Who Is Alexander Grothendieck? (2008) [pdf] | Hacker News Reader

Who Is Alexander Grothendieck? (2008) [pdf]

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74 pointsbenbreen30 comments

I am currently learning modern algebraic geometry (scheme theory) from Ravi Vakil's algebraic geometry in the time of COVID: https://math216.wordpress.com/agittoc-2020/.

It's a great ongoing course that offers amazing intuition into scheme theory. We're divided into "working group(oid)s" where we discuss the mathematics and solve the weekly homework assigned by Ravi. Best of all, anyone [all over the world] can join in on the fun! You get added to a discord and a zulip group, where all the discussion happens.

My favourite article about Grothendieck is the one titled "The Grothendieck-Serre Correspondence": https://webusers.imj-prg.fr/~leila.schneps/corr.pdf

This article describes both the mathematics, and the lives of Grothendieck and Serre through their exchange of letters. It's powerfully written, and provides great insight into both the mathematics and the two as people. The last line of the article is absolutely beautiful.

I'm also learning some algebraic geometry at the moment:

Some resources I have used are:

* video lectures by Richard Borcherds

* Lecture notes by Andreas Gathmann (https://www.mathematik.uni-kl.de/~gathmann/class/alggeom-200...)

* This blog: https://rigtriv.wordpress.com/ag-from-the-beginning/

* An infinite large napkin, by Evan Chen (https://venhance.github.io/napkin/Napkin.pdf)

It also found it helpful to learn some (algebraic) number theory, to get a sense of where some of the motivation comes from (e.g. elliptic curves, modular forms). Grothendieck's work is abstract, but he was always motivated by concrete problems (e.g. Weil conjectures).

Thanks for sharing, it looks really interesting, too bad I did not know about it earlier (but I will still try to watch the lectures). Are there more initiatives like that one? I know Terry Tao had open lectures online, so it is probably popular nowadays.

Stories like these suggest to me that genius level creativity equals intrinsic motivation plus time.

They also demonstrate that such motivation cannot be adjusted at will. It amounts to one's deepest understanding of where personal progress or best direction lies. Thus when Grothendieck or Swedenborg had religious experiences later in life their technical output ceased because their motivations had changed irrevocably.

> their technical output ceased

I think Grothendieck was still writing multi-1000-page mathematical manuscripts up until he died.

I know there are such unpublished manuscripts floating around the mathematical community.

As Wikipedia states " he lived secluded, still working tirelessly on mathematics until his death in 2014".

https://en.wikipedia.org/wiki/Alexander_Grothendieck

Some of his manuscripts can be downloaded here https://grothendieck.umontpellier.fr/archives-grothendieck/# but according to this (reliable) radio program [1] he was fascinated by the devil and only wrote about this at the end of his life

[1] https://www.franceculture.fr/emissions/la-conversation-scien...

Good point and it's not cut and dried but the character of his output had changed to the extent that it was not published in technical journals as it had been:

>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. His 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.)

My guess would be that he was working on himself rather than on the mathematics. Mathematics was merely the means and the medium. But I haven't read the material...!

>but the character of his output had changed to the extent that it was not published in technical journals as it had been

Grothendieck didn't publish much in journals at all, ever. He was famous for writing books, not technical articles, such as the EGA and SGA series. His later work was the same, and the resulting manuscripts were widely sought because they were really good stuff.

Before he died he also claimed to have many tens of thousands of pages more that would never see the light of day, and people have sought those documents ever since.

I'm quite familiar with his output because my PhD is in algebraic geometry, and I've worked through his (known) writings extensively.

Here [1] is his complete list of publications. You'll notice by far his output is books and lecture notes, with very few papers at any point in his career.

[1] https://webusers.imj-prg.fr/~leila.schneps/grothendieckcircl...

Thanks!

I should have written, 'They also demonstrate that such motivation cannot be adjusted at whim.'

Grothendieck's work is, for me, a rather perfect example of what's happened in the 20th century to mathematics, where the boundaries of knowledge have been pushed so hard and so far that there is almost no hope for anyone to even begin to understand the substance of the work outside a very tiny circle of people who pretty much dedicated life to that arcane corner of the field.

I really wish vulgarization was an actual scientific disciple rather than being done in an ad-hoc fashion by people who happen to be good at it.

I also really wish I could read a vulgarized summary of Grothendieck's body of work, and specifically:

    . why everyone is so excited about the work
    . what potential practical application do (or will) exist.

As another commenter mentioned, currently Ravi Vakil is teaching a course in modern algbraic geometry.

The course is largely based on Vakil's book in progress, which he titled The Rising Sea, after a quote from Grothendieck:

> I can illustrate the ... approach with the ... image of a nut to be opened. The first analogy that came to my mind is of immersing the nut in some softening liquid, and why not simply water? From time to time you rub so the liquid penetrates better, and otherwise you let time pass. The shell becomes more flexible through weeks and months — when the time is ripe, hand pressure is enough, the shell opens like a perfectly ripened avocado! . . .

> A different image came to me a few weeks ago. The unknown thing to be known appeared to me as some stretch of earth or hard marl, resisting penetration ... the sea advances insensibly in silence, nothing seems to happen, nothing moves, the water is so far off you hardly hear it ... yet finally it surrounds the resistant substance.

Here is, roughly speaking, a theorem that illustrates what modern algebraic geometry is good for.

Theorem. If you have two conic sections in the plane, which don't share a common component, then they intersect in exactly four points.

Here a "conic section" is just any quadratic equation in two variables, e.g. x^2 + y^2 + 3xy + 4x = 1. "Common component" means that the conic sections are identical or overlap in an entire line.

Now, here are some "examples".

Concentric circles, e.g. x^2 + y^2 = 1 and x^2 + y^2 = 4. They don't intersect at all, right? Ah, except you forgot to count points over the complex numbers, where they do.

Tangency, e.g. y = x^2 and x^2 + (y - 1)^2 = 1. These curves are tangent at (0, 0), so you have to count this point with multiplicity.

One major goal of modern algebraic geometry is to wrap these sorts of considerations into the foundations. So you have to work a lot harder to even say what a conic section is, or what it means for two of them to intersect. But, once you've laid the foundations in this manner, there are no special cases.

> Concentric circles, e.g. x^2 + y^2 = 1 and x^2 + y^2 = 4. They don't intersect at all, right? Ah, except you forgot to count points over the complex numbers, where they do.

How is this possible? Are you saying that there are pairs of complex numbers (x,y) such that x^2 + y^2 = 1 = 4?

You need to also count "points at infinity" in the "projective" plane. So the "projectivized" equations are actually X^2 + Y^2 = 1Z, and X^2 + Y^2 = 4Z. The intuition is similar to how 2 parallel lines will meet at the horizion (infinity).

Thanks, I think I got it.

Oops, brain fart. No, 1 is not equal to 4 even in Grothendieck's world. Scheme theory only gets you so far...

A correct example of what I had in mind is x^2 + y^2 = 1 and (x - 2)^2 + y^2 = 1.

That said, algebraic geometry takes care of this "bad example" also. This is done exactly as alcolade explained: consider "points at infinity" in projective space.

You aren't wrong. Until extremely recently, algebraic geometry was a field by and for the purest of the pure mathematicians. These days algebraic geometry has made its way into string theory.

https://en.wikipedia.org/wiki/Gromov%E2%80%93Witten_invarian...

A couple of his contributions:

1. A far reaching generalization of the Riemann-Roch theorem, which is now called the Grothendieck-Riemann-Roch theorem. As with a great deal of his work, it's about drawing conclusions about global structure from local data:

https://en.wikipedia.org/wiki/Riemann%E2%80%93Roch_theorem

2. Creating the machinery used to solve the Riemann hypothesis for finite number fields.

https://en.wikipedia.org/wiki/Weil_conjectures

His work wasn't focused on solving particular problems so much as it was on finding the right language with which to describe problems. The philosophy is that, with the right language, your proofs should become obvious. This is somewhat in the same spirit as Leibniz's quest for the 'Universal Characteristic'.

https://en.wikipedia.org/wiki/Characteristica_universalis

Geometric algebra could (will?) be used to simplify game engines, see Siggraph2019 Geometric Algebra:

https://www.youtube.com/watch?v=tX4H_ctggYo

Web site: https://bivector.net/

Geometric algebra and algebraic geometry are largely unrelated mathematical disciplines.

Algebraic geometry has to do with finding geometric structure in (the solutions of) systems of algebraic equations. Algebraic geometry is potentially useful whenever you're doing this, so cryptography, coding theory, optimization, ...

I disagree with the other comments. I can give you concrete reasons to care about algebraic geometry. I don't know enough of Grothendeick's vast generalizations yet to give you a good answer. I'm sure that I'll find applications of it, though ;)

Algebraic geometry, broadly construed, is the study of solutions to polynomial equations, just as linear algebra is the study of linear equations. I hope we'll both agree that linear algebra is used literally /everywhere/. Algebraic geometry sees a fair bit of use, mostly through the use of objects called as a Grobner basis, which allows us to solve for large systems of polynomial equations efficiently. The book "Ideals, Varieties, and Algorithms" goes into detail about this sort of "effective algebraic geometry" that's used to solve systems.

One algebraic geometry tool I have personally used is known as cylindrical algebraic decomposition. It's quantifier elimination for real polynomials, so you can use it to ask questions about behaviours of polynomials and compute answers to them. So if you have a problem that can be phrased as "can polynomials do this" [think safety/liveness properties], you can use cynlindrical algebraic decompostion to answer such questions.

My understanding is that Grothendeick's vast generalizations and perspectives allows one to take "geometric insight" gained from thinking about polynomials, and translate them into many many more settings. He had visions of number theory, so he built a lot of (very general) machinery, with an eye towards number theoretic problems. But really, the machinery is so general, and casts deep geometric insight on such a basic object of mathematics (rings and their ideals, as well as "what is gemometry") that I can see myself using what AG I know many, many times in the coming years.

Then there is also a whole branch of math called as tropical geometry which transports a lot of the AG machinery into piecewise functions. This is incredibly useful, because the AG machinery is very powerful, while piecewise linear functions are ubiquitous. It's early days [to my understanding] of tropical geometry, and I know woefully little about it. But I feel that if I learn more, I can gain a lot of useful algorithms and insight from the field. For more, there is an AMS intro article: https://www.ams.org/publications/journals/notices/201704/rno...

For more topological flavoured answer, check out the book Elementary Applied Topology by robert ghirst: https://www.math.upenn.edu/~ghrist/notes.html. It chronicles large swathes of algebraic topology and related fields in a clean, accessible style with applications.

Vulgarization is not valued in academia.

If you read German or just want more pictures, here are slides and handouts from a talk about Grothendieck https://jonathanweinberger.wordpress.com/2014/08/27/alexande...

This PDF weighs 11MB, for no good reason (there are few images in the document but nothing to justify 11MB). The web server is pitifully slow. Curiously, curl tells me the HTTPS cert has expired, but Firefox doesn't.

Unfortunately I wasn't able to find a decent mirror.

This 500KB version is the first result on google scholar searching by title.

https://www.jeanpierrevarlenge.com/app/download/826854410/Wh...

Also I think it should say (2006) not 2008:

> This article is a translation of the article “Wer ist Alexander Grothendieck?”, which originally appeared in German in the Annual Report 2006 of the Mathematics Research Institute in Oberwolfach, Germany

That's much better, thanks. (I overthought it and tried googling for a short extract from the article, should have done the obvious thing.)

AMS Notices have gone crazy with their file size; not sure why. Are they generating them from PS?

Becuase curl uses system certs as opposed to ones bundled with the browser. Also this is off-topic, read the article, he was an incredible human being.

>> Alexander Grothendieck was a mathematician who became the leading figure in the creation of modern algebraic geometry. His research extended the scope of the field and added elements of commutative algebra, homological algebra, sheaf theory and category theory to its foundations, while his so-called "relative" perspective led to revolutionary advances in many areas of pure mathematics. He is considered by many to be the greatest mathematician of the 20th century.

Wiki: https://en.wikipedia.org/wiki/Alexander_Grothendieck

what is the point of this? usually this type of comment is when there's something inscrutable in the title of a post but the title of this post is literally "Who Is Alexander Grothendieck?"; if you didn't know who he was before clicking you certainly know afterwards.

When the link doesn't load and yet you are stuck with this boiling question in the title, you start to look for answers in the comments to decide how long you are willing to wait for the said link.

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