Of Math, Geekdom, Comics, and Sex

I nearly wrote a blog about Paul Erdős once.

That statement in itself is almost a half-joke.

(I still remember what I would have blogged about, had I actually written the blog in the first place. In fact, this is inspiration to go ahead and blog about it in the near future.)

A friend of mine long ago introduced me to xkcd: A webcomic of romance, sarcasm, math, and language. I don't read it nearly as often as I should. I have a couple other friends who also read it - given the subject matter, it would be hard not to love it. The thing is, it is brainier and geekier than any of my friends can probably appreciate: this isn’t a knock on my friends; it’s just that I am deficient in having friends who are mathematicians.

Though there are numerous mathematics in-jokes in the comic – and please don’t let that scare you from reading the comic: it is easily one of the most clever, smart, charming, and even heartwarming comics out there – there is one particular case in point that inspired this post. Needless to say, it has something to do with Paul Erdős, (pronounced Air-dish) the late mathematician who was the most prolific in history.

The title is Convincing Pickup Line. A girl and a guy are sitting at a table. The girl is showing him something on a piece of paper and trying to convince the guy that they should get together. “We’re a terrible match,” she says. “But if we sleep together, it’ll make the local hookup network a symmetric graph,” to which he responds: “I can’t argue with that.”

A little bit more about Erdős: because he was so prolific, and, more importantly, had so many collaborators, he constitutes a unifying thread among mathematicians. Just like Bacon numbers link actors according to how many movies it takes to link them, through co-stars, to Kevin Bacon, mathematicians have Erdős numbers that depend on how many papers it takes to link them to Erdős, either directly or through collaborators. Having written one with Erdős himself gives you a number of 1, having written one with one of his direct collaborators gives you a number of 2, etc.

Mathematicians are a weird bunch. Not only do they maintain their lists of Erdős numbers, take pride in their low numbers, etc., they even discuss the network of mathematicians who have collaborated at various removes with Erdős as a mathematical object itself! One mathematician once published a paper on the Erdős number network, noting that if two particular mathematicians within it published a paper together, the network would have an interesting mathematical property. The sappy conclusion to that story is that the two mathematicians did indeed decide to collaborate, in order to give the network that property.

While only a mathophile is likely to be familiar with that story, it doesn’t take a geek to figure that it served as the inspiration for the comic. I’m willing to bet that even my friends who like xkcd are unfamiliar with that story. But what I found most amusing was the rollover caption for the strip, one that I didn’t notice for a while because of a glitch that keeps it from appearing in Firefox, but which confirmed that that story was indeed the inspiration for the comic:

“Check it out; I've had sex with someone who's had sex with someone who's written a paper with Paul Erdős!”

And since it might somehow be tangentially relevant to this post, I guess I should acknowledge that I once made out with a girl who’s had sex with Trent Reznor….