Local hidden-variable theory

A model in which measurement outcomes are determined by underlying variables, while influences between distant measurement sites cannot travel faster than light.

Bell's theorem: A theorem showing that no theory satisfying specified locality conditions reproduces all quantum-mechanical predictions. It derives testable limits that local hidden-variable models must obey.
EPR paradox: A 1935 argument that quantum mechanics might be incomplete because it permits distant correlations between entangled systems. It motivated the proposal that additional variables could restore a complete account.
Quantum mechanics: A physical theory describing matter and radiation through states, observables, and probabilistic measurement outcomes. Its predictions violate Bell inequalities, unlike the correlations allowed by local hidden-variable models.
Aspect's experiment: A series of 1980s experiments by Alain Aspect and collaborators testing Bell inequalities with entangled photons. The experiments found correlations inconsistent with local hidden-variable bounds.
Bell inequality: A bound on correlations among separated measurements implied by local realism. Its violation exposes the conflict between local hidden-variable assumptions and observed correlations.
Albert Einstein: A theoretical physicist whose work established relativity and reshaped modern physics. Einstein objected to quantum theory's apparent nonlocality and helped frame the completeness debate.
Bohmian mechanics: A deterministic interpretation of quantum mechanics in which particles have definite positions guided by a wavefunction. It supplies hidden variables but accepts explicit nonlocality.
Alain Aspect: A French physicist known for experiments testing Bell inequalities with entangled photons. His experiments strengthened the empirical case against local hidden-variable theories.
Locality: The principle that physical influences cannot propagate faster than light between spacelike-separated events. It supplies the no-faster-than-light influence condition in these models.
Boris Podolsky: A physicist who coauthored the 1935 EPR paper with Albert Einstein and Nathan Rosen. His collaboration helped formulate the argument that quantum mechanics omitted elements of reality.

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