Today we climb a narrow stair in Cambridge, run a palm along a scarred table, and pause at a pinhole cut in a shutter that turns noon into a blade. On the table lies a prism, a small triangle of glass that, to most hands, would be a trinket for teasing color out of sunlight. In these hands it becomes a witness. A beam slants in, strikes the glass, and falls on the opposite wall as a band of colors, edged cleanly enough that you can count where red surrenders to orange and where violet stops pretending to be blue. The man who set this up is young, intense, easily wounded, and immoderately patient. The room smells faintly of smoke and ground glass. He is Isaac Newton, and in this plain light he will teach a civilization to speak a new language—calculus for change, experiment for certainty, gravitation for cause—and he will train it to distrust even ...