Why the Universe Started from a Low Entropy State

TL;DR

This paper argues that gravitational backreaction constrains initial conditions for inflation, favoring high-energy inflation and suggesting the universe's low entropy start is a result of dynamic selection rather than thermodynamic probability.

Contribution

It introduces a dynamical framework showing gravitational backreaction imposes superselection rules on initial conditions, impacting the understanding of the universe's low entropy beginning.

Findings

High-energy inflation is stable against gravitational collapse.

Backreaction constrains initial conditions, leading to a superselection rule.

Thermostatistics cannot fully explain initial conditions due to gravitational degrees of freedom.

Abstract

We show that the inclusion of backreaction of massive long wavelengths imposes dynamical constraints on the allowed phase space of initial conditions for inflation, which results in a superselection rule for the initial conditions. Only high energy inflation is stable against collapse due to the gravitational instability of massive perturbations. We present arguments to the effect that the initial conditions problem {\it cannot} be meaningfully addressed by thermostatistics as far as the gravitational degrees of freedom are concerned. Rather, the choice of the initial conditions for the universe in the phase space and the emergence of an arrow of time have to be treated as a dynamic selection.