Max Karl Ernst Ludwig Planck

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1858-1947

German Physicist

Max Planck revolutionized physics by originating the quantum theory, which states that all radiant energy, such as light, is made up of irreducible packets called quanta. A quantum of electromagnetic radiation is called a photon. The energy a photon carries is proportional to its frequency. So, for example, an x-ray photon is more energetic than a photon of visible light, because x rays are of higher frequency than visible light. The constant of proportionality, h, has come to be called Planck's constant. Planck's particle-like model of light provided a way to explain the emission and absorption of energy bymatter. He was awarded the Nobel Prize in physics in 1918.

Planck was born on April 23, 1858, in Kiel, Germany, to a distinguished family that valued scholarship. Planck had many interests; he did well in all his school subjects from science and mathematics to the classics, was a skilled musician with perfect pitch, and enjoyed the outdoors. Upon graduation from secondary school, he found it difficult to choose a career from among all his enthusiasms, but he finally decided that his greatest strength was in physics. He received his doctorate at the University of Munich when he was only 21, and continued there as a lecturer for six years. In 1885 he became an associate professor at the University of Kiel, where his father taught law. Four years later, he was appointed to the University of Berlin, and he remained there for the rest of his professional life.

Planck developed his radiation law in an attempt to reconcile high- and low-frequency experimental evidence regarding the emission of energy by matter at various temperatures. However, when he went back to derive it from first principles, in the process originating the concept of the quantum, he found that he was forced to accept the statistical view of thermodynamics that had been put forth by Ludwig Boltzmann (1844-1906). This was rather distasteful to Planck, who preferred natural laws to be absolutely defined. He was later to join with Albert Einstein (1879-1955) and Erwin Schrödinger (1887-1961) in opposing the indeterminate nature of quantum mechanics, in which the position of a particle is defined as a probability distribution.

Planck was a greatly respected leader in the German physics community, highly influential even after his retirement from the university in 1928. He made Berlin into a major center for theoretical physics, bringing in luminaries such as Einstein, Schrödinger and Max von Laue (1879-1960), and it remained so until the rise of the Nazis threatened many of its members. Planck bravely made his protests directly to Adolf Hitler, and as his Jewish colleagues fled for their lives, he stayed in Germany to try to preserve what was left.

Planck had already endured a great deal of tragedy; his 1918 Nobel Prize was one of the few bright spots in his later life. His wife, to whom he was greatly devoted, died in 1909 after 22 years of marriage. Between 1916 and 1919 both of his daughters died in childbirth and one of his sons was killed in World War I. During World War II the house where Plancklived with his second wife, with whom he had had one son, was completely destroyed in a bombing raid. The only remaining child of Planck's first marriage became involved in a foiled plot to assassinate Hitler and was tortured and murdered by the German police in 1945. Although Planck had stoically persevered through all the previous sadness, the horror of his son's death at the hands of the Nazis was too much for the elderly physicist, and he lost his will to live. He died on October 4, 1947, in Göttingen at the age of 89.

Max Planck. (Library of Congress. Reproduced with permission.)