I just finished reading Stephen Hawking's, the Univers in  a Nutshell. It stretched my mind almost as much as the fourth dimension of time. But seriously, it was an excellent book that somewhat demystified Einstein's Theory of Relativity. He had me until "A Brane New World". I think I'm going to re-read that section. Hawking posits that Time and the Universe have a malleable shape and argues that it's yet another dimension that we do not quite understand.