The research leading to an understanding of the nature of light and the emission and absorption processes has been of paramount importance. It led from a beginning in 1900 to the development of quantum physics, reaching a high peak in the 1920s and a fruition towards the mid-century years with the completion of the very successful Quantum ElectroDynamic (QED) theory.
The manner in which these achievements have been treated by the Nobel Committee for Physics is both interesting and in some cases surprising.
The Wave-Particle Duality
A particle on the classical view is a concentration of energy and other properties in space and time, whereas a wave is spread out over a larger region of space and time. The question whether light are streams of particles (corpuscles) or waves is a very old one. This "either - or" formulation was classically natural and alien to the advanced "both - and" even the "neither - nor" solution of today. Early in the nineteenth century experiments were suggested and made to show that light is a wave motion. A key figure in this endeavour was Thomas Young, one of the most intelligent and clever scientists ever to live, who studied diffraction and interference of light already in 1803 with results that gave strong support to the wave theory of Christian Huygens as opposed to the particle or corpuscular theory of Isaac Newton. Further contributions were made by many other researchers, among them Augustin Jean Fresnel, who showed that light is a transverse wave.