God Does Not Play Dice

One of Einsteins many pioneering works was a paper he wrote in 1905 proposing that light could travel in the form of particles later called photons. His work led to quantum mechanics, the mathema­tical framework for describing matter and energy on a fundamental level. In his later years, Einstein was unhappy with quantum mechanicsand its description of reality in terms of probabilities as developed by Max Born and Niels Bohr. Einstein preferred the deterministic cause-and-effect of classical physics, writing that “The theory says a lot, but does not really bring us any closer to the secret of the "old one." I, at any rate, am convinced that He does not throw dice.”

Einstein used variants of this quote as well. For example, in a conversation with William Hermanns for the 1943 book Einstein and the Poet, he said "As I have said so many times, God doesn't play dice with the world."

Einstein’s views on quantum mechanics are often oversimplified. He accepted quantum mechanics for observable phenomena—his main concern was with its incompleteness in describing reality.