ABSTRACT
The possibility of Boltzmann Brains raises a number of large and difficult cosmological and philosophical questions. I cannot hope to resolve – or even to substantially address – all of these questions here. However, in this chapter, I try to do three things. First, I argue that though David Albert and Sean Carroll’s notion of “cognitive instability” is an interesting and important one, considerations of cognitive instability alone are not sufficient to rule out the hypothesis that I am a Boltzmann Brain. Second, I argue against James Hartle and Mark Srednicki’s conclusion that we can coherently believe both that most observers in the universe are Boltzmann Brains and yet that we (likely) aren’t. And third, I briefly survey the nature of the problems that Boltzmann Brains pose for several categories of cosmological hypotheses.
