Alexander Grothendieck

Alexander Grothendieck (born March 28, 1928 in Berlin) is one of the most important mathematicians of the 20th century. He is also one of its most extreme scientific personalities, with achievements over a short span of years that are still astounding in their broad scope and sheer bulk, and a lifestyle later in his career that alienated 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 in a letter to the media [1].

He is noted for his mastery of abstract approaches to mathematics, and his perfectionism in matters of formulation and presentation. In particular, his ability to derive concrete results using only very general methods is considered to be unique amongst mathematicians. 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 rumors, concerning his work habits and politics, confrontations with other mathematicians and the French authorities, his withdrawal from mathematics at age 42, his retirement and his subsequent lengthy writings.

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.)

EGA and SGA

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. The 'centre of gravity' of the SGA developments lies somewhat obliquely to the tools in fact required.

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.
Topoi.
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 topics 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. The word yoke, meaning a linkage, is derived from the same Indo-European root.

Life

Family and early life

Born to a Russian Jewish father, Alexander Shapiro, and a German mother, Hanka Grothendieck, in Berlin (there are conflicting accounts of his origins; see [2] and [3]), he was a displaced person during much of his childhood due to the upheavals of World War II.

Alexander lived with his parents both of whom were socialist revolutionaries, until 1933, 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.

During WWII

In 1939 Alexander came to France and lived in various camps for displaced persons with his mother, first at the Camp de Rieucros, spending 1942-44 at Le Chambon-sur-Lignon. His father was sent via Drancy to Auschwitz where he died in 1942.

Studies and contact with research mathematics

After the war, young Grothendieck studied mathematics in France, initially at the University of 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.

Initially, Grothendieck attended Henri Cartan's Seminar at École Normale Superieure, but lacking the necessary background to follow the high powered seminar, he moved to the University of Nancy where he wrote his dissertation under Laurent Schwartz in functional analysis, from 1950 to 1953. 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.

The IHES years

Installed at the IHES just south of Paris, which was founded in 1958, Grothendieck attracted attention, first by his spectacular Grothendieck-Riemann-Roch theorem, and then by an intense and highly productive activity of seminars (de facto, working groups drafting into foundational work some of the ablest French and other mathematicians, of the younger generation). Grothendieck himself practically ceased publication of papers through the conventional, learned journal route. He was however, for around a decade, able to play a dominant role in mathematics, gathering a strong school.

During this time he had officially as students Michel Demazure (who worked on SGA3, on group schemes), Luc Illusie (cotangent complex), Michel Raynaud, Jean-Louis Verdier (cofounder of the derived category theory) and Pierre Deligne. Collaborators on the SGA projects included also Mike Artin (étale cohomology) and Nick Katz (monodromy theory and Lefschetz pencils). Jean Giraud worked out torsor theory extensions of non-abelian cohomology. Many others were involved.

Politics and retreat from scientific community

Grothendieck's political views were considered to be radical left-wing and pacifist. 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. During that period he also released his work on Bertini type theorems contained in EGA 5 which was edited by Piotr Blass and finally published by the Grothendieck Circle in 2004.

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, stimulated by correspondence with Ronnie Brown and Tim Porter at Bangor, and 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 F. Morel and V. 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.

External links

O'Connor, John J.; Robertson, Edmund F., "Alexander Grothendieck", MacTutor History of Mathematics Archive, University of St Andrews
Alexander Grothendieck at the Mathematics Genealogy Project
Grothendieck Circle, collection of mathematical and biographical information, photos, links to his writings
- Grothendieck Circle discussion Forum
Institut des Hautes Études Scientifiques
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.