Help me understand indeterminism in standard quantum mechanics

[ojitojuntos]

TL;DR

Hello. I’m having a hard time understanding indeterminism and the notion of collapse. Does indeterminism suggest that the future of the universe is not fully “set”?

Hello guys. Im having some trouble understanding the role of randomness in quantum mechanics, and what does that mean for the notion of an “open future”.
For example, let’s say I take a quantum event, like some atom decaying. Does indeterminism mean that, besides predictability, if it were possible to rewind time before that decay, the moment of decay would vary?
Thanks in advance!

 

[PeterDonis]

Moderator's note: Thread moved to the QM interpretations subforum.

 

[PeterDonis]

Im having some trouble understanding the role of randomness in quantum mechanics

That role is interpretation dependent. In some interpretations, such as the MWI, there is no actual randomness anywhere; everything is entirely deterministic. The apparent randomness comes from the fact that the different branches of the wave function don't interfere, so in each individual branch, it appears as though one randomly chosen result happened. But actually, all possible results happen, each in its own branch.

Whereas, in interpretations where collapse is an actual physical process, the randomness is (or at least is claimed to be) inherent in whatever underlying dynamics produces collapses.

let’s say I take a quantum event, like some atom decaying. Does indeterminism mean that, besides predictability, if it were possible to rewind time before that decay, the moment of decay would vary?

Again, the answer is interpretation dependent.

In the MWI, there are multiple branches of the wave function at which the atom decays at different times. If you "rewound" the wave function to the start and "re-ran" it again, exactly the same branches would arise, because everything is deterministic.

Whereas in interpretations where collapse is an actual physical process, yes, whatever underlying dynamics is producing collapses might produce one (i.e., might produce a detection of the atom decaying) at a different time if things were "re-run" again with exactly the same initial conditions.

Note that in practice it's never possible to re-run things again with exactly the same initial conditions, so there's no way of actually testing claims along these lines.