It’s worthwhile to think about the number of people around you who are waiting for the world to end. There are people who must do it for a living: government employees who specialize in disaster relief and crisis response, civil engineers, military personnel—people who must imagine the end to make sure it never comes. But there are others: Fundamentalist evangelicals waiting for a rapture. Libertarian preppers who shun government and pride themselves on self-sufficiency. Conspiracy theorists and internet nihilists. Anyone remotely concerned with the future of the planet.