electroweak unification

Electroweak unification is the discovery that two of nature's forces that look utterly different — electromagnetism, which holds atoms together and is carried by the massless photon, and the weak force, which is feeble and short-ranged and carried by heavy W and Z bosons — are in fact two faces of a single underlying interaction. It is one of the crowning achievements of twentieth-century physics, on a par with Maxwell's earlier unification of electricity and magnetism.

The idea, built in the 1960s by Sheldon Glashow, Abdus Salam, and Steven Weinberg, is that at very high energies the photon and the W and Z bosons are siblings, governed by one symmetry and one underlying strength. At the everyday low energies we live in, that symmetry is hidden: the W and Z have acquired large masses while the photon stays massless, so the single force fractures into the two we observe. Raise the energy high enough — as colliders do — and the differences melt away, revealing the family resemblance. The theory wove the weak and electromagnetic forces into one mathematical framework and made bold, testable predictions.

Those predictions came true spectacularly. The theory required a brand-new kind of weak interaction (neutral currents via the Z), found in 1973, and it predicted the masses of the W and Z bosons before they were discovered in 1983 — and the masses matched. Glashow, Salam, and Weinberg shared the 1979 Nobel Prize. Electroweak unification is a pillar of the Standard Model and the template physicists hope to follow toward unifying the strong force too, though that grander dream remains unproven.