In 1961 Glashow proposed a gauge theory to unify the weak and electromagnetic interactions; this was based on a gauge group that was a product of SU(2) and U(1) but with massive gauge bosons mediating the weak interactions, in accord with the observation that weak interactions are short-range. Glashow’s theory turned out to be correct but it was not until later work by Steven Weinberg and Abdus Salam that it was realized that a gauge symmetry, being a broken symmetry, would give rise to massive gauge bosons. Glashow, Salam, and Weinberg shared the 1979 Nobel Prize for physics for this work. In 1964 Glashow proposed a fourth type of quark, which he called the charm quark. In the mid-1970s he was one of the major pioneers of grand unified theories.