Genius: The Life and Science of Richard Feynman

by James Gleick

Locks mixed human logic and mechanical logic. The designer’s strategy was constrained by the manufacturer’s convenience or the limits of the metal, as it was in so many of the bomb project’s puzzles. The official logic of a Los Alamos safe, as displayed in the dial’s numbers and hatch marks, indicated a million different combinations—three numbers from 0 to 99. Some experimentation, though, showed Feynman that the markings disguised a considerable margin of error, plus or minus two, attributable to plain mechanical slackness; if the correct number was 23, anything from 21 to 25 would work as well. When he was searching combinations systematically, therefore, he needed only to try one number in every five—0, 5, 10, 15 ... —to be sure of hitting the target. By thinking in terms of error ranges, instead of accepting the authority of the numerals on the dial, he brought a pragmatic physicist’s intuition to bear. That one insight effectively reduced the total combinations from one million to a mere eight thousand, almost few enough to try, given a few hours.