Bell's theorem

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Bell's theorem

[′belz ‚thir·əm]
(quantum mechanics)
A theorem which states that any hidden variable that satisifies the condition of locality cannot possibly reproduce all the statistical predictions of quantum mechanics, and which places upper limits, for the predictions of any such theory, on the strength of correlations between measurements of spatially separated objects, whereas quantum mechanics predicts very strong correlations between such measurements.
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He works through quantum interference, including observations of such phenomena as semi-transparent mirrors, interferometry, waves, dimensions and boundaries, and quantum key distribution, and then through quantum correlations, including distinguishability and its consequences, the Bell theorem, the theories of Schrodinger, Einstein, Podolski, and Rosen, the Aspect experiments, experimental metaphysics, and orthodox and not-so-orthodox explanations.
In addition, Howard has also drawn interesting conclusions on the relations between Einstein's own argument and the debates on hidden variable theories and the Bell theorem (Howard [1985, 1989]).' In Howard's view the distinction between separability and locality, as is formulated in Einstein's own incompleteness argument, is valuable also from a theoretical point of view, in that it implies a broader interpretation of the Bell theorem.
The distinction between separability and locality, although adequate, by no means implies that the Bell theorem forces us to renounce either separability or locality.
The formulation of Einstein's own incompleteness argument allowed Howard not only to distinguish sharply the principles of separability and locality in the argument but also to analyse the consequences of the Bell theorem for hidden variable theories with reference to this distinction.
Shimony argued that a peaceful coexistence can be established between QM and relativity theory, since the quantum-mechanical violation of outcome independence does not allow signalling.(4) Although the coexistence seems to be peaceful, the Bell theorem points out, among other things, the impossibility of interpreting the entanglement of quantum states as purely epistemic.