John Baez's Stuff

What's New?

Check out the latest news on the groupoidification program: Christopher Walker's oral exam talk on A categorification of Hall algebras. He passed his oral, by the way.

In week283 of This Week's Finds, see galaxies in visible, infrared, and ultraviolet light:

Read the mystery of who discovered the icosahedron: Theaetetus or the ancient Scots. Read about Lieven le Bruyn's detective work which helped solve this case! And learn an amazing fact, proved in the last book of Euclid's Elements, which relates regular polygons with 5, 6, and 10 sides.

Everyone's talking about them. Check out the Mandelbulbs:

Are squares A and B the same color?

Yes! If you don't believe me, look at this, and then read the Wikipedia article about this illusion invented by Edward Adelson of MIT.

My students and I got a grant from the Foundational Questions Institute to work on categorifying fundamental physics. We've been hard at work:

• Alex Hoffnung, Christopher Walker and I wrote a paper on a branch of math that unifies linear algebra and the study of groupoids: Higher-Dimensional Algebra VII: Groupoidification.

• Alex Hoffnung, Chris Rogers and I wrote a paper on Lie 2-algebras in classical field theory: Categorified Symplectic Geometry and the Classical String, which will appear in Communcations in Mathematical Physics. Chris and I then wrote a followup: Categorified Symplectic Geometry and the String Lie 2-Algebra.

• Alex Hoffnung and I wrote a paper on the foundations of differential geometry: Convenient Categories of Smooth Spaces, which will appear in in Transactions of the American Mathematical Society.

• John Huerta and I wrote a paper on the beautiful patterns of particle physics: The Algebra of Grand Unified Theories. Then we wrote one on Division Algebras and Supersymmetry.
• Mike Stay and I wrote a review of category theory and its applications: Physics, Topology, Logic and Computation: A Rosetta Stone, to appear in Bob Coecke's volume New Structures of Physics.

• Aaron Lauda and I wrote a big expository paper called A Prehistory of n-Categorical Physics, which should appear in Deep Beauty: Mathematical Innovation and the Search for an Underlying Intelligibility of the Quantum World, edited by Hans Halvorson.

• My former student Derek Wise, my colleague Laurent Freidel, his student Aristide Baratin and I wrote a paper on Infinite-Dimensional Representations of 2-Groups.

What's on This Site

• This Week's Finds in Mathematical Physics (my column)
• Fun Stuff (expository writings and other diversions)
• Nasty Stuff (human rights, economics and other scandals)
• Seminar (tons of course notes)
• Serious Stuff (my actual research)
• Talks (transparencies of my talks, info on forthcoming talks)
• Diary (random thoughts)

• The n-Category Café

For common questions about physics, you can't beat this:

• Frequently Asked Questions in Physics

If reading my stuff makes you want to ask questions, take a look at this.

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© 2009 John Baez
baez@math.removethis.ucr.andthis.edu