The author presents a motivating and comprehensive popular treatment of relativity, quantum mechanics and string theory. His entertaining style of presenting novel and abstract concepts, such as, submicroscopic strings vibrating in higher dimensions causing the physical properties of matter and energy and the curled nature and geometry of the extra dimensions, tends to be rather convincing of their validity. It entices the reader to seek more, especially since the book is now more than ten years old and therefore leaves out more recently formulated aspects of string theory.<br><br>However the treatment is incomplete because it leaves a number of intuitive questions unanswered or unconvincing.<br>1) why aren't three spatial dimensions sufficient to allow for the vibrating modes of strings?<br>2) why are the extra dimensions necessarily so small?<br>3) what might constitute the substance of strings?<br>4) why do vibrating strings cause the physical interactions of particles?<br>5) do objects have extent that completely covers the extra dimension? if so why can't that be true for large dimensions?<br>6) What about Calibi-Yau manifolds that make them the only possible geometry for the extra dimensions?<br><br>Another question, can string theory ever be used to find solutions for long distance space travel?