By comparison, dark energy makes dark matter look very simple and well understood: at least we know that it is matter. Dark energy could almost literally be anything. If a scientist from five hundred years in the future looked back in time at us, our current ideas about dark energy might seem hilarious to her, the way early men and women explaining the stars, the Sun, or the weather as being the result of gods dressed in robes seems quaint to us now. We know that there are powerful forces out there beyond our comprehension and that we have much to learn about the universe.
