Twin paradox

The twin paradox is a thought experiment that uses time travel to explore the idea of relativity. It involves two twins, one of whom travels away from Earth in a spaceship at close to the speed of light and then returns home.

When the traveling twin returns, they find that they are much younger than their non-traveling twin. This is because when you travel close to the speed of light, time slows down for you, while the time in the rest of the world carries on at a normal rate. This is known as 'time dilation'. So, while the traveling twin only experienced a few days on their journey, much more time had passed for their twin on earth.

This experiment helps us understand the idea that time does not pass at the same rate for everyone in the universe, and that time can be changed by speed.