Black holes and up-tunneling suppress Boltzmann brains
  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.
