Eternal Inflation, past and future

TL;DR

This paper reviews the concept of eternal inflation, discussing its implications for the universe's beginning, including the possibility of no initial singularity, eternal past, and time-symmetry.

Contribution

It provides a comprehensive review of eternal inflation and explores its profound implications for the universe's origin and temporal structure.

Findings

Eternal inflation may eliminate the need for a cosmological initial singularity.

The universe could be eternal and infinitely inflating in the past.

Eternal inflation might imply a form of cosmological time-symmetry.

Abstract

Cosmological inflation, if it occurred, radically alters the picture of the `big bang', which would merely point to reheating at the end of inflation. Moreover, this reheating may be only local, so that inflation continues elsewhere and forever, continually spawning big-bang-like regions. This chapter reviews this idea of `eternal inflation', then focuses on what this may mean for the ultimate beginning of the universe. In particular, I will argue that given eternal inflation, the universe may be free of a cosmological initial singularity, might be eternal (and eternally inflating) to the past, and might obey an interesting sort of cosmological time-symmetry.