Quantum mechanics is certainly imposing. But an inner voice tells me that it is not yet the real thing. 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.
Die Quantenmechanik ist sehr achtung-gebietend. Aber eine innere Stimme sagt mir, daß das doch nicht der wahre Jakob ist. Die Theorie liefert viel, aber dem Geheimnis des Alten bringt sie uns kaum näher. Jedenfalls bin ich überzeugt, daß der nicht würfelt.
Original text (German)
Notes from Wikiquote
Einstein himself used variants of this quote at other times. For example, in a 1943 conversation with William Hermanns recorded in Hermanns' book Einstein and the Poet, Einstein said: "As I have said so many times, God doesn't play dice with the world." (p. 58)