Most of us know of atoms and germs only by hearsay, and would be embarrassingly unable to give a good answer if a Martian anthropologist asked us how we knew that there are such things—since you can’t see them or hear them or taste them or feel them. If pressed, most of us would probably concoct some seriously mistaken lore about these invisible (but important!) things. We’re not the experts—we just go along with “what everybody knows,” which is just what the tribal people do. It happens that their experts have got it wrong.
