Talk:Local hidden-variable theory

Hanson experiments
This page still states that "but local hidden variable theory can still explain the probabilistic nature of quantum measurement due to loopholes in experimental Bell tests." This hasn't been true for a few months (doi:10.1038/nature15759). The Bell's Theorem/Inequalities page has already been updated; I suggest someone does so here. — Preceding unsigned comment added by 145.132.49.101 (talk) 01:23, 15 December 2015 (UTC)

Changed the statement about local realism guiding all scientific endaveor before QM. Newtonian gravity is not a local realist theory. Roadrunner 07:15, 21 Aug 2004 (UTC)

Newtonian gravitation is not local, true, but even Newton felt there was something wrong with Newtonian gravitation because it of that. (As well as other critics with their criticism of action-at-a-distance) And Newtonian gravitation was replaced by General Relativity, which IS local (and realistic), before the quantum mechanics of the 1920s. So you could say that local realism was indeed a guiding principle (of all valid physics) before qm. Pedantically, 67.118.118.112 01:09, 19 Jan 2005 (UTC)

NPOV warning?
I don't see any reason for the NPOV warning in the article. I can't see any discussion going on about the NPOV here, either. It seems like some disargreement has been going on between DrChinese and Caroline Thompson, but no discussion is taking place at all and the proble seems to be solved. The warning should be removed.--CWitte 11:43, 14 Mar 2005 (UTC)


 * IMHO the article doesn't match its lemma and what's to be said about LHVTs should be said in Hidden variable theory. The actual of Local hidden variable theory is just another spinoff from Bell test experiments. --Pjacobi 13:51, 2005 Mar 14 (UTC)

Summary
The artical really needs a summary of what it actually means and if it is violated or confirmed by real results. Apart from that i dont see the reason for the non-NPOV warning

"which has always been considered a desirable property by physicists" - that statement is lacking a neutral point of view. While that was once considered a desirable feature by the majority of physicists, I don't believe that it is nearly unanimus today. The Orthodox interpretation of quantum mechanics (Something like Von Neumann - Dirac's interpretation) is certainly not local. In fact, quantum mechanics is generally nonlocal and repreated experimental violations of Bell's inequality are (so far) unexplainable by anything other than nonlocal hidden variable theory, or nonlocal no hidden variable theory. Maybe one could introduce a fairly exotic mechanism to get around it (like the hidden time) mentioned in the article, I don't know. But for the moment, locality is dead in the minds of most phycisists.


 * Ahem! For the absence of explanation of the possible local hidden variable theories, invoking nothing exotic, you have to thank Dr Chinese, who, earlier this year, was the prime mover in deleting all references to my own work and removing the page on the Bell Test Loopholes.  It is the loopholes in the real experiments that make local HV theories possible as explanations for all the observed results.  What no local HV theory can do, though, is reproduce exactly the QM prediction.  The latter assumes perfect conditions and has never been tested.  This is why efforts to devise a genuinely "loophole-free" test continue.  See my user page for more, including the deleted page.

If you read the current local HV theory page carefully, you will find hints as to how these theories work as regards exploitation of the "detection loophole". This is the loophole that is related to possibility of altering the assumptions so as to get away from exact adherence to Malus' law. By assuming that detector responses not exactly proportional to intentities but, instead, are such that all very weak signals are ignored, we find Malus' law replaced by one that is similar in that is has peaks at the same places but has wider troughs. If the troughs are zero then when we integrate over polarisation directions (our HV) we can get predicted coincidence curves with visibility anything up to 1, in agreement with QM.

Incidentally, as regards a possible timing loophole, I don't think any of the ones mentioned are relevant. There is one that may well be, though. See a paper of mine: http://arxiv.org/abs/quant-ph. Caroline Thompson 09:15, 6 September 2005 (UTC)

Where's the definition
As a layman, I don't see an actual definition of the subject. Something like 'Local Hidden Variables are a characteristic of quantum particles, which each entangled particle carries which causes it to react the same way to a given measurment at a particular time no matter how far apart they are'. —Preceding unsigned comment added by 160.42.234.85 (talk) 15:49, 7 January 2008 (UTC)

Here is a possible model (hence implicitly a definition)
It is understandabable that a layman asks about the definition of LHV theories. And, indeed LHV theories are a result of Bell's way of looking at the subject. There could be some comfort in the idea that when scientists talk about local hidden variables nobody, including the scientists, really knows what they are talking about.

However, we can talk about restrictions in the results we can observe in experiment. In this way a differentiation between quantum mechanical and LHV can be formulated. The restrictions are known as the Bell inequalities. A special branch is the Clauser Horne Shimony and Holt contrast (i.e. CHSH contrast) that makes life very difficult for the concept of local hidden causality. That is the most clever contribution to science. Namely construe a (set of) restrictions such that only quantum mechanical correlation (i.e. distant interaction or non-local interaction or ... ) can violate that restriction.

Nevertheless and despite of the most rigourous test, I claim to have obtained a local hidden variables model that: 1. can " recover with any precision necessary" the quantum correlation between the two distant particles that travel to A and B, 2. This violation "goes" under locality conditions (A's result cannot be influenced by what we measure on the B side and vice versa) 3. The proposed hidden variables model can violate the CHSH contrast and 4. the model uses classical probability.

The use of probability arises from the idea that the local hidden variables are 'weighted' entities that, because a return to classical concepts like causality and locality, should also follow classical probability laws. I refer to my arXiv:0811.1746 paper.

Of course opponents will argue that the proposed model cannot be right because their derivations and experimentations cannot be wrong. This sounds just like dogmatism and totalitarian regimes but in fact it is not. The author agrees with the opponents of LHV on one point, namely, it is strange that a classical model can be construed because the inequalities apear so obvious. But, the author would like to add, the argumentation is also used in a prohibitive way by preventing the model to see daylight and attract attention of other scientists that may form their own opinion. This part of the "we are not wrong, hence you are" argumentation is not so nice, but ok we are humans too. The funny part is that the opponents of the LHV theories fail to see one extra nicety of LHV, namely, it explains the unexplainable. Namely, it replaces the mysterious non-local interaction from qm for entities that can be accessed in principle with experimental methods. If one wants to argue that in this way there is a return to Classical Physics well so be it. The author would like to note that in 1995 he published a paper in which it is demonstrated that Dirac's relativistic quantum mechanical equation can be obtained from Maxwell's classical field equations (J.F. Geurdes, Phys. Rev. E 51, 5151 (1995)). Perhaps that a deeper understanding of the quantum in the classical physics and the classical in the quantum physics may finally tear down the artificial barrier between the two concepts.

—Preceding unsigned comment added by 84.82.11.120 (talk) 19:21, 13 November 2008 (UTC)

clarification of "loophole theories" in first paragraph? to me, the mention of loopholes in the first paragraph doesn't make it clear that a very significant loophole is simply experimental issues around detection efficiency; although as I understand it those can be covered by an extra theoretical postulate, practically they are subject to removal through improved technology. —Preceding unsigned comment added by RiceMilk (talk • contribs) 22:45, 14 April 2009 (UTC)

Cos Sq Curves
Figure 2 does not contain $$\cos^2$$ curves. Squared real number curves are never negative. They are closer to 2 $$\cos^2$$ - 1 curves. Similarly, Figure 1 probably is suppose to be a $$\cos^2$$ curve. Here's an attempt to attach the correct versions: Figure 1: Figure 2: KenHoldeman (talk) 23:04, 6 December 2009 (UTC)

Competing explanation of Bell's theorem
This page gives a jolly good description of Bell's inequality as it relates to coincidences between events. In fact it may even be better than the one in the Bell's theorem page. This does not appear consistent. Don't get me wrong- they both describe the theory accurately, but it seems odd that I, somebody trying to understand the theory, should appeal to two different explanations within Wikipedia. Would it be better to combine the explanations of this topic from different pages and agree on some sort of consistent "definitive" (heaven forbid) description? — Preceding unsigned comment added by Trumpetboy101 (talk • contribs) 02:19, 16 December 2011 (UTC)

I have to agree with this, this entire page, as well-developed as it is, seems to represent a WP:CFORK. --dab (𒁳) 09:05, 18 April 2015 (UTC)

Local realism
Local realism redirects to this page but is not mentioned at all. Richard Gill (talk) 16:47, 8 June 2012 (UTC)
 * Dear Prof. Gill, thanks for your precious contributions to wikipedia. I made this change to the local realism #redirect. I hope this helps. Cheers. Maurice Carbonaro (talk) 16:27, 18 June 2012 (UTC)

Figure 1 graph appears to be wrong
I'm not an expert in this field (which is why I'm reading the article) but the graph in figure 1 appears to be wrong or at least inconsistent with the explanations in the text. For figure 1, if the experiment considers two atoms with opposite spins then for detectors with the same angle (a - b = 0) the expectation value as defined will be -1 (0 + 0 - 1/2 - 1/2) whereas the graph shows it to be +1. Either the explanation is wrong or I think the abscissa of the graph should be from -180 to +180 not 0 to 360. 130.246.132.178 (talk) 11:24, 21 October 2015 (UTC)

Explanation in paragraph 3 is screwed up
I believe "In particular, a measurement on one particle in one place can alter the probability distribution for the outcomes of a measurement on the other particle at a different location" This may be really really wrong or really really misleading. please someone with actual credentials follow up and fix this. Just want to bring attention to this. — Preceding unsigned comment added by 99.10.122.186 (talk) 09:22, 6 June 2019 (UTC)

Merge with hidden-variable theory?
Do we need two articles now? This one is short. Johnjbarton (talk) 14:42, 27 October 2023 (UTC)


 * Or just delete this article. The content does not match the title. An article about local hidden variables should explain what variables are at issue, how/why they must/can be hidden, and why "local" must be added. None of that here. Johnjbarton (talk) 16:55, 27 October 2023 (UTC)
 * I disagree. People have been proposing local hidden variable models for a long time, whether to reproduce part of quantum mechanics or to try to get around Bell's theorem somehow. (The former is much more respectable than the latter.) I restored the content removed in this edit: Bell provides a local hidden-variable model for pure states of and von Neumann measurements on a qubit in section 3 of his 1964 paper. He then goes on to point out how the specific correlations studied in the original EPR paper can be given an explanation using local hidden variables. It's related to Gleason's theorem because if you don't average over the hidden variable, you get a counterexample to Gleason's theorem, i.e., an assignment of probabilities to measurement outcomes that can't be written as an application of the Born rule. XOR&#39;easter (talk) 17:34, 27 October 2023 (UTC)
 * Perhaps "people have been proposing local hidden variable models" but that is not apparent from this article.
 * Thanks for restoring the edit, I was wrong about Bell's article. But the Gleason theorem claim is not clear in the article and the reference adds nothing. I don't understand from the article what it has to do with local hidden variables. Johnjbarton (talk) 17:51, 27 October 2023 (UTC)
 * What do you think about merging? Isn't the context for "local hidden variables" is a subset of hidden-variables? Johnjbarton (talk) 17:54, 27 October 2023 (UTC)
 * I think it could be expanded into a worthwhile page in its own right, while hidden-variable theory can cover all the proposals that are nonlocal, contextual, etc. It could probably work either as two articles or as one, but I'm currently inclined to keep it as two. XOR&#39;easter (talk) 18:13, 27 October 2023 (UTC)
 * I think it is priority to have a local hidden variables article because it is the one that is well defined. Hidden variables needs more exploration but can be very difficult to expand objectively.--ReyHahn (talk) 09:32, 30 October 2023 (UTC)