Since 1947, the Bulletin of the Atomic Scientists has kept a Doomsday Clock, moving the hands closer to, or farther from, midnight, the moment when civilization annihilates itself with nuclear weapons. In 2018, the clock was moved to two minutes before midnight, the closest it’s been to doomsday since the 1950s. Hawking worries that nuclear war or climate destruction may destroy civilization: “[E]ither a nuclear confrontation or environmental catastrophe will cripple the Earth at some point in the next 1,000 years” (150). He also believes that, eventually, a large asteroid—like the one that struck 65 million years ago and killed off the dinosaurs—will strike Earth, devastating life on the planet. Establishing colonies in space is one way to prevent the extinction of humanity: “Spreading out may be the only thing that saves us from ourselves” (150).

Unlike sci-fi stories, where the future is nearly perfect and stable, human civilization has never stood still. Recent centuries have seen an exponential growth of population, use of energy, and published books. At these rates, in 600 years, Earth’s people will be crowded shoulder-to-shoulder, and electricity use will make the planet red-hot.

As for a unified theory of science, the author thought in 1980 that by 2000 there was a 50-50 chance of success, but it didn’t happen.