Cosmology (from the Greek κόσμος, kosmos
"world" and -λογία, -logia "study of")
is the 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 scientific laws 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."
=== 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 red shift 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 founded 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
