# Willem de Sitter

(Redirected from De Sitter)
Willem de Sitter
Born 6 May 1872
Sneek
Died 20 November 1934 (aged 62)
Leiden
Nationality Dutch
Fields Physics
Alma mater Groningen University
Known for De Sitter Universe
Signature

Willem de Sitter (6 May 1872 – 20 November 1934) was a Dutch mathematician, physicist, and astronomer.

## Life and work

Born in Sneek, 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. He co-authored a paper with Albert 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 famous for his research on the planet Jupiter.

Willem de Sitter died after a brief illness in November 1934.[1][2][3]

## Honours

In 1912 he became a member of the Royal Netherlands Academy of Arts and Sciences.[4]

## Family

One of his sons, Ulbo de Sitter (1902 – 1980), was a Dutch geologist, and one of his sons was a Dutch sociologist Ulbo de Sitter (1930 – 2010).

Another son of Willem, Aernout de Sitter (1905 – 15 September 1944[5]), 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

Einstein, Ehrenfest, Willem de Sitter, Eddington, and Lorentz in Leiden (1923)
• On Einstein's theory of gravitation and its astronomical consequences, Monthly Notices of the Royal Astronomical Society 76 (1916) 699-728; 77 (1916) 155-184; 78 (1917) 3-28