John Baez's Stuff

What's New?

In week276 of This Week's Finds, hear the shocking news about this star:

Read about the Local Bubble, the Loop I Bubble, the cloudlets from Sco-Gen, and the "local fluff". Check out the nLab! And learn how Paul-André Mélliès and Nicolas Tabareau have taken some classic results of Lawvere on algebraic theories and generalized them to other kinds of theories, like PROPs.

Check out my new album:

Or, if you don't like music made by collaboration with a cellular automaton, try my short history of the Earth, aimed at physicists.

Robin Canup's simulation of Earth and Theia, 50 minutes after their initial collision.
Color indicates temperature.

Read about the Catlin Arctic Survey:

Check out the rings of Saturn's moon Rhea — and check out Greg Egan's light mill.

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

• Alex Hoffnung, Christopher Walker and I wrote a paper called Groupoidification Made Easy.

• Alex Hoffnung, Chris Rogers and I wrote a paper on Lie 2-algebras in classical field theory: Categorified Symplectic Geometry and the Classical String. 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 has been accepted for publication 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.
• 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.

• My former student Derek Wise, my colleague Laurent Freidel, his student Aristide Baratin and I wrote a big 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