nt - p h / 07 01 22 5 v 1 3 0 Ja n 20 07 Probability , Arrow of Time and Decoherence ∗

This paper relates both to the metaphysics of probability and to the physics of time asymmetry. Using the formalism of decoherent histories , it investigates whether intuitions about intrinsic time directedness that are often associated with probability can be justified in the context of no-collapse approaches to quantum mechanics. The standard (two-vector) approach to time symmetry in the decoherent histories literature is criticised, and an alternative approach is proposed, based on two decoherence conditions ('forwards' and 'backwards') within the one-vector formalism. In turn, considerations of forwards and backwards decoherence and of decoherence and recoherence suggest that a time-directed interpretation of probabilities, if adopted, should be both contingent and perspectival.