Facts change all the time. Smoking has gone from doctor-recommended to deadly. We used to think Earth was the center of the universe and that Pluto was a planet. For decades we were convinced that the brontosaurus was a real dinosaur. In short, what we know about the world is constantly changing. But it turns out there's an order to the state of knowledge, an explanation for how we know what we know. Knowledge in most fields evolves systematically and predictably, and this evolution unfolds in a fascinating way that can have a powerful impact on our lives.

BIOGRAPHY Samuel Arbesman is an applied mathematician and network scientist. He is a senior scholar at the Ewing Marion Kauffman Foundation and a fellow at the Institute for Quantitative Social Science at Harvard University. In addition, he writes for popular audiences as a contributor to Wired, and his essays about math and science have appeared in such places as the New York Times, The Atlantic and the Ideas section of the Boston Globe. Arbesman's first book about how knowledge changes over time, "The Half-Life of Facts" (Current/Penguin), will be published in September 2012.

Before joining the Kauffman Foundation, Arbesman was a research fellow in the Department of Health Care Policy at Harvard Medical School, and he completed a Ph.D. in computational biology at Cornell University in 2008.

www.arbesman.net