In physics, we like theories that are simple and broad-ranging. By “simple,” physicists usually mean a mathematical theory that rests on as few postulates as possible; by “broad-ranging,” we mean theories that can describe a wide class of phenomena, even when apparently not related. A quintessential example is Einstein’s theory of general relativity. Resting on a handful of simple principles, it successfully describes planetary orbits in this (and any) solar system, black holes, gravitational waves, and the expansion of the universe.
When theories are simple and broad-ranging, physicists call them “beautiful.” Nobel laureates Steven Weinberg and Frank Wilczek have compared such theories with Mozart’s musical compositions, masterful and perfect constructions where, as if by divine revelation, every note is where it should be: Take one out and the composition crumbles. Likewise, beautiful theories have a mathematical integrity that seems to be revealing something deep about nature, a sort of hidden code of Creation: From the very large to the very small, the universe has many layers, each built upon its own mathematical description. Are these not parts of a larger composition, a single unifying tune resonating through all of nature?