Gravity Seminars

Gravitational subsystems, such as black holes, are important objects of study in both classical and quantum gravity. Insight into the gravitational degrees of freedom of a subsystem can be gained by analyzing the symmetries and charges of gravity in the associated spacetime subregion. In this talk, I will use the covariant phase space formalism to make progress on this problem in general relativity, with a particular focus on subregions bounded by null hypersurfaces, such as event horizons or causal diamonds. Surprisingly, on null surfaces the gravitational field will turn out to have infinitely many symmetries, akin to the BMS symmetries at null infinity. In a completely general setting in which the subsystem can emit or absorb radiation, I will then derive an infinite set of charges and conservation laws on the null surface, and explain their significance for physics deep in the gravitational field. Finally, I will describe progress towards an understanding of black hole entropy through this formalism.