"Hyperspace" by Michio Kaku (1994)

"Another, more relevant example for our universe might be living in a curved space given by a hypersphere, a sphere in four dimensions.  If we look ahead, light will circle completely around the small perimeter of the hypersphere and return to our eyes.  Thus we will see someone standing in front of us, with his back facing us, a person who is wearing the same clothes as we are.  We look disapprovingly at the unruly, unkempt mass of hair on this person's head, and then remember that we forgot to comb our hair that day.

"Is this person a fake image created by mirrors?  To find out, we stretch out our hand and put it on his shoulder.  We find that the person in front of us is a real person, not just a fake.  If we look into the distance, in fact, we see an infinite number of identical people, each facing forward, each with his hand on the shoulder of the person in front.

"But what is most shocking is that we feel someone's hand sneaking up from behind, which then grabs our shoulder.  Alarmed, we look back, and see another infinite sequence of identical people behind us, with their faces turned the other way."

The author of this book is a professor of theoretical physics at City University in New York.  He has written several other books in the Popular Science genre, among which is "Physics of the Impossible," which has also been reviewed here.  He is a frequent guest of talk shows, and has spent much of his career making esoteric theories understandable to the untrained.

This book is divided into four sections.  The first section provides a background for our present understanding of higher dimensional theory.  The second section discusses the give and take between classical mechanics, Einstein's general and special relativity, quantum mechanics, the Standard Model, and "current" superstring theory.  The third section extrapolates from our present understanding of higher dimensions, and draws conclusions about the possibility of time travel and parallel universes.  The fourth section outlines scenarios involving the end of life on Earth, the end of our solar system, and the end of the universe.  All four of these sections are combined - somewhat haphazardly - into a conclusion that is about as inconclusive as conclusions ever get.

This book is a bit difficult, but those with the patience for the material will find it rewarding.  Many of the extra-dimensional theories that Kaku expounds are very interesting, and he adds a lot anecdotes and personal insights into what might, in other hands, be boring material.  Many of the concepts introduced in "Hyperspace" are also quite novel.

And although I want to recommend this book, it was written in 1994, making it 19 years old.  With respect to physics, this means that "Hyperspace" is now ANCIENT.  It offers a good background for those unacquainted with modern physics, but those looking for the most current information are encouraged to seek out "Physics of the Impossible," or still more recent works on the same subject.  A lot can happen in 19 years - especially in the sciences!