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Archive 1 |
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)
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)
"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)
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 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)
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.
Quantum mechanic in the top of article is offtopic. -- Камень ( talk) 22:07, 2 April 2009 (UTC)
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 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)
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)
I suggest that a redirect from locality (physics) might be helpful. 70.247.162.84 ( talk) 15:00, 8 September 2012 (UTC)
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
"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)
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)
Oh, come on. "[...] thus the principle of locality is false[2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]". Three quarters of the citations in the whole article are for this one sentence in the introduction. This is ridiculous. Is there no secondary source (or maybe 2-3) we could refer to instead of this enormous list of papers? -- Coffee2theorems ( talk) 19:36, 7 March 2009 (UTC)
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:
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)
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)
"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)
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)
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)
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)
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)
Current version of the article reads:
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)
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)
Can we carry on, Arnold, 45.49.226.155 ( talk) 19:13, 23 October 2018 (UTC)
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)
.-I'm not sure if that answered your question? -- Chetvorno TALK 22:38, 23 October 2018 (UTC)
bias in locality axioms,Arnold, 45.49.226.155 ( talk) 02:40, 24 October 2018 (UTC)
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)
Johnjbarton I saw your recent edit [7]. 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)
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)
![]() | This is an archive of past discussions. Do not edit the contents of this page. If you wish to start a new discussion or revive an old one, please do so on the current talk page. |
Archive 1 |
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)
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)
"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)
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 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)
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.
Quantum mechanic in the top of article is offtopic. -- Камень ( talk) 22:07, 2 April 2009 (UTC)
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 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)
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)
I suggest that a redirect from locality (physics) might be helpful. 70.247.162.84 ( talk) 15:00, 8 September 2012 (UTC)
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
"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)
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)
Oh, come on. "[...] thus the principle of locality is false[2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17]". Three quarters of the citations in the whole article are for this one sentence in the introduction. This is ridiculous. Is there no secondary source (or maybe 2-3) we could refer to instead of this enormous list of papers? -- Coffee2theorems ( talk) 19:36, 7 March 2009 (UTC)
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:
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)
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)
"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)
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)
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)
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)
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)
Current version of the article reads:
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)
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)
Can we carry on, Arnold, 45.49.226.155 ( talk) 19:13, 23 October 2018 (UTC)
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)
.-I'm not sure if that answered your question? -- Chetvorno TALK 22:38, 23 October 2018 (UTC)
bias in locality axioms,Arnold, 45.49.226.155 ( talk) 02:40, 24 October 2018 (UTC)
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)
Johnjbarton I saw your recent edit [7]. 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)
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)