"My own feeling is this: mathematics and computer science are the two unnatural sciences, the things that are man-made. We get to set up the rules so it doesn't matter the way the universe works – we create our own universe... And I feel strongly that they are different, but I tried to convince Bill Thurston and he disagreed with me. My opinion though is I can feel rather strongly when I am wearing my mathematician's cloak versus when I am wearing my computer scientist's cap."