In 1926 Max Born interprets Schrödinger's matter waves as probabilities. This finally confirms the statistical nature of quantum mechanics.
Einstein rejects this:
Quantum mechanics is very awe-inspiring. Yet an inner voice tells me that it's not the real Mc Coy. The theory delivers a lot, but it hardly brings us any closer to solving the mystery of the Old Man (God). I, at least, am convinced that He does not play dice.