An identical twin in space illustrates Einstein's special  theory of relativity.

The Twin Paradox

Can a cat be both alive and dead? Can a computer think? How does a tortoise beat Achilles in a race? Voiced by comedian David Mitchell, these fast-paced animations explain six famous thought experiments, from the ancient Greeks to Albert Einstein, that have changed the way we see the world. Subjects as vast as time travel, infinity, quantum mechanics and artificial intelligence, are squeezed into 60-second clips that will tickle your funny bone and blow your mind.