Professor Walter David Neumann, 78, of Princeton, NJ, died peacefully, after a long struggle with Alzheimer’s, on Tuesday morning, September 24, 2024, at Artis Senior Living of Princeton Junction with loving family by his side. Born in Cardiff, Wales, to Bernhard and Hanna (Von Caemmerer) Neumann, Walter, a pure mathematician, had been a Princeton resident for the last 24 years.
Unusually, Walter’s parents were both group theorists (a branch of mathematics), and, until they found jobs at the same university, they must have been one of the first academic “two-cities” families. Walter’s older brother Peter and a cousin Mike Newman were also group theorists, at Oxford and the Australian National University respectively. After an undergraduate degree from the University of Adelaide, Australia, Walter earned his doctorate in topology from Bonn University, Germany, under the direction of the late Friedrich Hirzebruch.
Walter’s first American positions were at the University of Maryland and the Ohio State University. He later moved to Melbourne University, Australia, and, finally, to Barnard College and Columbia University, from which he retired in 2021. He also held visiting teaching and research positions at, among others, Aarhus University (Denmark), the University of Michigan, the University of California at Berkeley, Warwick University (England), and — numerous times — the Max Planck Institute for Mathematics in Bonn, and Princeton’s Institute for Advanced Study.
Walter was an exceptionally broad mathematician, internationally renowned for major breakthroughs in fields of mathematics that included low-dimensional topology, hyperbolic geometry, geometric group theory, and singularity theory. He felt that mathematicians do their best work not only when they’re young but also when they’re new to a field. His own career proved the truth of his theory.
According to the most recent of his many collaborators, Anne Pichon of Marseille University, Walter was also “a wonderful human being — deeply modest, warm, humble, and remarkably generous, both as a person and as a mathematician. Walter was especially generous with young mathematicians, always offering his time and guidance. He had a rare ability to listen during mathematical discussions with his many collaborators and friends, making everyone feel heard and valued. His enthusiasm for mathematics was contagious, and working with him was a constant source of joy.”
Walter is survived by his wife of 52 years, Anne Waldron Neumann, his daughter Hannah Neumann, and a granddaughter Noelle Paquiot. A Zoom memorial will be held on Saturday, October 5 at 9 a.m. ET in order to accommodate both Australian and European relatives, friends, and mathematical colleagues.