No Subject

2-categories are also fundamental to my work on spin foam models
of quantum gravity, but I have done my best to keep that fact secret, 
to avoid scaring the physicists: 

An introduction to spin foam models of BF theory and quantum gravity, 
in Geometry and Quantum Physics, eds. Helmut Gausterer and Harald Grosse, 
Lecture Notes in Physics, Springer-Verlag, Berlin.  Available as 
http://xxx.lanl.gov/abs/gr-qc/9905087

Best,
John Baez