2 Drexler K. E., Nanosystems: Molecular Machinery, Manufacturing, and Computation, New York, John Wiley & Sons, Inc., 1992.
4 Bostrom N., ‘How Long Before Superintelligence?’, International Journal of Futures Studies, ii (1998); Kurzweil R., The Age of Spiritual Machines: When Computers Exceed Human Intelligence, New York, 1999. The lower estimate is in Moravec H., Robot: Mere Machine to Transcendent Mind, Oxford, 1999.
6 The Virgo Supercluster contains only a small part of the colonizable resources in the universe, but it is sufficiently big to make the point. The bigger the region we consider, the less certain we can be that significant parts of it will not have been colonized by a civilization of non-terrestrial origin by the time we could get there.
7 Utilitarians commonly regard time-discounting as inappropriate in evaluating moral goods (see e.g. Brandt R. B., Morality, Utilitarianism, and Rights, Cambridge, 1992, pp. 23 f.). However, it is not clear that utilitarians can avoid compromising on this principle in view of the possibility that our actions could conceivably have consequences for an infinite number of persons (a possibility that we set aside for the purposes of this paper).
9 This formulation of the position is not necessarily the best possible one, but it is simple and will serve for the purposes of this paper.
10 Or whatever the population is likely to be at the time when doomsday would occur.
11 See e.g. Vinge V., ‘The Coming Technological Singularity’, Whole Earth Review, winter issue (1993).
12 Freitas R. A. Jr, Nanomedicine, vol. 1, Georgetown, Landes Bioscience, 1999.
13 E.g. Moravec, Kurzweil, and Vinge; Drexler E., Engines of Creation, New York, 1986.
14 On the person-affecting view, the relevant factor is not the temporal location of a person per se. In principle, effects on the well-being of a past or a future person could also be an appropriate target for moral concern. In practice, however, the effect on the well-being of past persons is likely to be relatively small or even zero (depending on which conception of well-being one adopts), and the effect (of any action that has a significant effect on the future) on not-yet-existing persons is very likely to be such that competing alternative actions would lead to separate sets of possible persons coming into existence, for example as a result of different sperms fertilizing different eggs, and thus there would typically be no future persons whose level of well-being is affected by our current actions. Our actions might affect which future persons there will be, but on the person-affecting view, such results provide no general moral reasons for action. One exception are fetuses and fertilized eggs, which are not yet persons, but which may become persons in the future, and whose lives our current actions may influence.
15 I'm grateful for comments from John Broome, Milan Cirkovic, Roger Crisp, Robin Hanson, and James Lenman, and for the financial support of a British Academy Postdoctoral Award.