Recent developments in cosmology indicate that every history having a nonzero
probability is realized in infinitely many distinct regions of spacetime. Thus,
it appears that the universe contains infinitely many civilizations exactly
like our own, as well as infinitely many civilizations that differ from our own
in any way permitted by physical laws. We explore the implications of this
conclusion for ethical theory and for the doomsday argument. In the infinite
universe, we find that the doomsday argument applies only to effects which
change the average lifetime of all civilizations, and not those which affect
our civilization alone.Comment: 25 pages; v2: revised version to appear in British Journal for the
Philosophy of Scienc
