Planck, Max Karl Ernst Ludwig

Born Apr. 23, 1858, in Kiel; died Oct. 4, 1947, in Göttingen. German theoretical physicist.

The son of a lawyer, Planck studied at the universities of Munich (1874–77) and Berlin (1877–78). He also attended the lectures of H. von Helmholtz and G. Kirchhoff. Beginning in 1880 he was a privatdocent at the University of Munich, and subsequently a professor at the universities of Kiel (1885) and Berlin (1889). In 1894 he became a member of the Prussian Academy of Sciences, located in Berlin, and served as the academy’s permanent secretary from 1912 to 1943. Planck was also president of the Kaiser Wilhelm Society (renamed the Max Planck Society in 1948).

As a student, Planck, influenced by the writings of R. Clausius, became interested in thermodynamics. His early investigations were devoted to clarifying the concepts of entropy and irreversibility and substantiating the second law of thermodynamics, the subject of his doctoral dissertation (1879). His early studies also dealt with applying thermodynamics to physicochemical processes, in particular, with the dissociation of gases and with weak solutions (1883–88). On the basis of W. Nernst’s theory of electrolytes, Planck calculated the potential difference of two electrolytic solutions (1890). His works on the thermodynamic theory of radiation, which led to the se-miempirical establishment of the formula for the energy distribution in the electromagnetic spectrum of a blackbody (Planck’s radiation law), were of major importance. Planck presented this formula at a meeting of the Physical Society in Berlin and two months later, on Dec. 14, 1900, demonstrated its derivation, which is based on the assumption that the energy emitted by an oscillator is an integral multiple of the quantity hv, where v is the frequency of radiation and h is a new universal constant, which Planck called the elementary quantum of action (Planck’s constant). He later tried in vain to incorporate h in the scheme of classical concepts. The introduction of this quantity marked the birth of the era of a new physics—quantum physics.

Planck’s subsequent research was devoted to working out certain aspects of the theory of radiation, thermodynamics (including the substantiation of Le Châtelier’s principle), relativ-istic mechanics, and other fields. His monographs on the main branches of theoretical physics, noted for their depth and clarity of exposition, occupy an important place in Planck’s scientific legacy. In a number of articles and lectures, Planck discussed the philosophical and methodological problems of natural science. Beginning in 1895 he sharply criticized the positivist views of W. Ostwald, E. Mach, and others; subsequently he came out against physical indeterminism, insisting that recognition of the objectivity of natural laws and the causality principle is a necessary prerequisite for scientific knowledge.

Planck was a corresponding member of the St. Petersburg Academy of Sciences (1913), an honorary member of the Academy of Sciences of the USSR (1926), and a member of the London Royal Society (1926). He was awarded a Nobel Prize in 1918.