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Encyclopedia > Universe
Physical cosmology
Key topics
Universe · Big Bang
Age of the universe
Timeline of the Big Bang
Ultimate fate of the universe
Early universe
Inflation · Nucleosynthesis
GWB · Neutrino Background
Cosmic microwave background
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The Universe is defined as the summation of all particles and energy that exist and the space-time in which all events occur. Based on observations of the portion of the Universe that is observable, physicists attempt to describe the whole of space-time, including all matter and energy and events which occur, as a single system corresponding to a mathematical model. Our universe is also defined as one component part of a larger Multiverse. Universe may refer to: Look up universe in Wiktionary, the free dictionary. ... This article is about the physics subject. ... Image File history File links Size of this preview: 800 × 411 pixelsFull resolution‎ (1,237 × 635 pixels, file size: 1. ... For other uses, see Big Bang (disambiguation). ... The age of the universe, in Big Bang cosmology, refers to the time elapsed between the Big Bang and the present day. ... This article does not cite any references or sources. ... This box:      The ultimate fate of the universe is a topic in physical cosmology. ... In cosmology, Big Bang nucleosynthesis (or primordial nucleosynthesis) refers to the production of nuclei other than H-1, the normal, light hydrogen, during the early phases of the universe, shortly after the Big Bang. ... This article or section is in need of attention from an expert on the subject. ... The Cosmic Neutrino Background (CNB) is the background particle radiation composed of neutrinos. ... CMB redirects here. ... This article is about the physical phenomenon. ... Hubbles law is the statement in physical cosmology that the redshift in light coming from distant galaxies is proportional to their distance. ... The metric expansion of space is a key part of sciences current understanding of the universe, whereby space itself is described by a metric which changes over time. ... The Friedmann equations relate various cosmological parameters within the context of general relativity. ... // The Friedmann-Lemaître-Robertson-Walker (FLRW) metric is an exact solution of the Einstein field equations of general relativity and which describes a homogeneous, isotropic expanding/contracting universe. ... The shape of the Universe is an informal name for a subject of investigation within physical cosmology. ... It has been suggested that this article or section be merged into Large-scale structure of the cosmos. ... In astrophysics, the questions of galaxy formation and evolution are: How, from a homogeneous universe, did we obtain the very heterogeneous one we live in? How did galaxies form? How do galaxies change over time? A spectacular head-on collision between two galaxies is seen in this NASA Hubble Space... Astronomy and cosmology examine the universe to understand the large-scale structure of the cosmos. ... A pie chart indicating the proportional composition of different energy-density components of the universe. ... In physical cosmology, dark energy is a hypothetical form of energy that permeates all of space and tends to increase the rate of expansion of the universe. ... For other uses, see Dark matter (disambiguation). ... This lists a timeline of cosmological theories and discoveries. ... Observational cosmology is the study of the structure, the evolution and the origin of the universe through observation, using instruments such as telescopes and cosmic ray detectors. ... In astronomy, the 2dF Galaxy Redshift Survey (Two-degree-Field Galaxy Redshift Gurvey), or 2dFGRS is a redshift survey conducted by the Anglo-Australian Observatory in the 1990s. ... SDSS Logo The Sloan Digital Sky Survey or SDSS is a major multi-filter imaging and spectroscopic redshift survey using a dedicated 2. ... The Cosmic Background Explorer (COBE), also referred to as Explorer 66, was the first satellite built dedicated to cosmology. ... The Telescope being readied for launch The BOOMERanG experiment (Balloon Observations Of Millimetric Extragalactic Radiation and Geophysics) measured the cosmic microwave background radiation of a part of the sky during three sub-orbital (high altitude) balloon flights. ... Artist depiction of the WMAP satellite at the L2 point The Wilkinson Microwave Anisotropy Probe (WMAP) is a NASA satellite whose mission is to survey the sky to measure the temperature of the radiant heat left over from the Big Bang. ... “Einstein” redirects here. ... Stephen William Hawking, CH, CBE, FRS, FRSA, (born 8 January 1942) is a British theoretical physicist. ... Alexander Alexandrovich Friedman or Friedmann (Александр Александрович Фридман) (June 16, 1888 – September 16, 1925) was a Russian cosmologist and mathematician. ... Monsignor Georges Lemaître, priest and scientist. ... Edwin Powell Hubble (November 20, 1889 – September 28, 1953) was an American astronomer. ... Arno Allan Penzias (born April 26, 1933) is an American physicist and winner of the 1978 Nobel Prize in physics. ... Robert Woodrow Wilson Robert Woodrow Wilson (born January 10, 1936) is an American physicist. ... George Gamow (pronounced GAM-off) (March 4, 1904 – August 19, 1968) , born Georgiy Antonovich Gamov (Георгий Антонович Гамов) was a Ukrainian born physicist and cosmologist. ... Robert Henry Dicke (May 6, 1916 – March 4, 1997) was an American experimental physicist, who made important contributions to the fields of astrophysics, atomic physics, cosmology and gravity. ... Yakov Borisovich Zeldovich (Russian:Яков Борисович Зельдович) (March 8, 1914 – December 2, 1987) was a prolific Soviet physicist. ... John Cromwell Mather (b. ... George Fitzgerald Smoot III (born February 20, 1945) is an American astrophysicist and cosmologist awarded the 2006 Nobel Prize in Physics with John C. Mather for their discovery of the black body form and anisotropy of the cosmic microwave background radiation. This work helped cement the big-bang theory of... This is a list of cosmologists. ... In special relativity and general relativity, time and three-dimensional space are treated together as a single four-dimensional pseudo-Riemannian manifold called spacetime. ... See universe for a general discussion of the universe. ... This article is about matter in physics and chemistry. ... A mathematical model is an abstract model that uses mathematical language to describe the behaviour of a system. ... For other uses, see Multiverse (disambiguation). ...


The generally accepted scientific theory which describes the origin and evolution of the Universe is Big Bang cosmology, which describes the expansion of space from an extremely hot and dense state of unknown characteristics. The Universe underwent a rapid period of cosmic inflation that flattened out nearly all initial irregularities in the energy density; thereafter the universe expanded and became steadily cooler and less dense. Minor variations in the distribution of mass resulted in hierarchical segregation of the features that are found in the current universe; such as clusters and superclusters of galaxies. There are more than one hundred billion (1011) galaxies in the Universe,[1] each containing hundreds of billions of stars, with each star containing about 1057 atoms of hydrogen. In mathematics, theory is used informally to refer to a body of knowledge about mathematics. ... For other uses, see Big Bang (disambiguation). ... This article is about the physics subject. ... Expansion of space is an idea that space can actually expand. ... In physical cosmology, cosmic inflation is the idea that the nascent universe passed through a phase of exponential expansion that was driven by a negative-pressure vacuum energy density. ... Galaxy groups and clusters are super-structures in the spread of galaxies of the cosmos. ... Superclusters are large groupings of smaller galaxy groups and clusters, and are among the largest structures of the cosmos. ... For other uses, see Galaxy (disambiguation). ... Properties For alternative meanings see atom (disambiguation). ...


There are also non-scientific investigations that explore and describe the universe as a whole with their own separate cosmologies. Cosmology, from the Greek: κοσμολογία (cosmologia, κόσμος (cosmos) order + λογια (logia) discourse) is the study of the Universe in its totality, and by extension, humanitys place in it. ...

Contents

Etymology

The word "universe" is derived from Old French univers, from Latin universum, which combines uni- (the combining form of unus, or "one") with versus (perfect passive participle of vertere, or "turn"). The word, therefore, means "all turned into one" or "revolving as one" or "orbiting as one".


Name of our Universe

In the same way that the Moon refers to our (Earth's) moon, the Universe is used by some cosmologists to refer to our Universe. In this article, the Universe is equivalent to our observable Universe. For other moons in the solar system see natural satellite. ... This article is about Earth as a planet. ...


Theoretical and observational cosmologists vary in their usage of the term the Universe to mean either this whole system or just a part of this system.[2] Theoretical physics employs mathematical models and abstractions of physics in an attempt to explain experimental data taken of the natural world. ... This article is about the physics subject. ...


As used by observational cosmologists, the Universe most frequently refers to the finite part of space-time. The Universe is directly observable by making observations using telescopes and other detectors, and by using the methods of theoretical and empirical physics for studying its components. Physical cosmologists assume that the observable part of (comoving) space (also called our universe) corresponds to a part of a model of the whole of space, and usually not to the whole space. They use the term the Universe ambiguously to mean either the observable part of space, the observable part of space-time, or the entire space-time.[citation needed] This article needs to be cleaned up to conform to a higher standard of quality. ... This article does not cite any references or sources. ... A magnet levitating above a high-temperature superconductor demonstrates the Meissner effect. ... The comoving distance or conformal distance of two objects in the universe is the distance divided by a time-varying scale factor representing the expansion of the universe. ...


In order to clarify terminology, George Ellis, U. Kirchner and W.R. Stoeger recommend using the term the Universe for the theoretical model of all of the connected space-time in which we live, universe domain for the observable universe or a similar part of the same space-time, universe for a general space-time (either our own Universe or another one disconnected from our own), multiverse for a set of disconnected space-times, and multi-domain universe to refer to a model of the whole of a single connected space-time in the sense of chaotic inflation models.[3] George Ellis is the Distinguished Professor of Complex Systems at the University of Cape Town (South Africa), in the Department of Mathematics and Applied Mathematics. ... In mathematics, a set can be thought of as any collection of distinct objects considered as a whole. ... The theory created by Andrei Linde that states that our universe could have come from nothing more than hundred-thousandth of a gram of matter. ...


Observable portion

Main article: Observable universe

A majority of cosmologists believe that the observable universe is an extremely tiny part of the whole universe and that it is impossible to observe the whole of comoving space. It is presently unknown if this is correct, and remains under debate. According to studies of the shape of the Universe, it is possible that the observable universe is of nearly the same size as the whole of space.[4][5] If a version of the cosmic inflation scenario is correct, then there is no known way to determine if the whole universe is finite or infinite. If it is infinite, the observable Universe is just a tiny speck of the whole universe. See universe for a general discussion of the universe. ... See universe for a general discussion of the universe. ... The comoving distance or conformal distance of two objects in the universe is the distance divided by a time-varying scale factor representing the expansion of the universe. ... The shape of the Universe is an informal name for a subject of investigation within physical cosmology. ... In physical cosmology, cosmic inflation is the idea that the nascent universe passed through a phase of exponential expansion that was driven by a negative-pressure vacuum energy density. ... Infinity is a word carrying a number of different meanings in mathematics, philosophy, theology and everyday life. ...


Theory

Theoretical cosmologists study models of the whole of space-time which is connected together, and search for models which are consistent with physical cosmologists' model of space-time on the scale of the observable universe.[citation needed] Their models are speculative but use the methods of theoretical physics. [3] Theoretical physics employs mathematical models and abstractions of physics in an attempt to explain experimental data taken of the natural world. ... A Möbius strip, an object with only one surface and one edge; such shapes are an object of study in topology. ... See universe for a general discussion of the universe. ... Theoretical physics employs mathematical models and abstractions of physics in an attempt to explain experimental data taken of the natural world. ...


Multiverse

Main article: Multiverse

Some theorists extend their model of "all of space-time" beyond a single connected space-time to a set of disconnected space-times, or multiverse. For other uses, see Multiverse (disambiguation). ... In mathematics, a set can be thought of as any collection of distinct objects considered as a whole. ... For other uses, see Multiverse (disambiguation). ...


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. String theorist Michio Kaku offered several explanations to possible parallel universe phenomena. For other uses, see Black hole (disambiguation). ... For other uses, see Big Bang (disambiguation). ... Interaction in the subatomic world: world lines of pointlike particles in the Standard Model or a world sheet swept up by closed strings in string theory This box:      String theory is a model of fundamental physics, whose building blocks are one-dimensional extended objects called strings, rather than the zero... Michio Kaku (加來 道雄 Kaku Michio, born January 24, 1947 in the United States) is an American theoretical physicist, tenured professor, and co-founder of string field theory, a branch of superstring theory. ... Parallel universe or alternate reality in science fiction and fantasy is a self-contained separate reality coexisting with our own. ...


Physicist David Deutsch suggests that a multiverse is a consequence of the many-worlds interpretation, which he considers to be the best alternative explanation to the Copenhagen explanations of quantum theory first presented by Niels Bohr, over half a century ago.[citation needed] David Deutsch (born 1953) is a physicist at Oxford University. ... The many-worlds interpretation or MWI (also known as relative state formulation, theory of the universal wavefunction, many-universes interpretation, Oxford interpretation or many worlds), is an interpretation of quantum mechanics that claims to resolve all the paradoxes of quantum theory by allowing every possible outcome to every event to... Early twentieth century studies of the physics of very small-scale phenomena led to the Copenhagen interpretation. ... For a less technical and generally accessible introduction to the topic, see Introduction to quantum mechanics. ... Niels Henrik David Bohr (October 7, 1885 – November 18, 1962) was a Danish physicist who made fundamental contributions to understanding atomic structure and quantum mechanics, for which he received the Nobel Prize in Physics in 1922. ...


Evolution

Formation

Main articles: Age of the universe and Big Bang

The most important result of physical cosmology—that the universe is expanding—is derived from redshift observations and quantified by Hubble's Law. That is, astronomers observe that there is a direct relationship between the distance to a remote object (such as a galaxy) and the velocity with which it is receding. Conversely, if this expansion has continued over the entire age of the universe, then in the past, these distant, receding objects must once have been closer together. The age of the universe, in Big Bang cosmology, refers to the time elapsed between the Big Bang and the present day. ... For other uses, see Big Bang (disambiguation). ... This article is about the physics subject. ... The metric expansion of space is a key part of sciences current understanding of the universe, whereby space itself is described by a metric which changes over time. ... This article is about the physical phenomenon. ... Hubbles law is the statement in physical cosmology that the redshift in light coming from distant galaxies is proportional to their distance. ...


By extrapolating this expansion back in time, one approaches a gravitational singularity where everything in the universe was compressed into an infinitesimal point; an abstract mathematical concept that may or may not correspond to reality. This idea gave rise to the Big Bang Theory, the dominant model in cosmology today. A gravitational singularity (sometimes spacetime singularity) is, approximately, a place where quantities which are used to measure the gravitational field become infinite. ... For other uses, see Big Bang (disambiguation). ...


During the earliest era of the big bang theory, the universe is believed to have formed a hot, dense plasma. As expansion proceeded, the temperature steadily dropped until a point was reached when atoms could form. At about this time the background energy (in the form of photons) became decoupled from the matter, and was free to travel through space. The left-over energy continued to cool as the universe expanded, and today it forms the cosmic microwave background radiation. 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. For other uses, see Plasma. ... CMB redirects here. ... Cosmic inflation is the idea, first proposed by Alan Guth in 1981, that the nascent universe passed through a phase of exponential expansion (the inflationary epoch) that was driven by a negative pressure vacuum energy density. ...


Examination of small variations in the microwave background radiation provides information about the nature of the universe, including the age and composition. 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) years, with a margin of error of about 1 % (± 200 million years). Other methods of estimation give different ages ranging from 11 billion to 20 billion.[6] Most of the estimates cluster in the 13–15 billion year range.[7][8] The age of the universe, in Big Bang cosmology, refers to the time elapsed between the Big Bang and the present day. ... The National Aeronautics and Space Administration (NASA) (IPA [ˈnæsÉ™]) is an agency of the United States government, responsible for the nations public space program. ... Artist depiction of the WMAP satellite at the L2 point The Wilkinson Microwave Anisotropy Probe (WMAP) is a NASA satellite whose mission is to survey the sky to measure the temperature of the radiant heat left over from the Big Bang. ... One thousand million (1,000,000,000) is the natural number following 999,999,999 and preceding 1,000,000,001. ... The top portion of this graphic depicts probability densities (for a binomial distribution) that show the relative likelihood that the true percentage is in a particular area given a reported percentage of 50%. The bottom portion of this graphic shows the margin of error, the corresponding zone of 95% confidence. ...


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. Additional discoveries and refinements of theories prompted him to update and reissue that book in 1993. Steven Weinberg (born May 3, 1933) is an American physicist. ... For other uses, see Big Bang (disambiguation). ...

See also: Timeline of the Big Bang

This article does not cite any references or sources. ...

Pre-matter soup

Until recently, the first hundredth of a second after the Big Bang was a mystery, leaving Weinberg and others unable to describe exactly what the universe would have been like during this period. 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.[9] The Relativistic Heavy Ion Collider at Brookhaven National Laboratory. ... ≠ Aerial view of Brookhaven National Laboratory. ...


At these energies, the quarks that comprise protons and neutrons (ups and downs) 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.[10] For other uses, see Quark (disambiguation). ... For other uses, see Proton (disambiguation). ... This article or section does not adequately cite its references or sources. ... In particle physics, gluons are subatomic particles that cause quarks to interact, and are indirectly responsible for the binding of protons and neutrons together in atomic nuclei. ...


Protogalaxies

Main article: Protogalaxy

Moving forward to after the existence of matter, more information is coming in on the formation of galaxies. It is believed that the earliest galaxies were tiny "dwarf galaxies" that released so much radiation they stripped gas atoms of their electrons. This gas, in turn, heated up and expanded, and thus was able to obtain the mass needed to form the larger galaxies that we know today.[11] [12] In cosmology, a protogalaxy is a cloud of gas which is forming into a galaxy. ...


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 nearby bright galaxies, and if such galaxies are spread 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. This view, taken with infrared light, is a false-color image of a quasar-starburst tandem with the most luminous starburst ever seen in such a combination. ...


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 theory predict more nearby small galaxies.


Ultimate fate

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). Potential consequences of this revelation lends credence to the Big Rip, the Big Freeze, and Heat death of the universe theories. For a more detailed discussion of other theories, see the ultimate fate of the universe. This box:      The ultimate fate of the universe is a topic in physical cosmology. ... This article is about the cosmological theory. ... While in the popular mind, eternity often simply means existing for an infinite, i. ... The accelerating universe is the observation that the universe appears to be expanding at an accelerated rate. ... The Big Rip is a cosmological hypothesis about the Ultimate fate of the universe, in which the matter of the universe, from stars and galaxies to atoms and subatomic particles, are progressively torn apart by the expansion of the universe at a certain time in the future. ... scenario in which the universe becomes too cold to sustain life due to continued expansion and the decay of free energy due to the action of entropy. ... The heat death is a possible final state of the universe, in which it has run down to a state of no free energy to sustain motion or life. ... This box:      The ultimate fate of the universe is a topic in physical cosmology. ...


Composition

The currently observable universe appears to have a geometrically flat space-time containing the equivalent mass-energy density of 9.9 × 10-30 grams per cubic centimetre. This mass-energy appears to consist of 73% dark energy, 23% cold dark matter and 4% atoms. Thus the density of atoms is on the order of a single hydrogen nucleus (or atom) for every four cubic meters of volume.[13] The exact nature of dark energy and cold dark matter remain a mystery. In physical cosmology, dark energy is a hypothetical form of energy that permeates all of space and tends to increase the rate of expansion of the universe. ... For other uses, see Dark matter (disambiguation). ...


It is theorized that, during the early phases of the big bang, equal amounts of matter and antimatter were formed. However, through a CP-violation, physical processes resulted in an asymmetry in the amount of matter as compared to anti-matter. This asymmetry explains the amount of residual matter found in the universe today, as nearly all the matter and anti-matter would otherwise have annihilated each other when they came into contact.[14] For other senses of this term, see antimatter (disambiguation). ... CP-symmetry is a symmetry obtained by a combination of the C-symmetry and the P-symmetry. ...


Prior to the formation of the first stars, the chemical composition of the Universe consisted primarily of hydrogen (75% of total mass), with a lesser amount of helium-4 (4He) (24% of total mass) and trace amounts of the isotopes deuterium (2H), helium-3 (3He) and lithium (7Li).[15][16] Subsequently the interstellar medium within galaxies has been steadily enriched by heavier elements. These are introduced as a result of supernova explosions, stellar winds and the expulsion of the outer envelope of evolved stars.[17] This article is about the chemistry of hydrogen. ... Helium-4 is a non-radioactive and light isotope of helium. ... For other uses, see Isotope (disambiguation). ... Deuterium, also called heavy hydrogen, is a stable isotope of hydrogen with a natural abundance in the oceans of Earth of approximately one atom in 6500 of hydrogen (~154 PPM). ... This article is about the chemical element named Lithium. ... The interstellar medium (or ISM) is the name astronomers give to the tenuous gas and dust that pervade interstellar space. ... For other uses, see Supernova (disambiguation). ...


The big bang left behind a background flux of photons and neutrinos. The temperature of the background radiation has steadily decreased as the universe expands, and now primarily consists of microwave energy equivalent to a temperature of 2.725 K.[18] The neutrino background is not observable with present-day technology, but is theorized to have a density of about 150 neutrinos per cubic centimetre.[19] For other uses, see Neutrino (disambiguation). ... For other uses, see Kelvin (disambiguation). ...

See also: Abundance of the chemical elements

The abundance of a chemical element measures how relatively common the element is, or how much of the element there is by comparison to all other elements. ...

Physical structure

Size

The deepest visible-light image of the cosmos, the Hubble Ultra Deep Field.
The deepest visible-light image of the cosmos, the Hubble Ultra Deep Field.
Main article: Observable universe

Very little is known about the size of the universe. It may be trillions of light years across, or even infinite in size. A 2003 paper[20] claims to establish a lower bound of 24 gigaparsecs (78 billion light years) on the size of the universe, but there is no reason to believe that this bound is anywhere near tight. See shape of the Universe for more information. Download high resolution version (900x900, 105 KB)Description: Galaxies, galaxies everywhere - as far as NASAs Hubble Space Telescope can see. ... Download high resolution version (900x900, 105 KB)Description: Galaxies, galaxies everywhere - as far as NASAs Hubble Space Telescope can see. ... This high-resolution image of the HUDF includes galaxies of various ages, sizes, shapes, and colors. ... See universe for a general discussion of the universe. ... One million million (1,000,000,000,000) is the natural number following 999,999,999,999 and preceding 1,000,000,000,001. ... The shape of the Universe is an informal name for a subject of investigation within physical cosmology. ...


The observable (or visible) universe, consisting of all locations that could have affected us since the Big Bang given the finite speed of light, is certainly finite. The comoving distance to the edge of the visible universe is about 46.5 billion light years in all directions from the earth; thus the visible universe may be thought of as a perfect sphere with the Earth at its center and a diameter of about 93 billion light years.[21] Note that many sources have reported a wide variety of incorrect figures for the size of the visible universe, ranging from 13.7 to 180 billion light years. See Observable universe for a list of incorrect figures published in the popular press with explanations of each. The speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning swiftness.[1] It is the speed of all electromagnetic radiation, including visible light, in a vacuum. ... The comoving distance or conformal distance of two objects in the universe is the distance divided by a time-varying scale factor representing the expansion of the universe. ... See universe for a general discussion of the universe. ...


Shape

An important open question of cosmology is the shape of the universe. Mathematically, which 3-manifold best represents the spatial part of the universe? The shape of the Universe is an informal name for a subject of investigation within physical cosmology. ... Astronomy and cosmology examine the universe to understand the large-scale structure of the cosmos. ... On a sphere, the sum of the angles of a triangle is not equal to 180° (see spherical trigonometry). ...


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 the surface of 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.[22] Euclid Euclidean geometry is a mathematical system attributed to the Greek mathematician [[Euclid]] of Alexandria. ... For other uses of this term, see Spacetime (disambiguation). ... Artist depiction of the WMAP satellite at the L2 point The Wilkinson Microwave Anisotropy Probe (WMAP) is a NASA satellite whose mission is to survey the sky to measure the temperature of the radiant heat left over from the Big Bang. ...


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). 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. A geometrical object is called simply connected if it consists of one piece and doesnt have any circle-shaped holes or handles. Higher-dimensional holes are allowed. ... In mathematics, a subset of Euclidean space Rn is called compact if it is closed and bounded. ... For other uses, see Sphere (disambiguation). ... In mathematics, a 3-sphere is a higher-dimensional analogue of a sphere. ...


If the universe were compact and without boundary, it would be possible after traveling a sufficient distance to arrive back where one began. Hence, the light from stars and galaxies could pass through the observable universe more than once. If the universe were multiply-connected and sufficiently small (and of an appropriate, perhaps complex, shape) then conceivably one might be able to see once or several times around it in some (or all) directions. Although this possibility has not been ruled out, the results of the latest cosmic microwave background research make this appear very unlikely. WMAP image of the CMB anisotropy,Cosmic microwave background radiation(June 2003) The cosmic microwave background radiation (CMB) is a form of electromagnetic radiation that fills the whole of the universe. ...


Homogeneity and isotropy

Fluctuations in the microwave background radiation. NASA/WMAP image.

While there is considerable fractalized structure at the local level (arranged in a hierarchy of clustering), on the highest orders of distance the universe is very homogeneous. On these scales the density of the universe is very uniform, and there is no preferred direction or significant asymmetry to the universe. This homogeneity is a requirement of the Friedmann-Lemaître-Robertson-Walker metric employed in modern cosmological models.[23] Image File history File links Size of this preview: 800 × 411 pixelsFull resolution‎ (1,237 × 635 pixels, file size: 1. ... Image File history File links Size of this preview: 800 × 411 pixelsFull resolution‎ (1,237 × 635 pixels, file size: 1. ... // The Friedmann-Lemaître-Robertson-Walker (FLRW) metric is an exact solution of the Einstein field equations of general relativity and which describes a homogeneous, isotropic expanding/contracting universe. ...


The question of anisotropy in the early universe was significantly answered by the Wilkinson Microwave Anisotropy Probe, which looked for fluctuations in the microwave background intensity.[24] The measurements of this anisotropy have provided useful information and constraints about the evolution of the universe. Artist depiction of the WMAP satellite at the L2 point The Wilkinson Microwave Anisotropy Probe (WMAP) is a NASA satellite whose mission is to survey the sky to measure the temperature of the radiant heat left over from the Big Bang. ...


To the limit of the observing power of astronomical instruments, objects radiate and absorb energy according to the same physical laws as they do within our own galaxy.[25] Based on this, it is believed that the same physical laws and constants are universally applicable throughout the observable universe. No confirmed evidence has yet been found to show that physical constants have varied since the big bang, and the possible variation is becoming well constrained.[26] For a list of set rules, see Laws of science. ...


Other terms

Colorized version of the Flammarion woodcut. The original was published in Paris in 1888
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.) Image File history File linksMetadata Universum. ... Image File history File linksMetadata Universum. ... Image and text from page 163 of Latmosphère: météorologie populaire, by Camille Flammarion, 1888. ... This article is about the study of the past in human terms. ... The Ancient and Medieval cosmos as depicted in Peter Apians Cosmographia (Antwerp, 1539). ... Macrocosm and microcosm is an ancient Greek schema of seeing the same patterns reproduced in all levels of reality. ... For the definition of the word microcosm, see here. ...


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".[27] For other uses, see World (disambiguation). ... This article is about Earth as a planet. ... Nicolaus Copernicus (in Latin; Polish Mikołaj Kopernik, German Nikolaus Kopernikus - February 19, 1473 – May 24, 1543) was a Polish astronomer, mathematician and economist who developed a heliocentric (Sun-centered) theory of the solar system in a form detailed enough to make it scientifically useful. ... Layers of Atmosphere - not to scale (NOAA)[1] Outer space, sometimes simply called space, refers to the relatively empty regions of the universe outside the atmospheres of celestial bodies. ...


Notes and references

  1. ^ Mackie, Glen (February 1, 2002). To see the Universe in a Grain of Taranaki Sand. Swinburne University. Retrieved on 2006-12-20.
  2. ^ JSTOR: One Universe or Many?
  3. ^ a b (2004) "Multiverses and physical cosmology". Monthly Notices of the Royal Astronomical Society 347: 921–936. Retrieved on 2007-01-09. 
  4. ^ Luminet, Jean-Pierre; Boudewijn F. Roukema (1999). "Topology of the Universe: Theory and Observations". Proceedings of Cosmology School held at Cargese, Corsica, August 1998. Retrieved on 2007-01-05. 
  5. ^ Luminet, Jean-Pierre; J. Weeks, A. Riazuelo, R. Lehoucq, J.-P. Uzan (2003). "Dodecahedral space topology as an explanation for weak wide-angle temperature correlations in the cosmic microwave background". Nature 425: 593. Retrieved on 2007-01-09. 
  6. ^ Britt, Robert Roy (2003-01-03). Age of Universe Revised, Again. space.com. Retrieved on 2007-01-08.
  7. ^ Wright, Edward L (2005). Age of the Universe. UCLA. Retrieved on 2007-01-08.
  8. ^ Krauss, Lawrence M.; Brian Chaboyer (3 January 2003). "Age Estimates of Globular Clusters in the Milky Way: Constraints on Cosmology". Science 299 (5603): 65-69. American Association for the Advancement of Science. Retrieved on 2007-01-08. 
  9. ^ Heavy Ion Collisions. Brookhaven National Laboratory.
  10. ^ Thomas Ludlam, Larry McLerran (October 2003). What Have We Learned From the Relativistic Heavy Ion Collider?. Physics Today. Retrieved on 2007-01-10.
  11. ^ [Tan] (2007-01-15). New 'Hobbit' Galaxies Discovered Around Milky Way. space.com. Retrieved on 2007-03-01.
  12. ^ Dwarf Spheroidal Galaxies. The Uppsala Astronomical Observatory. Retrieved on 2007-03-01.
  13. ^ Hinshaw, Gary (February 10, 2006). What is the Universe Made Of?. NASA WMAP. Retrieved on 2007-01-04.
  14. ^ Antimatter. Particle Physics and Astronomy Research Council (October 28, 2003). Retrieved on 2006-08-10.
  15. ^ Wright, Edward L. (September 12, 2004). Big Bang Nucleosynthesis. UCLA. Retrieved on 2007-01-05.
  16. ^ M. Harwit, M. Spaans (2003). "Chemical Composition of the Early Universe". The Astrophysical Journal 589 (1): 53-57. 
  17. ^ C. Kobulnicky, E. D. Skillman (1997). "Chemical Composition of the Early Universe". Bulletin of the American Astronomical Society 29: 1329. 
  18. ^ Hinshaw, Gary (December 15, 2005). Tests of the Big Bang: The CMB. NASA WMAP. Retrieved on 2007-01-09.
  19. ^ Dumé, Belle (June 16, 2005). Background neutrinos join the limelight. Institute of Physics Publishing. Retrieved on 2007-01-09.
  20. ^ Neil J. Cornish, David N. Spergel, Glenn D. Starkman, and Eiichiro Komatsu, Constraining the Topology of the Universe. astro-ph/0310233
  21. ^ Lineweaver, Charles; Tamara M. Davis (2005). Misconceptions about the Big Bang. Scientific American. Retrieved on 2007-03-05.
  22. ^ http://map.gsfc.nasa.gov/m_mm/mr_content.html
  23. ^ N. Mandolesi, P. Calzolari, S. Cortiglioni, F. Delpino, G. Sironi (1986). "Large-scale homogeneity of the Universe measured by the microwave background". Letters to Nature 319: 751-753. 
  24. ^ Hinshaw, Gary (November 29, 2006). New Three Year Results on the Oldest Light in the Universe. NASA WMAP. Retrieved on 2006-08-10.
  25. ^ Strobel, Nick (May 23, 2001). The Composition of Stars. Astronomy Notes. Retrieved on 2007-01-04.
  26. ^ Have physical constants changed with time?. Astrophysics (Astronomy Frequently Asked Questions). Retrieved on 2007-01-04.
  27. ^ Albert Einstein (1952). Relativity: The Special and the General Theory (Fifteenth Edition), ISBN 0-517-88441-0.

is the 32nd day of the year in the Gregorian calendar. ... Also see: 2002 (number). ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 354th day of the year (355th in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 9th day of the year in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 5th day of the year in the Gregorian calendar. ... This article is about the physical universe. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 9th day of the year in the Gregorian calendar. ... Year 2003 (MMIII) was a common year starting on Wednesday of the Gregorian calendar. ... is the 3rd day of the year in the Gregorian calendar. ... Space. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 8th day of the year in the Gregorian calendar. ... Binomial name Ucla xenogrammus Holleman, 1993 The largemouth triplefin, Ucla xenogrammus, is a fish of the family Tripterygiidae and only member of the genus Ucla, found in the Pacific Ocean from Viet Nam, the Philippines, Palau and the Caroline Islands to Papua New Guinea, Australia (including Christmas Island), and the... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 8th day of the year in the Gregorian calendar. ... is the 3rd day of the year in the Gregorian calendar. ... Year 2003 (MMIII) was a common year starting on Wednesday of the Gregorian calendar. ... Science is the journal of the American Association for the Advancement of Science (AAAS). ... The American Association for the Advancement of Science (AAAS) is an organization that promotes cooperation between scientists, defends scientific freedom, encourages scientific responsibility and supports scientific education for the betterment of all humanity. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 8th day of the year in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 10th day of the year in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 15th day of the year in the Gregorian calendar. ... Space. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 60th day of the year (61st in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 60th day of the year (61st in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 4th day of the year in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 222nd day of the year (223rd in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 5th day of the year in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 9th day of the year in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 9th day of the year in the Gregorian calendar. ... Scientific American is a popular-science magazine, published (first weekly and later monthly) since August 28, 1845, making it the oldest continuously published magazine in the United States. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... This article is about the day. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 222nd day of the year (223rd in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 4th day of the year in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 4th day of the year in the Gregorian calendar. ... “Einstein” redirects here. ...

See also

In physics and cosmology, the anthropic principle states that we should take into account the constraints that our existence as observers imposes on the sort of universe that we could observe. ... For other uses, see Big Bang (disambiguation). ... This article is about the cosmological theory. ... scenario in which the universe becomes too cold to sustain life due to continued expansion and the decay of free energy due to the action of entropy. ... Cosmology, from the Greek: κοσμολογία (cosmologia, κόσμος (cosmos) order + λογια (logia) discourse) is the study of the Universe in its totality, and by extension, humanitys place in it. ... In 1979, Freeman Dyson published a paper in which he argued that in an open universe, it would be possible for an intelligent being to think an infinite number of thoughts. ... Esoteric cosmology is cosmology that is an intrinsic part of an esoteric or occult system of thought. ... A false vacuum is a metastable sector of a quantum field theory which appears to be a perturbative vacuum but is unstable to instanton effects which tunnel to a lower energy state. ... The final anthropic principle (FAP) is defined by physicists John D. Barrow and Frank J. Tiplers 1986 book The Anthropic Cosmological Principle as a generalization of the anthropic principle as follows: Final anthropic principle (FAP): Intelligent information-processing must come into existence in the Universe, and, once it comes... The deepest visible-light image of the cosmos. ... For other uses, see Gaia. ... The heat death is a possible final state of the universe, in which it has run down to a state of no free energy to sustain motion or life. ... According to Hindu Philosophy, the universe (or multiverse) never came to be at some particular point, but always has been, always will be, but is perpetually in flux. ... Kardashev scale projections ranging from 1900 to 2100. ... A multiverse (or meta-universe) is the hypothetical set of multiple possible universes (including our universe) that together comprise all of physical reality. ... A few religious cosmologies involve ideas such as cyclic universes which can be interpreted as multiverses. ... Omega point is a term invented by French Jesuit Pierre Teilhard de Chardin to describe the ultimate maximum level of complexity-consciousness, considered by him the aim towards which consciousness evolves. ... For the definition, see Life. ... The Rare Earth hypothesis is a hypothesis in planetary astronomy and astrobiology which argues that the emergence of complex multicellular life (metazoa) on Earth required an extremely unlikely combination of astrophysical and geological events and circumstances. ... For other uses, see Reality (disambiguation). ... The shape of the Universe is an informal name for a subject of investigation within physical cosmology. ... This box:      The ultimate fate of the universe is a topic in physical cosmology. ... A world view (or worldview) is a term calqued from the German word Weltanschauung (pronounced ) Welt is the German word for world, and Anschauung is the German word for view or outlook. It implies a concept fundamental to German philosophy and epistemology and refers to a wide world perception. ...

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