Black holes and the multiverse

TL;DR

This paper explores how vacuum bubbles and domain walls during inflation can lead to black hole formation, potentially creating a multiverse with observable astrophysical consequences and implications for dark matter and supermassive black holes.

Contribution

It introduces a generic mechanism for black hole formation from inflationary bubbles and domain walls, linking early universe physics to multiverse structure and observable phenomena.

Findings

Black holes from bubbles can serve as dark matter candidates.

Black hole mass spectrum depends on model parameters.

Multiverse structure involves eternally inflating baby universes connected by wormholes.

Abstract

Vacuum bubbles may nucleate and expand during the inflationary epoch in the early universe. After inflation ends, the bubbles quickly dissipate their kinetic energy; they come to rest with respect to the Hubble flow and eventually form black holes. The fate of the bubble itself depends on the resulting black hole mass. If the mass is smaller than a certain critical value, the bubble collapses to a singularity. Otherwise, the bubble interior inflates, forming a baby universe, which is connected to the exterior FRW region by a wormhole. A similar black hole formation mechanism operates for spherical domain walls nucleating during inflation. As an illustrative example, we studied the black hole mass spectrum in the domain wall scenario, assuming that domain walls interact with matter only gravitationally. Our results indicate that, depending on the model parameters, black holes produced in this scenario can have significant astrophysical effects and can even serve as dark matter or as seeds for supermassive black holes. The mechanism of black hole formation described in this paper is very generic and has important implications for the global structure of the universe. Baby universes inside super-critical black holes inflate eternally and nucleate bubbles of all vacua allowed by the underlying particle physics. The resulting multiverse has a very non-trivial spacetime structure, with a multitude of eternally inflating regions connected by wormholes. If a black hole population with the predicted mass spectrum is discovered, it could be regarded as evidence for inflation and for the existence of a multiverse.