Talk:Hidden-variable theory

message: Hidden variables theory was developed after quantum theory made its debut in the late 1920's. Its most modern supporter is physicist David Bohm. It proposes that the uncertainty that characterizes quantum theory and the nature of the so-called wave function for matter is just a result of our not having a complete set of variables in order to fully describe the quantum state. If we did have the full set of variables, or so the theory goes, the new ones would make the quantum state fully deterministic rather that fundamentally indeterminate as it now seems to be. The new variables seem to be extremely well 'hidden' because modern quantum theory now accounts for all of the quantities that experimentally we seem to have a good handle on such as position, time, spin, charge, energy and momentum. 
The idea is similar to the role that atoms played in understanding thermodynamics. In the late 19th century, Boltzman proposed that heat could be understood as simply the kinetic energy associated with atoms, however, many senior physicists of the day disbelieved the idea that atoms existed. Einstein later described Brownian motion in terms of atoms bouncing off of dust, and 10 years later the idea of atoms became firmly established. 
In 1932, the great mathematician John von Neumann wrote a highly influential book on Quantum Mechanics in which this theory was treated as a purely mathematical theory as though it were a branch of mathematics. He presented in this great work, a proof that no hidden-variable theory could ever reproduce the results of quantum mechanics. This is where the discussion remained until David Bohm, then in Brazil in the 1950's, refuted von Neumann's proof and wrote two papers which presented a specific model in which hidden-variables could exist, and in which quantum mechanics as we know it was preserved. However, each individual system is in a precisely definable state determined by definite laws. Quantum probabilities are a practical necessity, not a reflection that there is a lack of complete determination of the properties of matter. In other words, quantum mechanics was just another form of classical mechanics free of probabilities. indeterminism and all the other enigmas of the quantum world. 
What Bohm had done is to find a statement by von Neumann that was true most of the time, but that under certain circumstances would not hold. This mathematical statement was the crux of his proof that hidden-variable theory was impossible. Bohm found an exception to this statement, and developed his model of a hidden-variable theory to occupy this logical niche in von Neumann's otherwise correct proof. 
In the early 1960's the physicist John Stewart Bell and his physicist wife went to work at Stanford University. John Bell had always been intrigued and even a bit obsessed by the foundations of quantum theory, von Neumann's work, and the so-called Einstein-Podolsky-Rosen experiment, and he took this new opportunity to investigate this hazy area in physics. What he ultimately came up with was a surprisingly simple experimental test which defined in rather absolute terms just what kind of theory quantum mechanics is, and what the possibilities would have to be for ANY challenger to it. 
Bell's Theorem, expressed in a simple equation called an 'inequality', could be put to a direct test. It is a reflection of the fact that no signal containing any information can travel faster than the speed of light. This means that if hidden-variables theory exists to make quantum mechanics a deterministic theory, the information contained in these 'variables' cannot be transmitted faster than light. This is what physicists call a 'local' theory. John Bell discovered that, in order for Bohm's hidden-variable theory to work, it would have to be very badly 'non-local' meaning that it would have to allow for information to travel faster then the speed of light. This means that, if we accept hidden-variable theory to clean up quantum mechanics because we have decided that we no longer like the idea of assigning probabilities to events at the atomic scale, we would have to give up special relativity. This is an unsatisfactory bargain.
(Caroline Thompson 22:48, 30 Jun 2004 (UTC)
replies: text: The edit history shows that the Talk commentary was written by the original contributor of the article. As it stands, the original commentary shows that Bohm's hidden variable theory is ill-founded. (See, for example, the last two sentences, ending in unsatisfactory bargain) But the last word has not been written on this topic. Ancheta Wis 06:34, 19 Jan 2005 (UTC)
thread_title: Introduction

message: "In 1927, Einstein produced a hidden-variables interpretation of Erwin Schrödinger's wave mechanics.  But he abandoned the effort prior to publication when he found that even his own hidden-variables interpretation involved a kind of failure of spacial separability that Schrödinger later dubbed "entanglement".
From elsewhere in the article:  this effect is due to identical particles being indistinguishable.  (The wave equations are local.)
"Albert Einstein as a Philosopher of Science", by Don A. Howard, Physics Today, December 2005
David R. Ingham 23:57, 30 January 2006 (UTC)
thread_title:  Albert Einstein's effort 

message: This article looks like a bunch of informative sections without much cohesion. Please expand the intro and make the article more coherent and less ambiguous. (I'd do it myself but I don't know much about the topic.) Thanks --Zoz 23:26, 3 March 2006 (UTC)
replies: text: I agree.  As it stands, it's quite informative and well-written, but the cohesion could be improved.  And it needs better references.  I'll put it on my watchlist and come back to it this weekend.  I'd like to find some peer-reviewed resources on this topic (for or against doesn't matter to me - I just want to learn more and have the current state of knowledge on this topic properly represented in the article).  Cheers, Astrobayes 22:22, 27 June 2006 (UTC)
thread_title:  Cleanup 

message: Any objections?  --Michael C. Price talk 01:38, 24 August 2006 (UTC)
thread_title: Merge with [[Bohmian mechanics]]

message: The sentence: "Later, Bell's theorem would prove (in the opinion of most physicists and contrary to Einstein's assertion) that local hidden variables are impossible." is technically misleading.  Most readers will not click the link and will assume based on the context of the paragraph that local hidden variables ~= hidden variables.  It would be more helpful to say something like ".. Belle's theorem would prove that any hidden variable theory that is consistent with quantum mechanics is lon-local".  I'm not sure what the best way to phase this is to capture the fact that HVT isn't strictly impossible but rather inconsistent with relativity while still being totally accurate and including good wikilinks.
Any ideas?
Olleicua (talk) 05:15, 29 November 2009 (UTC)
thread_title:  Local Hidden Variables 

message: Regarding "This rules out local hidden variable theories, but does not rule out non-local ones (which would refute quantum entanglement)."  I don't get the parenthetical.  I would be inclined to say the non-local ones would support quantum entanglement.  Maybe someone lost a "not"?  —Preceding unsigned comment added by 67.183.113.131 (talk) 21:32, 8 September 2010 (UTC)
thread_title:  SECTION: EPR Paradox & Bell's Theorem 

message: 1. Unless I missed it, the article does not say who used the term first. Quoting EPR with a parenthesis is no good. von Neumann used "hidden" parameters. 
2. In the lead,  think the reference to God's dice is irrelevant. Myrvin (talk) 06:46, 18 April 2011 (UTC)
thread_title:  Some comments 

message: If De Broglie-Bohm "is in fact just a reformulation of conventional quantum mechanics obtained by rearranging the equations and renaming the variables" (from the intro) and "nevertheless it [De Broglie-Bohm] is a hidden variable theory" (also from intro) then the statement (from Motivation section) "in a system of trapped ions, quantum mechanics conflicts with hidden variable theories regardless of the quantum state of the system" CANNOT also be true.  Otherwise, in a system of trapped ions, a reformulation of conventional quantum mechanics that is also a hidden variable theory would conflict with hidden variable theories regardless of the quantum state of the system.  At least one of the three statements above, as written, must therefore be false.  I think this article needs the attention of an expert.
Ross Fraser (talk) 07:31, 16 July 2011 (UTC)
thread_title:  Contradiction 

message: Do we want to extend coverage to other fringe theories with hidden variables? John Pons (talk) 07:30, 7 November 2011 (UTC)
thread_title: Other approaches

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thread_title:  External links modified 

message: Is this new section relevant? I doubt. Just technical notes from introduction to probability theory, with no special relevance here. Boris Tsirelson (talk) 04:53, 14 August 2017 (UTC)
thread_title:  Classes of hidden variables 

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thread_title:  External links modified 

message: The initial paragraph contains a quote from Einstein of "I am convinced God does not play dice", attributed to a private letter to Max Born, dated 4 December 1926. In my collected letters, however, the quote is "I, at any rate, am convinced that He [God] is not playing at dice". This comes from: Irene Born, transl., The Born Einstein Letters: Correspondence between Albert Einstein and Max and Hedwig Born from 1916 to 1955 with commentaries by Max Born (Macmillan Press, 1971), p.91.TonyP (talk) 17:53, 17 October 2020 (UTC)
replies: text: The quote is essentially the same, minus the conjunctive expression "at any rate".  Since the quote in the lede is given outside of the context of its full paragraph, it seems to be simply a matter of improved style to leave off the conjunction, and to convert the pronoun "He" to its referent, as is commonly done.  By the way, further down in the article, in the section "God does not play dice", the full paragraph of the quote is given, as translated in The Collected Papers of Albert Einstein, Volume 15: The Berlin Years: Writings & Correspondence, June 1925-May 1927 (English Translation Supplement), p. 403  J-Wiki (talk) 04:32, 18 October 2020 (UTC)
replies: text:  Then I'm afraid it's paraphrasing rather than being a direct quote, either of Einstein or of Hedwig's translation. Things like this get copied all around the Internet, and into respectable publications, because no one bothers to check the original source. I have a similar misquote of Einstein where the words are fundamentally different TonyP (talk) 09:34, 18 October 2020 (UTC)
replies: text:  I've now made it clear in the first reference for the sentence that this is a common paraphrasing, and added a second reference with direct link to full source letter.J-Wiki (talk) 03:10, 19 October 2020 (UTC)
thread_title: Misquote of Einstein

message: Hidden-variable theories are not universally "proposals to provide deterministic explanations of quantum mechanical phenomena", the addition of a complete specification of the state and properties of a system does not preclude indeterminacy. Indeed there are stochastic hidden variable theories, as a quick peruse through the literature would reveal and as is even mentioned in this article with Stochastic quantum mechanics as an example. Determinism is of course relevant historically and as a motivation for developing hidden-variable theories so it should be mentioned, but the lead is incorrect. Volteer1 (talk) 10:58, 19 January 2021 (UTC)
replies: text: I agree. It is very misleading. Roger (talk) 19:31, 11 October 2022 (UTC)
thread_title:  "Deterministic" in the lead