homung suggests that there may be immutable laws of the universe that mean there are only a finite number of apocalyptic technologies. Note that even if the probability of such technological limits is small, in order for Phil's argument to work, either that probability would have to be infinitesimal, or some of the doomsday devices have to continue to be threatening after the various attack/defense strategies reach a very mature level of development. All of the probabilities look finite to me.