Max (Karl Ernst Ludwig) Planck

Erich Kretschmann
Walther Meißner
Walter Schottky
Max von Laue
Max Abraham
Moritz Schlick

Life and work

Childhood and youth

Planck came from a traditional, intellectual family.

Max Planck was born in Kiel to Johann Julius Wilhelm Planck and his second wife, Emma Patzig. In 1867 the family moved to Munich, and Planck was enrolled in Munich's Königliches Maximilians gymnasium, where he came under the tutelage of Hermann Müller, a mathematician who took an interest in the youth and taught him astronomy and mechanics as well as mathematics. It was from Müller that Planck first learned the principle of conservation of energy.

Education

Planck was extremely gifted when it came to music: he took singing lessons in addition to playing the piano, organ and cello, and composing songs and operas.

The Munich physics professor Philipp von Jolly advised him against going into physics, saying, "in this field, almost everything is already discovered, and all that remains is to fill a few holes." Planck replied that he did not wish to discover new things, only to understand the known fundamentals of the field, and began his studies in 1874 at the University of Munich. Under Jolly's supervision, Planck performed the only actual experiments of his scientific career (studying the diffusion of hydrogen through heated platinum), but soon transferred to theoretical physics.

In October 1878 Planck passed his qualifying exams and in February of 1879 defended his dissertation, Über den zweiten Hauptsatz der mechanischen Wärmetheorie (On the second fundamental theorem of the mechanical heat theory).

Academic career

With the completion of his habilitation thesis, Planck became an unpaid private lecturer in Munich, waiting until he would be offered an academic position.

In April 1885 the University of Kiel appointed Planck an associate professor of theoretical physics. In 1907 Planck was appointed to Boltzmann's position in Vienna, but turned it down to stay in Berlin.

Family

In March 1887 Planck married Marie Merck (1861-1909), sister of a school fellow, and moved with her into a sublet apartment in Kiel. Four children were born to the couple: Karl (1888-1916), the twins Emma (1889-1919) and Grete (1889-1917), and Erwin Planck (1893-1945).

After the appointment to Berlin the Planck family lived in a villa in Berlin-Grunewald, Wangenheimstraße 21. In the vicinity of this address several other professors of Berlin University were living, among them the famous theologian Adolf von Harnack, who became a close friend of Planck. Soon the Planck home became a social and cultural centre;

After several happy years the Planck family was struck by a series of disasters: in October 1909 Marie Planck died, possibly from tuberculosis. In March 1911 Max Planck married his second wife, Marga von Hoesslin (1882-1948);

During the First World War Planck's oldest son, Karl, was killed in action in Verdun, and Erwin had already in 1914 been taken prisoner by the French.

Finally in January 1945 his youngest son Erwin, to whom Max Planck had been particularly close, was executed by the Nazis because of his participation in the failed attempt to assassinate Hitler in July 1944. 1911)

Professor at Berlin University

In Berlin, Planck joined the local Physical Society. from 1905 to 1909 Planck was the president of the DPG.

Planck started a six-semester course of lectures on Theoretical Physics, "dry, somewhat impersonal" according to Lise Meitner, "using no notes, never making mistakes, never faltering; Planck did not establish an actual "school", the number of his graduate students was only about twenty all together, among them the following:

Black-body radiation

In 1894 Planck turned his attention to the problem of black-body radiation.

By interpolating between the laws of Wien and Rayleigh-Jeans Planck found the famous Planck black-body radiation law which described the experimentally observed black-body spectrum very well;

The central assumption behind his derivation was the supposition that the electromagnetic energy could be emitted only in quantized form, in other words, the energy could only be a multiple of an elementary unit E = hν, where h is Planck's constant, also known as Planck's action quantum (introduced already in 1899), and ν is the frequency of the radiation.

At first Planck considered that the quantisation was only as "a purely formal assumption ... nowadays this assumption, incompatible with classical physics, is regarded as the birth of quantum physics and the greatest intellectual accomplishment of Planck's career (however, Ludwig Boltzmann had already in 1877, in a theoretical paper, been discussing the possibility that the energy states of a physical system could be discrete). It was in recognition of this accomplishment that Planck was awarded the Nobel prize for physics in 1918.

The discovery of Planck's constant enabled 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.

Subsequently, Planck tried to grasp the meaning of the energy quanta, but to no avail. Even several years later, other physicists like Rayleigh, Jeans, and Lorentz set Planck's constant to zero in order to align with classical physics, but Planck knew well that this constant had a precise nonzero value.

Max Born wrote about Planck: "He was by nature and by the tradition of his family conservative, averse to revolutionary novelties and sceptical towards speculations. Planck was among the few who immediately recognized the significance of the special theory of relativity. Planck also contributed considerably to extend the special theory of relativity.

However, Einstein's hypothesis of light quanta (photons), based on Philipp Lenard's 1902 discovery of the photoelectric effect, was initially rejected by Planck;

In 1910 Einstein pointed out the anomalous behavior of specific heat at low temperatures as another example of a phenomenon which defies explanation by classical physics. Planck and Nernst, in order to clarify the increasing number of contradictions, organised the First Solvay Conference (Brussels 1911); at this meeting Einstein was finally able to convince Planck.

Meanwhile Planck had been appointed dean of Berlin University, whereby it was possible for him to call Einstein to Berlin and establish a new professorship for him (1914).

World War and Weimar Republic

At the onset of the First World War Planck was not immune to the general excitement of the public: "... Admittedly, he refrained from the extremes of nationalism, e.g., he voted successfully for a scientific paper from Italy receiving a prize from the Prussian Academy of Sciences in 1915 (Planck was one of its four permanent presidents), although at that time Italy was about to join the Allies; nevertheless the infamous "Manifesto of the 93 intellectuals", a polemic pamphlet of war propaganda, was also signed by Planck, while Einstein retained a strictly pacifistic attitude which almost led to his imprisonment (from which he was only saved by his Swiss citizenship). But already in 1915 Planck revoked (after several meetings with Dutch physicist Lorentz) parts of the Manifesto, and in 1916 he signed a declaration against German annexationism.

In the turbulent post-war years, Planck, by now the highest authority of German physics, issued the slogan "persevere and continue working" to his colleagues. In this time Planck held leading positions also at Berlin University, the Prussian Academy of Sciences, the German Physical Society and the Kaiser-Wilhelm-Gesellschaft (which in 1948 became the Max-Planck-Gesellschaft);

Quantum mechanics

At the end of the 1920s Bohr, Heisenberg and Pauli had worked out the Copenhagen interpretation of quantum mechanics, but it was rejected by Planck, as also by Schrödinger and Laue;

Nazi dictatorship and Second World War

When the Nazis seized power in 1933, Planck was seventy-four;

Hahn asked Planck to gather well-known German professors in order to issue a public proclamation against the treatment of Jewish professors, but Planck replied, "If you are able to gather today 30 such gentlemen, then tomorrow 150 others will come and speak against it, because they are eager to take over the positions of the others." Under Planck's leadership, the Kaiser-Wilhelm-Gesellschaft (KWG) avoided open conflict with the Nazi regime; Planck tried to discuss the issue with Adolf Hitler but was unsuccessful.

One year later, Planck, being the president of the KWG since 1930, organised in a somewhat provocative style an official commemorative meeting for Haber.

As the political climate in Germany gradually became more hostile, Johannes Stark, prominent exponent of Deutsche Physik ("German Physics", also called "Aryan Physics") attacked Planck, Sommerfeld and Heisenberg for continuing to teach the theories of Einstein, calling them "white Jews." The "Hauptamt Wissenschaft" (Nazi government office for science) started an investigation of Planck's ancestry, but all they could find out was that he was "1/16 Jewish."

In 1938, Planck celebrated his eightieth birthday; Planck protested by resigning his presidency.

During the Second World War, the increasing number of Allied bombing campaigns against Berlin forced Planck and his wife to leave the city temporarily and live in the countryside.

Final years

After the war, a number of German physicists assembled in Göttingen in order to reestablish the Kaiser-Wilhelm-Gesellschaft. In July of 1945, Planck agreed to act formally as its president, again. Despite his deteriorating health, Planck resumed travelling in order to give public talks. On 1 April 1946, Planck was succeeded as president of the KWG by Otto Hahn.

Honours and medals

References and further reading