Thermodynamics of dynamical black holes

The thermal nature of black hole horizons has engendered a revolution in physics since its discovery in the 1970s. The first result of this thesis is to extend the analysis of black hole thermodynamics from horizons to arbitrary ordinary surfaces for static spacetimes. It is proved that ordinary surfaces do not obey the same first law as black hole horizons, even for static spacetimes. This result undermines the thermodynamic assumptions of the emergent gravity program. The second result of this thesis is to rigorously generalize black hole thermodynamics to dynamical spacetimes. The final part is about a new phenomenon we discovered that only exist for dynamical black holes.