Toe central problem of physics today revolves around this conundrum:  Gravity is governed by Einstein's relativity theory, which requires that space-time is smooth.  Gravity has been experimentally verified.  Atomic forces are govered by quantum mechanics, which requires that space-time is bumpy, foamy, and irregular.  These atomic forces have been experimentally verified.<br>How can space time be smooth for gravity, and yet be bumpy for quantum machanics?  Enter string theory.<br>This book is a terrific introduction not only to string theory, but to relativity and quantum mechanics as well.  The first half of the book reviews the history and development of these theories, since they are a fundamental component  of string theory.  In particular, Greene's treatment of relativity uses some outstanding analogies to explain time dilation and gravitational warping.  I thought I understood the basics of relativity; this book still taught me a few things.<br>Analogies are this author's strength.  He uses them at every step to avoid the need to complex mathematical formulae.  There are no formulae in this book (some will think that a minus, but I view it as a plus.)  Using analogies, he's able to provide a comprehensible view of what 10-dimensional spacetime would be like, and how expanding one of the other dimensions might affect life in the Universe.  These 5 pages alone are probably worth the price of the book.<br>If you want a glimpse of one of the cutting-edge areas of particle physics research without needing to study math for 10 years, this book can give it to you.