Max Planck

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Lore & Background

Max Planck was born on 23 April 1858 in Kiel, the son of Johann Julius Wilhelm Planck and his second wife, Emma Patzig. He was baptized with the name of Karl Ernst Ludwig Marx Planck; by the age of ten he signed with the name Max and used this for the rest of his life. Planck came from a traditional, intellectual family: his paternal great-grandfather and grandfather were both theology professors at the University of Göttingen; his father was a law professor at Kiel University and the Ludwig-Maximilians-Universität München. Planck was the sixth child in the family, though two of his siblings were from his father's first marriage. Among his earliest memories was the marching of Prussian and Austrian troops into Kiel during the Second Schleswig War in 1864. In 1867, the family moved to Munich, where Planck enrolled at Maximiliansgymnasium. There, his mathematical talents emerged early and he later came under the tutelage of Hermann Müller, a mathematician who taught him astronomy and mechanics as well as mathematics. It was from Müller that Planck first learned the law of conservation of energy. Planck graduated early, at age 17. Planck was gifted in music; he took singing lessons and played piano, organ and cello, and composed songs and operas. Per Encyclopædia Britannica, "He possessed the gift of absolute pitch and was an excellent pianist who daily found serenity and delight at the keyboard, enjoying especially the works of Schubert and Brahms." In 1874, Planck enrolled at the Ludwig-Maximilians-Universität München. Under professor Philipp von Jolly's supervision, Planck performed the only experiments of his scientific career, studying the diffusion of hydrogen through heated platinum, but then transferred to theoretical physics. Jolly advised Planck against going into theoretical physics; Planck recalls that in 1878, Jolly argued that physics was almost complete, being a "highly developed, nearly fully matured science, that through the crowning achievement of the discovery of the principle of conservation of energy will arguably soon take its final stable form". In 1877, Planck went to the Friedrich Wilhelm University of Berlin for a year of study with physicists Hermann von Helmholtz and Gustav Kirchhoff and mathematician Karl Weierstrass. He wrote that Helmholtz was never quite prepared, spoke slowly, miscalculated endlessly, and bored his listeners, while Kirchhoff spoke in carefully prepared lectures which were dry and monotonous. He soon became a close friend with Helmholtz. While there he undertook a program of mostly self-study of Rudolf Clausius' writings, which led him to choose thermodynamics as his field. In October 1878, Planck passed his qualifying exams and in February 1879 defended his thesis "Über den zweiten Hauptsatz der mechanischen Wärmetheorie" (On the second law of mechanical heat theory). He briefly taught mathematics and physics at his former school in Munich. By the year 1880, Planck had obtained the two highest academic degrees offered in Europe: a doctorate degree and his habilitation thesis entitled "Gleichgewichtszustände isotroper Körper in verschiedenen Temperaturen" (Equilibrium states of isotropic bodies at different temperatures). In 1880, Planck became a Privatdozent (unsalaried lecturer) at the Ludwig-Maximilians-Universität München. In April 1885, Planck was appointed associate professor of Theoretical Physics at Kiel University. He published his Treatise on Thermodynamics in 1897. In 1889, Planck was named the successor to Kirchhoff's position at the Friedrich Wilhelm University of Berlin – presumably thanks to Helmholtz's intercession – and by 1892 became Full Professor. In 1907, he was offered Ludwig Boltzmann's position in Vienna, but turned it down to stay in Berlin. During 1909, as a professor at the Friedrich Wilhelm University of Berlin, he was invited to become the Ernest Kempton Adams Lecturer in Theoretical Physics at Columbia University in New York City. He retired from Berlin on 10 January 1926, and was succeeded by Erwin Schrödinger. As a professor at Berlin, Planck joined the local Physical Society. He later wrote: "In those days I was essentially the only theoretical physicist there, whence things were not so easy for me, because I started mentioning entropy, but this was not quite fashionable, since it was regarded as a mathematical spook". Thanks to his initiative, the various local Physical Societies of Germany merged in 1898 to form the German Physical Society (Deutsche Physikalische Gesellschaft, DPG); from 1905 to 1909 Planck was the president. Planck started a six-semester course of lectures on theoretical physics, "dry, somewhat impersonal" according to Lise Meitner, "using no notes, never making mistakes, never faltering; the best lecturer I ever heard" according to an English participant, James R. Partington, who continues: "There were always many standing around the room. As the lecture-room was well heated and rather close, some of the listeners would from time to time drop to the floor, but this did not disturb the lecture." Planck did not establish an actual "school"; the number of his graduate students was only about 20, among them: Max Abraham (1897), Max von Laue (1903), Moritz Schlick (1904), Walther Meissner (1906), Fritz Reiche (1907), Walter Schottky (1912), and Walther Bothe (1914). In his thesis in 1879, Planck summarized Clausius' writings, pointing out contradictions and inaccuracies in their formulation and then clarifying them. He generalized the validity of the second law to all processes in nature; Clausius had limited its application to reversible processes and thermal processes. Planck dealt intensively with the new concept of entropy and emphasized that entropy is not only a property of a physical system, but at the same time a measure of the irreversibility of a process: If entropy is generated in a process, it is irreversible, since entropy cannot be destroyed according to the second law. In reversible processes, the entropy remains constant. He presented this fact in detail in 1887 in a series of treatises entitled "On the Principle of the Increase of Entropy".

Reader's Guide

Max Planck's significance lies in his foundational role in quantum theory, which transformed physics. His discovery of energy quanta, for which he received the 1918 Nobel Prize, introduced the idea that energy is emitted in discrete packets, not continuously. This led to the Planck constant, a fundamental constant in quantum mechanics, and the Planck relation, which states that the energy of a photon is proportional to its frequency. He also derived a set of natural units, now called Planck units, based on physical constants. His work on entropy and thermodynamics, influenced by Clausius, was central to his early career. As a professor at Berlin, he helped merge local physical societies into the German Physical Society and served as its president. The Max Planck Society, named after him, continues to support scientific research across many disciplines. His legacy is as a key figure in the shift from classical to modern physics.

Did You Know?

• Planck was baptized with the name Karl Ernst Ludwig Marx Planck, but by age ten he signed with the name Max and used it for the rest of his life.
• He possessed the gift of absolute pitch and was an excellent pianist, enjoying especially the works of Schubert and Brahms.
• Under professor Philipp von Jolly, Planck performed the only experiments of his scientific career, studying the diffusion of hydrogen through heated platinum.
• Planck's lectures were so packed that listeners would sometimes drop to the floor from the heat, but this did not disturb the lecture.
• He was twice President of the Kaiser Wilhelm Society, which was renamed the Max Planck Society in 1948.