Abstract
We just described two theories of elementary interactions: quantum chromodynamics (QCD), the theory of strong interactions, and quantum electroweakdynamics (QEWD), the unified theory of the electromagnetic and weak interactions. Both of these theories are in excellent agreement with observation, both are gauge theories, and each is the crowning achievement of many years of work. The question that of course comes to mind now is: Can these two theories be unified into a single theory? It is important to emphasize that we want a unification of them more or less the way they are, and not a new theory that replaces them. Individually they are excellent theories, and we certainly do not want to throw them away. Since both are gauge theories, our new theory would also have to be a gauge theory.
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