No Doomsday Argument without Knowledge of Birth Rank: a Defense of Bostrom

Abstract

The Doomsday Argument says we should increase our subjective probability that Doomsday will occur once we take into account how many humans have lived before us. One objection to this conclusion is that we should accept the Self-Indication Assumption (SIA): ’Given the fact that you exist, you should (other things equal) favor hypotheses according to which many observers exist over hypotheses on which few observers exist’. Nick Bostrom argues that we should not accept the SIA, because it can be used without knowledge of birth rank. Bradley Monton tries to construct a Doomsday Argument without knowledge of birth rank. I argue that Monton fails. The argument he constructs has implicit knowledge of birth rank and it is this knowledge that does the work. Furthermore, I argue that provided we don’t have certain specific information about the future, the Doomsday Argument requires knowledge of birth rank.