As a growing acceptance of the Compton effect spread slowly across the experimental, phenomenological (approximations) and theoretical realms of the physicists’ concerns, five themes emerged related to how this blog is supposed to be approaching the world of the mesons. First, we can say good-bye to the fading of the aether; it is pretty much as faded as it will ever be by 1923. Second, we can say hello to the proto-photon as it emerges from the work of Einstein and Schroedinger and immediately runs into trouble with Bohr and the BKS theory which picture emission and absorption as acting in a virtual, statistically-governed region resembling a tiny patch of the old energy-storing aether. Third, as Schroedinger and Born get a handle on probability amplitudes, the amplitude approach immediately runs into trouble with Bohr and Heisenberg’s “Copenhagen Interpretation” much to the confusion of a century of quantum mechanists. Fourth, new techniques for partially quantized approximation emerge (such as the Born and Klein-Nishina) just in time to deal with a steady rise in the energies that experiments can deal with. And fifth, with the working out of field theories, new levels of theoretical approximations and refinements via perturbations and paths are developed – which gets us to the mid-1960s which is as far as this blog is going to go.

Hopefully, some of this all will be unraveled in future posts.

Meanwhile, a quick look at the development of atomic models because Bohr and Sommerfeld have some roles to play as we get into the details of things after Bohr and Sommerfeld do their atomic modelling.

First a quick preview of some bibliographic excursions – just enough here to get to an even quicker look at atomic models:

Helge Kragh, *Niels Bohr and the Quantum* *Atom* – a whole chapter on the Bohr-Sommerfeld Theory and great summaries
of the Thomson and Rutherford atomic models.

Suman Seth’s book about Sommerfeld. *Crafting
the Quantum *

Herman Haken and Hans Christoph Wolf’s *The
Physics of Atoms and Quanta*…which has a whole chapter on the Bohr atom and
Sommerfeld’s extension of the Bohr model and Sommerfeld’s elucidation of new
quantum aspects of atomic electrons.

And then right on into Thomson’s atomic model – our first atomic model (a summary of Kragh pages 12-17):

After some early variations on the atomic theme, by 1904, Thomson’s atomic model was based on a massless, positively charged sphere of atomic dimensions stuffed with thousands of electrons which contained the mass of the atom and its negative charge. This mass of electrons ran on circles subject to Larmor’s radiative power formulation which described them as energy via radiation caused by their acceleration as they went around and around. However, with enough electrons the whole thing could be made relatively stable both electrodynamically and mechanically if one used the right amount of vortex-based oscillations. The outermost rings of electrons would be packed but interactively neutral.

Such atoms could be sketchily fitted into the ballpark values found for radioactivity, light emission and absorption and the scattering of beta particles (electrons, ie Thomson Scattering). Unfortunately for the model, by 1906, Thomson’s own experimental work showed that atoms had thousands of times fewer electrons than the model needed to function. This also brough up the question of where the atomic mass came from if it didn’t result from the presence of thousands of gyrating electrons.

For some reason this sequence of models and structures (from 1900 to 1904) are generally referred to as the “plum pudding” model, as if the electrons were just tastefully sprinkled in the massless positive sphere. Actually, there were thousands of them and they were moving and oscillating in rings – so nothing about Thomson’s atomic model really suggests a plum pudding at all nor was it ever anything like a simple model that has say one electron for Hydrogen and two for Helium – though Thomson’s experimental work did suggest exactly that. Note also that in the Thomson model electrons move very actively, though in very large numbers. Apparently, this is not easy to visualize, possibly because it is hard to imagine the necessary thousands of electrons. Anyway, next time the Rutherford model which could be seen as something like this: