**Timeline of universe cosmology** lists the sequence of cosmological theories and discoveries in chronological order. The most modern developments follow the scientific development of the discipline of Physical cosmology.

**Timeline of universe cosmology: Pre-1900.**

**Timeline of universe cosmology: Timeline of universe cosmology: 3rd century BC**- Aristarchus of Samos proposes a Sun-centered Universe.**Timeline of universe cosmology: Timeline of universe cosmology: 2nd century**- Ptolemy proposes an Earth-centred Universe, with the Sun and planets revolving around the Earth.**Timeline of universe cosmology: c500 onwards**- Several astronomers propose a Sun-centered universe, including Aryabhata, Bhaskara I, Ibn al-Shatir, and Copernicus.**Timeline of universe cosmology: 1576**- Thomas Digges modifies the Copernican system by removing its outer edge and replacing the edge with a star-filled unbounded space.**Timeline of universe cosmology: 1610**- Johannes Kepler uses the dark night sky to argue for a finite universe.**Timeline of universe cosmology: 1687**- Sir Isaac Newton's laws describe large-scale motion throughout the universe.**Timeline of universe cosmology: 1720**- Edmund Halley puts forth an early form of Olbers' paradox.**Timeline of universe cosmology: 1744**- Jean-Philippe de Cheseaux puts forth an early form of Olbers' paradox.**Timeline of universe cosmology: 1791**- Erasmus Darwin pens the first description of a cyclical expanding and contracting universe.**Timeline of universe cosmology: 1826**- Heinrich Wilhelm Olbers puts forth Olbers' paradox.**Timeline of universe cosmology: 1848**- Edgar Allan Poe offers first correct solution to Olbers' paradox in an essay that also suggests the expansion and collapse of the universe.

**Timeline of universe cosmology: 1900-1949.**

**Timeline of universe cosmology: 1905**- Albert Einstein publishes the special theory of relativity, positing that space and time are not separate continuums.**Timeline of universe cosmology: 1915**- Albert Einstein publishes the General Theory of Relativity, showing that an energy density warps Spacetime.**Timeline of universe cosmology: 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.**Timeline of universe cosmology: 1922**- Vesto Slipher summarizes his findings on the spiral nebulae's systematic redshifts.**Timeline of universe cosmology: 1922**- Alexander Friedmann finds a solution to the Einstein field equations which suggests a general expansion of space.**Timeline of universe cosmology: 1927**- Georges Lemaître discusses the creation event of an expanding universe governed by the Einstein field equations.**Timeline of universe cosmology: 1928**- Howard Percy Robertson briefly mentions that Vesto Slipher's redshift measurements combined with brightness measurements of the same galaxies indicate a redshift-distance relation.**Timeline of universe cosmology: 1929**- Edwin Hubble demonstrates the linear redshift-distance relation and thus shows the expansion of the universe.**Timeline of universe cosmology: 1933**- Edward Milne names and formalizes the cosmological principle.**Timeline of universe cosmology: 1934**- Georges Lemaître interprets the cosmological constant as due to a Vacuum energy with an unusual perfect fluid Equation of state.**Timeline of universe cosmology: 1938**- Paul Dirac suggests the large numbers hypothesis, that the gravitational constant may be small because it is decreasing slowly with time.**Timeline of universe cosmology: 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.**Timeline of universe cosmology: 1948**- Hermann Bondi, Thomas Gold, and Fred Hoyle propose steady state cosmologies based on the perfect cosmological principle.**Timeline of universe cosmology: 1948**- George Gamow predicts the existence of the cosmic microwave background radiation by considering the behavior of primordial radiation in an expanding universe.

**Timeline of cosmology: 1950 to 1999.**

**Timeline of universe cosmology: 1950**- Oskar Klein proposes a*meta-galaxy*model, a first indication of the Alfvén-Klein model.**Timeline of universe cosmology: 1950**- Fred Hoyle derisively coins the term "Big Bang".**Timeline of universe cosmology: 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.**Timeline of universe cosmology: 1961**- Robert Dicke argues that carbon-based life can only arise when the gravitational force is small, because this is when burning stars exist; first use of the weak anthropic principle.**Timeline of universe cosmology: 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 decay exponentially in time.**Timeline of universe cosmology: 1964**- Fred Hoyle and Roger Tayler point out that the primordial helium abundance depends on the number of neutrinos.**Timeline of universe cosmology: 1965**- Hannes Alfvén proposes the now-discounted concept of ambiplasma to explain baryon asymmetry.**Timeline of universe cosmology: 1965**- Martin Rees and Dennis Sciama analyze quasar source count data and discover that the quasar density increases with redshift.**Timeline of universe cosmology: 1965**- Arno Penzias and Robert Wilson, astronomers at Bell labs discover the 2.7 K*microwave background radiation*, which earns them the 1978 Nobel Prize in Physics. Robert Dicke, James Peebles, Peter Roll and David Todd Wilkinson interpret it as relic from the big bang.**Timeline of universe cosmology: 1966**- Stephen Hawking and George Ellis show that any plausible general relativistic cosmology is singular.**Timeline of universe cosmology: 1966**- James Peebles shows that the hot Big Bang predicts the correct helium abundance.**Timeline of universe cosmology: 1967**- Andrei Sakharov presents the requirements for baryogenesis, a baryon-antibaryon asymmetry in the universe.**Timeline of universe cosmology: 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.**Timeline of universe cosmology: 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.**Timeline of universe cosmology: 1969**- Charles Misner formally presents the Big Bang horizon problem.- 1969 - Robert Dicke formally presents the Big Bang flatness problem.
**Timeline of universe cosmology: 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.**Timeline of universe cosmology: 1974**- Robert Wagoner, William Fowler, and Fred Hoyle show that the hot Big Bang predicts the correct deuterium and lithium abundances.**Timeline of universe cosmology: 1976**- Alex Shlyakhter uses samarium ratios from the Oklo prehistoric natural nuclear fission reactor in Gabon to show that some laws of physics have remained unchanged for over two billion years.**Timeline of universe cosmology: 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.**Timeline of universe cosmology: 1981**- Viacheslav Mukhanov and G. Chibisov propose that quantum fluctuations could lead to large scale structure in an inflationary universe.**Timeline of universe cosmology: 1981**- Alan Guth proposes the inflationary Big Bang universe as a possible solution to the horizon and flatness problems.**Timeline of universe cosmology: 1990**- Preliminary results from NASA's COBE mission confirm the cosmic microwave background radiation is an isotropic blackbody to an astonishing one part in 10^{5}precision, thus eliminating the possibility of an integrated starlight model proposed for the background by steady state enthusiasts.**Timeline of universe cosmology: 1990s**- Ground based cosmic microwave background experiments measure the first peak, determine that the universe is geometrically flat.**Timeline of universe cosmology: 1998**- Controversial evidence for the fine structure constant varying over the lifetime of the universe is first published.**Timeline of universe cosmology: 1998**- Adam Riess, Saul Perlmutter and others discover the cosmic acceleration in observations of Type Ia supernovae providing the first evidence for a non-zero cosmological constant. This is confirmed by measurements of the cosmic microwave background radiation by the BOOMERanG experiment.

**Timeline of cosmology: Since 2000.**

**Timeline of universe cosmology: 2003**- NASA's WMAP takes more detailed pictures of the cosmic microwave background radiation than were obtained by the BOOMERanG experiment. The image can be interpreted to indicate that the universe is 13.7 billion years old (within one percent error) and confirm that the Lambda-CDM model and the inflationary theory are correct.

**Timeline of universe cosmology: 2006**- The long-awaited three-year WMAP results are released, confirming previous analysis, correcting several points, and including polarization data.

**Reference to the Timeline of cosmology.**

- Bunch, Bryan, and Alexander Hellemans, "
*The History of Science and Technology: A Browser's Guide to the Great Discoveries, Inventions, and the People Who Made Them from the Dawn of Time to Today*". ISBN 0-618-22123-9.

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