I should start with the fact that I'm not a physicist. I read the book and this review is about what I understood from reading the book.<br><br>The main purpose of the book is to present string theory as the fundamental theory to explain the universe (the first chapter and page 386). Considering the fact that the author is a string theorist, this is not surprising. Although a great effort is made to show string theory as a viable theory, my main take is not how powerful string theory is, but quite the opposite how weak, at least currently, it is.<br><br>The theory is not a result of any experimental observations. Strings are proposed to be vibrating tiny objects (strings) which nobody has observed directly or indirectly. It is built on some mathematical equations that nobody knows how to solve. Not only that, its approximating equations cannot even be solved. Page 19 reads: “… and those of other experts in the field indicate that it could be decades or even centuries before string theory is fully developed and understood. This may well be true. In fact, the mathematics of string theory is so complicated that, to date, no one even knows the exact equations of the theory. Instead, physicists know only approximations to these equations, and even the approximate equations are so complicated that they as yet have been only partially solved.”<br><br>The main problem with string theory is that it is almost completely built in people’s imaginations. But no one knows if that imagination will match with the realities of the physical world. It is even worse than this: Even the imagination is half baked. (There are incomplete and unsolvable mathematical equations behind imaginations though!) I’m completely disappointed with string theory. The author makes an effort to promote string theory but promoting an incomplete theory is a risky business. The author admits that all the efforts put into string theory may turn futile some time in the future.<br><br>There is a great summary of the two other big challenges faced by the physicists of the 20th century. A good summary of special relativity and general relativity are given in the first chapters, with lots of analogies.<br><br>It is still a good book for people who are not physicists and are interested in what string theory is about.