Question of the Week, 3.1.2011
One of the Albert Einstein’s mistakes  was refusing the quantum mechanics. It’s very well known that he was in dispute with Niels Bohr and was rejecting the probabilistic character of quantum mechanics saying that : “God does not play dice!” (but apparently he does…).
Quantum mechanics says that a wave function (or more precisely, a state vector) evolves according to the Schroedinger equation into a linear superposition of different states and this in fact happens in a perfectly deterministic way. When measuring, one obtains only one result and the system somehow “collapses” into the measured state. According to Copenhagen interpretation of quantum mechanics, the squares of the absolute values of expansion coefficients in the aforementioned linear superposition correspond to probabilities. But this interpretation does not say anything about how the system “collapses”. This is called the measurement problem .
The Copenhagen rules clearly work, so they have to be accepted. But what is the connection between the deterministic dynamics and probabilistic interpretation? The measurement problem is still not fully resolved and there exist more interpretations of quantum mechanics dealing with it in different ways.