"What's New In Physics"

John Baez's Stuff

I'm a mathematical physicist. I'm about to make a big career shift: I've been working on n-categories and fundamental physics, but now I'm going to the Centre for Quantum Technologies in Singapore for two years, and I plan to think about technology and the global ecological crisis. I'll probably keep thinking about the old stuff a bit, too.

What's New?

When you make fuel from corn, do you use more energy than you gain? Join the discussion on Azimuth.

"Week304" of This Week's Finds features the third part of my interview with Nathan Urban. Learn how Lake Agassiz flooded out into the Northern Atlantic and made temperatures in Europe plunge by shutting down the Atlantic Meridional Overturning Circulation, or AMOC. Could global warming cause a similar event? Learn about Urban's work on this question. It's a great introduction to the mathematics of climate modelling!

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 that unifies linear algebra and the study of groupoids: Higher-Dimensional Algebra VII: Groupoidification. This will appear in Theory and Application of Categories. We are now working on the next two papers in this series, which will treat Hecke algebras and Hall algebras in more detail. The first will be called Higher-Dimensional Algebra VIII: the Hecke Bicategory. This will be based on a paper by Alex Hoffnung called The Hecke Bicategory.

   

• 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, which will appear in Homology, Homotopy and Applications.

   

• 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, which was published in the Bulletin of the American Mathematical Society. Then we wrote one called Division Algebras and Supersymmetry I, which will appear in Proceedings of the NSF/CBMS Conference on Topology, C*-Algebras, and String Theory. Then we wrote a sequel: Division Algebras and Supersymmetry II. We wrote an expository article on the octonions which will appear Scientific American. And we wrote a survey paper, Invitation to Higher Gauge Theory, which will appear in General Relativity and Gravitation.

   

• 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 for Physics. We also wrote a paper on Algorithmic thermodynamics.

Also:

• Aaron Lauda and I wrote a big expository paper called A Prehistory of n-Categorical Physics, which will 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, which will appear as a book in Memoirs of the American Mathematical Society.

Here's a great photo of zodiacal light versus the Milky Way, taken in Tenerife by Daniel Lopez:

• 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)

Also try my blog at:

• The n-Category Café

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

• Frequently Asked Questions in Physics

I don't maintain this Physics FAQ - Don Koks does, so please send any comments about it to him, not me!

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

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