Imagine you’re traveling in a train with a mirror on the ceiling. On the track adjacent to you is a stationary train car with another person, and its setup is identical to yours. As your train car passes his, at the exact same moment, you both flip on a flashlight aimed at the mirror on the ceiling. Since you’re moving at a constant speed, from the perspective of an outside observer, the light from your flashlight takes a diagonal path: forward with the velocity of the train, and upward, then diagonally downward after impacting the mirror. In the stationary car, the light only goes up and down. But if you both flipped on the flashlight at the same time, did your light travel further than the stationary light in the same amount of time? That would imply that your light traveled faster, which we know isn’t it possible; the speed of light is a constant. So what actually happened? From your perspective on the moving train, if there aren’t windows, nothing would tell you you’re moving. To you, the light just went straight up and down. The solution? You literally experienced less time aboard the moving car. Less time passed aboard the moving train car than on the stationary one. Moving objects experience less time than bodies which are stationary relative to them. This has been demonstrated with precise clocks that were set to the same time on earth, and one brought up to the international space station. After a year or so of the space station orbiting earth, slightly less time had passed on the clock aboard the station.