There are facts, and then there are facts. We expect some facts to be fluid — the population of Earth, for example — but, as it turns out, we probably shouldn’t expect anything we know to remain static. Things that feel like unalterable truths, like the number of chromosomes in human cells (which was 48, until somebody noticed it wasn’t), can suddenly shift. Author Samuel Arbesman, an applied mathematician, explores the nature of knowledge: Why it changes, how it changes, and why this is so vital for scientific exploration. Knowledge, like life itself, evolves. Science regularly revises its truths to include new discoveries. The book is also a history of the field of scientometrics, “the science of science,” a way of quantifying the growth of ideas. The author shows, too, how the principles of scientometrics can be applied to other fields. Examination of various surviving copies of Chaucer’s The Canterbury Tales, for instance, allowed researchers to track back to Chaucer’s own original version. Fascinating, engagingly written, and just mind-bending enough to spur readers to revisit their own mental catalogs of knowledge. Samuel Arbesman is a senior scholar at the Ewing Marion Kauffman Foundation and a fellow at Harvard’s Institute for Quantitative Social Science.