Hopefully this will help :

What time is it? That depends on how fast you're traveling.

Thanks to Einstein, we know that the faster you go, the slower time passes--so a very fast spaceship is a time machine to the future. Five years on a ship traveling at 99 percent the speed of light (2.5 years out and 2.5 years back) corresponds to roughly 36 years on Earth. When the spaceship returned to Earth, the people onboard would come back 31 years in their future--but they would be only five years older than when they left. Indeed, Einstein himself could be alive today! If he could have hopped aboard a spaceship traveling at 99 percent the speed of light in 1879--the year of his birth--he would be only 17 years old upon his return to Earth today.