Nobody knows what the heck it is, but it is officially repulsive. And man is it powerful! More powerful than gravity, even.While gravity holds things together at the local level (and by local I mean within galaxies and even between them, forming galactic clusters) some unknown force is working behind the scenes and across the universe to pull everything apart. Scientists have only come to realize this dark force in recent years, by discovering that the universe is expanding at an ever-increasing pace.

Having no clue what it is, they've labeled it dark energy.

The past year was a good one for proving that dark energy is at work. Calculations have been refined: The repulsive force dominates the universe, comprising 65 percent of its makeup.

(Similarly unseen and exotic dark matter makes up 30 percent of the universe, leaving us with a universe that contains just 5 percent normal matter and energy.)