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Agent of change
December 31, 2004
Airhead
Somehow, Ann Coulter consistently succeeds in making Jessica Simpson sound like Harold Bloom:
To The People Of Islam:
Just think: If we’d invaded your countries, killed your leaders and converted you to Christianity YOU’D ALL BE OPENING CHRISTMAS PRESENTS RIGHT ABOUT NOW!
Merry Christmas
Remind me, again, why the media persist in treating her as a respectable source of conservative opinion?
Topological M-Theory
Topological String Theory is a rich and beautiful subject. It associates a Calabi-Yau 3-fold, with a set of invariants which have both significance in enumerative algebraic geometry and which play a physical role in the supergravity theory obtained by compactifying physical type-II strings on .
Recently, a lot of interest has surrounded the possibility of topological M-Theory, a theory which might compute similar interesting invariants for a 7-manifold, , of -holonomy. There’s a paper by Dijkgraaf et al on Hitchin’s theory. More recently, Nikita Nekrasov has written up his talk at Strings 2004.
Both papers are very intriguing, but neither contains what the authors (or the reader) might happily call a satisfactory formulation of “topological M-Theory.”
Since it’s the Holidays, I’m going to go out on a limb and — Scrooge-like — suggest that, perhaps, there’s a reason for this.
In a nutshell, the reason “why” there’s topological string theory is that there is a rich set of “nonrenormalization theorems” protecting various couplings in the supergravity theory. This protected subsector of the physical theory is what is computed by the topological theory.
On the other hand, the generic supergravity theory, which would result from compactifying the physical M-theory on a -manifold, , doesn’t have (as far as we know) a set of protected coupling which might plausibly be computed by topological M-Theory on .
There are very special theories which do have such protected couplings. But these, typically, are related to some theories, and the protected subsector is computed by the corresponding topological string theory.
One of the “axioms” of topological M-Theory is that, on , it should reduce to topological String Theory on . The question is whether there’s anything new that might be found on manifolds, , of irreducible holonomy?
Even if the answer turns out to be “no,” it does not necessarily follow that the whole exercise is pointless. If nothing else, a 7-dimensional formulation might furnish a proof (or even a satisfactory statement) of the conjectured S-duality of the Topological A- and B-models on .
I’m still rather optimistic about the subject. But I do have this nagging fear that the difficulties making sense of the proposals on the table are not just a case of me being dense, but are indicative of something fundamental.
December 17, 2004
The Pace of Innovation
If you read any other blogs besides this one, you’ve probably heard that MovableType blogs are currently being hammered by a “new breed” of spambot. Webhosts are shutting down MT installations in self-defence. SixApart has offered soothing words that a fix is on the way.
As it turns out, the spammers in question had been visiting golem, upwards of a thousand times a day, until I … umh … made them go away. But to know that, you’d have to read my server logs. They had no noticeable effect on server load or on the amount of comment spam I’ve received (4 in the past two months).
Gleening what I can from the experience of others, what strikes me is how little innovation a spambot writer needs to exercise to get his 15 minutes of fame. This “new breed” of spambot differs from the ones in common usage a year ago in only two respects
- Taking a page from the crapflooders, it operates from behind multiple anonymous proxies. Thus it can deposit hundreds of spam comments in a short interval of time, while evading MT’s lame-ass, ineffective comment throttle1.
- Upon finding a comment-script to post to (by looking for the POST method of the comment-entry form), it cycles through the
BlogIDparameter, thus depositing spam on all of the blogs hosted by that MT installation.
Other than that, apparently, it’s no more sophisticated than the easily-defeated spambots of yesteryear. You don’t even need to do something mildly sophisticated to render it ineffective.
So why the brouhaha?
Because an unprotected MT installation will buckle under the load of a crapflood (and, apparently, because MT3.x is even worse than MT2.x in this regard). So this spambot’s author’s decision to go for quantity over quality has made for a lot of unhappy people, right now.
Trackback Spam (Update)
Lest anyone think I am totally sanguine about beating these spammers, let me hasten to say that I am not. Changing only a few lines of code in their spambot, they could convert to sending Trackback spam instead of Comment spam. And neither I, nor anyone else, would have any good way of defending against them. Sure trackback throttling (incorporated into MT 3.1) would stem the tide. But, unlike comments, which can be made difficult for machines to POST, trackbacks are supposed to be POSTed by machines.
My one thought on the matter was to demand that the URL of the trackback resolve to the same IP address as where the trackback ping came from, or at least to the same /24. Theoretically, the blogging software that produced the trackback ping is running on the same host as website in question. Trackback pings sent by spammers via anonymous proxies, however, would not match.
I was halfway through coding up a plugin for MT 3.1, when it occurred to me to wonder how my existing, legitimate, trackback pings would have faired under such a system. So I wrote a little script to comb through the trackback pings I’ve received, and retrospectively apply this test to them. The results were a bit disappointing:
Of 172 trackback pings,
- 65 matched IP addresses exactly
- 13 more were in the same /24
- 89 didn’t come even close to matching
- 5 DNS lookups failed
This exaggerates the problem somewhat. Some of these pings are over 2 years old. If the person changed webhosts in the interim, the IP addresses certainly wouldn’t match today, even if they did match when the trackback was originally POSTed. But still, it looks like this strategy would have blocked over half the legitimate trackbacks I’ve received.
Back to the drawing board…
Update 2: Endearing Moderation
Chad Everett has created a plugin that has similar functionality to my forced comment previews, without the need to hack the MT source-code. Actually, as far as I can understand, his plugin doesn’t actually force a preview so much as toss any non-previewed comments into a moderation queue. As I’ve explained, mine was primarily a way to enforce XHTML validation and only secondarily to deter comment spam. So I say, “Moderation, schmoderation! If it hasn’t been previewed/validated, you can’t post it.”
I actually got another spam comment tonight, which was of the endearing, hand-crafted sort that you see once you’ve eliminated the mechanized ones. The author came in on the following Google search
http://www.google.ca/search?q=.edu+mt-comments&hl=en&lr=&c2coff=1&start=60&sa=N
deciphered, as best he could, the entry in question, and the left the comment
I have a blog with XHTML 1.1 and I have tried employing your Mathenable feature and I keep getting the same error code default #F3423 substring expected could I be applying it incorrectly as maybe my lib/mt/app is a different library version.
Really delightful! Alas, his URL no longer points to some schlocky bargain-finds-on-ebay site….
1 If you want effective comment throttling, you need to install a plugin (a plugin!).