A pie chart indicating the proportional composition of different energy-density components of the universe. Roughly ninety-five percent is exotic dark matter and dark energy.

Physical Cosmology

Physical Cosmology

Universe · Big Bang Age of the universe Timeline of the Big Bang... Ultimate fate of the Universe Image File history File links Cosmological_composition. ... Image File history File links Cosmological_composition. ... A pie chart is a circular chart divided into sectors, illustrating relative magnitudes or frequencies. ... In astrophysics and cosmology, dark matter is matter, not directly observed and of unknown composition, that does not emit or reflect enough electromagnetic radiation to be detected directly, but whose presence can be inferred from gravitational effects on visible matter. ... In physical cosmology, dark energy is a hypothetical form of energy that permeates all of space and has strong negative pressure. ... Image File history File links Download high resolution version (2198x1274, 1278 KB)WMAP map of CMB anisotropy, from NASA.gov File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Physical cosmology, as a branch of astrophysics, is the study of the large-scale structure of the universe and is concerned with fundamental questions about its formation and evolution. ... Universe is a word derived from the Old French univers, which in turn comes from the Latin roots unus (one) and versus (a form of vertere, to turn). Based on observations of the observable universe, physicists attempt to describe the whole of space-time, including all matter and energy and... According to the Big Bang theory, the universe emerged from an extremely dense and hot state (singularity). ... The age of the universe, according to the Big Bang theory, is the time elapsed between the Big Bang and the present day. ... A graphical timeline is available here: Graphical timeline of the Big Bang This timeline of the Big Bang describes the events that have occurred and will occur according to the scientific theory of the Big Bang, using the cosmological time parameter of comoving coordinates. ... The ultimate fate of the universe is a topic in physical cosmology. ...

Early universe

Inflation · Nucleosynthesis Cosmic microwave background 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. ... In cosmology, the cosmic microwave background radiation (most often abbreviated CMB but occasionally CMBR, CBR or MBR, also referred as relic radiation) is a form of electromagnetic radiation discovered in 1965 that fills the entire universe. ...

Expanding universe

Redshift · Hubble's law Metric expansion of space Friedmann equations · FLRW metric Redshift of spectral lines in the optical spectrum of a supercluster of distant galaxies (right), as compared with that of the Sun (left). ... 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. ...

Structure formation

Shape of the universe Structure formation Galaxy formation Large-scale structure 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. ...

Components

Lambda-CDM model Dark energy · Dark matter In physical cosmology, dark energy is a hypothetical form of energy that permeates all of space and has strong negative pressure. ... In astrophysics and cosmology, dark matter is matter, not directly observed and of unknown composition, that does not emit or reflect enough electromagnetic radiation to be detected directly, but whose presence can be inferred from gravitational effects on visible matter. ...

History

Timeline of cosmology... This lists a timeline of cosmological theories and discoveries. ...

Cosmology experiments

Observational cosmology 2dF · SDSS CoBE · BOOMERanG · WMAP 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 BOOMERanG experiment (Balloon Observations Of Millimetric Extragalactic Radiation and Geophysics) measured the cosmic microwave background radiation (CMB) 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. ...

Scientists

Einstein · Lemaître · Friedman Hubble · Penzias · Wilson Gamow · Dicke · Zel'dovich Mather · Smoot · others Albert Einstein( ) (March 14, 1879 – April 18, 1955) was a German-born theoretical physicist who is widely considered to have been one of the greatest physicists of all time. ... Father Georges-Henri Lemaître (July 17, 1894 – June 20, 1966) was a Belgian Roman Catholic priest, honorary prelate, professor of physics and astronomer. ... Alexander Alexandrovich Friedman or Friedmann (Александр Александрович Фридман) (June 16, 1888 – September 16, 1925) was a Russian cosmologist and mathematician. ... // For the politician, see Edwin N. Hubbell. ... 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 partial list of persons who have made major contributions to the development of standard mainstream Cosmology. ...

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ΛCDM or Lambda-CDM is an abbreviation for Lambda-Cold Dark Matter. It is frequently referred to as the concordance model of big bang cosmology, since it attempts to explain cosmic microwave background observations, as well as large scale structure observations and supernovae observations of the accelerating expansion of the universe. It is the simplest known model that is in general agreement with observed phenomena. According to the Big Bang theory, the universe emerged from an extremely dense and hot state (singularity). ... Physical cosmology, as a branch of astrophysics, is the study of the large-scale structure of the universe and is concerned with fundamental questions about its formation and evolution. ... 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. ... Astronomy and cosmology examine the universe to understand the large-scale structure of the cosmos. ... Multiwavelength X-ray image of the remnant of Keplers Supernova, SN 1604. ... 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. ...

• Λ (Lambda) stands for the cosmological constant which is a dark energy term that allows for the current accelerating expansion of the universe. The cosmological constant is often described in terms of Ω_Λ, the fraction of the energy density of a flat Universe in the form of the cosmological constant. Currently, 0.74, implying 74% of the energy density of the present universe is in this form.

• Cold dark matter is the model where the dark matter is explained as being cold (i.e. not thermalized), non-baryonic, collisionless dust. This component makes up 22% of the energy density of the present universe. The remaining 4% is all of the matter and energy that makes up the atoms and photons that are the building blocks of planets, stars, and gas clouds in the universe.

• The model assumes a nearly scale-invariant spectrum of primordial perturbations and a universe without spatial curvature. It also assumes that it has no observable topology, so that the universe is much larger than the observable particle horizon. These are predictions of cosmic inflation.

These are the simplest assumptions for a consistent, physical model of cosmology. However, ΛCDM is a model. Cosmologists anticipate that all of these assumptions will not be borne out exactly, after more is learned about the applicable fundamental physics. In particular, cosmic inflation predicts spatial curvature at the level of 10⁻⁴ to 10⁻⁵. It would also be surprising if the temperature of dark matter were absolute zero. Moreover, ΛCDM says nothing about the fundamental physical origin of dark matter, dark energy and the nearly scale-invariant spectrum of primordial curvature perturbations: in that sense, it is merely a useful parameterization of ignorance. The cosmological constant (usually denoted by the Greek capital letter lambda: Λ) was proposed by Albert Einstein as part of his theory of general relativity to achieve a stationary universe. ... In physical cosmology, dark energy is a hypothetical form of energy that permeates all of space and has strong negative pressure. ... Cold dark matter (or CDM) is a refinement of the big bang theory, as well as being one possible variation of the more generic Dark Matter theory. ... In astrophysics and cosmology, dark matter is matter, not directly observed and of unknown composition, that does not emit or reflect enough electromagnetic radiation to be detected directly, but whose presence can be inferred from gravitational effects on visible matter. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... In particle physics, the baryons are a family of subatomic particles including the proton and the neutron (collectively called Greek barys, meaning heavy, as they are heavier than the other main groups of particles. ... In physics, scale invariance is the feature of physical objects of laws that do not change if the space is magnified, i. ... Look up perturbation in Wiktionary, the free dictionary. ... The shape of the Universe is an informal name for a subject of investigation within physical cosmology. ... A Möbius strip, a surface with only one side and one edge; such shapes are an object of study in topology. ... It has been suggested that this article or section be merged into Observable universe. ... 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. ... An abstract model (or conceptual model) is a theoretical construct that represents physical, biological or social processes, with a set of variables and a set of logical and quantitative relationships between them. ...

Parameters

The model has six parameters. The Hubble constant determines the rate of expansion of the universe, as well as the critical density for closure of the universe, ρ₀. Densities for baryons, dark matter and dark energy are given as Ωs, which are the ratio of the true density to the critical density: e.g. Ω_b = ρ_b / ρ₀. Since the ΛCDM model assumes a flat universe, these densities sum to one, and the density of dark energy is not a free parameter. The optical depth to reionization determines the red shift of reionization. Information about the density fluctuations is determined by the amplitude of the primordial fluctuations (from cosmic inflation) and the spectral index, which measures how the fluctuations change with scale (n_s = 1 corresponds to a scale-invariant spectrum). Hubbles law is the statement in physical cosmology that the redshift in light coming from distant galaxies is proportional to their distance. ... In cosmology, the Big Crunch is a hypothesis that states the universe will stop expanding and start to collapse upon itself; a counterpart to the Big Bang. ... Optical depth is a measure of transparency, and is defined as the fraction of radiation that is scattered between a point and the observer. ... This article is about the light phenomenon. ... In Big Bang cosmology, Reionization is the process that reionized the matter in the universe after the epoch of galaxy formation. ...

The errors quoted are 1σ: that is, there is statistically a 68% likelihood that the true value falls within the upper and lower error bounds. The errors are not Gaussian, and they have been derived using a Markov chain Monte Carlo analysis by the Wilkinson Microwave Anisotropy Probe collaboration (Spergel et al. 2006) which also uses Sloan Digital Sky Survey and Type Ia supernova data. Probability density function of Gaussian distribution (bell curve). ... Markov chain Monte Carlo (MCMC) methods (which include random walk Monte Carlo methods) are a class of algorithms for sampling from probability distributions based on constructing a Markov chain that has the desired distribution as its stationary distribution. ... 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. ... Dr. David Nathaniel Spergel (born March 25, 1961, in Rochester, New York) is an American theoretical astrophysicist and Princeton University professor known for his work on the WMAP mission. ... SDSS Logo The Sloan Digital Sky Survey or SDSS is a major multi-filter imaging and spectroscopic redshift survey using a dedicated 2. ... Multiwavelength X-ray image of the remnant of Keplers Supernova, SN 1604. ...

Stellar parallax motion The parsec (symbol pc) is a unit of length used in astronomy. ... Hubbles law is the statement in astronomy that the redshift in light coming from distant galaxies is proportional to their distance. ...

Extended models

Possible extensions of the simplest "vanilla" ΛCDM model are to allow quintessence rather than a cosmological constant. In this case, the equation of state of dark energy is different from −1. Cosmic inflation predicts tensor fluctuations (gravitational waves). Their amplitude is parameterized by the tensor-to-scalar ratio, which is determined by the energy scale of inflation. Other modifications allow for spatial curvature or a running spectral index, which are generally viewed as inconsistent with cosmic inflation. In physics, quintessence is a hypothetical form of dark energy postulated as an explanation of observations of an accelerating universe. ... The cosmological constant (usually denoted by the Greek capital letter lambda: Λ) was proposed by Albert Einstein as part of his theory of general relativity to achieve a stationary universe. ... In cosmology, the equation of state of a perfect fluid is characterized by a dimensionless number w, equal to the ratio of its pressure p to its energy density ρ: . It is closely related to the thermodynamic equation of state and ideal gas law. ... In physics, a gravitational wave is a fluctuation in the curvature of spacetime which propagates as a wave, traveling outward from a moving object or system of objects. ...

Allowing these parameters will generally increase the errors in the vanilla parameters quoted above, and may also shift the observed values somewhat.

These are consistent with a cosmological constant, w = − 1, and no spatial curvature Ω_k = 0. There is some evidence for a running spectral index, but it is not statistically significant. Theoretical expectations suggest that the tensor-to-scalar ratio r should be between 0 and 0.3, and so should be tested in the near future. An electronvolt (symbol: eV) is the amount of energy gained by a single unbound electron when it falls through an electrostatic potential difference of one volt. ... Neutrinos are elementary particles. ...

References

• D. N. Spergel et al. (WMAP collaboration) (March 2006). "Wilkinson Microwave Anisotropy Probe (WMAP) three year results: implications for cosmology". 
• M. Tegmark et al. (SDSS collaboration), Cosmological Parameters from SDSS and WMAP, Phys. Rev. D69 103501 (2004).
• D. N. Spergel et al. (WMAP collaboration), First year Wilkinson Microwave Anisotropy Probe (WMAP) observations: determination of cosmological parameters, Astrophys. J. Suppl. 148 175 (2003).
• R. Rebolo et al. (VSA collaboration), Cosmological parameter estimation using Very Small Array data out to l=1500, Monthly Notices of the Royal Astronomical Society, Volume 353, Issue 3, pp. 747-759
• J. P. Ostriker and P. J. Steinhardt, Cosmic Concordance, arXiv:astro-ph/9505066.