His father, a professor of law at the University of Kiel, gave his son a deep sense of integrity, fairness, and the value of intellectual achievement—traits that characterized Planck’s behavior through all phases of his life. He studied physics at the universities of Munich and Berlin. In Berlin, he had the opportunity to interact directly with such famous scientists as Gustav Kirchhoff (1824–1887) and Rudolf Clausius (1822–1888). The former introduced Planck to the classical interpretations of blackbody radiation, while the latter challenged him with the significance of the second law of thermodynamics and the elusive concept of entropy.
In 1879, Planck received his doctoral degree in physics from the University of Munich. From 1880 to 1885, he remained at Munich as a lecturer in physics. In 1885, he was appointed associate professor in physics at the University of Kiel, and he remained in that position until 1889, when he succeeded Kirchhoff as professor of physics at the University of Berlin. He remained in that position until his retirement in 1926.
While teaching at the University of Berlin at the end of the nineteenth century, Planck began to address the very puzzling problem involved with the emission of energy by a blackbody radiator as a function of its temperature. He solved this problem by introducing a bold new formula that successfully described the behavior of a blackbody radiator over all portions of the electromagnetic spectrum. To reach his successful formula, Planck assumed that the atoms of the blackbody only emitted their radiation in discrete, individual energy packets—which he called quanta.
In his classic paper published in late 1900, Planck presented the new blackbody radiation formula. He included the revolutionary idea that the energy for a blackbody resonator at a frequency (ν) is simply the product hν, where h is a universal constant, now called Planck’s constant. This 1900 paper, published in Annalen der Physik, contained Planck’s most important work and represented a major turning point in the history of physics. The introduction of quantum theory had profound implications on all modern physics, from the way scientists treated subatomic phenomena to the way they modeled the behavior of the universe on cosmic scales.
Yet Planck himself was a reluctant revolutionary. For years, he felt that he had only created the quantum postulate as a “convenient means” of explaining his blackbody radiation formula. Other physicists, however, were quick to seize Planck’s quantum postulate and then go forth and complete Planck’s revolutionary movement—displacing classical physics with modern physics. For example, Albert Einstein (1879–1955) quickly used Planck’s quantum postulate to explain the photoelectric effect in 1905, and Niels Bohr (1885–1962) applied quantum mechanics in 1913 to create his world-changing model of the hydrogen atom. Planck received the 1918 Nobel Prize in physics in recognition of his epoch-making investigations into quantum theory.
He maintained a strong and well-respected reputation as a physicist even after his retirement from the University of Berlin in 1926. But as Planck climbed to the pinnacle of professional success, his personal life was marked with nothing but tragedy. At approximately the same time that he received his Nobel Prize, his oldest son, Karl, died in combat in World War I, and both his twin daughters, Margarete and Emma, died during childbirth, about a year apart. Then, in the 1930s, when Adolph Hitler seized power in Germany, Planck, in his capacity as the elder statesman of the German scientific community, bravely praised Einstein and other German-Jewish physicists in open defiance of the ongoing Nazi persecutions. Planck even met personally with Hitler to try to stop the attacks against Jewish scientists. But Hitler ignored Planck’s pleas. As a final gesture of protest, Planck resigned as president of the Kaiser Wilhelm Institute in 1937—a leadership position in German science in which he had proudly served with great distinction since 1930. Today, that institution is called the Max Planck Institute in his honor.
During the closing days of World War II, personal tragedy continued to haunt this gentle, brilliant scientist. His second son, Erwin, was brutally tortured and then executed by the Gestapo for his role in the unsuccessful 1944 assassination attempt against Hitler. Just weeks before the war ended, Planck’s home in Berlin was destroyed by Allied bombs. Finally, in the last days of the war, U.S. troops launched a daring rescue across wartorn Germany to keep Planck from being captured by the advancing Russian Army. That military action allowed Planck to spend the remainder of his life in the relative safety of the Allied-occupied portion of Germany. On October 3, 1947, at the age of 89, Planck died peacefully in Göttingen, Germany.
Antonine Henri Becquerel (1852 – 1908)
