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Universe
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{{dablink|For other uses, see
Universe (disambiguation).}}
Image:Universe.jpg Hubble Ultra Deep Field.html" title="Meaning of thumb thumb|right|The deepest visible-light image of the cosmos, the [[Hubble Ultra Deep Field..html" title="Meaning of right|The deepest visible-light image of the cosmos, the [[Hubble Ultra Deep Field">thumb|right|The deepest visible-light image of the cosmos, the [[Hubble Ultra Deep Field.">right|The deepest visible-light image of the cosmos, the [[Hubble Ultra Deep Field">thumb|right|The deepest visible-light image of the cosmos, the [[Hubble Ultra Deep Field.
Image:Universum.jpg thumb|Universum - C. Flammarion, Woodcut, Paris 1888, Coloration : Heikenwaelder Hugo, Vienna 1998
The term '''universe''' has a variety of meanings based on the context in which it is described. In
materialism materialist philosophy philosophical terms, the universe is the summation of all particles that exist and the space in which all events occur which has an equivalent idea amongst some theoretical scientists known as the '''total universe'''. In
cosmology cosmological terms, the universe is thought to be a
finite or
infinity infinite Spacetime space-time continuum in which all matter and energy exist. (It has been hypothesized by some scientists that the universe may be part of a system of many other universes, known as the
multiverse.) The terms '''known universe''', '''
observable universe''', or '''visible universe''' are often used to describe the part of the universe that can be seen or otherwise observed by humanity. Due to the fact that
cosmic inflation removes vast parts of the total universe from our
particle horizon observable horizon, most cosmologists currently accept that it is impossible to observe the whole continuum and may use '''our universe''', referring only to that knowable by human beings in particular.
Expansion and age, and the Big Bang theory
{{main|Age of the universe}}
{{cosmology}}
The most important result of
cosmology, the understanding that the universe is expanding, is derived from
redshift observations and quantified by
Hubble's Law. Extrapolating this expansion back in time, one approaches a
gravitational singularity, a rather abstract mathematical concept, which may or may not correspond to reality. This gives rise to the
Big Bang theory, the dominant model in cosmology today. The
age of the universe from the time of the Big Bang, was estimated to be about 13.7
1 E9 billion (13.7 × 10
9) years, with a
margin of error of about 1 % (± 200 million years), according to
NASA's
WMAP (Wilkinson Microwave Anisotropy Probe). However, this is based on the assumption that the underlying model used for data analysis is correct. Other methods of estimating the age of the universe give different ages.
A fundamental aspect of the Big Bang can be seen today in the observation that the farther away from us
galaxy galaxies are, the faster they move away from us. It can also be seen in the
cosmic microwave background radiation which is the much-attenuated radiation that originated soon after the Big Bang. This background radiation is remarkably uniform in all directions, which cosmologists have attempted to explain by an early period of
inflationary expansion following the Big Bang.
Size of the universe and observable universe
{{main|Observable universe}}
There is disagreement over whether the universe is indeed finite or infinite in spatial extent and volume. Many astronomers and cosmologists believe the universe is infinite due to recent findings in NASA's WMAP project supporting a flat(therefore infinite) universe
However, the observable universe, consisting of all locations that could have affected us since the Big Bang given the finite
speed of light, is certainly finite. The edge of the
cosmic light horizon is 13.7 billion
light years (4.19
gigaparsec Gpc) distant. The ''present distance'' (
comoving distance) to the edge of the observable universe is larger, due to the ever increasing rate at which the universe has been expanding; it is estimated to be about 78
billion light years (7.8 × 10
10 light years, or 7.4 × 10
26 m). This would make the comoving
volume, of the known universe, equal to 1.9 × 10
33 cubic light years (assuming this region is perfectly
sphere spherical). The observable universe contains about 7 × 10
22 stars, organized in about 100 billion
galaxy galaxies, which themselves form
groups and clusters of galaxies clusters and
superclusters. The number of galaxies may be even larger, based on the
Hubble Deep Field observed with the
Hubble Space Telescope. The Hubble Space Telescope discovered galaxies such as
Abell 1835 IR1916, which are over 13 billion
light years from Earth.
Both popular and professional research articles in cosmology often use the term "universe" when they really mean "observable universe". This is because unobservable physical phenomena are scientifically irrelevant; that is, they cannot affect any events that we can perceive. See also
Causality (physics).
Shape of the universe
{{main articles|
Shape of the universe, and
Large-scale structure of the cosmos}}
An important open question of cosmology is the shape of the universe. Mathematically, which
3-manifold represents best the spatial part of the universe?
Firstly, whether the universe is spatially ''flat'', i.e. whether the rules of
Euclidean geometry are valid on the largest scales, is unknown. Currently, most cosmologists believe that the observable universe is very nearly spatially flat, with local wrinkles where massive objects distort
spacetime, just as a lake is (nearly) flat. This opinion was strengthened by the latest data from
WMAP, looking at "acoustic oscillations" in the cosmic microwave background radiation temperature variations.
Secondly, whether the universe is
multiply connected, is unknown. The universe has no spatial boundary according to the standard Big Bang model, but nevertheless may be spatially finite (
compact space compact). This can be understood using a two-dimensional analogy: the surface of a
sphere has no edge, but nonetheless has a finite area. It is a two-dimensional surface with constant curvature in a third dimension. The
3-sphere is a three-dimensional equivalent in which all three dimensions are constantly curved in a fourth.
If the universe is indeed spatially finite, as described, then traveling in a "straight" line, in any given direction, would theoretically cause one to eventually arrive back at the starting point.
Strictly speaking, we should call the stars and galaxies "views" of stars and galaxies, since it is possible that the universe is multiply-connected and sufficiently small (and of an appropriate, perhaps complex, shape) that we can see once or several times around it in various, and perhaps all, directions. (Think of a
house of mirrors.) If so, the actual number of physically distinct stars and galaxies would be smaller than currently accounted. Although this possibility has not been ruled out, the results of the latest
cosmic microwave background research make this appear very unlikely.
Fate of the universe
Depending on the average density of matter and energy in the universe, it will either keep on expanding forever or it will be gravitationally slowed down and will eventually collapse back on itself in a "
Big Crunch". Currently the evidence suggests not only that there is insufficient mass/energy to cause a recollapse, but that the expansion of the universe seems to be accelerating and will accelerate for the whole of
eternity (see
accelerating universe accelerating Universe). Other ideas of the fate of our universe include the
Big Rip, the
Big Freeze, and
Heat death of the universe theory. For a more detailed discussion of other theories, see the
ultimate fate of the universe.
Multiverse
There is some speculation that multiple universes exist in a higher-level
multiverse (also known as a megaverse), our universe being one of those universes. For example, matter that falls into a black hole in our universe could emerge as a Big Bang, starting another universe. However, all such ideas are currently untestable and cannot be regarded as anything more than speculation. The concept of parallel universes is understood only when related to
string theory.
Other terms
Different words have been used throughout
history to denote "all of space", including the equivalents and variants in various languages of "heavens," "cosmos," and "world."
Macrocosm has also been used to this effect, although it is more specifically defined as a system that reflects in large scale one, some, or all of its component systems or parts. (Similarly, a
microcosm is system that reflects in small scale a much larger system of which it is a part.)
Although words like
world and its equivalents in other languages now almost always refer to the planet
Earth, they previously referred to everything that exists—see
Copernicus, for example—and still sometimes do (as in "the whole wide world"). Some languages use the word for "world" as part of the word for "outer space", e.g. in the
German language German word "Weltall".
See also
*
Cosmic latte - the color of the Universe
*
Cosmology
*
Cosmos
*
Multiverse
*
Time travel
References
*
Albert Einstein (1952). ''Relativity: The Special and the General Theory (Fifteenth Edition)'', ISBN 0-517-88441-0
External links
-
Richard Powell: ''An Atlas of the Universe'' - a series of images at various scales, with explanations.
-
Cosmos - an "illustrated dimensional journey from microcosmos to macrocosmos"
-
A Review of the Universe - Structures, Evolutions, Observations, and Theories
-
Age of the Universe at Space.Com
-
My So-Called Universe by Jim Holt, on various arguments for and against an infinite Universe and parallel universes
-
Parallel Universes by Max Tegmark
-
Logarithmic Maps of the Universe
-
Seti@Home - the Search for Extraterrestrial Intelligence
-
Seti@Home Teamsearch for Extraterrestrial Intelligence
-
Universe - Space Information Centre by Exploreuniverse.com
-
Number of Galaxies in the Universe
-
Size of the Universe at Space.Com
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Book 'History of the Universe' web site
Category:Universe
Category:Environments
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csb:Swiatnica
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Category:Cosmology
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