Willem de Sitter
Willem de Sitter ( born May 6, 1872 in Sneek, † November 20, 1934 in Leiden ) was a Dutch astronomer.
Life
Sitter studied mathematics at the University of Groningen. By Jacobus Kapteyn his interest in astronomy was aroused. From 1908 he was professor of astronomy at the University of Leiden and served 1925/26, as rector of the University of Leiden.
In 1913 he published a series of articles in which he showed that the speed of light is independent of the speed of the light source. This confirms the theory of special relativity, and showed that the emission theory of light.
Sitters experience in celestial mechanics proved 1916/17 as useful as he described the astronomical consequences of Einstein's general theory of relativity in a series of articles. This work aroused in the UK interested in this theory, at a time when the cultural and scientific relations of England were to Germany severely restricted by the First World War, and led directly to the expedition of Arthur Stanley Eddington in 1919. Between 1919 and 1934, he director of the observatory in Leiden.
He used acquaintances, inter alia, to Albert Einstein. On the basis of the theory of relativity in 1917, he described the first time an expanding universe ( de Sitter space ). At that time the de Sitter model, however, was not seen as a dynamic ( expanding ) model of the universe, but as a stationary solution (there are several representations depending on the choice of coordinates ). The " counterpart " to this, the anti - de Sitter space, won in the 1990s meaning in string theory. The de Sitter model was considered the model of a stationary universe and was until the early 1930s, in addition to the stationary model of Einstein the dominant cosmological model. In contrast to the Einstein model, it said a Rotverschiebungseffekt advance. Today it is seen as a special case of ( dynamic ) Friedmann solutions with vanishing cosmological constant and matter.
In 1932 he published the so-called Einstein - de Sitter model, a flat universe with no cosmological Term Both were at the time in California. The work stood for the distancing of both Einstein and by de Sitter of the cosmological constant, which was with the realization of a dynamic, expanding universe then no longer necessary.
1925 to 1928 he was President of the International Astronomical Union. In 1931 he was awarded the Gold Medal of the Royal Astronomical Society and in 1934 with the Jules Janssen Award.