# The quantum theory of light pdf

An introduction to quantum mechanics. What is the quantum theory of light pdf field theory? What is the Dirac equation?

Permutation of particles – Are particles like gloves? 1925 which predate modern quantum mechanics.

The theory was never complete or self-consistent, but was rather a set of heuristic corrections to classical mechanics. The theory is now understood as the semi-classical approximation to modern quantum mechanics. Sommerfeld quantization condition, a procedure for selecting out certain states of a classical system as allowed states: the system can then only exist in one of the allowed states and not in any other state. The old quantum theory was sparked by the 1900 work of Max Planck on the emission and absorption of light, and began in earnest after the work of Albert Einstein on the specific heats of solids.

Einstein, followed by Debye, applied quantum principles to the motion of atoms, explaining the specific heat anomaly. In 1913, Niels Bohr identified the correspondence principle and used it to formulate a model of the hydrogen atom which explained the line spectrum. In the next few years Arnold Sommerfeld extended the quantum rule to arbitrary integrable systems making use of the principle of adiabatic invariance of the quantum numbers introduced by Lorentz and Einstein. This allowed the orbits of the electron to be ellipses instead of circles, and introduced the concept of quantum degeneracy.

The theory would have correctly explained the Zeeman effect, except for the issue of electron spin. Sommerfeld’s model was much closer to the modern quantum mechanical picture than Bohr’s. Throughout the 1910s and well into the 1920s, many problems were attacked using the old quantum theory with mixed results. Molecular rotation and vibration spectra were understood and the electron’s spin was discovered, leading to the confusion of half-integer quantum numbers.