Can anyone find a hole in this argument against free will?

I would really like to believe that we have free will, but this argument is very convincing:

1. The universe is composed of subatomic particles.
2. The trajectory each of those particles was set in motion by the Big Bang.
3. This trajectory, combined with the laws governing the interactions between said particles, determine all their present and possible movements.
4. The human brain is composed of particles, which are in motion.
5. Therefore, all the interactions in the human brain which govern behavior are determined by the interactions of particles, which are in turn determined by the aforementioned forces.
6. Therefore, everything you do, from whether you have Captain Crunch for breakfast on Thursday, to whether you accept a job, to whether to move your arm a little to the left was predetermined at the moment of the big bang.

Without recourse to God or the idea of a soul (I’ve had that discussion at least ten thousand times), can you find any flaws in the above argument?