Eternal Inflation With Non-Inflationary Pocket Universes

TL;DR

This paper investigates how different measure proposals in eternal inflation influence the likelihood of inhabiting various types of pocket universes, favoring emergent and cyclic models with small initial Hubble rates.

Contribution

It demonstrates that current measure proposals predict a preference for pocket universes with small Hubble rates, especially cyclic ones, impacting our understanding of universe types in eternal inflation.

Findings

Leading measures favor small Hubble rate universes.

Cyclic and emergent universe models are more probable.

Cyclic universes can produce habitable conditions repeatedly.

Abstract

Eternal inflation produces pocket universes with all physically allowed vacua and histories. Some of these pocket universes might contain a phase of slow-roll inflation, some might undergo cycles of cosmological evolution and some might look like the galilean genesis or other "emergent" universe scenarios. Which one of these types of universe we are most likely to inhabit depends on the measure we choose in order to regulate the infinities inherent in eternal inflation. We show that the currently leading measure proposals, namely the global light-cone cut-off and its local counterpart, the causal diamond measure, as well as closely related proposals, all predict that we should live in a pocket universe that starts out with a small Hubble rate, thus favoring emergent and cyclic models. Pocket universes which undergo cycles are further preferred, because they produce habitable conditions repeatedly inside each pocket.