The possibility that the universe is infinite, and that it might therefore contain an infinite number of morally relevant beings, is a challenge to moral theories that instruct us to increase the good in the
world . Briefly, the trouble is that in an infinite universe the amount of good may be infinite no matter what we do, and it is difficult to compare infinities.
Bostrom, Nick (2016) Infinite ethics, Analysis and
metaphysics, vol. 10, pp. 9–59.
An in-depth discussion of the potential moral implications of an infinite universe.