According to M-theory, the universe has eleven dimensions

In 1995 the physicist Edward Witten proposed that the five competing versions of string theory were really views of one underlying theory, which he called M-theory. It only works if spacetime has exactly eleven dimensions: the three we walk around in, time, and seven more curled up too small to see.

Witten said the M could stand for “magic, mystery or membrane”, as you like. And eleven is not an arbitrary choice: in 1978 the physicist Werner Nahm showed that eleven is the largest number of dimensions in which a theory of this kind can work at all. Physics, it seems, also goes up to eleven.

Nobody has yet found a way to test M-theory. But if it is right, then everything, including the clock you keep glancing at, is built on an eleven.