Edward N. Lorenz, the MIT meteorologist often called the father of chaos theory, has died of cancer at the age of 90. His 1972 AAAS talk “Predictability: Does the Flap of a Butterfly’s Wings in Brazil Set Off a Tornado in Texas?” described the idea that has since come to be known as the “butterfly effect,” in which very small changes in the initial conditions of certain classes of dynamic systems lead to profoundly different outcomes. Lorenz’s work became widely popularized with the publication of James Gleick’s 1988 book Chaos: Making a New Science.

One of Lorenz’s most recognizable demonstrations of a chaotic system was a waterwheel which alternated, seemingly randomly (but actually chaotically), from turning clockwise to turning counter-clockwise, depending on how fast it was turning and how much water was in each of the wheel’s cups. A downloadable computer simulation of the Lorenz waterwheel can be found here.

Although started in meteorology, chaos theory, the closely related complexity theory, and the more general nonlinear dynamical systems theory, have found application in a wide range of scientific disciplines. In a 1991 award ceremony for Lorenz it was claimed that chaos theory had “brought about one of the most dramatic changes in mankind’s view of nature since Sir Isaac Newton.” In psychology the idea was taken up most famously by Fred Abraham, Linda Smith, Esther Thelen, and philosopher Tim van Gelder.

Reuters’ obituary of Lorenz can be found here. The Associated Press’ longer obituary (on the Canadian Broadcasting Corporation News website) is here.