Recent developments in cosmology indicate that every history having a nonzeroprobability is realized in infinitely many distinct regions of spacetime. Thus,it appears that the universe contains infinitely many civilizations exactlylike our own, as well as infinitely many civilizations that differ from our ownin any way permitted by physical laws. We explore the implications of thisconclusion for ethical theory and for the doomsday argument. In the infiniteuniverse, we find that the doomsday argument applies only to effects whichchange the average lifetime of all civilizations, and not those which affectour civilization alone.
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