When everything follows strict laws in the universe, where does probability come from?

Question

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.

possible duplicate of Is the universe fundamentally deterministic? — ACuriousMind, Jan 07 '15 at 01:13
Probability in physics comes from us repeating the (assumed to be) same experiment over and over again and using the law of large numbers to approximate probability (which is defined axiomatically in a mathematical theory) with frequency, which is a measurable quantity in nature. — CuriousOne, Jan 07 '15 at 01:31

score 1 · Answer 1 · answered Jan 07 '15 at 02:44

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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.

answered Jan 07 '15 at 02:44

Sofia

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So what's indeterministic about the Schroedinger equation? You throw an initial state in, you get a purely deterministic final state out. You throw the linear combination of two initial states in, you get the same linear combination of their final states out. Classical mechanics doesn't nearly have such nice features. – CuriousOne Jan 07 '15 at 04:06
Did I say that Schrodinger equation is non-deterministic? – Sofia Jan 07 '15 at 04:11
" Thus far, the microscopic world seems as purely non-deterministic.". So you were not referring to the usual description of the microscopic world? – CuriousOne Jan 07 '15 at 04:14
http://en.wikipedia.org/wiki/Schr%C3%B6dinger_equation – Sofia Jan 07 '15 at 04:28

When everything follows strict laws in the universe, where does probability come from?

1 Answers1