“There are known knowns; there are things we know we know. We also know there are known unknowns; that is to say, we know there are some things we do not know. But there are also unknown unknowns — the ones we don’t know we don’t know.” — Donald Rumsfeld, secretary of defense, 2002 When I was growing up during the Cold War, the news media would occasionally report on the Doomsday Clock. This was an estimate of the risk of nuclear war maintained by atomic scientists at the University of Chicago. During an international crisis they would move the …