Willem de Sitter (6May 187220November 1934) was a Dutch mathematician, physicist, and astronomer. He is known for the de Sitter universe is a

cosmological model Physical cosmology is a branch of cosmology concerned with the study of cosmological models. A cosmological model, or simply cosmology, provides a description of the largest-scale structures and dynamics of the universe and allows study of fu ...

, which was named after him.

Life and work

Born in

Sneek Sneek (; ) is a List of cities in the Netherlands by province, city southwest of Leeuwarden and the seat of the former municipality of Sneek in the province of Friesland, Netherlands. As of 2011 it is the seat of the municipality of Súdw ...

, Netherlands, de Sitter studied

mathematics Mathematics is a field of study that discovers and organizes methods, Mathematical theory, theories and theorems that are developed and Mathematical proof, proved for the needs of empirical sciences and mathematics itself. There are many ar ...

at the

University of Groningen The University of Groningen (abbreviated as UG; , abbreviated as RUG) is a Public university#Continental Europe, public research university of more than 30,000 students in the city of Groningen (city), Groningen, Netherlands. Founded in 1614, th ...

and then joined the

Groningen Groningen ( , ; ; or ) is the capital city and main municipality of Groningen (province), Groningen province in the Netherlands. Dubbed the "capital of the north", Groningen is the largest place as well as the economic and cultural centre of ...

astronomical Astronomy is a natural science that studies celestial objects and the phenomena that occur in the cosmos. It uses mathematics, physics, and chemistry in order to explain their origin and their overall evolution. Objects of interest include ...

laboratory. He worked at the Cape Observatory in

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...

(1897–1899). Then, in 1908, De Sitter was appointed to the chair of astronomy at

Leiden University Leiden University (abbreviated as ''LEI''; ) is a Public university, public research university in Leiden, Netherlands. Established in 1575 by William the Silent, William, Prince of Orange as a Protestantism, Protestant institution, it holds the d ...

. He was director of the Leiden Observatory from 1919 until his death. De Sitter made major contributions to the field of

physical cosmology Physical cosmology is a branch of cosmology concerned with the study of cosmological models. A cosmological model, or simply cosmology, provides a description of the largest-scale structures and dynamics of the universe and allows study of fu ...

. In 1916-17. he published a series of papers describing the consequences of

Albert Einstein Albert Einstein (14 March 187918 April 1955) was a German-born theoretical physicist who is best known for developing the theory of relativity. Einstein also made important contributions to quantum mechanics. His mass–energy equivalence f ...

theory of relativity The theory of relativity usually encompasses two interrelated physics theories by Albert Einstein: special relativity and general relativity, proposed and published in 1905 and 1915, respectively. Special relativity applies to all physical ph ...

to the understanding of astronomy, which were directly affected

Arthur Eddington Sir Arthur Stanley Eddington, (28 December 1882 – 22 November 1944) was an English astronomer, physicist, and mathematician. He was also a philosopher of science and a populariser of science. The Eddington limit, the natural limit to the lu ...

's 1919 findings in the famous experiment of the

solar eclipse A solar eclipse occurs when the Moon passes between Earth and the Sun, thereby obscuring the view of the Sun from a small part of Earth, totally or partially. Such an alignment occurs approximately every six months, during the eclipse season i ...

. He co-authored a paper with Einstein in 1932 in which they discussed the implications of cosmological data for the curvature of the universe. He also came up with the concept of the De Sitter space and De Sitter universe, a solution for Einstein's

general relativity General relativity, also known as the general theory of relativity, and as Einstein's theory of gravity, is the differential geometry, geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of grav ...

in which there is no matter and a positive

cosmological constant In cosmology, the cosmological constant (usually denoted by the Greek capital letter lambda: ), alternatively called Einstein's cosmological constant, is a coefficient that Albert Einstein initially added to his field equations of general rel ...

. This results in an exponentially expanding, empty universe. De Sitter was also well-known for his research on the motions of the moons of

Jupiter Jupiter is the fifth planet from the Sun and the List of Solar System objects by size, largest in the Solar System. It is a gas giant with a Jupiter mass, mass more than 2.5 times that of all the other planets in the Solar System combined a ...

, and was invited to give the

George Darwin Sir George Howard Darwin (9 July 1845 – 7 December 1912) was an English barrister and astronomer, the second son and fifth child of Charles Darwin and Emma Darwin. He is known for the harmonic analysis of the theory of tides. The Darwin s ...

Lecture at the

Royal Astronomical Society The Royal Astronomical Society (RAS) is a learned society and charitable organisation, charity that encourages and promotes the study of astronomy, planetary science, solar-system science, geophysics and closely related branches of science. Its ...

in 1931. Willem de Sitter died after a brief illness in November 1934.

Honours

In 1912, he became a member of the

Royal Netherlands Academy of Arts and Sciences The Royal Netherlands Academy of Arts and Sciences (, KNAW) is an organization dedicated to the advancement of science and literature in the Netherlands. The academy is housed in the Trippenhuis in Amsterdam. In addition to various advisory a ...

Awards

* James Craig Watson Medal (1929) *

Bruce Medal The Catherine Wolfe Bruce Gold Medal is awarded every year by the Astronomical Society of the Pacific for outstanding lifetime contributions to astronomy. It is named after Catherine Wolfe Bruce, an American patroness of astronomy, and was ...

(1931) *

Gold Medal of the Royal Astronomical Society The Gold Medal of the Royal Astronomical Society is the highest award given by the Royal Astronomical Society (RAS). The RAS Council have "complete freedom as to the grounds on which it is awarded" and it can be awarded for any reason. Past awar ...

(1931) * Prix Jules Janssen, the highest award of the

Société astronomique de France The Société astronomique de France (SAF; ), the France, French astronomical society, is a non-profit association in the public interest organized under French law (Association loi de 1901). Founded by astronomer Camille Flammarion in 1887, its ...

, the French astronomical society (1934)

Named after him

*The crater De Sitter on the Moon *Asteroid 1686 De Sitter * De Sitter universe * De Sitter space *

Anti-de Sitter space In mathematics and physics, ''n''-dimensional anti-de Sitter space (AdS''n'') is a symmetric_space, maximally symmetric Lorentzian manifold with constant negative scalar curvature. Anti-de Sitter space and de Sitter space are na ...

* De Sitter invariant special relativity * Einstein–de Sitter universe * De Sitter double star experiment * De Sitter precession * De Sitter–Schwarzschild metric

Family

One of his sons,

Ulbo de Sitter Lamoraal Ulbo de Sitter (6 March 1902 – 12 May 1980) was a Dutch geologist at Leiden University, where he was the founder of the school of structural geology. De Sitter was known for his research on the geology of the Alps and Pyrenees. Hi ...

(1902 – 1980), was a Dutch geologist, and one of Ulbo's sons was a Dutch sociologist

(1930 – 2010). Another son of Willem, Aernout de Sitter (1905 – 15 September 1944Obituary Notes of Astronomers
at www.astro.uni-bonn.de), was the director of the Bosscha Observatory in

Lembang Lembang is a town and administrative village of West Bandung Regency in the province of Jawa Barat, West Java in Java (island), Java, Indonesia. The town has about 17,000 inhabitants (at census 2010). The population of the Lembang District was 17 ...

Indonesia Indonesia, officially the Republic of Indonesia, is a country in Southeast Asia and Oceania, between the Indian Ocean, Indian and Pacific Ocean, Pacific oceans. Comprising over List of islands of Indonesia, 17,000 islands, including Sumatra, ...

(then the Dutch East Indies), where he studied the Messier 4

globular cluster A globular cluster is a spheroidal conglomeration of stars that is bound together by gravity, with a higher concentration of stars towards its center. It can contain anywhere from tens of thousands to many millions of member stars, all orbiting ...

Selected publications

* * ** * * * On Einstein's theory of gravitation and its astronomical consequences: *# *# *#

References

External links

* * P.C. van der Krui
''Willem de Sitter (18721934)''
in: History of science and scholarship in the Netherlands. * A. Blaauw
''Sitter, Willem de (1872–1934)''
in Biografisch Woordenboek van Nederland.

(four articles)

Obituaries

(one line)

(one paragraph)

{{DEFAULTSORT:Sitter, Willem De 1872 births 1934 deaths 19th-century Dutch astronomers 19th-century Dutch mathematicians 20th-century Dutch astronomers Dutch relativity theorists 20th-century Dutch mathematicians Cosmologists People from Sneek Academic staff of Leiden University University of Groningen alumni Members of the Royal Netherlands Academy of Arts and Sciences Foreign associates of the National Academy of Sciences Recipients of the Gold Medal of the Royal Astronomical Society Presidents of the International Astronomical Union