John Stewart Bell turned the debate about completing quantum mechanics into a constraint on observable correlations. In his 1964 analysis of a spin singlet state, each distant spin result depends on the local measurement direction and a shared hidden variable, but not on the other measurement direction. These assumptions constrain the joint correlations in a way incompatible with the quantum mechanics predictions. The result explains what an experiment can discriminate: it tests a class of local hidden-variable theories, rather than simply asking whether measurements are unpredictable.[ref]
On the Einstein Podolsky Rosen paradox by John Stewart Bell. Sections II–V, local response functions and the correlation constraint
Author of the 1964 Bell theorem argument.
Portrait of John Stewart Bell
. CERN, portrait of John Bell, June 1982; CERN archive record 1823937. CC BY 4.0, via Wikimedia Commons. Source.
John Stewart Bell was a notable physicist, best known for his work in quantum mechanics and for formulating Bell's Theorem. Born on June 28, 1928, in Belfast, Northern Ireland, and passing away on October 25, 1990, Bell made significant contributions to understanding the foundations of quantum physics, particularly regarding the concept of entanglement.
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