Edward N. Lorenz, the MIT meteorologist whose efforts to use computers to increase the precision of weather forecasts inadvertently led to the discovery of chaos theory and demonstrated that precise long-range forecasts are impossible, died of cancer Wednesday at his home in Cambridge, Mass. He was 90.
Lorenz was perhaps best known for the title of a 1972 paper, "Predictability: Does the Flap of a Butterfly's Wings in Brazil Set Off a Tornado in Texas?" The memorable title pithily summarized the essence of chaos theory -- that very small changes in a system can have very large and unexpected consequences.
Although the chaos theory was initially applied to weather forecasting, it subsequently found its way into a wide variety of scientific and nonscientific applications, including the geometry of snowflakes and the predictability of which movies will become blockbusters.
His work "profoundly influenced a wide range of basic sciences and brought about one of the most dramatic changes in mankind's view of nature since Sir Isaac Newton," wrote the committee that awarded him the 1991 Kyoto Prize for basic sciences in the field of earth and planetary sciences.
By showing that there are limits to the predictability of many systems, Lorenz "put the last nail in the coffin of the Cartesian universe and fomented what some have called the third scientific revolution of the 20th century, following on the heels of relativity and quantum physics," said atmospheric scientist Kerry Emanuel of the Massachusetts Institute of Technology.
Lorenz was also "a perfect gentleman, and through his intelligence, integrity and humility set a very high standard for his and succeeding generations," he added.
One dramatic conclusion of his work is that it is impossible to predict weather more than three weeks ahead of time with any degree of certainty.
The roots of chaos theory date to at least the late 19th century, when French physicist Henri Poincare discovered to his chagrin that it was not possible to calculate the stability of a celestial system containing more than two bodies -- at least using techniques available at the time.
That was a shock because Newton's laws of gravity and motion promise order and predictability, and Poincare concluded that there must be other equations that would eliminate the problem. In the absence of computers, however, there was little anyone could do to test that thesis.
