Semiclassical Roles for Classical Orbits

Abstract

The precursor of quantum mechanics due to Bohr and Sommerfeld was already seen by Einstein [1] as applicable only to classically integrable dynamics. It has since been developed into a systematic semiclassical approximation, as sketched in Chap. 5. No prepotent guesses proved possible as to what quantum mechanics has to say about chaotic motion; the pertinent semiclassical approximations came into view with a delay of nearly 50 years in Gutzwiller’s pioneering work.