John Leslie comes to tell us that the end of the world is closer than we think

Mark Greenberg in the London Review of Books:

John Leslie comes to tell us that the end of the world is closer than we think. His book is no ordinary millennial manifesto, however. Leslie is a sophisticated philosopher of science, and the source of his message is not divine revelation, apocalyptic fantasy or anxiety about the year-2000 computer problem, but ‘the Doomsday Argument’ – an a priori argument that seeks support in probability theory. In fact, the most interesting questions The End of the World raises are not, despite its subtitle, about our eventual demise. Rather, they concern our susceptibility, when thinking about risk, uncertainty and probability, to a kind of cognitive illusion. The Doomsday Argument is a case-study in ‘probabilistic illusion’, for it rests on a web of insidious intuitions, hidden assumptions and seductive but imprecise analogies.

The Argument claims that the observation that we are alive now increases the probability that Homo sapiens will become extinct in the relatively near future. It does not predict Doom at a specific time or with a specific probability. Its conclusion is more abstract and puzzling: whatever our best estimate would be (based on all available evidence, including the latest scientific, historical or other research) of the probability that our species is relatively close to extinction, it must be revised upwards. In reaching this conclusion, the Argument does not rely on evidence in the ordinary sense or, indeed, on anything peculiar to our present situation; it would yield the same conclusion at any point in human history.

It may seem preposterous that such a conclusion could be reached by armchair reasoning from the mere fact of our being alive now. Yet it would be wrong to rush to judgment. The counter-intuitive nature of probability is itself a reason for caution; moreover, the Doomsday Argument involves issues about time and existence, which are themselves notoriously resistant to intuition.

More here.