I have enjoyed Brian Greene's work for many years and had this in hard copy.  I wanted to reread it in electronic form as a more convenient format.  I found that I  again became lost in thought as Brian lead me through M theory and hyperspace planes / dimensions.  Admittedly, while appealing as a theory the concept of strings operating in Calabi-Yau manifolds while exhibiting frequency shifts can never be scientifically tested.  Struggling with the Heisenberg principle with electrons, how can possibly test for strings assuming that principle remains operative?<br><br>However, I have read critics who consider his work as "pop science."  While he does not go deeply in the the maths behind quantum mechanics, his intent was not to write a text book.  One challenge we face, and have since the dawn of scientific method is the communication of new paradigms and complex concepts into a more digestible form for our societies.  Only through engaging society in such a manner can be establish a broad base for priority change in terms of improved education, sustainable growth, investment  in the long view of society, and to prepare the next generations to manage our scarce resources properly while pushing the scientific frontier forward.  Authors and theorists such as Dr. Greene may error on the side of simplicity in this instance, but do it in the best, most beneficial and engaging manner possible.  Excellent read which I highly recommend.