When I was in high school, I read a brief book excerpt in Time about Robert Oppenheimer, the physicist who led the Manhattan Project and who was later accused of passing nuclear secrets to the USSR. The excerpt proved memorable because it was the first time I’d ever given a second thought to the vagaries of national security and foreign policy. Was it safer for the world to have one nuclear power or for it to have two, with the one balancing the other? And if you settled on the latter, did you have a greater moral obligation to the state or to your conscience?

As I found out later, one of the people who helped America resolve such questions was Hans Bethe. A brilliant physicist in his own right, Bethe headed the theoretical division of the Manhattan Project, and then later played an active and instrumental role in getting the Senate to ratify several arms-control treaties.

Sadly, Bethe passed away last week, at 98. If you want to learn more about one of the more interesting lives of the 20^th century, I recommend starting with his obituary in this week’s Economist.