Quantum statistics and locality

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 observables in relativistic quantum physics. The analysis is based on a discussion of coincidence experiments and leads to a quantitative measure of deviation from locality. Hence, it may be applied in intrinsically nonlocal theories such as string theory and field theory on noncommutative spacetime. (c) 2005 Elsevier B.V. All rights reserved.