Will the human race become extinct fairly shortly? Have the dangers been underestimated, and ought we to care?
The Introduction will give the book’s main arguments, particularly a ‘doomsday argument’ originated by the cosmologist Brandon Carter. We ought to have some reluctance to believe that we are very exceptionally early, for instance in the earliest 0.001 per cent, among all humans who will ever have lived. This would be some reason for thinking that humankind will not survive for many more centuries, let alone colonize the galaxy.
Taken just by itself, the doomsday argument could do little to tell us how long humankind will survive. What it might indicate, though, is that the likelihood of Doom Soon is greater than we would otherwise think. Here, ‘otherwise-thinking’ involves taking account of well-recognized dangers like those of pollution and nuclear war.
There are also many other hazards which are seldom considered: for example, the risk that physicists of the future, experimenting at immensely high energies, will upset a spacefilling ‘scalar field’ and destroy the world, a possibility taken seriously by some leading theorists.
There are even risks coming from philosophical arguments. There is the following argument, for example: that any possible humans of the future couldn’t be missing any benefits if they were never in fact born, because you have to be born before you can really miss things.
Despite all this, the book’s third chapter, ‘Judging the risks’, is fairly optimistic. Humans may well spread right through their galaxy.