Main Page | See live article | Alphabetical index Timeline of cosmology 1576 - Thomas Digges modifies the Copernican system by removing its outer edge and replacing the edge with a star-filled unbounded space 1610 - Johannes Kepler uses the dark night sky to argue for a finite universe 1720 - Edmund Halley puts forth an early form of Olbers' paradox 1744 - Jean-Phillipe de Cheseaux puts forth an early form of Olbers' paradox 1826 - Heinrich Olbers puts forth Olbers' paradox 1917 - Willem de Sitter derives an isotropic static cosmology with a cosmological constant as well as an empty expanding cosmology with a cosmological constant, termed a de Sitter universe 1922 - Vesto Slipher summarizes his findings on the spiral nebulae's systematic redshifts 1922 - Alexander Friedmann finds a solution to the Einstein field equations which suggests a general expansion of space 1927 - Georges Lemaître discusses the creation event of an expanding universe governed by the Einstein field equations 1928 - Harold Robertson briefly mentions that Vesto Slipher's redshift measurements combined with brightness measurements of the same galaxies indicate a redshift-distance relation 1929 - Edwin Hubble demonstrates the linear redshift-distance relation and thus shows the expansion of the universe 1933 - Edward Milne names and formalizes the cosmological principle 1934 - Georges Lemaître interprets the cosmological constant as due to a vacuum energy with an unusual perfect fluid equation of state 1938 - Paul Dirac presents a cosmological theory where the gravitational constant decreases slowly so that the age of the universe divided by the atomic light-crossing time always equals the ratio of the electric force to the gravitational force between a proton and electron 1948 - Ralph Alpher, Hans Bethe("in absentia"), and George Gamow examine element synthesis in a rapidly expanding and cooling universe and suggest that the elements were produced by rapid neutron capture 1948 - Hermann Bondi, Thomas Gold, and Fred Hoyle propose steady state cosmologies based on the perfect cosmological principle 1951 - William McCrea shows that the steady state C-field can be accommodated within general relativity by interpreting it as a contribution to the energy-momentum tensor with an unusual equation of state 1961 - Robert Dicke argues that carbon-based life can only arise when the Dirac large numbers hypothesis is true because this is when burning stars exist; first use of the weak anthropic principle 1963 - Fred Hoyle and Jayant Narlikar show that the steady state theory can explain the isotropy of the universe because deviations from isotropy and homogeneity exponentially decay in time 1964 - Fred Hoyle and Roger Tayler point out that the primordial helium abundance depends on the number of neutrinos 1965 - Martin Rees and Dennis Sciama analyze quasar source count data and discover that the quasar density increases with redshift 1965 - Edward Harrison resolves Olbers' paradox by noting the finite lifetime of stars 1966 - Stephen Hawking and George Ellis show that any plausible general relativistic cosmology is singular 1966 - Jim Peebles shows that the hot Big Bang predicts the correct helium abundance 1967 - Andrei Sakharov presents the requirements for a baryon-antibaryon asymmetry in the universe 1967 - John Bahcall, Wal Sargent, and Maarten Schmidt measure the fine-structure splitting of spectral lines in 3C191 and thereby show that the fine-structure constant does not vary significantly with time 1968 - Brandon Carter speculates that perhaps the fundamental constants of nature must lie within a restricted range to allow the emergence of life; first use of the strong anthropic principle 1969 - Charles Misner formally presents the Big Bang horizon problem 1969 - Robert Dicke formally presents the Big Bang flatness problem 1973 - Edward Tryon proposes that the universe may be a large scale quantum mechanical vacuum fluctuation where positive mass-energy is balanced by negative gravitational potential energy 1974 - Robert Wagoner, William Fowler, and Fred Hoyle show that the hot Big Bang predicts the correct deuterium and lithium abundances 1976 - A.I. Shlyakhter uses samarium ratios from the prehistoric natural fission reactor in Gabon to show that some laws of physics have remained unchanged for over two billion years 1977 - Gary Steigman, David Schramm, and James Gunn examine the relation between the primordial helium abundance and number of neutrinos and claim that at most five lepton families can exist 1980 - Alan Guth proposes the inflationaryary Big Bang universe as a possible solution to the horizon and flatness problems 2001 - Evidence that the fine structure constant does vary over the lifetime of the universe becomes conclusive. 2003 - NASA's WMAP takes first detailed "baby picture" of the universe by means of the Cosmic microwave background radiation. The image reveals the universe is 13.7 billion years old (within one percent error) and that the inflationaryary theory is correct. This article is from Wikipedia. All text is available under the terms of the GNU Free Documentation License.