Sheldon Glashow studied under Julian Schwinger at Harvard and developed important theories of electromagnetic and nuclear particle interaction, which laid the groundwork for the next generation of research on quarks and leptons. In 1961, he published a theory extending electroweak unification models, a concept which was later developed further by Abdus Salam and a former high school classmate of Glashow's, Steven Weinberg. For this work, these three men shared the Nobel Prize for Physics in 1979. In 1964 with James Bjorken, Glashow predicted the existence of the charm quark, an important idea in the theory of quarks, and in 1973 with physicist Howard Georgi, he proposed the first grand unified theory. He is among the most outspoken opponents of string theory, which he has called "a new version of medieval theology".