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Metric Expansion Of Space
The metric expansion of space is the increase of the distance between two distant parts of the universe with time.[1] It is an intrinsic expansion whereby the scale of space itself changes. It means that the early universe did not expand "into" anything and does not require space to exist "outside" the universe - instead space itself changed, carrying the early universe with it as it grew. This is a completely different kind of expansion than the expansions and explosions seen in daily life. It also seems to be a property of the entire universe as a whole rather than a phenomenon that applies just to one part of the universe or can be observed from "outside" it. Metric expansion is a key feature of Big Bang
Big Bang
cosmology, is modeled mathematically with the Friedmann-Lemaître-Robertson-Walker metric and is a generic property of the universe we inhabit
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Galaxy Group
A galaxy group[2] or group of galaxies[3] (GrG[4]) is an aggregation of galaxies comprising about 50 or fewer gravitationally bound members, each at least as luminous as the Milky Way
Milky Way
(about 1010 times the luminosity of the Sun); collections of galaxies larger than groups that are first-order clustering are called galaxy clusters.[5] The groups and clusters of galaxies can themselves be clustered, into superclusters of galaxies. The Milky Way
Milky Way
galaxy is part of a group of galaxies called the Local Group.[6]Contents1 Characteristics 2 Types2.1 Compact Groups 2.2 Fossil Groups 2.3 Proto-Groups3 List 4 See also 5 Notes 6 ReferencesCharacteristics[edit] Groups of galaxies are the smallest aggregates of galaxies. They typically contain no more than 50 galaxies in a diameter of 1 to 2 megaparsecs (Mpc).[NB 1] Their mass is approximately 1013 solar masses
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Dark Radiation
Dark radiation
Dark radiation
(also dark electromagnetism)[1] is a postulated type of radiation that mediates interactions of dark matter. By analogy to the way photons mediate electromagnetic interactions between particles in the Standard Model
Standard Model
(called baryonic matter in cosmology), dark radiation is proposed to mediate interactions between dark matter particles.[1] Similar to dark matter particles, the hypothetical dark radiation does not interact with Standard Model particles. There has been no notable evidence for the existence of such radiation, but since baryonic matter contains multiple interacting particle types, it is reasonable to suppose that dark matter does also
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Radiation
In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium.[1][2] This includes:electromagnetic radiation, such as radio waves, microwaves, visible light, x-rays, and gamma radiation (γ) particle radiation, such as alpha radiation (α), beta radiation (β), and neutron radiation (particles of non-zero rest energy) acoustic radiation, such as ultrasound, sound, and seismic waves (dependent on a physical transmission medium) gravitational radiation, radiation that takes the form of gravitational waves, or ripples in the curvature of spacetime. Radiation
Radiation
is often categorized as either ionizing or non-ionizing depending on the energy of the radiated particles. Ionizing radiation carries more than 10 eV, which is enough to ionize atoms and molecules, and break chemical bonds. This is an important distinction due to the large difference in harmfulness to living organisms
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Energy
In physics, energy is the quantitative property that must be transferred to an object in order to perform work on, or to heat, the object.[note 1] Energy
Energy
is a conserved quantity; the law of conservation of energy states that energy can be converted in form, but not created or destroyed. The SI unit of energy is the joule, which is the energy transferred to an object by the work of moving it a distance of 1 metre against a force of 1 newton. Common forms of energy include the kinetic energy of a moving object, the potential energy stored by an object's position in a force field (gravitational, electric or magnetic), the elastic energy stored by stretching solid objects, the chemical energy released when a fuel burns, the radiant energy carried by light, and the thermal energy due to an object's temperature. Mass
Mass
and energy are closely related
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Baryonic Matter
A baryon is a composite subatomic particle made up of three quarks (a triquark, as distinct from mesons, which are composed of one quark and one antiquark). Baryons and mesons belong to the hadron family of particles, which are the quark-based particles. The name "baryon" comes from the Greek word for "heavy" (βαρύς, barys), because, at the time of their naming, most known elementary particles had lower masses than the baryons. As quark-based particles, baryons participate in the strong interaction, whereas leptons, which are not quark-based, do not. The most familiar baryons are the protons and neutrons that make up most of the mass of the visible matter in the universe. Electrons (the other major component of the atom) are leptons. Each baryon has a corresponding antiparticle (antibaryon) where quarks are replaced by their corresponding antiquarks
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Cold Dark Matter
In cosmology and physics, cold dark matter (CDM) is a hypothetical form of dark matter whose particles moved slowly compared to the speed of light (the cold in CDM) since the universe was approximately one year old (a time when the cosmic particle horizon contained the mass of one typical galaxy); and interact very weakly with ordinary matter and electromagnetic radiation (the dark in CDM). It is believed that approximately 84.54% of matter in the Universe
Universe
is dark matter, with only a small fraction being the ordinary baryonic matter that composes stars, planets and living organisms.Contents1 History 2 Structure formation2.1 Lambda CDM model3 Composition 4 Challenges 5 See also 6 References 7 Further readingHistory[edit] The theory[clarification needed] was originally published in 1982 by three independent groups of cosmologists; James Peebles,[1] J
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Warm Dark Matter
Warm dark matter
Warm dark matter
(WDM) is a hypothesized form of dark matter that has properties intermediate between those of hot dark matter and cold dark matter, causing structure formation to occur bottom-up from above their free-streaming scale, and top-down below their free streaming scale. The most common WDM candidates are sterile neutrinos and gravitinos. The WIMPs (weakly interacting massive particles), when produced non-thermally could be candidates for warm dark matter. In general, however the thermally produced WIMPs are cold dark matter candidates.Contents1 keVins and GeVins 2 See also 3 References 4 Further readingkeVins and GeVins[edit] One possible WDM candidate particle with a mass of a few keV comes from introducing two new, zero charge, zero lepton number fermions to the Standard Model
Standard Model
of Particle Physics: "keV-mass inert fermions" (keVins) and "GeV-mass inert fermions" (GeVins)
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Inhomogeneous Cosmology
In cosmology and general relativity, inhomogeneous cosmology in the most general sense (totally inhomogeneous universe) is modelling the universe as a whole with the spacetime which does not possess any spacetime symmetries. Typically considered cosmological spacetimes have either the maximal symmetry which composes of three translational symmetries and three rotational symmetries (homogeneity and isotropy with respect to every point of spacetime), the translational symmetry only (homogeneous models), or the rotational symmetry only (spherically symmetric models). Models with less symmetries (e.g. axisymmetric) are also considered as symmetric. However, it is common to call spherically symmetric models or non-homogeneous models as inhomogeneous. In inhomogeneous cosmology the large-scale structure of the universe is modelled by exact solutions of the Einstein field equations (i.e
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Hot Dark Matter
Hot dark matter
Hot dark matter
(HDM) is a theoretical form of dark matter which consists of particles that travel with ultrarelativistic velocities. Dark matter
Dark matter
is a form of matter that neither emits nor absorbs light. Within physics, this behavior is characterized by dark matter
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Phantom Energy
Phantom energy is a hypothetical form of dark energy satisfying the equation of state with w < − 1 displaystyle w<-1 . It possesses negative kinetic energy, and predicts expansion of the universe in excess of that predicted by a cosmological constant, which leads to a Big Rip.Contents1 Consequences1.1 Big Rip
Big Rip
mechanism2 References 3 Further readingConsequences[edit] The existence of phantom energy could cause the expansion of the universe to accelerate so quickly that a scenario known as the Big Rip, a possible end to the universe, occurs. Big Rip
Big Rip
mechanism[edit] Main article: Big Rip The expansion of the universe reaches an infinite degree in finite time, causing expansion to accelerate without bounds
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Galaxy Cluster
A galaxy cluster, or cluster of galaxies, is a structure that consists of anywhere from hundreds to thousands of galaxies that are bound together by gravity[1] with typical masses ranging from 1014–1015 solar masses. They are the largest known gravitationally bound structures in the universe and were believed to be the largest known structures in the universe until the 1980s, when superclusters were discovered.[2] One of the key features of clusters is the intracluster medium (ICM). The ICM consists of heated gas between the galaxies and has a peak temperature between 2–15 keV that is dependent on the total mass of the cluster. Galaxy
Galaxy
clusters should not be confused with star clusters, such as open clusters, which are structures of stars within galaxies, or with globular clusters, which typically orbit galaxies. Small aggregates of galaxies are referred to as galaxy group rather than clusters of galaxies
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Supercluster
A supercluster is a large group of smaller galaxy clusters or galaxy groups;[1] it is among the largest-known structures of the cosmos. The Milky Way
Milky Way
is part of the Local Group
Local Group
galaxy group (which contains more than 54 galaxies), which in turn is part of the Laniakea Supercluster.[2] This supercluster spans over 500 million light-years, while the Local Group
Local Group
spans over 10 million light-years.[1] The number of superclusters in the observable universe is estimated to be 10 million.[3] Galaxies are grouped into clusters instead of being dispersed randomly. Clusters of galaxies, in turn, are grouped together to form superclusters. Typically, superclusters contain dozens of individual clusters throughout an area of space about 150 million light-years across. Unlike clusters, most superclusters are not bound together by gravity
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Planck Epoch
In particle physics and physical cosmology, Planck units are a set of units of measurement defined exclusively in terms of five universal physical constants, in such a manner that these five physical constants take on the numerical value of 1 when expressed in terms of these units. Originally proposed in 1899 by German physicist Max Planck, these units are also known as natural units because the origin of their definition comes only from properties of nature and not from any human construct. Planck units are only one system of several systems of natural units, but Planck units are not based on properties of any prototype object or particle (that would be arbitrarily chosen), but rather on only the properties of free space. Planck units have significance for theoretical physics since they simplify several recurring algebraic expressions of physical law by nondimensionalization
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Quintessence (physics)
In physics, quintessence is a hypothetical form of dark energy, more precisely a scalar field, postulated as an explanation of the observation of an accelerating rate of expansion of the universe, rather than due to a true cosmological constant. The first example of this scenario was proposed by Ratra and Peebles (1988).[1] The concept was expanded to more general types of time-varying dark energy and the term "quintessence" was first introduced in a paper by Robert R. Caldwell, Rahul Dave and Paul Steinhardt.[2] It has been proposed by some physicists to be a fifth fundamental force. [3][4][5]Quintessence differs from the cosmological constant explanation of dark energy in that it is dynamic; that is, it changes over time, unlike the cosmological constant which, by definition, does not change. It is suggested that quintessence can be either attractive or repulsive depending on the ratio of its kinetic and potential energy
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Photon Epoch
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. The photon epoch started after most leptons and anti-leptons were annihilated at the end of the lepton epoch, about 10 seconds after the Big Bang.[1] Atomic nuclei were created in the process of nucleosynthesis which occurred during the first few minutes of the photon epoch. For the remainder of the photon epoch, the universe contained a hot dense plasma of nuclei, electrons and photons. 379,000 years after the Big Bang
Big Bang
the temperature of the universe fell to the point where nuclei could combine with electrons to create neutral atoms
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