Boltzmann brains and the scale-factor cutoff measure of the multiverse

@article{Simone2010BoltzmannBA,
  title={Boltzmann brains and the scale-factor cutoff measure of the multiverse},
  author={Andrea De Simone and Alan Harvey Guth and Andrei Linde and Mahdiyar Noorbala and Michael P. Salem and Alexander Vilenkin},
  journal={Physical Review D},
  year={2010},
  volume={82},
  pages={063520}
}
To make predictions for an eternally inflating 'multiverse', one must adopt a procedure for regulating its divergent spacetime volume. Recently, a new test of such spacetime measures has emerged: normal observers - who evolve in pocket universes cooling from hot big bang conditions - must not be vastly outnumbered by 'Boltzmann brains' - freak observers that pop in and out of existence as a result of rare quantum fluctuations. If the Boltzmann brains prevail, then a randomly chosen observer… 

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