Peter Michael Rosenthal (June 1, 1941 – May 25, 2024) was an American-Canadian mathematician, lawyer, and activist who was Professor of Mathematics at the University of Toronto, and an adjunct professor of law at the University of Toronto Law School.
Early life and family Rosenthal grew up in a Jewish family in Flushing, Queens, New York with his parents, Harold (1913–1983) and Esther (1914–1985), and two younger brothers, Erik and Walter. Rosenthal described himself as a "red diaper baby". His father was a high school math teacher and his mother was a left-wing activist who had been a member of the Communist Party in her youth. His maternal grandmother, Sonia, had immigrated to New York from Russia after the failed 1905 Russian Revolution and was a supporter of the Bolsheviks. Rosenthal himself was also a committed activist and in 1960 participated in protests at the Woolworth's in Flushing in solidarity with the sit-ins at Woolworth's in Greensboro, North Carolina protesting racial segregation. Rosenthal had poor grades in high school and barely graduated, but after nearly failing in college due to the time he spent attending civil rights and anti-nuclear protests, he began to focus on his studies at Queens College, excelling in math. Erik Rosenthal is an emeritus professor of mathematics at the University of New Haven. Their youngest brother, Walter (Wally) Rosenthal, is a community activist and trade unionist in New York City who taught at York College after retiring from the United States Postal Service. Both Erik and Wally were civil rights and anti-war activists in the 1960s.
Mathematics career Rosenthal graduated from Queens College, City University of New York with a B.S. in mathematics in 1962. In 1963 he obtained an MA in Mathematics and in 1967 a Ph.D. in mathematics from the University of Michigan; his Ph.D. thesis advisor was Paul Halmos. His thesis, "On lattices of invariant subspaces" concerns operators on Hilbert space, and most of his subsequent research was in operator theory and related fields. Much of his work was related to the invariant subspace problem, the still-unsolved problem of the existence of invariant subspaces for bounded linear operators on Hilbert space. He made substantial contributions to the development of reflexive and reductive operator algebras and to the study of lattices of invariant subspaces, composition operators on the Hardy-Hilbert space and linear operator equations. His publications include many with his long-time collaborator Heydar Radjavi, including the book Invariant Subspaces (Springer-Verlag, 1973; second edition 2003). In 1967, Rosenthal moved to Canada to accept an assistant professorship at the University of Toronto where he remained for the rest of his career, eventually becoming a full professor and retiring as a professor emeritus. Rosenthal supervised the Ph.D. theses of fifteen students and the research work of a number of post-doctoral fellows.
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