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.
Check out the first video from The Open University's YouTube channel below. Then jump in to view all the videos.
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That isn't the twin paradox
There is no paradox in the scenario given--it may seem odd to those who aren't familiar with special relativity, but there is no inherent contradiction.
What IS an apparent paradox is that the twin who stays at home, Al, is the one who is moving in the frame of reference of Bert, the twin in the spaceship. If Al is the one who appears to Bert to be moving at nearly the speed of light, then it is Al's clock that slows down (and it actually does, to Bert). If this is true, then which twin actually ages faster?
The paradox is solved by the fact that Bert has to accelerate when he leaves Earth, accelerate again when he has to stop and turn around, and finally accelerate once more when he has to stop at Earth. This isn't special relativity, it is general relativity, and Einstein didn't come up with that until more than 10 years after he discovered special relativity.