Brian Green is great but I found is apopogism for string theory to be weak sauce. Sure, the developement of string theory has involved some impresive mathematics and if people keep working at it I am sure they will continue to discover new and interesting theroms about abstract geometrical and alegraic structures, but string theory was conceived with very specific goals in mind for physics which have all fallen apart. String theory requires supersymetry which predicted that we would see aditional particles below a particular energy level which did not happen. It has not been shown that any of the many possible vaccum states in string theory give a spectrum of fundemental particles which match the standard model. Niether has it been shown that actually reproduces general relativity in the clasical limit, all that can be said about string theory "quantizing gravity" is that one of the string modes is a massless spin-2 particle. The hypothetical "graviton" of general relativity is also a massles spin-2 particle but it has not been shown that the massles spin-2 particle in string theory is the graviton of general relativity.