This book is an attempt to share some of the fascinating and exciting ideas of modern theoretical physics with a non-mathematical audience. I also hope to give some appreciation of the exceptionally creative people who have generated these ideas. I had no intention of writing a comprehen- sive history of these ideas, however; I apologize to those physicists whose important contributions I may have omitted. Several people have contributed directly to the writing of this book, and I would like to take this chance to thank them. Clive Horwood of Praxis Publishing and Paul Farrell of Copernicus...