M theory and quantum mechanics

String theory has the peculiar property that quantum formulas were discovered before any classical formulas and that the quantum formulas are unusually beautiful. It has always been perplexingly hard to find an underlying classical theory via whose quantization string theory could be effectively understood. Nowadays, in the light of quantum duality symmetries and the unification of the different string theories in M theory, we are beginning to suspect a relation between quantum and classical physics quite different from what we have had before. The matrix model may be pointing the way, but we have not yet grasped its implications.