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Granite Geek: Why Do Mathematicians Love Blackboards So Much?

Bas van Dijk via Flickr CC

Here’s a fun fact about mathematicians: they love chalkboards.  Especially the old fashioned ones, with actual chalk and those dusty erasers.  There are a variety of reasons why this might be true, and to untangle them we turn to David Brooks. He’s a reporter for the Concord Monitor and writer at, and a regular guest on NHPR’sAll Things Considered.

Transcript has been edited for clarity.

So before we get into the reasons why mathematicians really love chalkboards, tell us why are we even talking about this.

We’re talking about it because it’s a really cool subject!  No, we’re talking about it because there’s a guy named Michael Barany, who’s a post-doctoral fellow in the department of history at Dartmouth. And his background is in mathematics. He got his undergrad degree in mathematics. And he is interested in the sociology of mathematics.

Most of us think of math as being this kind of pure thought that ascends from on high, but it’s a human activity. It’s done by people. So as a result it’s interesting to look at what affects how people do it.  And part of that is if you spend any time with mathematicians you will notice blackboards. He noticed it. So part of his research is looking at how mathematicians use black boards and why they use blackboards. And as I talk in my column in the Monitor, there have been cases in which universities have tried to upgrade buildings and said, “Okay guys, we’re going to give you all these cool smart boards,” and mathematicians said, “No! Don’t take away our black boards! We love them!”

And when administration came back to them and said, “Okay, why do you love them so much,” what did they say?

Tradition is certainly a lot of it.  The idea of some famous mathematician standing up there at the black board and writing on a blackboard is just iconic. And if you’re not using a blackboard it’s almost like you’re not a serious mathematician. So that’s certainly part of it.  Just have it.

But other sciences have used blackboards, too, and they’ve generally moved beyond them. So the question is what is it about blackboards that math like? So Barany has some ideas that I thought were really interesting.

Let’s hear them.

So one of them is noise. And I’m not talking about fingernails on the blackboard, I’m talking about the click, click, click that chalk makes when you’re writing.  It’s much louder than any other writing implement would be. And as a result it’s much harder to interrupt somebody who’s writing on a blackboard. So if you’re up there, it’s like there’s this noise that keeps you from saying “Wait a minute! What about this?” whereas if you’re writing with a marker on a whiteboard, it’s easier to interrupt. This actually leads to longer flow of thoughts, which is important in mathematics; you’re not breaking it up as much. So that’s one possibility. 

Another one is sort of functional aspects. One is that it’s hard to write small. If you’ve ever written in chalkboard, it’s hard to write small. 

You have to write big.

You have to write big. Easier to see. But also it means you can fit fewer character on, you have to be more concise. And frankly, conciseness is what mathematics is. Mathematics is distilling information down to the minimum amount of characters. That’s really the essence of it. So that contributes to it.

And you write that this doctor that you interviewed carries around his own chalk.

Oh, absolutely. And that is not unusual at all. My son is in a Ph.D program in mathematics and he talks about some of his professors that carry around their own chalk. Particularly colored chalk. You want different colors to emphasize different parts of the formula, the equations, or the proofs you’re doing.  And if you have your own chalk – you happen to like the mount of dust produces, or you like how the line goes – you carry around your own because you never know. You show up and they have crummy chalk. That would be horrible.

Another thing he talked about that’s actually useful, and this is my favorite one, he said that blackboards smudge productively, which is just a great line. You know, you’re writing on a blackboard and oops, you make a mistake, you can rub it out with your hand, or you rub it out with an eraser. And it’s really easy to do. But it’s really hard to do it completely. You can’t get rid of it entirely. There’s always a little bit of a smudge and you write over it. And I’ve always thought that was a bad thing. And he argues that for mathematics, and particularly mathematics research, it’s a good thing because a lot of math research involves taking existing concepts and applying them in new ways. And so if you’ve written an existing equation everybody’s familiar with and then rubbed out a part of it and written something new over it, there is a visual sign that you have taken an existing concept and tweaked it, which is sort of like a reminder to the people in the audience that this is how you approach it. This is not some new thing you’ve brought down from on high, it’s an alteration of an existing one.

So there are actual reasons for this, not just feelings about it. Practical reasons.

Yes, I believe there are practical reasons. And if you go into serious math institutes you will see blackboards in the hallways so that people walking along and say, “You know, I had this idea,” they can stop, pick up chalk, and start writing on a blackboard. And there are rumors that there are some places where there are even blackboards in the bathrooms, but I’m not sure that’s actually true.

I’ve seen some at pubs, but maybe not universities. And there was no math written on those.

Oh, but there should have been! But actually that’s the point. All these funky restaurants that are using stuff, they don’t put up whiteboards, they put up blackboards. There’s something about the aura of a blackboard.

It makes me wonder what do scientists in other fields sort of cling to? Like chemists. What do they cling to in the same way that mathematicians cling to blackboards?

Boy, chemistry was always my weak point. Barany mentions chemists specifically because when you’re working in a lab you’re always writing on your glasswear. You’re labeling whatever’s in it. As a result they’re very comfortable with using markers. So they made the transition from blackboard to whiteboard quite easily. So that might be one way in which the habits of your field have altered.   

Peter Biello is the host of All Things Considered and Writers on a New England Stage at New Hampshire Public Radio. He has served as a producer/announcer/host of Weekend Edition Saturday at Vermont Public Radio and as a reporter/host of Morning Edition at WHQR in Wilmington, North Carolina.
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