Professor Steven Sperber retires after 48-year University of Minnesota career

MINNEAPOLIS / ST. PAUL (7/2/2025) – After nearly half a century as a faculty member at the University of Minnesota School of Mathematics, Professor Steven Sperber retired on May 25, 2025. Coincidentally, the date of Sperber’s retirement fell on his 80th birthday. Over the course of his notable career, Sperber made a number of foundational contributions to number theory and arithmetic geometry. 

Origin points

Sperber was born and raised in Brooklyn, New York. His interest in mathematics started at a young age, when he began competing in mathematics competitions at S.J. Tilden High School. Upon completion of his high school education in 1962, Sperber went on to Brooklyn College. Here Sperber continued his involvement in mathematics competitions, coming in second place with his team in the national Putnam Exam in 1963.

In 1966, Sperber embarked on his graduate studies at Harvard University. He transferred to the University of Pennsylvania in 1967, where he worked under the advisement of Professor Stephen Shatz. A few years into his graduate studies, Sperber met Professor Bernard Dwork at the Institute of Advanced Scientific Studies in France. Sperber was deeply inspired by Dwork’s work connecting p-adic methods with classical analysis in the study of questions in arithmetic algebraic geometry and number theory. 

“A critical moment in my career development was my meeting and then working under the mentorship of Bernard Dwork, a wonderful man and a wonderful mathematician,” Sperber says. “I remember sitting in his office and raising a question on a technical computation. It momentarily confused Dwork as well. He took up the chalk and said "two experts like us should be able to work through this". His including me in that moment was both generous and inspiring.”

Sperber obtained his PhD from the University of Pennsylvania in 1975. His dissertation, titled “P-adic hypergeometric functions and their cohomology,” was just the tip of the iceberg. Arithmetic algebraic geometry and number theory would remain at the core of his research for the rest of his career. 

A collaborative career

In the fall of 1977, Sperber began his faculty career at the University of Minnesota as an Assistant Professor. He received promotion to Associate Professor in 1980, and to full Professor in 1983. His mathematical research made crucial progress in the areas of number theory and arithmetic geometry, especially through the study of exponential sums and p-adic cohomology. Beginning with his doctoral work, Sperber advanced the understanding of multiple Kloosterman sums by connecting them to classical confluent hypergeometric differential equations and revealing deep arithmetic properties of their associated L-functions. 

At Minnesota, Sperber found a diverse faculty of mathematicians eager to collaborate. In a partnership with Prof. Yasutaka Sibuya, and despite their differing mathematical backgrounds, Sperber and Sibuya successfully established crucial arithmetic properties of power series solutions of algebraic differential equations. Through the various veins of his research, Sperber also received mathematical support from colleagues Messing, Goldman, Reiner, Stanton, Eagon, and Roberts. Sperber and Messing’s friendship and mathematical collaboration spans more than 65 years, going all the way back to their high school days in Brooklyn.

Nearly all of Sperber’s research was highly collaborative in nature. He credits inter-collegiate collaboration as a key to success. “I was incredibly fortunate to have worked with so many outstanding mathematicians, including Adolphson, Bombieri, Haessig, Sibuya, Denef, Doran, Dwork, Hong, Kelly, Libgober, Salerno, Varchenko, Voight, and Whitcher,” Sperber writes. Of his 93 articles and papers available via Google Scholar, 80 were published with one or more co-authors.

Sperber and Prof. Alan Adolphson, also a student of Dwok, have fostered a mathematical partnership for half a century. Together, they developed a rich theory of L-functions tied to toric exponential sums, where they established key results about cohomological vanishing, purity of roots, and relationships between Newton and Hodge polygons. These insights were powerful tools to evaluate the arithmetic complexity of exponential sums and to generalize classical theorems such as Chevalley-Warning. Over several decades, Sperber and Adolphson extended this framework to more general settings, including multiplicative character sums, affine and twisted exponential sums, and families of Calabi-Yau hypersurfaces. 

In another long-running collaboration, Sperber and Prof. Douglas Haessig investigated families of nondegenerate exponential sums. Findings from this research apply to the study of the unit root L-function and symmetric power L-functions of these families. A further branch of Sperber’s work touched on mirror symmetry, proving invariance of arithmetic data for different “alternative mirror” families. His use of p-adic methods uncovered precise information about the size, shape, and divisibility of exponential sums and L-functions, establishing new bridges between p-adic analysis, algebraic geometry, and arithmetic. All in all, Sperber’s research has had a lasting impact on the field, shaping modern approaches to questions at the interface of geometry and number theory.

In addition to his research program, Sperber took an active role in advancing the department’s educational mission. From 2006 to 2018, Sperber led the Math Honors Program, where he introduced innovations such as the development of a year-long proof-based calculus sequence tailored for honors students preparing for graduate study in mathematics. He also taught many honors courses, including one especially memorable Honors Algebra course from which five of his undergraduates went on to earn doctoral degrees in mathematics. Sperber’s dedication to mathematics education and research also took him abroad, through visiting positions including work at the Institute for Advanced Study at Princeton, the Institute of Advanced Scientific Studies in France, the Math Sciences Research Institute at Berkeley, as well as other institutions in France, Italy, China, and the former Soviet Union.

The next chapter

Outside of mathematics, Sperber has a passion for the arts. He has been a longtime participant in the Florence Hill long-pose cooperative, specializing in figurative drawing and painting. His works have appeared in a number of juried exhibitions in the Twin Cities. In his retirement, he is looking forward to more art, more theorems, and more time with family and friends. As he reflects on his career and advice for the next generation of mathematicians, Sperber suggests: “Based on my own experience, my advice would be to interact and collaborate with others. It is more fun and more rewarding.”