Renormalization has become perhaps the single most important advance in theoretical physics in 50 years

Charlie Wood in Quanta:

In the 1940s, trailblazing physicists stumbled upon the next layer of reality. Particles were out, and fields — expansive, undulating entities that fill space like an ocean — were in. One ripple in a field would be an electron, another a photon, and interactions between them seemed to explain all electromagnetic events.

There was just one problem: The theory was glued together with hopes and prayers. Only by using a technique dubbed “renormalization,” which involved carefully concealing infinite quantities, could researchers sidestep bogus predictions. The process worked, but even those developing the theory suspected it might be a house of cards resting on a tortured mathematical trick.

“It is what I would call a dippy process,” Richard Feynman later wrote. “Having to resort to such hocus-pocus has prevented us from proving that the theory of quantum electrodynamics is mathematically self-consistent.”

Justification came decades later from a seemingly unrelated branch of physics.

More here.