Time dilation is possibly the weirdest part of Einstein’s Theory of Special Relativity. According to time dilation, the faster you travel, the slower your time moves. But why does this happen? It’s actually a result of the fact that light always travels at the same speed, regardless of one’s frame of reference.
The first of these two videos describes how the constancy of the speed of light implies the existence of time dilation. The second video explains how time dilation allows for intergalactic travel, and in this case to the Andromeda Galaxy.
Time Dilation Explained:
Intergalactic Travel & Time Dilation: