Yesterday marked the passing of Hans Bethe, the last of the great physicists from the Manhattan Project. I had the privilege of seeing Bethe speak twice when I was a graduate student at MIT in the late 1980's. Bethe was in his early eighties at the time and was still sharp as a tack. One talk was on neutrino oscillations and the other was on disarmament policy. Both talks were well thought out and exhibited the clear thinking that marked Bethe's career.
The amazing thing about Bethe was that he remained relevant for much of the twentieth century. Bethe was held in the highest regard by both his peers and the political establishment throughout his life. He was Sommerfeld's graduate student. His Nobel Prize work on energy production in stars was done in 1938. He played an important role in the development of QED and was Richard Feynman's mentor. He was instrumental in pushing for arms limitation treaties and derailing the Star Wars space-based anti-missile defense during the Reagan administration. He and John Bahcall wrote a landmark paper outlining how the solar neutrino problem was finally solved in 1990. He was a true giant among giants.