NationMaster - Encyclopedia: Cosmic neutrino background

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 No higher resolution available. ... 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. ... The Universe is defined as the summation of all particles and energy that exist and the space-time in which all events occur. ... According to the Big Bang model, the universe emerged from an extremely dense and hot state. ... 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 GWB · Neutrino Background 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. ... This article or section is in need of attention from an expert on the subject. ... 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-LemaÃ®tre-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 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. ... In astrophysics and cosmology, dark matter refers to hypothetical matter of unknown composition that does not emit or reflect enough electromagnetic radiation to be observed 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 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. ...
Scientists
Einstein · Friedman · Lemaître Hubble · Penzias · Wilson Gamow · Dicke · Zel'dovich Mather · Smoot · others â€œEinsteinâ€ redirects here. ... Alexander Alexandrovich Friedman or Friedmann (ÐÐ»ÐµÐºÑÐ°Ð½Ð´Ñ€ ÐÐ»ÐµÐºÑÐ°Ð½Ð´Ñ€Ð¾Ð²Ð¸Ñ‡ Ð¤Ñ€Ð¸Ð´Ð¼Ð°Ð½) (June 16, 1888 â€“ September 16, 1925) was a Russian cosmologist and mathematician. ... Father Georges-Henri LemaÃ®tre (July 17, 1894 â€“ June 20, 1966) was a Belgian Roman Catholic priest, honorary prelate, professor of physics and astronomer. ... Edwin Powell Hubble (November 29, 1889 â€“ 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 â€“ August 19, 1968) , born Georgiy Antonovich Gamov (Ð“ÐµÐ¾Ñ€Ð³Ð¸Ð¹ ÐÐ½Ñ‚Ð¾Ð½Ð¾Ð²Ð¸Ñ‡ Ð“Ð°Ð¼Ð¾Ð²) was a Ukrainian born physicist and cosmologist. ... Robert Henry Dicke (May 6, 1916 â€“ 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:Ð¯ÐºÐ¾Ð² Ð‘Ð¾Ñ€Ð¸ÑÐ¾Ð²Ð¸Ñ‡ Ð—ÐµÐ»ÑŒÐ´Ð¾Ð²Ð¸Ñ‡) (March 8, 1914 â€“ 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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The Cosmic Neutrino Background (CNB) is the background particle radiation composed of neutrinos. Neutrinos are elementary particles denoted by the symbol Î½. Travelling close to the speed of light, lacking electric charge and able to pass through ordinary matter almost undisturbed, they are extremely difficult to detect. ...

Like the CMB, the CNB is a relic of the big bang, and while the CMB dates from when the universe was 300,000 years old, the CNB decoupled from matter when the universe was 2 seconds old. It is estimated that the CNB has a temperature of 1.9 kelvins or lower. Neutrinos are notoriously difficult to detect, and because these particles are so cold, the CNB might never be observed directly. 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. ... According to the Big Bang model, the universe emerged from an extremely dense and hot state. ...

Derivation of the temperature of the CNB

Given the temperature of the CMB, the temperature of the CNB can be estimated. Before neutrinos decoupled from the rest of matter, the universe primarily consisted of neutrinos, electrons, positrons and photons, all in thermal equilibrium with each other. Once the temperature dropped below the masses of the W and Z bosons, the neutrinos decoupled from the rest of matter. At this point, neutrinos and photons still had the same temperature. When the temperature dropped below the mass of the electron, most electrons and positrons annihilated, transfering their heat and entropy to photons. So the ratio of the temperature of the photons before and after the electron-positron annihiliation is the same as the ratio of the temperature of the photons and the neutrinos today. To find this ratio, we assume that the entropy of the universe was approximately conserved by the electron-positron annihilation. Then using Properties The electron (also called negatron, commonly represented as e−) is a subatomic particle. ... A positron is the antiparticle of the electron. ... In physics, the photon (from Greek Ï†Ï‰Ï‚, phÅs, meaning light) is the quantum of the electromagnetic field; for instance, light. ... In thermodynamics, a thermodynamic system is in thermodynamic equilibrium if its energy distribution equals a Maxwell-Boltzmann-distribution. ... In physics, the W and Z bosons are the elementary particles that mediate the weak nuclear force. ... Electron-positron annihilation is the process that occurs when an electron (which is matter) and a positron (which is antimatter) collide. ...

$sigma propto gT^3$ ,

where $σ$ is the entropy, $g$ is the effective number of degrees of freedom and $T$ is the temperature, we find that The phrase degrees of freedom is used in three different branches of science: in physics and physical chemistry, in mechanical and aerospace engineering, and in statistics. ...

$left(frac{g_0}{g_1}right)^{1/3} = frac{T_1}{T_0}$ ,

where the subscript 0 denotes before the electron-positron annihilation and 1 denotes after. To find $g 0$ , we add the degrees of freedom for electrons, positrons and photons:

2 for photons, since they are massless bosons
2(7/8) each for electrons and positrons, since they are fermions

$g 1$ is just 2 for photons. So Boson (game) Bosons, named after Satyendra Nath Bose, are particles which form totally-symmetric composite quantum states. ... Fermions, named after Enrico Fermi, are particles which form totally-antisymmetric composite quantum states. ...

$frac{T_nu}{T_gamma} = left(frac{4}{11}right)^{1/3}$ .

Given the current value of $T γ = 2.73K$ , it follows that $T_nu approx 1.9 rm K$ .

The above discussion is valid for massless neutrinos, which are always relativistic. If neutrinos have a positive rest mass, they become non-relativistic when the thermal energy $3 / 2 k T ν$ falls well below the rest mass energy $m ν c 2$ . Non-relativistic matter cools faster than relativistic matter as the Universe expands. Precise calculations, keeping the entropy of each fermion constant, give for today's neutrino temperature $T_nu approx 1.6 cdot 10^{-4} left(m_nu / 1 rm eV right)^{-1} rm K$ .

Derivation of the temperature of the CNB GA_googleFillSlot("encyclopedia_square");

See also

Derivation of the temperature of the CNB