If a friend tells you “I’ve seen a UFO!” what would you think? It might have been an alien spacecraft—or perhaps the friend was mistaken. The first possibility requires numerous unproven assumptions about extraterrestrial life; the second is consistent with what we know about human fallibility. The 14th-century Franciscan friar William of Occam was never troubled by flying saucers, but he did see the importance of eliminating unnecessary assumptions—the principle known as Occam’s Razor. It forms the central theme of Johnjoe McFadden’s “Life Is Simple,” a tour through two millennia of scientific discovery.
