## March 2009

### 8 posts

Earlier this year a middle schooler emailed me to ask me what my favorite mathematical symbol was. I didn’t have a good answer, because I’d never thought about it at length, and I ended up giving him the old standby answer: 0. The apparent contradictory nature of having something stand for nothing kept humanity from developing it for some time, and its existence allows numbers to be written in the modern base 10 (or base anything) form. Books have been written about the innovation, like this one, or this one.

Honestly, though, I don’t have much of a personal connection to zero. The symbol I find really compelling, though, is the arrow. Let me explain why.

First of all, it’s everywhere. I can’t think of a mathematical subfield that doesn’t involve drawing arrows (each with their own precise mathematical meaning). We call them morphisms, mappings, functions, edges of directed grahps, etc., but it seems like they’re always present. The idea of moving your problem from here to there is central in mathematics.

Second, I love the implication of movement. There’s a line about chess, that “the threat is more powerful than the move.” Understanding how to look at a chess board as a place where forces are exerting themselves represents a leap forward in one’s ability with the game. Similarly, feeling a mathematical situation as *wanting* to be represented elsewehre is a key part of a developed (or developing) mathematical intuition.

Third, it’s powerful. It’s shocking how much information is carried in arrowed diagrams. They allow you to ignore clutter and focus just on what is essential. Category theory is a dramatic example of this—everything is reduced to objects and the arrows between them.

So, to that middle schooler I led astray with an out-of-date, impersonal answer, I hope you find this post.

There’s a line in Brecht’s *Galileo* where the eponymous character says, and I paraphrase, that in his lifetime he saw astronomy come out into the public sphere in a way it never had before. I believe this is such a moment for mathematics, and I also believe that it’s on the way out.

Been busy lately with teaching and other stuff, but I’m still here and blogging. And, a fellow grad just gave me a copy of his manuscript on math in his life (I plan to write a very similar book sometime), so I’ll be reading that and writing about it soon. But, I have to give a final to my students tomorrow, and it’s very important to calibrate the difficulty of these things correctly. Stay tuned!

I wasn’t expecting it, but someone on fluther managed to answer my question (see last post). Now I’m in an interesting position: I have a hunch that whenever this certain algebraic equation has nontrivial solutions, that corresponds to the geometric objects I’m studying being the same as each other. But there doesn’t seem to be any clear reason this would be true. As always, I need to know more. There’s a paper I’m going to dive in to, which might have the answer, or point me on the right path.

First of all, someone commented that it’s not really a conference, since it lasts for six months. More like a program. I’ve been in a tiny bit of a conundrum when talk times roll around: do I attend the talks, or do I keep at my own work, where I’ve built up some momentum? Or to I go to the talk and surreptitiously keep doing my own work? That last option was the one I often took, but the last two days I opted to avoid MSRI altogether, and hit a cafe and a library on the respective days. I find that now I prefer libraries to cafes. I particularly like the enormous vaulted library study halls, where row after row of student works in silence. This is a new preference. One thing about being a grad student: you’re always taking note of your study preferences: how, where, and when do you work best? How much uninterrupted time do you need, and how many breaks? Do you need to eat before you work, or drink tea? I understand writers go through the same thing. About half of A Moveable Feast seemed taken up with this kind of detail.

So while I have generally preferred cafes and tea houses, I’m now thinking the library will be a better spot to head to. I’m thinking that the Seattle downtown library will be a good place to set up shop for a while.

I posted an algebraic question that came up in my work on fluther. I got some pretty interesting responses back, but nothing, ultimately, that will help me too much. I think the problem I was looking at doesn’t have a simple answer. I’m in a strange position anyway, because it’s easy to prove that a certain thing can’t happen, but very hard to prove (at least with what I know now) that it does happen. I need to know more. I’ve been sticking primarily to just one of the three main tools at my disposal to help me work; today I started reading more deeply into a second. I have a feeling I’ll have to have a pretty good command of all three to make real progress. There’s always this fantasy that you can learn just enough to make your breakthrough. But whenever I shy away from something, it turns out I need it later. Time to really push in to every available resource at my disposal.