John C. Baez's Blog, page 49

UN Climate Action Summit

Hello, I’m Christian Williams. I study category theory with John Baez at U.C. Riverside. I’ve written two posts on Azimuth about promising distributed computing endeavors. I believe in the power of applied theory—that’s why I left my life in Texas just to work with John. But lately I’ve begun to wonder if these great ideas will help the world quickly enough.

I want to discuss the big picture, and John has kindly granted me this platform with such a diverse, intelligent, and caring audience. T...

The Binary Octahedral Group

The complex numbers together with infinity form a sphere called
the Riemann sphere. The 6 simplest numbers on this sphere lie at points we could call the north pole, the south pole, the east pole, the west pole, the front pole and the back pole. They’re the corners of an octahedron!

On the Earth, I’d say the “front pole” is where the prime meridian meets the equator at 0°N 0°E. It’s called Null Island, but there’s no island there—just a buoy. Here it is:

Where’s the back pole, the east p...

Civilizational Collapse (Part 4)

This is part 4 of an intermittent yet always enjoyable series:

• Part 1: the rise of the ancient Puebloan civilization in the American Southwest from 10,000 BC to 750 AD.

• Part 2: the rise and collapse of the ancient Puebloan civilization from 750 AD to 1350 AD.

• Part 3: a simplified model of civilizational collapse.

This time let’s look at the collapse of Greek science and resulting loss of knowledge!

The Antikythera mechanism, found undersea in the Mediterranean, dates to somewhere bet...

Carbon Offsets

A friend asks:

A quick question: if somebody wants to donate money to reduce his or her carbon footprint, which org(s) would you recommend that he or she donate to?

Do you have a good answer to this? I don’t want answers that deny the premise. We’re assuming someone wants to donate money to reduce his or her carbon footprint, and choosing an organization based on this. We’re not comparing this against other activities, like cutting personal carbon emissions or voting for politicians who wan...

2020 Category Theory Conferences

 

Yes, my last post was about ACT2019, but we’re already planning next year’s applied category theory conference and school! I’m happy to say that Brendan Fong and David Spivak have volunteered to run it at MIT on these dates:

• Applied Category Theory School: June 29–July 3, 2020.
• Applied Category Theory Conference: July 6–10, 2020.

The precise dates for the other big category theory conference, CT2020, have not yet been decided. However, it will take place in Genoa sometime in the inte...

Applied Category Theory 2019 Talks

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The talks at ACT2019 are listed above—click for a more readable version. Below you can read what Jules Hedges and I wrote about all those talks, and get links to the papers they’re based on:

• Jules Hedges, Applied Category Theory 2019.

You can also see videos of some talks, created by Jelle Herold with help from Fabrizio Genovese:

• Giovanni de Felice, Functorial question answering.

• Antonin Delpeuch, Autonomization of monoidal categories.

• Colin Zwanziger, Natural model semantics for c...

Applied Category Theory 2019 Program

Bob Coecke, David Spivak, Christina Vasilakopoulou and I are running a conference on applied category theory:

• Applied Category Theory 2019, 15–19 July, 2019, Lecture Theatre B of the Department of Computer Science, 10 Keble Road, Oxford.

You can now see the program here, or below. Hope to see you soon!

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Applied Category Theory 2019 – Program

Bob Coecke, David Spivak, Christina Vasilakopoulou and I are running a conference on applied category theory:

• Applied Category Theory 2019, 15–19 July, 2019, Lecture Theatre B of the Department of Computer Science, 10 Keble Road, Oxford.

You can now see the program here, or below. Hope to see you soon!

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Structured Cospans

My grad student Kenny Courser gave a talk at the 4th Symposium on Compositional Structures. He spoke about his work with Christina Vasilakopolou and me. We’ve come up with a theory that can handle a broad class of open systems, from electrical circuits to chemical reaction networks to Markov processes and Petri nets. The idea is to treat open systems as morphisms in a category of a particular kind: a ‘structured cospan category’.

Here is his talk:

• Kenny Courser, Structured cospans.

In a cou...

Terawatt-Scale Photovoltaics

Here’s a cool paper which seems to be freely available:

• Nancy M. Haegel et al., Terawatt-scale photovoltaics: transform global energy, Science 364 (2019), 836–838.

Important topic! Here’s the abstract:

Solar energy has the potential to play a central role in the future global energy system because of the scale of the solar resource, its predictability, and its ubiquitous nature. Global installed solar photovoltaic (PV) capacity exceeded 500 GW at the end of 2018, and an estimated additiona...