Islands in Multiverse Models

TL;DR

This paper investigates multiverse models in 2D gravity theories, revealing that large subregions develop islands causing a Page-like transition, which impacts the understanding of measures in eternal inflation.

Contribution

It introduces a calculation of von Neumann entropy in 2D multiverse models showing island formation and a Page transition, linking quantum information to cosmological measures.

Findings

Islands form in large subregions, covering most of the multiverse.

A Page-like transition occurs when subregions are sufficiently large.

The results connect quantum entropy with cosmological measures in eternal inflation.

Abstract

We consider multiverse models in two-dimensional linear dilaton-gravity theories as toy models of false vacuum eternal inflation. Coupling conformal matter we calculate the Von Neumann entropy of subregions. When these are sufficiently large we find that an island develops covering most of the rest of the multiverse, leading to a Page-like transition. This resonates with a description of multiverse models in semiclassical quantum cosmology, where a measure for local predictions is given by saddle point geometries which coarse-grain over any structure associated with eternal inflation beyond one's patch.