Is probability in quantum physics just an assumption? In case of classic physics we can determine strict position of any body at any time by given initial conditions using laws such as Newton’s second law.
In case of quantum physics we are talking only about the possibility of finding some object at some point of space. For example we can only calculate probability of finding electron at some distance from nuclear.
If to consider the electrons case, it seems like the processes that go there are so tiny and so fast, so people just does not have technologies and knowledges to measure them, so they invented the way to describe it only by probability, based on the experimental measurements. Possibly, before the classic physics was created, some people also described macro events using probabilities.
I have always been wondering is the fact we using probability instead of specific value is just because we do not understand, we do not know the way how to calculate the exact values, or in nature there indeed exists something random, that could be described only by probability?
 A: This is an interesting question. To some extent it is somewhat philosophical - is there true randomness? Here is my take on the question.
As of now, the best theory to describe the way our universe works at the smallest scale is through Quantum Physics. Quantum physics is inherently random. This has been found through numerous experiments.
For example, the famous Heisenberg's Uncertainty Principle is not an experimental error or inadequacy of our modern day technology in measuring accurate calculations. Rather, it is a fundamental uncertainty and unpredictability of our universe which gives rise to this randomness. The more we try to make accurate measurements of either position or momentum, the more uncertain we are about the other variable. This fact has been proven through scientific experiments [and again I emphasize, it is due to the fundamental randomness in our nature and not because of our inadequate technology].
The double slit experiment also illustrates the unpredictability of individual behavior. In addition, it raises an interesting observation that despite the unpredictability of individual behavior, ensemble behavior can still be determined precisely. This is a dichotomy that exists beyond quantum mechanics. In thermodynamics, group behavior can be predictable and deterministic according to a set of well defined equations. However, each individual element in the system is random and unpredictable. For a deeper understanding into this dichotomy, check out this interesting article: https://www.quantamagazine.org/how-randomness-can-arise-from-determinism-20191014/
It is not easy wrapping your head around this idea. Even Einstein himself struggled with seeing the laws of nature as random as seen from his highly popularized quote "God does not play dice with the Universe". Hope this help shed some light and perspective on the issue. Stay curious!
A: There is something that is only described by probability: it's the square of the wave function. The wave function itself isn't probability, it's a probability amplitude (that is: the square root of a probability times a complex phase factor that is unchanged by a global phase rotation everywhere)...which if kind of...not classical.
