ABSTRACT
The concept of quanta was considered by many physicists as a mathematical trick. The quantum hypothesis of light was successful in explaining the photoelectric effect. Max Planck realized that the ultraviolet catastrophe could be eliminated by assuming that the average energy depends on the frequency of a mode and each mode could only take up energy in well-defined discrete portions. The assumption of the discrete energy distribution required a modification of the equipartition theorem. Planck introduced "discrete portions" so that he might apply Stefan Boltzmann's statistical ideas to calculate the energy density distribution of the blackbody radiation. The solution to the blackbody problem may be developed from a calculation of the average energy of a harmonic oscillator of frequency ν in thermal equilibrium at temperature T. The chapter re-examines the Compton scattering experiment. A significant feature of the derivation of the Compton scattering formula is that it relied essentially on special relativity.
