Editing Hidden-variable theory (section)

== Bohm's hidden-variable theory ==
{{Main|de Broglie–Bohm theory}}

In 1952, [[David Bohm]] proposed a hidden variable theory. Bohm unknowingly rediscovered (and extended) the idea that Louis de Broglie's [[pilot wave theory]] had proposed in 1927 (and abandoned) – hence this theory is commonly called "de Broglie-Bohm theory". Assuming the validity of Bell's theorem, any deterministic hidden-variable theory that is [[consistency|consistent]] with [[quantum mechanics]] would have to be [[Principle of locality|non-local]], maintaining the existence of instantaneous or faster-than-light relations (correlations) between physically separated entities.

Bohm posited ''both'' the quantum particle, e.g. an electron, and a hidden 'guiding wave' that governs its motion. Thus, in this theory electrons are quite clearly particles. When a [[double-slit experiment]] is performed, the electron goes through either one of the slits. Also, the slit passed through is not random but is governed by the (hidden) pilot wave, resulting in the wave pattern that is observed.

In Bohm's interpretation, the (non-local) [[quantum potential]] constitutes an implicate (hidden) order which organizes a particle, and which may itself be the result of yet a further implicate order: a ''superimplicate order'' which organizes a field.<ref>David Pratt: [http://www.theosophy-nw.org/theosnw/science/prat-boh.htm "David Bohm and the Implicate Order"]. Appeared in ''Sunrise magazine'', February/March 1993, Theosophical University Press</ref> Nowadays Bohm's theory is considered to be one of many [[interpretations of quantum mechanics]]. Some consider it the [[simplicity|simplest]] theory to explain quantum phenomena.<ref>Michael K.-H. Kiessling: "Misleading Signposts Along the de Broglie–Bohm Road to Quantum Mechanics", ''Foundations of Physics'', volume 40, number 4, 2010, pp. 418–429 ([https://doi.org/10.1007%2Fs10701-009-9327-4 abstract])</ref> Nevertheless, it ''is'' a hidden-variable theory, and necessarily so.<ref>"While the testable predictions of Bohmian mechanics are isomorphic to standard Copenhagen quantum mechanics, its underlying hidden variables have to be, in principle, unobservable. If one could observe them, one would be able to take advantage of that and signal faster than light, which – according to the special theory of relativity – leads to physical temporal paradoxes." J. Kofler and A. Zeilinger, "Quantum Information and Randomness", ''European Review'' (2010), Vol. 18, No. 4, 469–480.</ref> The major reference for Bohm's theory today is his book with [[Basil Hiley]], published posthumously.<ref>D. Bohm and B. J. Hiley, ''[https://books.google.com/books?isbn=041512185X The Undivided Universe]'', Routledge, 1993, {{ISBN|0-415-06588-7}}.</ref>

A possible weakness of Bohm's theory is that some (including Einstein, Pauli, and Heisenberg) feel that it looks contrived.<ref>{{Cite journal|author=Wayne C. Myrvold |year=2003 |title=On some early objections to Bohm's theory |journal=International Studies in the Philosophy of Science |volume=17 |number=1 |pages=8–24 |url=http://publish.uwo.ca/~wmyrvold/Bohm.pdf/ |doi=10.1080/02698590305233 |s2cid=10965929 |url-status=dead |archive-url=https://web.archive.org/web/20140702002502/http://publish.uwo.ca/~wmyrvold/Bohm.pdf |archive-date=2014-07-02 }}</ref> (Indeed, Bohm thought this of his original formulation of the theory.<ref name="Bohm1957">{{cite book|author=David Bohm|title=Causality and Chance in Modern Physics|year=1957|publisher=Routledge & Kegan Paul and D. Van Nostrand|isbn=0-8122-1002-6|page=110}}</ref>)  Bohm said he considered his theory to be unacceptable as a physical theory due to the guiding wave's existence in an abstract multi-dimensional configuration space, rather than three-dimensional space.<ref name="Bohm1957"/>