Bell on Bell's theorem: The changing face of nonlocality

TL;DR

This paper traces the evolving interpretation of Bell's theorem from 1964 to 1990, highlighting its detachment from quantum mechanics and its broader implications for nonlocality and Lorentz-covariance in quantum theory.

Contribution

It clarifies the historical and conceptual development of Bell's theorem and emphasizes the importance of the Everett interpretation for a Lorentz-covariant quantum theory.

Findings

Bell's nonlocality notion shifted from quantum mechanics to broader probabilistic theories.

Bell's theorem became detached from quantum mechanics after 1976.

A Lorentz-covariant quantum theory without action-at-a-distance is possible in the Everett interpretation.

Abstract

Between 1964 and 1990, the notion of nonlocality in Bell's papers underwent a profound change as his nonlocality theorem gradually became detached from quantum mechanics, and referred to wider probabilistic theories involving correlations between separated beables. The proposition that standard quantum mechanics is itself nonlocal (more precisely, that it violates `local causality') became divorced from the Bell theorem per se from 1976 on, although this important point is widely overlooked in the literature. In 1990, the year of his death, Bell would express serious misgivings about the mathematical form of the local causality condition, and leave ill-defined the issue of the consistency between special relativity and violation of the Bell-type inequality. In our view, the significance of the Bell theorem, both in its deterministic and stochastic forms, can only be fully understood by taking into account the fact that a fully Lorentz-covariant version of quantum theory, free of action-at-a-distance, can be articulated in the Everett interpretation.