Einstein: His Life and Universe

by Walter Isaacson

That was not necessarily a problem. But here was the rub: there was no way to determine which direction an emitted photon might go. In addition, there was no way to determine when it would happen. If an atom was in a state of higher energy, it was possible to calculate the probability that it would emit a photon at any specific moment. But it was not possible to determine the moment of emission precisely. Nor was it possible to determine the direction. No matter how much information you had. It was all a matter of chance, like the roll of dice. That was a problem. It threatened the strict determinism of Newton’s mechanics. It undermined the certainty of classical physics and the faith that if you knew all the positions and velocities in a system you could determine its future. Relativity may have seemed like a radical idea, but at least it preserved rigid cause-and-effect rules. The quirky and unpredictable behavior of pesky quanta, however, was messing with this causality.