Sunday, November 01, 2015

Leo P. Kadanoff, Physicist of Phase Transitions, Dies at 78

Leo P. Kadanoff at his lab in 2003.
CreditThomas A. Witten
Leo P. Kadanoff, a physicist who provided critical insights into the transformations of matter from one state to another, died last Monday in Chicago. He was 78.
The cause was respiratory failure, said theUniversity of Chicago, where he was a professor from 1978 until his retirement in 2003.
A member of the National Academy of Sciences and a fellow of the American Academy of Arts and Sciences, he received the National Medal of Science in 1999.
“He won basically every prize except theNobel Prize, and many people thought he should have won the Nobel,” said Emil Martinec, a physics professor at the University of Chicago who directs the university’s Kadanoff Center for Theoretical Physics.
Dr. Kadanoff’s biggest scientific contribution came in the 1960s as scientists were trying to understand phase transitions, when matter changes from one form to another.
A Cornell chemist, Benjamin Widom, had come up with mathematical relationships that described behavior associated with second-order phase transitions, which include the boiling of water to steam at a particular temperature and pressure. But Dr. Widom did not have an underlying physical explanation for why these relationships existed.
Dr. Kadanoff turned to a simple model of another second-order phase transition — ferromagnetism. In some materials, atoms act like tiny bar magnets and line up to produce a magnetic field. With rising temperatures, the atoms become jumbled, and the magnetic field diminishes, and above a certain temperature, the magnetic field disappears.
What Dr. Kadanoff found was that the jumbling had a fractal-like appearance. The patterns of fluctuations on a small scale possessed the same statistical distribution as much larger fluctuations. By looking first at small regions containing just a few atoms and then using those results to analyze ever larger regions, Dr. Kadanoff could reproduce Dr. Widom’s mathematical observations.
“He was a master of boiling things down to the simplest possible form and then extracting the most important consequences that follow from that,” said Nigel Goldenfeld, a professor of physics at the University of Illinois. “That’s how he gained penetrating insights into very complicated problems where other people didn’t see what was going on, because they were too confused by the complications.”
At Cornell, another physicist, Kenneth G. Wilson, took Dr. Kadanoff’s work and came up with a more general mathematical theory.
The approach proved useful not only in the understanding of phase transitions, but also a wide range of phenomena, including the interactions of elementary particles and how a drop of water breaks in two.
In 1980, Dr. Kadanoff shared a prestigious physics prize from the Wolf Foundation in Israel with Dr. Wilson and Michael Fisher, one of Dr. Wilson’s collaborators.
Two years later, the Nobel Prize in Physics honored the same advances — but only Dr. Wilson received the prize. At the time, Dr. Wilson said he would have expected the Nobel committee to honor Dr. Fisher and Dr. Kadanoff as well. “Yes, I was very surprised and especially so that I’m getting the prize alone,” Dr. Wilson told The New York Times.
Leo Philip Kadanoff was born on Jan. 14, 1937, in New York City. He attended Harvard, obtaining bachelor’s, master’s and doctoral degrees in physics.
After leaving Harvard, he conducted postdoctoral research at the Bohr Institute for Theoretical Studies in Copenhagen. He became a professor at the University of Illinois in 1962, then moved to Brown University in 1969 and then to the University of Chicago in 1978.
Dr. Kadanoff served as president of the American Physical Society in 2007.
His first marriage, to Diane Gordon, ended in divorce.
Dr. Kadanoff is survived by his wife, Ruth; three daughters, Marcia Kadanoff, Felice Kadanoff and Betsy Kadanoff; a stepdaughter, Michal Ditzian; and four grandchildren.
Dr. Kadanoff’s research interests jumped around, from pattern formation to turbulence and chaos. “Even urban planning,” Dr. Goldenfeld said. “He was really one of the pioneers of interdisciplinary science.”
The Kadanoff Center for Theoretical Physics was created in 2003 with an anonymous $3.5 million gift to bring together physicists from different specialties, mirroring Dr. Kadanoff’s penchant for bringing disparate scientists together to tackle problems.
“He brought some pure mathematicians and computer scientists together’’ for one project, said Sidney Nagel, one of Dr. Kadanoff’s colleagues at the University of Chicago. “He brought me in as an experimentalist, and he tried to stir the pot.”
Dr. Nagel also recalled that even though Dr. Kadanoff was a theorist, he was curious about the latest experimental results, including one time when Dr. Nagel was studying the behavior of avalanches, using piles of mustard seeds.
“He grabbed a bunch and started eating them,” Dr. Nagel said. “We were pretty amazed. This great man was coming down and eating our experiment.”

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