Which of the following physicists did NOT work on the Manhattan project?

The story behind the answer

Murray Gell-Mann did not work on the Manhattan Project; he was a teenager during World War II and later became famous for introducing the quark model of particle physics, winning the 1969 Nobel Prize. By contrast, J. Robert Oppenheimer was the scientific director at Los Alamos, Richard Feynman was a young physicist handling calculations and safety issues, and John von Neumann contributed decisive mathematics to implosion design and shock-wave theory—key to the plutonium bomb.

The Manhattan Project (1942–1945) built the first nuclear weapons, mobilizing top scientists across physics, math, and engineering. To remember: Gell-Mann = quarks, not bombs; Oppenheimer, Feynman, and von Neumann were central to the wartime atomic effort.