Jerry Paul Gollub was a remarkably creative physicist who conducted foundational experiments in nonlinear dynamics, including the first observation and characterization of the transition from order to chaos in fluid systems. His work contributed greatly to the understanding of complex dynamical behavior. His lucid papers and lectures made him widely sought as a lecturer at universities and international conferences.

Jerry Paul Gollub

Jerry was born in Saint Louis, Missouri, on 9 September 1944 and died in Haverford, Pennsylvania, on 8 June 2019. He graduated with an AB degree from Oberlin College in 1966 and with a PhD from Harvard University in 1971; his thesis adviser was Michael Tinkham. His primary appointment during the entirety of his professional career, from 1971 to 2012, was at Haverford College. In 1997 he was named the John and Barbara Bush Professor of Natural Sciences. His steadfast commitment to undergraduate education and to Haverford led him to decline offers of professorships at several major research universities.

In his Haverford laboratory, Jerry mentored more than 100 undergraduates and worked with postdocs and with graduate students from the University of Pennsylvania, where he was an adjunct professor. Because of the world-class research he conducted, in 1986 he became the first recipient of the American Physical Society (APS) Prize for a Faculty Member for Research in an Undergraduate Institution. He also held visiting appointments at the University of Paris VII in 1985, École Normale Supérieure in 1991, and the Weizmann Institute of Science in 1997–98.

My fondest memories of Jerry are from the period 1974–75, when we collaborated on experiments designed to test Lev Landau’s 1944 prediction that the transition to turbulence would occur through an infinite sequence of instabilities, each adding a new frequency to the motion, as the Reynolds number was increased. In our intense collaboration, Jerry and I developed a deep friendship and a research style and purpose that we sustained throughout our careers.

Our experiments, conducted at the City College of New York, yielded time series of the fluid velocity measured at a point between concentric cylinders. As the inner cylinder rotation rate (proportional to the Reynolds number) was increased, power spectra of the velocity time series revealed a transition from time-independent flow to a state characterized by a single frequency, in accord with the Landau picture. At a higher Reynolds number, a second frequency component, incommensurate with the first, appeared in the power spectrum, just as Landau had anticipated. With further increase in the Reynolds number, however, the spectra contained increasing broadband noise but no additional discrete frequency components. The noisy behavior differed from the expected Landau scenario, but the observation was consistent with models and analyses of chaos developed in the 1960s and 1970s.

In the 1980s Jerry and his group at Haverford developed a technique for visualizing spatial patterns in convecting fluids. With it, they investigated how competition between different spatiotemporal modes led to chaos. In the late 1980s, Jerry used particle-tracking methods to characterize chaotic mixing in time-periodic convective flows, the formation of fractal and dendritic structures in solidification processes, and pattern formation and chaos in surface waves. He also conducted a series of imaginative experiments on the dynamics of granular materials. In 2008–9 Jerry was a Leverhulme Visiting Professor at Cambridge University, where he collaborated with Raymond Goldstein, who had developed green algae as model organisms for biological fluid dynamics. Their experiments revealed diffusive yet non-Gaussian tracer statistics in suspensions of swimming microorganisms.

From 2000 to 2002, Jerry served as cochair of the National Research Council committee that produced the study Learning and Understanding: Improving Advanced Study of Mathematics and Science in U.S. High Schools. In 2005–8 he served on the National Academy of Sciences governing council.

Jerry was awarded the 2003 APS Fluid Dynamics Prize “for his elucidation of chaos, instabilities, mixing and pattern formation.” He also served for three decades in many APS elected and appointed positions, including on the council and the executive board.

Jerry is greatly missed by his many friends, students, postdocs, and other collaborators throughout the world. His innovative experiments on the complex dynamics of systems driven away from thermodynamic equilibrium will have lasting influence. He will also be remembered as a tireless advocate for high school and undergraduate science education, especially in physics, and for his contributions to the general good of the broad scientific community.