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

By Andrea De Simone, A. Guth, Andrei Linde, Mahdiyar Noorbala, Michael P. Salem, A. Vilenkin. 2008

139 citations recorded by the source corpus.

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 would be overwhelmingly likely to be surrounded by an empty world, where all but vacuum energy has redshifted away, rather than the rich structure that we observe. Using the scale-factor cutoff measure, we calculate the ratio of Boltzmann brains to normal observers. We find the ratio to be finite, and give an expression for it in terms of Boltzmann brain nucleation rates and vacuum decay rates. We discuss the conditions that these rates must obey for the ratio to be acceptable, and we discuss estimates of the rates under a variety of assumptions.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics, Statistical and Nonlinear Physics

View Paper: https://www.semanticscholar.org/paper/5a93eb5481e1640adb08c6c9c5e63480af17d831

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Citations in the corpus

Inflationary Cosmology after Planck 2013 (2014, background): “The second of the two measures proposed in [58], the scale factor cutoff measure, also does not suffer from this problem and remains quite popular [169].”
Making predictions in the multiverse (2011, background): “[31] suggested one way of modifying the proposal to avoid this issue.”