Faculty Research and Publications

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Browsing Faculty Research and Publications by Subject "Causality"

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    Peaceful coexistence or armed truce?: quantum nonlocality and the spacetime view of the world
    (University of Toronto, 1991) Peacock, Kent A.
    This thesis is concerned with a critical examination of the notion of “peaceful coexistence” between quantum mechanics and the theory of relativity. This phrase, coined by Abner Shimony, is meant to suggest that quantum mechanics does not predict any observable conflict with the relativistic picture of causation, even though quantum mechanics, a fundamentally nonlocal theory, does clearly violate a condition called “outcome independence” which would seem to be implicit in any local realistic theory. The main justification that Shimony and others have cited for this view is the NoSignalling Theorem, the claim that quantum nonlocality cannot be exploited to violate the relativistic picture of causation by sending controllable signals outside the light cone. (This would be a violation of what Shimony and Jarrett have called “parameter independence”.) I examine the various proofs that have been given of this theorem, and show that they are essentially circular in the sense that they either incorporate such strongassumptionsaboutthelocalizabilityorcommutativityofobservablesastorender them incapable of dealing with the very cases they should be best equipped to treat, or else simply presume some condition equivalent to relativistic causality. Quantum mechanics has therefore not been shown to provide a categorical prohibition against violations of relativity; the question of peaceful coexistence remains open. I argue that this circumstance should not be viewed as surprising since relativity, being a classical theory, should be expected to be only an approximation. In conclusion I sketch some requisites for a genuinely quantal theory of spacetime.