Also a "stationary" world appears to contract in the direction one is going, and time appears to slow down on it. But to someone on that world, it's the gotta-go-fast racer who's contracting in the direction of travel and who has the slowed down time. Some weird thing I don't know much about happens with acceleration and deceleration so the fastinator can experience a smaller amount of time in total than on the world they passed. It's how
a ship can get to the center of the galaxy -
by accelerating and slowing down at 1 g continually - in about 20 years, but with about 30,000 years over here.