Black Holes and Decoherence
Aidan Chatwin-Davies (Caltech)
In a fully quantum gravitational treatment, the wave function that characterizes the process of black hole formation and evaporation must describe an ensemble of possible black hole geometries and matter configurations. I will discuss a proposal to understand the emergence of such an ensemble as a decoherence process, in which decohered branches of the wavefunction correspond to semiclassical geometries together with effective field theoretic states. Quantum mechanics dictates that evolution at the level of the global wave function should be unitary. On the other hand, questions about the position and smoothness of horizons only make sense at the level of individual branches. I will discuss the implications of this proposal for the black hole information puzzle. In particular, we will see that the existence of multiple decoherent branching structures constitutes a sort of Hilbert space complementarity.