View source for Max Planck

{{Short description|German theoretical physicist (1858–1947)}}
{{Hatnote group|
{{Redirect|Planck|other uses|Planck (disambiguation)}}
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{{Use dmy dates|date=February 2021}}
{{Use American English|date=May 2017}}
{{Infobox scientist
| name              = Max Planck
| image             = Max Planck by Hugo Erfurth 1938cr - restoration1.jpg
| caption           = Planck in 1938
| birth_name        = Max Karl Ernst Ludwig Planck
| birth_date        = {{Birth date|1858|04|23|df=yes}}
| birth_place       = [[Kiel]], [[German Confederation]]
| death_date        = {{Death date and age|1947|10|04|1858|04|23|df=yes}}
| death_place       = [[Göttingen]], Germany
| resting_place     = ''[[Stadtfriedhof (Göttingen)|Stadtfriedhof]]'', Göttingen
| alma_mater        = {{Plain list|
* {{Nowrap|[[Ludwig Maximilian University of Munich|University of Munich]] ([[Doctor of Philosophy|Dr. phil.]])}}
* [[Humboldt University of Berlin|University of Berlin]] ([[Habilitation|Dr. habil.]])
}}
| known_for         = {{Plain list|
* [[Old quantum theory]]
* [[Planck's law]]
* [[Planck constant]]
* [[Planck units]]
* [[Planck postulate]]
* ''[[List of things named after Max Planck|See list]]''
}}
| spouses           = {{Plain list|
* {{Marriage|Marie Merck|1887|1909|end=died}}
* {{Marriage|Marga von Hösslin|1911}}
}}
| children          = 5, including [[Erwin Planck|Erwin]]
| awards            = {{Plain list|
* {{No wrap|[[Nobel Prize in Physics]] (1918)}}
* [[Fellow of the Royal Society#Foreign member|ForMemRS]] (1926)<ref name="frs">{{Cite journal | last1 = Born | first1 = M. | author-link = Max Born| title = Max Karl Ernst Ludwig Planck. 1858–1947 | doi = 10.1098/rsbm.1948.0024 | journal = [[Obituary Notices of Fellows of the Royal Society]] | volume = 6 | issue = 17 | pages = 161–188| year = 1948 | doi-access = free }}</ref> 
* [[Lorentz Medal]] (1927)
* [[Copley Medal]] (1929)
* [[Max Planck Medal]] (1929)
* [[Goethe Prize]] (1945)
}}
| fields            = {{Plain list|
* [[Thermodynamics]]
* [[Quantum mechanics|Quantum physics]]
}}
| work_institutions = {{Plain list|
* University of Munich <br/> (1880–1885)
* [[University of Kiel]] <br/> (1885–1889)
* University of Berlin <br/> (1889–1926)
}}
| thesis_title      = Über den zweiten Hauptsatz der mechanischen Wärmetheorie
| thesis_url        = https://edoc.hu-berlin.de/handle/18452/734
| thesis_year       = 1879
| doctoral_advisor  = [[Alexander von Brill]]<ref name=MGP>{{Cite web|title=Max Planck - The Mathematics Genealogy Project|url= https://www.genealogy.math.ndsu.nodak.edu/id.php?id=20750|website=genealogy.math.ndsu.nodak.edu|access-date=31 May 2025}}</ref>
| academic_advisors = {{Plain list|
* [[Hermann von Helmholtz]]
* [[Philipp von Jolly]]
* [[Gustav Kirchhoff]]
* [[Karl Weierstrass]]
}}
| doctoral_students = {{Collapsible list|title={{Nobold|''See list''}}
 | [[Hans von Euler-Chelpin]] (1895)<ref name=PhysicsTree>{{Cite web|title=Max Planck - Physics Tree|url=https://academictree.org/physics/peopleinfo.php?pid=16601|website=academictree.org|access-date=15 July 2025}}</ref>
 | [[Max Abraham]] (1897)
 | [[Max von Laue]] (1903)
 | [[Moritz Schlick]] (1904)
 | [[Kurd von Mosengeil]] (1906)<ref name=MGP/>
 | [[Walther Meissner]] (1907)
 | [[Wolfgang Köhler]] (1909)<ref name=PhysicsTree/>
 | [[Walter H. Schottky]] (1912)
 | [[Walther Bothe]] (1914)
 | [[Erich Kretschmann]] (1914)<ref name=MGP/>
 | [[Hartmut Kallmann]] (1920)<ref name=PhysicsTree/>
 | [[Erich Schumann]] (1922)<ref name=MGP/>
 }}
| notable_students  = {{Collapsible list|title={{Nobold|''See list''}}
 | [[Richard Becker (physicist)|Richard Becker]]<ref name=MGP/>
 | [[George Ellery Hale]]<ref name=PhysicsTree/>
 | [[Gustav Ludwig Hertz]]<ref name=MGP/>
 | [[Elizabeth Laird (physicist)|Elizabeth Laird]]<ref name=PhysicsTree/>
 | [[Lise Meitner]]<ref name=PhysicsTree/>
 | [[Ernest Merritt]]<ref name=PhysicsTree/>
 | [[Eugene Wigner]]<ref name=PhysicsTree/>
 | [[Ernst Zermelo]]<ref name=PhysicsTree/>
 }}
| signature         = Max Planck signature.svg
}}

'''Max Karl Ernst Ludwig Planck''' ({{IPA|de|maks ˈplaŋk|lang|De-Max Planck.ogg}}; 23 April 1858 – 4 October 1947) was a German [[Theoretical physics|theoretical physicist]] whose discovery of energy [[quantum|quanta]] won him the [[Nobel Prize in Physics]] in 1918.<ref>[http://nobelprize.org/nobel_prizes/physics/laureates/1918/ The Nobel Prize in Physics 1918] {{Webarchive|url=https://web.archive.org/web/20150905113018/http://www.nobelprize.org/nobel_prizes/physics/laureates/1918/ |date=5 September 2015 }}. Nobelprize.org. Retrieved on 5 July 2011.</ref>

Planck made many substantial contributions to theoretical physics, but his fame as a physicist rests primarily on his role as the originator of [[Quantum mechanics|quantum theory]] and one of the founders of [[modern physics]],<ref>{{Cite book |last=Fraenkel |first=Abraham |url=https://books.google.com/books?id=nudODQAAQBAJ&pg=PA96 |title=Recollections of a Jewish Mathematician in Germany |publisher=Birkhäuser |year=2016 |isbn=978-3-319-30845-6 |location=Basel, Switzerland |page=96}}</ref><ref>{{cite web | url=https://historydata.com/biographies/physicists/max-planck/ | title=Max Planck: Unveiling the Father of Quantum Theory | work=History Data | date=13 February 2024 }}</ref> which revolutionized understanding of [[atom]]ic and [[Subatomic particle|subatomic]] processes. He is known for the [[Planck constant]], which is of foundational importance for quantum physics, and which he used to derive a set of [[Unit of measurement|units]], now called [[Planck units]], expressed only in terms of [[physical constant]]s.<ref>{{Cite journal |date=2022-04-07 |title=The Planck Constant |url=https://www.nist.gov/physics/explainers/planck-constant |journal=NIST |language=en}}</ref>

Planck was twice President of the [[Kaiser Wilhelm Society]]. In 1948 it was renamed the [[Max Planck Society]], and today includes 83 institutions representing a wide range of scientific directions.

== Early life and education ==
Max Karl Ernst Ludwig Planck was born on 23 April 1858 in [[Kiel]], Holstein, the son of 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 (given name)|Marx]]'' was indicated as the [[Vorname|"appellation name"]].<ref>Christoph Seidler, [http://www.spiegel.de/wissenschaft/mensch/0,1518,549404,00.html ''Gestatten, Marx Planck''] {{webarchive|url=https://web.archive.org/web/20110629070656/http://www.spiegel.de/wissenschaft/mensch/0,1518,549404,00.html |date=29 June 2011 }}, Spiegel Online, 24 April 2008</ref> However, by the age of ten he signed with the name ''Max'' and used this for the rest of his life.<ref>[https://www.mpg.de/560620/pressemitteilung20080424 Press release] {{Webarchive|url=https://web.archive.org/web/20091018023747/http://mpg.de/bilderBerichteDokumente/dokumentation/pressemitteilungen/2008/pressemitteilung20080424/index.html|date=18 October 2009}} of the [[Max Planck Society]] about Max Planck's name.</ref>

Planck came from a traditional, intellectual family. His paternal great-grandfather and grandfather were both theology professors in [[University of Göttingen|Göttingen]]; his father was a law professor at the [[University of Kiel]] and [[Ludwig Maximilian University of Munich|Munich]]. One of his uncles was also a judge.<ref name=":0">{{Cite book|url=https://books.google.com/books?id=W3GvwcZEYwsC&q=max+planck+move+munich&pg=PT5|title=Max Planck: Revolutionary Physicist|last=Weir|first=Jane|date=2009|publisher=Capstone|isbn=978-0-7565-4073-9|language=en}}</ref>

Planck was the sixth 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 [[Kingdom of Prussia|Prussian]] and [[Austrian Empire|Austrian]] troops into Kiel during the [[Second Schleswig War]] in 1864.<ref name=":0" />

In 1867, the family moved to [[Munich]], where Planck enrolled at ''Maximiliansgymnasium''. There, his mathematical talents emerged early<ref>{{Cite web |title=Max Planck {{!}} Encyclopedia.com |url=https://www.encyclopedia.com/people/science-and-technology/physics-biographies/max-planck |access-date=2024-05-08 |website=www.encyclopedia.com}}</ref><ref>{{Cite book |last=Brown |first=Brandon R. |url=https://books.google.com/books?id=IrqyBwAAQBAJ&pg=PA14 |title=Planck: Driven by Vision, Broken by War |date=2015 |publisher=Oxford University Press |isbn=978-0-19-021947-5 |pages=14 |language=en}}</ref> and he later 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.<ref>''Encyclopædia Britannica: Max Planck''</ref> 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]].

In 1874, Planck enrolled at the [[University of Munich]]. Under professor [[Philipp von 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]]. Jolly advised Planck against going into theoretical physics; Planck recalls that in 1878, Jolly argued that physics was almost complete, being a "highly developed, nearly fully matured science, that through the crowning achievement of the discovery of the [[principle of conservation of energy]] will arguably soon take its final stable form".<ref>{{Cite journal |last=Wells |first=James D. |date=2016-03-06 |title=Prof. von Jolly's 1878 prediction of the end of theoretical physics as reported by Max Planck |url=http://deepblue.lib.umich.edu/handle/2027.42/163719 |journal=Scholardox |hdl=2027.42/163719 |language=}}</ref>

In 1877, Planck went to the [[University of 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 a close friend with Helmholtz. While there he undertook a program of mostly self-study of [[Rudolf Clausius]]' writings, which led him to choose [[thermodynamics]] as his field.

[[File:Max Planck 1878.GIF|left|thumb|Planck in 1878]]

In October 1878, Planck passed his qualifying exams and in February 1879 defended his thesis ''Über den zweiten Hauptsatz der mechanischen Wärmetheorie'' (On the second law of mechanical heat theory). 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.<ref name=":0" /> He then presented his ''[[venia legendi]]'' (habilitation) thesis titled ''Gleichgewichtszustände isotroper Körper in verschiedenen Temperaturen'' (Equilibrium states of isotropic bodies at different temperatures).

== Career and research ==
In 1880, Planck became a ''[[Privatdozent]]'' (unsalaried lecturer) at 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 [[theory of heat|heat theory]] and discovered one after another the same [[Thermodynamics|thermodynamic]]al formalism as [[Josiah Willard Gibbs|Gibbs]] without realizing it. Clausius' ideas on [[entropy]] occupied a central role in his work.

In April 1885, Planck was appointed Associate Professor of Theoretical Physics at the [[University of Kiel]]. Further work on entropy and its treatment, especially as applied in [[physical chemistry]], followed. He published his ''Treatise on Thermodynamics'' in 1897.<ref>{{cite book|last=Planck|first=Max|title=Vorlesungen über Thermodynamik|year=1897|publisher=Verlag Von Veit & Company|location=Leipzig|url=http://gutenberg.org/ebooks/31564|access-date=27 June 2012|archive-url=https://web.archive.org/web/20120624020935/http://www.gutenberg.org/ebooks/31564|archive-date=24 June 2012|url-status=live}} English translation: {{cite book|last=Planck|first=Max|title=Treatise on Thermodynamics|year=1903|publisher=Longmans, Green, and Company|location=London|url=https://archive.org/details/treatiseonthermo00planrich|quote=Treatise on Thermodynamics.|access-date=27 June 2012|archive-url=https://web.archive.org/web/20120220105403/http://www.archive.org/details/treatiseonthermo00planrich|archive-date=20 February 2012|url-status=live}}</ref> He proposed a thermodynamic basis for [[Svante Arrhenius]]'s theory of [[electrolyte|electrolytic]] [[dissociation (chemistry)|dissociation]].

In 1889, Planck was named the successor to Kirchhoff's position at the [[University of Berlin]]<ref>{{cite web |url=https://www.nobelprize.org/nobel_prizes/physics/laureates/1918/planck-bio.html |title=Max Planck – Biographical |website=Nobelprize.org |publisher=Nobel Prize Organisation |access-date=26 February 2017 |archive-url=https://web.archive.org/web/20170226040835/http://www.nobelprize.org/nobel_prizes/physics/laureates/1918/planck-bio.html |archive-date=26 February 2017 |url-status=live }}</ref> – presumably thanks to Helmholtz's intercession – and by 1892 became Full Professor. In 1907, he was offered [[Ludwig 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 Lectures|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 [[Albert Potter Wills|A. P. Wills]].<ref>{{cite book|author=Jacques Hadamard|title=Four lectures on mathematics: delivered at Columbia University in 1911|url=https://archive.org/details/cu31924060184375|access-date=5 July 2011|year=1915|publisher=Columbia University Press|pages=[https://archive.org/details/cu31924060184375/page/n24 7]–}}</ref> He was elected to the [[American Academy of Arts and Sciences]] in 1914.<ref>{{Cite web |date=2023-02-09 |title=Max Karl Ernst Ludwig Planck |url=https://www.amacad.org/person/max-karl-ernst-ludwig-planck |access-date=2023-06-22 |website=American Academy of Arts & Sciences |language=en}}</ref> He retired from Berlin on 10 January 1926,<ref>{{cite web|title=Max Planck – Humboldt-Universität zu Berlin|url=https://www.hu-berlin.de/en/about/history/nobel-laureates/planck/|website=www.hu-berlin.de|access-date=15 May 2016|language=en|archive-url=https://web.archive.org/web/20160531054648/https://www.hu-berlin.de/en/about/history/nobel-laureates/planck/|archive-date=31 May 2016|url-status=live}}</ref> and was succeeded by [[Erwin Schrödinger]].<ref>{{cite web|title=Erwin Schrödinger – Humboldt-Universität zu Berlin|url=https://www.hu-berlin.de/en/about/history/nobel-laureates/schroedinger|website=www.hu-berlin.de|access-date=15 May 2016|language=en|archive-url=https://web.archive.org/web/20160531080108/https://www.hu-berlin.de/en/about/history/nobel-laureates/schroedinger|archive-date=31 May 2016|url-status=live}}</ref> He was elected to the [[National Academy of Sciences]] in 1926 and to the [[American Philosophical Society]] in 1933.<ref>{{Cite web |title=Max Planck |url=http://www.nasonline.org/member-directory/deceased-members/20001902.html |access-date=2023-06-22 |website=www.nasonline.org}}</ref><ref>{{Cite web |title=APS Member History |url=https://search.amphilsoc.org/memhist/search?creator=+Max+Planck&title=&subject=&subdiv=&mem=&year=&year-max=&dead=&keyword=&smode=advanced |access-date=2023-06-22 |website=search.amphilsoc.org}}</ref>

=== Professor at Berlin University ===
As a professor at the University of 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".<ref>
{{cite journal
 |last1     = Verband Deutscher Elektrotechniker
 |last2     = Elektrotechnischer Verein (Berlin, Germany)
 |year      = 1948
 |journal   = ETZ: Elektrotechnische Zeitschrift
 |title     = ETZ: Elektrotechnische Zeitschrift: Ausg. A.
 |volume    = 69
 |issue     = A
 |publisher = VDE-Verlag
 |language  = de
 |url       = https://books.google.com/books?id=ZFE7AAAAMAAJ
}}, [https://www.google.com/search?&tbs=bks%3A1&q=planck++%22damals+der+einzige+theoretische%22 Snipped extract] {{Webarchive|url=https://web.archive.org/web/20170405025654/http://www.google.com/search?&tbs=bks%3A1&q=planck++%22damals+der+einzige+theoretische%22 |date=5 April 2017 }}</ref> 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.

[[File:Max Planck Wirkungsquantums 20050815.jpg|thumb|right|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"{{Citation needed|date=March 2025}} according to [[Lise Meitner]], "using no notes, never making mistakes, never faltering; the best lecturer I ever heard"{{Citation needed|date=March 2025}} according to an English participant, [[J. R. Partington|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."{{Citation needed|date=March 2025}} Planck did not establish an actual "school"; the number of his graduate students was only about 20, among them:{{Citation needed|date=March 2025}}
* 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)<ref>{{cite web|url=https://www.genealogy.math.ndsu.nodak.edu/id.php?id=20750|title=Max Planck – The Mathematics Genealogy Project|website=www.genealogy.math.ndsu.nodak.edu|access-date=5 June 2017|archive-url=https://web.archive.org/web/20170608023459/https://www.genealogy.math.ndsu.nodak.edu/id.php?id=20750|archive-date=8 June 2017|url-status=live}}</ref>

=== Entropy ===
[[Thermodynamics]], also known as the "mechanical theory of heat" at the end of the 19th century, had emerged at the beginning of this century from an attempt to understand the functioning of steam engines and to improve their efficiency. In the 1840s, several researchers independently discovered and formulated the law of conservation of energy, which is now also known as the [[first law of thermodynamics]]. In 1850, [[Rudolf Clausius]] formulated the so-called [[second law of thermodynamics]], which states that a voluntary (or spontaneous) transfer of energy is only possible from a warmer to a colder body, but not vice versa. In England at this time [[William Thomson, 1st Baron Kelvin|William Thomson]] came to the same conclusion.

Clausius generalized his formulation further and further and came up with a new formulation in 1865. To this end, he introduced the concept of [[entropy]], which he defined as a measure of the reversible supply of heat in relation to the absolute temperature.

The new formulation of the second law, which is still valid today, was: "Entropy can be created, but never destroyed". Clausius, whose work Planck read as a young student during his stay in Berlin, successfully applied this new law of nature to mechanical, thermoelectric and chemical processes.

In his thesis in 1879, Planck summarized Clausius' writings, pointing out contradictions and inaccuracies in their formulation and then clarifying them. In addition, he generalized the validity of the second law to all processes in nature; Clausius had limited its application to reversible processes and thermal processes. Furthermore, Planck dealt intensively with the new concept of entropy and emphasized that entropy is not only a property of a physical system, but at the same time a measure of the irreversibility of a process: If entropy is generated in a process, it is irreversible, since entropy cannot be destroyed according to the second law. In reversible processes, the entropy remains constant. He presented this fact in detail in 1887 in a series of treatises entitled "On the Principle of the Increase of Entropy".<ref>{{cite journal |last1=Vlasak |first1=Weldon |title=Planck's theory and thermodynamics |journal=Chemical Innovation |date=February 2001 |volume=31 |issue=2 |pages=56–59 |url=https://pubsapp.acs.org/subscribe/archive/ci/31/i02/html/02learning.html |access-date=7 August 2024}}</ref>

In his study of the concept of entropy, Planck did not follow the molecular, probabilistic interpretation that prevailed at the time, as these do not provide absolute proof of universality. Instead, he pursued a phenomenological approach and was also skeptical of atomism. Even though he later abandoned this attitude in the course of his work on the law of radiation, his early work impressively shows the possibilities of thermodynamics in solving concrete physicochemical problems.<ref name="Hoffmann29f">Hoffmann: ''Max Planck.'' Munich 2008, p.&nbsp;29.</ref><ref name="Hartmann156f">Hartmann: ''Max Planck als Mensch und Denker.'' 3. revised edition, Basel 1953, p.&nbsp;156.</ref>

Planck's understanding of entropy included the realization that the maximum of entropy corresponds to the equilibrium state. The accompanying conclusion that knowledge of the Entropy allows all laws of thermodynamic equilibrium states to be derived corresponds to the modern understanding of such states. Planck therefore chose equilibrium processes as his research focus and, based on his habilitation thesis, researched the coexistence of aggregate states and the equilibrium of gas reactions, for example. This work on the frontier of chemical thermodynamics also received great attention due to the rapidly expanding chemical work at that time.

Independently of Planck, [[Josiah Willard Gibbs]] had also discovered almost all the knowledge Planck gained about the properties of physicochemical equilibria and published them from 1876 onwards. Planck was unaware of these essays, and they did not appear in German until 1892. However, both scientists approached the topic in different ways, while Planck dealt with irreversible processes, Gibbs looked at equilibria. This approach was finally able to prevail because of its simplicity, but Planck's approach is attributed the greater universality.<ref>Hoffmann: ''Max Planck.'' Munich 2008, p.&nbsp;31&nbsp;f.</ref>

=== Black-body radiation ===
[[File:Max Planck 1901.GIF|thumb|Planck in 1901]]

In 1894, Planck turned his attention to the problem of [[black-body radiation]]. 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 had agreed with the experimentally observed evidence. [[Wilhelm Wien]] proposed [[Wien approximation|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, as predicted by [[classical physics]]. However, contrary to many textbooks, this was not a motivation for Planck.<ref name="Kragh">For a solid approach to the complexity of Planck's intellectual motivations for the quantum, for his reluctant acceptance of its implications, see Helge Kragh, 
[https://physicsworld.com/a/max-planck-the-reluctant-revolutionary/ Max Planck: the reluctant revolutionary] {{Webarchive|url=https://web.archive.org/web/20181105061830/https://physicsworld.com/a/max-planck-the-reluctant-revolutionary/ |date=5 November 2018 }}, ''Physics World''. December 2000.</ref>

Planck's first proposed solution to the problem in 1899 followed from what he 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, however, it was found that experimental evidence did not confirm the new law at all, to Planck's frustration. He revised his approach and now derived the first version of the famous [[Planck's law of black-body radiation|Planck black-body radiation law]], which described clearly the experimentally observed black-body spectrum. 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 version, now relying on [[Ludwig Boltzmann|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. Planck was deeply suspicious of the philosophical and physical implications of such an interpretation of Boltzmann's approach; thus 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".<ref name="Kragh"/>

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 [[Quantization (physics)|quantized]] form, in other words, the energy could only be a multiple of an elementary unit:
: <math>E = h\nu</math>
where {{math|''h''}} is the [[Planck constant]], also known as Planck's action quantum (introduced already in 1899), and {{math|''ν''}} is the frequency of the radiation. Note that the elementary units of energy discussed here are represented by {{math|''hν''}} and not simply by {{math|''ν''}}. Physicists now call these quanta photons, and a photon of frequency {{math|''ν''}} will have its own specific and unique energy. The total energy at that frequency is then equal to {{math|''hν''}} multiplied by the number of photons at that frequency.

[[File:Max Planck Nobel 1918.jpg|thumb|left|Planck in 1918, the year he was awarded the [[Nobel Prize in Physics]] for his work on [[Quantum mechanics|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|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 the Planck constant enabled him to define a new universal set of [[Planck units|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 a discussion with his son in December 1918 Planck described his discovery as 'a discovery of the first rank, comparable perhaps only to the discoveries of Newton'.<ref>Egginton, William, ''[https://us5.campaign-archive.com/?e=01376ceb1d&u=6557fc90400ccd10e100a13f4&id=dc364d6f8b The Rigor of Angels: Max Planck unleashed a revolution in physics]'', pp. 52–54, Pantheon, Delancy Place, 2023</ref> In recognition of Planck's fundamental contribution to a new branch of physics, he was awarded the Nobel Prize in Physics for 1918; (he received the award in 1919).<ref>Kragh, Helge (1 December 2000), Max Planck: the reluctant revolutionary, PhysicsWorld.com</ref><ref>{{cite web|url=https://www.nobelprize.org/nobel_prizes/physics/laureates/1918/|title=The Nobel Prize in Physics 1918|website=www.nobelprize.org|access-date=11 June 2017|archive-url=https://web.archive.org/web/20170609233007/http://www.nobelprize.org/nobel_prizes/physics/laureates/1918/|archive-date=9 June 2017|url-status=live}}</ref>

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 such as [[John William Strutt, 3rd Baron Rayleigh|Rayleigh]], [[James Jeans|Jeans]], and [[Hendrik Lorentz|Lorentz]] set the Planck 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."<ref>Heilbron, 2000, [https://books.google.com/books?id=d5zKH2Bx2AwC&pg=PA8 p. 8] {{Webarchive|url=https://web.archive.org/web/20180417074508/https://books.google.com/books?id=d5zKH2Bx2AwC&pg=PA8 |date= 2018 }}</ref>

[[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."<ref name="frs"/>

=== Einstein and the theory of relativity ===
<!-- Commented out: [[File:Max-Planck-und-Albert-Einstein.jpg|thumb|Max Planck presents [[Albert Einstein]] with the Max-Planck medal, Berlin 28 June 1929]] -->

In 1905, three 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 (physics)|action]].<ref>''Einstein and the Quantum'', A.Douglas Stone, Princeton University Press, Princeton and Oxford, chapter 9, ''Tripping the light heuristic'', 2013.</ref>

Einstein's hypothesis of light ''quanta'' ([[photons]]), based on [[Heinrich Hertz#Electromagnetic research|Heinrich Hertz's]] 1887 discovery (and further investigation by [[Philipp Lenard#Photoelectric investigations|Philipp Lenard]]) of the [[photoelectric effect]], was initially rejected by Planck. He was unwilling to discard completely [[James Clerk Maxwell|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]] ..."<ref>{{Cite book|title=Atoms and Photons and Quanta, Oh My!: Ask the physicist about atomic, nuclear, and quantum physics|last=Baker|first=F. Todd|publisher=Morgan & Claypool Publishers|year=2015|isbn=978-1-62705-940-4}}</ref>

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 [[Walther 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."<ref>Heilbron, 2000, [https://books.google.com/books?id=d5zKH2Bx2AwC&pg=PA72 p. 72] {{Webarchive|url=https://web.archive.org/web/20150320070521/http://books.google.com/books?id=d5zKH2Bx2AwC&pg=PA72 |date=20 March 2015 }}</ref><ref>
{{cite book
 |title=Quantum mechanics at the crossroads: new perspectives from history, philosophy and physics
 |first1=James |last1=Evans
 |first2=Alan S. |last2=Thorndike
 |publisher=Springer
 |year=2007
 |isbn=978-3-540-32663-2
 |page=31
 |url=https://books.google.com/books?id=S3FOuMYHcqIC
 |access-date=14 October 2016
 |archive-url=https://web.archive.org/web/20150320051740/http://books.google.com/books?id=S3FOuMYHcqIC
 |archive-date=20 March 2015
 |url-status=live
}} [https://books.google.com/books?id=S3FOuMYHcqIC&pg=PA31 Extract of page 31] {{Webarchive|url=https://web.archive.org/web/20150320054630/http://books.google.com/books?id=S3FOuMYHcqIC&pg=PA31 |date=20 March 2015 }}</ref> Planck also signed the infamous "[[Manifesto of the Ninety-Three|Manifesto of the 93 intellectuals]]", a pamphlet of polemic war propaganda (while Einstein retained a strictly pacifistic attitude which almost led to his imprisonment, only being spared thanks to his [[Swiss (people)|Swiss]] citizenship).

In 1915, when Italy was still a neutral power, Planck 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.

=== 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 held leading positions at Berlin University, the Prussian Academy of Sciences, the German Physical Society, and the [[Kaiser Wilhelm Society]] (which became the [[Max Planck Society]] in 1948). 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]].<ref>{{cite web |url=http://www.dwc.knaw.nl/biografie/pmknaw/?pagetype=authorDetail&aId=PE00002335 |title=Max Karl Ernst Ludwig Planck (1858–1947) |publisher=Royal Netherlands Academy of Arts and Sciences |access-date=4 August 2015 |archive-url=https://web.archive.org/web/20150910170739/http://www.dwc.knaw.nl/biografie/pmknaw/?pagetype=authorDetail&aId=PE00002335 |archive-date=10 September 2015 |url-status=live }}</ref>

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".<ref>
{{cite book
 |title=The demon and the quantum: from the pythagorean mystics to Maxwell's demon and quantum mystery
 |first1=Robert J. |last1=Scully
 |first2=Marlan O. |last2=Scully
 |publisher=Wiley-VCH
 |year=2007
 |isbn=978-3-527-40688-3
 |page=90
 |url=https://books.google.com/books?id=mQHswDNUbvMC
 |access-date=14 October 2016
 |archive-url=https://web.archive.org/web/20150320043330/http://books.google.com/books?id=mQHswDNUbvMC
 |archive-date=20 March 2015
 |url-status=live
}}, [https://books.google.com/books?id=mQHswDNUbvMC&pg=PA90 Chapter 7, p 90] {{Webarchive|url=https://web.archive.org/web/20150320084201/http://books.google.com/books?id=mQHswDNUbvMC&pg=PA90 |date=20 March 2015 }}</ref>

=== Quantum mechanics ===
[[File:Nernst, Einstein, Planck, Millikan, Laue in 1931.jpg|thumb|330px|From left to right: [[Walther Nernst|Nernst]], [[Albert Einstein|Einstein]], '''Planck''', [[Robert Millikan|Millikan]], and [[Max von Laue|Laue]] at a dinner given by von Laue in Berlin on 11 November 1931]]

At the end of the 1920s, [[Niels Bohr]], [[Werner Heisenberg]], and [[Wolfgang 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 [[Schrödinger equation#Particles as waves|wave mechanics]] would soon render quantum theory{{snd}} his own child{{snd}} unnecessary. This was not to be the case, however. Further work only served to underscore the enduring central importance of quantum theory, even against his and Einstein's philosophical revulsions. Here Planck experienced the truth of his own earlier observation from his struggle with the older views during 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."<ref>Quoted in Thomas Kuhn, ''[[The Structure of Scientific Revolutions]]'' (1970 ed.): p. 150.</ref>

=== Nazi dictatorship and the Second World War ===
When the Nazis came to power in 1933, Planck was 74 years old. He witnessed many Jewish friends and colleagues expelled from their positions and humiliated, and hundreds of scientists emigrate 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.<ref name="IJ">{{cite web|title=Johanna Kranold Stein|url=http://www.legacy.com/obituaries/theithacajournal/obituary.aspx?n=johanna-kranold-stein&pid=87920213|website=Ithaca Journal|publisher=Legacy.com|access-date=10 October 2016|archive-url=https://web.archive.org/web/20161011142403/http://www.legacy.com/obituaries/theithacajournal/obituary.aspx?n=johanna-kranold-stein&pid=87920213|archive-date=11 October 2016|url-status=live}}</ref> 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."<ref>In a slightly different translation, Hahn remembers Planck saying: "If you bring together 30 such men today, then tomorrow 150 will come to denounce them because they want to take their places." This translated quote is found in: Heilbron, 2000, p. 150. Heilbron, at the end of the paragraph, on p. 151, cites the following references to Hahn's writings: Otto Hahn ''Einige persönliche Erinnerungen an Max Planck'' MPG, ''Mitteilungen'' (1957) p. 244, and Otto Hahn ''My Life'' (Herder and Herder, 1970) p. 140.</ref> Under Planck's leadership, the [[Kaiser Wilhelm Society]] (KWG) avoided open conflict with the Nazi regime, except concerning the Jewish Fritz Haber. In May 1933 Planck requested and received an interview with the recently appointed Chancellor of Germany [[Adolf Hitler]] to discuss the issue, telling him that the "forced emigration of Jews would kill German science and Jews could be good Germans", to which the chancellor replied "but we don't have anything against the Jews, only against communists". Planck was therefore unsuccessful, since this reply "took from him every basis for further negotiation",<ref>{{cite book |last1=Clary |first1=David |title=Schrödinger in Oxford |date=2022 |page=54|bibcode=2022scox.book.....C }}</ref> as to Hitler "the Jews are all Communists, and these are my enemies." In the following year, 1934, Haber died in exile.<ref>{{Cite journal|last=O'Flaherty|first=James C.|date=1956|title=Max Planck and Adolf Hitler|url=https://www.jstor.org/stable/40222051|journal=AAUP Bulletin|volume=42|issue=3|pages=437–444|doi=10.2307/40222051|jstor=40222051|issn=0001-026X|url-access=subscription}}</ref>

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 the ''[[Deutsche Physik]]'' ("German Physics", also called "Aryan Physics") attacked Planck, [[Arnold 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 denied it.<ref>Heilbron, 2000, [https://books.google.com/books?id=d5zKH2Bx2AwC&pg=PA191 p. 191] {{Webarchive|url=https://web.archive.org/web/20150320084452/http://books.google.com/books?id=d5zKH2Bx2AwC&pg=PA191 |date=20 March 2015 }}</ref>

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, as part of their process of ''[[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 Planck|Erwin]] was arrested by the [[Gestapo]] following the attempted assassination of Hitler in the {{awrap|[[20 July plot]]}}. He was tried and sentenced to death by the [[People's Court (Germany)|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.<ref>{{cite web|url=http://physics.nobel.brainparad.com/max_karl_ernst_ludwig_planck.html |title=Max Karl Ernst Ludwig Planck |access-date=17 June 2010 |url-status=dead |archive-url=https://web.archive.org/web/20080512151051/http://physics.nobel.brainparad.com/max_karl_ernst_ludwig_planck.html |archive-date=12 May 2008 }}</ref>

== Personal life and death ==
[[File:Stadtfriedhof Göttingen Max Planck Familie.jpg|thumb|Planck's grave in Göttingen]]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 Planck|Erwin]] (1893–1945).

After living in 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 [[Hermann von Helmholtz|Helmholtz]].

After several happy years, in July 1909 Marie Planck died, possibly of [[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 [[Battle of Verdun|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 Planck]], to whom he had been particularly close, was sentenced to death by the ''[[People's Court (German)|Volksgerichtshof]]'' (People's Court) because of his participation in the [[July 20 plot|failed attempt to assassinate Hitler]] in July 1944. Erwin was executed on 23 January 1945.<ref>{{cite book|author1=Jürgen Heideking|author2=Christof Mauch|title=American Intelligence and the German Resistance to Hitler: A Documentary History|url=https://books.google.com/books?id=xoTWkzhf2uUC&pg=PA361|access-date=5 July 2011|year=1998|publisher=Westview Press|isbn=978-0-8133-3636-7|pages=361–|archive-url=https://web.archive.org/web/20130603082521/http://books.google.com/books?id=xoTWkzhf2uUC&pg=PA361|archive-date=3 June 2013|url-status=live}}</ref>

After World War II ended, Planck, his second wife, and their son were brought to a relative in [[Göttingen]], where Planck died on October 4, 1947. He is buried at the ''[[Stadtfriedhof]]'' (City Cemetery) in Göttingen.<ref>{{Citation|url = https://www.youtube.com/watch?v=qHPEHvRPkM4|title = Max Planck's Grave at Göttingen, Germany| date=January 2016 |publisher = Youtube|access-date = 4 January 2016|archive-url = https://web.archive.org/web/20160318002953/https://www.youtube.com/watch?v=qHPEHvRPkM4|archive-date = 18 March 2016|url-status = live}}</ref>

== Religious views ==
[[File:DBPB 1952 99 Max Planck.jpg|thumb|Planck on a West German stamp (1952)]]

Planck was a member of the [[Lutheranism|Lutheran Church]] in Germany.<ref>Erich Dinkler, "Planck, Max", in ''Die Religion in Geschichte und Gegenwart'', Third Edition, Volume V, Tübingen (Germany), 1961, col. 404–405</ref> He was very tolerant toward alternative views and [[religions]].<ref name="adherents.com"/> In a lecture in 1937 entitled "Religion und 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.<ref>[http://www.encyclopedia.com/topic/Max_Planck.aspx The Life Max Planck] {{Webarchive|url=https://web.archive.org/web/20121102190708/http://www.encyclopedia.com/topic/Max_Planck.aspx |date=2 November 2012 }}. encyclopedia.com. Retrieved on 7 March 2012.</ref><ref name="adherents.com">{{usurped|[https://web.archive.org/web/20170810130831/http://www.adherents.com/people/pp/Max_Planck.html The Religious Affiliation of Physicist Max Planck]}}. adherents.com. Retrieved on 5 July 2011.</ref>{{tertiary source inline|date=November 2025|reason=One of these sources is an encyclopedia, and the other is only quoting another source (which might be verifiable as the proper source for this paragraph).}}

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."<ref>"''Das Wesen der Materie''" [The Nature of Matter], speech at Florence, Italy (1944) (from Archiv zur Geschichte der Max-Planck-Gesellschaft, Abt. Va, Rep. 11 Planck, Nr. 1797)</ref>

Planck argued that the concept of God is important to both religion and science, but in different ways: "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".<ref>"Religion and Natural Science" (Lecture Given 1937) ''Scientific Autobiography and Other Papers'', trans. F. Gaynor (New York, 1949), pp. 184</ref>

Furthermore, Planck wrote, <blockquote>..."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.<ref>Max Planck, Scientific Autobiography and Other Papers</ref></blockquote>

Noted historian of science [[John L. Heilbron]] characterized Planck's views on God as [[deist]]ic.<ref>{{cite book|title=The Dilemmas of an Upright Man: Max Planck and the Fortunes of German Science|year=1986|publisher=Harvard University Press|isbn=978-0-674-00439-9|author=J. L. Heilbron|page=198|quote=On the other side, Church spokesmen could scarcely become enthusiastic about Planck's deism, which omitted all reference to established religions and had no more doctrinal content than Einstein's Judaism. It seemed useful therefore to paint the lily, to improve the lesson of Planck's life for the use of proselytizers and to associate the deanthropomorphizer of science with a belief in a traditional Godhead.}}</ref> Heilbron further relates that when asked about his religious affiliation, Planck replied that although he had always been deeply religious, he did not believe "in a personal God, let alone a Christian God".<ref>Heilbron, 2000, [https://books.google.com/books?id=d5zKH2Bx2AwC&pg=PA198 page 198] {{Webarchive|url=https://web.archive.org/web/20180417074505/https://books.google.com/books?id=d5zKH2Bx2AwC&pg=PA198 |date=17 April 2018 }}</ref>

== Posthumous honors ==
{{Further|List of things named after Max Planck}}

<!---- translation of  https://de.wikipedia.org/wiki/Max_Planck#Postume_Ehrungen (26 July 2025)--->
* In 1953, the German Post Office Berlin honored Max Planck with a 30-pfennig stamp in the series "Men from Berlin's History."
* From 1957 to 1971, the Federal Republic's 2-[[Deutsche Mark|DM]] coins featured Max Planck's portrait.
* In 1958, a commemorative plaque was unveiled in the forecourt of the Humboldt University of Berlin.
* In 1958, the [[Max Planck Society]] presented a bust of Planck, created in 1939, to the Physical Society of the [[GDR]]. The bust has been on display in the exhibition room of the Magnushaus since 1991.
* In 1970, the lunar crater Planck and the adjacent valley Vallis Planck were named after Planck.
* In 1983, the [[GDR]] issued a 5-mark commemorative coin to mark his 125th birthday. This was not a circulating coin, but was primarily sold for foreign currency.
* In 1989, a Berlin commemorative plaque was unveiled at Planck's former residence in [[Grunewald (locality)|Berlin-Grunewald]].
* In 2008, a special postage stamp and a 10-[[Euro]] silver commemorative coin were issued to mark his 150th birthday.
* In 2014, Google celebrated Planck's 156th birthday with a Google Doodle on April 23.
* In 2022, his bust was placed in [[Walhalla (memorial)|Walhalla]].<ref>[https://www.br.de/nachrichten/kultur/bueste-von-physiker-max-planck-kommt-in-die-walhalla,TBd2OG7 ''Büste von Physiker Max Planck kommt in die Walhalla'']</ref>

== Publications ==
[[File:Planck, Max – Vorlesungen über die Theorie der Wärmestrahlung, 1906 – BEIC 6567602.jpg|thumb|''Vorlesungen über die Theorie der Wärmestrahlung'', 1906]]
* {{cite journal
 |last1=Planck |first1=M.
 |author1-link=Max Planck
 |year=1900a
 |title=Über eine Verbesserung der Wienschen Spektralgleichung
 |journal=[[Verhandlungen der Deutschen Physikalischen Gesellschaft]]
 |volume=2 |pages=202–204
 |url=https://archive.org/stream/verhandlungende01goog#page/n212/mode/2up
}} Translated in {{cite book
 |last1=ter Haar |first1=D.
 |author1-link=Dirk ter Haar
 |year=1967
 |chapter=On an Improvement of Wien's Equation for the Spectrum
 |chapter-url=http://www.ffn.ub.es/luisnavarro/nuevo_maletin/Planck%20%281900%29,%20Improvement%20of%20Wien%27s.pdf
 |title=The Old Quantum Theory
 |publisher=[[Pergamon Press]]
 |pages=79–81
 |lccn=66029628
}}
* {{cite journal
 |last1=Planck |first1=M.
 |author1-link=Max Planck
 |year=1900b
 |title=Zur Theorie des Gesetzes der Energieverteilung im Normalspectrum
 |journal=[[Verhandlungen der Deutschen Physikalischen Gesellschaft]]
 |volume=2 |page=237
 |url=https://archive.org/stream/verhandlungende01goog#page/n246/mode/2up
}} Translated in {{cite book
 |last1=ter Haar
 |first1=D.
 |author1-link=Dirk ter Haar
 |year=1967
 |chapter=On the Theory of the Energy Distribution Law of the Normal Spectrum
 |chapter-url=http://www.ffn.ub.es/luisnavarro/nuevo_maletin/Planck%20%281900%29,%20Distribution%20Law.pdf
 |title=The Old Quantum Theory
 |publisher=[[Pergamon Press]]
 |page=82
 |lccn=66029628
 |access-date=5 April 2014
 |archive-date=20 September 2016
 |archive-url=https://web.archive.org/web/20160920053757/http://www.ffn.ub.es/luisnavarro/nuevo_maletin/Planck%20%281900%29,%20Distribution%20Law.pdf
 |url-status=dead
}}
* {{cite journal
 |last1=Planck |first1=M.
 |author1-link=Max Planck
 |year=1900c
 |title=Entropie und Temperatur strahlender Wärme
 |trans-title=Entropy and Temperature of Radiant Heat
 |journal=[[Annalen der Physik]]
 |volume=306 |issue=4 |pages=719–737
 |bibcode=1900AnP...306..719P
 |doi=10.1002/andp.19003060410
 |url=https://zenodo.org/record/1423979
}}
*{{cite journal
 |last1=Planck |first1=M.
 |author1-link=Max Planck
 |year=1900d
 |title=Über irreversible Strahlungsvorgänge
 |trans-title=On Irreversible Radiation Processes
 |journal=[[Annalen der Physik]]
 |volume=306
 |issue=1
 |pages=69–122
 |bibcode=1900AnP...306...69P
 |doi=10.1002/andp.19003060105
 |url=https://zenodo.org/record/1423973
}}
* {{cite journal|last1=Planck|first1=M.|author1-link=Max Planck|year=1901|title=Ueber das Gesetz der Energieverteilung im Normalspektrum|journal=[[Annalen der Physik]]|volume=309|issue=3|pages=553–563|doi=10.1002/andp.19013090310|bibcode=1901AnP...309..553P|doi-access=free}} Translated in {{cite web
 |last1       = Ando |first1      = K.
 |title       = On the Law of Distribution of Energy in the Normal Spectrum
 |url         = http://theochem.kuchem.kyoto-u.ac.jp/Ando/planck1901.pdf
 |access-date  = 13 October 2011
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20111006162543/http://theochem.kuchem.kyoto-u.ac.jp/Ando/planck1901.pdf
 |archive-date = 6 October 2011
 |df          = dmy-all
}}
* {{cite book
 |last1=Planck |first1=M.
 |author1-link=Max Planck
 |year=1903
 |title=Treatise on Thermodynamics
 |url=https://archive.org/stream/treatiseonthermo00planuoft#page/n7/mode/2up
 |others=Ogg, A. (transl.)
 |publisher=Longmans, Green & Co
 |location=London
 |ol=7246691M
}}
* {{cite book
 |last1=Planck |first1=M.
 |author1-link=Max Planck
 |year=1906
 |title=Vorlesungen über die Theorie der Wärmestrahlung
 |url=https://archive.org/details/vorlesungenberd03plangoog |publisher=J.A. Barth
 |location=Leipzig
 |lccn=07004527
}}
* {{cite book
 |last1=Planck |first1=M.
 |author1-link=Max Planck
 |others=Masius, M. (transl.)
 |year=1914
 |title=The Theory of Heat Radiation
 |publisher=P. Blakiston's Son & Co.
 |edition=2nd
 |ol=7154661M
}}
* {{cite book
 |last1=Planck |first1=M.
 |author1-link=Max Planck
 |others=[[Albert Potter Wills|Wills, A. P.]] (transl.)
 |year=1915
 |title=Eight Lectures on Theoretical Physics
 |publisher=[[Dover Publications]]
 |isbn=0-486-69730-4
}}
* {{cite book
 |last1=Planck |first1=M.
 |author1-link=Max Planck
 |year=1908
 |title=Prinzip der Erhaltung der Energie
 |url=https://books.google.com/books?id=prgnAAAAMAAJ
 |location=Leipzig
 |publisher=B.G.Teubner
|isbn=978-0-598-83768-4
 }}
* {{cite journal
 |last1=Planck |first1=M.
 |author1-link=Max Planck
 |year=1943
 |title=Zur Geschichte der Auffindung des physikalischen Wirkungsquantums
 |journal=[[Naturwissenschaften]]
 |volume=31 |issue=14–15 |pages=153–159
 |bibcode=1943NW.....31..153P
 |doi=10.1007/BF01475738
 |s2cid=44899488
}}

== See also ==
{{Portal|Biographies|Physics}}
* [[German inventors and discoverers]]
* [[Photon polarization]]
* [[Statue of Max Planck]]
* [[Zero-point energy]]

== Notes ==
<references group="lower-alpha" />
== References ==
{{reflist}}

== Sources ==
* [[Amir Aczel|Aczel, Amir D.]] ''Entanglement'', Chapter 4. (Penguin, 2003) {{ISBN|978-0-452-28457-9}}
* {{cite book |title=The Dilemmas of an Upright Man: Max Planck and the Fortunes of German Science |first1=J. L. |last1=Heilbron |author-link= John L. Heilbron |publisher=Harvard University Press |year=2000 |isbn=0-674-00439-6 |url=https://books.google.com/books?id=d5zKH2Bx2AwC}}
* [[Clifford A. Pickover|Pickover, Clifford A.]] ''Archimedes to Hawking: Laws of Science and the Great Minds Behind Them'', Oxford University Press, 2008, {{ISBN|978-0-19-533611-5}}
* {{cite book |last1=Medawar |first1=Jean |last2=Pyke |first2=David | title = Hitler's Gift: The True Story of the Scientists Expelled by the Nazi Regime | location = New York | publisher = Arcade Publishing | year = 2012 | type = Paperback | isbn = 978-1-61145-709-4}}
* Rosenthal-Schneider, Ilse ''Reality and Scientific Truth: Discussions with Einstein, von Laue, and Planck'' (Wayne State University, 1980) {{ISBN|0-8143-1650-6}}

== External links ==
{{commons|Max Planck}}
{{wikiquote}}
* {{Gutenberg author |id=35343| name=Max Planck}}
* {{FadedPage|id=Planck, Max|name=Max Planck|author=yes}}
* {{Internet Archive author |sname=Max Planck}}
* {{Librivox author |id=9626}}
* [https://web.archive.org/web/20060828134833/http://alsos.wlu.edu/qsearch.aspx?browse=people%2FPlanck%2C+Max Annotated bibliography for Max Planck] from the Alsos Digital Library for Nuclear Issues
* [https://www.britannica.com/eb/article-9108525/Max-Planck Max Planck] – Encyclopædia Britannica article
* [http://www.nobel-winners.com/Physics/max_karl_ernst_ludwig_planck.html Max Planck Biography] – www.nobel-prize-winners.com
* [http://www.mpg.de/english/ Max Planck Institutes of Natural Science and Astrophysics]
* [https://www.youtube.com/watch?time_continue=175&v=5mwHXBn6mcM Max Planck – Selbstdarstellung im Filmportrait (1942)], [Cinematic self-portrait of Max Planck], Berlin-Brandenburgische Akademie der Wissenschaften, 1942
* {{Nobelprize}} including the Nobel Lecture, 2 June 1920 ''The Genesis and Present State of Development of the Quantum Theory''
* [http://www.max-planck.mpg.de Life–Work–Personality] – Exhibition on the 50th anniversary of Planck's death
* {{PM20|FID=pe/013674}}

{{Copley Medallists 1901-1950}}
{{Nobel Prize in Physics Laureates 1901-1925}}
{{1918 Nobel Prize winners}}
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