In this MinutePhysics video, the channel takes on the famous “twins paradox,” which provides a hypothetical situation to explain special relativity. In the twins scenario, one twin stays in the same place as the other flies out into space in a rocket ship, only to turn around and come back. We already know that moving things experience time more slowly, so the twin staying on Earth may assume that they are older than the astronaut twin. However, the twin on the rocket ship “sees” the Earth and the other twin moving.
As the twins watch each other, time seems to be faster to each observer relative to the other, yet we already know that the moving twin experiences less time because of the motion. This is the same reason that atomic clocks on satellites and on Earth register slightly different times. So how is it possible that time can appear to be faster for both of two different twins at the same time? And of the two twins, one Earthbound and the other exploring the galaxy, who is actually older?
MinutePhysics explains that the mystery is solved by Lorentz transformations, and provides a great way to think about the problem visually. Spoiler alert: riding on rocket ships can keep you younger.