According to Albert Einstein time travel is possible, but you can only travel forward in time.
If a spaceship is traveling at the speed of light, time slows down for the spaceship and its passengers.
Space travelers who travel to the nearest star system and return to Earth at this speed might have a few years pass by on the ship’s calendar, but when they return to Earth they will find that a century has passed.
They will have traveled forward in time.
According to Einstein, even time is relative; the only constant is the speed of light.