ABSTRACT

The beginning of the twentieth century brought surprising nonclas-

sical phenomena. Max Planck’s explanation of black-body radiation

[1], the work of Albert Einstein on the photoelectric effect [2],

and Niels Bohr’s model to account for the electron orbits around

the nuclei [3] established what is now known as the old quantum theory. To describe and explain these effects, phenomenological models and theories were first developed, without any rigorous

and global justification. In order to provide a complete explanation

for the underlying physics of such new nonclassical phenomena,

physicists were forced to abandon classical mechanics to develop

novel, abstract, and imaginative formalisms.