True randomness in QM

[Alex K]

I think it goes too far to say that the consensus is that #2 true randomness is at the bottom of Quantum uncertainty. There is a consensus to use something like the Copenhagen interpretation (or should I say prescription) for all practical calculations in order to not get bogged down with metaphysical questions. That means that virtually everyone, for pragmatic reasons, uses a prescription to calculate results which does not contain rhe additional information (so called hidden variables) which would uniquely determine the result of a measurement involving quantum uncertainty. I believe people don't necessarily choose to do that because they believe in their hearts that there must be true randomness at the bottom of QM, but rather because it makes no difference for the result of any calculation if we included a (usually more complicated) deterministic description with hidden variables : we don't know the values of these hidden variables anyways, and they are constructed precisely such that ignorance of the hidden variable reproduces the same statistical distribution as true quantum randomness. Someone who "believes" in a deterministic interpretation of qm will generally still use the copenhagen or similar prescriptions to calculate concrete results because it is simple.

The Everett "many worlds" interpretation is a special case because it is relatively simple, and it is deterministic, but it has no hidden variables and is not deterministic from the perspective of any single observer. There is no way to determine in principle what a randomly chosen observer in the mwi will measure, because everything happens to some observer, and it is your selection of observer which determines the result xe observes, not any variable.