ST from what I have read and what my limited understanding is difficult to wrap ones mind around its concepts. That the fabric of existance is vibrations eminating from strings the size of planke's length made of god knows what vibrating in some strange shaped 11 dimention space to produce the subatomic and fundlemental particles that make up the physical reality of the universe. It is almost like Brian Greene is saying Ok what needs to exist for my math to work out? 9 dimentions dont work? Ok let have 10, oh ten collapses the theory? Let make it 11 dimentions. I have hard enough time trying to imagine 5 dimentions let alone 11. As far as I know it is still a speculative theory that uses fantastic mathmatics and assertions to attempt to merge GR with QM. Not a very entertaining book IMO