# Quantum statistics and locality

March 21, 2004

It is shown that two observers have mutually commuting observables if they
are able to prepare in each subsector of their common state space some state
exhibiting no mutual correlations. This result establishes a heretofore missing
link between statistical and locality (commensurability) properties of the
observables of spacelike separated observers in relativistic quantum physics,
envisaged four decades ago by Haag and Kastler. It is based on a discussion of
coincidence experiments and suggests a physically meaningful quantitative
measure of possible violations of Einstein causality.

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