The Birth of Quantum Physics - Boltzmann, Planck, Einstein, Nernst, and others

At the end of the 19th century due to the rapid growth of artificial illumination there developed a need for quantitative optical data and relevant standards. Hence, in the optical laboratory of the Physikalisch-Technische Reichsanstalt in Berlin the spectral distribution of the light intensity was measured over a large frequency range. The new data could not be explained in terms of the existing models. Between October and December 1900 Max Planck arrived at his famous radiation law based on Boltzmann’s probabilistic entropy expression. As a key novelty Planck introduced the quantization of the radiation energy in terms of the discrete energy elements hν, with the universal constant h. Whereas Planck did not accept the full impact of the new quantum physics for nearly 10 years, it was Albert Einstein with his light quanta in 1905 and his quantized lattice vibrations in 1906, and a few years later Walther Nernst with his specific heat measurements, who strongly pushed the new ideas about the quantum physics.