What does it mean "to prove to exist"? empirically? How do we measure 'will' empirically (let alone qualify it as "free").Whose definition of "free will" do we use in this dilemma? Consider the thought experiment, if we were to make 1000 thousand "copies" of our universe and observe the events in each of those universes, the determinism supporter will say that the universes will be exactly the same (all future events included). This problem is quite complex, and that is why I don't feel like your statement is correct. For the traditional objections to determinism please see
this link. Philosophers have been arguing this for ages, I personally think it comes down to your worldview (if you are a materialistic, you will hold that everything is a presupposed sequence of chemical interactions, including will/choice. If you are dualist, like me, you will think differently).
Since you posted this in a religious debate dir, I will try and answer this question from a Hindu perceptive. Note, my other Hindu brothers and sisters may differ, here (because Hinduism is an umbrella of philosophies). Now, I believe in dualism, which in essentially means that consciousness and its byproducts (i.e the intellect, ability to will,desire,act. I will call this the "mind") are not products of material elements (chemicals), but rather a non-physical entity. While both interact in many ways, they are non-identical and have separate functions. Therefore while genetics and even environmental factors may influence the mind, the mind is still independent in its desire to will. While I believe that the Will is not "free" in the sense that there are
no tendencies to will/desire/choose in certain ways, the mind still has a ability to exercise some degree of choice that is not dependent on genetics and/or the environment.
Dualism asserts that the very desire to will arises not from chemical interactions within the brain, but another entity (which we call the
atma or soul). Since, this entity is not dependent on genetics and the environment and separate from them, it holds that will is not deterministic. However, neither is this will free, because our body (which is composed of genetics and environment) may influence the mind to act in certain ways. This is essentially a form of compatibilism. Quoting from an article about this topic (
Vedic view on free-will):
"The Vedic view about free will is that there is a soul which makes choices. The soul is transcendent and cannot be measured by material measurements; however, its presence can be detected by the
consequences it creates on its own experiences. To validate these consequences, we need a law that makes accurate predictions, and this law is called the law of
karma. It is as much a natural law as other laws in science, although it deals in truth conditions, and not meanings (or physical states).
For instance, if you are driving from home to work, and there are many possible routes that you could take, the selection of these routes appears to be a choice. However, the critic of choice argues that this selection is subject to
constraints such as the time you start, the time you want to arrive, the amount of speed you would like to drive at, the errands you would want to perform on the way, other co-passengers you might be picking on the way, the level of road rage you are prepared to deal with, etc. Once you take these factors into account, the choice is no longer free. The problem of choice essentially reduces to a mathematical
optimization problem, such as the Traveling Salesman Problem.
This criticism is not flawed, but it misses a key point, namely that which factors need to be optimized is not given by the reasoning itself. Furthermore, within optimization which things have to be maximized or minimized isn’t given. In short, once you define the problem to be solved, the solution is mathematical and rational. But how do you know which problem you are going to solve? The car by itself doesn’t have the problem of choosing a route. Then why do
we have that problem?" "
I also wrote a bit about this in the topic on free will on the Hinduism directory (check that out too for some arguements):