Black holes and up-tunneling suppress Boltzmann brains

TL;DR

The paper argues that black hole nucleation and rapid inflation suppress Boltzmann brain dominance in eternal inflation, ensuring ordinary observers are more common than Boltzmann brains under certain conditions.

Contribution

It introduces the idea that black hole and rapid inflation nucleation rates surpass Boltzmann brain rates, impacting the measure problem in eternal inflation.

Findings

Black hole nucleation rate exceeds Boltzmann brain rate for masses above the Planck mass.

Small, rapidly inflating regions also have higher nucleation rates than Boltzmann brains.

These processes influence the distribution of vacua in eternal inflation.

Abstract

Eternally inflating universes lead to an infinite number of Boltzmann brains but also an infinite number of ordinary observers. If we use the scale factor measure to regularize these infinities, the ordinary observers dominate the Boltzmann brains if the vacuum decay rate of each vacuum is larger than its Boltzmann brain nucleation rate. Here we point out that nucleation of small black holes should be counted in the vacuum decay rate, and this rate is always larger than the Boltzmann brain rate, if the minimum Boltzmann brain mass is more than the Planck mass. We also discuss nucleation of small, rapidly inflating regions, which may also have a higher rate than Boltzmann brains. This process also affects the distribution of the different vacua in eternal inflation.