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Bell's theorem is a term encompassing a number of closely related results in physics, all of which determine that quantum mechanics is incompatible with local hidden-variable theories, given some basic assumptions about the nature of measurement.
In quantum mechanics, superdeterminism is a loophole in Bell's theorem.By postulating that all systems being measured are correlated with the choices of which measurements to make on them, the assumptions of the theorem are no longer fulfilled.
John Stewart Bell FRS [2] (28 July 1928 – 1 October 1990) [3] was a physicist from Northern Ireland and the originator of Bell's theorem, an important theorem in quantum physics regarding hidden-variable theories.
One of the assumptions of Bell's theorem is the one of locality, namely that the choice of setting at a measurement site does not influence the result of the other. The motivation for this assumption is the theory of relativity, that prohibits communication faster than light. For this motivation to apply to an experiment, it needs to have space ...
Subsequently, Bell test experiments have demonstrated broad violation of these constraints, ruling out such theories. [3] Bell's theorem, however, does not rule out the possibility of nonlocal theories or superdeterminism; these therefore cannot be falsified by Bell tests.
This second result became known as the Bell theorem. To understand the first result, consider the following toy hidden-variable theory introduced later by J.J. Sakurai: [ 25 ] : 239–240 in it, quantum spin-singlet states emitted by the source are actually approximate descriptions for "true" physical states possessing definite values for the z ...
Calculating expectations based on Bell's work implies that for quantum physics the assumption of "local realism" must be abandoned. [14] Bell's theorem proves that every type of quantum theory must necessarily violate locality or reject the possibility of extending the mathematical description with outcomes of measurements which were not ...
The first rudimentary experiment designed to test Bell's theorem was performed in 1972 by Clauser and Stuart Freedman at University of California, Berkeley. [9] In 1973, at Harvard University, Pipkin and Holt's experiments suggested the opposite conclusion, negating that quantum mechanics violates the Bell inequalities. [8]