Why does he do it?
He didn't open a parachute at the end (or do anything else to stop his fall), so was he committing suicide? That doesn't make sense, because too many people didn't bother to stop him. What was going on?
Also, based on the book at the end, it looks like there are two cities on the inside of a large sphere, each upside-down from the other's perspective. Also, it looks like gravity pulls on people in different directions based on the city they are from. This means that if an inhabitant of one city went to the other, he would fall up from that city (and then back down towards his own).
Is this correct?