Free will is one of the easiest hard questions, as millennia-old philosophical dilemmas go. Though this impossible question is generally considered fully and completely dissolved on Less Wrong, aspiring reductionists should try to solve it on their own.
Such questions must be dissolved. Bad things happen when you try to answer them. It inevitably generates the worst sort of Mysterious Answer to a Mysterious Question: The one where you come up with seemingly strong arguments for your Mysterious Answer, but the "answer" doesn't let you make any new predictions even in retrospect, and the phenomenon still possesses the same sacred inexplicability that it had at the start.
Mystery exists in the mind, not in reality. If I am ignorant about a phenomenon, that is a fact about my state of mind, not a fact about the phenomenon itself. All the more so, if it seems like no possible answer can exist: Confusion exists in the map, not in the territory. Unanswerable questions do not mark places where magic enters the universe. They mark places where your mind runs skew to reality.
On the contrary, people often insist that determinism would indeed make choice futile even in such clear-cut situations. Accordingly, many reject determinism and invent an incoherent ‘‘free will’’ to preserve a sense of efficacy of their actions. Even those who explicitly disavow free will may still need to pretend other- wise in order to salvage the feeling that choices matter (for example, Minsky advocates such a subterfuge in The Society of Mind, p. 307). When I reflect that the future and past alike sit immutably in spacetime, I do feel an uncomfortable challenge to the notion that my choices make a difference, even in the most clear-cut instances.
I don’t have any position on free will or the mind/body problem. I don’t understand them. I doubt anyone else does either!