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the matrix reloaded

Published May 1, 2012 by lieven

The dinosaurs among you may remember that before this blog we had the ‘na&g-forum’ to accompany our master-class in noncommutative algebra & geometry.

That forum ran on an early flat-panel iMac G4 which was, for lack of a better name, baptized ‘the matrix’.

The original matrix did survive the unification of the three Antwerp universities and a move to a different campus but then died around bloomsday 2007 and was replaced by an intel iMac.

This second matrix did host a number of blogs and projects started (and usually ended rather quickly) such as ‘MoonshineMath’, a muMath-site called noncommutative.org, the ‘F-un Mathematics’ blog dedicated to the field with one element and, of course, this blog.

About a month ago matrix-II was replaced by a state-of-the-art iMac running 10.7. The transition went smooth apart from the fact that 10.7 doesn’t like ‘localhost’ but prefers ‘127.0.0.1’ in setting up wordpress blogs.

Besides neverendingbooks, matrix-III runs angs@t – angs+ which is the blog of the antwerp noncommutative geometry seminar. It will be revamped over the summer and will probably be the website for our renewed master-class, starting next year.

The ‘F-un Mathematics’ blog was dropped in the transition but still survives at Ghent University where it is managed by Koen Thas.

As far as NeverendingBooks is concerned i hope to make a fresh start with blogging and will try to get more structure in this site by changing to a responsive wordpress theme (‘These responsive, fluid, or adaptive WordPress themes, automatically adjust according to the screen size, resolution and device on which they are being viewed’).

As a result this page will look weird from time to time over the next week or so. My apologies.

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noncommutative geometry at the Lorentz center

Published March 24, 2012 by lieven

This week i was at the conference Noncommutative Algebraic Geometry and its Applications to Physics at the Lorentz center in Leiden.



It was refreshing to go to a conference where i knew only a handful of people beforehand and where everything was organized to Oberwolfach perfection. Perhaps i’ll post someday on some of the (to me) more interesting talks.

Also interesting were some discussions about the Elsevier-boycot-fallout and proposals to go beyong that boycot and i will certainly post about that later. At the moment there is still an embargo on some information, but anticipate a statement from the editorial board of the journal of number theory soon…

I was asked to talk about “algebraic D-branes”, probably because it sounded like an appropriate topic for a conference on noncommutative algebraic geometry claiming to have connections with physics. I saw it as an excuse to promote the type of noncommutative geometry i like based on representation schemes.

If you like to see the slides of my talk you can find the handout-version here. They should be pretty self-exploratory, but if you like to read an unedited version of what i intended to tell with every slide you can find that text here.

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Manin’s three-space-2000

Published January 30, 2012 by lieven

Almost three decades ago, Yuri Manin submitted the paper “New dimensions in geometry” to the 25th Arbeitstagung, Bonn 1984. It is published in its proceedings, Springer Lecture Notes in Mathematics 1111, 59-101 and there’s a review of the paper available online in the Bulletin of the AMS written by Daniel Burns.

In the introduction Manin makes some highly speculative but inspiring conjectures. He considers the ring

$$\mathbb{Z}[x_1,\ldots,x_m;\xi_1,\ldots,\xi_n]$$

where $\mathbb{Z}$ are the integers, the $\xi_i$ are the “odd” variables anti-commuting among themselves and commuting with the “even” variables $x_j$. To this ring, Manin wants to associate a geometric object of dimension $1+m+n$ where $1$ refers to the “arithmetic dimension”, $m$ to the ordinary geometric dimensions $(x_1,\ldots,x_m)$ and $n$ to the new “odd dimensions” represented by the coordinates $(\xi_1,\ldots,\xi_n)$. Manin writes :

“Before the advent of ringed spaces in the fifties it would have been difficult to say precisely what me mean when we speak about this geometric object. Nowadays we simply define it as an “affine superscheme”, an object of the category of topological spaces locally ringed by a sheaf of $\mathbb{Z}_2$-graded supercommutative rings.”

Here’s my own image (based on Mumford’s depiction of $\mathsf{Spec}(\mathbb{Z}[x])$) of what Manin calls the three-space-2000, whose plain $x$-axis is supplemented by the set of primes and by the “black arrow”, corresponding to the odd dimension.

Manin speculates : “The message of the picture is intended to be the following metaphysics underlying certain recent developments in geometry: all three types of geometric dimensions are on an equal footing”.

Probably, by the addition “2000” Manin meant that by the year 2000 we would as easily switch between these three types of dimensions as we were able to draw arithmetic schemes in the mid-80ties. Quod non.

Twelve years into the new millenium we are only able to decode fragments of this. We know that symmetric algebras and exterior algebras (that is the “even” versus the “odd” dimensions) are related by Koszul duality, and that the precise relationship between the arithmetic axis and the geometric axis is the holy grail of geometry over the field with one element.

For aficionados of $\mathbb{F}_1$ there’s this gem by Manin to contemplate :

“Does there exist a group, mixing the arithmetic dimension with the (even) geometric ones?”

Way back in 1984 Manin conjectured : “There is no such group naively, but a ‘category of representations of this group’ may well exist. There may exist also certain correspondence rings (or their representations) between $\mathsf{Spec}(\mathbb{Z})$ and $x$.”

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