A reasonable thing that just might work

TL;DR

This paper derives Tsirelson's bound, a fundamental limit in quantum mechanics, from relativistic causality, nonlocality, and classical limit assumptions, and explores replacing nonlocality with local retrocausality as a more reasonable axiom.

Contribution

It provides a derivation of Tsirelson's bound from fundamental principles and proposes local retrocausality as a potentially more reasonable axiom than nonlocality.

Findings

Tsirelson's bound follows from relativistic causality, nonlocality, and classical limit.

Superquantum correlations violate the classical limit under relativistic causality.

Replacing nonlocality with local retrocausality offers a new perspective on quantum foundations.

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.