Max Planck

Claimed and Written by Daniel Kurniawan for PHYS2211

Max Karl Ernst Ludwig Planck was a German theoretical physicist most famous for the discovery of Black-Body Radiation and originating quantum theory. He was awarded the Nobel Prize in Physics in 1918 for his theory, which revolutionized our understanding or atomic and subatomic processes.

Early Life

Planck was born in Kiel, Germany, on April 23, 1858 to Julius Wilhelm and Emma Planck. Planck was brought up in a large family - he was the sixth child - that valued scholarship, honesty, fairness, and generosity. His family greatly respected the church and state, displaying the importance of these values within the family. He began elementary school in Kiel, and although he was not the top student, he always came somewhere between third and eighth in the class. His best subject, as surprising as it sounds, was music, as he possessed the gift of perfect pitch and was an excellent pianist. He was also awarded the prize in catechism and good conduct almost every year.

When Planck was nine years old, his father, who was a distinguished jurist and professor of law at the University of Kiel, received an appointment at the University of Munich, where a teacher by the name of Hermann Müller stimulated Planck's interest in physics. After graduating at the age of 17, Planck ultimately chose physics as his career path because he had become deeply impressed by the absolute nature of the law of conservation of energy. Planck describes why he chose physics:

"The outside world is something independent from man, something absolute, and the quest for the laws which apply to this absolute appeared to me as the most sublime scientific pursuit in life.”

University Education and Career

Planck entered the University of Munich in the fall of 1874, however found very little encouragement to pursue a future in physics. He spent a year at the University of Berlin, where he had the opportunity to be taught by great research scientists Hermann von Helmholtz and Gustav Robert Kirchoff, however he was very unimpressed by their lectures. He returned to Munich and received his doctorate of philosophy in July 1879 at the age of 21. The following year he finished his dissertation at Munich and became a lecturer. He spent five years teaching at the University of Munich, then was appointed Associate Professor of Theoretical Physics at the University of Kiel, with the help of his father. Two years later he married Marie Merck in 1887, and they went on to have four children, Karl (1888), the twins Emma and Grete (1889) and Erwin (1893), of whom only Erwin was to survive past the First World War. In 1889, he succeeded Kirchoff and became a professor at the University of Berlin, where he came to venerate Helmholtz as a mentor and colleague. Though he had only nine doctoral students altogether, his lectures on all branches of theoretical physics went through many editions and exerted great influence in that particular field. He remained a professor in Berlin until his retirement in 1926.

Scientific Contribution

Black-Body Radiation

While teaching in Berlin, Planck studied thermodynamics - in particular examining the distribution of energy according to wavelength. By combining the formulas of Wilhelm Wien and Rayleigh, Planck announced a new formula referred to as Planck's radiation formula. Two months later, Planck introduced the quanta of energy by making a complete theoretical deduction of his formula and giving up classical physics. He knew how the entropy of the radiation had to depend mathematically upon its energy in the high-frequency region if Wien’s law held there. He also saw what this dependence had to be in the low-frequency region in order to reproduce the experimental results there. Planck guessed that he should try to combine these two expressions in the simplest way possible, and to transform the result into a formula relating the energy of the radiation to its frequency. He presented his theoretical explanation involving this quanta of energy on December 14, 1900 at a meeting of the Physikalische Gesellschaft in Berlin. He announced his derivation of the relationship which was centered around the idea that the energy emitted by a resonator could only take on discrete values or quanta. The energy for a resonator of frequency is hv where h is a universal constant, known as Planck's constant.

The discovery of Planck’s constant equipped him to define a new universal set of physical units (such as the Planck length and the Planck mass), all based on fundamental physical constants. Planck’s work on the quantum theory was published in the Annalen der Physik. His work is summarized in two books Thermodynamik (Thermodynamics) and Theorie der Wärmestrahlung (Theory of heat radiation).

A YouTube Video of Planck's logic in Black-Body Radiation and the beginning of quantum mechanics can be found here.

Later Life

Second Marriage and World War I

In 1909 Planck's wife Marie passed away, presumably from tuberculosis. In 1911, Planck married his second wife, Marga von Hoesslin, who bore him a third son, Hermann, the same year. By the time of the German annexation and World War I in 1914 (which Planck initially welcomed, but later argued against), he was effectively the highest authority of German physics, as one of the four permanent presidents of the Prussian Academy of Sciences, and a leader in the influential umbrella body, the Kaiser Wilhelm Society. By the end of the 1920s, Niels Bohr, Werner Heisenberg, and Wolfgang Pauli had worked out the "Copenhagen Interpretation" of quantum mechanics, and the quantum theory which Planck’s work had triggered became ever more established, even if Planck himself was never quite comfortable with some of its philosophical implications.

Nobel Prize in Physics

Planck was just 42 years old in 1900 when he made his famous discovery of the black body radiation law. This was not only Planck's most important work but in addition it marked a turning point in the history of physics. In 1918, this discovery won him the Nobel Prize in Physics.

World War II

Planck was 74 years old when the Nazis seized power in 1933, and he typically avoided conflict with the Nazi regime, although he did organize a provocative official commemorative meeting after the death in exile of fellow physicist Fritz Haber. He also succeeded in secretly enabling a number of Jewish scientists to continue working in institutes of the Kaiser Wilhelm Society for several years.

The “Deutsche Physik” movement attacked Planck, Arnold Sommerfeld and Werner Heisenberg among others for continuing to teach the theories of Einstein, calling them "white Jews". When his term as president of the Kaiser Wilhelm Society ended in 1936, the Nazi government pressured him to refrain from seeking another term. At the end of 1938, the Prussian Academy of Sciences lost its independence and was taken over by Nazis, and Planck protested by resigning his presidency. He bravely refused to join the Nazi party, despite coming under significant political pressure to do so.

Allied bombing campaigns against Berlin during the Second World War forced Planck and his wife to leave the city temporarily to live in the countryside, and his house in Berlin was completely destroyed by an air raid in 1944. He continued to travel frequently, giving numerous public lectures, including talks on Religion and Science (he was a devoted and persistent adherent of Christianity all his life).

Death

World War II brought further tragedy. Planck’s house in Berlin was completely destroyed by bombs in 1944. His younger son, Erwin, was implicated in the attempt made on Hitler’s life on July 20, 1944, and in early 1945 he was killed at the hands of the Gestapo. Planck’s will to live was greatly crushed by this act. At war’s end, American officers took Planck and his second wife, Marga von Hoesslin, whom he had married in 1910 and by whom he had had one son, to Göttingen, West Germany. Planck died here on October 4, 1947 at the age of 89.