Einstein, Ehrenfest, Willem de Sitter, Eddington, and Lorentz in Leiden (1923)
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 well-known for his research on the motions of the moons of Jupiter, 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.
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