It's easy to take corned beef sandwiches for granted. There's no mystery about them. They simply exist.
But corned beef sandwiches, along with everything else in the universe, raise a critical question in the minds of physicists: Why do they exist?
In the earliest moments of the universe, energy turned into matter. But matter comes in two forms, matter and antimatter. And when a particle of matter encounters a particle of antimatter, they annihilate each other — and all you're left with is light.