March 24, 2010 — "Dad, I finished my homework. Why?"
The father thinks for a moment. He realizes the answer involves explaining the state of the world prior to the child doing the homework. It involves explaining the complex probabilities that combined would calculate the odds the child was going to do the homework. And it likely involved explaining quantum mechanics.
The father shrugs and says "Because you have free will, and chose to do it."
Thus was born the notion of free will, a concept to explain why we have gone down certain paths when alternatives seemed perfectly plausible. We attribute the past to free will, and we attribute the unpredictability of the future to free will as well (i.e. "we haven't decided yet").
The problem is, this is wrong. You never choose just one path to go down. In fact, you go down all the paths. The catch is you only get to observe one.
In one world the child did their homework. In another world, they didn't.
The child who did their homework will never encounter the child who didn't, but they both exist, albeit in different universes or dimensions. Both of them are left wondering why they "chose" the way they did. The reality is that they chose nothing. They're both just along for the ride.
Even the smug boy who says free will doesn't exist, is just one branch of the smug boy.