‘Imagine a room awash in gasoline,’ said the American scientist Carl Sagan in 1980. ‘There are two implacable enemies in that room. One of them has nine thousand matches. The other has seven thousand matches. Each of them is concerned about who’s ahead, who’s stronger. Well, that’s the kind of situation we are actually in.’ In his landmark book and television series Cosmos, Sagan examined the evolution of unicellular life forms into Homo sapiens over millennia, a mere blip in the history of the universe, and wondered whether we will extinguish ourselves through mutually assured destruction. Nearly forty-five years later, the Cold War is a distant memory, nuclear stockpiles have been reduced and atomic weapons are often forgotten as an existential threat to humanity. They’ve been eclipsed as concerns by global warming; some doomsayers even take the possibility of an asteroid strike more seriously.

But the United States and Russia still maintain hundreds of intercontinental ballistic missiles with nuclear warheads, on hair-trigger alert. They have hundreds more nuclear missiles and bombs aboard submarines and aircraft that can be launched in minutes. As it pursues its war with Ukraine, Russia has ordered drills with tactical nuclear weapons. The United States is planning