Are there parallel universes? Universes in which, rather than reading this article, you are still asleep; in which you are happier, unhappier, richer, poorer, or even dead? The answer is "possibly". It's a controversial claim but one that has won more and more followers over the last few decades.
Some general ideas in very few words and without equations.
At the heart of modern physics lurks a terrible puzzle: the two main theories that describe the world we live in just won't fit together.