  Pythagoras' theorem lies at the heart of physics as well as mathematics, yet
its historical origins are obscure. We highlight a purely pictorial,
gestalt-like proof that may have originated during the Zhou Dynasty.
Generalizations of the Pythagorean theorem to three, four and more dimensions
undergird fundamental laws including the energy-momentum relation of particle
physics and the field equations of general relativity, and may hint at future
unified theories. The "pre-mathematical" nature of this theorem lends support
to the Eddingtonian view that "the stuff of the world is mind-stuff."
