Does Inflation Provide Natural Initial Conditions for the Universe?

TL;DR

This paper explores how inflationary cosmology can naturally originate from a nearly-empty universe with small vacuum energy, addressing initial conditions and the arrow of time.

Contribution

It proposes that a nearly-empty spacetime with small vacuum energy can spontaneously trigger inflation, offering a natural explanation for the universe's initial conditions.

Findings

Inflation can begin spontaneously in a nearly-empty universe.

A small vacuum energy facilitates the onset of inflation.

This scenario accounts for the universe's low-entropy initial state.

Abstract

If our universe underwent inflation, its entropy during the inflationary phase was substantially lower than it is today. Because a low-entropy state is less likely to be chosen randomly than a high-entropy one, inflation is unlikely to arise through randomly-chosen initial conditions. To resolve this puzzle, we examine the notion of a natural state for the universe, and argue that it is a nearly-empty spacetime. If empty space has a small vacuum energy, however, inflation can begin spontaneously in this background. This scenario explains why a universe like ours is likely to have begun via a period of inflation, and also provides an origin for the cosmological arrow of time.