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Lorenz, Edward Norton, 1917–2008, American meteorologist and pioneer of chaos theory, b. West Hartford, Conn., Ph.D. Massachusetts Institute of Technology, 1948. Lorenz became interested in meteorology while working as a weather forecaster during World War II, and after earning his doctorate in meteorology taught at the Massachusetts Institute of Technology (1948–1987). In 1961, while working with computer models to determine why it was so difficult to predict weather accurately, he stumbled upon what is now known as chaos theory or deterministic chaos. His work in chaotic behavior in the mathematical modeling of weather systems led to a 1972 talk entitled "Predictability: Does the Flap of a Butterfly's Wings in Brazil Set Off a Tornado in Texas?" that gave chaos theory the term "butterfly effect" for the concept that small changes in the initial conditions of a nonlinear system can produce a major change in the results (see nonlinear dynamics).

See J. Gleick, *Chaos* (1987).

*The Columbia Electronic Encyclopedia,* 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.