Max Planck

Max Planck (1858-1947), German physicist and Nobel laureate, who was the originator of quantum theory.

Planck was born in Kiel, Germany, on April 23, 1858, into an academic family. His father was professor of constitutional law at the University of Kiel. In 1867 the family moved to Munich, where Planck attended secondary school at the famous Maximilian Gymnasium. He showed particular promise in music, playing the piano and organ, and toyed with the idea of following a musical career. Instead, he decided to study physics, first at the University of Munich, which he entered in 1874, and from 1877 at the University of Berlin, where his teachers included Karl Weierstrass, Hermann Ludwig Ferdinand von Helmholtz, and Gustav Kirchhoff. He returned to Munich, received his doctorate in 1879 with a thesis on the second law of thermodynamics, and continued to work for his habilitation (which qualifies the recipient to teach at a university), which was awarded in 1880, after he had submitted his thesis on entropy and the mechanical theory of heat. He was privatdozent (lecturer) at the University of Munich from 1880 to 1885, and lived with his parents during the five years that he held this unsalaried post. He was appointed associate professor of theoretical physics at the University of Kiel in 1885. In 1888 he succeeded Kirchhoff at the University of Berlin, first as extraordinary professor of theoretical physics, promoted in 1892 to ordinary professor. He remained there until his retirement in 1927.

Planck did his most brilliant work in Berlin. As a result of studying the phenomenon of blackbody radiation, he postulated in 1900 his revolutionary idea that energy is radiated in small, discrete units, which he called “quanta”. This meant rejecting the commonly held view at the time that the second law of thermodynamics was an absolute law of nature, and accepting instead the interpretation of Ludwig Boltzmann that it was a statistical law. Developing this law further, Planck discovered a universal constant of nature, which came to be known as Planck’s constant. This states that the energy of each quantum is equal to the frequency of the radiation multiplied by the universal constant. His ideas, however, did not supersede the theory that radiation is propagated waves. Physicists now believe that electromagnetic radiation combines the properties of both waves and particles.

Planck’s quantum theory marked a turning point in classical physics, but its far-reaching effects were not appreciated by him, nor was it generally accepted until its application could account for many discrepancies between observed phenomena and classical theory. Early successful applications were the explanation by Albert Einstein of the photoelectric effect (1905) and the calculation by Niels Bohr of spectral lines (1913). Planck was aged 42 years when he made his historic quantum announcement. Further development was left to others, and formed the basis of an entirely new field of physics, known as quantum mechanics, which provided a foundation for research in such fields as nuclear power. Planck, like Einstein, could never accept the acausal nature of quantum mechanics. Both believed that it was a transitory phase that eventually would evolve into a more satisfactory theory describing the harmony of nature.

Sadly, the period of Planck’s life after the triumph of quantum theory was filled with tragedy. His first wife, Marie Meck, whom he had married in 1885, died in 1909. Two years later he married her cousin, Marga von Hösslin. Of the two sons of his first marriage one was killed in 1916 during World War I, and the other was executed for his part in an unsuccessful attempt to assassinate Adolf Hitler in 1944. His twin daughters both died in childbirth. He was survived by the one son from his second marriage.

Planck received many honours for his work, notably the 1918 Nobel Prize for Physics. He was elected a Fellow of The Royal Society in 1926, and was awarded the society’s Copley Medal in 1928. In 1930 he was elected president of the Kaiser Wilhelm Gesellschaft for the Advancement of Science, the leading association of German scientists, which was renamed the Max Planck Society in 1948. He endangered himself by openly criticizing the Nazi regime that came to power in Germany in 1933 and was forced out of the society in 1937.

He remained in Germany during World War II, moving from Berlin to Rogätz, near Magdeburg, in 1943. His home in the suburbs of Berlin was destroyed by fire after an air raid in 1944, when the flames consumed his irreplaceable scientific notebooks. He was taken to Göttingen by the Allies at the end of the war, and at the age of 87 he again became president of the Kaiser Wilhelm Gesellschaft in 1945-1946 to help with the reconstruction of German science. He died at Göttingen on October 4, 1947. Among his writings that have been translated into English are The Theory of Heat Radiation (2nd rev. ed. 1913; trans. 1914; reprinted 1991), Where Is Science Going? (trans. 1932; reprinted 1981), Introduction to Theoretical Physics (5 vols., 1932-1933), and Philosophy of Physics (1936; reissued 1963). He described his own life in his Scientific Autobiography and Other Papers (trans. 1949; reissued 1968). See also Planck’s Radiation Law.