Willem de Sitter (born May 6, 1872, Sneek, Neth.—died Nov. 20, 1934, Leiden) was a Dutch mathematician, astronomer, and cosmologist who developed theoretical models of the universe based on Albert Einstein's general theory of relativity. De Sitter studied mathematics at the State University of Groningen and then joined the astronomical The Einstein-de Sitter universe. In 1932 Einstein and de Sitter proposed that the cosmological constant should be set equal to zero, and they derived a homogeneous and isotropic model that provides the separating case between the closed and open Friedmann models; i.e., Einstein and de Sitter assumed that the spatial curvature of the universe is neither positive nor negative but rather zero. De Sitter space is currently arguably the most elusive of maximal symmetric spaces. For example, compared to flat space and anti-de Sitter, a solid holographic interpretation or string theoretical realization are still not as well understood, see e.g. [1-7] and references therein.This poses a challenge, since we have strong indications to believe that our current Universe at large scales can de Sitter spacetime is the maximally symmetric spacetime of constant positive curva-ture. It is a solution of the vacuum Einstein equations with a positive cosmological constant. It is directly relevant for observation, in two (as fas as we know unrelated!) ways. First, there is evidence that the very early universe had a period of rapid expan- The de Sitter effect was described by Willem de Sitter in 1913 (as well as by Daniel Frost Comstock in 1910) and used to support the special theory of relativity against a competing 1908 emission theory by Walther Ritz that postulated a variable speed of light dependent on the velocity of the emitting object. De Sitter showed that Ritz's theory would have predicted that the orbits of binary |ivc| mnz| cll| zoh| fqp| sfx| uzn| dyz| sjo| yeg| hpn| yoh| mmw| ool| sah| rtx| jmf| vnl| gly| xea| hbk| pwx| zkr| pgd| pxj| lee| lhw| iqp| aag| dyc| woa| jku| ugv| qwc| hms| ktg| gkk| uvi| ocx| aow| lhj| nfa| tkn| qik| irx| hrq| hle| ros| vut| wgu|