Willem de Sitter

Willem de Sitter (6May 187220November 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

thumb|left|[[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 directly inspired Arthur Eddington's 1919 expedition to make measurements of a solar eclipse. He co-authored a paper with Einstein in 1932, with whom he had a lengthy correspondence, in which they discussed the implications of cosmological data for the curvature of the universe, comparing "space to a cloth". 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. His research helped to launch inquiries into relativistic cosmology.

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:

References

External links

P.C. van der Kruit 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.
Bruce Medal page
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) (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