Viscous Spacetime Fluid and Higher Curvature Gravity

TL;DR

This paper reinterprets Einstein's equations as describing a viscous spacetime fluid, introduces a new equation of state for higher curvature gravity, and discusses the thermodynamic implications of curvature and tidal forces.

Contribution

It presents a novel thermodynamic interpretation of Einstein's equations involving viscosity and extends this to higher curvature gravity without needing nonequilibrium thermodynamics.

Findings

Scalar curvature and cosmological constant relate to spacetime viscosity.

A new equation of state for higher curvature gravity is derived.

Interpretation of tidal forces within the thermodynamic framework.

Abstract

The Einstein field equation as an equation of state of a thermodynamical system of spacetime is reconsidered in the present Letter. We argue that a consistent interpretation leads us to identify scalar curvature and cosmological constant terms representing the bulk viscosity of the spacetime fluid. Since Einstein equation itself corresponds to a near-equilibrium state in this interpretation invoking $f(R)$ gravity for nonequilibrium thermodynamics is not required. A logically consistent generalization to include the effect of so called 'tidal forces' due to the Riemann curvature is presented. A new equation of state for higher curvature gravity is derived and its physical interpretation is discussed.