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Max Karl Ernst Ludwig Planck
1858 - 1947

The German physicist Max Karl Ernst Ludwig Planck discovered the quantum of action which provided the key concept for the development of quantum theory.


Max Planck was born on April 23, 1858, in Kiel. The son of a distinguished jurist and professor of law, he inherited and sustained the family tradition of idealism, trustworthiness, conservatism, and devotion to church and state. Planck studied at the University of Munich (1875-1877) and the University of Berlin (1877-1878). At Berlin he took courses from Hermann von Helmholz and Gustav Kirchhoff.

Returning to Munich, Planck completed his thesis for his doctorate in 1879. It was on the second law of thermodynamics, Planck's favorite theme throughout his long and productive life. However, his keen insight into the second law of thermodynamics gained him no professional recognition whatsoever. Displaying his characteristically indomitable will, Planck refused to become discouraged and to allow his researches to be interrupted.

In 1880 Planck completed his Habilitationsschrift, which enabled him to become a privatdozent (lecturer) at the University of Munich. In that tenuous position he waited in vain for years to receive an offer of a professorship, longing to be independent professionally, as well as from his parents, with whom he was still living. He submitted a paper, "The Nature of Energy, " In 1885 for a prize to be awarded by the University of Göttingen in 1887. He received the second prize (the first prize was not awarded), and in 1889, after the death of Kirchhoff, he became associate professor at Berlin. Three years later he was promoted to full professor. He remained in Berlin for the rest of his life.

Planck's early years at Berlin were also the years during which his scientific horizons expanded enormously. There was at the time great interest in physical chemistry, and he contributed to this field, first, by introducing key concepts such as thermodynamic potentials, and, second, by applying these concepts to specific problems. Many of his early researches are in his famous Lectures on Thermodynamics (1897), in which he also introduced many of our modern definitions, symbols, and examples.

Blackbody Radiation and Quantum of Action

In 1897 Planck returned to the second law of thermodynamics. What attracted his attention were the experiments being carried out at the National Physical Laboratory in Berlin-Charlottenburg on so-called blackbody radiation, the radiation emitted by a "perfect emitter, " that is, a body that reemits all of the radiation incident on it. Of particular interest was the spectral energy distribution - the amount of energy emitted at each radiant frequency - of blackbody radiation. Planck sought to relate this radiation to the second law of thermodynamics. In 1900 he obtained a new radiation formula by interpolation between two experimentally determined spectral limits, the high-frequency limit consistent with Wien's law and the low-frequency limit consistent with the data of Planck's colleagues Rubens and Kulbaum. Planck's law had been discovered.

Planck's law was no more than a "lucky intuition, " as Planck called it. This was terribly unsatisfactory, and therefore he immediately began "the task of investing it with a true physical meaning." "After a few weeks of the most strenuous work of my life, " he recalled, "the darkness lifted and an unexpected vista began to appear." Two crucial insights were involved. The first involved a profound break in Planck's conception of the second law of thermodynamics. In all of his earlier researches, he had regarded the second law as "absolute" as the first - both were laws that admitted of no exceptions. Now he found himself driven inexorably to the conviction that Ludwig Boltzmann, not he, had been correct in arguing that the second law is an irreducibly statistical law: the entropy is directly related to the probability that a given microscopic (atomic) state will occur.

Planck's second insight involved a sharp break with all earlier physical theory. He found that to theoretically derive his interpolated blackbody radiation law, it was necessary to assume, contrary to all earlier assumptions, that the energy stored in the blackbody oscillators is not indefinitely divisible but is actually built up out of an infinite number of "bits, " or quanta of energy. He concluded that the energy of each quantum is a multiple of the quantum energy hf, where f is the frequency of the oscillator and h is now universally known as "Planck's constant" or "Planck's quantum of action."

Other Scientific Work

When Planck in 1900 made the discovery that immortalized his name and won for him the Nobel Prize in 1919 and numerous other honours, he was 42 years old. In subsequent years he continued to work at a steady pace and contribute to topics of current interest. In addition to the work already discussed, he studied the statistical aspects of white light, dispersion, and the optical properties of metals; probed various topics in statistical mechanics and kinetic theory; and applied quantum theory to systems of many degrees of freedom, to molecular rotational spectra, and to chemical bonding.

Planck was one of the first to champion Albert Einstein's 1905 special theory of relativity. Planck's deep interest in relativity, and his general admiration and appreciation of Einstein's revolutionary insights, made it natural that he should try to persuade Einstein to join the Berlin faculty. He succeeded in bringing Einstein to Berlin in 1914.

Last Decades

As permanent secretary (1912-1938) of the mathematics-physics section of the Prussian Academy of Science and as president (1920-1937) of the Kaiser Wilhelm Gesellschaft (now called the Max Planck Gesellschaft), Planck saw many of his esteemed Jewish colleagues, including Einstein, persecuted. As James Franck, who resigned his Göttingen professorship in protest against Hitler's policies, recalled, "Planck hated Hitler's laws, but they were the Law and therefore must be obeyed as long as they were in force." Planck at one point tried personally to convince Hitler of the damage he was doing German science, but his words had no effect. Planck's Berlin villa was destroyed by bombs. His son Erwin was involved in the July 1944 attempt on Hitler's life and in 1945 died at the hands of the Gestapo. Planck died in Göttingen on Oct. 4, 1947.


Max Karl Ernst Ludwig Planck was born in Kiel, Germany, on April 23, 1858, the son of Julius Wilhelm and Emma (née Patzig) Planck. His father was Professor of Constitutional Law in the University of Kiel, and later in Göttingen.

Planck studied at the Universities of Munich and Berlin, where his teachers included Kirchhoff and Helmholtz, and received his doctorate of philosophy at Munich in 1879. He was Privatdozent in Munich from 1880 to 1885, then Associate Professor of Theoretical Physics at Kiel until 1889, in which year he succeeded Kirchhoff as Professor at Berlin University, where he remained until his retirement in 1926. Afterwards he became President of the Kaiser Wilhelm Society for the Promotion of Science, a post he held until 1937. The Prussian Academy of Sciences appointed him a member in 1894 and Permanent Secretary in 1912.

Planck's earliest work was on the subject of thermodynamics, an interest he acquired from his studies under Kirchhoff, whom he greatly admired, and very considerably from reading R. Clausius' publications. He published papers on entropy, on thermoelectricity and on the theory of dilute solutions.

At the same time also the problems of radiation processes engaged his attention and he showed that these were to be considered as electromagnetic in nature. From these studies he was led to the problem of the distribution of energy in the spectrum of full radiation. Experimental observations on the wavelength distribution of the energy emitted by a black body as a function of temperature were at variance with the predictions of classical physics. Planck was able to deduce the relationship between the energy and the frequency of radiation. In a paper published in 1900, he announced his derivation of the relationship: this was based on the revolutionary idea that the energy emitted by a resonator could only take on discrete values or quanta. The energy for a resonator of frequency v is hv where h is a universal constant, now called Planck's constant.

This was not only Planck's most important work but also marked a turning point in the history of physics. The importance of the discovery, with its far-reaching effect on classical physics, was not appreciated at first. However the evidence for its validi ty gradually became overwhelming as its application accounted for many discrepancies between observed phenomena and classical theory. Among these applications and developments may be mentioned Einstein's explanation of the photoelectric effect.

Planck's work on the quantum theory, as it came to be known, was published in the Annalen der Physik. His work is summarized in two books Thermodynamik (Thermodynamics) (1897) and Theorie der Wärmestrahlung (Theory of heat radiation) (1906).

He was elected to Foreign Membership of the Royal Society in 1926, being awarded the Society's Copley Medal in 1928.

Planck faced a troubled and tragic period in his life during the period of the Nazi government in Germany, when he felt it his duty to remain in his country but was openly opposed to some of the Government's policies, particularly as regards the persecuti on of the Jews. In the last weeks of the war he suffered great hardship after his home was destroyed by bombing.

He was revered by his colleagues not only for the importance of his discoveries but for his great personal qualities. He was also a gifted pianist and is said to have at one time considered music as a career.

Planck was twice married. Upon his appointment, in 1885, to Associate Professor in his native town Kiel he married a friend of his childhood, Marie Merck, who died in 1909. He remarried her cousin Marga von Hösslin. Three of his children died young, leaving him with two sons.

He suffered a personal tragedy when one of them was executed for his part in an unsuccessful attempt to assassinate Hitler in 1944.

He died at Göttingen on October 4, 1947.


Planck was born at Kiel in Germany, where his father was a professor of civil law at the university. He was educated at the universities of Berlin and Munich where he obtained his doctorate in 1880. He began his teaching career at the University of Kiel moving to Berlin in 1889 and being appointed (1892) professor of theoretical physics, a post he held until his retirement in 1928.

Although Planck's early work was in thermodynamics, in 1900 he published a paper, Zur Theorie der Gesetzes der Energieverteilung im Normal-Spektrum (On The Theory of the Law of Energy Distribution in the Continuous Spectrum), which ranks him with Albert Einstein as one of the two founders of 20th-century physics. It is from this paper that quantum theory originated.

A major problem in physics at the end of the 19th century lay in explaining the radiation given off by a hot body. It was known that the intensity of such radiation increased with wavelength up to a maximum value and then fell off with increasing wavelength. It was also known that the radiation was produced by vibrations of the atoms in the body. For a perfect emitter (a so-called black body, which emits and absorbs at all wavelengths) it should have been possible to use thermodynamics to give a theoretical expression for black-body radiation. Various ‘radiation laws’ were derived. Thus Wilhelm Wien in 1896 derived a law that applied only at short wavelengths. Lord Rayleigh and James Jeans produced a law applying at long wavelengths, but predicting that the body should have a massive emission of short-wavelength energy – the so-called ‘ultraviolet catastrophe’.

Planck's problem was initially a technical one; he was simply searching for an equation that would allow the emission of radiation of all wavelengths by a hot body to be correctly described. He hit upon the idea of correlating the entropy of the oscillator with its energy. Following his intuition he found himself able to obtain a new radiation formula, which was in close agreement with actual measurements under all conditions.

There was, however, something unusual about the Planck formula. He had found that in seeking a relationship between the energy emitted or absorbed by a body and the frequency of radiation he had to introduce a constant of proportionality, which could only take integral multiples of a certain quantity. Expressed mathematically, E = nhν, where E is the energy, h is the constant of proportionality, ν is the frequency, and n = 0, 1, 2, 3, 4, etc. It follows from this that nature was being selective in the amounts of energy it would allow a body to accept and to emit, allowing only those amounts that were multiples of hν. The value of h is very small, so that radiation of energy at the macroscopic level where n is very large is likely to seem to be emitted continuously.

Planck's introduction of what he called the ‘elementary quantum of action’ was a revolutionary idea – a radical break with classical physics. Soon other workers began to apply the concept that ‘jumps’ in energy could occur. Einstein's explanation of the photoelectric effect (1905), Niels Bohr's theory of the hydrogen atom (1913), and Arthur Compton's investigations of x-ray scattering (1923) were early successes of the quantum theory. In 1918 Planck was awarded the Nobel Prize for physics. The constant h (6.626196 × 10–34 joule second) is known as the Planck constant – the value

    “h = 6.62 × 10–27 erg.sec”

    is engraved on his tombstone in Göttingen.

By the time of his retirement Planck had become the leading figure in German science and was therefore to play a crucial role in its relations with the Nazis. His attitude was that of prudent cooperation with the overriding aim of retaining the integrity of German science and preventing it from falling into international ridicule. Although he did not publicly protest against the harassment of Jewish scientists, considering such barbarisms a temporary madness, he did, in 1933, raise the issue with Hitler himself. He argued that the racial laws of 1933, barring Jews from government positions, would endanger the pre-eminence of German science. Hitler is reported to have expressed a willingness to do without science for a few years. Nor did Planck succeed in protecting the institutions of German science for in 1939 the presidency of the academy went to a party member, T. Vahlen, who lost no time in turning it virtually into an organ of the party.

Planck's later years, despite the honours that came his way, were indeed bitter ones. “My sorrow cannot be expressed in words,” he lamented at one point. During World War I his elder son Karl died from wounds suffered in action, and his twin daughters, Grete and Emma, died during childbirth in 1917 and 1919 respectively. In World War II he was forced to witness the destruction of his country and of German science and its institutions. His own home, with all his possessions, was totally destroyed by allied bombing in 1944. Worst of all, his one surviving child, Erwin, was executed in 1945 for complicity in the 1944 attempt to assassinate Hitler.


Karl Ernst Ludwig Marx Planck, better known as Max Planck (April 23, 1858 – October 4, 1947) was a German physicist. He is considered to be the founder of quantum theory, and one of the most important physicists of the twentieth century.

Planck came from a traditional, intellectual family. His paternal great-grandfather and grandfather were both theology professors in Göttingen, his father was a law professor in Kiel and Munich, and his paternal uncle was a judge.
Max Planck's signature at ten years of age.

Planck was born in Kiel, Holstein, to Johann Julius Wilhelm Planck and his second wife, Emma Patzig. He was baptised with the name of Karl Ernst Ludwig Marx Planck; of his given names, Marx was indicated as the primary name. However, already by the age of ten he signed with the name Max, which he used for the rest of his life.

He was the sixth child in the family, though two of his siblings were from his father's first marriage. Among his earliest memories was the marching of Prussian and Austrian troops into Kiel during the Danish-Prussian war of 1864. In 1867 the family moved to Munich, and Planck enrolled in the Maximilians gymnasium school, 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. Planck graduated early, at age 17. This is how Planck first came in contact with the field of physics.

Planck was gifted when it came to music. He took singing lessons and played piano, organ and cello, and composed songs and operas. However, instead of music he chose to study physics.

The Munich physics professor Philipp von Jolly advised Planck 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 experiments of his scientific career, studying the diffusion of hydrogen through heated platinum, but transferred to theoretical physics.

In 1877 he went to Berlin for a year of study with physicists Hermann von Helmholtz and Gustav Kirchhoff and the mathematician Karl Weierstrass. He wrote that Helmholtz was never quite prepared, spoke slowly, miscalculated endlessly, and bored his listeners, while Kirchhoff spoke in carefully prepared lectures which were dry and monotonous. He soon became close friends with Helmholtz. While there he undertook a program of mostly self-study of Clausius's writings, which led him to choose heat theory as his field.

In October 1878 Planck passed his qualifying exams and in February 1879 defended his dissertation, Über den zweiten Hauptsatz der mechanischen Wärmetheorie (On the second fundamental theorem of the mechanical theory of heat). He briefly taught mathematics and physics at his former school in Munich.

In June 1880 he presented his habilitation thesis, Gleichgewichtszustände isotroper Körper in verschiedenen Temperaturen (Equilibrium states of isotropic bodies at different temperatures).

Academic career

With the completion of his habilitation thesis, Planck became an unpaid private lecturer in Munich, waiting until he was offered an academic position. Although he was initially ignored by the academic community, he furthered his work on the field of heat theory and discovered one after another the same thermodynamical formalism as Gibbs without realizing it. Clausius's ideas on entropy occupied a central role in his work.

In April 1885 the University of Kiel appointed Planck as associate professor of theoretical physics. Further work on entropy and its treatment, especially as applied in physical chemistry, followed. He proposed a thermodynamic basis for Svante Arrhenius's theory of electrolytic dissociation.

Within four years he was named the successor to Kirchhoff's position at the University of Berlin — presumably thanks to Helmholtz's intercession — and by 1892 became a full professor. In 1907 Planck was offered Boltzmann's position in Vienna, but turned it down to stay in Berlin. During 1909 he was the Ernest Kempton Adams Lecturer in Theoretical Physics at Columbia University in New York City. He retired from Berlin on 10 January 1926, and was succeeded by Erwin Schrödinger.


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

After the appointment to Berlin, the Planck family lived in a villa in Berlin-Grunewald, Wangenheimstraße 21. Several other professors of Berlin University lived nearby, among them theologian Adolf von Harnack, who became a close friend of Planck. Soon the Planck home became a social and cultural centre. Numerous well-known scientists, such as Albert Einstein, Otto Hahn and Lise Meitner were frequent visitors. The tradition of jointly performing music had already been established in the home of Helmholtz.

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

During the First World War Planck's oldest son, Karl, was killed in action at Verdun, and Erwin was taken prisoner by the French in 1914. Grete died in 1917 while giving birth to her first child. Her sister died two years later the same way, after marrying Grete's widower. Both granddaughters survived and were named after their mothers. Planck endured these losses stoically.

In January 1945 his second son, Erwin, to whom he had been particularly close, was sentenced to death by the Volksgerichtshof because of his participation in the failed attempt to assassinate Hitler in July 1944. Erwin was hanged on 23 January 1945.

Professor at Berlin University

In Berlin, Planck joined the local Physical Society. He later wrote about this time: "In those days I was essentially the only theoretical physicist there, whence things were not so easy for me, because I started mentioning entropy, but this was not quite fashionable, since it was regarded as a mathematical spook". Thanks to his initiative, the various local Physical Societies of Germany merged in 1898 to form the German Physical Society (Deutsche Physikalische Gesellschaft, DPG); from 1905 to 1909 Planck was the president.

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; the best lecturer I ever heard" according to an English participant, James R. Partington, who continues: "There were always many standing around the room. As the lecture-room was well heated and rather close, some of the listeners would from time to time drop to the floor, but this did not disturb the lecture". Planck did not establish an actual "school", the number of his graduate students was only about 20, among them:

Max Abraham 1897 (1875 - 1922)
Moritz Schlick 1904 (1882 - 1936)
Walther Meißner 1906 (1882 - 1974)
Max von Laue 1906 (1879 - 1960)
Fritz Reiche 1907 (1883 - 1960)
Walter Schottky 1912 (1886 - 1976)
Walther Bothe 1914 (1891 - 1957)

Black-body radiation

In 1894 Planck turned his attention to the problem of black-body radiation. He had been commissioned by electric companies to create maximum light from lightbulbs with minimum energy. The problem had been stated by Kirchhoff in 1859: how does the intensity of the electromagnetic radiation emitted by a black body (a perfect absorber, also known as a cavity radiator) depend on the frequency of the radiation (e.g., the color of the light) and the temperature of the body? The question had been explored experimentally, but no theoretical treatment agreed with experimental values. Wilhelm Wien proposed Wien's law, which correctly predicted the behaviour at high frequencies, but failed at low frequencies. The Rayleigh-Jeans law, another approach to the problem, created what was later known as the "ultraviolet catastrophe", but contrary to many textbooks this was not a motivation for Planck.

Planck's first proposed solution to the problem in 1899 followed from what Planck called the "principle of elementary disorder", which allowed him to derive Wien's law from a number of assumptions about the entropy of an ideal oscillator, creating what was referred to as the Wien-Planck law. Soon it was found that experimental evidence did not confirm the new law at all, to Planck's frustration. Planck revised his approach, deriving the first version of the famous Planck black-body radiation law, which described the experimentally observed black-body spectrum well. It was first proposed in a meeting of the DPG on 19 October 1900 and published in 1901. This first derivation did not include energy quantization, and did not use statistical mechanics, to which he held an aversion. In November 1900, Planck revised this first approach, relying on Boltzmann's statistical interpretation of the second law of thermodynamics as a way of gaining a more fundamental understanding of the principles behind his radiation law. As Planck was deeply suspicious of the philosophical and physical implications of such an interpretation of Boltzmann's approach, his recourse to them was, as he later put it, "an act of despair ... I was ready to sacrifice any of my previous convictions about physics."

The central assumption behind his new derivation, presented to the DPG on 14 December 1900, 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 ... actually I did not think much about it..."; nowadays this assumption, incompatible with classical physics, is regarded as the birth of quantum physics and the greatest intellectual accomplishment of Planck's career (Ludwig Boltzmann had been discussing in a theoretical paper in 1877 the possibility that the energy states of a physical system could be discrete). The full interpretation of the radical implications of Planck's work was advanced by Albert Einstein in 1905—for this reason, the philosopher and historian of science Thomas Kuhn argued that Einstein should be given credit for quantum theory more so than Planck, since Planck did not understand in a deep sense that he was "introducing the quantum" as a real physical entity. It was in recognition of his monumental accomplishment that Planck was awarded the Nobel Prize in 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. "My unavailing attempts to somehow reintegrate the action quantum into classical theory extended over several years and caused me much trouble." 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. "I am unable to understand Jeans' stubbornness — he is an example of a theoretician as should never be existing, the same as Hegel was for philosophy. So much the worse for the facts, if they are wrong."

Max Born wrote about Planck: "He was by nature and by the tradition of his family conservative, averse to revolutionary novelties and skeptical towards speculations. But his belief in the imperative power of logical thinking based on facts was so strong that he did not hesitate to express a claim contradicting to all tradition, because he had convinced himself that no other resort was possible."

Einstein and the theory of relativity

In 1905 the three epochal papers of the hitherto completely unknown Albert Einstein were published in the journal Annalen der Physik. Planck was among the few who immediately recognized the significance of the special theory of relativity. Thanks to his influence this theory was soon widely accepted in Germany. Planck also contributed considerably to extend the special theory of relativity.

Einstein's hypothesis of light quanta (photons), based on Philipp Lenard's 1902 discovery of the photoelectric effect, was initially rejected by Planck. He was unwilling to discard completely Maxwell's theory of electrodynamics. "The theory of light would be thrown back not by decades, but by centuries, into the age when Christian Huygens dared to fight against the mighty emission theory of Isaac Newton ..."

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, seeking to clarify the increasing number of contradictions, organized the First Solvay Conference (Brussels 1911). At this meeting Einstein was 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). Soon the two scientists became close friends and met frequently to play music together.

World War and Weimar Republic

At the onset of the First World War Planck was not immune to the general excitement of the public: "... besides of much horrible also much unexpectedly great and beautiful: the swift solution of the most difficult issues of domestic policy through arrangement of all parties... the higher esteem for all that is brave and truthful..." Admittedly, he refrained from the extremes of nationalism. 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. 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 (he was 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, now the highest authority of German physics, issued the slogan "persevere and continue working" to his colleagues. In October 1920 he and Fritz Haber established the Notgemeinschaft der Deutschen Wissenschaft (Emergency Organization of German Science), aimed at providing support for destitute scientific research. A considerable portion of the monies they distributed were raised abroad. 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). Under such conditions he was hardly able to conduct research.

He became a member of the Deutsche Volks-Partei (German People's Party), the party of Nobel Peace Prize laureate Gustav Stresemann, which aspired to liberal aims for domestic policy and rather revisionistic aims for international politics. He disagreed with the introduction of universal suffrage and later expressed the view that the Nazi dictatorship resulted from "the ascent of the rule of the crowds".

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 well as Schrödinger, Laue, and Einstein. Planck expected that wave mechanics would soon render quantum theory—his own child—unnecessary. This was not to be the case, however. Further work only cemented quantum theory, even against his and Einstein's philosophical revulsions. Planck experienced the truth of his own earlier observation from his struggle with the older views in his younger years: "A new scientific truth does not triumph by convincing its opponents and making them see the light, but rather because its opponents eventually die, and a new generation grows up that is familiar with it."

Nazi dictatorship and Second World War

When the Nazis seized power in 1933, Planck was 74. He witnessed many Jewish friends and colleagues expelled from their positions and humiliated, and hundreds of scientists emigrated from Germany. Again he tried the "persevere and continue working" slogan and asked scientists who were considering emigration to remain in Germany. He hoped the crisis would abate soon and the political situation would improve. There was also a deeper argument against emigration. Emigrating German non-Jewish scientists would need to look for academic positions abroad, but these positions better served Jewish scientists, who had no chance of continuing to work in Germany.

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, except concerning Fritz Haber. Planck tried to discuss the issue with Adolf Hitler but was unsuccessful. In the following year, 1934, Haber died in exile.

One year later, Planck, having been the president of the KWG since 1930, organized in a somewhat provocative style an official commemorative meeting for Haber. He also succeeded in secretly enabling a number of Jewish scientists to continue working in institutes of the KWG for several years. In 1936, his term as president of the KWG ended, and the Nazi government pressured him to refrain from seeking another term.

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 80th birthday. The DPG held a celebration, during which the Max-Planck medal (founded as the highest medal by the DPG in 1928) was awarded to French physicist Louis de Broglie. At the end of 1938 the Prussian Academy lost its remaining independence and was taken over by Nazis (Gleichschaltung). Planck protested by resigning his presidency. He continued to travel frequently, giving numerous public talks, such as his talk on Religion and Science, and five years later he was sufficiently fit to climb 3,000-meter peaks in the Alps.

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. In 1942 he wrote: "In me an ardent desire has grown to persevere this crisis and live long enough to be able to witness the turning point, the beginning of a new rise." In February 1944 his home in Berlin was completely destroyed by an air raid, annihilating all his scientific records and correspondence. Finally, he got into a dangerous situation in his rural retreat due to the rapid advance of the Allied armies from both sides. After the end of the war he was brought to a relative in Göttingen.

Planck endured many personal tragedies after the age of 50. In 1909, his first wife died after 22 years of marriage, leaving him with two sons and twin daughters. Planck's oldest son, Karl, was killed in action in 1916. His daughter Margarete died in childbirth in 1917, and another daughter, Emma, married her late sister's husband and then also died in childbirth, in 1919. During World War II, Planck's house in Berlin was completely destroyed by bombs in 1944 and his youngest son, Erwin, was implicated in the attempt made on Hitler's life in the July 20 plot. Consequently, Erwin died a horrible death at the hands of the Gestapo in 1945. Although it is said that Erwin could have been spared had Planck joined the Nazi Party Planck took a stand and refused to join, as a consequence Erwin was hanged. Erwin's death destroyed Planck's will to live. By the end of the war, Planck, his second wife and his son by her, moved to Göttingen where he died on October 4, 1947.

Religious view

Planck was a devoted and persistent adherent of Christianity from early life to death, but he was very tolerant towards alternative views and religions, and so was discontented with the church organizations' demands for unquestioning belief.

The God in which Planck believed was an almighty, all-knowing, benevolent but unintelligible God that permeated everything, manifest by symbols, including physical laws. His view may have been motivated by an opposition like Einstein's and Schrödinger's against the positivist, statistical subjective quantum mechanics universe of Bohr, Heisenberg and others. Planck was interested in truth and Universe beyond observation, and objected to atheism as an obsession with symbols.

Planck regarded the scientist as a man of imagination and faith, "faith" interpreted as being similar to "having a working hypothesis". For example the causality principle isn't true or false, it is an act of faith. Thereby Planck may have indicated a view that points toward Imre Lakatos' research programs process descriptions, where falsification is mostly tolerable, in faith of its future removal.










This web page was last updated on: 23 December, 2008