## February 21, 2023

### This Week’s Finds (51–100)

#### Posted by John Baez

Grab a copy of this:

These are the second fifty issues of my column, from April 23, 1995 to March 23, 1997. They discuss quantum gravity, topological quantum field theory and other topics in mathematics and physics. They were typeset in 2020 by Tim Hosgood. Since then I’ve edited them more and changed most references to preprints into references to published papers and/or the arXiv. If you see typos or other problems please report them. (I already know the cover page looks weird).

By the way, I’ve also done a lot more editing of the first 50 issues, with help from Fridrich Valach, so please grab a new copy of this even if you already have it:

*This Week’s Finds in Mathematical Physics (1–50)*, 241 pages.

But let me say a bit more about what’s in issues 51–100.

## February 14, 2023

### Category Theory Outreach Panel

#### Posted by John Baez

They just don’t quit! Besides their *Joy of Abstraction* book club, the Topos Institute also has *another* way for you to start learning category theory. It’s called the CT Outreach Panel, and it’s happening on March 16, 2023 at 17:00 UTC.

Some of the best explainers of category theory in the world—Emily Riehl, Eugenia Cheng, Tai-Danae Bradley, Paul Dancstep and Oliver Lugg—will explain their approaches to the subject and answer questions.

You can submit questions here:

https://topos.site/ct-outreach-self-learners/

For more details, read on….

## February 12, 2023

### Talk on the Tenfold Way

#### Posted by John Baez

There are ten ways that a substance can have symmetry under time reversal, switching particles and holes, both or neither. But this fact turns out to extend far beyond condensed matter physics! It’s built into the fabric of mathematics in a deep way.

I gave a talk on this at Nicohl Furey’s seminar Algebra, Particles and Quantum Theory, and you can see a video of my talk here.

You can also watch another version, where I explain this stuff to my friend James Dolan.

## February 10, 2023

### The Joy of Abstraction

#### Posted by John Baez

The Topos Institute is excited to announce a book club for *The Joy of Abstraction* by Eugenia Cheng.

## February 5, 2023

### Applied Category Theory 2023

#### Posted by John Baez

You can now submit a paper if you want to give a talk here:

- 6th Annual International Conference on Applied Category Theory (ACT2023), University of Maryland, July 31 — August 4, 2023.

This event will be hybrid, so you can give a talk even if you can’t attend in person.