Abstract

The two defining elements of quantum mechanics are Heisenberg’s uncertainty principle, and a subtle form of non-locality which Einstein famously called “spooky action at a distance”. The first principle states that there are measurements whose results cannot be simultaneously predicted with certainty. The second that when performing measurements on two or more separated systems the outcomes can be correlated in a way that defies the classical world. These two fundamental features have thus far been separate and distinct concepts. Here we show that they are inextricably and quantitatively linked. Quantum mechanics cannot be more non-local without violating the uncertainty principle. In fact, the link between uncertainty and non-locality holds for all physical theories. More specifically, the degree of non-locality of any theory is solely determined by two factors—one being the strength of the uncertainty principle, and the second one being the strength of a property which Schrodinger called “steering”. The latter determines which states can be prepared at one location given a measurement at another, and in most theories of nature this is determined by causality alone.