The Multiverse in an Inverted Island

TL;DR

This paper explores how entanglement islands in an eternally inflating multiverse can resolve redundancies in its global spacetime description, offering a finite, predictive framework for cosmology.

Contribution

It introduces the concept that entanglement islands emerge in bubble universes, reducing degrees of freedom and regularizing infinities in the multiverse.

Findings

Entanglement islands surround large regions in bubble universes.

The emergence of islands reduces the effective degrees of freedom.

This mechanism regularizes infinities and addresses the measure problem.

Abstract

We study the redundancies in the global spacetime description of the eternally inflating multiverse using the quantum extremal surface prescription. We argue that a sufficiently large spatial region in a bubble universe has an entanglement island surrounding it. Consequently, the semiclassical physics of the multiverse, which is all we need to make cosmological predictions, can be fully described by the fundamental degrees of freedom associated with certain finite spatial regions. The island arises due to mandatory collisions with collapsing bubbles, whose big crunch singularities indicate redundancies of the global spacetime description. The emergence of the island and the resulting reduction of independent degrees of freedom provides a regularization of infinities which caused the cosmological measure problem.