Astronomers propose an experiment that may close the last major loophole of Bell's inequality -- a 50-year-old theorem that, if violated by experiments, would mean that our universe is based not on the textbook laws of classical physics, but on the less-tangible probabilities of quantum mechanics. Such a quantum view would allow for seemingly counterintuitive phenomena such as entanglement, in which the measurement of one particle instantly affects another, even if those entangled particles are at opposite ends of the universe. Among other things, entanglement -- a quantum feature Albert Einstein skeptically referred to as "spooky action at a distance"...