Max Planck

German physicist

• Born: April 23, 1858; Kiel, Denmark (now Germany)
• Died: October 4, 1947; Göttingen, West Germany (now Germany)

Planck’s 1900 discovery that light consists of infinitesimal “quanta” and his articulation of quantum theory replaced classical physics with modern quantum physics. This work not only resulted in Planck’s receiving the Nobel Prize in Physics in 1918 but also laid the groundwork for the achievements of many other Nobel laureates.

Primary field: Physics

Specialties: Theoretical physics; quantum mechanics

Early Life

Born into an intellectual family, Max Planck spent most of his early life in Munich, where the family moved in the spring of 1867. Planck’s father was a professor of civil law at the university in Kiel. Planck’s forebears included many lawyers and clergymen, which may have contributed to his lifelong respect for the law and interest in religion.

In May 1867, Planck was enrolled in Munich’s Königliche Maximilian-Gymnasium, where he came under the tutelage of Hermann Muller, a mathematician who took an interest in the youth and taught him astronomy and mechanics as well as mathematics. It was from Muller that Planck first learned the principle of the conservation of energy that underlay much of his eventual work in thermodynamics and quantum theory.

When Planck entered the University of Munich in October 1874, he concentrated on mathematics, even though he was widely gifted in the arts. At Munich, his interest in physics grew. However, his mathematics professors believed that nothing new remained to be discovered in the field.

Planck became ill during his first year at Munich and missed two years of school. In the winter term of 1877–78, when he was well enough to resume his studies, he entered the University of Berlin, where he decided to study theoretical physics, as he was interested in the nature of the universe.

In Berlin, Planck studied with physicists Hermann von Helmholtz, Gustav Kirchhoff, and Rudolf Clausius. Although his doctoral dissertation on the second law of thermodynamics was undistinguished, he graduated summa cum laude in 1879. He taught mathematics and physics briefly at his former secondary school in Munich and, in 1880, received a teaching position at the University of Munich. At that time, theoretical physics was viewed as an unpromising field.

In 1885, Planck became an associate professor of physics at the University of Kiel, where he remained until 1888. He was then appointed assistant professor and director of the Institute for Theoretical Physics to replace the deceased Kirchhoff. Planck rose to professor in 1892 and remained at Berlin until his retirement in 1926.

Life’s Work

Planck’s early work in the laws of thermodynamics and his early interest in the principle of the conservation of energy figured largely in his research from his early teaching days at Kiel through his first decades at the University of Berlin. Although he had been reared on classical physics, Planck began to realize that the laws of classical physics deviated greatly from results obtained in experimental physics. He found the greatest disparities not in the field of optics but rather in thermodynamics. The problems stemmed from the measurement of radiant energy in the frequency spectrum of blackbodies.

Kirchhoff had deduced that radiant energy is independent of the nature of its radiating substance, reasoning that blackbodies, which absorb all frequencies of light, should therefore radiate all frequencies of light. Energy at that time was considered infinitely divisible, a theory that led to many anomalies and seeming contradictions in physics. Problems arose because of the emission discrepancies between lower-frequency ranges and higher-frequency ranges.

International physicists working on this problem reached conflicting conclusions. Work in the field was at an impasse when Planck devised a classically simple equation that explained the distribution of radiation over the full range of frequencies, basing his equation on the daring supposition that energy is not an indivisible flow but composed of tiny particles, which he named quanta after the Latin word meaning “How many?” Incidental to this discovery was his determination of a way to measure the absolute weight of molecules and atoms.

Planck’s theory showed that the energy of various frequencies of light from violet to red contain different energies, a quantum of violet containing twice the energy of a quantum of red and requiring twice the energy to radiate from a blackbody, making such radiation improbable. Although Planck initially doubted his findings, other scientists began to realize his theory’s validity. Soon fellow physicist Albert Einstein based much of his work on photoelectric effect, which classical physics could not explain, on quantum theory. Planck embraced Einstein’s theory of relativity eagerly because of its absolutism and because of its presentation of the velocity of light.

Now firmly established at the University of Berlin, Planck was instrumental in bringing Einstein to the Berliner Akademie in 1914 as a professor without teaching obligations and as director of the Kaiser Wilhelm Institute for Physics, which Planck eventually headed. Planck also nominated Einstein for the Nobel Prize in Physics in 1921, and Einstein received the prize one year later.

Quantum mechanics became the most important field of physics in the first half of the twentieth century, followed closely by the field of quantum electrodynamics; both were developments that evolved from Planck’s original insights and from his expression of the ratio between the size of a quantum and its frequency (represented by the symbol h).

With Nazi leader Adolf Hitler’s rise to power, Planck decided to remain in Germany, although he deplored what was happening. His respect for the law was deeply ingrained, and he felt duty-bound as a citizen to live within the laws but to work from within to change them. He intervened unsuccessfully for Jewish friends and colleagues who were being sent to death camps.

As a Nobel laureate of enormous prestige, Planck scheduled an interview with Hitler and tried to dissuade him from the genocide that was overwhelming Nazi Germany. Planck’s intervention did not deter Hitler from his disastrous course, however. Before the end of the war, Planck had lost his home and all of his papers to a bombing raid, had once been trapped for several hours in a collapsed air-raid shelter, and had suffered the Nazis’ execution of his son Erwin, a former secretary of state accused of plotting to assassinate Hitler.

When the Allies came into Germany in May 1945, Planck and his second wife, who had fled to Magdeburg after the destruction of their home near Berlin, were again homeless. American soldiers rescued Planck and had him sent to a hospital in Göttingen, where he lived for his few remaining years. He continued his professional activities, giving his last public lecture on scientific pseudoproblems in 1946.

Impact

Planck lived another twenty-one years after his retirement. His search for the meaning of the universe and for the nature of existence persisted in his later years. He wrote on general subjects, developing some of his earlier lectures and essays into fuller works. Five volumes of Planck’s work in theoretical physics were published in English under the title Introduction to Theoretical Physics (1932–33). His highly philosophical Physikalische Gesetzlichkeit im Lichte neuer Forschung (1926) and Das Weltbild der neuen Physik (1929; combined in The Universe in the Light of Modern Physics, 1931) exhibited Planck’s search for absolutes in a broadly religious context.

His general works Where Is Science Going? (1932) and Wege zur Physikalischen Erkenntnis (1933; The Philosophy of Physics, 1936) were combined with The Universe in the Light of Modern Physics and published in English under the title The New Science (1959). Planck’s autobiography Wissenschaftliche Selbstbiographie (1948; Scientific Autobiography and Other Papers, 1949) was published posthumously.

In 1930, Planck had become president of the Kaiser Wilhelm Society of Berlin, which was renamed the Max Planck Society in his honor. In his final years, he again became president of the society.

Bibliography

Heilbron, J. L. The Dilemmas of an Upright Man: Max Planck and the Fortunes of German Science. Cambridge: Harvard UP, 2000. Print. Biography focusing on Planck’s career. After rising to the pinnacle of German scientific achievement, Planck suffered morally and intellectually as he continued to serve his country during World Wars I and II.

Hermann, Armin. The Genesis of Quantum Theory (1899–1913). Cambridge: MIT P, 1971. Print. Presents a study of the pioneering work Planck did in the late 1880s and early 1890s as he moved toward the discovery of quanta.

Planck, Max. A Survey of Physical Theory. Trans. R. Jones and D. H. Williams. 1925. New York: Dover, 2011. Print. An overview of developments and theories in physics, featuring a detailed account of Planck’s work with quantum theory.