"... Broken symmetries in physics go back to work in the 1950s on superconductivity. From the modern perspective (or at least, a modern perspective) a superconductor is nothing but a place where electromagnetic gauge invariance is spontaneously broken to a discrete subgroup, and from this assumption one can derive all the exact properties of superconductors, such as the Meissner effect, persistent currents, flux quantization, and the formula for the Josephson frequency."