Victor Weisskopf in personal letter to Hans Bethe (1950s). "We used to sit in the cafes of Copenhagen and debate the nature of reality as if we were gods. Then the dark years came, and the cafes emptied. Some of us fled, some of us hid, and some of us built bombs. Now, we sit in these air-conditioned American universities, given every honor, while the bones of our friends are buried under the rubble of Europe. Every time I pick up a piece of chalk, I feel like a ghost who escaped a shipwreck, wondering why I was allowed to survive just to write numbers on a board."