Why will he read that the clock at the finish line is years ahead of his own clock, even if it is running the same speed as the one at the starting line? If there was a person in the rest frame, he would predict that time went slower for the person in the space ship. If this was true as well, why isn't he the one who is younger than the person who traveled?
The theory says that time goes slower for both the person in the space ship and in the rest frame. It says that time goes slower in rest frame relative to space ship frame, and time goes slower in space ship frame relative to rest frame. This can't be true if there is only one truth. Also when the two frames arrives at equal velocity, they predict only one truth. However it seems like some kind of acceleration is necessary for them to predict and arrive at the same truth. Thus I am curious about the role of acceleration as well.