Unlike everyday objects, quantum particles can be linked over long distances, behaving as one integrated whole, even though they are so widely separated they can’t communicate, even at the speed of light. Einstein hated the idea, which he called “spooky action at a distance.” In the 1960s the physicist John Bell proposed a method to confirm whether quantum particles were really spooky. Physicist Mark Alford first encountered this experiment, called the Bell test or the Einstein-Podolsky-Rosen experiment, in the form of pages of equations and, taking pity on students everywhere, has found a way to describe it that more of us can understand. Here, he explains the logic behind a famous experiment designed to tell whether quantum mechanics is spooky or nonspooky.
MEET THE SCIENTIST
Mark Alford is professor of physics and department chair at Washington University in St. Louis. He studies quark matter, a high density state of matter that might be found in neutron stars.