Scientists say it is the closest they’ve come to real magic. In October, a team of physicists in the Netherlands reported in the journal Nature the most definitive evidence yet for what Einstein called “spooky action at a distance”—subtle and seemingly inexplicable connections between objects in the quantum realm. This month, teams in Vienna and in Boulder, Colorado, weighed in with equally dramatic results. Two or more particles can act in a coordinated way, no matter how far apart they may be, and they do so without sending out a sound wave, beaming a radio signal, or otherwise communicating across the gap that separates them. Their spooky synchronicity has many of the qualities of the Force: You can’t use it to misdirect stormtroopers or feel the pain of a distant planetary holocaust, but it does bind together the fates of things that could lie on opposite sides of the galaxy. And it violates our deepest intuitions about nature.
Physicists have tried for decades to explain away the phenomenon, which is known as quantum entanglement. With these latest experiments, they’ve pretty much run out of prosaic explanations. You might think, for example, that the particles are no more mysterious than socks, which are coordinated for the simple reason that you paired them when folding the laundry. But experiments have ruled out the possibility that particles remain matched due to any kind of advance preparation. The particles are behaving like bewitched socks: They’re not white, pink, or any other color. They don’t actually have a color when you put them on. They take on a color only when observed. You look at the left sock and—boom!—it turns pink. You look at the right, and it, too, is pink. The socks are choosing a color on the fly, and they are choosing the same color. (You can see why this strikes physicists as magical.)
Nor could some exotic force be passing between the particles, because the particles are being measured at exactly the same moment; it is only at that moment that they settle into a given state (or color, in the socks metaphor), according to the standard interpretation of quantum theory. Any force that transmitted the information to the other particle would need to propagate instantaneously. That would violate Einstein’s theory of relativity, and in any case, instantaneous propagation isn’t propagation in any meaningful sense of the term.