text: I will recommend the book "The elegant universe" by Brian Greene. He is a researcher in the field and however has a very clear and easy to follow way of explaining very complicated issues. Here is the link: http://www.amazon.com/Elegant-Universe-Superstrings-Dimensions-Ultimate/dp/0375708111/sr=8-1/qid=1162812819/ref=pd_bbs_1/002-4909890-8627210?ie=UTF8&s=books