The Universe, according to cosmologists, is divided into three unequal portions. In the big bargain bin near the exit aisle, you'll find dark energy. Dark energy's job is to push everything apart. There's lots of it, and no one knows why. Then, next to dark energy, on a display shelf, you'll find a smaller amount of dark matter. Regular matter, the stuff you and I can see, is tucked off to the side: small and barely noticeable.