Physical cosmology

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 Expanding universe Redshift · Hubble's law Metric expansion of space Friedmann equations FLRW metric Structure formation Shape of the universe Structure formation Galaxy formation Large-scale structure Components Lambda-CDM model Dark energy · Dark matter History Timeline of cosmology... Experiments Observational cosmology 2dF · SDSS COBE · BOOMERanG · WMAP Scientists Einstein · Hawking · Friedman · Lemaître · Hubble · Penzias · Wilson · Gamow · Dicke · Zel'dovich · Mather · Smoot· others

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Graphical timeline of the Big Bang

This timeline of the Big Bang describes the events according to the scientific theory of the Big Bang, using the cosmological time parameter of comoving coordinates. This article is about the physics subject. ... For other uses, see Universe (disambiguation). ... For other uses, see Big Bang (disambiguation). ... This box:      This article is about scientific estimates of the age of the universe. ... 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. ... This box:      Hubbles law is a statement in physical cosmology which states that the redshift in light coming from distant galaxies is proportional to their distance. ... This box:      The metric expansion of space is a key part of sciences current understanding of the universe, whereby spacetime itself is described by a metric which changes over time in such a way that the spatial dimensions grow or stretch as the universe gets older. ... 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. ... Image File history File links Timeline_icon. ... This timeline of the Big Bang shows the sequence of events as predicted by the Big Bang theory, from the beginning of the Planck Epoch to the end of the Epoch of Nucleosynthesis (and beginning of the Epoch of Galaxies). ... In mathematics, theory is used informally to refer to a body of knowledge about mathematics. ... For other uses, see Big Bang (disambiguation). ... 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. ...

Observations suggest that the universe as we know it began around 13.7 billion years ago. Since then, the evolution of the universe has passed through three phases. The very early universe, which is still poorly understood, was the split second in which the universe was so hot that particles had energies higher than those currently accessible in particle accelerators on Earth. Therefore, while the basic features of this epoch have been worked out in the big bang theory, the details are largely based on educated guesses. Helium atom (schematic) Showing two protons (red), two neutrons (green) and two electrons (yellow). ... For the DC Comics Superhero also called Atom Smasher, see Albert Rothstein. ...

Following this period, in the early universe, the evolution of the universe proceeded according to known high energy physics. This is when the first protons, electrons and neutrons formed, then nuclei and finally atoms. With the formation of neutral hydrogen, the cosmic microwave background was emitted. Particle physics is a branch of physics that studies the elementary constituents of matter and radiation, and the interactions between them. ... For alternative meanings see proton (disambiguation). ... Properties The electron (also called negatron, commonly represented as e−) is a subatomic particle. ... Properties In physics, the neutron is a subatomic particle with no net electric charge and a mass of 940 MeV/c² (1. ... Plural: nuclei In chemistry and physics, the nucleus (atomic nucleus) is the collection of protons and neutrons in the center of an atom that carries the bulk of the atoms mass and positive charge. ... Properties For alternative meanings see atom (disambiguation). ... 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. ...

Then matter started to aggregate into the first stars and quasars, and ultimately galaxies, clusters of galaxies and superclusters formed. There are several alternative theories about the ultimate fate of the universe. This article is about the astronomical object. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... 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. ... This box:      The ultimate fate of the universe is a topic in physical cosmology. ...

The very early universe

All ideas concerning the very early universe (cosmogony) are necessarily speculative. As of today no accelerator experiments probe energies of sufficient magnitude to provide any insight into the period. All proposed scenarios differ radically, some examples being: the Hartle-Hawking initial state, string landscape, brane inflation, string gas cosmology, and the ekpyrotic universe. Some of these are mutually compatible, while others are not. To meet Wikipedias quality standards, this article or section may require cleanup. ... In theoretical physics, the Hartle-Hawking state, named after James Hartle and Stephen Hawking, is a hypothetical vector in the Hilbert space of a theory of quantum gravity that describes the wave function of the Universe. ... The string landscape is an idea to implement the anthropic principle, in particular Steven Weinbergs proposal for anthropic selection of the vacuum density, in string theory. ... 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. ... The ekpyrotic universe or ekpyrotic scenario is a cosmological theory of the origin of the universe. ...

Augustinian era

Before the Big Bang

In 1952, George Gamow, one of the founding fathers of Big Bang cosmology, proposed that the period before the Big Bang be called the Augustinian era,^[1] after the philosopher Saint Augustine, who believed time was solely a property of the God-created Universe, so that there was no time prior to the creation of the universe. The phrase "Augustinian Era" is meant to convey the idea that the known laws of physics break down in a gravitational singularity of infinite density at the time zero of the Big Bang, so that according to the theory of general relativity there were no times prior to that point. However, physicists believe that general relativity becomes incompatible with quantum mechanics at the Planck scale, so that the predictions of general relativity cannot be trusted before the Planck era when energies and temperatures reached the Planck scale, and that we need a theory of quantum gravity before we can say anything about times before the Planck era.^[2] 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. ... St. ... A gravitational singularity (sometimes spacetime singularity) is, approximately, a place where quantities which are used to measure the gravitational field become infinite. ... Look up zero in Wiktionary, the free dictionary. ... For a generally accessible and less technical introduction to the topic, see Introduction to general relativity. ... For a generally accessible and less technical introduction to the topic, see Introduction to quantum mechanics. ... In physics, Planck units are physical units of measurement originally proposed by Max Planck. ... Named after Max Planck, in cosmology the Planck epoch is the earliest period of time in the history of the universe, from zero to 10-43 seconds (one Planck time), during which all four fundamental forces were unified and elementary particles did not exist. ... Quantum gravity is the field of theoretical physics attempting to unify quantum mechanics, which describes three of the fundamental forces of nature, with general relativity, the theory of the fourth fundamental force: gravity. ...

The Planck epoch

Up to 10^-43 seconds after the Big Bang

Main article: Planck epoch

If supersymmetry is correct, then during this time the four fundamental forces — electromagnetism, weak nuclear force, strong nuclear force and gravity — all have the same strength, so they are possibly unified into one fundamental force. Little is known about this epoch, although different theories propose different scenarios. Einstein's theory of general relativity proposes a gravitational singularity before this time, but under these conditions the theory is expected to break down due to quantum effects. Physicists hope that proposed theories of quantum gravity, such as string theory and loop quantum gravity, will eventually lead to a better understanding of this epoch. Named after Max Planck, in cosmology the Planck epoch (or Planck Era) is the earliest period of time in the history of the universe, from zero to 10-43 seconds (one Planck time), during which all four fundamental forces were unified and elementary particles did not yet exist. ... This article or section is in need of attention from an expert on the subject. ... Electromagnetism is the physics of the electromagnetic field: a field which exerts a force on particles that possess the property of electric charge, and is in turn affected by the presence and motion of those particles. ... The weak nuclear force or weak interaction is one of the four fundamental forces of nature. ... The strong nuclear force or strong interaction (also called color force or colour force) is a fundamental force of nature which affects only quarks and antiquarks, and is mediated by gluons in a similar fashion to how the electromagnetic force is mediated by photons. ... Gravity is a force of attraction that acts between bodies that have mass. ... For a generally accessible and less technical introduction to the topic, see Introduction to general relativity. ... A gravitational singularity (sometimes spacetime singularity) is, approximately, a place where quantities which are used to measure the gravitational field become infinite. ... For a generally accessible and less technical introduction to the topic, see Introduction to quantum mechanics. ... Quantum gravity is the field of theoretical physics attempting to unify quantum mechanics, which describes three of the fundamental forces of nature, with general relativity, the theory of the fourth fundamental force: gravity. ... This box:      String theory is a still developing mathematical approach to theoretical physics, whose original building blocks are one-dimensional extended objects called strings. ... Loop quantum gravity (LQG), also known as loop gravity and quantum geometry, is a proposed quantum theory of spacetime which attempts to reconcile the seemingly incompatible theories of quantum mechanics and general relativity. ...

The grand unification epoch

Between 10^-43 seconds and 10^-36 seconds after the Big Bang ^[3]

Main article: Grand unification epoch

As the universe expands and cools from the Planck epoch, gravity begins to separate from the fundamental gauge interactions: electromagnetism and the strong and weak nuclear forces. Physics at this scale may be described by a grand unified theory in which the gauge group of the Standard Model is embedded in a much larger group, which is broken to produce the observed forces of nature. Eventually, the grand unification is broken as the strong nuclear force separates from the electroweak force. This occurs as soon as inflation does. According to some theories, this should produce magnetic monopoles. In cosmology, assuming that nature is described by a GUT, the grand unification epoch was an era very, very soon after the Big Bang in which the temperature was comparable to the characteristic temperatures of grand unified theories. ... This box:      The metric expansion of space is a key part of sciences current understanding of the universe, whereby spacetime itself is described by a metric which changes over time in such a way that the spatial dimensions grow or stretch as the universe gets older. ... In physics, gauge theories are a class of physical theories based on the idea that symmetry transformations can be performed locally as well as globally. ... Gauge theories are a class of physical theories based on the idea that symmetry transformations can be performed locally as well as globally. ... The Standard Model of Fundamental Particles and Interactions For the Standard Model in Cryptography, see Standard Model (cryptography). ... In physics, the electroweak theory presents a unified description of two of the four fundamental forces of nature: electromagnetism and the weak nuclear force. ... In physics, magnetic monopole is a term describing a hypothetical particle that could be quickly clarified to a person familiar with magnets but not electromagnetic theory as a magnet with only one pole. In more accurate terms, it would have net magnetic charge. Interest in the concept stems from particle...

The electroweak epoch

Between 10^-36 seconds and 10^-12 seconds after the Big Bang^[4]

Main article: Electroweak epoch

The temperature of the universe is low enough (10²⁸K) to separate the strong force from the electroweak force (the name for the unified forces of electromagnetism and the weak interaction). This phase transition triggers a period of exponential expansion known as cosmic inflation. After inflation ends, particle interactions are still energetic enough to create large numbers of exotic particles, including W and Z bosons and Higgs bosons. In physical cosmology the electroweak epoch was the period in the evolution of the early universe when the temperature of the universe was high enough to merge electromagnetism and the weak interaction into a single electroweak interaction (> 100 GeV). ... Electromagnetism is the physics of the electromagnetic field: a field which exerts a force on particles that possess the property of electric charge, and is in turn affected by the presence and motion of those particles. ... The weak interaction (often called the weak force or sometimes the weak nuclear force) is one of the four fundamental interactions of nature. ... 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. ... In physics, the W and Z bosons are the elementary particles that mediate the weak nuclear force. ... The Higgs boson, also known as the God particle, is a hypothetical massive scalar elementary particle predicted to exist by the Standard Model of particle physics. ...

The inflationary epoch

Between 10^-36 seconds and 10^-32 seconds after the Big Bang

Main article: Inflationary epoch

The temperature, and therefore the time, at which cosmic inflation occurs is not known for certain. During inflation, the universe is flattened (its curvature is critical) and the universe enters a homogeneous and isotropic rapidly expanding phase in which the seeds of structure formation are laid down in the form of a primordial spectrum of nearly-scale-invariant fluctuations. Some energy from photons becomes virtual quarks and hyperons, but these particles decay quickly. One scenario suggests that prior to cosmic inflation, the universe was cold and empty, and the immense heat and energy associated with the early stages of the big bang was created through the phase change associated with the end of inflation. The inflationary epoch is the term used in cosmology to describe the brief time in the very early universe when, according to inflation theory, the universe was expanding exponentially. ... 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. ... The shape of the Universe is an informal name for a subject of investigation within physical cosmology. ... Isotropic means independent of direction. Isotropic radiation has the same intensity regardless of the direction of measurement, and an isotropic field exerts the same action regardless of how the test particle is oriented. ... In physics, scale invariance is the feature of physical objects of laws that do not change if the space is magnified, i. ... In physics, a virtual particle is a particle which exists for such a short time and space that its energy and momentum do not have to obey the usual relationship. ... For other uses, see Quark (disambiguation). ... In particle physics, a hyperon is any subatomic particle which is a baryon (and hence a hadron and a fermion) with non-zero strangeness, but with zero charm and zero bottomness. ...

Reheating

During reheating, the exponential expansion that occurred during inflation ceases and the potential energy of the inflaton field decays into a hot, relativistic plasma of particles. If grand unification is a feature of our universe, then cosmic inflation must occur during or after the grand unification symmetry is broken, otherwise magnetic monopoles would be seen in the visible universe. At this point, the universe is dominated by radiation; quarks, electrons and neutrinos form. The inflaton is the generic name of the unidentified scalar field (and its associated particle), that may be responsible for an episode of inflation in the very early universe. ... For other uses, see Plasma. ... Promotional picture Symmetry Breaking is a rock band from Northern New Jersey, in the United States. ... For other uses, see Electron (disambiguation). ... For other uses, see Neutrino (disambiguation). ...

Baryogenesis

Main article: Baryogenesis

No known physics can explain the fact that there are so many more baryons in the universe than antibaryons. In order for this to be explained, the Sakharov conditions must be met at some time after inflation. There are hints that this is possible in known physics and from studying grand unified theories, but the full picture is not known. Baryogenesis is the generic designation for the physical processes that generate matter (more specifically, a class of fundamental particle called baryon) from an otherwise matter-empty state (such as it is generally believed to be the state of the Universe at its onset, the so-called Big Bang). ... Combinations of three u, d or s-quarks with a total spin of 3/2 form the so-called baryon decuplet. ... For other senses of this term, see antimatter (disambiguation). ... Baryogenesis is the generic designation for the hypothetical physical processes that generated an asymmetry between baryons and anti-baryons in the very early universe. ...

The early universe

After cosmic inflation ends, the universe is filled with a quark-gluon plasma. From this point onwards the physics of the early universe is better understood, and less speculative. A QGP is formed at the collision point of two relativistically accelerated gold ions in the center of the STAR detector at the relativistic heavy ion collider at the Brookhaven national laboratory. ...

Supersymmetry breaking

Main article: Supersymmetry breaking

If supersymmetry is a property of our universe, then it must be broken at an energy as low as 1 TeV, the electroweak symmetry scale. The masses of particles and their superpartners would then no longer be equal, which could explain why no superpartners of known particles have ever been observed. In particle physics, supersymmetry breaking is the process to obtain a seemingly non-supersymmetric physics from a supersymmetric theory which is a necessary step to reconcile supersymmetry with actual experiments. ... This article or section is in need of attention from an expert on the subject. ... A TeV is a teraelectronvolt, i. ... In supersymmetry, it is proposed that every fermion should have a partner boson, known as its Superpartner. ...

The quark epoch

Between 10^-12 seconds and 10^-6 seconds after the Big Bang

Main article: Quark epoch

In electroweak symmetry breaking, at the end of the electroweak epoch, all the fundamental particles are believed to acquire a mass via the Higgs mechanism in which the Higgs boson acquires a vacuum expectation value. The fundamental interactions of gravitation, electromagnetism, the strong interaction and the weak interaction have now taken their present forms, but the temperature of the universe is still too high to allow quarks to bind together to form hadrons. In physical cosmology the quark epoch was the period in the evolution of the early universe when the fundamental interactions of gravitation, electromagnetism, the strong interaction and the weak interaction had taken their present forms, but the temperature of the universe was still too high to allow quarks to bind... This box:      The Higgs mechanism, also called the Brout-Englert-Higgs mechanism, Higgs-Kibble mechanism or Anderson-Higgs mechanism, was proposed in 1964 by Robert Brout and Francois Englert [1], independently by Peter Higgs [2] and by Gerald Guralnik, C. R. Hagen, and Tom Kibble [3] following earlier work by... The Higgs boson, also known as the God particle, is a hypothetical massive scalar elementary particle predicted to exist by the Standard Model of particle physics. ... In quantum field theory the vacuum expectation value (also called condensate) of an operator is its average, expected value in the vacuum. ... A fundamental interaction is a mechanism by which particles interact with each other, and which cannot be explained by another more fundamental interaction. ... Gravity redirects here. ... Electromagnetism is the physics of the electromagnetic field: a field which exerts a force on particles that possess the property of electric charge, and is in turn affected by the presence and motion of those particles. ... The strong interaction or strong force is today understood to represent the interactions between quarks and gluons as detailed by the theory of quantum chromodynamics (QCD). ... The weak interaction (often called the weak force or sometimes the weak nuclear force) is one of the four fundamental interactions of nature. ...

The hadron epoch

Between 10^-6 seconds and 1 second after the Big Bang

Main article: Hadron epoch

The quark-gluon plasma which composes the universe cools until hadrons, including baryons such as protons and neutrons, can form. At approximately 1 second after the Big Bang neutrinos decouple and begin travelling freely through space. This cosmic neutrino background, while unlikely to ever be observed in detail, is analogous to the cosmic microwave background that was emitted much later. (See above regarding the quark-gluon plasma, under the String Theory epoch) In physical cosmology, the hadron epoch was the period in the evolution of the early universe during which the mass of the Universe was dominated by hadrons. ... A hadron, in particle physics, is a subatomic particle which experiences the nuclear force. ... For other uses, see Proton (disambiguation). ... This article or section does not adequately cite its references or sources. ... For other uses, see Neutrino (disambiguation). ... The Cosmic Neutrino Background (CNB) is the background particle radiation composed of neutrinos. ... 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. ...

The lepton epoch

Between 1 second and 3 minutes after the Big Bang

Main article: Lepton epoch

The majority of hadrons and anti-hadrons annihilate each other at the end of the hadron epoch, leaving leptons and anti-leptons dominating the mass of the universe. Approximately 3 seconds after the Big Bang the temperature of the universe falls to the point where new lepton/anti-lepton pairs are no longer created and most leptons and anti-leptons are eliminated in annihilation reactions, leaving a small residue of leptons. In physical cosmology, the lepton epoch was the period in the evolution of the early universe in which the leptons dominated the mass of the universe. ... In physics, a lepton is a particle with spin-1/2 (a fermion) that does not experience the strong interaction (that is, the strong nuclear force). ... For other uses, see Annihilation (disambiguation). ...

The photon epoch

Between 3 minutes and 380,000 years after the Big Bang

Main article: Photon epoch

After most leptons and anti-leptons are annihilated at the end of the lepton epoch the energy of the universe is dominated by photons. These photons are still interacting frequently with charged protons, electrons and (eventually) nuclei, and continue to do so for the next 300,000 years. In physical cosmology, the photon epoch was the period in the evolution of the early universe in which photons dominated the energy of the universe. ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ... The nucleus of an atom is the very small dense region, of positive charge, in its centre consisting of nucleons (protons and neutrons). ...

Nucleosynthesis

Between 3 minutes and 20 minutes after the Big Bang^[5]

Main article: Big Bang nucleosynthesis

During the photon epoch the temperature of the universe falls to the point where atomic nuclei can begin to form. Protons (hydrogen ions) and neutrons begin to combine into atomic nuclei in the process of nuclear fusion. However, nucleosynthesis only lasts for about seventeen minutes, after which time the temperature and density of the universe has fallen to the point where nuclear fusion cannot continue. At this time, there is about three times more hydrogen than helium-4 (by mass) and only trace quantities of other nuclei. 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. ... The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing sustainable fusion power. ...

Matter domination: 70,000 years

At this time, the densities of non-relativistic matter (atomic nuclei) and relativistic radiation (photons) are equal. The Jeans length, which determines the smallest structures that can form (due to competition between gravitational attraction and pressure effects), begins to fall and perturbations, instead of being wiped out by radiation free-streaming, can begin to grow in amplitude. The Jeans Length is the oscillation wavelength below which stable oscillations rather than gravitational collapse will occur. ...

Recombination: 240,000-310,000 years

See also: Cosmic microwave background

WMAP data shows the microwave background radiation variations throughout the Universe from our perspective, though the actual variations are much smoother than the diagram suggests

Hydrogen and helium atoms begin to form and the density of the universe falls. This is thought to have occurred somewhere between 240,000 and 310,000 years after the Big Bang.^[6] During recombination decoupling occurs, causing the photons to evolve independently from the matter. Most importantly, this means that the photons that compose the cosmic microwave background are a picture of the universe during this epoch. 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. ... 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. ... 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. ...

Dark ages

See also: 21 centimeter radiation

Before decoupling occurs most of the photons in the universe are interacting with electrons and protons in the photon-baryon fluid. The universe is opaque or "foggy" as a result. There is light but not light we could observe through telescopes. The baryonic matter in the universe consisted of ionized plasma, and it only became neutral when it gained free electrons during "recombination," thereby releasing the photons creating the CMB. When the photons were released (or decoupled) the universe became transparent. At this point the only radiation emitted is the 21 cm spin line of neutral hydrogen. There is currently an observational effort underway to detect this faint radiation, as it is in principle an even more powerful tool than the cosmic microwave background for studying the early universe. 21 centimeter radiation is radiation produced during a hyperfine transition of neutral hydrogen from the triplet to the singlet state. ... This article or section does not adequately cite its references or sources. ...

Structure formation

See also: Large-scale structure of the cosmos and Structure formation

The Hubble Ultra Deep Fields often showcase galaxies from an ancient era that tell us what the early Stelliferous Age was like.

Another Hubble image shows an infant galaxy forming nearby, which means this happened very recently on the cosmological timescale. This is evidence that the Universe is not quite finished with galaxy formation yet.

Structure formation in the big bang model proceeds hierarchically, with smaller structures forming before larger ones. The first structures to form are quasars, which are thought to be bright, early active galaxies, and population III stars. Before this epoch, the evolution of the universe could be understood through linear cosmological perturbation theory: that is, all structures could be understood as small deviations from a perfect homogeneous universe. This is computationally relatively easy to study. At this point non-linear structures begin to form, and the computational problem becomes much more difficult, involving, for example, N-body simulations with billions of particles. Astronomy and cosmology examine the universe to understand the large-scale structure of the cosmos. ... It has been suggested that this article or section be merged into Large-scale structure of the cosmos. ... 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. ... Download high resolution version (981x961, 621 KB)Image from Hubble of I Zwicky 18: a baby galaxy in a grown-up Universe SOURCE: http://hubblesite. ... Download high resolution version (981x961, 621 KB)Image from Hubble of I Zwicky 18: a baby galaxy in a grown-up Universe SOURCE: http://hubblesite. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... An active galaxy is a galaxy where a significant fraction of the energy output is not emitted by the normal components of a galaxy: stars, dust and interstellar gas. ... Population III stars are a hypothetical population of extremely massive stars that are believed to have been formed in the early universe. ... Perturbation theory comprises mathematical methods that are used to find an approximate solution to a problem which cannot be solved exactly, by starting from the exact solution of a related problem. ... The n-body problem is the problem of finding, given the initial positions, masses, and velocities of n bodies, their subsequent motions as determined by classical mechanics, i. ...

Reionization

See also: Reionization and 21 centimeter radiation

The first quasars form from gravitational collapse. The intense radiation they emit reionizes the surrounding universe. From this point on, most of the universe is composed of plasma. Schematic timeline of the universe, depicting reionizations place in cosmic history. ... 21 centimeter radiation is radiation produced during a hyperfine transition of neutral hydrogen from the triplet to the singlet state. ... For other uses, see Plasma. ...

Formation of stars

See also: Star formation

The first stars, most likely Population III stars, form and start the process of turning the light elements that were formed in the Big Bang (hydrogen, helium and lithium) into heavier elements. However, as of yet there have been no observed Population III stars which leaves star formation a mystery.^[7] Star formation is the process by which dense parts of molecular clouds collapse into a ball of plasma to form a star. ... Population III stars are a hypothetical population of extremely massive stars that are believed to have been formed in the early universe. ... Population III stars are a hypothetical population of extremely massive stars that are believed to have been formed in the early universe. ...

Formation of galaxies

See also: Galaxy formation

Large volumes of matter collapse to form a galaxy. Population II stars are formed early on in this process, with Population I stars formed later. Recent research conducted by the Galaxy Zoo project suggests that galaxies have a parity violation, with a greater number rotating anticlockwise when seen from Earth^[8]. In astrophysics, the questions of galaxy formation and evolution are: How, from a homogeneous universe, did we obtain the very inhomogeneous one we live in? How did galaxies form? How do galaxies change over time? The formation of galaxies is still one of the most active research areas in astrophysics... Stars can be grouped into two general types called Population I and Population II. The criteria for classification include space velocity, location in the galaxy, age, chemical composition, and differences in distribution on the Hertzsprung-Russell diagram. ... Stars can be grouped into two general types called Population I and Population II. The criteria for classification include space velocity, location in the galaxy, age, chemical composition, and differences in distribution on the Hertzsprung-Russell diagram. ... Galaxy Zoo is an online project which invites members of the public to assist in classifying over a million galaxies. ... In physics, a parity transformation (also called parity) is the simultaneous flip in the sign of all spatial coordinates: A 3×3 matrix representation of P would have determinant equal to -1, and hence cannot reduce to a rotation. ...

Johannes Schedler's project has identified a quasar CFHQS 1641+3755 at 12.7 billion light-years away^[9], when the Universe was just 7 percent of its present age.

On July 11, 2007, using the 10 metre Keck II telescope on Mauna Kea, Richard Ellis of the California Institute of Technology at Pasadena and his team found six star forming galaxies about 13.2 billion light years away and therefore created when the universe was only 500 million years old ^[10]. Only about 10 of these really early objects are currently known ^[11]

The Hubble Ultra Deep Field shows a number of small galaxies merging to form larger ones, at 13 billion light years, when the Universe was only 5% its current age^[12]. This high-resolution image of the HUDF includes galaxies of various ages, sizes, shapes, and colors. ...

Based upon the emerging science of nucleocosmochronology, the Galactic thin disk of the Milky Way is estimated to have been formed 8.3 ± 1.8 billion years ago^[13]. Nucleocosmochronology is the study of the evolution of the Universe with respect to the four fundamental processes of Nucleosynthesis. ...

Formation of groups, clusters and superclusters

See also: Large-scale structure of the cosmos

Gravitational attraction pulls galaxies towards each other to form groups, clusters and superclusters. Astronomy and cosmology examine the universe to understand the large-scale structure of the cosmos. ...

Formation of our solar system: 8 billion years

See also: Solar system

Finally, objects on the scale of our solar system form. Our sun is a late-generation star, incorporating the debris from many generations of earlier stars, and formed roughly 5 billion years ago, or roughly 8 to 9 billion years after the big bang. This article is about the Solar System. ...

Today: 13.7 billion years

The best current data estimates the age of the universe today as 13.7 billion years since the big bang. Since the expansion of the universe appears to be accelerating, superclusters are likely to be the largest structures that will ever form in the universe. The present accelerated expansion prevents any more inflationary structures entering the horizon and prevents new gravitationally bound structures from forming. This box:      This article is about scientific estimates of the age of the universe. ... Superclusters are large groups of smaller galaxy groups and clusters, and are among the largest structures of the cosmos. ...

Ultimate fate of the universe

Main article: Ultimate fate of the universe

As with interpretations of what happened in the very early universe, advances in fundamental physics are required before it will be possible to know the ultimate fate of the universe with any certainty. Below are some of the main possibilities. This box:      The ultimate fate of the universe is a topic in physical cosmology. ...

Heat death: 1-100 trillion years

See also: Heat death

This scenario is generally considered to be the most likely, as it occurs if the universe continues expanding as it has been. Over a time scale on the order of a trillion years, existing stars burn out, and the main universe goes dark. The universe approaches a highly entropic state. Over a much longer time scale in the eras following this, galaxies collapse into black holes which subsequently evaporate via Hawking radiation. In some grand-unification theories, proton decay will convert the remaining interstellar gas into positrons and electrons, which then recombine into photons. In this case, the universe will indefinitely consist solely of a bath of uniform radiation, which is slowly redshifted to lower and lower energy, thus freezing it. The heat death is a possible final state of the universe, in which it has reached maximum entropy. ... For other uses, see: information entropy (in information theory) and entropy (disambiguation). ... In physics, Hawking radiation (also known as Bekenstein-Hawking radiation) is a thermal radiation thought to be emitted by black holes due to quantum effects. ...

Big crunch: 100 billion years to ?? years

See also: Big Crunch

If the energy density of dark energy were negative or the universe were closed, then it would be possible that the expansion of the universe would reverse and the universe would contract towards a hot, dense state. This would be analogous to a time-reversal of the big bang. This is often proposed as part of an oscillatory universe scenario, such as the cyclic model. Current observations suggest that this model of the universe is unlikely to be correct, and the expansion will continue. This article is about the cosmological theory. ... 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. ... The shape of the Universe is an informal name for a subject of investigation within physical cosmology. ... For other uses, see Big Bang (disambiguation). ... The oscillatory universe is a cosmological model, originally derived by Alexander Friedman in 1922 and developed by Richard Tolman from 1934, in which the universe undergoes a series of oscillations, each beginning with a big bang and ending with a big crunch. ... The cyclic model is a brane cosmology model of the creation of the universe, derived from the earlier ekpyrotic model. ...

Big rip

See also: Big Rip

This scenario is possible only if the energy density of dark energy actually increases without limit over time. Such dark energy is called phantom energy and is unlike any known kind of energy (except the energy of virtual particles). In this case, the expansion rate of the universe will increase without limit. Gravitationally bound systems, such as clusters of galaxies, galaxies, and ultimately the solar system will be torn apart. Eventually the expansion will be so rapid as to overcome the electromagnetic forces holding molecules and atoms together. Finally even atomic nuclei will be torn apart and the universe as we know it will end in an unusual kind of gravitational singularity. In other words, the universe will expand so much that the electromagnetic force holding things together will fall to this expansion, making things fall apart. 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. ... 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. ... Phantom energy is a hypothetical form of dark energy with equation of state . ... In physics, a virtual particle is a particle which exists for such a short time and space that its energy and momentum do not have to obey the usual relationship. ... A gravitational singularity (sometimes spacetime singularity) is, approximately, a place where quantities which are used to measure the gravitational field become infinite. ...

Vacuum metastability event

See also: False vacuum

If our universe is in a very long-lived false vacuum, it is possible that the universe will tunnel into a lower energy state. If this happens, all structures will be destroyed instantaneously, without any forewarning. 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. ... 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. ... Quantum tunneling is the quantum-mechanical effect of transitioning through a classically-forbidden energy state. ...

References

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. ...

External links

• PBS Online (2000). From the Big Bang to the End of the Universe - The Mysteries of Deep Space Timeline. Retrieved March 24, 2005.
• Schulman, Eric (1997). The History of the Universe in 200 Words or Less. Retrieved March 24, 2005.
• Space Telescope Science Institute Office of Public Outreach (2005). Home of the Hubble Space Telescope. Retrieved March 24, 2005.
• Fermilab graphics (see "Energy time line from the Big Bang to the present" and "History of the Universe Poster")
• Exploring Time from Planck time to the lifespan of the universe
• Astronomers' first detailed hint of what was going on less than a trillionth of a second after time began
• The Universe Adventure