Gravity as an emergent phenomenon

Abstract

There are strong reasons to believe that the gravitational interaction — described in terms of a metric on a smooth space–time — is an emergent, long wavelength phenomenon, like elasticity. I describe a concrete framework for realizing this paradigm against the backdrop of several recent results. In this perspective, quantum fluctuations of the microscopic degrees of freedom of the space–time lead to residual random displacements of any null surface. The latter can be described in terms of an effective theory using an action associated with the normal displacements of the null surfaces. Extremizing this action leads to an equation determining the background geometry. The resulting theory is Einstein gravity at the lowest order with the Lanczos–Lovelock type quantum corrections. The metric is not a dynamical variable in this approach and gravity arises as a coarse-grained statistical feature of an underlying microscopic theory.