The Uncertainty Principle Determines the Nonlocality of Quantum Mechanics

Quantum Connection A system that is quantum mechanically entangled with another distant system can be predicted by measuring the distant system. This form of “action-at-a-distance,” or nonlocality, seemingly contradicts Heisenberg's uncertainty principle, which is one of the fundamental aspects of quantum mechanics. Oppenheim and Wehner (p. 1072) show that the degree of nonlocality in quantum mechanics is actually determined by the uncertainty principle. The unexpected connection between nonlocality and uncertainty holds true for other physical theories besides quantum mechanics. The two central elements of quantum theory, once assumed to be distinct concepts, are shown to be linked. Two central concepts of quantum mechanics are Heisenberg’s uncertainty principle and a subtle form of nonlocality that Einstein famously called “spooky action at a distance.” These two fundamental features have thus far been distinct concepts. We show that they are inextricably and quantitatively linked: Quantum mechanics cannot be more nonlocal with measurements that respect the uncertainty principle. In fact, the link between uncertainty and nonlocality holds for all physical theories. More specifically, the degree of nonlocality of any theory is determined by two factors: the strength of the uncertainty principle and the strength of a property called “steering,” which determines which states can be prepared at one location given a measurement at another.