Gravitational energy, local holography and non-equilibrium thermodynamics
We study the properties of gravitational systems in finite regions bounded by gravitational screens. We present a detailed construction of the total energy of such regions and of the energy and momentum balance equations due to the flow of matter and gravitational radiation through the screen. We establish that the gravitational screen possesses analogs of surface tension, internal energy, and viscous stress tensor, while the conservations are analogs of nonequilibrium balance equations for a viscous system. This gives a precise correspondence between gravity in finite regions and nonequilibrium thermodynamics.