Universe
Content
The Universe is all of time and space and its contents.[8][9][10][11] The Univer
se includes planets, stars, galaxies, the contents of intergalactic space, the s
mallest subatomic particles, and all matter and energy. The observable universe
is about 28 billion parsecs (91 billion light-years) in diameter at the present
time.[2] The size of the whole Universe is not known and may be infinite.[12] Ob
servations and the development of physical theories have led to inferences about
the composition and evolution of the Universe.
Throughout recorded history, cosmologies and cosmogonies, including scientific m
odels, have been proposed to explain observations of the Universe. The earliest
quantitative geocentric models were developed by ancient Greek philosophers and
Indian philosophers.[13][14] Over the centuries, more precise astronomical obser
vations led to Nicolaus Copernicus's heliocentric model of the Solar System and
Johannes Kepler's improvement on that model with elliptical orbits, which was ev
entually explained by Isaac Newton's theory of gravity. Further observational im
provements led to the realization that the Solar System is located in a galaxy c
omposed of billions of stars, the Milky Way. It was subsequently discovered that
our galaxy is just one of many. Observations of the distribution of these galax
ies and their spectral lines have led to many of the theories of modern physical
cosmology. The discovery in the early 20th century that galaxies are systematic
ally redshifted suggested that the Universe is expanding, and the discovery of t
he cosmic microwave background radiation suggested that the Universe had a begin
ning.[15] Finally, observations in the late 1990s indicated the rate of the expa
nsion of the Universe is increasing[16] indicating that the majority of energy i
s most likely in an unknown form called dark energy.[17][18] The majority of mas
s in the universe also appears to exist in an unknown form, called dark matter.[
17][18]
The Big Bang theory is the prevailing cosmological model describing the developm
ent of the Universe. Space and time were created in the Big Bang, and these were
imbued with a fixed amount of energy and matter; as space expands, the density
of that matter and energy decreases. After the initial expansion, the Universe c
ooled sufficiently to allow the formation first of subatomic particles and later
of simple atoms. Giant clouds of these primordial elements later coalesced thro
ugh gravity to form stars. Assuming that the prevailing model is correct, the ag
e of the Universe is measured to be 13.798±0.037 billion years.[1][19]
There are many competing hypotheses about the ultimate fate of the Universe. Phy
sicists and philosophers remain unsure about what, if anything, preceded the Big
Bang. Many refuse to speculate, doubting that any information from any such pri
or state could ever be accessible. There are various multiverse hypotheses, in w
hich some physicists have suggested that the Universe might be one among many un
iverses that likewise exist.[20][21]
Contents [hide]
1 Definition
2 Etymology
2.1 Synonyms
3 Chronology and the Big Bang
4 Properties
4.1 Shape
4.2 Size and regions
4.3 Age and expansion
4.4 Spacetime
5 Contents
5.1 Dark energy
5.2 Dark matter
5.3 Ordinary Matter
5.4 Particles
5.4.1 Hadrons
5.4.2 Leptons
5.4.3 Bosons
5.4.4 Photons
6 Geometry
7 Theories of physics
7.1 Special relativity
7.2 General relativity
7.2.1 Solving Einstein's field equations
7.3 Multiverse hypothesis
7.4 Fine-tuned Universe
8 Historical development
8.1 Mythologies
8.2 Philosophical models
8.3 Astronomical concepts
9 See also
10 References
11 Bibliography
12 Further reading
13 External links
13.1 Videos
Definition
Part of a series on
Physical cosmology
Full-sky image derived from nine years' WMAP data
Big Bang · Universe
Age of the universe
Chronology of the universe
Early universe[show]
Expansion · Future[show]
Components · Structure[show]
Experiments[show]
Scientists[show]
Subject history[show]
Category Category
Portal icon Cosmology portal
Portal icon Astronomy portal
v t e
The Universe is customarily defined as everything that exists, everything that h
as existed, and everything that will exist.[22][23][24] According to our current
understanding, the Universe consists of three constituents: spacetime, forms of
energy, including electromagnetic radiation and matter, and the physical laws t
hat relate them. The Universe also encompasses all of life, all of history, and
some philosophers and scientists even suggest that it encompasses ideas such as
mathematics.[25][26][27]
Etymology
The word universe derives from the Old French word univers, which in turn derive
s from the Latin word universum.[28] The Latin word was used by Cicero and later
Latin authors in many of the same senses as the modern English word is used.[29
] The Latin word derives from the poetic contraction unvorsum
first used by Lucr
etius in Book IV (line 262) of his De rerum natura (On the Nature of Things) whi
ch connects un, uni (the combining form of unus, or "one") with vorsum, versum (
a noun made from the perfect passive participle of vertere, meaning "something r
otated, rolled, changed").[29]
se includes planets, stars, galaxies, the contents of intergalactic space, the s
mallest subatomic particles, and all matter and energy. The observable universe
is about 28 billion parsecs (91 billion light-years) in diameter at the present
time.[2] The size of the whole Universe is not known and may be infinite.[12] Ob
servations and the development of physical theories have led to inferences about
the composition and evolution of the Universe.
Throughout recorded history, cosmologies and cosmogonies, including scientific m
odels, have been proposed to explain observations of the Universe. The earliest
quantitative geocentric models were developed by ancient Greek philosophers and
Indian philosophers.[13][14] Over the centuries, more precise astronomical obser
vations led to Nicolaus Copernicus's heliocentric model of the Solar System and
Johannes Kepler's improvement on that model with elliptical orbits, which was ev
entually explained by Isaac Newton's theory of gravity. Further observational im
provements led to the realization that the Solar System is located in a galaxy c
omposed of billions of stars, the Milky Way. It was subsequently discovered that
our galaxy is just one of many. Observations of the distribution of these galax
ies and their spectral lines have led to many of the theories of modern physical
cosmology. The discovery in the early 20th century that galaxies are systematic
ally redshifted suggested that the Universe is expanding, and the discovery of t
he cosmic microwave background radiation suggested that the Universe had a begin
ning.[15] Finally, observations in the late 1990s indicated the rate of the expa
nsion of the Universe is increasing[16] indicating that the majority of energy i
s most likely in an unknown form called dark energy.[17][18] The majority of mas
s in the universe also appears to exist in an unknown form, called dark matter.[
17][18]
The Big Bang theory is the prevailing cosmological model describing the developm
ent of the Universe. Space and time were created in the Big Bang, and these were
imbued with a fixed amount of energy and matter; as space expands, the density
of that matter and energy decreases. After the initial expansion, the Universe c
ooled sufficiently to allow the formation first of subatomic particles and later
of simple atoms. Giant clouds of these primordial elements later coalesced thro
ugh gravity to form stars. Assuming that the prevailing model is correct, the ag
e of the Universe is measured to be 13.798±0.037 billion years.[1][19]
There are many competing hypotheses about the ultimate fate of the Universe. Phy
sicists and philosophers remain unsure about what, if anything, preceded the Big
Bang. Many refuse to speculate, doubting that any information from any such pri
or state could ever be accessible. There are various multiverse hypotheses, in w
hich some physicists have suggested that the Universe might be one among many un
iverses that likewise exist.[20][21]
Contents [hide]
1 Definition
2 Etymology
2.1 Synonyms
3 Chronology and the Big Bang
4 Properties
4.1 Shape
4.2 Size and regions
4.3 Age and expansion
4.4 Spacetime
5 Contents
5.1 Dark energy
5.2 Dark matter
5.3 Ordinary Matter
5.4 Particles
5.4.1 Hadrons
5.4.2 Leptons
5.4.3 Bosons
5.4.4 Photons
6 Geometry
7 Theories of physics
7.1 Special relativity
7.2 General relativity
7.2.1 Solving Einstein's field equations
7.3 Multiverse hypothesis
7.4 Fine-tuned Universe
8 Historical development
8.1 Mythologies
8.2 Philosophical models
8.3 Astronomical concepts
9 See also
10 References
11 Bibliography
12 Further reading
13 External links
13.1 Videos
Definition
Part of a series on
Physical cosmology
Full-sky image derived from nine years' WMAP data
Big Bang · Universe
Age of the universe
Chronology of the universe
Early universe[show]
Expansion · Future[show]
Components · Structure[show]
Experiments[show]
Scientists[show]
Subject history[show]
Category Category
Portal icon Cosmology portal
Portal icon Astronomy portal
v t e
The Universe is customarily defined as everything that exists, everything that h
as existed, and everything that will exist.[22][23][24] According to our current
understanding, the Universe consists of three constituents: spacetime, forms of
energy, including electromagnetic radiation and matter, and the physical laws t
hat relate them. The Universe also encompasses all of life, all of history, and
some philosophers and scientists even suggest that it encompasses ideas such as
mathematics.[25][26][27]
Etymology
The word universe derives from the Old French word univers, which in turn derive
s from the Latin word universum.[28] The Latin word was used by Cicero and later
Latin authors in many of the same senses as the modern English word is used.[29
] The Latin word derives from the poetic contraction unvorsum
first used by Lucr
etius in Book IV (line 262) of his De rerum natura (On the Nature of Things) whi
ch connects un, uni (the combining form of unus, or "one") with vorsum, versum (
a noun made from the perfect passive participle of vertere, meaning "something r
otated, rolled, changed").[29]
