Advancing the Boltzmann Brain Skeptical Challenge

Some leading cosmological models predict that in the future history of the universe, there will be vast numbers of Boltzmann Brains (“brains” formed by chance in otherwise empty space), including many that are physical duplicates of your own brain and that (arguably) have conscious experiences indistinguishable from your own experiences. This article advances the skeptical challenge posed by this prediction in two ways. First, the author challenges the common assumption that scientific evidence for Boltzmann Brain superabundance presents a serious skeptical worry only if that evidence gives one reason to assign significant credence to the hypothesis that one is a Boltzmann Brain. On this assumption, Boltzmann Brain-related skeptical worries are easily swept aside. The author develops a new and more formidable Boltzmann Brain skeptical argument that is not committed to this assumption. Second, the author takes up recent objections to Center Indifference, a principle underlying Boltzmann Brain skeptical arguments. Dogramaci and Schoenfield (2025) have argued that Center Indifference imposes absurd constraints on one’s credences for certain scientific theories. The author shows that their arguments turn on some subtle confusions and that Center Indifference does not have the absurd implications that they attribute to it.