Jagat

[225px|thumb|Gambar kosmos terang tur katempo nu pangjerona, *[Hubble Ultra Deep Field*.]]

: *Artikel ieu nerangkeun jagat tina sawangan fiskal atawa émpirikal. Keur kagunaan séjén, tempo  {}.

Istilah **jagat** miboga sababaraha harti, dumasar kana kontéks nu dipigunakeunnana. Dina istilah  fisikal, **jagat total** nyaéta jumlah-jamléh tina sakabéh matéri nu aya, kaasup ruang di mana sakabéh kajadian lumangsung atawa bisa lumangsung. Bagéan tina jagat nu bisa katempo atawa kaawaskeun *geus kungsi'' kajadian disebut disebut **jagat nu dipikanyaho**, **jagat nu bisa diawaskeun**, atawa **jagat nu bisa katempo**. ku sabab inflasi kosmis miceun loba bagéan tina sakabéh jagatna tina horison nu bisa diawaskeun, lolobana ahli kosmologi narima yén henteu mungkin pikeun ngawaskeun sakabéh kontinuum sarta ku kituna bisa disebutkeun **jagat urang**, nujul kana ukur anu ilahar bisa dipikanyaho ku manusa. Dina istilah kosmologis, jagat dibayangkeun minangka kontinuum rohangan wanci nu  atawa  henteu aya watesna dina mana sakabéh matéri jeung énérgi aya. Sababaraha élmuwan merkirakeun yén jagat ieu mangrupa bagéan tina hiji sistim atawa loba deui jagat séjénna, nu disebut  multijagat.

## Ékspansi jeung umurna, téori Big Bang 
The most important result of physical 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, an abstract mathematical concept, which may or may not correspond to réality. This gives rise to the Big Bang theory, the dominant modél in cosmology today. The age of the universe from the time of the Big Bang, according to current information provided by NASA's WMAP (Wilkinson Microwave Anisotropy Probe), is estimated to be about 13.7  billion (13.7 × 109) yéars, with a margin of error of about 1 % (± 200 million yéars).  Other methods of estimating the age of the universe give different ages with a range from 11 billion to 20 billion. Most of the estimates cluster in the 13-15 billion yéar range.

A fundamental aspect of the Big Bang can be seen today in the observation that the farther away from us  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 éarly period of inflationary expansion following the Big Bang.

In the 1977 book *The First Three Minutes*, Nobel Prize-winner Steven Weinberg laid out the physics of what happened just moments after the Big Bang. As with most things in physics, that certainly wasn't the end of the story, as attested by the update and reissue of The First Three Minutes in 1993.

### *Pre-matter soup* 
Until recently, the first hundredth of a second was a bit of a mystery, léaving Weinberg and others unable to describe exactly what the universe would have been like. New experiments at the Relativistic Heavy Ion Collider in Brookhaven National Laboratory have provided physicists with a glimpse through this curtain of high energy, so they can directly observe the sorts of behavior that might have been taking place in this time frame.

At these énérgies, the quarks that comprise protons and neutrons were not yet joined together, and a dense, superhot mix of quarks and gluons, with some electrons thrown in, was all that could exist in the microseconds before it cooled enough to form into the sort of matter particles we observe today.

### Galaksi munggaran 
Fast forwarding to after the existence of matter, more information is coming in on the formation of galaxies. It is believed that the éarliest galaxies were tiny "dwarf galaxies" that reléased so much radiation they stripped gas atoms of their electrons. This gas, in turn, héated up and expanded, and thus was able to obtain the mass needed to form the larger galaxies that we know today.

Current telescopes are just now beginning to have the capacity to observe the galaxies from this distant time. Studying the light from quasars, they observe how it passes through the intervening gas clouds. The ionization of these gas clouds is determined by the number of néarby bright galaxies, and if such galaxies are spréad around, the ionization level should be constant. It turns out that in galaxies from the period after cosmic reionization there are large fluctuations in this ionization level. The evidence seems to confirm the pre-ionization galaxies were less common and that the post-ionization galaxies have 100 times the mass of the dwarf galaxies. 

The next generation of telescopes should be able to see the dwarf galaxies directly, which will help resolve the problem that many astronomical predictions in galaxy formation théory predict more néarby small galaxies.

## Ukuran jagat jeung jagat nu bisa diawaskeun 
There is no generally accepted théory making a pronouncement concerning whether the universe is indeed finite or infinite in spatial extent.  For an overview of the possibilities, see Shape of the 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 15.8 billion light years distant. The *present distance* (comoving distance) to the edge of the observable universe is larger, due to the ever incréasing rate at which the universe has been expanding; it is estimated to be about 78&nbsp; billion light yéars (7.8 × 1010 light yéars, or 7.4 × 1026 m). This would maké the volume, of the known universe, equal to 1.9 × 1033 cubic light yéars (assuming this region is perfectly  spherical). As of 2006, the observable universe is thought to contain about 7 × 1022 stars, organized in about 100 billion (1011) galaxies, which themselves form  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 éarth.

Both popular and professional reséarch articles in cosmology often use the term "universe" when they réally méan "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).

## Wangun jagat 
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 néarly spatially flat, with local wrinkles where massive objects distort spacetime, just as the surface of a lake is néarly 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 modél, but nevertheless may be spatially finite (compact). This can be understood using a two-dimensional analogy: the surface of a sphere has no edge, but nonetheless has a finite aréa. 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 théoretically cause one to eventually arrive back at the starting point.

Strictly spéaking, 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 reséarch maké this appéar very unlikely. 

## Nasib jagat 
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 eternity (see accelerating universe). Other idéas of the fate of our universe include the Big Rip, the Big Freeze, and Heat death of the universe théory. For a more detailed discussion of other théories, see the ultimate fate of the universe.

## Multijagat 
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 idéas 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. String théorist Michio Kaku offered several explanations to possible parallel universe phenomena.

## Istilah séjén 
[thumb|300px|Colorized version of the [Flammarion woodcut. The original was published in Paris in 1888.]]

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 a 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 word "Weltraum"
Albert Einstein (1952). *Relativity: The Special and the General Theory (Fifteenth Edition)*, ISBN 0-517-88441-0.

## Catetan jeung référénsi 
## Tumbu luar 
* ''Stephen Hawking's Universe*  - why is the universe the way it is?
* Richard Powell: *An Atlas of the Universe'' - images at various scales, with explanations.
* Cosmos - an "illustrated dimensional journey from microcosmos to macrocosmos" 
* Age of the Universe at Space.Com
* My So-Called Universe  arguments for and against an infinite and parallel universes
* Parallel Universes  by Max Tegmark
* Logarithmic Maps of the Universe 
* Seti@Home - the Search for Extraterrestrial Intelligence 
* Universe - Space Information Centre  by Exploreuniverse.com
* Number of Galaxies in the Universe
* Size of the Universe at Space.Com
* Illustration comparing the sizes of the planets, the sun, and other stars