Is quantum indeterministic?

Question

The question might look clear from a viewpoint of a non-physics guy but let me be more specific.

Can we say quantum leaps or waves or maybe the universe itself are completely indeterministic or do the scientists say that because of lack of information?

I am asking this because there are people telling me the you cannot know whether it is indeterministic because you might not have all the information needed to calculate the behaviour of the phenomenon. Also, some people argue that chaos is completely indeterministic.

Which is the case and why?

Answer 1

From my perspective quantum mechanics is deterministic. It gives us a set of rules for calculating quantities that we can observe. The outcomes (probability distributions) are uniquely determined by the initial conditions. This has been borne out by experiment for sufficiently simple systems.

Philosophically you might argue differently. Because quantum mechanics only predicts probability, perhaps it lacks determinism? Personally, I'm happy to accept that nature is fundamentally probabilistic at its smallest level. In that case, quantum mechanics is a fantastically deterministic framework.

Of course for large, real-life systems notions of chaos come into play. In classical mechanics this occurs when systems are sensitively dependent on initial conditions to such an extent that long-term prediction is impossible. Our understanding of chaos in the quantum realm is much less developed. Indeed it's a subject of active research, see here for instance.

I'd personally be very interested in hearing about this from somebody working on quantum chaos - any takers?