String theory is a controversial subject at the moment - some people think that it has drifted too far from experimentally testable results. One such person is Lee Smolin, and in The Trouble with Physics
he presents his case. As the book proceeds it includes quite a bit of modern physics, but Smolin manages to do this without technicalities, and so the book can be read by those without much experience of the subject. Not everyone will agree with what Smolin is saying, but he presents some well thought out arguments ant the book is definitely worth reading.
The first chapter looks at the 'Five great problems of theoretical physics' and the book goes on to look at the history of physics, showing how unification has become a highly desirable goal. Smolin then introduces string theory, showing how several revolutions have given it the status it has today, but he also describes the many problems he sees with the theory. He goes on to examine the experiments which will be able to test string theory over the next few years, and has plenty of suggestions for what might replace it if/when it is found wanting. The last part of the book shows that Smolin sees the problem as going beyond string theory and extending to the whole of academic science and in particular how it is funded. He tells of some of the things which influenced his career, and suggests what might be done in future to avoid the increasing rigidity of scientific research.