Albert Einstein: quantum mechanics quotes

This is post is a collection of quotes from Albert Einstein (1879-1955) about quantum mechanics. There are 4 quotes listed below chronologically.

1. "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." (Letter to Max Born, 1926)

2. "The development during the present century is characterized by two theoretical systems essentially independent of each other: the theory of relativity and the quantum theory. The two systems do not directly contradict each other; but they seem little adapted to fusion into one unified theory." (The Fundamentals of Theoretical Physics, 1940)

3. "If one adheres to this program, then one can hardly view the quantum-theoretical description as a complete representation of the physically real. If one attempts, nevertheless, so to view it, then one must assume that the physically real in B undergoes a sudden change because of a measurement in A. My physical instincts bristle at that suggestion." (Letter to Max Born, 1948)

4. "...by using an incomplete description, (in the main) only statistical statements can be obtained out of such description. If it should be possible to move forward to a complete description, it is likely that the laws would represent relations among all the conceptual elements of this description which, per se, have nothing to do with statistics." (Einstein's Reply to Criticisms, 1949)