Eternal inflation, bubble collisions, and the persistence of memory

TL;DR

This paper investigates how bubble collisions in eternal inflation create observable anisotropies that persist over time, challenging assumptions of homogeneity and isotropy in the universe.

Contribution

It provides a calculation of collision rates within bubble universes and demonstrates the persistent memory of the universe's beginning despite ongoing inflation.

Findings

Collision rate violates homogeneity and isotropy

Observers away from the bubble center see anisotropic collision patterns

Memory of the initial inflationary start persists indefinitely

Abstract

A ``bubble universe'' nucleating in an eternally inflating false vacuum will experience, in the course of its expansion, collisions with an infinite number of other bubbles. In an idealized model, we calculate the rate of collisions around an observer inside a given reference bubble. We show that the collision rate violates both the homogeneity and the isotropy of the bubble universe. Each bubble has a center which can be related to ``the beginning of inflation'' in the parent false vacuum, and any observer not at the center will see an anisotropic bubble collision rate that peaks in the outward direction. Surprisingly, this memory of the onset of inflation persists no matter how much time elapses before the nucleation of the reference bubble.