# Alexander Grothendieck

**Alexander Grothendieck** (born March 28, 1928, Berlin) was one of the most important mathematicians active in the 20th century. He was also one of its most extreme scientific personalities, with achievements over a short span of years that are still scarcely credible in their broad scope and sheer bulk, and an approach that antagonised even close followers. He made major contributions to algebraic geometry, homological algebra, and functional analysis. He was awarded the Fields Medal in 1966, and co-awarded the Crafoord Prize with Pierre Deligne in 1988. He declined the latter prize, on ethical grounds.

He is noted for his mastery of abstract approaches to mathematics, and his perfectionism in matters of formulation and presentation. Relatively little of his work after 1960 was published by the conventional route of the learned journal, circulating initially in duplicated volumes of seminar notes; his influence was to a considerable extent personal, on French mathematics and the Zariski school at Harvard University. He is the subject of many stories and some misleading rumours, concerning his work habits and politics, confrontations with other mathematicians and the French authorities, his withdrawal from mathematics at age 40, his retirement and his subsequent lengthy writings.

## Contents

## Mathematical achievements

Homological methods and sheaf theory had already been introduced in algebraic geometry by Jean-Pierre Serre, after sheaves had been invented by Kiyoshi Oka and Jean Leray. Grothendieck took them to a higher level, changing the tools and the level of abstraction.

Amongst his insights, he shifted attention from the study of individual varieties to the *relative point of view* (pairs of varieties related by a morphism), allowing a broad generalization of many classical theorems. This he applied first to the Riemann-Roch theorem, around 1956, which had already recently been generalized to any dimension by Hirzebruch. The Grothendieck-Riemann-Roch theorem was announced by Grothendieck at the initial Arbeitstagung in Bonn, in 1957. It appeared in print in a paper written by Armand Borel with Serre.

His foundational work on algebraic geometry is at a higher level of abstraction than all prior versions. He adapted the use of non-closed (*generic*) points, which led to the theory of schemes. He also pioneered the systematic use of nilpotents. As 'functions' these can take only the value 0, but they carry infinitesimal information, in purely algebraic settings. His *theory of schemes* has become established as the best universal foundation for this major field, because of its great expressive power as well as technical depth. In that setting one can use birational geometry, techniques from number theory, Galois theory and commutative algebra, and close analogues of the methods of algebraic topology, all in an integrated way.

Its influence spilled over into many other branches of mathematics, for example the contemporary theory of D-modules. (It also provoked adverse reactions, with many mathematicians seeking out more concrete areas and problems. Grothendieck is one of the few mathematicians who matches the French concept of maître à penser; some go further and call him maître-penseur.)

The bulk of Grothendieck's published work is collected in the monumental, and yet incomplete, *Éléments de géométrie algébrique* (EGA) and *Séminaire de géométrie algébrique* (SGA). Perhaps Grothendieck's deepest single accomplishment is the invention of the étale and l-adic cohomology theories, which explain an observation of André Weil's, that there is a deep connection between the topological characteristics of a variety and its diophantine (number theoretic) properties. For example, the number of solutions of an equation over a finite field reflects the topological nature of its solutions over the complex numbers. Weil realized that to prove such a connection one needed a new cohomology theory, but neither he nor any other expert saw how to do this until such a theory was found by Grothendieck. This program culminated in the proofs of the Weil conjectures by Grothendieck's student Pierre Deligne in the early 1970s after Grothendieck had largely withdrawn from mathematics.

### Major mathematical topics (from Récoltes et Semailles)

He wrote a retrospective assessment of his mathematical work (see the external link *La Vision* below). As his main mathematical achievements ("maître-thèmes"), he chose this collection of 12 topics (his chronological order):

- Topological tensor products and nuclear spaces
- "Continual" and "discrete" duality (derived categories and "six operations").
*Yoga*of the Grothendieck-Riemann-Roch theorem (K-theory, relation with intersection theory).- Schemes.
- Toposes.
- Étale cohomology including l-adic cohomology.
- Motives and the motivic Galois group (and Grothendieck categories)
- Crystals and crystalline cohomology,
*yoga*of De Rham and Hodge coefficients. - Topological algebra, infinity-stacks, 'dérivateurs', cohomological formalism of toposes as an inspiration for a new homotopic algebra
- Tame topology.
*Yoga*of anabelian geometry and Galois-Teichmüller theory.- Schematic point of view, or "arithmetics" for regular polyhedra and regular configurations of all sorts.

He wrote that the central theme of the above is that of topos theory, while the first and last were of the least importance to him.

Here the usage of *yoga* means a kind of 'meta-theory' that can be used heuristically.

## Life

### Childhood and studies

Born to a Russian Jewish father and German Protestant mother, he was a displaced person during much of his childhood due to the upheavals of World War II. Alexander lived with his father, Alexander Shapiro, and his mother, Hanka Grothendieck, both of whom were socialist revolutionaries. Until 1933 they lived together in Berlin. At the end of that year, Shapiro moved to Paris, and Hanka followed him the next year. They left Alexander with a family in Hamburg where he went to school. During this time, his parents fought in the Spanish Civil War. In 1939 Alexander came to France and lived in various camps for displaced persons with his mother. His father was sent to Auschwitz where he died in 1942. After the war, young Grothendieck studied mathematics in France, initially at Montpellier. He had decided to become a math teacher because he had been told that mathematical research had been completed early in the 20th century and there were no more open problems. However, his talent was noticed, and he was encouraged to go to Paris in 1948. He wrote his dissertation under Laurent Schwartz in functional analysis, from 1950. At this time he was a leading expert in the theory of topological vector spaces. However he set this subject aside by 1957 in order to work in algebraic geometry and homological algebra.

### Politics and retreat from scientific community

Grothendieck's radical left-wing and pacifist politics were doubtless born of his wartime experiences. He gave lectures on category theory in the forests surrounding Hanoi while the city was being bombed, to protest against the Vietnam war. He retired from scientific life around 1970, after having discovered the partly military funding of IHES (see pp. xii and xiii of SGA1, Springer Lecture Notes 224). He returned to academia a few years later as a professor at the University of Montpellier, where he stayed until his retirement in 1988. His criticisms of the scientific community are also contained in a letter written in 1988, in which he states the reasons for his refusal of the Crafoord Prize.

### Manuscripts written in the 1980s

While not publishing mathematical research in conventional ways during the 1980s, he produced several influential manuscripts with limited distribution, with both mathematical and biographical content.

*La longue marche à travers la theorie de Galois* (roughly *The Long Walk Through Galois Theory*) is an approximately 1600-page handwritten manuscript produced by Grothendieck during the years 1980-1981 and contains many of the ideas leading to the *Esquisse d'un Programme* (see below) and in particular studies the Teichmüller theory.

In 1983 he wrote a huge extended manuscript (about 600 pages) titled *Pursuing Stacks*, starting with a letter addressed to Daniel Quillen. This letter and successive parts were distributed from Bangor (see External Links below): in an informal manner, as a kind of diary, Grothendieck explained and developed his ideas on the relationship between algebraic homotopy theory and algebraic geometry and prospects for a noncommutative theory of stacks. The manuscript, which is being edited for publication by G. Maltsiniotis, later led to another of his monumental works *Les Dérivateurs*. Written in 1991 this latter opus of about 2000 pages further developed the homotopical ideas begun in *Pursuing Stacks*. Much of this work anticipated the subsequent development of the motivic homotopy theory of Morel and Voevodsky in the mid 1990s.

His *Esquisse d'un programme* (1984) is a proposal for a position at the Centre National de la Recherche Scientifique, which he held from 1984 to his retirement in 1988. Ideas from it have proved influential, and have been developed by others, in particular in a new field emerging as anabelian geometry. In *La Clef des Songes* he explains how the reality of dreams convinced him of God's existence.

The 2000-page autobiographical manuscript *Récoltes et Semailles* (1986) is now partly available on the internet in the French original, and an English translation is underway (these parts of Récoltes et Semailles are already translated to Russian and published in Moscow).

### Disappearance

In 1991, he left his home and disappeared. He is said to now live in the South of France and to entertain no visitors. Various false rumors have him living in Ardèche, herding goats and entertaining radical ecological theories. Though he has been inactive in mathematics for many years, he remains one of the greatest and most influential mathematicians of modern times.

## See also

- Grothendieck's Galois theory
- Grothendieck group
- Grothendieck's relative point of view
- Grothendieck-Riemann-Roch theorem
- Grothendieck's Séminaire de géométrie algébrique
- Grothendieck topology
- Grothendieck universe

## External links

- MacTutor biography
- Grothendieck Circle, collection of mathematical and biographical information, photos, links to his writings
- Institut des Hautes Études Scientifiques
- Récoltes et Semailles (original text)
- Grothendieck biography project by Roy Lisker. English translation of some parts of Récoltes et Semailles can be found here.
- Grothendieck biography (Part 1, Part 2) published in AMS Notices
- The origins of `Pursuing Stacks' This is an account of how `Pursuing Stacks' was written in response to a correspondence in English with Ronnie Brown and Tim Porter at Bangor, which continued until 1991.

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