Atoms, Photons, and Quantum Mechanics

Abstract

Quantum mechanics was the outcome of physicists’ twenty-five year struggle to understand the behavior of matter and light at the atomic level. This struggle began in 1900 when Max Planck explained the spectrum of light from a hot body by an ad hoc assumption that atoms absorb and emit light in bundles of energy. In 1905 Einstein argued convincingly that light is itself quantized in bundles of energy and used the idea to explain the photoelectric effect (Chap. 13). Rutherford and Moseley showed (Chaps. 16 and 17) that the atom is made of discrete elements, and Bohr showed (Chap. 17) that atoms take on definite, or as we say today, quantized states of energy.