Historians are always interested in how things change over time, and it helps for the survival of the profession that most things do. But there are certain moments in history when things don't just change, they change so radically that it feels like going over a waterfall in a kayak.

How do these moments of change come about? How can an entire social order change in a decade or two? And how does radical change in the social order not only occur, but succeed?

My guest David Potter untangles these questions in his new book Disruption: Why Things Change. David Potter is Francis W. Kelsey Collegiate Professor of Greek and Roman History and Arthur F. Thurnau Professor of Greek and Latin at the University of Michigan, making him a man with at least two chairs in his office. Previously he has written on prophecy and history, the origins of the Roman Empire, on sport in the Greco-Roman world—and many other books.