title: Nonequilibrium thermodynamics of spacetime.
abstract: It has previously been shown that the Einstein equation can be derived from the requirement that the Clausius relation dS=deltaQ/T hold for all local acceleration horizons through each spacetime point, where is one-quarter the horizon area change in Planck units and deltaQ and T are the energy flux across the horizon and the Unruh temperature seen by an accelerating observer just inside the horizon. Here we show that a curvature correction to the entropy that is polynomial in the Ricci scalar requires a nonequilibrium treatment. The corresponding field equation is derived from the entropy balance relation dS=deltaQ/T+diS, where diS is a bulk viscosity entropy production term that we determine by imposing energy-momentum conservation. Entropy production can also be included in pure Einstein theory by allowing for shear viscosity of the horizon.
authors.affiliation: Department of Physics, University of Maryland, College Park, Maryland 20742-4111, USA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Eling
authors.forename: Raf
authors.initials: R
authors.lastname: Guedens
authors.forename: Ted
authors.initials: T
authors.lastname: Jacobson