If superstring theory works, has no infinities, etc. Then what is wrong with it? It must describe some Universe unless there is a contradiction in it somewhere? If it predicts all particles and gravity what is missing from it? Is it not compatible with cosmology for instance? Is Superstring theory just an approximation? (Like classical mechanics is an approximation to quantum mechanics setting h=0, and c-->infinity ). So is superstring like M-theory as classical mechanics is to quantum mechanics, i.e. merely an approximation? i.e. classical mechanics is perfectly consistent on it's own (if we think of the world as consisting only of billiard balls), but there are some things it can't explain like radioactivity. In that case is there something that superstrings can't explain that we need M-Theory for? By M-Theory I mean some kind of theory with some parameters that can smoothly be tuned to get the various string theories.