@divbyzero.bsky.social - Dave Richeson

05 Oct 2026 20:33 +0000

I wanted to see how my calculus students could do creating a closed piecewise parametric curve for an impossible object. They made one side and could choose one of my shapes for the other side. Then I printed the objects. It went well, and I think I can ramp it up a little bit and

05 Oct 2026 15:09 +0000

My morning walk to work across the Dickinson College campus.

01 Oct 2026 17:39 +0000

Math professor poll: When you teach calculus, do you allow students to bring a notecard/formula sheet? a. No. They have to remember everything b. Yes, one 8.5"x11"/A4 sheet c. One note card d. I provide formulas e. Other

01 Oct 2026 17:21 +0000

This list made me sad. Not because of the song choices (well, not only because of the song choices). Their review of Built to Spill's "Carry the Zero" begins: "The two worst things in the world are breakups and math." 😭🤷‍♂️👎 [contains quote post or other embedded content]

27 Sep 2026 19:00 +0000

It is just geometry

25 Sep 2026 02:34 +0000

So... I just saw there's a film about the Unabomber coming out tomorrow... And it stars John Nash... I mean, Russell Crowe. https://www.imdb.com/title/tt6933238/ In all seriousness, I was in grad school at Northwestern when the Unabomber was caught, and Northwestern math professor Don Saari pointed said

20 Sep 2026 21:18 +0000

I was just reminded of this surprising fact: one pound of dimes, one pound of quarters, and one pound of half-dollars are each worth $20. So, if you grabbed a mixed assortment of these coins that weighed one pound, you'd have $20. (This doesn't apply to pennies or nickels.)

18 Sep 2026 13:52 +0000

I had a student ask the other day why we don't multiply vectors in the expected way (component-wise). So, ⊙=. My gut response was that we could, but it isn't as useful as the dot product or the cross product. But I decided to think about it and see if I could come up with 1/6

18 Sep 2026 00:13 +0000

Here are a few more impossible objects. This time, I printed the stand in black and the object in another color. It adds a lot of print time, but I like the final version better.

17 Sep 2026 14:18 +0000

Today in Multivariable Calc, I mentioned the connection between the cross product and quaternions. So I showed them a photo of me with the Hamilton plaque in Dublin from this summer!

16 Sep 2026 12:56 +0000

https://www.theguardian.com/science/2026/sep/16/uk-mathematician-debunks-myth-parthenon-optical-illusions

14 Sep 2026 16:56 +0000

Over the weekend, I had an idea: what if, instead of the objects appearing to sit horizontally in front of you, I modified them to appear vertically? Here are four test attempts.

11 Sep 2026 20:06 +0000

Friday afternoon print: lightning/thunder cloud impossible object. 🌧️⛈️🌧️

11 Sep 2026 12:21 +0000

This post got one like in 14 hours. I probably should have hinted at the math content: This is probably the first time the word hypocycloid has appeared in a humorous rap song on a late-night TV program. 😂 [contains quote post or other embedded content]

10 Sep 2026 21:39 +0000

"What's the Steelers' logo?" https://www.youtube.com/shorts/NwQg8nuyrNk

10 Sep 2026 20:10 +0000

Here's a thoughtful blog post about math and AI by Matt Baker. https://mattbaker.blog/2026/09/10/some-late-night-thoughts-on-ai-and-the-future-of-research-in-mathematics/

09 Sep 2026 11:42 +0000

Wow! So cool! [contains quote post or other embedded content]

07 Sep 2026 18:30 +0000

I just updated this web app I made last summer—it lets you design your own US weather maps for use in Multivariable Calculus classes. Now you can add cities to the map and save map settings for later. I also improved the UI. https://divisbyzero.github.io/isothermgenerator/ [contains quote post or other embedded content]

07 Sep 2026 13:06 +0000

Whenever I had a few minutes over the last few days, I created a new shape for my "impossible objects" library. Want to make a cactus/cowboy boot shape? You can now. I also implemented a visual picker to replace the drop-down menu. I plan to keep adding to it. https://divisbyzero.github.io/impossible-objects/

07 Sep 2026 12:37 +0000

What a lovely article about Joan Birman's seven-year mentorship of a teenage neighbor and the results they proved in braid theory. Joan Birman is now 99, and her neighbor is starting graduate school at Princeton. https://www.nytimes.com/2026/09/06/science/92-year-old-mathematician-apprentice.html

05 Sep 2026 14:57 +0000

A sword and a shield. The shape of the object is pretty crazy!

04 Sep 2026 13:03 +0000

I've been thinking about how to best display and view my impossible objects. Here's what I've come up with so far. The feet fit into the spinner to line up the object. The spinner turns 180°. The window forces the viewer to look down at a 45° angle. And the mirror has a slot to hold it at the

04 Sep 2026 00:51 +0000

The most recent Joy of Why podcast features a discussion about math and AI with moderators Janna Levin and Steven Strogatz and panelists Akshay Venkatesh, Ravi Vakil, and Alex Kontorovich. https://www.quantamagazine.org/live-from-icm-2026-what-is-math-for-in-the-age-of-ai-20260903/

03 Sep 2026 19:32 +0000

I thought this was an interesting math ed article about the ideas of "concept image" and "concept definition" in the most recent American Mathematical Monthly. https://www.tandfonline.com/doi/full/10.1080/00029890.2026.2663705

01 Sep 2026 23:01 +0000

A hyperbolic one-handed clock. You can see hours, minutes, and seconds. https://jpivarski.github.io/hyperbolic-map/clock.html

31 Aug 2026 13:32 +0000

So far, every student email I've received this semester has had late-teens/20-something grammar, punctuation, formatting, and enthusiasm. I never knew how much I would appreciate those traits in personal communication until I started receiving perfectly bland GenAI-written emails!

30 Aug 2026 01:27 +0000

Thumbs up or thumbs down?

28 Aug 2026 02:06 +0000

Since the semester starts in a few days, I thought I'd share a link to the web app I've been working on: https://divisbyzero.github.io/impossible-objects/. It lets you design your own impossible objects! Anyone can view and rotate them in a browser, but you can also download the OpenSCAD file to generate a