Elucidating Universal Principles in Complex Systems|
By Dorothy Wright
The questions that fire the imagination of Ayse Erzan ’70 have both physical and philosophical implications. A condensed-matter physicist, Erzan performs quantitative analyses of critical phenomena in phase transitions, disordered systems and self-organization in complex nonlinear systems. Her research has contributed to the body of knowledge suggesting that there are universal principles at work in physical and biological systems across a wide range of scales and time periods, from the formation of ice crystals to evolution.
A native of Ankara, Turkey, Erzan was home-schooled until third grade, when her parents enrolled her in private school. She went on to secondary school at the American College for Girls, where, she recalls, “A lot of subjects came naturally, but physics was the hardest for me, so I decided to do physics.”
At the urging of her physics teachers, Erzan applied to Bryn Mawr and was accepted, a placement exam placing her in junior year. “Bryn Mawr on the whole was a very positive experience,” she says. Upon graduation, “Like other young people coming to physics, I had this slightly starry-eyed, romantic idea that I would do particle physics and explore the basic building blocks of the physical world.”
At the State University of New York at Stony Brook, where she earned her doctorate, Erzan became interested in critical phenomena in phase transitions. “Phase transitions are very special,” she explains. “When water freezes, for example, this occurs at a very sharp temperature point. On each side of that point, the compounds are qualitatively different and their symmetry is different. In the liquid form, the molecules are spaced randomly, whereas in the solid or crystalline form they form a perfectly regular periodic structure. How this change comes about as you lower the temperature is a very beautiful question, and also a philosophical question. That fired my imagination.”
During the 1970s, Cornell physics professor Kenneth G. Wilson published a series of influential papers on his theory of critical phenomena in phase transitions, for which he received the Nobel Prize for physics in 1982. His research clarified how many different systems can show identical behavior at the critical point, as had been experimentally observed. “People like me, who graduated in 1976, were drawn naturally into the area of fractals, self-organized critical points and pattern formation in the 1980s,” Erzan says.
During the 1980s, Erzan was a visiting scientist, researcher, fellow and professor at various institutions throughout Europe, where she continued to conduct quantitative research into phase transitions and fractal growth in complex physical systems.
Returning to Turkey in 1990, Erzan joined the faculty of Istanbul Technical University, where she is now a professor of physics. She and her students turned their attention toward critical phenomena in biological systems, she explains, “because that was the area that seemed to present the most challenging problems, where the physicist had a chance to bring a completely different point of view.”
Recently Erzan and her colleagues have submitted a paper about their research into the origin of the unique folding configurations of proteins. Their calculations and modeling suggest that proteins with big energy gaps between their folded and unfolded states could have acted as refrigerants, enhancing the replication rates of those RNA which coded them. Their work is in line with the increasingly popular view that thermal and chemical gradients must have played an important role in prebiotic evolution, and casts doubt on a widely held theory that proteins’ form followed biological function. Instead, Erzan concludes, “Those proteins with a deeply folded native state would, in effect, have been selected in an evolutionary sense before specific biological functions came into being.”
The same geometrical patterns characterize the behavior of a wide range of physical and biological systems. “For the last 10 or 15 years, a question has been discussed and evaluated in many different ways: whether we can talk about generic laws or patterns that systems follow regardless of whether they are made up of water molecules or bacteria or human beings in a crowd or galaxies in outer space,” Erzan muses. “Since the 19th century, the physical sciences have followed a reductionist approach, but this does not necessarily ‘explain’ phenomena that are able to manifest themselves over a huge range of scales, almost from the atomic to the astronomical.”
Erzan says that examples at each end of that scale are few, but there are many intermediary examples — including sand piles, turbulent media, and earthquakes — in which the common denominator is a geometric effect called percolation, the formation of paths spanning a random network of clusters at a threshold concentration. “All of these phenomena may happen at many different scales, but nevertheless they follow the same patterns that can be described by the same geometrical concepts,” she says. “They display certain universal mathematical relationships.”
Erzan, who was among five female scientists honored with the 2003 L’Oreal-UNESCO Awards, delights in the challenges and rewards of science. “It is like a race against time,” she says. “You know other people are pursuing similar types of problems, and you try to do better, to get there first. That race is very much part of the fun.”
About the Author
Dorothy Wright contributes news and feature articles on science, technology, engineering and general interest topics to a variety of publications, including Civil Engineering and Engineering News Record.