When everything follows strict laws in the universe, where does probability come from? I am told that we can't predict whether we shall get a head or tail. We can only say that for an unbiased coin there is 50% probability for either. But coin is not case of Quantum Physics!
I have heard people say that such and such cannot be predicted, but it is obvious that if we have enough information about the event we can use the laws of universe and predict what will happen. So, is it possible to predict whether we get a head or tail in practice? I know we shall have to take into consideration the angular momentum of the coin, law of gravity, friction with air among many other things which I can't think of right now, ah perhaps the friction of the surface and how much bouncy it is.
 A: If you get a head or tail for a coin, it's not quantum mechanics QM). The fall of the coin is influenced by the small details of how you tossed it, or if you are out of the house, of the wind direction and other factors. One who knows all these factors can calculate precisely on which face the coin would fall. So, for macroscopic bodies, governed by Newtonian mechanics, the movement is fully predictable.
It's not the situation in QM. Thus far, the microscopic world seems as purely non-deterministic. The Schrodinger equation gives us the wave-function, and the wave-function gives probabilities of obtaining one result or another, but for the moment, we are unable to predict individual results.
So, in classical mechanics probabilities come from lack of knowledge, i.e. when we cannot measure exactly all the factors that influence the evolution of a system.
In QM, the probabilities come, so it seems, because the micro-world is not deterministic, and whatever we can calculate is the wave-function.
