The same but different
Michio Kaku went online to chat about parallel universes. Read his answers to your questions in the BBC Space site.
Princeton University - Prof Paul Steinhardt http://feynman.princeton.edu/~steinh/
Dr Michio Kaku www.mkaku.org
Superstring phenomenology and the brane-world
Hyperspace: a scientific odyssey through parallel universes, time warps and the tenth dimension, Michio Kaku
The Elegant Universe: superstrings, hidden dimensions and the quest for the ultimate theory, Brian Greene
Parallel Universes: the search for other worlds, Fred Alan Wolf
The Universe in a Nutshell, Stephen Hawking
Flatland: a romance of many dimensions, Edwin Abbott Abbott, Kendahl J Jubb. 19th century fiction, first published in 1884.