Q: These are Fermi questions—made famous by the physicist Enrico Fermi: one question he asked physics students was how many piano tuners are there in Chicago? He also estimated the blast from an atom bomb by how far some scraps of paper he threw up in the air were displaced from his observation point. These are common types of questions in physics PhD qualifying exams. Do you give Fermi any credit? – Dr J
A: Fermi was a master of this kind of analysis. The Nobel Prize-winning physicist Richard Feynman, who was himself a master of it, said (in his book, Surely You’re Joking, Mr. Feynman!) that Fermi was even better at it than he was.
How did Fermi become so skilled? Partly from the way he tried to understand physics. In the years just following World War II, physics underwent huge changes, many due to the development of quantum electrodynamics. Because Europe was physically devastated by the war, and because many of the leading physicists fled Europe for America, America became the scientific center of the world. Leading centers in America included Berkeley and Caltech on the West Coast and Princeton and Harvard on the East Coast. Conferences on both coasts meant lots of cross-country travel—which in those days meant taking the train or driving. On those trips, Fermi would sit in the back of the car and think about physics. He would pick one area of physics and review in his mind all that he understood about it, and try to figure out ways of thinking that made the results obvious. Before the distractions of email, the Internet, and cell phones were invented, that meant days of concentration and deliberate practice (for more on deliberate practice, see the above answer to the questions about improving one’s educated guessing).
--Sanjoy Mahajan, Freakonomics blog, on a benefit of uninterrupted thinking