The apparent Universe

Abstract

We exploit the parallel between dynamical black holes and cosmological spacetimes to describe the evolution of Friedmann–Lemaître–Robertson–Walker universes from the point of view of an observer in terms of the dynamics of the apparent horizon. Using the Hayward–Kodama formalism of dynamical black holes, we clarify the role of the Clausius relation to derive the Friedmann equations for a Universe, in the spirit of Jacobson’s work on the thermodynamics of spacetime. We also show how dynamics at the horizon naturally leads to the quantum-mechanical process of Hawking radiation. We comment on the connection of this work with recent ideas to consider our observable Universe as a Bose–Einstein condensate and on the corresponding role of vacuum energy.