Ja n 20 04 The Making of the Standard Model

I have been asked to review the history of the formation of the Standard Model. It is natural to tell this story as a sequence of brilliant ideas and experiments, but here I will also talk about some of the misunderstandings and false starts that went along with this progress, and why some steps were not taken until long after they became possible. The study of what was not understood by scientists, or was understood wrongly, seems to me often the most interesting part of the history of science. Anyway, it is an aspect of the Standard Model with which I am very familiar, for as you will see in this talk, I shared in many of these misunderstandings. I’ll begin by taking you back before the Standard Model to the 1950’s. It was a time of frustration and confusion. The success of quantum electrodynamics in the late 1940s had produced a boom in elementary particle theory, and then the market crashed. It was realized that the four-fermion theory of weak interactions had infinities that could not be eliminated by the technique of renormalization, which had worked so brilliantly in electrodynamics. The four-fermion theory was perfectly good as a lowest-order approximation, but when you tried to push it to the next order of perturbation theory you encountered unremovable infinities. The theory of strong interactions had a different problem; there was no difficulty in constructing renormalizable theories of the strong interactions like the original Yukawa theory but, because the strong interactions are strong, perturbation theory was useless, and one could do no practical calculations with these theories. A deeper problem with our understanding of both the weak and the strong interactions was that there was no rationale for any of these theories. The weak interaction theory was simply cobbled together to fit what experimen-