## November 26, 2010

### Over 4500 Entries in the nLab, and Its 2nd Birthday!

#### Posted by David Corfield

guest post by Zoran Škoda

The first entry of the n-Category Lab wiki appeared on November 28, 2008 02:18:19 marking the creation of the nLab; hence this Sunday morning it is 2 years old! Three days before the birthday its nominal count of pages reached 4500. This may be a proper moment to celebrate its wide usability already at its tender age and even more to invite people to use it more, and if possible to contribute. Like in our earlier update from May, we would like to point to some highlights in $n$Lab. But I somewhat run out of steam to dwell this time on the content and will rather outline some improvements in the content organization of the $n$Lab which may make it more attractive to you.

In my impression, in its first year, the $n$Lab was focused on our daily research needs and central areas of our interest: category theory, including higher, topoi, homotopy theory, topology, sheaves, stacks, simplicial objects, descent, cohomology (including differential), foundations and categorical aspects of physics. I have received signals from some users of $n$Lab that they do not contribute because they “do more concrete things”, say Lie algebras, representation theory, mathematical physics and so on and feel they do not wish to write about categories. But this is a misunderstanding: more stuff in related areas is very welcome and we need contributors telling us the story in nearby areas of algebra, mathematical physics, differential geometry and so on (of course, not that far an area that we can not understand, appreciate and connect to).

Seeing that we started in rather self-centered areas of categorical mathematics, it was difficult, in the first year, for a newcomer, to navigate through nLab and find out what interesting things (s)he can find there. Hence, in the last several months a great amount of activity was centered not only in creating new content but also around new lists/tables of pointers of content in particular fields of interest. In this vein, Urs has been very enthusiastic in adding floating tables of contents. For example, each entry in topos theory, e.g. subobject classifier has a floating table of contents for Topos theory on its right-hand side. It is a pull-down menu which helps you navigate through entries in the subject of the particular table. Even the HomePage uses one floating table, to help the newcomer, and there are top level tables for mathematics and for physics. One can navigate top-down to some subsubjects from there.

Another organizational change in the last year or so is that most discussions which would earlier take place in query boxes in $n$Lab entries shifted to the nForum, which is well structured for many-purpose activities, thanks to the software and maintenance care of Andrew Stacey. Some of the discussions are about spams, bugs, writing, future policies and software, while some are about mathematical research, where Todd, Toby, Urs, Domenico, Jim, Tim, Mike, John, David and others explain extensively to each other their insights. Some of the longer among such discussions happen in the Atrium section, especially under Mathematics, Physics and Philosophy.

I have personally made the effort to connect $n$Lab to the external sources of information and replaced the previous Online Resources page by a network of several resource pages including:

• top page math resources
• page math blogs (previous Online Resources) with list of blogs and wikis
• page math institutions with a selected list of top world institutes and links to AMS-maintained and some other lists of math societies and departments
• page math archives with a list of main archives of online content in areas of our interest; with few exceptions (like MathSciNet), subscription sites are avoided and free archives preferred
• page math resources by individuals where there are some extremely rich pages of individuals in the prime areas of $n$Lab (there are hundreds of pages on individual mathematicians in $n$Lab, here we list just few particularly useful links)
• page books and reviews in mathematical physics with selected list of major research level books in mathematical physics

While in the first year the physics entries were dwarfed by the mathematical part of $n$Lab, now we do have a non-negligeable physics content. We recommend an outline of the nPOV in physics in the entry (mainly by Urs Schreiber)

Some picture of $n$Lab’s physics content can be accessed from the links at the top page physicscontents.

Posted at November 26, 2010 1:42 PM UTC

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### Re: Over 4500 entries in the nLab and its 2nd birthday!

This is great! Happy birthday, $n$Lab. Having 4,500 articles already is really stunning. It also happens to be my birthday today, too — I wish I’d gained as much knowledge in the past 2 years as the $n$Lab has :).

Posted by: Jamie Vicary on November 26, 2010 7:31 PM | Permalink | Reply to this

### Re: Over 4500 entries in the nLab and its 2nd birthday!

Happy birthday, Jamie and $n$Lab. And more importantly, congratulations on your great acquired wisdom (both of you).

Posted by: Tom Leinster on November 26, 2010 9:59 PM | Permalink | Reply to this

### Re: Over 4500 entries in the nLab and its 2nd birthday!

Happy birthday, Jamie! Any birthday wishes for something you’d like to see at the nLab?

Posted by: Todd Trimble on November 26, 2010 10:15 PM | Permalink | Reply to this

### Re: Over 4500 entries in the nLab and its 2nd birthday!

I wish the $n$Lab had existed 30 years ago, when I starting to learn mathematics — not for the math that’s on the $n$Lab now, but so I could type in what I learned as I learned it! Instead, after the internet was invented, I resorted to This Week’s Finds.

I hope students visit the $n$Lab and add more explanations of mathematics to the pages there as they learn it. It may seem a bit intimidating, but I think anyone of good intent and reasonable intelligence will find the $n$Lab crew eager for help, and eager to help.

Right now I’m busy learning about ecology, climate change, climate modeling, energy technology, and the kinds of applied math needed in these subjects. As I learn things, I’m typing them into the Azimuth Project. This is a wiki running on the same software as the nLab, hosted on the same server, and managed by the same person: Andrew Stacey. Just as the nLab has its nForum, the Azimuth Project has its Azimuth Forum. There was no need to reinvent the wheel: this system works well!

Right now you can see some applied math pages here on the Azimuth Project. So far it’s mainly Tim van Beek, David Tweed and Graham Young who have been writing these pages. We’ve been thinking a lot about stochastic resonance as a possible explanation for how the Milankovitch cycles get amplified to produce glacial cycles. But that’s just one of many topics I want to learn about — and in practical terms, not even one of the most important. There’s so much to do. If anyone reading this is an applied mathematician, please join the fun — either on the Azimuth Project, or the nLab, or both!

Anyway, while I can’t resist talking about the Azimuth Project, my main point here is that the nLab has succeeded to the point where it seems like a system worth copying in other subjects.

Posted by: John Baez on November 27, 2010 6:11 AM | Permalink | Reply to this

### Re: Over 4500 entries in the nLab and its 2nd birthday!

Happy birthday nLab!

4500 in two years is an incredible amount, given the average information density of a page.

John said:

If anyone reading this is an applied mathematician, please join the fun — either on the Azimuth Project, or the nLab, or both!

On the Azimuth project the biggest topic today is climate modelling, where we try to understand the basic stuff, discuss some papers and explain the mathematical tools. An example is the prediction of the next glacial inception. There is a lot about mathematical statistics, of course, but people interested in, for example, functional analysis, could help out by expanding the page on wavelets (as a tool for time series analysis).

Posted by: Tim van Beek on November 28, 2010 2:06 PM | Permalink | Reply to this

### Re: Over 4500 entries in the nLab and its 2nd birthday!

John wrote:

Right now you can see some applied math pages here on the Azimuth Project. So far it’s mainly Tim van Beek, David Tweed and Graham Young who have been writing these pages.

I did notice before that you stole Tim van Beek away from the $n$Lab and made him do labor at Azimuth instead. I see that with much regret: he used to be our best AQFT contributor.

I count that as the second big bad effect that climate change already has on the $n$Lab. I hope you guys get that problem sorted out soon and come back to do something less profane.

Posted by: Urs Schreiber on November 29, 2010 4:24 PM | Permalink | Reply to this

### Re: Over 4500 entries in the nLab and its 2nd birthday!

The nlab clearly celebrated a little too heavily and this morning has woken up feeling decidedly worse for wear. Indeed, after staggering home from the pub, it appears to have gone in to the wrong house with the effect that (until it finds its house keys again), it is at http://nlab.mathforge.org.

Seriously, something’s gone wrong with the nameservers on the ncatlab.org domain which means that the nlab (and the other personal webs) can’t be accessed via ncatlab.org. The backup address is: http://nlab.mathforge.org, and similar for the personal webs.

Remarks:
1. We’ll get the ncatlab.org domain back in the right place just as soon as we can.
2. The nlab.mathforge.org links are not a temporary replacement, they are and have always been an alternative route to the nlab.
3. The azimuth project is not affected by this.
Posted by: Andrew Stacey on November 28, 2010 7:31 PM | Permalink | Reply to this

### Pay the piper

That’s what happens when you don’t pay your domain registration fees …

At least your domain has been parked, rather than snapped-up by an online purveyor of catfood (or whatever).

Posted by: Jacques Distler on November 28, 2010 11:26 PM | Permalink | PGP Sig | Reply to this

### Re: Over 4500 entries in the nLab and its 2nd birthday!

the lab is back at http://ncatlab.org/nlab/

Posted by: Urs Schreiber on December 3, 2010 10:11 PM | Permalink | Reply to this
Read the post Jet Categories at the nForum
Weblog: The n-Category Café
Excerpt: nLab activity
Tracked: October 21, 2013 10:30 AM

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