So that basicly means that interstellar spacetravel is not practical
Cause when you want to go to another galaxy you need to go VERY fast say 0.99 the speed of light (not 1 times cause then you transform into light
), But that causes the time to slow down for you, and thus from you perspective speed up time on earth, meaning when you come back, you aged not so much, but earth is centuries further
EDIT: also another thing I thougt about...
Speed is relative to the time it takes you to cover an amount of distance.
But because when you go very fast, time slows down, means it takes you the same time to cover a certain distance.
But again, that's something I thought would be the case, and not even sure if it's true
Let's call that "Ezra's theory of relativity
"