WILLEM DE SITTER

Willem De Sitter 1872-1934

Willem de Sitter, the son of a Dutch judge, president of the court in Arnhem in the Netherlands.
In this city there his first year of study. It was late in registering at the University of Groningen, in mathematical physics to study for a doctorate, he will be on the moons of Jupiter.
From 1897 to 1899, he worked at the Royal Observatory in Cape Town, South Africa, with David Gill. Then he returned to Groningen Kapteyn where he worked with until 1908. On December 6, 1898 wife Eleonora de Sitter Suermondt in Cape Town, South Africa. Eleonora was born in Surabaya in the Dutch East Indies and works as a teacher.
In 1908 he was appointed professor at Leiden University and from 1919 until his death, he will be director of the Leiden Observatory.
In 1913 he produced an argument based on the observation of double star systems showing that the speed of light is independent of the speed of the source. It was one of the first physicists to be interested in Einstein's general relativity, he understands better than anyone the cosmological implications.
In 1919, De Sitter works directly with Arthur Eddington in preparation for the expedition is to measure the gravitational deflection of light rays passing near the Sun during a total eclipse.
De Sitter, unlike Einstein, argues that relativity implies that the Universe is expanding. Only later, Einstein accepted the idea. In fact, Einstein introduced the cosmological constant in 1917 to answer the embarrassing question "why the universe does not collapse under the pull of gravity."

This rather arbitrary constant introduced by Einstein, was not necessary.
Einstein later said, "It's the biggest mistake of my life." But de Sitter tried to spread the theory in the scientific community, primarily through the publication of three articles on "gravitation theory of Einstein and its astronomical consequences," published in 1916 and 1917. This is the third article he introduced what would become "the de Sitter universe." According to W. De Sitter, general relativity can be used to show that the universe is expanding.
Einstein predicted, however, a static universe. Following the interpretation given by Edwin Powell Hubble spectra of distant galaxies, Einstein is on the side of Willem de Sitter. Subsequent work by De Sitter, together with those of Lemaître, Eddington and Gamow gave birth to modern cosmology.
One of the important works of de Sitter, is the publication of an article he wrote with Albert Einstein in 1932, in which scientists propose that there should be in the universe a lot of material that did not emit light. This matter is referred to today, dark matter and dark matter.
De Sitter is also famous for his work on the planet Jupiter. Sitter Crater on the Moon and the asteroid (1686) De Sitter bear his name. Willem de Sitter died of pneumonia at age 62 in 1934.

Image: Willem de Sitter was president of the International Astronomical Union from 1925 to 1928. His work gave rise to modern cosmology.