In about 2 hours I'll talk about using category theory to build epidemiology models here on YouTube. That's 17:00 UTC, or 10:00 am here in California.

Here are my talk slides:

I need breakfast first, though.

So, all together we have serious expertise in category theory, computer science, and epidemiology. Any two parts alone would not be enough for this project.

Moral: to apply category theory to real-world problems, you need a team.

And we're just getting started!

(7/n, n = 7)

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Evan started a seminar on epidemiological modeling - and my old grad school pal Nate Osgood showed up, along with his grad student Xiaoyan Li! He's a computer scientist who now runs the main COVID model for the government of Canada.


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This work would be impossible without the right team! Brendan Fong developed decorated cospans and then started the Topos Institute. My coauthors Evan Patterson and Sophie Libkind work there, and they know how to program using category theory.


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There's a lot more to say - but why not just come to my talk this Wednesday? It'll be 10 am in California. You can join via Zoom or watch it live-streamed on YouTube, or recorded later. Go to this link:


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But the key idea is 'compositional modeling'. This lets different teams build different models and then later assemble them into a larger model. The most popular existing software for stock-flow diagrams does not allow this. Category theory to the rescue!


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My talk is at a seminar on graph rewriting, so I'll explain how the math applies to graphs before turning to 'stock-flow diagrams', like this here.

Stock-flow diagrams are used to create models in epidemiology. There's a functor mapping them to dynamical systems. (2/n)

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It's finally here! 🎉 Software that uses category theory to let you build models of dynamical systems. We're going to train epidemiologists to use this to model the spread of disease. My first talk on this will be Wednesday June 29 at 17:00 UTC. You're invited!


However, that chart is not very helpful for atmospheric conditions, where the pressure is 100 kPa and temperature is between 0 °C and 50 °C. A more useful chart shows the density of moist air.

So it's a bit more complicated than I made it sound, but the basic idea is right.

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Caveat: for ideal gases at a given temperature and pressure, the density is simply proportional to the molecular weight! But water vapor is sometimes far from ideal. This chart shows the % deviation from ideality of water vapor's volume at various temperatures and pressures.

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One reason our planet is so dynamic: liquid water is denser than air, but water vapor is 𝘭𝘦𝘴𝘴 dense than air. So water keeps going up and coming down.

The reason: the molecular weight of N₂ is 14+14 = 28, and for O₂ it's 16+16 = 32, but for H₂O it's just 1+1+16 = 18.

In 1966, doctors in California tried a new approach to “cure” gay men:

“The goal was to paralyze patients, first their limbs and then their lungs, until they stopped breathing and felt as though they were drowning.”

Learn who blew the whistle!


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𝗛𝘂𝗺𝗼𝗿 𝗶𝗻 𝗮𝗱𝘃𝗲𝗿𝘀𝗶𝘁𝘆

In 1962, like many other gay men in California, Gene Ampon got diagnosed with “psychopathic personality disorder with pathologic sexuality”. They locked him up and drugged him.

But his spirit wasn't broken:


My talk was part of the Grothendieck Conference at Chapman University. You can see a bunch of other talks too - by Buzzard, Caramello, Landry, McLarty and more! I may tweet about some.

(3/n, n = 3)

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Here's my talk video. Slides are here:

I hope you get the basic idea: if primes are particles, zeros of the Riemann zeta function describe waves - and in Grothendieck's simplified version, they correspond to 'motives'.


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Trying to prove a simplified version of the Riemann Hypothesis led Grothendieck to discover 'motives': mysterious oscillating atoms of space.

I've been trying to understand motives. They're amazing! You can see my talk about them - a talk for amateurs, by an amateur.


In the future, with my smart home, I'll be able to do everything without ever leaving bed.

Luckily the fire department had already sent in 2 engines, 2 bulldozers, 2 hand crews and 2 officers.

They stopped the blaze when it was 3 acres in area, then stayed there for hours putting it out completely.

Whew! Just another night in the land of fire.


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Here in the dry lands it gets very hot in the day, but cool at night, so I sleep with the windows open. Last night I woke up around 4:00 am and smelled smoke. It was coming from outside.

I looked at Twitter. I saw that 1.6 miles away there was a rapidly spreading fire.


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