Talk:EPR paradox

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Section under "the crux of the matter" is wrongEdit

The section under "the crux of the matter" is wrong. By only measuring the x or z axis you cannot distinguish between a classical system with hidden variables and a quantum system. One has to measure at 45 degrees also. The description is wrong.

Sorry, I meant to put this somewhere else, but I do not know how to delete this.

Observer as VariableEdit

The impact of consciousness is unquestioned, how much more abstract is consciousness greater will its power both in size and complexity?

too complicated. needs clarity instead of obfuscation.Edit

"Violations of the conclusions of Bell's theorem are generally understood to have demonstrated that the hypotheses of Bell's theorem, also assumed by Einstein, Podolsky and Rosen, do not apply in our world.[5] Most physicists who have examined the issue concur that experiments, such as those of Alain Aspect and his group, have confirmed that physical probabilities, as predicted by quantum theory, do exhibit the phenomena of Bell-inequality violations that are considered to invalidate EPR's preferred "local hidden-variables" type of explanation for the correlations to which EPR first drew attention.[6][7]"

utterly incomprehensible. it starts with the violations that never actually get explained. also 'hypotheses of Bells theorem' needs thorough decoding: how many of those hypotheses are there? what they are? could not they simply be referred as 'Bells theorem'??'also assumed by E,P and R': does this mean that they agreed to bells theorem?? then how comes that bells theorem is described as a statement that the EPR paradox is a mistaken idea? needs clarification. a LOT of clarification. 'do not apply in our world': is this an overcomplicated way of restating bells theorem, like quantum models do not apply to objects several times the magnitude of elementary particles? if that was not meant to say then i am the living proof that the wordig is overcomplicated and instead of explaining the subject to a relatively educated laicist just obscures the thing it was supposed to clarify. 89.134.199.32 (talk) 21:09, 3 September 2019 (UTC).

Recent editsEdit

The change made to the introduction back in December and reverted back and forth since is unclear (and ungrammatical). The current version is much more satisfactory, although it does commit the common error of presuming that "the Copenhagen interpretation" was/is a well-defined thing, rather than a label applied well after the fact to the views of physicists who differed among themselves on important points. XOR'easter (talk) 21:15, 29 January 2020 (UTC)

The current lead is terrible. Strange prose, contentious interpretation of the paper, and the talk about "Copenhagen interpretation" is decidedly anachronistic. Tercer (talk) 23:07, 29 January 2020 (UTC)
Now that my headache has receded and I can think and express myself a little more clearly... yeah, "more satisfactory" is not good, by a long shot. I'm not a fan of they attempted to mathematically show that the wave function does not contain complete information about physical reality — it's just unclear what that is trying to say. The third paragraph (The essence of the paradox...) is not very clear either. On face value, it's not even right: it sounds like the conclusion was that one can measure both the position and the momentum of both of two correlated particles more accurately than Heisenberg's uncertainty principle allows. At least, I think that's what it is saying. But that's not at all what EPR actually argued. XOR'easter (talk) 03:36, 30 January 2020 (UTC)
OK, I have tried to do something with the lead, but I'm sure it still needs work, and the rest of the article is in a pretty miserable state. It doesn't describe Bohr's reply (the measurements of position and momentum are complementary experiments requiring different laboratory apparatus, so inferences from one can't be combined with inferences from the other). It doesn't include Bohm's version of the EPR thought experiment (measuring two entangled atoms with Stern–Gerlach devices). Somehow, it manages both to give only a cursory explanation of how Bell's theorem was a conceptual advance beyond EPR, and to jam in names and dates and terminology about variations on Bell's theorem that add nothing to an article that isn't about Bell's theorem. I tried to get away from the "the Copenhagen interpretation" talk in the lead, but it recurs in the article body, and every instance is an example of not paying attention to historians of science. It complains about oversimplified popularizations of the uncertainty principle, and in the next paragraph, endorses an oversimplified popularization of quantum computing. Etc. XOR'easter (talk) 04:30, 30 January 2020 (UTC)
Thanks for your edits, the article improved a lot. I've worked a bit on the lead, to eliminate repetition, use more straightforward language, and emphasize the point that EPR were not merely arguing against Bohr, but rather in favour of a hidden variables theory to supplant quantum mechanics.
I think the biggest problem with the article is the one I hinted at in the history section: it focusses only on the argument given in the EPR paper, which Einstein was not happy with. For him, what was crucial was not the violation of the uncertainty principle, but rather that he had demonstrated nonlocality in quantum mechanics, and proposed hidden variables as a way to heal it. This is the point Bell was addressing in his 1964 paper, showing that Einstein's cure couldn't work. Tercer (talk) 17:47, 2 February 2020 (UTC)
The new lead is better; thanks for working on it. I agree that the article needs to say more about Einstein's own view (which, IIRC, he stated in more places than just that 1936 essay), in contrast with the EPR paper. XOR'easter (talk) 18:14, 2 February 2020 (UTC)
Indeed, I've seen it in his correspondence with Schrödinger. We can use the version presented in section IV.C of arXiv:0706.2661, it's simple and precise (I'm feeling a bit bad about repeatedly citing this paper, as I completely disagree with the authors' epistemicity. I have to admit though that they did a great job on the history part). Tercer (talk) 18:40, 2 February 2020 (UTC)
There's also his contribution to the 1949 volume edited by Schilpp (cited in section V.A of arXiv:0706.2661). I recall the phrasing in that version being more polished than in the letter to Schrödinger, which might help if we're looking for any exact quotations. XOR'easter (talk) 18:51, 2 February 2020 (UTC)
Are you sure? I just read Einstein's essay, and he doesn't describe the argument at all there. He just makes some general remarks about why he thinks hidden-variable theories are a good idea. Tercer (talk) 19:38, 2 February 2020 (UTC)
Ah, so it was in the Autobiographical Notes section, not in the Reply to Criticism essay. I didn't think of looking in there. Thanks for including it, but I think it is in general not a good idea to directly quote primary sources, and in particular I find the version in arXiv:0706.2661 more clear. In particular, we should mention that Einstein didn't care about the uncertainty principle part, but only about nonlocality. Tercer (talk) 21:21, 2 February 2020 (UTC)

Overall I think I'd be happier with a paraphrase (and maybe a shorter quote than what I included, from one source or another), but for the sake of getting a section in place, I figured a briefish blockquote would be serviceable. Actually, I had typed it up with all the math tags to leave in a comment here, and then, after all that, I had the idea that it could go into the article itself. XOR'easter (talk) 21:25, 2 February 2020 (UTC)

Ok, I'll work on it tomorrow. Tercer (talk) 21:39, 2 February 2020 (UTC)
The new version looks good. XOR'easter (talk) 15:01, 3 February 2020 (UTC)
I'm glad you liked it. I was unsure whether to formalize Einstein's argument using the hypotheses of state space separability and locality, as they were precisely stated only by later authors. In the end I decided to write the argument in an informal style, it's a bit refreshing to see such a simple and straightforward argument in this complex discussion. Technical question: do you know how to cite a reference inside a reference? I tried to do that to mention that Ref. 15 is reproduced in Ref. 12, but I couldn't get it to work. Tercer (talk) 15:45, 3 February 2020 (UTC)
I believe one way to do something like that is to have a reference inside an endnote, using the {{efn}} template. See, e.g., the notes in thorium. XOR'easter (talk) 17:52, 3 February 2020 (UTC)
Thanks for the tip, done. Tercer (talk) 18:49, 3 February 2020 (UTC)

There has been a lot of outright blanking of information sourced from peer-reviewed publications outlining the evolution of understanding from Bohr, Bohm, Bell, "CHSH", Stapp, Eberhard, Fine, Pitowsky and more recently Griffiths, Philipp, Hess, Streater. Without this info the reader is back in 1935 and is left unaware of the progress that has been made in both theory and research. But presumeably the blankers decided they don't like the findings of these not insignificant researchers. 197.234.164.85 (talk) —Preceding undated comment added 17:57, 4 February 2020 (UTC)

The neutrality of the removed material was at best debatable, and in-depth discussion of Bell(-CSSH) inequalities belongs in an article about Bell(-CHSH) inequalities, not one on the EPR paradox. Mashing them together makes it much more difficult to distinguish what Bell did from what EPR did. This article, as it currently stands, does not leave the reader back in 1935, since it summarizes the Bohm version of EPR (1951), Bell's theorem (1964), and Sakurai's hidden-variable toy model (here credited to the 2010 edition, but IIRC it's in the 1994 one). XOR'easter (talk) 18:06, 4 February 2020 (UTC)
The mentioned authors represent a wide spectrum of views and all are well established academics whose findings and conclusions are published in peer reviewed journals so a claim of dubious neutrality doesn't stand. Looks more like WP:JDLI from recent editors. 197.234.164.85 (talk) —Preceding undated comment added 18:47, 6 February 2020 (UTC)
If you could be specific about what material you think should be added back we can discuss it. A generic complaint about blanking is not productive. Tercer (talk) 19:47, 6 February 2020 (UTC)
It is of course possible to write non-neutrally (or worse yet, just unclearly) about findings published in peer-reviewed journals, for example by taking obscure debates about niche aspects and blowing them out of proportion. In any case, the material is still there in the edit history, and I'd be happy to discuss specifics. XOR'easter (talk) 20:06, 6 February 2020 (UTC)

SteeringEdit

We should add a section about steering in this article. It is a formalisation of the EPR paradox, introduced in the seminal paper of Wiseman et al. arXiv:quant-ph/0612147 (arguably also by Schrödinger back in the day), and it his how EPR is often understood nowadays. Tercer (talk) 15:50, 6 March 2020 (UTC)

Sounds like a good idea. I think the term steering itself originated with Schrödinger (e.g., It is rather discomforting that the theory should allow a system to be steered or piloted into one or the other type of state at the experimenter's mercy in spite of his having no access to it.) XOR'easter (talk) 17:55, 6 March 2020 (UTC)
Yep, he did. I'm just saying that it's a bit of a stretch to attribute the current formulation of steering to Schrödinger. Anyway, I just checked, and someone created an article on quantum steering a couple of months ago. It's pretty bad. Also, steering is mentioned in a sentence in the quantum nonlocality article, and in a paragraph in the quantum entanglement article. Tercer (talk) 18:43, 6 March 2020 (UTC)
Return to "EPR paradox" page.