When we decide to do something and then do it, we feel we have total control of what we do. Do we?
Free Will is a funny thing because if an effect always follows a physical cause then a physical system should always be reacting to forces following a strict set of inviolable laws. No amount of wishful thinking could alter that. And yet that is what Free Will seems to accomplish.
If I think "should I move my arm or shouldn't I?" Then I decide to move it and I act on that decision and move the arm. This may sound trivial but it is a mystery.
Disturbingly, some experiments seem to indicate that Free Will may be an illusion. That the arm starts moving BEFORE we Will it to move.
If that's not scary, what is?
If Free Will turns out to be an illusion then consciousness has no influence on physical processes. It is merely an observer.
If Free Will is real, then the physical system gives rise to consciousness which then, independently of the system, can make decisions which can somehow influence the system. But how can this immaterial thing called consciousness affect the material system? What sort of interface is there between consciousness and matter?
Free Will is often used in arguments against the existence of God. At least of a Christian God. Free Will and an omniscient God are contradictory concepts because if God knows everything we will ever do, then we really have no Free Will, yet we are supposed to have freedom of choice.
Personally, I think Free Will is real. I have thought about it long and hard. I have examined this by introspection and by observing the world, and I think it's just too darn complicated to come up with simple, logical explanations for the feeling of Free Will and for what we observe. It flawlessly acts, long and short term.
And because Free Will is real, the universe cannot be deterministic.
This may sound like gobbledygook to some of you, but I think consciousness is a fundamental entity which, among other things, has the ability to "harness" quantum uncertainties to produce macroscopic changes.
I think the physical universe, stripped of all consciousness, may or may not be deterministic. So far everything seems to indicate that quantum uncertainties are real. That there are no hidden variables. But I don't think we have erased the last little bit of doubt.
I think we don't know enough about the universe or about consciousness. When we do, maybe we'll understand Free Will.