Time is not relative.
Excuse me, it most certainly IS!! It’s a thing called “time dilation” and it’s been demonstrated more then a few times (lol). Like, people that have traveled on rockets and the Space Shuttle and such, going at a high rate of speed, come back to Earth and their clocks don’t show as much time passed as clocks on Earth did. Granted, it’s only a difference of fractions of a second, I think, but it’s there. If we eventually develop the technology to have spaceships that travel at a significant fraction of the speed of light, both the people on the spaceship and people back on Earth would know.
One of my favorite songs by my favorite band, Queen, “’39″, is about just that. Space travelers who depart their home planet “in the year of ‘39″ and come back “in the year of ‘39″ a hundred years later. So a hundred years have passed for the people at home, but only one year went by for them. I actually did the calculations for that one time, and if I did it right, the “volunteers” would have had to been going at over 90% of lightspeed, which is completely beyond our technology right now of course….but excuse me for imagining that it COULD happen one day, lol :D
Also, the song was written by Brian May, who has an actual PhD in astrophysics, so he knows what he’s talking about!