Thread: DeSitter group SO(4,1) intro View Single Post

 Quote by john baez Excellent! Sure! A connection on a bundle $$P \to B$$ is a functor from the "path groupoid" of the base space B to the "transport groupoid" of the bundle. Very roughly speaking, it goes like this: The path groupoid has points of B as objects and paths in B as morphisms. The transport groupoid has fibers of P as objects and maps betwen fibers as morphisms. Here's how we get a functor. First send each point x in B to the fiber $$P_x$$ over that point - that's what our functor does to objects. Then send each path from x to y in B to the "parallel transport" map from $$P_y$$ to $$P_y$$ - this is what our functor does to morphisms. I'm omitting a lot of details. All this is explained more precisely in these talks of mine, based on a a paper with Urs Schreiber. But, we go a lot farther: we think of "2-connections" as 2-functors between 2-categories. This lets us do parallel transport not just along curves, but along surfaces. You can read a lot more about "connections as functors" in my introduction to bundles and connections. This may be a little less stressful than picking what you want out of a more fancy discussion. Here's a little puzzle: if we think of a connection as a functor, what's a gauge transformation?
Thanks for framing it that way, I find this way of thinking to be quite seductive, I'll certainly have a look at those references and think about that puzzle.

As I said in another post of mine, there couldn't be anyone more novice than me, but this all seems pretty accessible the way it's being described, bravo :)