Physicists have long suspected that quantum mechanics allows 2 observers to experience different, conflicting realities. Now they’ve performed the first experiment that proves it. They use 6 entangled photons to create 2 alternate realities—1 representing Wigner and 1 representing Wigner’s friend. Wigner’s friend measures the polarization of a photon and stores the result. Wigner then performs an interference measurement to determine if the measurement and the photon are in a superposition. The experiment produces an unambiguous result. It turns out that both realities can coexist even though they produce irreconcilable outcomes, just as Wigner predicted. That raises some fascinating questions that are forcing physicists to reconsider the nature of reality.

The experiment that Steinberg and his team conducted was analogous to the standard 2-slit experiment. They used photons rather than electrons, and instead of sending those photons through a pair of slits, they passed through a beam splitter, a device that directs a photon along one of 2 paths, depending on the photon’s polarization. The photons eventually reach a single-photon camera (equivalent to the screen in the traditional experiment) that records their final position. The question “Which of 2 slits did the particle pass through?” becomes “Which of 2 paths did the photon take?”

Einstein believed that there must exist hidden aspects of reality, not yet recognized within the conventional formulation of quantum theory, which would restore Einstein Sanity. In this view it is not so much that God does not play dice, but that the game he’s playing does not differ fundamentally from classical dice. It appears random, but that’s only because of our ignorance of certain “hidden variables.” Roughly: “God plays dice, but he’s rigged the game.” But as the predictions of conventional quantum theory, free of hidden variables, have gone from triumph to triumph, the wiggle room where one might accommodate such variables has become small and uncomfortable.