© picture taken by A.C.T. Wu (Univ. of Michigan) at the 1999 Yang Retirement Symposium at Stony Brook, Courtesy of AIP, Emilio Segrè Visual Archives.

At the Brookhaven National Laboratory in 1954, Chen-Ning Yang and Robert Mills created a mathematical construct that lay the groundwork for future efforts to unify the forces of nature. The Yang-Mills theory generalized QED to have more complicated force carriers—ones that interact with each other—in a purely theoretical construct. In the 1960s and beyond the theory proved invaluable to physicists who eventually won Nobel Prizes for their work in uniting electromagnetism and the weak force and understanding the strong force. (Unit: 2)