[tt] NYT: Edward N. Lorenz, a Meteorologist and a Father of Chaos Theory, Dies at 90

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Edward N. Lorenz, a Meteorologist and a Father of Chaos Theory, Dies at 90
http://www.nytimes.com/2008/04/17/us/17lorenz.html

By KENNETH CHANG

Edward N. Lorenz, a meteorologist who tried to predict the weather
with computers but instead gave rise to the modern field of chaos
theory, died Wednesday at his home in Cambridge, Mass. He was 90.

The cause was cancer, said his daughter Cheryl Lorenz.

In discovering "deterministic chaos," Dr. Lorenz established a
principle that "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," said a committee that awarded him
the 1991 Kyoto Prize for basic sciences.

Dr. Lorenz is best known for the notion of the "butterfly effect,"
the idea that a small disturbance like the flapping of a butterfly's
wings can induce enormous consequences.

As recounted in the book "Chaos" by James Gleick, Dr. Lorenz's
accidental discovery of chaos came in the winter of 1961. Dr. Lorenz
was running simulations of weather using a simple computer model.
One day, he wanted to repeat one of the simulations for a longer
time, but instead of repeating the whole simulation, he started the
second run in the middle, typing in numbers from the first run for
the initial conditions.

The computer program was the same, so the weather patterns of the
second run should have exactly followed those of the first. Instead,
the two weather trajectories quickly diverged on completely separate
paths.

At first, he thought the computer was malfunctioning. Then he
realized that he had not entered the initial conditions exactly. The
computer stored numbers to an accuracy of six decimal places, like
0.506127, while, to save space, the printout of results shortened
the numbers to three decimal places, 0.506. When typing in the new
conditions, Dr. Lorenz had entered the rounded-off numbers, and even
this small discrepancy, of less than 0.1 percent, completely changed
the end result.

Even though his model was vastly simplified, Dr. Lorenz realized
that this meant perfect weather prediction was a fantasy.

A perfect forecast would require not only a perfect model, but also
perfect knowledge of wind, temperature, humidity and other
conditions everywhere around the world at one moment of time. Even a
small discrepancy could lead to completely different weather.

Dr. Lorenz published his findings in 1963. "The paper he wrote in
1963 is a masterpiece of clarity of exposition about why weather is
unpredictable," said J. Doyne Farmer, a professor at the Santa Fe
Institute in New Mexico.

The following year, Dr. Lorenz published another paper that
described how a small twiddling of parameters in a model could
produce vastly different behavior, transforming regular, periodic
events into a seemingly random chaotic pattern.

At a meeting of the American Association for the Advancement of
Science in 1972, he gave a talk with a title that captured the
essence of his ideas: "Predictability: Does the Flap of a
Butterfly's Wings in Brazil Set Off a Tornado in Texas?"

Dr. Lorenz was not the first to stumble onto chaos. At the end of
the 19th century, the mathematician Henri Poincaré showed that the
gravitational dance of as few as three heavenly bodies was
hopelessly complex to calculate, even though the underlying
equations of motion seemed simple. But Poincaré's findings were
forgotten through the first three-quarters of the 20th century.

Dr. Lorenz's papers also attracted little notice until the
mid-1970s.

"When it finally penetrated the community, that was what started
people to really start to pay attention to this and led to
tremendous development," said Edward Ott, a professor of physics and
electrical engineering at the University of Maryland. "He
demonstrated a chaotic model in a real situation."

Born in 1917 in West Hartford, Conn., Edward Norton Lorenz received
a bachelor's degree in mathematics from Dartmouth College in 1938
and a master's degree in math from Harvard in 1940. He worked as a
weather forecaster during World War II, leading him to pursue
graduate studies in meteorology; he earned master's and doctoral
degrees in meteorology from the Massachusetts Institute of
Technology in 1943 and 1948.

Dr. Lorenz was a staff member of M.I.T.'s meteorology department
from 1948 to 1955, when he became an assistant professor. He was
promoted to professor in 1962 and served as head of the department
from 1977 to 1981. He became an emeritus professor in 1987.

In addition to his daughter Cheryl, of Eugene, Ore., Dr. Lorenz is
survived by another daughter, Nancy Lorenz of Roslindale, Mass; a
son, Edward H. Lorenz of Grasse, France; and four grandchildren. His
wife, Jane, died in 2001.

Dr. Lorenz remained active almost to the end of his life, in both
research and outdoor activities.

"He was out hiking two and one-half weeks ago," Cheryl Lorenz said,
"and he finished a paper a week ago with a colleague."