After Skool (previously) explains the concept of time dilation through colorful whiteboard animation. Citing Albert Einstein‘s Theory of Special Relativity, the animation illustrates how time is not the same for everyone, but instead measured by its observers in relation to their understood points of reference. This theory was demonstrated with a pair of atomic clocks of which only one went into space.
Such time dilation has been repeatedly demonstrated, for instance by small disparities in a pair of atomic clocks after one of them is sent on a space trip, or by clocks on the Space Shuttle running slightly slower than reference clocks on Earth, or clocks on GPS and Galileo satellites running slightly faster.