WSJ: When you discussed making "The Road" into a movie with John, did he press you on what had caused the disaster in the story?
CM: A lot of people ask me. I don't have an opinion. At the Santa Fe Institute I'm with scientists of all disciplines, and some of them in geology said it looked like a meteor to them. But it could be anything—volcanic activity or it could be nuclear war. It is not really important. The whole thing now is, what do you do? The last time the caldera in Yellowstone blew, the entire North American continent was under about a foot of ash. People who've gone diving in Yellowstone Lake say that there is a bulge in the floor that is now about 100 feet high and the whole thing is just sort of pulsing. From different people you get different answers, but it could go in another three to four thousand years or it could go on Thursday. No one knows.