Gravity: we barely ever think about it, at least until we slip on ice or stumble on the stairs. Of course, we know that gravity does far more than make things fall down. It governs the motion of planets around the Sun, holds galaxies together and determines the structure of the universe itself.
The modern theory of gravity is one of the most successful theories we have. At the same time, we still don't know everything about gravity, including the exact way it fits in with the other fundamental forces. But here are six weighty facts we do know about gravity.