While the quantum mechanical framework was being developed after Plank’s discovery in 1901, physicists were wrestling with the dual character of light (wave or particle?). Thomas Young’s double slit experiment in 1803, where interference patterns were observed, seemed to show without doubt that light was a wave phenomenon. However, Planck’s interpretation of black body radiation as light quanta, followed by Einstein’s explanation of the photoelectronic effect, both contradicted the light-as-wave theory. Additionally, a shocking discovery was made by Compton in 1925. Compton found that when he let X-rays (a form of light with extremely short wavelengths) collide head-on with a bundle of electrons, the X-rays were scattered as if they were particles. This phenomenon became known as the “Compton scattering experiment.”

At about that time, French physicist Louis de Broglie combined two simple formulas: Plank’s light quanta expression (*E = h**ν,* with ν as the frequency) and Einstein’s famous energy‑mass equation (*E = mc*^{2}). This led to another simple equation: λ* = h/mc*, with* λ *as wavelength. This equation really tells us that all matter has wave properties. However, since the mass, *m*, of most everyday visible objects is so large, their wavelengths are too small for us to notice any wave effect. But when we consider the small masses of atomic particles such as electrons and protons, their wavelengths become relevant and start to play a role in the phenomena we observe.

All this brought Erwin Schrödinger to the conclusion that electrons should be considered waves, and he developed a famous wave equation that very successfully described the behavior of electrons in a hydrogen atom. Schrödinger’s equation used a wave function to describe the probability of finding a rapidly moving electron at a certain time and place. In fact, the equation confirmed many ideas that Bohr used to build his empirical atom model. For instance, the equation correctly predicted that the lowest energy level of an atom could allow only two electrons, while the next level was limited to eight electrons, and so on. In the year 1933 Schrödinger was awarded the Nobel Prize for his wave equation.

Schrödinger had, as did Planck and Einstein, an extensive background in thermodynamics. From 1906 to 1910, he studied at the University of Vienna under Boltzmann’s successor, Fritz Hasenöhrl. Hasenöhrl was a great admirer of Boltzmann and in 1909 he republished 139 of the latter’s scientific articles in three volumes [Hasenöhrl, 1909]. It was through Hasenöhrl that Schödinger became very interested in Boltzmann’s statistical mechanics. He was even led to write of Boltzmann, *“His line of thoughts may be called my first love in science. No other has ever thus enraptured me or will ever do so again *[Schrödinger 1929].*” *Later he published books, (*Statistical Thermodynamics and What’s Life),* and several papers on specific heats of solids and other thermodynamic issues. [1]

© 2009 Copyright John Schmitz

[1] Taken from “The Second Law of Life”:http://www.elsevierdirect.com/product.jsp?isbn=9780815515371