Gödel, Escher, Bach: An Eternal Golden Braid. By Douglas R. Hofstadter.

It took me probably three or four years to get through this book; it's very dense, with puns and whatnot scattered throughout. I found myself stopping to reread passages, trying to pick up on the many meanings.

The main thesis of the book appears to be that just about any natural process can be simulated with a defined-state Turing machine, via number and computational theory, Gödel's Theorem, and several other things.

Unfortunately, the march of time has passed him by; chaos theory and fuzzy logic have pretty much shown that some neurological processes can't be accurately simulated on a Turing machine, at least not in any reasonable amount of time.

But, whatever. He takes his many disparate subject areas and ties them into a coherent hole; that's pretty impressive.