Origin of time and probability in quantum cosmology

Abstract: We discuss how the classical notions of time and causal structure may emerge together with quantum-mechanical probabilities from a universal quantum state. For this, the process of decoherence between semiclassical branches is important. Our discussion is based on quantum geometrodynamics, a canonical approach to quantum gravity. In this framework, a particular boundary condition may illuminate the issue of the arrow of (classical) time in connection to the growth of entanglement entropy.