Spontaneous Inflation and the Origin of the Arrow of Time

TL;DR

This paper proposes that spontaneous eternal inflation explains the thermodynamic arrow of time by allowing the universe to increase entropy unboundedly, resulting in a time-symmetric universe on large scales.

Contribution

It introduces a model where spontaneous inflation accounts for the arrow of time and predicts a universe that is statistically time-symmetric on ultra-large scales.

Findings

Inflation can increase the universe's entropy without bound.

The universe can be time-symmetric on large scales due to inflation occurring both forwards and backwards.

Spontaneous inflation provides a natural explanation for the thermodynamic arrow of time.

Abstract

We suggest that spontaneous eternal inflation can provide a natural explanation for the thermodynamic arrow of time, and discuss the underlying assumptions and consequences of this view. In the absence of inflation, we argue that systems coupled to gravity usually evolve asymptotically to the vacuum, which is the only natural state in a thermodynamic sense. In the presence of a small positive vacuum energy and an appropriate inflaton field, the de Sitter vacuum is unstable to the spontaneous onset of inflation at a higher energy scale. Starting from de Sitter, inflation can increase the total entropy of the universe without bound, creating universes similar to ours in the process. An important consequence of this picture is that inflation occurs asymptotically both forwards and backwards in time, implying a universe that is (statistically) time-symmetric on ultra-large scales.