On 23 April 1858, Max Planck (1858–1947) was born. A German theoretical physicist, his earliest work was on the subject of thermodynamics, an interest he acquired from his studies under Kirchhoff, whom he greatly admired, and very considerably from reading R. Clausius’ publications. He published papers on entropy, on thermoelectricity and on the theory of dilute solutions.
At the same time also the problems of radiation processes engaged his attention and he showed that these were to be considered as electromagnetic in nature. From these studies he was led to the problem of the distribution of energy in the spectrum of full radiation. Experimental observations on the wavelength distribution of the energy emitted by a black body as a function of temperature were at variance with the predictions of classical physics. Planck was able to deduce the relationship between the energy and the frequency of radiation. In a paper published in 1900, he announced his derivation of the relationship: this was based on the revolutionary idea that the energy emitted by a resonator could only take on discrete values or quanta. The energy for a resonator of frequency v is hv where h is a universal constant, now called Planck’s constant.
This was not only Planck’s most important work but also marked a turning point in the history of physics. The importance of the discovery, with its far-reaching effect on classical physics, was not appreciated at first. However the evidence for its validity gradually became overwhelming as its application accounted for many discrepancies between observed phenomena and classical theory. Among these applications and developments may be mentioned Einstein’s explanation of the photoelectric effect.
In 1918, he won the Nobel Prize in Physics for his development of quantum theory. Planck’s constant is named for him, a foundation of quantum formulation. He was revered by his colleagues not only for the importance of his discoveries but for his great personal qualities. He also organized conferences and authored philosophical works, among them Science and Faith (1930) and Where is Science Going? (1932).
Planck was twice married. Upon his appointment, in 1885, to Associate Professor in his native town Kiel he married a friend of his childhood, Marie Merck, who died in 1909. He remarried her cousin Marga von Hösslin. Three of his children died young, leaving him with two sons.
Planck faced a troubled and tragic period in his life during the period of the Nazi government in Germany, when he felt it his duty to remain in his country but was openly opposed to some of the Government’s policies, particularly as regards the persecution of the Jews. He suffered a personal tragedy when one of his sons, Ernst Planck, who was active in the Nazi resistance, was executed for his part in an unsuccessful attempt to assassinate Hitler in 1944.