Max Planck
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Planck in 1933
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| Born |
Karl Ernst Ludwig Marx Planck
23 April 1858 |
| Died | 4 October 1947 (aged 89) |
| Nationality | German |
| Alma mater | Ludwig Maximilian University of Munich |
| Known for | Planck constant Planck postulate Planck's law of black body radiation Third law of thermodynamics Fokker–Planck equation |
| Spouse(s) | Marie Merck (1887–1909) Marga von Hösslin (1911–1947) |
| Children | 5 |
| Awards |
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| Scientific career | |
| Fields | Physics |
| Institutions | |
| Thesis | On the Second Principles of Mechanical Heat Theory (1879) |
| Doctoral advisor | Alexander von Brill Gustav Kirchhoff Hermann von Helmholtz |
| Doctoral students | |
| Other notable students | Wolfgang Köhler Lise Meitner |
| Signature | |
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Karl Ernst Ludwig Marx Planck, ForMemRS (German: [ˈplaŋk]; English: /ˈplæŋk/; 23 April 1858 – 4 October 1947) was a German theoretical physicist whose discovery of energy quanta won him the Nobel Prize in Physics in 1918.
Planck made many contributions to theoretical physics, but his fame as a physicist rests primarily on his role as the originator of quantum theory, which revolutionized human understanding of atomic and subatomic processes. In 1948, the German scientific institution the Kaiser Wilhelm Society (of which Planck was twice president) was renamed the Max Planck Society (MPS). The MPS now includes 83 institutions representing a wide range of scientific directions.
Life and career
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 at the University of Kiel and Munich. One of his uncles was also 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 baptized with the name of Karl Ernst Ludwig Marx Planck; of his given names, Marx (a now obsolete variant of Markus or maybe simply an error for Max, which is actually short for Maximilian) was indicated as the "appellation name". However, by the age of ten he signed with the name Max and used this for the rest of his life.
He was the 6th child in the family, though two of his siblings
were from his father's first marriage. War was common during Planck's
early years and among his earliest memories was the marching of Prussian and Austrian troops into Kiel during the Second Schleswig War in 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.
Planck as a young man, 1878
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, but only to
understand the known fundamentals of the field, and so 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 the Friedrich Wilhelms University in Berlin for a year of study with physicists Hermann von Helmholtz and Gustav Kirchhoff and 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 thermodynamics 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 law of thermodynamics). He briefly taught mathematics and physics at his former school in Munich.
By the year 1880, Planck had obtained the two highest academic
degrees offered in Europe. The first was a doctorate degree after he
completed his paper detailing his research and theory of thermodynamics. He then presented his thesis called Gleichgewichtszustände isotroper Körper in verschiedenen Temperaturen (Equilibrium states of isotropic bodies at different temperatures), which earned him a habilitation.
Academic career
With the completion of his habilitation thesis, Planck became an unpaid Privatdozent
(German academic rank comparable to lecturer/assistant professor) 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 published his Treatise on Thermodynamics in 1897. He proposed a thermodynamic basis for Svante Arrhenius's theory of electrolytic dissociation.
In 1889 he was named the successor to Kirchhoff's position at the Friedrich-Wilhelms-Universität in 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, as a University of
Berlin professor, he was invited to become the Ernest Kempton Adams
Lecturer in Theoretical Physics at Columbia University in New York City. A series of his lectures were translated and co-published by Columbia University professor A. P. Wills. He retired from Berlin on 10 January 1926, and was succeeded by Erwin Schrödinger.
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. They had four
children: Karl (1888–1916), the twins Emma (1889–1919) and Grete
(1889–1917), and Erwin (1893–1945).
After the apartment in Berlin, the Planck family lived in a villa
in Berlin-Grunewald, Wangenheimstrasse 21. Several other professors
from University of Berlin lived nearby, among them theologian Adolf von Harnack,
who became a close friend of Planck. Soon the Planck home became a
social and cultural center. 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, 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 fifth child Hermann was born.
During the First World War Planck's second son Erwin was taken prisoner by the French in 1914, while his oldest son Karl was killed in action at Verdun.
Grete died in 1917 while giving birth to her first child. Her sister
died the same way two years later, after having married Grete's widower.
Both granddaughters survived and were named after their mothers. Planck
endured these losses stoically.
In January 1945, Erwin, to whom he had been particularly close, was sentenced to death by the Nazi Volksgerichtshof because of his participation in the failed attempt to assassinate Hitler in July 1944. Erwin was executed on 23 January 1945.
Professor at Berlin University
As a professor at the Friedrich-Wilhelms-Universität 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.
Plaque at the Humboldt University of Berlin: "Max Planck, discoverer of the elementary quantum of action h, taught in this building from 1889 to 1928."
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:
- 1897 Max Abraham (1875–1922)
- 1903 Max von Laue (1879–1960)
- 1904 Moritz Schlick (1882–1936)
- 1906 Walther Meissner (1882–1974)
- 1907 Fritz Reiche (1883–1960)
- 1912 Walter Schottky (1886–1976)
- 1914 Walther Bothe (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 (i.e., 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, agreed with experimental results at
low frequencies, but created what was later known as the "ultraviolet catastrophe" at high frequencies. However, 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
quantisation, 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, now known as the Planck postulate, that electromagnetic energy could be emitted only in quantized form, in other words, the energy could only be a multiple of an elementary unit:
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. Note that the elementary units of energy discussed here are represented by hν and not simply by ν. Physicists now call these quanta photons, and a photon of frequency ν will have its own specific and unique energy. The total energy at that frequency is then equal to hν multiplied by the number of photons at that frequency.
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Planck in 1918, the year he received the Nobel Prize in Physics for his work on quantum theory
At first Planck considered that quantisation was only "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
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 upon which much of quantum
theory is based. In recognition of Planck's fundamental contribution to a
new branch of physics, he was awarded the Nobel Prize in Physics for
1918 (he actually received the award in 1919).
Subsequently, Planck tried to grasp the meaning of 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 don't fit."
Max Born
wrote about Planck: "He was, by nature, a conservative mind; he had
nothing of the revolutionary and was thoroughly skeptical about
speculations. Yet his belief in the compelling force of logical
reasoning from facts was so strong that he did not flinch from
announcing the most revolutionary idea which ever has shaken physics."
Einstein and the theory of relativity
In 1905, the three epochal papers by 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. For example, he recast the theory in terms of
classical action.
Einstein's hypothesis of light quanta (photons), based on Heinrich Hertz's 1887 discovery (and further investigation by Philipp Lenard) 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 Christiaan 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.
First World War
At the onset of the First World War
Planck endorsed the general excitement of the public, writing that,
"Besides much that is horrible, there is also much that is unexpectedly
great and beautiful: the smooth solution of the most difficult domestic
political problems by the unification of all parties (and) ... the
extolling of everything good and noble."
Nonetheless, Planck refrained from the extremes of nationalism. In 1915, at a time when Italy was about to join the Allied Powers, he voted successfully for a scientific paper from Italy, which received a prize from the Prussian Academy of Sciences, where Planck was one of four permanent presidents.
Planck also signed the infamous "Manifesto of the 93 intellectuals",
a pamphlet of polemic war propaganda (while Einstein retained a
strictly pacifistic attitude which almost led to his imprisonment, being
spared by his Swiss citizenship). But in 1915 Planck, after several meetings with Dutch physicist Lorentz, revoked parts of the Manifesto. Then in 1916 he signed a declaration against German annexationism.
Post-war and the Weimar Republic
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
financial support for scientific research. A considerable portion of the
money the organization would distribute was raised abroad.
Planck also held leading positions at Berlin University, the Prussian Academy of Sciences, the German Physical Society and the Kaiser Wilhelm Society (which in 1948 became the Max Planck Society).
During this time economic conditions in Germany were such that he was
hardly able to conduct research. In 1926 Planck became a foreign member
of the Royal Netherlands Academy of Arts and Sciences.
During the interwar period, Planck 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 politics around the world.
Planck 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
From left to right: W. Nernst, A. Einstein, M. Planck, R.A. Millikan and von Laue at a dinner given by von Laue in Berlin on 11 November 1931
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, and by Schrödinger, Laue, and Einstein as well. 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 the Second World War
When
the Nazis came to 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 Nazi Germany.
Again he tried to "persevere and continue working" and asked scientists
who were considering emigration to remain in Germany. Nevertheless, he
did help his nephew, the economist Hermann Kranold, to emigrate to London after his arrest. He hoped the crisis would abate soon and the political situation would improve.
Otto 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 Society (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,
claiming that he was "1/16 Jewish", but Planck himself denied it.
Max Planck's grave in Göttingen
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-metre peaks in the Alps.
During the Second World War
the increasing number of Allied bombing missions against Berlin forced
Planck and his wife to temporarily leave the city 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. His rural retreat was threatened
by the rapid advance of the Allied armies from both sides.
In 1944, Planck's son Erwin was arrested by the Gestapo following the attempted assassination of Hitler in the 20 July plot. He was tried and sentenced to death by the People's Court in October 1944. Erwin was hanged at Berlin's Plötzensee Prison in January 1945. The death of his son destroyed much of Planck's will to live. After the end of the war Planck, his second wife, and his son by her were brought to a relative in Göttingen, where Planck died on October 4, 1947. His grave is situated in the old Stadtfriedhof (City Cemetery) in Göttingen.
Religious views
Planck was a member of the Lutheran Church in Germany. However, Planck was very tolerant towards alternative views and religions.
In a lecture in 1937 entitled "Religion and Naturwissenschaft" (Religion
and Natural Science) he suggested the importance of these symbols and
rituals related directly with a believer's ability to worship God, but
that one must be mindful that the symbols provide an imperfect
illustration of divinity. He criticized atheism for being focused on the
derision of such symbols, while at the same time warned of the
over-estimation of the importance of such symbols by believers.
He was tolerant and favorable to all religions. Although Planck
remained in the Lutheran Church, he did not promote Christian or
Biblical views. Planck believed "the faith in miracles must yield, step
by step, before the steady and firm advance of the facts of science, and
its total defeat is undoubtedly a matter of time."
In his 1937 lecture "Religion and Naturwissenschaft," Planck
expressed the view that God is everywhere present, and held that "the
holiness of the unintelligible Godhead is conveyed by the holiness of
symbols." Atheists, he thought, attach too much importance to what are
merely symbols. Planck was a churchwarden from 1920 until his death, and
believed in an almighty, all-knowing, beneficent God (though not
necessarily a personal one). Both science and religion wage a "tireless
battle against skepticism and dogmatism, against unbelief and
superstition" with the goal "toward God!"
Max Planck said in 1944, "As a man who has devoted his whole life
to the most clear headed science, to the study of matter, I can tell
you as a result of my research about atoms this much: There is no matter
as such. All matter originates and exists only by virtue of a force
which brings the particle of an atom to vibration and holds this most
minute solar system of the atom together. We must assume behind this
force the existence of a conscious and intelligent spirit (orig. geist).
This spirit is the matrix of all matter."
Planck regarded the scientist as a man of imagination and
Christian faith. He said: "Both religion and science require a belief in
God. For believers, God is in the beginning, and for physicists He is
at the end of all considerations… To the former He is the foundation, to
the latter, the crown of the edifice of every generalized world view".
On the other hand, Planck wrote, "...'to believe' means 'to
recognize as a truth,' and the knowledge of nature, continually
advancing on incontestably safe tracks, has made it utterly impossible
for a person possessing some training in natural science to recognize as
founded on truth the many reports of extraordinary occurrences
contradicting the laws of nature, of miracles which are still commonly
regarded as essential supports and confirmations of religious doctrines,
and which formerly used to be accepted as facts pure and simple,
without doubt or criticism. The belief in miracles must retreat step by
step before relentlessly and reliably progressing science and we cannot
doubt that sooner or later it must vanish completely."
Later in life, Planck's views on God were that of a deist. For example, six months before his death a rumour started that Planck had converted to Catholicism,
but when questioned what had brought him to make this step, he declared
that, although he had always been deeply religious, he did not believe
"in a personal God, let alone a Christian God."
