Question on the "probabilistic" nature of QM I read very recently something that I interpreted as stating that certain quantum-mechanical phenomena are necessarily probability-based: for instance the exact path traversed by a photon/electron in the double-slit experiment. That's all well and good, but the material seemed to make an implication that I've been having a lot of difficulty reconciling or finding an appropriate analogy for in classical terms: that the phenomenon in question, whatever it may be, is genuinely random. That is to say, the exact, actual result has no identifiable cause. The notion of randomness, to me, has always seemed like an idealisation: we create a situation in which an event has no actual cause, and therefore the occurrence of which can't be exactly predicted, and apply this model to situations in which we have insufficient information or methodology to obtain a perfect prediction. I wouldn't call such a situation "genuine randomness" because we can identify factors which contribute to causing the result, but the model fits well enough I suppose. Problem is, I can't think of any classical situations in which this notion of genuine randomness actually applies. If you consider, for example, a computerised random number generator, it can generate numbers that are approximately genuinely random very well in many cases, but it always needs a seed of some kind: an example of the cause-and-effect logic I've come to believe is necessary at a classical level. So, finally, the question(s): a good place to start would certainly be, am I just interpreting the information wrong? Do we know for sure that quantum mechanics obeys this genuine-randomness-dependent behaviour? If not, then what do we suppose determines the behaviour of quantum mechanical phenomena? If so, then how is it that the behaviour is determined without a cause? As always, any insight would be much appreciated. This has me quite puzzled.