A former colleague once introduced University of Maryland mathematician James A. Yorke as "the man who brought chaos to mathematics."
It wasn't a criticism. Yesterday it was announced that Yorke will share the 2003 Japan Prize in science and technology for his pioneering work in the relatively young mathematical field of "chaos" theory.
His theoretical research, and that of his multidisciplinary Chaos Group at Maryland's Institute for Physical Science and Technology, is now being used to illuminate complex real-world problems as diverse as infectious disease transmission, weather forecasting and population changes in biological systems.
The Japan Prize, announced yesterday in Tokyo, carries a $412,000 cash award. It is also an international honor highly regarded by scientists, who rank it just below the Nobel Prize and the Fields Medal in mathematics.
University of Maryland officials called Yorke's selection the highest honor received by a professor for work at College Park since historian Louis Harlan won a 1984 Pulitzer Prize for his biography of Booker T. Washington.
Unexpected honor
"It was a total surprise," Yorke said of the news that he had won. "A Spanish physicist had told me he was nominating me, and I told him not to bother. I didn't think I had a prayer."
Yorke said he plans to ask the Japan Prize foundation to give a third of his share of the cash prize to the University of Maryland, to seed further research.
UM President C.D. "Dan" Mote Jr. called Yorke's achievement "a distinction as great as any in the world. ... I am so pleased for him and for the inspiration his recognition will provide for others."
Yorke, 61, of Columbia, will share the honor (and split the cash) with Yale mathematician Benoit Mandelbrot, who is being honored for his work in the study of fractals, complex natural shapes that repeat themselves at different scales.
Two Japan Prizes are awarded each year in diverse fields. The second for 2003 was given for "visualizing techniques in medicine." It will go to Japanese scientist Seiji Ogawa, for his groundbreaking work in functional magnetic resonance imaging, now used widely in medical research and diagnosis.
Previous Japan Prize winners have included Robert C. Gallo, now director of the Institute for Human Virology, at the University of Maryland Biotechnology Institute, for his co-discovery of the HIV virus; Timothy Berners-Lee, inventor of the World Wide Web; and Dr. Donald A. Henderson of the Johns Hopkins University, for his work with others in eradicating smallpox.
Likened to Nobel
"The Japanese are rather disappointed this [award] isn't better known. It's their own Nobel Prize," said Bill Blandpied, who until this year directed the National Science Foundation's Tokyo office. "Among scientists it is very highly prized, very prestigious, and they [the Japanese] make a big show of it."
This year's honorees will receive their awards in April at elaborate ceremonies in Tokyo. The Japanese emperor and empress, the prime minister, other national leaders, diplomats and previous winners are expected to attend.
Japan Prize laureates are selected each December by the Science and Technology Foundation of Japan for work that has "advanced the frontiers of knowledge and served the cause of peace and prosperity for mankind."
Science of complexity
Yorke and Mandelbrot were honored for their work in the "science and technology of complexity."
"The world we live in is so complex that it is an enormous challenge to understand the fundamental nature of its complexities," the selection committee said. Yorke and Mandelbrot "have provided new frameworks for understanding complex phenomena, and have defined both their foundations and their applications."
Northwestern University math professor John Franks said scientists once presumed the natural world was "deterministic" - that is, predictable once you had the formulas to describe it. Planetary motions, for example, are predictable.
When they saw randomness, they assumed it was the result of a flawed experiment. "The insight for which Yorke is substantially responsible is that this is not the case," Franks said.
Chaos theory attempts to describe "nonlinear" phenomena - those in which small changes, or differences in initial conditions, lead quickly to large differences and seemingly random and unpredictable consequences, such as the weather and the stock markets.
Such systems began to get attention a century ago. But their importance was not appreciated until digital computers became capable of simulating and demonstrating their behavior. Yorke coined the use of the term chaos to describe such systems in a paper written in 1975 with T.Y. Li.
"I like to say that the last people to understand chaos were the scientists," Yorke said. "Everybody knows their lives are chaotic. ... This is because we know that small changes precede huge changes."
For example, he said, each individual child is the unpredictable consequence of an infinite number of chance occurrences and small decisions, from those that led to the parents' first meeting, to the winner in the race among millions of individual sperm toward the egg.
In meteorology, forecasters take many readings of temperature, pressure and other conditions around the world. But they make assumptions about millions more they can't directly measure. The uncertainties quickly multiply.
"After 36 hours," he said, "the two predictions will be twice as far apart as the initial guesses, on average. And every 36 hours they get twice as far apart. This is the nature of chaotic models."
"Predicting the weather - whether it's going to be rainy or sunny a month ahead - is basically impossible," he said.
Yorke's Chaos Group is working with the National Weather Service to improve the performance of computer forecast models, which start with similar assumptions but rapidly diverge. His team is looking for ways to check the models' performance against newly observed weather data. The conditions assumed by the least-accurate models can then be recalibrated to drag them back into alignment with the best, narrowing the forecast error.
Yorke's group is also using what it has learned about complex and chaotic systems to improve predictions for the spread of infectious diseases, such as AIDS, and to increase the efficiency of the decoding of the human genome.
"We're just looking for fascinating problems," he said.
James C. Alexander, chairman of the math department at Case Western Reserve University, once worked with Yorke at Maryland. He said Yorke's multidisciplinary Chaos Group "has a national and international reputation as a place where interesting science is done."
"He's generated an enormous number of ideas," Alexander said. "A lot of these ideas come from bouncing ideas back and forth with people, so they get involved."
Physics and math
Yorke received his bachelor's degree from Cornell University in 1963 and his doctorate in math from Maryland in 1966. He directed UM's Institute for Physical Science and Technology for 16 years before stepping down last year.
He now holds the title of Distinguished University Professor, the only UM faculty member ever to hold dual appointments in physics and math.
A fan of science fiction since the fifth grade, Yorke likes to listen to sci-fi books on audio tape while he drives or walks for exercise. He is married and has three grown children.
His wife, Ellen, is a medical physicist working in radiation medicine at Memorial Sloan-Kettering Cancer Center in New York.