Spacetime Equilibrium at Negative Temperature and the Attraction of Gravity

Abstract

We derive the Einstein equation from the condition that every small causal diamond is a variation of a flat empty diamond with the same free conformal energy, as would be expected for a near-equilibrium state. The attractiveness of gravity hinges on the negativity of the absolute temperature of these diamonds, a property we infer from the generalized entropy.

7 pages, Essay written for the Gravity Research Foundation 2019 Awards for Essays on Gravitation