Willem de Sitter

Template:Short description Template:Family name hatnote Template:Dutch name capitalization Willem de Sitter (6May 1872Template:Snd20November 1934) was a Dutch mathematician, physicist, and astronomer. He is known for the de Sitter universe, which is a cosmological model that was named after him.

Life and work

File:PhysicistsinLeiden.jpg

Albert Einstein, Paul Ehrenfest, Willem de Sitter, Arthur Eddington, and Hendrik Lorentz in Leiden (1923)

Born in Sneek, Netherlands, de Sitter studied mathematics at the University of Groningen and then joined the Groningen astronomical laboratory. He worked at the Cape Observatory in South Africa (1897–1899). Then, in 1908, De Sitter was appointed to the chair of astronomy at Leiden University. He was director of the Leiden Observatory from 1919 until his death.

De Sitter made major contributions to the field of physical cosmology. In 1916-17, he published a series of papers describing the consequences of Albert Einstein's theory of relativity to the understanding of astronomy, which were directly affected Arthur Eddington's 1919 findings in the famous experiment of the solar eclipse. 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 in which there is no matter and a positive cosmological constant. 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, and was invited to give the George Darwin Lecture at the Royal Astronomical Society 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.

Awards

• James Craig Watson Medal (1929)
• Bruce Medal (1931)
• Gold Medal of the Royal Astronomical Society (1931)
• Prix Jules Janssen, the highest award of the Société astronomique de France, 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
• 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 (1902 – 1980), was a Dutch geologist, and one of Ulbo's sons was a Dutch sociologist Ulbo de Sitter (1930 – 2010).

Another son of Willem, Aernout de Sitter (1905 – 15 September 1944), was the director of the Bosscha Observatory in Lembang, Indonesia (then the Dutch East Indies), where he studied the Messier 4 globular cluster.

Selected publications

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

See also

• De Sitter double star experiment
• De Sitter precession
• De Sitter invariant special relativity
• De Sitter space
• De Sitter universe
• Anti-de Sitter space
• The Dreams in the Witch House

External links

• P.C. van der Kruit Willem de Sitter (1872Template:Snd1934) in: History of science and scholarship in the Netherlands.
• A. Blaauw, Sitter, Willem de (1872–1934), in Biografisch Woordenboek van Nederland.
• Bruce Medal page Template:Webarchive
• Awarding of Bruce Medal: PASP 43 (1931) 125
• Awarding of RAS gold medal: MNRAS 91 (1931) 422
• de Sitter's binary star arguments against Ritz's relativity theory (1913) Template:Webarchive (four articles)

Obituaries

• AN 253 (1934) 495/496 (one line)
• JRASC 29 (1935) 1
• MNRAS 95 (1935) 343
• Obs 58 (1935) 22
• PASP 46 (1934) 368 (one paragraph)
• PASP 47 (1935) 65