This article gives a Bayesian argument showing that, even if your total empirical evidence confirms that you have zillions of duplicate Boltzmann Brains, that evidence does not confirm that you are a Boltzmann Brain. The article also attempts to explain what goes wrong with several of the sources of the temptation for thinking that such evidence does have skeptical implications.

Does the evidence that our universe contains fine-tuned life confirm the multiverse hypothesis? The answer depends on our approach to self-locating beliefs. In a recent paper, Isaacs, Hawthorne, and Russell (2022) offer two arguments for thinking that such evidence does confirm the multiverse hypothesis. First, they argue that the three leading approaches to self-locating beliefs all entail that such evidence confirms the multiverse hypothesis. Second, they present a pair of theorems showing that any approach to self-locating beliefs that satisfies certain (...) “reasonable” constraints will entail that such evidence confirms the multiverse hypothesis. I argue that Isaacs, Hawthorne, and Russell’s two arguments are not compelling, the first because they fail to consider some natural approaches to self-locating beliefs, the second because their theorems rely on a suspect premise that we should reject. Contra Issacs, Hawthorne, and Russell, I argue that on a natural approach to self-locating beliefs the evidence that our universe contains fine-tuned life needn’t confirm the multiverse hypothesis. (shrink)

According to the principle of indifference, when a set of possibilities is evidentially symmetric for you – when your evidence no more supports any one of the possibilities over any other – you're required to distribute your credences uniformly among them. Despite its intuitive appeal, the principle of indifference is often thought to be unsustainable due to the problem of multiple partitions: Depending on how a set of possibilities is divided, it seems that sometimes, applying indifference reasoning can require you (...) to assign incompatible credences to equivalent possibilities. This paper defends the principle of indifference from the problem of multiple partitions by offering two guides for how to respond. The first is for permissivists about rationality, and is modeled on permissivists' arguments for the claim that a body of evidence sometimes does not uniquely determine a fully rational credence function. The second is for impermissivists about rationality, and is modeled on impermissivists' arguments for the claim that a body of evidence does always uniquely determine a fully rational credence function. What appears to be a decisive objection against the principle of indifference is in fact an instance of a general challenge taking different forms familiar to both permissivists and impermissivists. (shrink)