Three ways to find comfort with the Bell proof and the results of the Bell experiments

TL;DR

This paper explores different interpretations of Bell's theorem, analyzing recent experiments and proposing three distinct philosophical and mathematical approaches to understanding quantum non-locality.

Contribution

It presents three authors' perspectives on reconciling Bell's theorem with quantum mechanics, including causal graph analysis, Hilbert-space reconstruction, and geometric hidden-variable models.

Findings

Bell experiments confirm violation of CHSH inequality

Different interpretations suggest abandoning locality, realism, or both

Proposes new models and philosophical reconstructions of quantum non-locality

Abstract

Bell's theorem states that no description of a Bell experiment can be simultaneously local, realistic in the sense of counterfactual definiteness, and free of conspiracy between settings and hidden state. The recent generation of experiments has confirmed the predicted violation of the CHSH inequality, so one of the assumptions must be abandoned. Which one, and how one reconstructs a coherent worldview after doing so, is a question on which many authors disagree. This paper is written by three such authors. All three reject both counterfactual definiteness and conspiratorial violation of statistical independence of setting choices and state. After a joint exposition of the classical half of Bell's theorem in the language of Pearl-style causal graphs, a joint summary of the loophole-free experiments, and a joint survey of the recent literature, each author states where they have presently arrived. Gill accepts irreducible and non-local quantum randomness and finds the choice between locality and realism a false dichotomy. In his later works, Bell derives counterfactual definiteness from classical local causality, and that is what has to go. The metaphysical concepts "realism", "locality", "causality" need to be reconsidered. Helland reconstructs the Hilbert-space formalism from a theory of accessible variables, and from this theory he concludes that every observer must be limited in a specific sense. Jongejan proposes a geometric hidden-variable construction in which the degree of violation of the CHSH inequality depends on the number of dimensions of space, Tsirelson's bound corresponding to three dimensions. The authors conclude with a discussion.