The EPR paradox, Bell's inequality, and the question of locality

TL;DR

This paper clarifies the assumptions behind Bell's inequality, emphasizing locality and counterfactual definiteness, and discusses how interpretations like many-worlds challenge these assumptions despite being deterministic and local.

Contribution

It provides a clear analysis of the minimal assumptions behind Bell's inequality and explores their implications using the many-worlds interpretation.

Findings

Bell's inequality relies on locality and counterfactual definiteness.

Many-worlds interpretation is deterministic, local, and realist but still violates Bell's inequality.

The debate centers on which assumptions are fundamental to quantum nonlocality.

Abstract

Most physicists agree that the Einstein-Podolsky-Rosen-Bell paradox exemplifies much of the strange behavior of quantum mechanics, but argument persists about what assumptions underlie the paradox. To clarify what the debate is about, we employ a simple and well-known thought experiment involving two correlated photons to help us focus on the logical assumptions needed to construct the EPR and Bell arguments. The view presented in this paper is that the minimal assumptions behind Bell's inequality are locality and counterfactual definiteness, but not scientific realism, determinism, or hidden variables, as is often suggested. We further examine the resulting constraints on physical theory with an illustration from the many-worlds interpretation of quantum mechanics -- an interpretation that we argue is deterministic, local, and realist, but that nonetheless violates the Bell inequality.