John W. Cahn, 1928-2016. Photo credit: National Institute of Standards and Technology.
The mathematics and materials science communities lost a giant when John W. Cahn died of myelodysplastic syndrome (MDS) on March 14, 2016. As tall and imposing as he was physically, his scientific accomplishments made him stand out even more. John is not only the
Cahn of the Cahn-Hilliard equation and the Allen-Cahn equation; he also developed the theory and some underlying mathematics for the thermodynamics and kinetics of an even broader range of materials phenomena. Spinodal decomposition, critical point wetting, shear coupling, quasicrystals, interface motion, and the importance of symmetries are all indelibly marked by John’s hand.
John was born in Germany as Hans Werner Cahn in 1928, though his family soon fled to the Netherlands and then to the United States to escape Hitler. English was the fifth language he learned as a child, though you would never guess it from hearing him speak. John grew up in New York City. He was a proud alumnus of Brooklyn Poly and went on to attend the University of Michigan, although his time there was interrupted by his service in the U.S. Armed Forces in postwar-occupied Japan. John ultimately receive his Ph.D. in physical chemistry from the University of California, Berkeley. He spent his early career in the General Electric (GE) Research Laboratory in Schenectady, NY, a mecca for practitioners in the new field of materials science. When GE turned its interests away from basic research, John became a professor at the Massachusetts Institute of Technology (MIT). His passion for mathematics in the service of materials science has been inspiring to so many of us in the field, through both firsthand experience and his work. After earning her Ph.D., Jean (co-author of this obituary) was an instructor at MIT when she volunteered to give a series of three lectures on soap bubble clusters. John attended them, introduced himself, and a lifetime of collaboration began.
John was married to Anne Hessing Cahn, a political scientist with major influence in arms control. When Anne got a job at the U.S. Arms Control and Disarmament Agency (ACDA) in President Jimmy Carter’s administration, John—not being particularly happy in the academic milieu at MIT—accepted an appointment as a Senior Scientist at the National Bureau of Standards, which later became the National Institute of Standards and Technology (NBS/NIST). Here, John found the freedom he had enjoyed at GE and flourished, avoiding managerial responsibility like the plague and finding his “students” to be quite teachable. Carol (co-author of this obituary) and her husband John Blendell followed John from MIT to NBS/NIST to work with him, and eventually Carol became John’s supervisor. To avoid confusion as to which John was which, Carol usually referred to her husband as “Blendell.”
John was truly interested in seeing women succeed in science, and talked about the work of women scientists all the time. Through him, we became acquainted with many female scientists and their work, which enriched our scientific lives. To this day we haven’t encountered another scientist who was more positive and encouraging to the women in his field.
Although trained as a physical chemist and transformed into a metallurgist by his mentor Cyril Stanley Smith, John became a member of the National Academy of Sciences in the Applied Mathematical Sciences section at a relatively young age. His awards include a Guggenheim Fellowship at the University of Cambridge from 1960 to 1961, Carnegie Mellon University’s Dickson Prize in Science, the Michelson-Morley Prize from Case Western Reserve University, the American Society of Metals (ASM) Albert Sauveur Achievement Award, the Samuel Wesley Stratton Award from the NBS/NIST, the Rockwell Medal, the Harvey Prize from the Israel Institute of Technology, and Gold Medals from Acta Metallurgica, the U.S. Department of Commerce, and the Japan Institute of Metals. John also received the 1998 National Medal of Science presented by President Bill Clinton, the 2001 Emil Heyn Medal from the German Metallurgical Society, the Franklin Institute’s 2002 Bower Award, and the 2011 Kyoto Prize in Advanced Technology for his work in materials science. He was a fellow of both ASM and the Minerals, Metals, and Materials Society (TMS), as well as a member of the National Academy of Engineering (NAE) and the American Academy of Arts and Sciences.
Several characteristics contributed to John’s scientific success and influence. When someone pointed out an error or omission he had made, he reacted with delight rather than defensiveness. Additionally, John deliberately wrote papers with lots of loose ends. While most people like to write the definitive paper on a subject, John preferred writing the first paper defining a field that others would then develop by tying together those loose ends.
After more than twenty years at NIST, John and Anne retired and moved to Seattle to be closer to their three children and many grandchildren. Unfortunately, John’s MDS diagnosis came all too soon. His colleagues held a small three-day interfaces conference with John on Bainbridge Island in September 2015 to celebrate how mathematics has permeated materials science, and in November he attended a delightful two-day event at the University of Michigan celebrating Sharon Glotzer’s naming as the John W. Cahn Distinguished University Professor of Engineering. After the meeting, he was happy to see that Jean, John Blendell, and Edwin Garcia were pursuing a problem in grain growth that he had reminded us of at the Bainbridge Island meeting. “Aha!” he said. “A posthumous paper!” After having the opportunity to say goodbye to his friends and colleagues, John lived his last days surrounded by his loving family.