A Man Smudges Productively

Austin Kleon writes about chalkboards, quoting this NYT article:

In many fields of science and investigation, blackboards have been replaced with whiteboards or slide show presentations. But chalk is cheaper and biodegradable. It smells better than whiteboard markers and is easier to clean up, mathematicians say. It is also more fun to write with.

One of the chalkophiles he cites says that “the value [of chalk] is in using it up.” This is one reason I love using wooden pencils. Yes, you have to sharpen them, but you get to measure your work against the diminishing length. Empty pens, too, give me the same satisfaction.

Austin’s post reminded me of this NHPR story (that’s New Hampshire Public Radio) about why mathematicians love using chalkboards. Here are a few of the juicier quotes.

On the sound chalk makes on the chalkboard:

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.

On the size of the writing:

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.

On “productive smudging”:

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.