Jim Baggott in Aeon:
The theory produces a good deal but hardly brings us closer to the secret of the Old One,’ wrote Albert Einstein in December 1926. ‘I am at all events convinced that He does not play dice.’
Einstein was responding to a letter from the German physicist Max Born. The heart of the new theory of quantum mechanics, Born had argued, beats randomly and uncertainly, as though suffering from arrhythmia. Whereas physics before the quantum had always been about doing this and getting that, the new quantum mechanics appeared to say that when we do this, we get that only with a certain probability. And in some circumstances we might get the other.
Einstein was having none of it, and his insistence that God does not play dice with the Universe has echoed down the decades, as familiar and yet as elusive in its meaning as E = mc2. What did Einstein mean by it? And how did Einstein conceive of God?
More here.