Towards observable signatures of other bubble universes II: Exact solutions for thin-wall bubble collisions

TL;DR

This paper analyzes the effects of thin-wall bubble collisions in false vacuum eternal inflation, providing exact solutions and criteria for observable signatures that could potentially be detected within our universe.

Contribution

It offers new exact solutions for bubble collisions, criteria for post-collision dynamics, and formulas for emitted radiation, advancing understanding of observable signatures of other universes.

Findings

Criteria for domain wall acceleration post-collision

Minimal-impact collision solutions identified

Derived formula for radiation energy density

Abstract

We assess the effects of a collision between two vacuum bubbles in the thin-wall limit. After describing the outcome of a generic collision possessing the expected hyperbolic symmetry, we focus on collisions experienced by a bubble containing positive vacuum energy, which could in principle contain our observable universe. We provide criteria governing whether the post-collision domain wall accelerates towards or away from this "observation" bubble, and discuss the implications for observers located at various positions inside of the bubble. Then, we identify the class of solutions which have minimal impact on the interior of the observation bubble, and derive a simple formula for the energy density of a shell of radiation emitted from such a collision. In the context of a universe undergoing false vacuum eternal inflation, these solutions are perhaps the most promising candidates for collisions that could exist within our past light cone, and therefore in principle be observable.