Foundations of Physics

, Volume 33, Issue 10, pp 1469–1493

Nonlocal Hidden-Variable Theories and Quantum Mechanics: An Incompatibility Theorem

  • A. J. Leggett

DOI: 10.1023/A:1026096313729

Cite this article as:
Leggett, A.J. Foundations of Physics (2003) 33: 1469. doi:10.1023/A:1026096313729


It is argued that among possible nonlocal hidden-variable theories a particular class (called here “crypto-nonlocal” or CN) is relatively plausible on physical grounds. CN theories have the property that (for example) the two photons emitted in an atomic cascade process are indistinguishable in their individual statistical properties from photons emitted singly, and that in the latter case the effects of nonlocality are unobservable. It is demonstrated that all CN theories are constrained by inequalities which are violated by the quantum-mechanical predictions; these inequalities bear no simple relation to Bell's inequalities, and an explicit example is constructed of a CN theory which violates the latter. It is also shown that while existing experiments cannot rule out general CN theories, they do rule out (subject to a few caveats such as the usual ones concerning the well-known “loopholes”) the subclass in which the photon polarizations are linear.

quantum mechanics hidden-variable theories nonlocality 

Copyright information

© Plenum Publishing Corporation 2003

Authors and Affiliations

  • A. J. Leggett
    • 1
  1. 1.Department of PhysicsUniversity of IllinoisUrbana

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