1When astronomers carefully measured distant explosions of dying stars, they discovered something that nobody had ever expected.
2The universe is not simply growing; it is actually growing faster and faster as time goes by.
3To explain this strange behaviour, scientists proposed the existence of a mysterious force which they called dark energy.
4Nobody knows what dark energy really is, yet it seems to make up most of the universe.
5All the stars, planets, and people we have ever known form only a tiny fraction of everything.
6Some researchers believe dark energy is a basic property of empty space itself, constantly pushing the cosmos apart.
7Others suspect that our best theory of gravity may simply be wrong on the largest scales.
8New space telescopes will map millions of galaxies and test these competing ideas over the coming decade.
9Whatever the answer turns out to be, it will rewrite the textbooks of physics once again.
10For now, the most powerful force shaping the entire universe remains a complete and utterly fascinating mystery.