John C. Baez's Blog, page 45
March 24, 2020
MIT Categories Seminar
The MIT Categories Seminar is an informal teaching seminar in category theory and its applications, with the occasional research talk. This spring they are meeting online each Thursday, 12 noon to 1pm Eastern Time.
The talks are broadcast over YouTube here, with simultaneous discussion on the Category Theory Community Server. (To join the channel, click here.) Talks are recorded and remain available on the YouTube channel.
Here are some forthcoming talks:
March 26: David Jaz Myers (Johns...
Category Theory Community Server
My student Christian Williams has started a community server for category theory, computer science, logic, as well as general science and industry. In just a few days, it has grown into a large and lively place, with people of many backgrounds and interests. Please feel free to join!
Join here:
https://categorytheory.zulipchat.com/join/52grbi4jw3b989fywh56pull/
and from then on you can just go here:
March 23, 2020
ACT@UCR Seminar
Coronavirus is forcing massive changes on the academic ecosystem, and heres another:
Were having a seminar on applied category theory at U. C. Riverside, organized by Joe Moeller and Christian Williams.
It will take place on Wednesdays at 5 pm UTC, which is 10 am in California or 1 pm on the east coast of the United States, or 6 pm in England. It will be held online via Zoom, here:
https://ucr.zoom.us/j/607160601
We will have discussions online here:
https://categorytheory.zulipchat.com/
The...
Applied Category Theory 2020 (Part 2)
Due to the coronavirus outbreak, many universities are moving activities online. This is a great opportunity to open up ACT2020 to a broader audience, with speakers from around the world.
The conference will take place July 6-10 online, coordinated by organizers in Boston USA. Each day there will be around six hours of live talks, which will be a bit more spaced out than usual to accommodate the different time zones of our speakers. All the talks will be both live streamed and recorded on...
March 20, 2020
From the Octahedron to E8
Heres a fun challenge for people confined due to coronavirus.
The E8 lattice is a thing of beauty, taking full advantage of the magic properties of the number 8. The octahedron has 8 sides. Wouldnt it be cool if you could build the E8 lattice from the humble octahedron?
David Harden thinks hes found a way! But I havent carefully checked that it works: it takes some calculations. Can you check it?
He wrote about it here:
David L. Harden, What other lattices are obtainable from this...
March 14, 2020
The Hardest Math Problem
Not about coronavirus just to cheer you up:
Puzzle. What math problem has taken the longest to be solved? It could be one thats solved now, or one thats still unsolved.
Lets start by looking at one candidate question. Can you square the circle with compass and straightedge? After this question became popular among mathematicians, it took at least 2295 years to answer it!
Its often hard to find when a classic math problem was first posed. As for squaring the circle, MacTutor traces it back to...
February 29, 2020
Applied Category Theory 2020 (Part 1)
Heres the big annual conference on applied category theory:
ACT2020, 2020 July 610, online worldwide. Organized by Brendan Fong and David Spivak.
This happens right after the applied category theory school, which will take place June 29 July 3. There will also be a tutorial day on Sunday July 5, with talks by Paolo Perrone, Emily Riehl, David Spivak and others.
To give a talk at ACT2020, you have to submit a paper. You can submit either original research papers or extended abstracts of...
Applied Category Theory 2020
Here’s the big annual conference on applied category theory:
• Applied Category Theory 2020, 2020 June 6-10, MIT, Cambridge Massachusetts. Organized by Brendan Fong and David Spivak.
This happens right after the applied category theory school, which will be held in the same location June 29 – July 3.
I’ll let you know when you can submit papers to give talks! We’re busy setting up the framework for refereeing those papers. Right now the conference website says this:
Applied category theory...
February 27, 2020
Topos Theory (Part 8)
Let’s look at an example of a presheaf topos, to see what various things I’ve been talking about actually look like—especially the subobject classifier.
Our example will illustrate the connection between topos theory and intuitionistic logic: that is, logic where the law of excluded middle, “p or not p”, fails. Intuitionistic logic goes back to Brouwer, who happens to have been born this very day in 1881. Topos theory formalizes intuitionistic logic in a way he might not have liked. But it...
February 23, 2020
Postdocs in Categories and Chemistry
The University of Southern Denmark wants to hire several postdocs who will use category theory to design enzymes. This sounds like a wonderful job for people who like programming, chemistry and categories—and especially double pushout rewriting. The application deadline is 20 March 2020. The project is described here and the official job announcement is here.
Let me quote a bit from the job announcement:
Several two-year postdoc positions starting 1 July 2020 are available at the University...
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