who have worked on this article. I know from experience how difficult it can be to get consensus on nontechnical language for the introduction, particularly for an esoteric and controversial topic like this. But on behalf of novices interested in QM I would like to ask if we can do better. -- Chetvorno TALK 06:48, 9 March 2015 (UTC)


 * Rewrote and expanded introduction. -- Chetvorno TALK 08:58, 30 April 2015 (UTC)

What is "Ian Thomson's dispositional quantum mechanics" (ref 6)?
Reference 6 is listed as "Ian Thomson's dispositional quantum mechanics" which links to "http://www.generativescience.org/". Does someone have a more accurate link? I'm not even going to try to guess whether this meets WP:RS. When dealing with esoteric interpretations of quantum mechanics (rather than "mainstream"), what 'is' an RS? Jimw338 (talk) 04:29, 27 June 2015 (UTC)

Incorrect statement about entanglement and Bell's inequalities
"Local realism is a significant feature of classical mechanics, of general relativity, and of electrodynamics; but quantum mechanics largely rejects this principle due to the theory of distant quantum entanglements, an interpretation rejected by Einstein in the EPR paradox but subsequently proven by Bell's inequalities." ( Ben Dov, Y. Local Realism and the Crucial experiment. ) [moved reference up here to not clutter the bottom of the talk page Jimw338 (talk) 04:33, 27 June 2015 (UTC)]

I don't think its correct here to say that the "interpretation" of "distant quantum entanglements" was proven by Bell's inequalities. Its my understanding that alternatives to "action at a distance" is not yet ruled out. As it says at the top of this page: " To date, no test has simultaneously closed all loopholes to the idea that entangled particles violate the principle of locality or engage in superluminal communication.".

So I think the statement "interpretation rejected by Einstein in the EPR paradox but subsequently proven by Bell's inequalities" is either misleading or entirely incorrect.

Fresheneesz (talk) 20:36, 27 January 2015 (UTC)

Surely all interpretations are nonlocal
I do not understand all this talk of one interpretation being nonlocal and another not. All interpretations are mathematically isomorphic so (to my way of thinking) they are ALL nonlocal as is the world which they describe.

Keith Bowden (Birkbeck College) Keithbowden (talk) 14:57, 5 February 2008 (UTC)


 * To the best of my knowledge: there is a subtle difference between what you might call "quantum nonlocality", i.e. the violation of Bell-type inequalities, and the "principle of local action", i.e. the idea that the physical state of an object is affected only by its immediate surroundings. Either of these might be called locality, and the former will certainly hold for any interpretation of QM. Arguably however, some interpretations such as Many-Worlds also satisfy the latter by avoiding wave-function collapse, so that the complete physical state of one side is unaffected by a measurement at the other. --Sabri Al-Safi (talk) 09:02, 3 May 2011 (UTC)

Robert Griffiths (advocating Consistent Histories approach) holds that "the world which they describe" is not nonlocal. Source: http://quantum.phys.cmu.edu/CQT/chaps/cqt01.pdf, http://quantum.phys.cmu.edu/CQT/chaps/cqt24.pdf , http://arxiv.org/abs/1512.01443. To quote him: "There is no spooky action at a distance in the real world we live in if it is governed by the laws of quantum mechanics." Believe it or not, there was, and is a serious debate about "interpretations" and as I see it, even interpretations of interpretations. This situation is arguably a disgrace to science, but c'mon, have you ever seen a scientist ashamed of anything? — Preceding unsigned comment added by 178.42.79.67 (talk) 21:20, 16 February 2016 (UTC)

Bias
I think the whole presentation is kind of biased towards "classical-ish" interpretations, inspired by Copenhagen. E.g. defining realism in terms of measurement results, and implicitly assuming that "actual definite properties of a physical system" are the classical properties, such as momentum, and not the QM properties, i.e. the wave function. This subject is disputed and should be described as such, presenting all views. http://arxiv.org/abs/1512.01443, http://quantum.phys.cmu.edu/CQT/chaps/cqt24.pdf , http://quantum.phys.cmu.edu/CQT/chaps/cqt01.pdf (sorry for posting these links in more than one place, but I don't know which is best). I know I'm quoting just Griffiths here, but he's the first one that I came across presenting a local realistic interpretation of QM. — Preceding unsigned comment added by 178.42.79.67 (talk) 21:34, 16 February 2016 (UTC)

Einstein rejected 'as being a paradox'?
I'll give a whole quote from the article:

'Local realism is a feature of classical mechanics, and of classical electrodynamics; but quantum mechanics theories reject the principle, based on the experimental evidence of distant quantum entanglements: an interpretation that Einstein rejected (as being a paradox), but which is supported by a 1972 experiment based on Bell's 1964 inequality theorem.'

Okay, I have difficulty with stating that 'quantum mechanics theories' supposedly 'reject the principle'. I don't think that a theory can reject a principle, though maybe I'd just rephrase that the theory contradicts the principle. But note, that the rest of the sentence, as it turns out, states that '...quantum mechanics theories reject the principle, based on the experimental evidence..' And then this is called 'an interpretation'. I know that I am quibbling about details, but I think one might try very hard, here, to separate what is an 'interpretation' from what is 'experimental evidence'.

Of course, these matters are abstract. But I think that this discussion in the article is ultimately unclear on the question whether local realism, as it were, or put it this way a certain kind of realism, is a kind of realism that is obviously wrong. I am unclear on whether the idea, here, is that you can call it straw man realism since it exists just to be disproven -- is it a kind of realism that actual practicing realists (and anyone that cares about agreeing with observations) do not believe in. Perhaps, arguably, though the article seems to fudge the question, perhaps we already know, as it were, exactly what happens. There is no freedom there is no choice. This is not opinion and it is not speculation it is what happens. We know exactly what determines the outcome and it isn't local. I mean to just emphasize an idea clearly, here. The idea that if you want to understand what happens we know what happens, such that maybe I should probably just hire a production crew to make videos that just show it. Einstein believed in 'local realism', okay, was he right or was he wrong?

Let me go back over local realism hopefully more clearly than the article does it. The idea of this Einsteinian principle of local realism, is that All information in quantum systems is localised. Measuring or otherwise interacting with a quantum system S has no effect on distant systems from which S is dynamically isolated, even if they are entangled with S. Now, the article mentions Bell's theorem, and I gather a sort of impression that it is a prima facie refutation of Einstein’s conclusion. And okay, can we get clear on this question whether quantum physics is entirely consistent with Einstein’s criterion, or not? Well, of course, there is the matter of all phenomena that have been thought to demonstrate nonlocality in quantum physics.

I think that Einstein's own position was that reality does not have a nonlocal character, this is his 'local realism', but also, according to Einstein, neither does quantum theory have a nonlocal character. Agree or disagree with him, but his problem is not with quantum theory per se, is it? He's one of the inventors of it. Yes, Einstein thinks that the locality premise, as it were, is true. And yes, that means that something went wrong, but not with 'quantum theory'. Einstein saw the practice of assigning a single-valued (albeit stochastic) variable to a physical quantity whose true descriptor is a matrix. And he figured that this has to lead to inconsistency. Note that the article says something vague about Einstein having a problem with 'paradox', here: 'quantum mechanics theories reject the principle, based on the experimental evidence of distant quantum entanglements: an interpretation that Einstein rejected (as being a paradox)..'

The problem, actually, for Einstein, is that quantum theory is entirely local but appears nonlocal in the mathematically equivalent Schrödinger picture, which disguises the locality of quantum physical processes. Einstein did not believe that quantum theory (and the physical reality it describes) is nonlocal. Think of Einstein as wanting to make explicit what is implicit, indeed quite well hidden, in what I have described as a 'picture', because it's not quanum theory itself, but a 'picture', that is optimised for predicting the outcomes of processes given how they were prepared, but (notoriously) not for explaining how the outcomes come about. There is some kind of information flow issue, here, on the face of it, I mean maybe this 'picture' misrepresents information flow, and it's not just Einstein who thinks so.

Actually, having taken 30 minutes considering this, I don't have any suggestions for improvement. This stuff is complicated and difficult to explain. But saying 'quantum mechanics theories reject the principle' is speaking rather loosely, because it is *people* that 'reject'. And such loose turns of phrase multiply too much, I think, when I see '...quantum mechanics theories reject the principle, based on the experimental evidence..' And then this is called 'an interpretation'. So I'll repeat that one might try very hard, here, to separate what is an 'interpretation' from what is 'experimental evidence'. It's hard, indeed it's too hard for me too, but we need to reduce some of the vague gestures, here..DanLanglois (talk) 11:43, 15 February 2018 (UTC)

Definition of realism
Current version of the article reads:
 * Local realism is the combination of the principle of locality with the "realistic" assumption that all objects must objectively have pre-existing values for any possible measurement before these measurements are made.

This is an extremely strong definition of "realism" which is already demolished by von Neumann's "silly" anti-hidden variables proof. Even a somewhat weaker form is ruled out by the (Bell)-Kochen-Specker theorem. Usually, local realism is cited as the position ruled out by Bell's theorem, but Bell's inequality holds for HV theories that escape both von Neumann and Kochen-Specker, therefore the above definition is grossly misleading. As per the Travis Norsen preprint referenced here, it is unclear whether the term "realism" in "local realism" actually denotes anything, or whether this is simply a weaselish way of saying "locality". I hope someone who supports the claim that "local realism" adds a distinct assumption can explain what it actually is, in the face of Norsen's criticisms. PaddyLeahy 03:08, 2 June 2007 (UTC)

As I understand it "local realism" is a term applied to CLASSICAL physics. Keithbowden (talk) 19:09, 6 February 2008 (UTC)

As Robert Griffiths points out, Bell's inequality rules out CLASSICAL local realism. To my common-sense understanding what he tries to say is that people are trying to re-interpret the results of QM back into classical notions and then of course they fail. In other words, Consistent Histories (the interpretation Griffiths advocates) is locally realistic, provided that the "real" physical property is (represented by) the wave function, not momentum or the like (which are classical approximations, invalid in general). Sources: http://arxiv.org/abs/1512.01443, http://quantum.phys.cmu.edu/CQT/chaps/cqt24.pdf ) — Preceding unsigned comment added by 178.42.79.67 (talk) 21:10, 16 February 2016 (UTC)


 * To weigh in on this old discussion, the notion of realism in the article does not necessarily say anything about the value assignments being noncontextual; this can be thought of as coming from the locality assumption. Nonetheless, I think this article requires a lot of cleanup. Porphyro (talk) 07:55, 4 July 2018 (UTC)

Move discussion in progress
There is a move discussion in progress on Talk:Quantum nonlocality which affects this page. Please participate on that page and not in this talk page section. Thank you. —RMCD bot 17:44, 6 July 2018 (UTC)

Move discussion in progress has been closed
Can we carry on, Arnold,45.49.226.155 (talk) 19:13, 23 October 2018 (UTC)

Is Observation independent of observer locality
Is this article improved, if Observation is posited as independent of a locality that includes a observer interaction as part of the measurement/test, Arnold,45.49.226.155 (talk) 19:24, 23 October 2018 (UTC)
 * Locality is a property of an interaction between objects. All interactions between non-entangled objects are always local, meaning the influence (particle or wave) travels between them at or below the speed of light. For example, if your wireless laptop is 30 feet away from your router, and you download a webpage, there is roughly a 30 nanosecond delay between the time each bit of information is transmitted by the router's antenna and when it is received by the laptop's antenna, because the radio waves from the router take that long to travel at the speed of light and affect the receiving antenna.    In contrast, objects which are quantum entangled, for example two photons which have been emitted from an atom in separate directions with opposite spins, can violate locality; when the spin of one photon is measured, and its superposition of spins collapses into one spin, the other photon instantly collapses into the opposite spin, even if the two particles are millions of light-years apart..

.-I'm not sure if that answered your question? --ChetvornoTALK 22:38, 23 October 2018 (UTC)


 * -Thank you, but better defining Relativity seems to be my search. observer locality is referenced as part of the principle of locality in quantum measurement (measure). While Observation is an axiomatic-independent to fundamental interactions and non-influential to the principle of locality. That observer locality, completes quantum realism, when Observation is present in space time relativity, Arnold45.49.226.155 (talk) 00:36, 24 October 2018 (UTC)


 * This talk page is for discussion about improving the article. It is not intended for general debate about the subject. Prokaryotic Caspase Homolog (talk) 01:27, 24 October 2018 (UTC)
 * -Thank you, this is a attempt to improve an article via a post modern talk, about whether Observation is influential or not, if found independent it can become an improvement in understanding locality limits from including observer

bias in locality axioms,Arnold,45.49.226.155 (talk) 02:40, 24 October 2018 (UTC)

S.I.?
The lede contains the abbreviation "S.I.", but what this stands for is not at all clear (to me, at least). Attic Salt (talk) 18:36, 18 November 2019 (UTC)


 * It stands for "statistical independence". Some editor has been replacing the term "realism" with this term.  I don't know enough about quantum mechanics and the various meanings of "realism" used in the EPR debate to know if this is legitimate, but I think the article should stick to widely accepted terminology.  Most of the articles I've read say that the violation of the Bell inequality means QM violates either locality or "realism", and I haven't heard the term "statistical independence" used much w.r.t. EPR. --ChetvornoTALK 21:37, 18 November 2019 (UTC)


 * Local realism redirects here, so I think we need the term realism defined. --ChetvornoTALK 23:42, 18 November 2019 (UTC)


 * I think the confusing opaque term "statistical independence" in the article should be changed back to "realism". The term "realism", as an assumption that may be violated by the EPR experiments, is widely used by Einstein and most writers on the subject   . It has a precise definition, and even if some modern views regard it as irrelevant  it should be addressed.   The "statistical independence" or "free will" violation loophole is not the same as realism violation, it refers to a 3rd more unlikely reason beside locality or realism violation for the failure of the Bell inequality; that nature is subtlely biasing the setup of the entire experiment (, last para), .   The section Realism in the article is totally incomprehensible, unsourced (the only citation is a single arxiv preprint), and does not address the concept of realism as used by most scientists.  It should be rewritten. --ChetvornoTALK 21:15, 25 November 2019 (UTC)
 * Okay, thank you for this thoughtful response. I invite you to make the substitution. Attic Salt (talk) 20:57, 25 November 2019 (UTC)
 * Thanks. I need to read up on the subject before doing anything. The phrase counterfactual definiteness is also a possibility; it seems to my untutored brain to have almost the same definition as "realism".  If somebody who actually knows about this stuff wants to take a crack, that's fine. --ChetvornoTALK 21:15, 25 November 2019 (UTC)

What does the EPR paper say?
I saw your recent edit. What is exactly in conflict here? I think that the EPR paper is important to introduce the topic but I agree that the wording is loose. Can we work it back in? ReyHahn (talk) 19:28, 4 October 2023 (UTC)


 * I'm not against describing the EPR paper as the spark for the quantum locality discussions. I don't think it is essential in this article (on "principle of locality"); I would agree that it would be essential in the quantum nonlocality article.
 * I think the article should be about the title topic and the EPR paper does not directly address that topic. Rather, the paper is about the completeness of the wavefunction as a description of reality, using the principle in its analysis. Thus it is an application of a (classical) locality principle.
 * Unfortunately the paper never says such a thing. It never even uses the word "local" or "locality", or "simultaneous" or "speed of light" or "entanglement". So the sentence I deleted was an unsourced fabrication. Later analysis might claim the the EPR paper, when interpreted in modern terms "meant" those things, but we need a reference for that.
 * I hope this answers your questions.
 * Now how to proceed? The topic is quite complex, although I fear that it is one of these topics where "everyone knows" the answer.
 * My plan was to find a ref that amounts to your "EPR paper is important to introduce the topic", then try to work on quantum nonlocality with the idea of eventually reworking the current article to avoid the history altogether, focusing just on the "principle of locality" for QM. WDYT? Johnjbarton (talk) 21:12, 4 October 2023 (UTC)
 * Hmmm I will have to look at it again, I did not remember that EPR did no use "locality" in its terminology, you may have a point here. What about EPR-Bohm? I advice intense caution, the sources are even to this day are murky. Philosophers have taken some ground in this matter. The lack of consensus on which words to use make this topic awful. I guess we can source it but I would advise to intentionally use ambiguous terms in the points of conflict, if not we will have to go into the math but it might get too technical.--ReyHahn (talk) 21:20, 4 October 2023 (UTC)
 * I found a ref with a clear intro, take a look. Johnjbarton (talk) 21:36, 4 October 2023 (UTC)
 * I think a lot of this issue is the combination "local realism". Since we famously have dozens of serious contenders for QM "reality", the combination is almost impossible to manage. See eg Federico Laudisa,
 * "How and when did locality become ‘local realism’? A historical and critical analysis (1963–1978)",
 * Studies in History and Philosophy of Science, Volume 97, 2023, Pages 44-57, ISSN 0039-3681, https://doi.org/10.1016/j.shpsa.2022.11.008. Johnjbarton (talk) 21:45, 4 October 2023 (UTC)
 * Lovely article from Reid and Drummond, first time looking at it. However I would avoid "quantum nonlocality" in the text that you added, also it sparked a debate between them? or with somebody else? Local realism basically means local hidden variable theory, from what I have read authors use "local" and "real" in different ways making it almost impossible to be clear on where they differ, however when local realism is used altogether it is clear what it is being violated here.--ReyHahn (talk) 21:49, 4 October 2023 (UTC)
 * From the review: "Owing to the subsequent work of Bell, we now know what EPR did not know: local realism, the “realistic philosophy of most working scientists” (Clauser and Shimony, 1978), is itself in question. Thus, an experimental realization of the EPR proposal provides a way to demonstrate a type of entanglement inextricably connected with quantum nonlocality." So maybe the link can stay if we work on the text somehow? Johnjbarton (talk) 22:01, 4 October 2023 (UTC)
 * The link to quantum nonlocality? Its already set as Template:Main article. My problem with using "quantum nonlocality" in an article about the principle of locality is that it leads to the conclusion that quantum implies violation of locality (some but not all agree on this), when in fact it implies violation of local realism (everyone agrees on this). So it leads to confusion when terms are not defined in advance, even if vaguely.--ReyHahn (talk) 22:06, 4 October 2023 (UTC)
 * I agree on "quantum nonlocality". Not sure about the replacement. I think it implies a lot of understanding by readers to connect the dots.
 * Clauser, John F., and Abner Shimony. "Bell's theorem. Experimental tests and implications." Reports on Progress in Physics 41.12 (1978): 1881.
 * Says:
 * "Consequently, it can now be asserted with reasonable confidence that either the thesis of realism or that of locality must be abandoned."
 * I think that is what you are saying. Local + realism fails; pick one. Johnjbarton (talk) 22:12, 4 October 2023 (UTC)
 * I used this "Hence, the discussion, for the greater part of the subsequent 30 years, was pursued perhaps more at physicists’ cocktail parties than in the mainstream of modern research." from the end of the EPR history in Clauser and Shimony to swap the hidden variables link with simply "the nature of reality". They then move on to Bell just like the article. Johnjbarton (talk) 22:27, 4 October 2023 (UTC)
 * Yes, this is what I am saying (note that John Bell personally disagrees with the idea that violating realism is enough, Bell argued that his theorem implies that quantum mechanics necessarily violates locality, so those that side with Bell have a different mantra). I agree with the current paragraph, thanks.--ReyHahn (talk) 22:53, 4 October 2023 (UTC)

"relativistic quantum field theory is manifestly local"
In their review "Quantum information and relativity theory" Asher Peres and Daniel R. Terno Rev. Mod. Phys. 76, 93 – Published 6 January 2004 have a section called "Quantum nonlocality?"

"Bell’s theorem (1964) asserts that it is impossible to mimic quantum theory by introducing a set of objective local “hidden” variables. It follows that any classical imitation of quantum mechanics is necessarily nonlocal. However Bell’s theorem does not imply the existence of any nonlocality in quantum theory itself."

(Notice that they nicely side step "realism" by using "classical").

This seems relevant to the article. (To be sure, it would be relevant to quantum nonlocality but I'm not sure I have the patience). Johnjbarton (talk) 02:54, 5 October 2023 (UTC)
 * My summary on the problem of discussing locality in quantum mechanics in depth:
 * Most physicists (except for superdeterminists and loophole researchers) agree that the Bell tests show that quantum mechanics violates local hidden variables/local realism.
 * Everybody agrees that entanglement cannot be used to send information faster than light.
 * EPR authors supported local realism, Bohr supported that there were violations of realism and not locality, Bohm and Bell supported violations of locality and not realism.
 * Point of conflict 1: realism is badly defined, EPR seem to connect it to counterfactual definiteness even if this term is rarely used. Bell attached realism to determinism. Bohr seems to associate it to the probabilistic or non probabilistic nature of quantum mechanics. Modern authors define more complicated terms.
 * Point of conflict 2: locality is badly defined and it is sometimes mixed with causality or "spooky" action-at-a-distance. Some authors argue that all interactions in physics are local and associate it to the lack of action-at-a-distance. Some see the violations of Bell theorem as to be in conflict with special relativity, so argue that locality must remain. Bohmians/pilot waveist/Bell supporters, argue that locality is violated as "classical" probabilties (again vaguely defined here) cannot be written in as being independent of the two particles (you need nonlocal hidden variables). For even more conflict, relativistic quantum field theory "locality" is included as one of the Wightman axioms but it is unclear if it is the same locality as the one in local realism. Quantum nonlocality=violation of local hidden variables is a misnomer in this sense as it supports one vision of the argument, quantum nonlocality clearly does not mean violation of Wightman axiom.
 * Point of conflict 3: not everybody likes the term local realism. Bell argued that locality is always violated and the it should be preferable to talk about "local causality" (I admit that I still do not get the difference between local causality and locality/causality in the Bell sense). But that discussion should be resolved in another article on Bell's beable theory.
 * Wiki decisions to make : keep/remove the term "local realism" from this page. If removed it can be replaced with local hidden variables which seems to be a more clear model. However then people looking for local realism in Wikipedia would be directed (as it was a few years ago) to EPR paradox which is a bad thing to do as the authors barely use the term and the resolution is in another page (Bell theorem). Explain/avoid to explain what quantum nonlocality means, dig deep into the definitions in conflic above. Explain/avoid to explan the position of Einstein/Bohr/Bell on this.
 * Hope this helps.--ReyHahn (talk) 12:17, 5 October 2023 (UTC)
 * Your summary fairly represents the sources I have read. Per Wikipedia, I think this is the point of view that should be reported (except of course the editorializing aspects). I'm in favor of keeping eg "local realism" even though I personally think it is impossible to define. We need to report on the difficulties in definition, as annoying as that is. Johnjbarton (talk) 15:12, 5 October 2023 (UTC)