Seriously. As an undergrad my thesis was on elliptic curves and modular forms, and I've done applied industrial research that invoked toric varieties, so it's not like I'm a partisan here. But this can't be a representative crosssection of mathematical questions. How can this be fixed? (I mean the word "fixed".)
closed as off topic by Ben Webster♦ Nov 20 '09 at 19:49
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13$\begingroup$ Because AG is awesome? $\endgroup$ – Kevin H. Lin Nov 20 '09 at 18:03

4$\begingroup$ Aren't (say) PDE awesome too? $\endgroup$ – Steve Huntsman Nov 20 '09 at 18:05

10$\begingroup$ Because there are a lot of algebraic geometers here? $\endgroup$ – Qiaochu Yuan Nov 20 '09 at 18:16

9$\begingroup$ Sorry to shut down the party, but this question obviously should be on tea.mathoverflow.net, not the site itself. $\endgroup$ – Ben Webster♦ Nov 20 '09 at 19:51

3$\begingroup$ One other contributing factor could be that many other subject areas (algebraic topology, category theory, ...) already have mailing lists where you can ask MOstyle questions. $\endgroup$ – Andreas Holmstrom Nov 21 '09 at 14:04
I agree that the founder effect is a significant factor, but I also have another (more crackpotish) theory. I think some disciplines, like algebraic geometry, are harder to pick up in a traditional classroom setting, or out of a book. In practice, they are more often learned like a language, through repeated exposure and watching other people do it. Of course, to some extent this is true for most disciplines, but I think its more true for algebraic geometry than for analogously hard disciplines. If you grant my point, then there would be an overrepresentation of these disciplines on the internet, because they are looking for explanations and intuition unavailable in technical contexts. I think a similar statement is true for category theory, for instance.

$\begingroup$ To add a comment from a nonAGer, the disciplines I am interested in are welldocumented and intuitive enough that most of the questions I have thought of for MO have been resolved by a simple Internet / other reference check, so they never got posted. $\endgroup$ – Jason Dyer Nov 20 '09 at 19:10

2$\begingroup$ Greg's comment strikes me as being onto something. Modern AG (I think of Grothendieck as the dividing line) is very abstract, especially considering its basis in very concrete objects. At the same time part of Grothendieck's legacy is that a lot of "folk" results from EGA and SGA weren't formalized and reworked in the same way that results in other disciplines would have been. The result seems to be a genuinely different culture. Combine that with a steep learning curve... $\endgroup$ – Steve Huntsman Nov 20 '09 at 19:28

$\begingroup$ Moving on to the other part of my original question, might it be useful to (say) invite leaders from a crosssection of fields to occasionally post questions appropriate to the site as a way of driving the distribution to uniformity? $\endgroup$ – Steve Huntsman Nov 20 '09 at 19:30

$\begingroup$ Also I think the founder effect makes a lot of sense, but doesn't fully explain it. $\endgroup$ – Steve Huntsman Nov 20 '09 at 19:32
Founder effect. The people who launched the site are mostly in Greater Algebraic Geometry, and they naturally post a lot, which in turn induces people (like me) who are inclined towards these areas to visit the site a lot. If the site becomes widely popular I'd expect to see a distribution of questions which "looks like mathematics," to paraphrase Bill Clinton.
We have been here before with the arXiv. This site is (somewhat inadvertently) a massive work of social engineering. It is a social dynamical system, and it spreads where it wants to spread. Yes it is the founder effect, but it is more general than that. It is going to spread unevenly in different areas for a long time.
To amplify Greg Muller's answer, introductory courses in algebraic geometry tend to have a lot of definitions and wave vaguely at motiviation. So students starting out in the field often want to find "native speakers" who can help them understand how everything fits together.
I'm sure that founder effect is also a big factor, as JSE suggests.
I think that in some fields people are more active in the internet. There seems to be some correlation between the most popular tags here and the number of blogs in the corresponding section in the mathematics/statistics blog wiki here:
http://wiki.henryfarrell.net/wiki/index.php/Mathematics/Statistics
I do not know the relative proportion of algebraic geometers to other mathematicians but it may be in some fields the internet is more useful than others and there is more activity of the people in the field.

$\begingroup$ Sounds reasonable enough, but I've got to imagine that there are at least as many (say) PDEers as AGers. And the PDE crowd (lots of use of computers in applications) could be expected to have a strong predilection for something like this site. $\endgroup$ – Steve Huntsman Nov 20 '09 at 19:36

$\begingroup$ My impression is that the only PDE person who's particularly active in the "mathosphere" is Terence Tao. I don't have an explanation for why. $\endgroup$ – Qiaochu Yuan Nov 20 '09 at 19:47

2$\begingroup$ Qiaochu, I don't know that that's true, I just think that he's the most visible one, and his work spans a number of areas, so he's more connected to other internetactive mathematicians. $\endgroup$ – Harrison Brown Nov 20 '09 at 20:28