How come we live in 3 dimensions? Not 2, not 4, not 7.3, but 3? Is there something special about that number of dimensions? This video tries to explain.

While there's no obvious answer—it's kinda just the case—there are some compelling theories as to why our universe works best in 3D. But I'll let New Scientist explain—they can do a far better job than I. [New Scientist]