Editing Max Born (section)

===Berlin and Frankfurt===
Born settled in as a young academic at Göttingen as a {{lang|de|[[Privatdozent]]}}. In Göttingen, Born stayed at a [[boarding house]] run by Sister Annie at Dahlmannstraße 17, known as El BoKaReBo.  The name was derived from the first letters of the last names of its boarders: "El" for Ella Philipson (a medical student), "Bo" for Born and Hans Bolza (a physics student), "Ka" for [[Theodore von Kármán]] (a {{lang|de|Privatdozent}}), and "Re" for Albrecht Renner (another medical student). A frequent visitor to the boarding house was [[Paul Peter Ewald]], a doctoral student of [[Arnold Sommerfeld]] on loan to Hilbert at Göttingen as a special assistant for physics. [[Richard Courant]], a mathematician and {{lang|de|Privatdozent}}, called these people the "in group".{{sfn|Greenspan|2005|pp=49–55}}

In 1912, Born met Hedwig (Hedi) Ehrenberg, the daughter of a [[Leipzig University]] law professor, and a friend of Carl Runge's daughter [[Iris Runge|Iris]]. She was of Jewish background on her father's side, although he had become a practising [[Lutheran]] when he got married, as did Max's sister Käthe. Despite never practising his religion, Born refused to convert, and his wedding on 2 August 1913 was a garden ceremony. However, he was baptised as a Lutheran in March 1914 by the same pastor who had performed his wedding ceremony. Born regarded "religious professions and churches as a matter of no importance".{{sfn|Greenspan|2005|pp=61–62}} His decision to be baptised was made partly in deference to his wife, and partly due to his desire to assimilate into German society.{{sfn|Greenspan|2005|pp=61–62}} The marriage produced three children: two daughters, Irene, born in 1914, and Margarethe (Gritli), born in 1915, and a son, [[Gustav Victor Rudolf Born|Gustav]], born in 1921.{{sfn|Born|2002|p=225}} Through marriage, Born is related to jurists [[Victor Ehrenberg (jurist)|Victor Ehrenberg]], his father-in-law, and [[Rudolf von Jhering]], his wife's maternal grandfather, as well as to philosopher and theologian [[Hans Ehrenberg]], and is a great uncle of British comedian [[Ben Elton]].{{sfn|Born|2002|pp=238–241}}

By the end of 1913, Born had published 27 papers, including important work on relativity and the dynamics of crystal lattices (3 with [[Theodore von Karman]]),{{sfn|Greenspan|2005|pp=56–62}} which became a book.{{sfn|Kemmer|Schlapp|1971|p=20}} In 1914, he received a letter from [[Max Planck]] explaining that a new [[professor extraordinarius]] chair of [[theoretical physics]] had been created at the [[University of Berlin]]. The chair had been offered to [[Max von Laue]], but he had turned it down. Born accepted.{{sfn|Greenspan|2005|pp=63–67}} The [[First World War]] was now raging. Soon after  arriving in Berlin in 1915, he enlisted in an Army signals unit. In October, he joined the [[Artillerie Prüfungskommission]], the Army's Berlin-based artillery research and development organisation, under [[Rudolf Ladenburg]], who had established a special unit dedicated to the new technology of [[sound ranging]]. In Berlin, Born formed a lifelong friendship with Einstein, who became a frequent visitor to Born's home.{{sfn|Greenspan|2005|pp=70–75}} Within days of [[Armistice with Germany|the armistice]] in November 1918, Planck had the Army release Born. A chance meeting with [[Fritz Haber]] that month led to discussion of the manner in which an [[ionic compound]] is formed when a [[metal]] reacts with a [[halogen]], which is today known as the [[Born–Haber cycle]].{{sfn|Greenspan|2005|pp=83–86}}

Even before Born had taken up the chair in Berlin, von Laue had changed his mind, and decided that he wanted it after all.{{sfn|Greenspan|2005|pp=63–67}}  He arranged with Born and the faculties concerned for them to exchange jobs. In April 1919, Born became [[professor ordinarius]] and Director of the Institute of Theoretical Physics on the science faculty at the [[University of Frankfurt am Main]].{{sfn|Kemmer|Schlapp|1971|p=20}} While there, he was approached by the University of Göttingen, which was looking for a replacement for [[Peter Debye]] as Director of the Physical Institute.{{sfn|Kemmer|Schlapp|1971|p=21}} "Theoretical physics," Einstein advised him, "will flourish wherever ''you'' happen to be; there is no other Born to be found in Germany today."{{sfn|Greenspan|2005|p=96}}  In negotiating for the position with the education ministry, Born arranged for another chair, of experimental physics, at Göttingen for his long-time friend and colleague [[James Franck]].{{sfn|Kemmer|Schlapp|1971|p=21}}

In 1919 [[Elisabeth Bormann]] joined the Institut für Theoretische Physik as his assistant.<ref>{{Cite book |title=Biografien bedeutender österreichischer Wissenschafterinnen: "Die Neugier treibt mich, Fragen zu stellen"|date=2018|first1=Ilse Erika |last1=Korotin |first2=Nastasja |last2=Stupnicki|isbn=978-3-205-20238-7|location=Wien |publisher=Böhlau Verlag |oclc=1038390215}}</ref> She developed the first atomic beams. Working with Born, Bormann was the first to measure the [[Mean free path|free path]] of atoms in gases and the size of molecules.<ref>{{cite web|title=Goethe-Universität — "Historic Site" Plaque for Frankfurt Physics|url=https://www.goethe-university-frankfurt.de/81694072/Historic_Site__Plaque_for_Frankfurt_Physics|access-date=2021-08-03|website=www.goethe-university-frankfurt.de}}</ref><ref>{{Cite journal|last=Toennies|first=J. Peter|title=Serendipitous Meanderings and Adventures with Molecular Beams|date=June 2004|url=http://www.annualreviews.org/doi/10.1146/annurev.physchem.55.081203.151413|journal=Annual Review of Physical Chemistry|language=en|volume=55|issue=1|pages=1–33|doi=10.1146/annurev.physchem.55.081203.151413|pmid=15117245|bibcode=2004ARPC...55....1T|issn=0066-426X|access-date=4 August 2021|archive-date=3 August 2021|archive-url=https://web.archive.org/web/20210803205238/https://www.annualreviews.org/doi/10.1146/annurev.physchem.55.081203.151413}}</ref>