Fermi tried to inculcate this facility in his students. He would demand of them, without warning, answers to seemingly unanswerable questions. How many grains of sand are there on the world’s beaches? How far can a crow fly without stopping? How many atoms of Caesar’s last breath do you inhale with each lungful of air? Such “Fermi questions” (as they are now known) required students to draw upon their understanding of the world and their everyday experience and make rough approximations, rather than rely on bookwork or prior knowledge.
