The Doomsday Argument Adam & Eve, UN++, and Quantum Joe

The Doomsday argument purports to show that the risk of the human species going extinct soon has been systematically underestimated. This argument has something in common with controversial forms of reasoning in other areas, including: game theoretic problems with imperfect recall, the methodology of cosmology, the epistemology of indexical belief, and the debate over so-called fine-tuning arguments for the design hypothesis. The common denominator is a certain premiss: the Self-Sampling Assumption. We present two strands of argument in favor of this assumption. Through a series of thought experiments we then investigate some bizarre prima facie consequences – backward causation, psychic powers, and an apparent conflict with the Principal Principle. The Self-Sampling Assumption and its use in the Doomsday argument Let a person’s birth rank be her position in the sequence of all observers who will ever have existed. For the sake of argument, let us grant that the human species is the only intelligent life form in the cosmos. Your birth rank is then approximately 60 billionth, for that is the number of humans who have lived before you. The Doomsday argument proceeds as follows. Compare two hypotheses about how many humans there will have been in total: h1: = “There will have been a total of 200 billion humans.” h2: = “There will have been a total of 200 trillion humans.” Suppose that after considering the various empirical threats that could cause human extinction (species-destroying meteor impact, nuclear Armageddon, self-replicating