Edward N. Lorenz, requiescat in pace ...

[Dave Monroe]

April 17, 2008
Edward N. Lorenz, a Meteorologist and a Father of Chaos Theory, Dies at 90
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."

http://www.nytimes.com/2008/04/17/us/17lorenz.html