Hi Tim, it's really interesting to see you here. (For those who don't know, I knew Tim from the cypherpunks mailing list. Hal Finney was an active member of the list as well. See http://www.activism.net/cypherpunk/crypto-anarchy.html if you're wondering what a cypherpunk is.) Two of the most prominent cypherpunks I know are now on my Everything mailing list. I wonder what that means... Anyway, welcome!
I remember your post on the cypherpunks list about category theory, but I have to admit I didn't pay it much attention since it didn't seem very relevent at the time. I guess this is my second chance to learn about category theory, so there are some questions for you. Suppose I had the time for only one book, which would you recommend? Also, can you elaborate a bit more on the motivation behind category theory? Why was it invented, and what problems does it solve? What's the relationship between category theory and the idea that all possible universes exists? Does it help understand or formalize the notion of "all possible universes"? I know in logic there is the concept of a categorical theory meaning all models of the theory are isomorphic. Does that have anything to do with category theory?