
Cosmology (from
Greek κόσμος, ''kosmos'' "world" and -λογία, ''-logia'' "study of") is a branch of
astronomy concerned with the studies of the origin and evolution of the
universe, from the
Big Bang to today and on into the
future. It is the
scientific study of the
origin, evolution, and eventual fate of the
universe.
Physical cosmology is the scientific study of the universe's origin, its large-scale structures and dynamics, and its
ultimate fate, as well as the
laws of science that govern these areas.
The term ''cosmology'' was first used in English in 1656 in
Thomas Blount's ''Glossographia'', and in 1731 taken up in Latin by
German philosopher Christian Wolff, in ''Cosmologia Generalis''.
Religious or mythological cosmology is a body of beliefs based on
mythological,
religious, and
esoteric literature and traditions of
creation myths and
eschatology.
Physical cosmology is studied by scientists, such as
astronomers and
physicists, as well as
philosophers, such as
metaphysicians,
philosophers of physics, and
philosophers of space and time. Because of this shared scope with
philosophy,
theories in physical cosmology may include both
scientific and non-scientific propositions, and may depend upon assumptions that cannot be
tested. Cosmology differs from astronomy in that the former is concerned with the Universe as a whole while the latter deals with individual
celestial objects. Modern physical cosmology is dominated by the
Big Bang theory, which attempts to bring together
observational astronomy and
particle physics;
more specifically, a standard parameterization of the Big Bang with
dark matter and
dark energy, known as the
Lambda-CDM model.
Theoretical astrophysicist David N. Spergel has described cosmology as a "historical science" because "when we look out in space, we look back in time" due to the finite nature of the
speed of light.
Disciplines
Physics and
astrophysics have played a central role in shaping the understanding of the universe through scientific observation and experiment.
Physical cosmology was shaped through both mathematics and observation in an analysis of the whole universe. The universe is generally understood to have begun with the
Big Bang, followed almost instantaneously by
cosmic inflation; an
expansion of space from which the universe is thought to have emerged
13.799 ± 0.021 billion years ago.
Cosmogony studies the origin of the Universe, and
cosmography maps the features of the Universe.
In
Diderot's
Encyclopédie, cosmology is broken down into uranology (the science of the heavens), aerology (the science of the air), geology (the science of the continents), and hydrology (the science of waters).
Metaphysical cosmology has also been described as the placing of humans in the universe in relationship to all other entities. This is exemplified by
Marcus Aurelius's observation that a man's place in that relationship: "He who does not know what the world is does not know where he is, and he who does not know for what purpose the world exists, does not know who he is, nor what the world is."
Discoveries
Physical cosmology
Physical cosmology is the branch of physics and astrophysics that deals with the study of the physical origins and evolution of the Universe. It also includes the study of the nature of the Universe on a large scale. In its earliest form, it was what is now known as "
celestial mechanics", the study of the
heavens. Greek philosophers
Aristarchus of Samos,
Aristotle, and
Ptolemy proposed different cosmological theories. The
geocentric Ptolemaic system was the prevailing theory until the 16th century when
Nicolaus Copernicus, and subsequently
Johannes Kepler and
Galileo Galilei, proposed a
heliocentric system. This is one of the most famous examples of
epistemological rupture in physical cosmology.
Isaac Newton's ''
Principia Mathematica'', published in 1687, was the first description of the
law of universal gravitation. It provided a physical mechanism for
Kepler's laws and also allowed the anomalies in previous systems, caused by gravitational interaction between the planets, to be resolved. A fundamental difference between Newton's cosmology and those preceding it was the
Copernican principle—that the bodies on earth obey the same
physical laws as all the celestial bodies. This was a crucial philosophical advance in physical cosmology.
Modern scientific cosmology is usually considered to have begun in 1917 with
Albert Einstein's publication of his final modification of
general relativity in the paper "Cosmological Considerations of the General Theory of Relativity" (although this paper was not widely available outside of Germany until the end of
World War I). General relativity prompted
cosmogonists such as
Willem de Sitter,
Karl Schwarzschild, and
Arthur Eddington to explore its astronomical ramifications, which enhanced the ability of
astronomers to study very distant objects. Physicists began changing the assumption that the Universe was static and unchanging. In 1922
Alexander Friedmann introduced the idea of an expanding universe that contained moving matter. Around the same time (1917 to 1922) the
Great Debate took place, with early cosmologists such as
Heber Curtis and
Ernst Öpik determining that some
nebulae seen in telescopes were separate galaxies far distant from our own.
In parallel to this dynamic approach to cosmology, one long-standing debate about the structure of the cosmos was coming to a climax. Mount Wilson astronomer
Harlow Shapley championed the model of a cosmos made up of the
Milky Way star system only; while
Heber D. Curtis argued for the idea that spiral nebulae were star systems in their own right as island universes. This difference of ideas came to a climax with the organization of the
Great Debate on 26 April 1920 at the meeting of the U.S.
National Academy of Sciences in
Washington, D.C. The debate was resolved when
Edwin Hubble detected
Cepheid Variables in the
Andromeda Galaxy in 1923 and 1924. Their distance established spiral nebulae well beyond the edge of the Milky Way..
Subsequent modelling of the universe explored the possibility that the
cosmological constant, introduced by Einstein in his 1917 paper, may result in an
expanding universe, depending on its value. Thus the
Big Bang model was proposed by the
Belgian priest
Georges Lemaître in 1927 which was subsequently corroborated by
Edwin Hubble's discovery of the
redshift in 1929 and later by the discovery of the
cosmic microwave background radiation by
Arno Penzias and
Robert Woodrow Wilson in 1964. These findings were a first step to rule out some of many
alternative cosmologies.
Since around 1990, several dramatic advances in observational cosmology have transformed cosmology from a largely speculative science into a predictive science with precise agreement between theory and observation. These advances include observations of the microwave background from the
COBE,
WMAP and
Planck satellites, large new galaxy
redshift surveys including
2dfGRS and
SDSS, and observations of distant
supernovae and
gravitational lensing. These observations matched the predictions of the
cosmic inflation theory, a modified
Big Bang theory, and the specific version known as the
Lambda-CDM model. This has led many to refer to modern times as the "golden age of cosmology".
On 17 March 2014, astronomers at the
Harvard-Smithsonian Center for Astrophysics announced the detection of
gravitational waves, providing strong evidence for
inflation and the
Big Bang.
However, on 19 June 2014, lowered confidence in confirming the
cosmic inflation findings was reported.
On 1 December 2014, at the ''Planck 2014'' meeting in
Ferrara,
Italy, astronomers reported that the
universe is
13.8 billion years old and is composed of 4.9%
atomic matter, 26.6%
dark matter and 68.5%
dark energy.
Religious or mythological cosmology
Religious or mythological cosmology is a body of beliefs based on
mythological,
religious, and
esoteric literature and traditions of
creation and
eschatology.
Philosophical cosmology

Cosmology deals with the world as the totality of space, time and all phenomena. Historically, it has had quite a broad scope, and in many cases was found in religion. In modern use metaphysical cosmology addresses questions about the Universe which are beyond the scope of science. It is distinguished from religious cosmology in that it approaches these questions using philosophical methods like
dialectics. Modern metaphysical cosmology tries to address questions such as:
* What is the origin of the Universe? What is its first cause? Is its existence necessary? (see
monism,
pantheism,
emanationism and
creationism)
* What are the ultimate material components of the Universe? (see
mechanism,
dynamism,
hylomorphism,
atomism)
* What is the ultimate reason for the existence of the Universe? Does the cosmos have a purpose? (see
teleology)
* Does the existence of consciousness have a purpose? How do we know what we know about the totality of the cosmos? Does cosmological reasoning reveal metaphysical truths? (see
epistemology)
Historical cosmologies
Table notes: the term "static" simply means not expanding and not contracting. Symbol ''G'' represents Newton's
gravitational constant; Λ (Lambda) is the
cosmological constant.
See also
*
Earth science
*
Lambda-CDM model
*
Absolute time and space
*
Galaxy formation and evolution
*
Illustris project
*
List of astrophysicists
*
Big History
*
Non-standard cosmology
*
Jainism and non-creationism
*
Taiji (philosophy)
*
Universal rotation curve
*
Warm inflation
References
External links
NASA/IPAC Extragalactic Database (NED)NED-Distances
from the American Institute of Physics
Introduction to CosmologyDavid Lyth's lectures from the ICTP Summer School in High Energy Physics and Cosmology
*
The Sophia Centre The Sophia Centre for the Study of Cosmology in Culture, University of Wales Trinity Saint David
Genesis ''cosmic chemistry'' module"The Universe's Shape" BBC Radio 4 discussion with Sir Martin Rees, Julian Barbour and Janna Levin (''In Our Time'', 7 February 2002)
{{Portal bar|Astronomy|Space
*