Time: ***UPDATE*** CANCELLED ***UPDATE*** Venue: New Law School Theatre 026 Title: Sharp polynomial bounds on mixing rates for dispersing billiards and Lorentz gases Abstract: In this talk, we consider mixing properties of Lorentz gas models (introduced by H. Lorentz in 1905) and their discrete time counterparts (dispersing billiards). Various general results on polynomial mixing rates (upper and lower bounds) will be described. For instance, the infinite horizon Lorentz gas was conjectured by physicists to mix at the rate 1/t; this was proved in recent joint work with Peter Balint & Oliver Butterley. Sharp lower bounds and asymptotics for mixing rates were obtained in recent joint work with Henk Bruin & Dalia Terhesiu. Biography: Ian Melbourne is a professor of mathematics at the University of Warwick. His research interests lie in ergodic theory and dynamical systems, with links to probability theory and stochastic analysis (in particular, rough paths). Currently he is Managing Editor of the journal Ergodic Theory & Dynamical Systems as well as an editor for Transactions of the AMS.