I came here interested in M-theory but there are no threads like yours and selfadjoints. (Also I just got a response to my request for an explanation of what is wrong with M-theory (S&M theory as he called it) with a long discouraging report on the subject. Basically he said that "if it's correct we will know - in about 150 years" ha ha. Hopefully it won't take as long for LQG). I will therefore start with LQG and Rovelli's book which looks easier and more leisurely then Thiemann.