IN THE FALL OF 2012 , scientists at the Large Hadron Collider in Geneva, Switzerland, embarked on a new series of high-energy experiments. No one knows exactly what they were attempting to do, but a little after 3 p.m. on a Thursday afternoon came the Big Mistake, and in the blink of an eye, many possible universes all condensed into a single reality. In some of these universes, little had changed; it didn’t make a big difference, for example, which team won the 2011 World Series. In other universes, there were more important divergences: The Gray Emissary, who was carrying gifts of advanced technology, wasn’t shot down at Roswell in 1947; the Black Death didn’t devastate Europe in the fourteenth century; the dinosaurs didn’t die out; Nikola Tesla conquered the world with a robot army, and so on. The Cold War went nuclear in eighty-three percent of the possible universes, and in three percent the French unloaded their entire nuclear arsenal on the town of Peshtigo, Wisconsin, because it had to be done.
When reality stabilized again, an instant after the Big Mistake, the familiar Earth of the twenty-first century was replaced by one formed from many different realities. The year is now 2162 (or 151, or 32,173, or Six Monkey Slap-Slap, depending on your point of view.