While his physical theories and experiments were an impenetrable mystery to his second wife, Elsa, she often expressed a desire to learn. "Couldn't you tell me a little about your work?" she asked one day. "People talk a lot about it, and I appear so stupid when I say I know nothing." Einstein, after a moment's thought, produced a curious solution to her human problem: "If people ask," he advised, "tell them you know all about it, but can't tell them, as it is a great secret!"