9 v 1 9 A ug 1 99 5 NONLOCALITY AS AN AXIOM FOR QUANTUM THEORY

Quantum mechanics and relativistic causality together imply nonlocality: nonlo-cal correlations (that violate the CHSH inequality) and nonlocal equations of motion (the Aharonov-Bohm effect). Can we invert the logical order? We consider a conjecture that nonlocality and relativistic causality together imply quantum mechanics. We show that correlations preserving relativistic causality can violate the CHSH inequality more strongly than quantum correlations. Also, we describe nonlocal equations of motion, preserving rel-ativistic causality, that do not arise in quantum mechanics. In these nonlocal equations of motion, an experimenter " jams " nonlocal correlations between quantum systems. 1. INTRODUCTION Two aspects of quantum nonlocality are nonlocal correlations and nonlocal equations of motion. Nonlocal correlations arise in settings such as the one discussed by Einstein, Podolsky and Rosen 1. As Bell 2 showed (and Aspect has reviewed in his lecture here) no theory of local variables can reproduce these correlations. The Aharonov-Bohm effect 3 is also nonlocal in that an electromagnetic field influences an electron in a region where the field vanishes. The field induces a relative phase between two sets of paths available to an electron, displacing the interference pattern between the two sets of paths. Thus, the Aharonov-Bohm effect implies nonlocal equations of motion. 4 Both aspects of quantum non-locality arise within nonrelativistic quantum theory. However, the very definition of a local variable is relativistic: a local variable can be influenced only by events in its backward light cone, and can influence events only in its forward light cone. In this sense, quantum mechanics and relativity together imply nonlocality. They coexist because quantum correlations preserve relativistic causality (i.e. they do not allow us to transmit signals faster than