Gravitational sub systems\, such as black holes\, are important objects of study in both cla ssical and quantum gravity. Insight into the gravitational degrees of free dom of a subsystem can be gained by analyzing the symmetries and charges o f gravity in the associated spacetime subregion. In this talk\, I will use the covariant phase space formalism to make progress on this problem in g eneral 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 comple tely general setting in which the subsystem can emit or absorb radiation\, I will then derive an infinite set of charges and conservation laws on th e null surface\, and explain their significance for physics deep in the gr avitational field. Finally\, I will describe progress towards an understan ding of black hole entropy through this formalism.

\n DTSTART:20211115T180000Z LOCATION:Online\, Room via Zoom SUMMARY:Symmetries and Charges of Gravitational Subsystems END:VEVENT END:VCALENDAR