Ron Avni

Leading cosmological theories engender a controversial puzzle which has prompted philosophers to propose competing epistemological solutions and physicists to propose methodological changes to cosmology. The puzzle arises from the prediction that every brain on Earth will eventually be vastly outnumbered by physical duplicates formed by random collisions of particles in outer space. Supposing that this prediction is correct, shouldn't you believe that your brain is probably one of these vastly more typical extraterrestrial brains, since you cannot infer your brain's origin from your experiential state? But supposing that your brain is one of these extraterrestrial brains, why be confident in the cosmological theories, since you never actually received testimony supporting these theories? Proposals in the literature either deny the rationality of believing theories that make the prediction or deny the typicality of your brain among its duplicates. This paper argues that these proposals are not entirely satisfactory. Instead, one should be confident in theories making the prediction on the supposition that your brain is one of the extraterrestrial brains. The upshots include that it may be rational to believe that your brain is probably an extraterrestrial brain and that cosmologists should not alter their methodology in response to the puzzle.

Rinard (2019) brings to our attention the fact that, typically, the questions What should I believe? and What should I do? are treated differently. A typical answer to the first question is Believe according to the evidence, and a typical answer to the second question is Do what is right. But Rinard rejects this dichotomy. In its place, she argues for a view which she calls “Equal Treatment” in which one should believe according to the same considerations that govern what one should do. Christensen (forthcoming) aptly situates Equal Treatment as a limit case of a recent movement towards taking pragmatic factors as partly determining what one should believe, in that Equal Treatment is a purely pragmatic view. Does Rinard’s case for a purely pragmatic view succeed? This paper argues that the answer is no. Three objections that target key parts of Rinard’s case for Equal Treatment are presented. The upshot is that the dichotomy between the answers to What should I believe? and What should I do? seems robust against strong attempts to dismantle it.