A Reasonable Thing That Just Might Work

Abstract

In 1964, John Bell proved that quantum mechanics is \unreasonable (to use Einstein’s term): there are nonlocal bipartite quantum correlations. But they are not the most nonlocal bipartite correlations consistent with relativistic causality (\no superluminal signalling): also maximally nonlocal \superquantum (or \PR-box) correlations are consistent with relativistic causality. I show that|unlike quantum correlations|these correlations do not have a classical limit consistent with relativistic causality. The generalization of this result to all stronger-than-quantum nonlocal correlations is a derivation of Tsirelson’s bound|a theorem of quantum mechanics|from the three axioms of relativistic causality, nonlocality, and the existence of a classical limit. But is it reasonable to derive (a part of) quantum mechanics from the unreasonable axiom of nonlocality?! I consider replacing the nonlocality axiom with an equivalent axiom that even Bell and Einstein might have considered reasonable: an axiom of local retrocausality.