Poul Heegaard

{{Short description|Danish mathematician (1871–1948)}}

{{Infobox scientist

|name = Poul Heegaard

|image = 44154 Poul Heegaard.jpg

|image_size = 200px

|caption = Poul Heegaard, ca. 1940

|birth_date = {{birth date|1871|11|2|df=y}}

|birth_place = Copenhagen

|death_date = {{death date and age|1948|2|7|1871|11|2|df=y}}

|death_place = Oslo

|nationality = Danish

|ethnicity =

|fields = Topology

|workplaces = University of Copenhagen, University of Oslo

|alma_mater = University of Copenhagen

|doctoral_advisor =

|thesis_title = Forstudier til en topologisk Teori for de algebraiske Fladers Sammenhæng

|thesis_url = http://www.maths.ed.ac.uk/~aar/papers/heegaardthesis.pdf

|thesis_year = 1898

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Poul Heegaard ({{IPA|da|ˈhe̝ˀˌkɒˀ|lang|Da-heegaard.oga}}; November 2, 1871, Copenhagen - February 7, 1948, Oslo) was a Danish mathematician active in the field of topology. His 1898 thesis introduced a concept now called the Heegaard splitting of a 3-manifold. Heegaard's ideas allowed him to make a careful critique of work of Henri Poincaré. Poincaré had overlooked the possibility of the appearance of torsion in the homology groups of a space.

He later co-authored, with Max Dehn, a foundational article on combinatorial topology, in the form of an encyclopedia entry.{{cite book | last1=Dehn | first1=Max | author1-link=Max Dehn | last2=Heegaard | first2=Poul | chapter=Analysis situs | jfm=38.0510.14 | title=Enzyklop. d. math. Wissensch. | volume=III | number=1 | pages=153–220 | year=1907 }}

Heegaard studied mathematics at the University of Copenhagen from 1889 to 1893. Following years of travelling, and teaching mathematics, he was appointed professor at University of Copenhagen in 1910. An English translation of his 1898 thesis, which laid a rigorous topological foundation for modern knot theory, may be found at https://www.maths.ed.ac.uk/~v1ranick/papers/heegaardenglish.pdf. The section on "a visually transparent representation of the complex points of an algebraic surface" is especially important.

In 1936, Heegaard served as the President of The Third International Congress of Nationalists at The Nobel Institute. Following a talk titled "A Biologist's View of the Future of the White Race," Heegaard hosted a garden party for the Congress participants.{{Cite web |date=1936 |title=Programme of the Congress |url=https://catalog.archives.gov/id/325727778?objectPage=107#object-thumb--107 |website=National Archives |publisher=The Norwegian Committee of the Nationalist Academy for International Justice}}

Following a dispute with the faculty over, among other things, the hiring of Harald Bohr as professor at the University (which Heegaard opposed);{{citation

| last1 = Munkholm | first1 = Ellen S.

| last2 = Munkholm | first2 = Hans J.

| contribution = Poul Heegaard

| doi = 10.1016/B978-044482375-5/50035-3

| mr = 1721129

| pages = 925–946

| publisher = North-Holland, Amsterdam

| title = History of topology

| year = 1999| isbn = 978-0-444-82375-5

}}; see in particular [https://books.google.com/books?id=7iRijkz0rrUC&pg=PA937 pp. 937–938]. Heegaard accepted a professorship at Oslo in Norway, where he worked till his retirement in 1941.