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 BCE — Mesopotamian cosmology
has a flat, circular Earth enclosed in a cosmic
ocean.
ca. 12th century BCE — 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 BCE — The Babylonian world map
shows the Earth surrounded by the cosmic ocean,
with seven islands arranged around it so as
to form a seven-pointed star.
Contemporary Biblical cosmology reflects the
same view of a flat, circular Earth swimming
on water and overarched by the solid vault
of the firmament to which are fastened the
stars.
4th century BCE — Aristotle proposes an
Earth-centered universe in which the Earth
is stationary and the cosmos (or universe)
is finite in extent but infinite in time
4th century BCE — De Mundo - Five elements,
situated in spheres in five regions, the less
being in each case surrounded by the greater
— namely, earth surrounded by water, water
by air, air by fire, and fire by ether — make
up the whole Universe.
3rd century BCE — Aristarchus of Samos proposes
a Sun-centered universe
3rd century BCE — Archimedes in his essay
The Sand Reckoner, estimates the diameter
of the cosmos to be the equivalent in stadia
of what we call two light years
2nd century BCE — Seleucus of Seleucia elaborates
on Aristarchus' heliocentric universe, using
the phenomenon of tides to explain heliocentrism
2nd century CE — Ptolemy proposes an Earth-centered
universe, with the Sun, moon, and visible
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
Revealed in the 6th century, the Qur'an mentions
Chapter 21: Verse 30 - "Have those who disbelieved
not considered that the heavens and the earth
were a joined entity, and We separated them
... "
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 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."
He argued that there exists an infinite outer
space beyond the known world, and that there
could be an infinite number of universes.
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
1729 - James Bradley discovers the aberration
of light, due to the Earth's motion around
the Sun.
1744 — Jean-Philippe de Cheseaux puts forth
an early form of Olbers' paradox
1755 — Immanuel Kant asserts that the nebulae
are really galaxies separate from, independent
of, and outside the Milky Way Galaxy; he calls
them island universes.
1785 — William Herschel proposes the theory
that our Sun is at or near the center of the
galaxy.
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
1837 - Following over 100 years of unsuccessful
attempts, Friedrich Bessel, Thomas Henderson
and Otto Struve measure the parallax of a
few nearby stars; this is the first measurement
of any distances outside the solar system.
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
1860s - William Huggins develops astronomical
spectroscopy; he shows that the Orion nebula
is mostly made of gas, while the Andromeda
nebula (later called Andromeda galaxy) is
probably dominated by stars.
== 1900–1949 ==
1905 — Albert Einstein publishes the Special
Theory of Relativity, positing that space
and time are not separate continua
1912 - Henrietta Leavitt discovers the period-luminosity
law for Cepheid variable stars, which becomes
a crucial step in measuring distances to other
galaxies.
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, on the
distances to spiral nebulae, takes place at
the Smithsonian
1921 — The National Research Council (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
1923 — Edwin Hubble measures distances to
a few nearby spiral nebulae (galaxies), the
Andromeda Galaxy (M31), Triangulum Galaxy
(M33), and NGC 6822.
The distances place them far outside our Milky
Way, and implies that fainter galaxies are
much more distant, and the universe is composed
of many 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 P. 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
1933 — Fritz Zwicky shows that the Coma
cluster of galaxies contains large amounts
of dark matter.
This result agrees with modern measurements,
but is generally ignored until the 1970s.
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 coins the term "Big Bang",
saying that it was not derisive; it was just
a striking image meant to highlight the difference
between that and the Steady-State model.
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
1963 - Maarten Schmidt discovers the first
quasar; these soon provide a probe of the
universe back to substantial redshifts.
1965 — Hannes Alfvén proposes the now-discounted
concept of ambiplasma to explain baryon asymmetry
and supports the idea of an infinite universe.
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 a 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
1967 — Robert Wagoner, William Fowler, and
Fred Hoyle show that the hot Big Bang predicts
the correct deuterium and lithium abundances
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
1970 — Vera Rubin and Kent Ford measure
spiral galaxy rotation curves at large radii,
showing evidence for substantial amounts of
dark matter.
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
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.
1980 — Alan Guth and Alexei Starobinsky
independently propose the inflationary Big
Bang universe as a possible solution to the
horizon and flatness problems.
1981 — Viacheslav Mukhanov and G. Chibisov
propose that quantum fluctuations could lead
to large scale structure in an inflationary
universe.
1982 — The first CfA galaxy redshift survey
is completed.
1982 — Several groups including James Peebles,
J. Richard Bond and George Blumenthal propose
that the universe is dominated by cold dark
matter.
1983 - 1987 — The first large computer simulations
of cosmic structure formation are run by Davis,
Efstathiou, Frenk and White.
The results show that cold dark matter produces
a reasonable match to observations, but hot
dark matter does not.
1988 — The CfA2 Great Wall is discovered
in the CfA2 redshift survey.
1988 — Measurements of galaxy large-scale
flows provide evidence for the Great Attractor.
1990 — Preliminary results from NASA's COBE
mission confirm the cosmic microwave background
radiation has a blackbody spectrum 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.
1992 — Further COBE measurements discover
the very small anisotropy of the cosmic microwave
background, providing a "baby picture" of
the seeds of large-scale structure when the
universe was around 1/1100th of its present
size and 380,000 years old.
1996 - The first Hubble Deep Field is released,
providing a clear view of very distant galaxies
when the universe was around one-third of
its present age.
1998 — Controversial evidence for the fine
structure constant varying over the lifetime
of the universe is first published.
1998 — The Supernova Cosmology Project and
High-Z Supernova Search Team discover cosmic
acceleration based on distances to Type Ia
supernovae, providing the first direct evidence
for a non-zero cosmological constant.
1999 — Measurements of the cosmic microwave
background radiation with finer resolution
than COBE, (most notably by the BOOMERanG
experiment see Mauskopf et al., 1999, Melchiorri
et al., 1999, de Bernardis et al. 2000) provide
evidence for oscillations (the first acoustic
peak) in the anisotropy angular spectrum,
as expected in the standard model of cosmological
structure formation.
The angular position of this peak indicates
that the geometry of the universe is close
to flat.
== Since 2000 ==
2001 — The 2dF Galaxy Redshift Survey (2dF)
by an Australian/British team gave strong
evidence that the matter density is near 25%
of critical density.
Together with the CMB results for a flat universe,
this provides independent evidence for a cosmological
constant or similar dark energy.
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 Wilkinson Microwave Anisotropy
Probe (WMAP) obtained full-sky detailed pictures
of the cosmic microwave background radiation.
The images can be interpreted to indicate
that the universe is 13.7 billion years old
(within one percent error), and are very consistent
with the Lambda-CDM model and the density
fluctuations predicted by inflation.
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.
2005 — The Sloan Digital Sky Survey (SDSS)
and 2dF redshift surveys both detected the
baryon acoustic oscillation feature in the
galaxy distribution, a key prediction of cold
dark matter models.
2006 — The long-awaited three-year WMAP
results are released, confirming previous
analysis, correcting several points, and including
polarization data.
2006–2011 — Improved measurements from
WMAP, new supernova surveys ESSENCE and SNLS,
and baryon acoustic oscillations from SDSS
and WiggleZ, continue to be consistent with
the standard Lambda-CDM model.
2014 — On March 17, 2014, astrophysicists
of the BICEP2 collaboration announced the
detection of inflationary gravitational waves
in the B-mode power spectrum, which if confirmed,
would provide clear experimental evidence
for the theory of inflation.
However, on June 19, 2014, lowered confidence
in confirming the cosmic inflation findings
was reported.
2016 — On February 11, 2016, LIGO Scientific
Collaboration and Virgo Collaboration announced
that gravitational waves were directly detected
by two LIGO detectors.
The waveform matched the prediction of General
relativity for a gravitational wave emanating
from the inward spiral and merger of a pair
of black holes of around 36 and 29 solar masses
and the subsequent "ringdown" of the single
resulting black hole.
The second detection verified that GW150914
is not a fluke, thus opens entire new branch
in astrophysics, gravitational-wave astronomy.
== See also ==
=== Physical cosmology ===
Chronology of the universe
Graphical timeline of the Big Bang
Graphical timeline from Big Bang to Heat Death
Timeline of cosmic microwave background astronomy
List of cosmologists
Non-standard cosmology
=== 
Belief systems ===
Buddhist cosmology
Jain cosmology
Jainism and non-creationism
Hindu cosmology
Maya mythology
=== Others ===
Cosmology@Home
