I don't think that's technically correct. From what I've read and seen, many physicists believe the math points firmly in that direction, but there has been no observational evidence confirming these ideas. Until string theory is able to make predictions that are confirmed by observation, these ideas remain firmly in the hypothesis stage.
Really NEJ, that's interesting. So why did he put it in a pop physics book I wonder? I'm just reading The Grand Design at the moment. A bit misleading isn't it?