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Bell's theorem is a ‘no-go theorem’ that draws an important distinction between quantum mechanics (QM) and the world as described by classical mechanics. This theorem is named after John Stewart Bell. In its simplest form, Bell's theorem states:〔 Bell himself wrote: "If (hidden variable theory ) is local it will not agree with quantum mechanics, and if it agrees with quantum mechanics it will not be local. This is what the theorem says." John Bell, ''Speakable and Unspeakable in Quantum Mechanics'', Cambridge University Press, 1987, p. 65.〕 Cornell solid-state physicist David Mermin has described the appraisals of the importance of Bell's theorem in the physics community as ranging from "indifference" to "wild extravagance". Lawrence Berkeley particle physicist Henry Stapp declared: "Bell's theorem is the most profound discovery of science."〔 (Quote on p. 271)〕 Bell's theorem rules out local hidden variables as a viable explanation of quantum mechanics (though it still leaves the door open for non-local hidden variables). Bell concluded: Bell summarized one of the least popular ways to address the theorem, superdeterminism, in a 1985 BBC Radio interview: == Historical background == In the early 1930s, the philosophical implications of the current interpretations of quantum theory troubled many prominent physicists of the day, including Albert Einstein. In a well-known 1935 paper, Boris Podolsky and co-authors Einstein and Nathan Rosen (collectively "EPR") sought to demonstrate by the EPR paradox that QM was incomplete. This provided hope that a more-complete (and less-troubling) theory might one day be discovered. But that conclusion rested on the seemingly reasonable assumptions of ''locality'' and ''realism'' (together called "local realism" or "local hidden variables", often interchangeably). In the vernacular of Einstein: locality meant no instantaneous ("spooky") action at a distance; realism meant the moon is there even when not being observed. These assumptions were hotly debated in the physics community, notably between Nobel laureates Einstein and Niels Bohr. In his groundbreaking 1964 paper, "On the Einstein Podolsky Rosen paradox",〔〔Reprinted in 〕 physicist John Stewart Bell presented an analogy (based on spin measurements on pairs of entangled electrons) to EPR's hypothetical paradox. Using their reasoning, he said, a choice of measurement setting here should not affect the outcome of a measurement there (and vice versa). After providing a mathematical formulation of locality and realism based on this, he showed specific cases where this would be inconsistent with the predictions of QM theory. In experimental tests following Bell's example, now using quantum entanglement of photons instead of electrons, John Clauser and Stuart Freedman (1972) and Alain Aspect ''et al''. (1981) demonstrated that the predictions of QM are correct in this regard, although relying on additional unverifiable assumptions that open loopholes for local realism. In Oct 2015 Hensen and co-workers reported that they performed a loophole-free Bell test which might force one to reject at least one of the principles of locality, realism, or freedom (the last leads to alternative superdeterministic theories). Two of these logical possibilities, non-locality and non-realism, correspond to well-developed interpretations of quantum mechanics, and have many supporters; this is not the case for the third logical possibility, non-freedom. Conclusive experimental evidence of the violation of Bell's inequality would drastically reduce the class of acceptable deterministic theories but would not falsify absolute determinism, which was described by Bell himself as “... not just inanimate nature running on behind-the-scenes clockwork, but with our behaviour, including our belief that we are free to choose to do one experiment rather than another, absolutely predetermined.” However, Bell himself considered absolute determinism an implausible solution. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Bell's theorem」の詳細全文を読む スポンサード リンク
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