Also see this piece by Steven Weinberg: http://www.nybooks.com/articles/2017/01/19/trouble-with-quantum-mechanics/ http://www.nybooks.com/articles/2017/01/19/t

Also see this piece by Steven Weinberg: http://www.nybooks.com/articles/2017/01/19/trouble-with-quantum-mechanics/ http://www.nybooks.com/articles/2017/01/19/trouble-with-quan... "One common answer is that, in a measurement, the spin (or whatever else is measured) is put in an interaction with a macroscopic environment that jitters in an unpredictable way. For example, the environment might be the shower of photons in a beam of light that is used to observe the system, as unpredictable in practice as a shower of raindrops. Such an environment causes the superposition of different states in the wave function to break down, leading to an unpredictable result of the measurement. (This is called decoherence.) It is as if a noisy background somehow unpredictably left only one of the notes of a chord audible. But this begs the question. If the deterministic Schrödinger equation governs the changes through time not only of the spin but also of the measuring apparatus and the physicist using it, then the results of measurement should not in principle be unpredictable. So we still have to ask, how do probabilities get into quantum mechanics?"