Timeline of cosmology

This timeline of cosmological theories and discoveries is a chronological record of the development of humanity's understanding of the cosmos over the last two-plus millennia. Modern cosmological ideas follow the development of the scientific discipline of physical cosmology.

Pre-1900

ca. 16th century BC — In Babylonian cosmology, particularly that depicted in the Enûma Eliš, the Earth and heavens were seen as a "spatial whole, even one of round shape," revolving around the "cult-place of the deity" rather than the Earth,[1] and it was believed that there is a plurality of heavens and earths.[2]
ca. 12th century BC — The Rigveda has some cosmological hymns, particularly in the late book 10, notably the Nasadiya Sukta which describes the origin of the universe, originating from the monistic Hiranyagarbha or "Golden Egg".
6th century BC — The Babylonian world map shows Babylon on the Euphrates, surrounded by a circular landmass showing Assyria, Armenia and several cities, in turn surrounded by a "bitter river" (Oceanus), with seven islands arranged around it so as to form a seven-pointed star. Contemporary Biblical cosmology of the Tanakh reflects the same view of the Earth as a plain or a hill figured like a hemisphere, swimming on water and overarched by the solid vault of the firmament. To this vault are fastened the stars.
4th century BC — Aristotle proposes an Earth-centered universe in which the Earth is stationary and the universe is finite in extent but infinite in time
3rd century BC — Aristarchus of Samos proposes a Sun-centered universe
2nd century BC — Seleucus of Seleucia elaborates on Aristarchus' heliocentric universe, using the phenomenon of tides to explain heliocentrism
2nd century AD — Ptolemy proposes an Earth-centered universe, with the Sun and planets revolving around the Earth
5th-11th centuries — Several astronomers propose a Sun-centered universe, including Aryabhata, Albumasar and Al-Sijzi
6th century — John Philoponus proposes a universe that is finite in time and argues against the ancient Greek notion of an infinite universe
ca. 8th century — Puranic Hindu cosmology, in which the Universe goes through repeated cycles of creation, destruction and rebirth, with each cycle lasting 4.32 billion years.
9th-12th centuries — Al-Kindi (Alkindus), Saadia Gaon (Saadia ben Joseph) and the Al-Ghazali (Algazel) support a universe that has a finite past and develop two logical arguments against the notion of an infinite past, one of which is later adopted by Immanuel Kant
964 — Abd al-Rahman al-Sufi (Azophi), a Persian astronomer, makes the first recorded observations of the Andromeda Galaxy and the Large Magellanic Cloud, the first galaxies other than the Milky Way to be observed from Earth, in his Book of Fixed Stars
12th century — Fakhr al-Din al-Razi discusses Islamic cosmology, rejects Aristotle's idea of an Earth-centered universe, and, in the context of his commentary on the Qur'anic verse, "All praise belongs to God, Lord of the Worlds," proposes that the universe has more than "a thousand thousand worlds beyond this world such that each one of those worlds be bigger and more massive than this world as well as having the like of what this world has."[3] He argued that there exists an infinite outer space beyond the known world,[4] and that there could be an infinite number of universes.[5]
13th century — Nasīr al-Dīn al-Tūsī provides the first empirical evidence for the Earth's rotation on its axis
15th century — Ali Qushji provides empirical evidence for the Earth's rotation on its axis and rejects the stationary Earth theories of Aristotle and Ptolemy
15th-16th centuries — Nilakantha Somayaji and Tycho Brahe propose a universe in which the planets orbit the Sun and the Sun orbits the Earth, known as the Tychonic system
1543 — Nicolaus Copernicus publishes his heliocentric universe in his De revolutionibus orbium coelestium
1576 — Thomas Digges modifies the Copernican system by removing its outer edge and replacing the edge with a star-filled unbounded space
1584 — Giordano Bruno proposes a non-hierarchical cosmology, wherein the Copernican solar system is not the center of the universe, but rather, a relatively insignificant star system, amongst an infinite multitude of others
1610 — Johannes Kepler uses the dark night sky to argue for a finite universe
1687 — Sir Isaac Newton's laws describe large-scale motion throughout the universe
1720 — Edmund Halley puts forth an early form of Olbers' paradox
1744 — Jean-Philippe de Cheseaux puts forth an early form of Olbers' paradox
1791 — Erasmus Darwin pens the first description of a cyclical expanding and contracting universe in his poem The Economy of Vegetation
1826 — Heinrich Wilhelm Olbers puts forth Olbers' paradox
1848 — Edgar Allan Poe offers first correct solution to Olbers' paradox in Eureka: A Prose Poem, an essay that also suggests the expansion and collapse of the universe

1900–1949

1905 — Albert Einstein publishes the Special Theory of Relativity, positing that space and time are not separate continua
1915 — Albert Einstein publishes the General Theory of Relativity, showing that an energy density warps spacetime
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
1920 — The Shapley-Curtis Debate takes place at the Smithsonian
1921 — The National Research Counsil(NRC) published the official transcript of the Shapley-Curtis Debate
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
1924 — Edwin Hubble discovers that the universe is composed of thousands of galaxies.
1927 — Georges Lemaître discusses the creation event of an expanding universe governed by the Einstein field equations. From its solutions to the Einstein equations, he predicts the distance-redshift relation.
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
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 suggests the large numbers hypothesis, that the gravitational constant may be small because it is decreasing slowly with time
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
1948 — George Gamow predicts the existence of the cosmic microwave background radiation by considering the behavior of primordial radiation in an expanding universe

1950–1999

1950 — Fred Hoyle derisively coins the term "Big Bang".
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
1965 — Hannes Alfvén proposes the now-discounted concept of ambiplasma to explain baryon asymmetry.
1965 — Martin Rees and Dennis Sciama analyze quasar source count data and discover that the quasar density increases with redshift.
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.
1966 — Stephen Hawking and George Ellis show that any plausible general relativistic cosmology is singular
1966 — James Peebles shows that the hot Big Bang predicts the correct helium abundance
1967 — Andrei Sakharov presents the requirements for baryogenesis, 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 — 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
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.
1981 — Viacheslav Mukhanov and G. Chibisov propose that quantum fluctuations could lead to large scale structure in an inflationary universe
1981 — Alan Guth proposes the inflationary Big Bang universe as a possible solution to the horizon and flatness problems
1990 — Preliminary results from NASA's COBE mission confirm the cosmic microwave background radiation is an isotropic blackbody to an astonishing one part in 105 precision, thus eliminating the possibility of an integrated starlight model proposed for the background by steady state enthusiasts.
1990s — Ground based cosmic microwave background experiments measure the first peak, determine that the universe is geometrically flat.
1998 — Controversial evidence for the fine structure constant varying over the lifetime of the universe is first published.
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.
1999 — Measurements of the cosmic microwave background radiation (most notably by the BOOMERanG experiment see Mauskopf et al., 1999, Melchiorri et al., 1999, de Bernardis et al. 2000) provide evidence for oscillations (peaks) in the anisotropy angular spectrum as expected in the standard model of cosmological structure formation. These results indicates that the geometry of the universe is flat. Together with large scale structure data, this provides complementary evidence for a non-zero cosmological constant.

Since 2000

2002 — The Cosmic Background Imager (CBI) in Chile obtained images of the cosmic microwave background radiation with the highest angular resolution of 4 arc minutes. It also obtained the anisotropy spectrum at high-resolution not covered before up to l ~ 3000. It found a slight excess in power at high-resolution (l > 2500) not yet completely explained, the so-called "CBI-excess".
2003 — NASA's WMAP obtained full-sky detailed pictures of the cosmic microwave background radiation. 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.
2003 — The Sloan Great Wall is discovered.
2004 — The Degree Angular Scale Interferometer (DASI) first obtained the E-mode polarization spectrum of the cosmic microwave background radiation.
2006 — The long-awaited three-year WMAP results are released, confirming previous analysis, correcting several points, and including polarization data.