Grigory Margulis
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Grigory Margulis  

Grigory Margulis


Born 
Moscow, Soviet Union 
February 24, 1946
Nationality  Russian, American^{[1]} 
Alma mater  Moscow State University 
Known for 
Diophantine approximation Lie groups Superrigidity theorem Arithmeticity theorem Expander graphs Oppenheim conjecture 
Awards 
Fields Medal (1978) Lobachevsky Prize (1996) Wolf Prize (2005) 
Scientific career  
Fields  Mathematics 
Institutions  Yale University 
Doctoral advisor  Yakov Sinai 
Doctoral students 
Emmanuel Breuillard Hee Oh 
Gregori Aleksandrovich Margulis (Russian: Григо́рий Алекса́ндрович Маргу́лис, first name often given as Gregory, Grigori or Grigory; born February 24, 1946) is a RussianAmerican^{[2]} mathematician known for his work on lattices in Lie groups, and the introduction of methods from ergodic theory into diophantine approximation. He was awarded a Fields Medal in 1978 and a Wolf Prize in Mathematics in 2005, becoming the seventh mathematician to receive both prizes. In 1991, he joined the faculty of Yale University, where he is currently the Erastus L. De Forest Professor of Mathematics.^{[3]}
Contents
Biography
Margulis was born in Moscow, Soviet Union. He received his PhD in 1970 from the Moscow State University, starting research in ergodic theory under the supervision of Yakov Sinai. Early work with David Kazhdan produced the Kazhdan–Margulis theorem, a basic result on discrete groups. His superrigidity theorem from 1975 clarified an area of classical conjectures about the characterisation of arithmetic groups amongst lattices in Lie groups.
He was awarded the Fields Medal in 1978, but was not permitted to travel to Helsinki to accept it in person. His position improved, and in 1979 he visited Bonn, and was later able to travel freely, though he still worked in the Institute of Problems of Information Transmission, a research institute rather than a university. In 1991, Margulis accepted a professorial position at Yale University.
Margulis was elected a member of the U.S. National Academy of Sciences in 2001.^{[4]} In 2012 he became a fellow of the American Mathematical Society.^{[5]}
In 2005, Margulis received the Wolf Prize for his contributions to theory of lattices and applications to ergodic theory, representation theory, number theory, combinatorics, and measure theory.
Mathematical contributions
Margulis's early work dealt with Kazhdan's property (T) and the questions of rigidity and arithmeticity of lattices in semisimple algebraic groups of higher rank over a local field. It had been known since the 1950s (Borel, HarishChandra) that a certain simpleminded way of constructing subgroups of semisimple Lie groups produces examples of lattices, called arithmetic lattices. It is analogous to considering the subgroup SL(n,Z) of the real special linear group SL(n,R) that consists of matrices with integer entries. Margulis proved that under suitable assumptions on G (no compact factors and split rank greater or equal than two), any (irreducible) lattice Γ in it is arithmetic, i.e. can be obtained in this way. Thus Γ is commensurable with the subgroup G(Z) of G, i.e. they agree on subgroups of finite index in both. Unlike general lattices, which are defined by their properties, arithmetic lattices are defined by a construction. Therefore, these results of Margulis pave a way for classification of lattices. Arithmeticity turned out to be closely related to another remarkable property of lattices discovered by Margulis. Superrigidity for a lattice Γ in G roughly means that any homomorphism of Γ into the group of real invertible n × n matrices extends to the whole G. The name derives from the following variant:
 If G and G' are semisimple algebraic groups over a local field without compact factors and whose split rank is at least two and Γ and Γ^{$'$} are irreducible lattices in them, then any homomorphism f: Γ → Γ^{$'$} between the lattices agrees on a finite index subgroup of Γ with a homomorphism between the algebraic groups themselves.
(The case when f is an isomorphism is known as the strong rigidity.) While certain rigidity phenomena had already been known, the approach of Margulis was at the same time novel, powerful, and very elegant.
Margulis solved the Banach–Ruziewicz problem that asks whether the Lebesgue measure is the only normalized rotationally invariant finitely additive measure on the ndimensional sphere. The affirmative solution for n ≥ 4, which was also independently and almost simultaneously obtained by Dennis Sullivan, follows from a construction of a certain dense subgroup of the orthogonal group that has property (T).
Margulis gave the first construction of expander graphs, which was later generalized in the theory of Ramanujan graphs.
In 1986, Margulis gave a complete resolution of the Oppenheim conjecture on quadratic forms and diophantine approximation. This was a question that had been open for half a century, on which considerable progress had been made by the Hardy–Littlewood circle method; but to reduce the number of variables to the point of getting the bestpossible results, the more structural methods from group theory proved decisive. He has formulated a further program of research in the same direction, that includes the Littlewood conjecture.
Selected publications
Books
 Discrete subgroups of semisimple Lie groups, Ergebnisse der Mathematik und ihrer Grenzgebiete (3) [Results in Mathematics and Related Areas (3)], 17. SpringerVerlag, Berlin, 1991. x+388 pp. ISBN 354012179X MR1090825^{[6]}
 On some aspects of the theory of Anosov systems. With a survey by Richard Sharp: Periodic orbits of hyperbolic flows. Translated from the Russian by Valentina Vladimirovna Szulikowska. SpringerVerlag, Berlin, 2004. vi+139 pp. ISBN 3540401210 MR2035655^{[7]}
Lectures
 Oppenheim conjecture. Fields Medallists' lectures, 272–327, World Sci. Ser. 20th Century Math., 5, World Sci. Publ., River Edge, NJ, 1997 MR1622909
 Dynamical and ergodic properties of subgroup actions on homogeneous spaces with applications to number theory. Proceedings of the International Congress of Mathematicians, Vol. I, II (Kyoto, 1990), 193–215, Math. Soc. Japan, Tokyo, 1991 MR1159213
Papers
 Explicit grouptheoretic constructions of combinatorial schemes and their applications in the construction of expanders and concentrators. (Russian) Problemy Peredachi Informatsii 24 (1988), no. 1, 51–60; translation in Problems Inform. Transmission 24 (1988), no. 1, 39–46
 Arithmeticity of the irreducible lattices in the semisimple groups of rank greater than 1, Invent. Math. 76 (1984), no. 1, 93–120 MR0739627
 Some remarks on invariant means, Monatsh. Math. 90 (1980), no. 3, 233–235 MR0596890
 Arithmeticity of nonuniform lattices in weakly noncompact groups. (Russian) Funkcional. Anal. i Prilozen. 9 (1975), no. 1, 35–44
 Arithmetic properties of discrete groups, Russian Math. Surveys 29 (1974) 107–165 MR0463353
References
 ^ http://www.nasonline.org/memberdirectory/members/3012527.html
 ^ http://www.nasonline.org/memberdirectory/members/3012527.html
 ^ "Yale's Margulis Wins 2005 Wolf Prize for Mathematics". Yale University Office of Public Affairs. 20050223.
 ^ National Academy of Sciences Elections. Notices of the American Mathematical Society, vol. 48 (2001), no. 7, p. 722
 ^ List of Fellows of the American Mathematical Society, retrieved 20130202.
 ^ Zimmer, Robert J. (1992). "Review: Discrete subgroups of semisimple Lie groups, by G. A. Margulis" (PDF). Bull. Amer. Math. Soc. (N.S.). 27 (1): 198–202. doi:10.1090/s027309791992003063.
 ^ Parry, William (2005). "Review: On some aspects of the theory of Anosov systems, by G. A. Margulis, with a survey "Periodic orbits of hyperbolic flows", by Richard Sharp" (PDF). Bull. Amer. Math. Soc. (N.S.). 42 (2): 257–261. doi:10.1090/S0273097905010517.
Further reading
 J. Tits (1980). Olli Lehto (ed.), ed. The work of Gregori Aleksandrovitch Margulis. Proceedings of the ICM (Helsinki, 1978). 1. Helsinki: Academia Scientiarum Fennica. pp. 57–63. ISBN 9514103521. MR 0562596. Zbl 0426.22011. Archived from the original on 20130212. 1978 Fields Medal citation.
External links
 O'Connor, John J.; Robertson, Edmund F., "Grigory Margulis", MacTutor History of Mathematics archive, University of St Andrews.
 "Grigory Margulis's results". International Mathematical Olympiad.
 Grigory Margulis at the Mathematics Genealogy Project
 21stcentury mathematicians
 Members of the United States National Academy of Sciences
 Fellows of the American Mathematical Society
 Institute for Advanced Study visiting scholars
 Soviet mathematicians
 Russian Jews
 Russian mathematicians
 American people of RussianJewish descent
 Fields Medalists
 Moscow State University alumni
 Yale University faculty
 Wolf Prize in Mathematics laureates
 People from Moscow
 1946 births
 Living people
 Alexander von Humboldt Fellows
 International Mathematical Olympiad participants
 Dynamical systems theorists