In everyday life, most of us assumes every event and object has a cause in some sense. I am wondering if the same is true for quantum physics.
Does the random nature of quantum phenomena mean they have no cause or does the theory say that causes of quantum randomness are unknown?
The word "random" is used here in its ontological sense.
Best Answer
Per request, made to an answer from a comment:
It was John Stuart Bell in 1964who proved by simple arithmetics that there are no hidden local variables behind the statistical nature of quantum processes, and behind the spooky non-locality displayed by entangled particles. Consequently, the paradox presented in the 1935 Einstein-Podolsky-Rosen paper upon which they claimed that quantum physics cannot be complete ("since it relies on statistical laws, it cannot give the ultimate full description of nature") is inherently wrong.
We understand causality as a relation that links post-events (effect) to prior-events (cause) (note that this does not necessarily mean similar chronological sequence, see here). In this sense, observable phenomena are dependent on deeper, possibly hidden variables, that nevertheless can be usually uncovered, at least at the macroscopic level. However, as Bell has proven, there are no hidden variables responsible for lowest-level quantum processes e.g. the random decay of radioactive elements. Therefore I would say that there exist no lower-level, ultimate cause for these processes.