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

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...

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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In cosmology, the cosmic microwave background radiation (most often abbreviated CMB but occasionally CMBR, CBR or MBR, also referred to as relic radiation) is a form of electromagnetic radiation discovered in 1965 that fills the entire universe ^[1]. It has a thermal 2.725° kelvin black body spectrum which peaks in the microwave range at a frequency of 160.2 GHz, corresponding to a wavelength of 1.9 mm. Most cosmologists consider this radiation to be the best evidence for the Big Bang model of the universe. CMB can mean: Core-mantle boundary Combat Medical Badge Cosmic microwave background radiation Bandaranaike International Airport (IATA airport code) China Motor Bus, formerly a franchised bus services provider of Hong Kong Coastal Motor Boat, British torpedo boats of WWI Cash Money Brothas, a now defunct Chicago street gang C.M... This article is about the physics subject. ... Image File history File links No higher resolution available. ... For other uses, see Universe (disambiguation). ... 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. ... 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. ... 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. ... 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. ... This article is about the physics subject. ... Electromagnetic waves can be imagined as a self-propagating transverse oscillating wave of electric and magnetic fields. ... For other uses, see Kelvin (disambiguation). ... As the temperature decreases, the peak of the black body radiation curve moves to lower intensities and longer wavelengths. ... This article is about the type of Electromagnetic radiation. ... This article is about the SI unit of frequency. ... For other uses, see Big Bang (disambiguation). ...

Features

The cosmic microwave background spectrum measured by the FIRAS instrument on the COBE satellite is the most precisely measured black body spectrum in nature. The data points and error bars on this graph are obscured by the theoretical curve.

The cosmic microwave background is isotropic to roughly one part in 100,000: the root mean square variations are only 18 µK.^[2] The Far-Infrared Absolute Spectrophotometer (FIRAS) instrument on the NASA Cosmic Background Explorer (COBE) satellite has carefully measured the spectrum of the cosmic microwave background. FIRAS compared the CMB with a reference black body and no difference could be seen in their spectra. Any deviations from the black body form that might still remain undetected in the CMB spectrum over the wavelength range from 0.5 to 5 mm must have a weighted rms value of at most 50 parts per million (0.005%) of the CMB peak brightness.^[3] This made the CMB spectrum the most precisely measured black body spectrum in nature. Image File history File links Download high resolution version (905x749, 54 KB)FIRAS spectrum from COBE available from [1] with the caption Cosmic Microwave Background (CMB) spectrum plotted in waves per centimeter vs. ... Image File history File links Download high resolution version (905x749, 54 KB)FIRAS spectrum from COBE available from [1] with the caption Cosmic Microwave Background (CMB) spectrum plotted in waves per centimeter vs. ... The Cosmic Background Explorer (COBE), also referred to as Explorer 66, was the first satellite built dedicated to cosmology. ... As the temperature decreases, the peak of the black body radiation curve moves to lower intensities and longer wavelengths. ... In statistics, a data point is a single typed measurement. ... In statistics, the standard error of a measurement, value or quantity is the standard deviation of the process by which it was generated, after adjusting for sample size. ... 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 mathematics, the root mean square or rms is a statistical measure of the magnitude of a varying quantity. ... In physics, spectrophotometry is the quantitative study of spectra. ... This article is about the American space agency. ... The Cosmic Background Explorer (COBE), also referred to as Explorer 66, was the first satellite built dedicated to cosmology. ... As the temperature decreases, the peak of the black body radiation curve moves to lower intensities and longer wavelengths. ... In mathematics, the root mean square or rms is a statistical measure of the magnitude of a varying quantity. ...

The cosmic microwave background is a prediction of Big Bang theory. In the theory, the early universe was made up of a hot plasma of photons, electrons and baryons. The photons were constantly interacting with the plasma through Thomson scattering. As the universe expanded, adiabatic cooling caused the plasma to cool until it became favourable for electrons to combine with protons and form hydrogen atoms. This happened at around 3,000 K or when the universe was approximately 380,000 years old (z=1088). At this point, the photons scattered off the now neutral atoms and began to travel freely through space. This process is called recombination or decoupling (referring to electrons combining with nuclei and to the decoupling of matter and radiation respectively). For other uses, see Big Bang (disambiguation). ... For other uses, see Plasma. ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ... Properties The electron (also called negatron, commonly represented as e−) is a subatomic particle. ... Combinations of three u, d or s-quarks with a total spin of 3/2 form the so-called baryon decuplet. ... In physics, Thomson scattering is the scattering of electromagnetic radiation by a charged particle. ... 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. ... Properties The electron (also called negatron, commonly represented as e−) is a subatomic particle. ... For alternative meanings see proton (disambiguation). ... This article is about the chemistry of hydrogen. ... This article does not cite any references or sources. ... In physics, decoupling is the general phenomenon in which the interactions between some physical objects (such as elementary particles) disappear. ...

The photons have continued cooling ever since; they have now reached 2.725 K and their temperature will continue to drop as long as the universe continues expanding. Accordingly, the radiation from the sky we measure today comes from a spherical surface, called the surface of last scattering, from which the photons that decoupled from interaction with matter in the early universe, 13.7 billion years (13.7 G yr) ago, are just now reaching observers on Earth. The big bang suggests that the cosmic microwave background fills all of observable space, and that most of the radiation energy in the universe is in the cosmic microwave background, which makes up a fraction of roughly 5×10^-5 of the total density of the universe.^[4]

Two of the greatest successes of the big bang theory are its prediction of its almost perfect black body spectrum and its detailed prediction of the anisotropies in the cosmic microwave background. The recent Wilkinson Microwave Anisotropy Probe has precisely measured these anisotropies over the whole sky down to angular scales of 0.2 degrees.^[5] These can be used to estimate the parameters of the standard Lambda-CDM model of the big bang. Some information, such as the shape of the Universe, can be obtained straightforwardly from the cosmic microwave background, while others, such as the Hubble constant, are not constrained and must be inferred from other measurements.^[6] As the temperature decreases, the peak of the black body radiation curve moves to lower intensities and longer wavelengths. ... 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. ... A pie chart indicating the proportional composition of different energy-density components of the universe. ... The shape of the Universe is an informal name for a subject of investigation within physical cosmology. ... Hubbles law is the statement in astronomy that the redshift in light coming from distant galaxies is proportional to their distance. ...

History

See also: Discovery of cosmic microwave background radiation and Timeline of cosmic microwave background astronomy

The cosmic microwave background was predicted in 1948 by George Gamow and Ralph Alpher, and by Alpher and Robert Herman. Moreover, Alpher and Herman were able to estimate the temperature of the cosmic microwave background to be 5 K, though two years later, they re-estimated it at 28 K.^[18]. Although there were several previous estimates of the temperature of space (see timeline), these suffered from two flaws. First, they were measurements of the effective temperature of space, and did not suggest that space was filled with a thermal Planck spectrum; second, they are dependent on our special place at the edge of the Milky Way galaxy and did not suggest the radiation is isotropic. Moreover, they would yield very different predictions if Earth happened to be located elsewhere in the universe.^[19] Dr. Andrew McKellar (February 2, 1910–May 6, 1960) was a Canadian astronomer. ... Front of the main telescope building Dominion Astrophysical Observatory, located on Little Saanich Mountain, in Saanich, British Columbia, was completed in 1918 by the Canadian Government. ... Robert Henry Dicke (May 6, 1916 – March 4, 1997) was an American physicist and astrophysicist. ... 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. ... Ralph Asher Alpher (born 1921) is a U.S. cosmologist. ... It has been suggested that this article or section be merged into Discovery of cosmic microwave background radiation. ... 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. ... 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. ... A. G. Doroshkevich is a Russian (and former Soviet) theoretical astrophysicist and cosmologist. ... Igor Dmitriyevich Novikov (Russian: ) (born November 10, 1935 in Moscow) is a Russian (and former Soviet) theoretical astrophysicist and cosmologist. ... Arno Allan Penzias (born April 26, American physicist. ... Robert Woodrow Wilson Robert Woodrow Wilson (born January 10, 1936) is an American physicist. ... Philip James Edwin Peebles (born April 25, 1935) is an Canadian-American astronomer. ... David Todd Wilkinson (13 May 1935 – 5 September 2002) was a world-renowned pioneer in the field of cosmology, specializing in the study of the cosmic microwave background radiation (CMB) left over from the Big Bang. ... RELIKT-1 (sometimes RELICT-1 from Russian РЕЛИКТ-1) - a Soviet cosmic microwave background anisotropy experiment onboard the Prognoz 9 satellite (launched 1 July 1983) first gave only upper limits on the large-scale anisotropy, but reanalysis of the data in 1992 claimed a signal roughly compatible with the later experiments. ... RELIKT-1 (sometimes RELICT-1 from Russian РЕЛИКТ-1) - a Soviet cosmic microwave background anisotropy experiment onboard the Prognoz 9 satellite (launched 1 July 1983) first gave only upper limits on the large-scale anisotropy, but reanalysis of the data in 1992 claimed a signal roughly compatible with the later experiments. ... The Cosmic Background Explorer (COBE), also referred to as Explorer 66, was the first satellite built dedicated to cosmology. ... This article concerns the accidental discovery of cosmic microwave background radiation. ... Timeline of cosmic microwave background astronomy 1934 - Richard Tolman shows that black-body radiation in an expanding universe cools but remains thermal 1941 - Andrew McKellar uses the excitation of CN doublet lines to measure that the effective temperature of space is about 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. ... Ralph Asher Alpher (born 1921) is a U.S. cosmologist. ... It has been suggested that this article or section be merged into Discovery of cosmic microwave background radiation. ... As the temperature decreases, the peak of the black body radiation curve moves to lower intensities and longer wavelengths. ... The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Galaxia Kuklos; or simply the Galaxy) is a barred spiral galaxy in the Local Group, and has special significance to humanity as the location of the solar system, which is located near the Orion...

The 1948 results of Gamow and Alpher were not widely discussed. However, they were rediscovered by Robert Dicke and Yakov Zel'dovich in the early 1960s. The first published recognition of the CMB radiation as a detectable phenomenon appeared in a brief paper by Soviet astrophysicists A. G. Doroshkevich and Igor Novikov, in the spring of 1964.^[20] In 1964, David Todd Wilkinson and Peter Roll, Dicke's colleagues at Princeton University, began constructing a Dicke radiometer to measure the cosmic microwave background^[21]. In 1965, Arno Penzias and Robert Woodrow Wilson at the Crawford Hill location of Bell Telephone Laboratories in nearby Holmdel Township, New Jersey had built a Dicke radiometer that they intended to use for radio astronomy and satellite communication experiments. Their instrument had an excess 3.5 K antenna temperature which they could not account for. After receiving a telephone call from Crawford Hill, Dicke famously quipped: "Boys, we've been scooped."^[22] A meeting between the Princeton and Crawford Hill groups determined that the antenna temperature was indeed due to the microwave background. Penzias and Wilson received the 1978 Nobel Prize in Physics for their discovery. Robert Henry Dicke (May 6, 1916 – March 4, 1997) was an American physicist and astrophysicist. ... Yakov Borisovich Zeldovich (Russian:Яков Борисович Зельдович) (March 8, 1914 – December 2, 1987) was a prolific Soviet physicist. ... CCCP redirects here. ... A. G. Doroshkevich is a Russian (and former Soviet) theoretical astrophysicist and cosmologist. ... Igor Dmitriyevich Novikov (Russian: ) (born November 10, 1935 in Moscow) is a Russian (and former Soviet) theoretical astrophysicist and cosmologist. ... David Todd Wilkinson (13 May 1935 – 5 September 2002) was a world-renowned pioneer in the field of cosmology, specializing in the study of the cosmic microwave background radiation (CMB) left over from the Big Bang. ... Princeton University is a private coeducational research university located in Princeton, New Jersey. ... Arno Allan Penzias (born April 26, American physicist. ... Robert Woodrow Wilson Robert Woodrow Wilson (born January 10, 1936) is an American physicist. ... Crawford Hill is located in Holmdel Township, New Jersey. ... Bell Telephone Laboratories or Bell Labs was originally the research and development arm of the United States Bell System, and was the premier corporate facility of its type, developing a range of revolutionary technologies from telephone switches to specialized coverings for telephone cables, to the transistor. ... Holmdel Township is a township in Monmouth County, New Jersey, United States. ... Noise temperature: At a pair of terminals, the temperature of a passive system having an available noise power per unit bandwidth at a specified frequency equal to that of the actual terminals of a network. ... Hannes Alfvén (1908–1995) accepting the Nobel Prize for his work on magnetohydrodynamics [1]. List of Nobel Prize laureates in Physics from 1901 to the present day. ...

The interpretation of the cosmic microwave background was a controversial issue in the 1960s with some proponents of the steady state theory arguing that the microwave background was the result of scattered starlight from distant galaxies. Using this model, and based on the study of narrow absorption line features in the spectra of stars, the astronomer Andrew McKellar wrote in 1941: "It can be calculated that the 'rotational temperatureˡ of interstellar space is 2 K."^[23] However, during the 1970s the consensus was established that the cosmic microwave background is a remnant of the big bang. This was largely because new measurements at a range of frequencies showed that the spectrum was a thermal, black body spectrum, a result that the steady state model was unable to reproduce. In cosmology, the steady state theory (also known as the Infinite Universe Theory or continuous creation) is a model developed in 1948 by Fred Hoyle, Thomas Gold, Hermann Bondi and others as an alternative to the Big Bang theory (known, usually, as the standard cosmological model). ... Dr. Andrew McKellar (February 2, 1910–May 6, 1960) was a Canadian astronomer. ... The rotational temperature is commonly used in thermodynamics, to simplify certain equations. ... As the temperature decreases, the peak of the black body radiation curve moves to lower intensities and longer wavelengths. ...

The Horn Antenna on which Penzias and Wilson discovered the cosmic microwave background.

Harrison, Peebles and Yu, and Zel'dovich realized that the early universe would have to have inhomogeneities at the level of 10^-4 or 10⁻⁵.^[24] Rashid Sunyaev later calculated the observable imprint that these inhomogeneities would have on the cosmic microwave background.^[25] Increasingly stringent limits on the anisotropy of the cosmic microwave background were set by ground based experiments, but the anisotropy was first detected by the Differential Microwave Radiometer instrument on the COBE satellite.^[26] Download high resolution version (1397x1098, 156 KB)The Horn Antenna in Holmdel Township, New Jersey. ... Download high resolution version (1397x1098, 156 KB)The Horn Antenna in Holmdel Township, New Jersey. ... A horn antenna is used for the transmission and reception of microwave signals. ... Rashid Alievich Sunyaev (Рашид Алиевич Сюняев) was born in Tashkent, Uzbek SSR, on March 1, 1943 and educated at the Moscow Institute of Physics and Technology and Moscow University. ... The Cosmic Background Explorer (COBE), also referred to as Explorer 66, was the first satellite built dedicated to cosmology. ...

Inspired by the COBE results, a series of ground and balloon-based experiments measured cosmic microwave background anisotropies on smaller angular scales over the next decade. The primary goal of these experiments was to measure the scale of the first acoustic peak, which COBE did not have sufficient resolution to resolve. The first peak in the anisotropy was tentatively detected by the Toco experiment and the result was confirmed by the BOOMERanG and MAXIMA experiments.^[27]. These measurements demonstrated that the Universe is approximately flat and were able to rule out cosmic strings as a major component of cosmic structure formation, and suggested cosmic inflation was the right theory of structure formation. 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. ... The shape of the Universe is an informal name for a subject of investigation within physical cosmology. ... A cosmic string is a hypothetical 1-dimensional topological defect in the fabric of spacetime. ... 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 second peak was tentatively detected by several experiments before being definitively detected by WMAP, which has also tentatively detected the third peak. Several experiments to improve measurements of the polarization and the microwave background on small angular scales are ongoing. These include DASI, WMAP, BOOMERanG and the Cosmic Background Imager. Forthcoming experiments include the Planck satellite, Atacama Cosmology Telescope and the South Pole Telescope. 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. ... The Cosmic Background Imager (or CBI) is a 13-element interferometer perched at an elevation of 5000 metres at Llano de Chajnantor Observatory in the Chilean Andes. ... Planck is a European Space Agency satellite to be launched in 2007. ... The Atacama Cosmology Telescope (ACT) is currently under construction on Cerro Toco in Chile, and is scheduled to see first light in 2006. ... The South Pole Telescope. ...

WMAP image of the CMB temperature anisotropy.

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. ... 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. ... 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. ...

Relationship to the Big Bang

CMB made Big Bang the standard and confirmed radiation should fill the universe. The standard hot big bang model of the universe requires that the initial conditions for the universe are a Gaussian random field with a nearly scale invariant or Harrison-Zel'dovich spectrum. This is, for example, a prediction of the cosmic inflation model. This means that the initial state of the universe is random, but in a clearly specified way in which the amplitude of the primeval inhomogeneities is 10^-5. Therefore, meaningful statements about the inhomogeneities in the universe need to be statistical in nature. This leads to cosmic variance in which the uncertainties in the variance of the largest scale fluctuations observed in the universe are difficult to accurately compare to theory. A Gaussian random field is random field involving Gaussian probability density functions of the variables. ... In physics, scale invariance is the feature of physical objects of laws that do not change if the space is magnified, i. ... 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. ... This article is about the field of statistics. ... Cosmic variance is the idea that we are only able to observe one universe at one particular time, so it is difficult to make statistical statements about cosmology on the scale of the entire universe. ...

Temperature

The cosmic microwave background radiation and the cosmological red shift are together regarded as the best available evidence for the Big Bang (BB) theory. The discovery of the CMB in the mid-1960s curtailed interest in alternatives such as the steady state theory. The CMB gives a snapshot of the Universe when, according to standard cosmology, the temperature dropped enough to allow electrons and protons to form hydrogen atoms, thus making the universe transparent to radiation. When it originated some 400,000 years after the Big Bang — this time period is generally known as the "time of last scattering" or the period of recombination or decoupling — the temperature of the Universe was about 3,000 K. This corresponds to an energy of about 0.25 eV, which is much less than the 13.6 eV ionization energy of hydrogen. Since then, the temperature of the radiation has dropped by a factor of roughly 1100 due to the expansion of the Universe. As the universe expands, the CMB photons are redshifted, making the radiation's temperature inversely proportional to the Universe's scale length. For details about the reasoning that the radiation is evidence for the Big Bang, see Cosmic background radiation of the Big Bang. This article is about the light phenomenon. ... For other uses, see Big Bang (disambiguation). ... A non-standard cosmology is any cosmological framework that has been, or still is, proposed as an alternative to the big bang model of physical cosmology. ... In cosmology, the steady state theory (also known as the Infinite Universe Theory or continuous creation) is a model developed in 1948 by Fred Hoyle, Thomas Gold, Hermann Bondi and others as an alternative to the Big Bang theory (known, usually, as the standard cosmological model). ... For other uses, see Universe (disambiguation). ... For other uses, see Electron (disambiguation). ... For other uses, see Proton (disambiguation). ... This article is about the chemistry of hydrogen. ... To help compare orders of magnitude of different times this page lists times between 320 000 years and 3 200 000 years (1013 seconds and 1014 seconds) See also times of other orders of magnitude. ... Recombination usually refers to the biological process of genetic recombination and meiosis, a genetic event that occurs during the formation of sperm and egg cells. ... In physics, decoupling is the general phenomenon in which the interactions between some physical objects (such as elementary particles) disappear. ... To help compare different orders of magnitude this page lists temperatures between 1,000 kelvins and 10,000 kelvins. ... The electronvolt (symbol eV) is a unit of energy. ... Redshift of spectral lines in the optical spectrum of a supercluster of distant galaxies (right), as compared with that of the Sun (left). ... This article is about proportionality, the mathematical relation. ... The scale factor, parameter of Friedmann-Lemaître-Robertson-Walker model, is a function of time which represents the relative expansion of the universe. ... For other uses, see Big Bang (disambiguation). ...

The power spectrum of the cosmic microwave background radiation temperature anisotropy in terms of the angular scale (or multipole moment). The data shown come from the WMAP (2006), Acbar (2004) Boomerang (2005), CBI (2004) and VSA (2004) instruments.

Image File history File links Download high resolution version (2039x1661, 131 KB)WMAP three year temperature spectrum from [1] File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Image File history File links Download high resolution version (2039x1661, 131 KB)WMAP three year temperature spectrum from [1] File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Multipole moments in mathematics and mathematical physics are an orthogonal basis for the decomposition of a function, based on the response of a field to point sources that are brought infinitely close to each other. ... 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. ... ACBAR is an experiment to measure the anisotropy of the Cosmic microwave background. ... 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. ... The Cosmic Background Imager (or CBI) is a 13-element interferometer perched at an elevation of 5000 metres at Llano de Chajnantor Observatory in the Chilean Andes. ... The Very Small Array is a 14-element interferometer perched at an elevation of 3000 metres on Tenerife in the Canary Islands. ...

Primary anisotropy

The anisotropy of the cosmic microwave background is divided into two sorts: primary anisotropy – which is due to effects which occur at the last scattering surface and before – and secondary anisotropy – which is due to effects, such as interactions with hot gas or gravitational potentials, between the last scattering surface and the observer. Look up anisotropy in Wiktionary, the free dictionary. ...

The structure of the cosmic microwave background anisotropies is principally determined by two effects: acoustic oscillations and diffusion damping (also called collisionless damping or Silk damping). The acoustic oscillations arise because of a competition in the photon-baryon plasma in the early universe. The pressure of the photons tends to erase anisotropies, whereas the gravitational attraction of the baryons – which are moving at speeds much less than the speed of light – makes them tend to collapse to form dense haloes. These two effects compete to create acoustic oscillations which give the microwave background its characteristic peak structure. The peaks correspond, roughly, to resonances in which the photons decouple when a particular mode is at its peak amplitude. Joseph Silk is the Savilian Chair of Astronomy at the University of Oxford. ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ... Combinations of three u, d or s-quarks with a total spin of 3/2 form the so-called baryon decuplet. ...

The peaks contain interesting physical signatures. The angular scale of the first peak determines the curvature of the Universe (but not the topology of the Universe). The second peak Рtruly the ratio of the odd peaks to the even peaks Рdetermines the reduced baryon density. The third peak can be used to extract information about the dark matter density. The shape of the Universe is an informal name for a subject of investigation within physical cosmology. ... A M̦bius strip, an object with only one surface and one edge; such shapes are an object of study in topology. ...

The locations of the peaks also give important information about the nature of the primordial density perturbations. There are two fundamental types of density perturbations -- called "adiabatic" and "isocurvature." A general density perturbation is a mixture of these two types, and different theories that purport to explain the primordial density perturbation spectrum predict different mixtures.

• For adiabatic density perturbations, the fractional overdensity in each matter component (baryons, photons ...) is the same. That is, if there is 1% more energy in baryons than average in one spot, then with a pure adiabatic density perturbations there is also 1% more energy in photons, and 1% more energy in neutrinos, than average. Cosmic inflation predicts that the primordial perturbations are adiabatic.

• With isocurvature density perturbations, the sum of the fractional overdensities is zero. That is, a perturbation where at some spot there is 1% more energy in baryons than average, 1% more energy in photons than average, and 2% lower energy in neutrinos than average, would be a pure isocurvature perturbation. Cosmic strings would produce mostly isocurvature primordial perturbations.

The CMB spectrum is able to distinguish these two because these two types of perturbations produce different peak locations. Isocurvature density perturbations produce a series of peaks whose angular scales (l-values of the peaks) are roughly in the ratio 1 : 3 : 5 ..., while adiabatic density perturbations produce peaks whose locations are in the ratio 1 : 2 : 3 ... ^[28] Observations are consistent with the primordial density perturbations being entirely adiabatic, providing key support for inflation, and ruling out many models of structure formation involving, for example, cosmic strings. Combinations of three u, d or s-quarks with a total spin of 3/2 form the so-called baryon decuplet. ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ... 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. ... A cosmic string is a hypothetical 1-dimensional topological defect in the fabric of spacetime. ...

Collisionless damping is caused by two effects, when the treatment of the primordial plasma as a fluid begins to break down: A fluid is defined as a substance that continually deforms (flows) under an applied shear stress regardless of the magnitude of the applied stress. ...

• the increasing mean free path of the photons as the primordial plasma becomes increasingly rarefied in an expanding universe
• the finite thickness of the last scattering surface (LSS), which causes the mean free path to increase rapidly during decoupling, even while some Compton scattering is still occurring.

These effects contribute about equally to the suppression of anisotropies on small scales, and give rise to the characteristic exponential damping tail seen in the very small angular scale anisotropies. For sound waves in an enclosure, the mean free path is the average distance the wave travels between reflections off of the enclosures walls. ...

The thickness of the LSS refers to the fact that the decoupling of the photons and baryons does not happen instantaneously, but instead requires an appreciable fraction of the age of the Universe up to that era. One method to quantify exactly how long this process took uses the photon visibility function (PVF). This function is defined so that, denoting the PVF by P(t), the probability that a CMB photon last scattered between time t and t+dt is given by P(t)dt.

The maximum of the PVF (the time where it is most likely that a given CMB photon last scattered) is known quite precisely. The first-year WMAP results put the time at which P(t) is maximum as 372 +/- 14 kyr ^[29]. This is often taken as the "time" at which the CMB formed. However, to figure out how long it took the photons and baryons to decouple, we need a measure of the width of the PVF. The WMAP team finds that the PVF is greater than half of its maximum value (the "full width at half maximum", or FWHM) over an interval of 115 +/- 5 kyr. By this measure, decoupling took place over roughly 115,000 years, and when it was complete, the universe was roughly 487,000 years old.

Late time anisotropy

After the creation of the CMB, it is modified by several physical processes collectively referred to as late-time anisotropy or secondary anisotropy. After the emission of the CMB, ordinary matter in the universe was mostly in the form of neutral hydrogen and helium atoms, but from observations of galaxies it seems that most of the volume of the intergalactic medium (IGM) today consists of ionized material (since there are few absorption lines due to hydrogen atoms). This implies a period of reionization in which the material of the universe breaks down into hydrogen ions. Intergalactic space is the physical space between galaxies. ... In Big Bang cosmology, reionization is the process that reionized the matter in the universe after the dark ages. It is the second of two major phase changes of hydrogen gas in the universe. ...

The CMB photons scatter off free charges such as electrons that are not bound in atoms. In an ionized universe, such electrons have been liberated from neutral atoms by ionizing (ultraviolet) radiation. Today these free charges are at sufficiently low density in most of the volume of the Universe that they do not measurably affect the CMB. However, if the IGM was ionized at very early times when the universe was still denser, then there are two main effects on the CMB:

1. Small scale anisotropies are erased (just as when looking at an object through fog, details of the object appear fuzzy).
2. The physics of how photons scatter off free electrons (Thomson scattering) induces polarization anisotropies on large angular scales. This large angle polarization is correlated with the large angle temperature perturbation.

Both of these effects have been observed by the WMAP satellite, providing evidence that the universe was ionized at very early times, at a redshift of larger than 17. The detailed provenance of this early ionizing radiation is still a matter of scientific debate. It may have included starlight from the very first population of stars (population III stars), supernovae when these first stars reached the end of their lives, or the ionizing radiation produced by the accretion disks of massive black holes. In physics, Thomson scattering is the scattering of electromagnetic radiation by a charged particle. ... Redshift of spectral lines in the optical spectrum of a supercluster of distant galaxies (right), as compared with that of the Sun (left). ... Population III stars are a hypothetical population of extremely massive stars that are believed to have been formed in the early universe. ...

The period after the emission of the cosmic microwave background and before the observation of the first stars is semi-humorously referred to by cosmologists as the dark age, and is a period which is under intense study by astronomers (See 21 centimeter radiation). Dark Ages can refer to the following. ... 21 centimeter radiation is radiation produced during a hyperfine transition of neutral hydrogen from the triplet to the singlet state. ...

Other effects that occur between reionization and our observation of the cosmic microwave background which cause anisotropies include the Sunyaev-Zel'dovich effect, in which a cloud of high energy electrons scatters the radiation, transferring some energy to the CMB photons, and the Sachs-Wolfe effect, which causes photons from the cosmic microwave background to be gravitationally redshifted or blue shifted due to changing gravitational fields. The Sunyaev-Zeldovich effect (SZ effect or Sunyaev-Zeldovich theory) is due to high energy electrons distorting the cosmic microwave background radiation (CMB) through the inverse Compton effect, in which some of the high energy of the electrons is transferred to the low energy photons. ... The Sachs-Wolfe effect is a property of the cosmic background radiation (CBR), in which gravitational bodies redshift the CBR, causing it to appear uneven. ... In modern physics the photon is the elementary particle responsible for electromagnetic phenomena. ...

E polarization measurements as of March 2006 in terms of angular scale (or multipole moment). The polarization is much more poorly measured than the temperature anisotropy.

Image File history File links Download high resolution version (853x732, 17 KB)WMAP three-year polarization (EE) spectrum. ... Image File history File links Download high resolution version (853x732, 17 KB)WMAP three-year polarization (EE) spectrum. ... Multipole moments in mathematics and mathematical physics are an orthogonal basis for the decomposition of a function, based on the response of a field to point sources that are brought infinitely close to each other. ...

Polarization

The cosmic microwave background is polarized at the level of a few microkelvins. There are two types of polarization, called E-modes and B-modes. This is in analogy to electrostatics, in which the electric field (E-field) has a vanishing curl and the magnetic field (B-field) has a vanishing divergence. The E-modes arise naturally from Thomson scattering in an inhomogeneous plasma. The B-modes, which have not been measured and are thought to have an amplitude of at most a 0.1 µK, are not produced from the plasma physics alone. They are a signal from cosmic inflation and are determined by the density of primordial gravitational waves. Detecting the B-modes will be extremely difficult, particularly given that the degree of foreground contamination is unknown, and the weak gravitational lensing signal mixes the relatively strong E-mode signal with the B-mode signal.^[30] In electrodynamics, polarization (also spelled polarisation) is the property of electromagnetic waves, such as light, that describes the direction of their transverse electric field. ... Electrostatics (also known as static electricity) is the branch of physics that deals with the phenomena arising from what seem to be stationary electric charges. ... For other uses, see Curl (disambiguation). ... In vector calculus, the divergence is an operator that measures a vector fields tendency to originate from or converge upon a given point. ... In physics, Thomson scattering is the scattering of electromagnetic radiation by a charged particle. ... 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, 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. ... This article is in need of attention from an expert on the subject. ...

Microwave background observations

Main article: Cosmic microwave background experiments

Subsequent to the discovery of the CMB, hundreds of cosmic microwave background experiments have been conducted to measure and characterize the signatures of the radiation. The most famous experiment is probably the NASA Cosmic Background Explorer (COBE) satellite that orbited in 1989–1996 and which detected and quantified the large scale anisotropies at the limit of its detection capabilities. Inspired by the initial COBE results of an extremely isotropic and homogeneous background, a series of ground- and balloon-based experiments quantified CMB anisotropies on smaller angular scales over the next decade. The primary goal of these experiments was to measure the angular scale of the first acoustic peak, for which COBE did not have sufficient resolution. These measurements were able to rule out cosmic strings as the leading theory of cosmic structure formation, and suggested cosmic inflation was the right theory. During the 1990's, the first peak was measured with increasing sensitivity and by 2000 the BOOMERanG experiment reported that the highest power fluctuations occur at scales of apporoximately one degree. Together with other cosmological data, these results implied that the geometry of the Universe is flat. A number of ground-based interferometers provided measurements of the fluctuations with higher accuracy over the next three years, including the Very Small Array, Degree Angular Scale Interferometer (DASI) and the Cosmic Background Imager. In fact, DASI made the first detection of the polarization of the CMB. Cosmic background radiation spectrum as determined with the COBE satellite, (top) uncorrected, (middle) corrected for the dipole term due to our peculiar velocity, (bottom) corrected for contributions from the dipole term and from our galaxy. ... This article is about the American space agency. ... The Cosmic Background Explorer (COBE), also referred to as Explorer 66, was the first satellite built dedicated to cosmology. ... Year 1989 (MCMLXXXIX) was a common year starting on Sunday (link displays 1989 Gregorian calendar). ... Year 1996 (MCMXCVI) was a leap year starting on Monday (link will display full 1996 Gregorian calendar). ... A cosmic string is a hypothetical 1-dimensional topological defect in the fabric of spacetime. ... 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 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. ... The intuitive idea of flatness is important in several fields. ... Interferometry is the applied science of combining two or more input points of a particular data type, such as optical measurements, to form a greater picture based on the combination of the two sources. ... The Very Small Array is a 14-element interferometer perched at an elevation of 3000 metres on Tenerife in the Canary Islands. ... The Degree Angular Scale Interferometer (DASI) is a telescope located in Antarctica. ... The Cosmic Background Imager (or CBI) is a 13-element interferometer perched at an elevation of 5000 metres at Llano de Chajnantor Observatory in the Chilean Andes. ...

In June 2001, NASA launched a second CMB space mission, WMAP, to make much more precise measurements of the large scale anisotropies over the full sky. The first results from this mission, disclosed in 2003, were detailed measurements of the angular power spectrum to below degree scales, tightly constraining various cosmological parameters. The results are broadly consistent with those expected from cosmic inflation as well as various other competing theories, and are available in detail at NASA's data center for Cosmic Microwave Background (CMB) (see links below). Although WMAP provided very accurate measurements of the large angular-scale fluctuations in the CMB (structures about as large in the sky as the moon), it did not have the angular resolution to measure the smaller scale fluctuations which had been observed using previous ground-based interferometers. June 2001 : January - February - March - April - May - June - July - August - September - October - November - December June 1 - Royal Family of Nepal massacred. ... This article is about the American space agency. ... 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. ... 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. ... Interferometry is the applied science of combining two or more input points of a particular data type, such as optical measurements, to form a greater picture based on the combination of the two sources. ...

A third space mission, the Planck Surveyor, is to be launched in 2008. Planck employs both HEMT radiometers as well as bolometer technology and will measure the CMB on smaller scales than WMAP. Unlike the previous two space missions, Planck is a collaboration between NASA and ESA (the European Space Agency). Its detectors got a trial run at the Antarctic Viper telescope as ACBAR (Arcminute Cosmology Bolometer Array Receiver) experiment – which has produced the most precise measurements at small angular scales to date – and at the Archeops balloon telescope. WMAP image, unrelated to Planck The Planck Surveyor is the third Medium-Sized Mission (M3) of ESAs Horizon 2000 Scientific Programme. ... HEMT stands for High Electron Mobility Transistor, and is also called heterostructure FET (HFET). ... Rendition of an imaging bolometer from Los Alamos National Laboratory A bolometer is a device for measuring incident electromagnetic radiation. ... ESA redirects here. ... ACBAR is an experiment to measure the anisotropy of the Cosmic microwave background. ... Wikipedia does not have an article with this exact name. ...

Additional ground-based instruments such as the South Pole Telescope in Antarctica and the proposed Clover Project and Atacama Cosmology Telescope in Chile will provide additional data not available from satellite observations, possibly including the B-mode polarization. The South Pole Telescope. ... Clover is a new experiment which has been designed to measure the B-mode polarization of the Cosmic Microwave Background down to a sensitivity limited by the foreground contamination due to lensing, allowing the detection of primordial gravitational waves in the Universe. ... The Atacama Cosmology Telescope (ACT) is currently under construction on Cerro Toco in Chile, and is scheduled to see first light in 2006. ...

References