NationMaster - Encyclopedia: Cosmological model

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. Cosmology involves itself with studying the motions of the celestial bodies and the first cause. For most of human history, it has been a branch of metaphysics. Cosmology as a science originates with the Copernican principle, which implies that celestial bodies obey identical physical laws to those on earth, and Newtonian mechanics, which first allowed us to understand those motions. This is now called celestial mechanics. Physical cosmology, as it is now understood, began with the twentieth century development of Albert Einstein's theory of general relativity and better astronomical observations of extremely distant objects. Cosmology, from the Greek: κοσμολογία (cosmologia, κόσμος (cosmos) world + λογια (logia) discourse) is the study of the universe in its totality and by extension mans place in it. ... Spiral Galaxy ESO 269-57 Astrophysics is the tree of astronomy that deals with the physics of the universe, including the physical properties (luminosity, density, temperature and chemical composition) of astronomical objects such as stars, galaxies, and the interstellar medium, as well as their interactions. ... The deepest visible-light image of the cosmos. ... Categories: Wikipedia cleanup | Stub | Philosophy of science | Religious Philosophy | Theology ... Metaphysics (Greek words meta = after/beyond and physics = nature) is a branch of philosophy concerned with the study of first principles and being (ontology). ... Wikimedia Commons has media related to: Science For the scientific journal named Science, see Science (journal). ... The Copernican principle is the philosophical statement that no special observers should be proposed. ... A physical law, scientific law, or a law of nature is a scientific generalization based on empirical observations of physical behavior. ... The original version of the physical discipline of mechanics, due to Sir Isaac Newton, who developed the theory over a period from about 1664, until the publication of his great work, known as the Principia, in 1687. ... Celestial mechanics is a division of astronomy dealing with the motions and gravitational effects of celestial objects. ... (19th century - 20th century - 21st century - more centuries) Decades: 1900s 1910s 1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s The 20th century lasted from 1901 to 2000 in the Gregorian calendar (often from (1900 to 1999 in common usage). ... The factual accuracy of this article is disputed. ... General relativity (GR) is the geometrical theory of gravitation published by Albert Einstein in 1915. ... Lunar astronomy: the large crater is Daedalus, photographed by the crew of Apollo 11 as they circled the Moon in 1969. ...

The twentieth century advances made it possible to speculate about the origins of the universe and allowed scientists to establish the big bang as the leading cosmological theory, which most cosmologists now accept as the basis for their theory and observations. (Some people still advocate alternative cosmologies such as the plasma cosmology and steady state theory, although professional cosmologists generally agree that the big bang best explains observations.) Physical cosmology, roughly speaking, deals with the very largest objects in the universe (galaxies, clusters and superclusters), the very earliest distinct objects to form (quasars) and the very early universe, when it was nearly homogeneous (hot big bang, cosmic inflation and the cosmic microwave background radiation). According to the Big Bang theory, the Universe originated in an extremely dense and hot state (bottom). ... A non-standard cosmology is a cosmological framework that fundamentally contradicts one of the basic aspects of the big bang model of physical cosmology. ... Plasma cosmology is a non-standard cosmological model based on the electromagnetic properties of astrophysical plasmas. ... 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). ... NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 56,000 light years in diameter and approximately 60 million light years distant. ... Galaxy groups and clusters are the largest gravitationally-bound objects. ... Superclusters are large groups of smaller galaxy groups and clusters, and are among the largest structures of the cosmos. ... This view, taken with infrared light, is a false-color image of a quasar-starburst tandem with the most luminous starburst ever seen in such a combination. ... According to the Big Bang theory, the Universe originated in an extremely dense and hot state (bottom). ... Cosmic inflation is the idea, first proposed by Alan Guth in 1981, that the nascent universe passed through a phase of exponential expansion (the inflationary epoch) that was driven by a negative pressure vacuum energy density. ... In cosmology, the cosmic microwave background radiation (most often abbreviated CMB but occasionally CMBR, CBR or MBR) is a form of electromagnetic radiation discovered in 1965. ...

Cosmology is unusual in physics for drawing heavily on the work of particle physicists' experiments, and research into phenomenology and even string theory; from astrophysicists; from general relativity research; and from plasma physics. A black hole concept drawing by NASA. Physics (from the Greek, Ï†Ï…ÏƒÎ¹ÎºÏŒÏ‚ (physikos), natural, and Ï†ÏÏƒÎ¹Ï‚ (physis), nature) is the science of the natural world dealing with the fundamental constituents of the universe, the forces they exert on one another, and the results produced by these forces. ... Particles erupt from the collision point of two relativistic (100GeV) gold ions in the STAR detector of the Relativistic Heavy Ion Collider. ... Research is an active, diligent, and systematic process of inquiry in order to discover, interpret and/or revise facts. ... An artists impression of a 6-dimensional Calabi-Yau manifold, a leading model for extra dimensions in spacetime. ... Spiral Galaxy ESO 269-57 Astrophysics is the tree of astronomy that deals with the physics of the universe, including the physical properties (luminosity, density, temperature and chemical composition) of astronomical objects such as stars, galaxies, and the interstellar medium, as well as their interactions. ... General relativity (GR) is the geometrical theory of gravitation published by Albert Einstein in 1915. ... A Plasma lamp In physics and chemistry, a plasma is an ionized gas, and is usually considered to be a distinct phase of matter. ...

History of physical cosmology

Modern cosmology developed along tandem observational and theoretical tracks. In 1915, Albert Einstein developed his theory of general relativity. At the time, physicists were prejudiced to believe in a perfectly static universe without beginning or end. Einstein added a cosmological constant to his theory to try to force it to allow for a static universe with matter in it. The so-called Einstein universe is, however, unstable. It is bound to eventually start expanding or contracting. The cosmological solutions of general relativity were found by Alexander Friedmann, whose equations describe the Friedmann-Lemaître-Robertson-Walker universe, which may expand or contract. The timeline of cosmology lists the sequence of cosmological theories and discoveries in chronological order. ... This is a (very inadequate) list of cosmologists. ... General relativity (GR) is the geometrical theory of gravitation published by Albert Einstein in 1915. ... The cosmological constant (usually denoted by the Greek capital letter lambda: Î›) occurs in Einsteins theory of general relativity. ... Alexander Alexandrovich Friedman (June 16, 1888 – September 16, Russian cosmologist and mathematician. ... The Friedmann-LemaÃ®tre-Robertson-Walker (FLRW) metric describes a homogeneous, isotropic expanding/contracting universe. ...

In the 1910s, Vesto Slipher and later Carl Wilhelm Wirtz interpreted the red shift of spiral nebulae as a Doppler shift that indicated they were receding from Earth. However, it is notoriously difficult to determine the distance to astronomical objects: even if it is possible to measure their angular size it is usually impossible to know their actual size or luminosity. They did not realize that the nebulae were actually galaxies outside our own Milky Way, nor did they speculate about the cosmological implications. In 1927, the Belgian catholic priest Georges Lemaître independently derived the Friedmann-Lemaître-Robertson-Walker equations and proposed, on the basis of the recession of spiral nebulae, that the universe began with the "explosion" of a "primeval atom"—what was later called the big bang. In 1929, Edwin Hubble provided an observational basis for Lemaître's theory. Hubble proved that the spiral nebulae were galaxies and measured their distances by observing Cepheid variable stars. He discovered a relationship between the redshift of a galaxy and its luminosity. He interpreted this as evidence that the galaxies are receding in every direction at speeds (relative to the Earth) directly proportional to their distance. This fact is known as Hubble's law. The relationship between distance and speed, however, was accurately ascertained only relatively recently: Hubble was off by a factor of ten.-1... Vesto Melvin Slipher (November 11, 1875 – November 8, 1969) was an American astronomer. ... Carl Wilhelm Wirtz was an astronomer who spent his time between Germany and the Observatory of Strasbourg. ... This article is about the light phenomenon. ... The Triangulum Emission Nebula NGC 604 lies in a spiral arm of Galaxy M33, 2. ... The Doppler effect is the apparent change in frequency or wavelength of a wave that is perceived by an observer moving relative to the source of the waves. ... Earth is the third planet from the Sun. ... Angular size is a measurement of how large or small something is using rotational measurement (degrees of arc, arc_minutes, and arc-seconds). ... Luminosity has different meanings in several different fields of science. ... A NASA artists conception of what the Milky Way would look like if seen off-axis. ... 1927 (MCMXXVII) was a common year starting on Saturday (link will take you to calendar). ... Roman Catholic priest LCDR Allen R. Kuss (USN) aboard USS Enterprise A priest or priestess is a holy man or woman who takes an officiating role in worship of any religion, with the distinguishing characteristic of offering sacrifices. ... Georges-Henri LemaÃ®tre (July 17, 1894 â€“ June 20, 1966) was a Belgian Roman Catholic priest and astronomer. ... Properties An atom (Greek Î¬Ï„Î¿Î¼Î¿Î½ from Î¬: non and Ï„Î¿Î¼Î¿Î½: divisible) is a submicroscopic structure found in all ordinary matter. ... 1929 (MCMXXIX) was a common year starting on Tuesday (link will take you to calendar). ... Edwin Hubble Edwin Powell Hubble (November 20, 1889 â€“ September 28, 1953) was an American astronomer, noted for his discovery of galaxies beyond the Milky Way and the cosmic red shift. ... A Cepheid variable or Cepheid is a member of a particular class of variable stars, notable for a fairly tight correlation between their period of variability and absolute luminosity. ... Redshift of spectral lines in the optical spectrum of a supercluster of distant galaxies (right), as compared to that of the Sun (left). ... Luminosity has different meanings in several different fields of science. ... Hubbles law is the statement in physical cosmology that the redshift in light coming from distant galaxies is proportional to their distance. ...

Given the cosmological principle, Hubble's law suggested that the universe was expanding. This idea allowed for two opposing possibilities. One was Lemaître's Big Bang theory, advocated and developed by George Gamow. The other possibility was Fred Hoyle's steady state model in which new matter would be created as the galaxies moved away from each other. In this model, the universe is roughly the same at any point in time. The Cosmological Principle is a principle invoked in cosmology that severely restricts the large variety of possible cosmological theories: On large scales, the Universe is homogeneous and isotropic. ... Sir Fred Hoyle Sir Fred Hoyle (June 24, 1915 in Yorkshire â€“ August 20, 2001 in Bournemouth, England) was a British astronomer, notable for a number of his theories that run counter to current astronomical opinion, and a writer of science fiction, including a number of books co-authored by his... For alternative meanings see steady state (disambiguation). ...

For a number of years the support for these theories was evenly divided. However, the observational evidence began to support the idea that the universe evolved from a hot dense state. Since the discovery of the cosmic microwave background in 1965 it has been regarded as the best theory of the origin and evolution of the cosmos. Before the late 1960s, many cosmologists thought the infinitely dense singularity at the starting time of Friedmann's cosmological model was a mathematical over-idealization, and that the universe was contracting before entering the hot dense state and starting to expand again. This is Richard Tolman's oscillatory universe. In the sixties, Stephen Hawking and Roger Penrose demonstrated that this idea was unworkable, and the singularity is an essential feature of Einstein's gravity. This led the majority of cosmologists to accept the Big Bang, in which the universe we observe began a finite time ago. 1965 (MCMLXV) was a common year starting on Friday (link goes to calendar). ... The 1960s decade refers to the years from 1960 to 1969, inclusive. ... Singularity has several different meanings: mathematical singularity - a point where a mathematical function goes to infinity or is in certain other ways ill-behaved. ... Richard C. Tolman was California Institute of Technology professor of physical chemistry and mathematical physics. ... The oscillatory universe is the hypothesis, attributable to Richard Tolman, that the universe undergoes an infinite series of oscillations, each beginning with a big bang and ending with a big crunch. ... Stephen Hawking in 2005 Professor Stephen William Hawking, D.Phil. ... Sir Roger Penrose, OM, FRS (born 8 August 1931) is an English mathematical physicist and Emeritus Rouse Ball Professor of Mathematics at the University of Oxford. ...

Areas of study

Below, some of the most active areas of inquiry in cosmology are described, in roughly chronological order. This does not include all of the big bang cosmology, which is presented in cosmological timeline. This timeline attempts to show the best scientific estimates of the timings of past events and predictions of the approximate timing of hypothetical future events with cosmological significance. ...

The very early universe

While the early, hot universe appears to be well explained by the big bang from roughly 10^-33 seconds onwards, there are several problems. One is that there is no compelling reason, using current particle physics, to expect the universe to be flat, homogeneous and isotropic (see the cosmological principle). Moreover, grand unified theories of particle physics suggest that there should be magnetic monopoles in the universe, which have not been found. These problems are resolved by a brief period of cosmic inflation, which drives the universe to flatness; smooths out anisotropies and inhomogeneities to the observed level; and exponentially dilutes the monopoles. The physical model behind cosmic inflation is extremely simple, however it has not yet been confirmed by particle physics, and there are difficult problems reconciling inflation and quantum field theory. Some cosmologists think that string theory and brane cosmology will provide an alternative to inflation. According to the Big Bang theory, the Universe originated in an extremely dense and hot state (bottom). ... The shape of the Universe is a subject of investigation within cosmology. ... It has been suggested that this article or section be merged with homogeneity. ... 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. ... The Cosmological Principle is a principle invoked in cosmology that severely restricts the large variety of possible cosmological theories: On large scales, the Universe is homogeneous and isotropic. ... Grand unification, grand unified theory, or GUT is a theory in physics that unifies the strong interaction and electroweak interaction. ... In physics, a magnetic monopole is a hypothetical particle that may be loosely described as a magnet with only one pole (see electromagnetic theory for more on magnetic poles). ... Cosmic inflation is the idea, first proposed by Alan Guth in 1981, that the nascent universe passed through a phase of exponential expansion (the inflationary epoch) that was driven by a negative pressure vacuum energy density. ... Quantum field theory (QFT) is the application of quantum mechanics to fields. ... An artists impression of a 6-dimensional Calabi-Yau manifold, a leading model for extra dimensions in spacetime. ... Brane cosmology is a protoscience motivated by, but not rigorously derived from, superstring theory and M-theory. ...

Another major problem in cosmology is what has caused the universe to contain more particles than antiparticles. Cosmologists can use X-ray observations to deduce that the universe is not split into regions of matter and antimatter, but rather is predominantly made of matter. This problem is called the baryon asymmetry, and the theory to describe the resolution is called baryogenesis. The theory of baryogenesis was worked out by Andrei Sakharov in 1967, and requires a violation of the particle physics symmetry, called CP-symmetry, between matter and antimatter. Particle accelerators, however, measure too small a violation of CP-symmetry to account for the baryon asymmetry. Cosmologists and particle physicists are trying to find additional violations of the CP-symmetry in the early universe that might account for the baryon asymmetry. Antimatter or contra-terrene matter is matter that is composed of the antiparticles of those that constitute normal matter. ... In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz... Baryogenesis is the generic designation for the physical processes that generate matter (more specifically, a class of fundamental particle called baryon) from an otherwise matter-empty state (such as it is generally believed to be the state of the Universe at its onset, the so-called Big Bang). ... Andrei Sakharov, 1943 Andrei Dmitrievich Sakharov (ÐÐ½Ð´Ñ€ÐµÌÐ¹ Ð”Ð¼Ð¸ÌÑ‚Ñ€Ð¸ÐµÐ²Ð¸Ñ‡ Ð¡Ð°ÌÑ…Ð°Ñ€Ð¾Ð², May 21, 1921 â€“ December 14, 1989), was an eminent Soviet-Russian nuclear physicist, dissident and human rights activist. ... Square with symmetry group D4 Symmetry is a characteristic of geometrical shapes, equations, and other objects; we say that such an object is symmetric with respect to a given operation if this operation, when applied to the object, does not appear to change it. ... CP-symmetry is a symmetry obtained by a combination of the C-symmetry and the P-symmetry. ...

Both the problems of baryogenesis and cosmic inflation of these problems are very closely related to particle physics, and their resolution might come from high energy theory and experiment, rather than through observations of the universe. A 1960s single stage 2MeV linear Van de Graaff accelerator, here opened for maintenance A particle accelerator is a device which uses electric and/or magnetic fields to propel electrically charged particles to high speeds. ...

Big bang nucleosynthesis

Big Bang Nucleosynthesis is the theory of the formation of the elements in the early universe. It finished when the universe was about three minutes old and its temperature fell enough that nuclear fusion ceased. Because the time in which big bang nucleosynthesis occurred was so short, only the very lightest elements were produced, unlike in stellar nucleosynthesis. Starting from hydrogen ions (protons), it principally produced deuterium, helium-4 and lithium. Other elements were produced in only trace abundances. While the basic theory of nucleosynthesis has been understood for decades (it was developed in 1948 by George Gamow, Ralph Asher Alpher and Robert Herman) it is an extremely sensitive probe of physics at the time of the big bang, as the theory of big bang nucleosynthesis connects the abundances of primordial light elements with the features of the early universe. Specifically, it can be used to test the equivalence principle, to probe dark matter and test neutrino physics. Some cosmologists have proposed that big bang nucleosynthesis suggests there is a fourth "sterile" species of neutrino. In cosmology, Big Bang nucleosynthesis (alternately: 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. ... Temperature is the physical property of a system which underlies the common notions of hot and cold; the material with the higher temperature is said to be hotter. ... The deuterium-tritium (D-T) fusion reaction is considered the most promising for producing fusion power. ... Cross section of a red giant showing nucleosynthesis and elements formed Stellar nucleosynthesis is the collective term for the nuclear reactions taking place in stars to build the nuclei of the heavier elements. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... // An ion is an atom or group of atoms with a net electric charge. ... Properties In physics, the proton (Greek proton = first) is a subatomic particle with an electric charge of one positive fundamental unit (1. ... Deuterium, also called heavy hydrogen, is a stable isotope of hydrogen with a natural abundance of one atom in 6500 of hydrogen. ... General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Atomic mass 4. ... General Name, Symbol, Number lithium, Li, 3 Chemical series alkali metals Group, Period, Block 1, 2, s Appearance silvery white/gray Atomic mass 6. ... George Gamow (pronounced GAM-off) (March 4, 1904 â€“ August 19, 1968) , born Georgiy Antonovich Gamow (Ð“ÐµÐ¾Ñ€Ð³Ð¸Ð¹ ÐÐ½Ñ‚Ð¾Ð½Ð¾Ð²Ð¸Ñ‡ Ð“Ð°Ð¼Ð¾Ð²) 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. ... THERE IS NO SUCH THING< MWAHAHAHAHAHAHAHA> In relativity, the equivalence principle is applied to several related concepts dealing with gravitation and the uniformity of physical measurements in different frames of reference. ... This refers to the cosmological use of the term. ... The neutrino is an elementary particle. ...

Cosmic microwave background

The cosmic microwave background is radiation left over from decoupling, when atoms first formed, and the radiation produced in the big bang stopped Thomson scattering from charged ions. The radiation, first observed in 1965 by Arno Penzias and Robert Woodrow Wilson, has a perfect thermal black-body spectrum. It has a temperature of 2.7 kelvins today and is isotropic to one part in 10⁵. Cosmological perturbation theory, which describes the evolution of slight inhomogeneities in the early universe, has allowed cosmologists to precisely calculate the angular power spectrum of the radiation, and it has been measured by the recent satellite experiments (COBE and WMAP) and many ground and balloon-based experiments (such as Degree Angular Scale Interferometer, Cosmic Background Imager, and Boomerang). One of the goals of these efforts is to measure the basic parameters of the Lambda-CDM model with increasing accuracy, as well as to test the predictions of the big bang model and look for new physics. The recent measurements made by WMAP, for example, have placed limits on the neutrino masses. 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. ... In physics, decoupling is the general phenomenon in which the interactions between some physical objects (such as elementary particles) disappear. ... Properties For alternative meanings see atom (disambiguation). ... Thomson scattering is the scattering of electromagnetic radiation by a charged particle. ... Arno Allan Penzias (born April 26, American physicist. ... Robert Woodrow Wilson (born January 10, 1936) is an American physicist. ... As the temperature decreases, the peak of the black body radiation curve moves to lower intensities and longer wavelengths. ... The kelvin (symbol: K) is the SI unit of temperature, and is one of the seven SI base units. ... The power spectrum is a plot of the portion of a signals power (energy per unit time) falling within given frequency bins. ... The Cosmic Background Explorer (COBE), also referred to as Explorer 66, was the first satellite built dedicated to cosmology. ... Alternate meaning: WMAP (AM) 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 on the Chajnantor plateau in the Chilean Andes. ... The Boomerang experiment measured the cosmic microwave background radiation during three sub_orbital balloon flights. ... Î›CDM or Lambda-CDM is an abbreviation for Lambda-Cold Dark Matter. ...

Newer experiments are trying to measure the polarization of the cosmic microwave background, which will provide further confirmation of the theory as well as information about cosmic inflation, and the so-called secondary anisotropies, such as the Sunyaev-Zel'dovich effect and Sachs-Wolfe effect, which are caused by interaction between galaxies and clusters with the cosmic microwave background. In electrodynamics, polarization (also spelled polarisation) is a property of waves, such as light and other electromagnetic radiation. ... 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. ... NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 56,000 light years in diameter and approximately 60 million light years distant. ... Galaxy groups and clusters are the largest gravitationally-bound objects. ...

Formation and evolution of large-scale structure

Understanding the formation and evolution of the largest and earliest structures (ie, quasars, galaxies, clusters and superclusters) is one of the largest efforts in cosmology. Cosmologists study a model of hierarchical structure formation in which structures form from the bottom up, with smaller objects forming first, while the largest objects, such as superclusters, are still assembling. The most straightforward way to study structure in the universe is to survey the visible galaxies, in order to construct a three-dimensional picture of the galaxies in the universe and measure the matter power spectrum. This is the approach of the Sloan Digital Sky Survey and the 2dF Galaxy Redshift Survey. Astronomy and cosmology examine the universe to understand the 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 inhomogeneous one we live in? How did galaxies form? How do galaxies change over time? The formation of galaxies is still one of the most active research areas in astrophysics... This view, taken with infrared light, is a false-color image of a quasar-starburst tandem with the most luminous starburst ever seen in such a combination. ... NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 56,000 light years in diameter and approximately 60 million light years distant. ... Galaxy groups and clusters are the largest gravitationally-bound objects. ... Superclusters are large groupings of smaller galaxy groups and clusters, and are among the largest structures of the cosmos. ... The power spectrum is a plot of the portion of a signals power (energy per unit time) falling within given frequency bins. ... The Sloan Digital Sky Survey or SDSS is a major redshift survey using a dedicated 2. ... 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. ...

An important tool for understanding these structure formation is simulations, which cosmologists use to study the gravitational aggregation of matter in the universe, as it clusters into filaments, superclusters and voids. Most simulations contain only non-baryonic cold dark matter, which should suffice to understand the universe on the largest scales, as there is much more dark matter in the universe than visible, baryonic matter. More advanced simulations are starting to include baryons and study the formation of individual galaxies. Cosmologists study these simulations to see if they agree with the galaxy surveys, and to understand any discrepancy. In astronomy, filaments are one of the largest known structures in the Universe, thread-like structures with a typical length of 70 to 150 megaparsec that form the boundaries between large voids in the universe. ... Look up Void in Wiktionary, the free dictionary Void can refer to: Aether as the source of all elements, the quintessence. ... Cold dark matter (or CDM) is a refinement of the big bang theory that contains the additional assumption that most of the matter in the Universe consists of material which cannot be observed by its electromagnetic radiation and hence is dark while at the same time the particles making up...

Other, complementary techniques will allow cosmologists to measure the distribution of matter in the distant universe and to probe reionization. These include: In Big Bang cosmology, Reionization is the process that reionized the matter in the universe after the epoch of galaxy formation. ...

These will help cosmologists settle the question of when the first quasars formed. The Lyman alpha Forest is the sum of absorption lines seen in spectra of distant galaxies and quasars, beginning from the Lyman alpha line at 121. ... A gravitational lens is formed when the light from a very distant, bright source (such as a quasar) is bent around a massive object (such as a massive galaxy) between the source object and the observer. ...

Dark matter

Evidence from big bang nucleosynthesis, the cosmic microwave background and structure formation suggests that about 25% of the mass of the universe consists of non-baryonic dark matter, whereas only 4% consists of visible, baryonic matter. The gravitational effects of dark matter are well understood, as it behaves like cold, non-radiative dust which forms around haloes around galaxies. Dark matter has never been detected in the laboratory: the particle physics nature of dark matter is completely unknown. However, there are a number of candidates, such as a stable supersymmetric particle, a weakly interacting massive particle, an axion, a massive compact halo object or even a modification of gravity at small accelerations (MOND) or an effect from brane cosmology. This refers to the cosmological use of the term. ... Radioactive decay is the set of various processes by which unstable atomic nuclei (nuclides) emit subatomic particles (radiation). ... The galactic halo is a region of space surrounding spiral galaxies, including our galaxy, the Milky Way. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... This article is about the hypothetical class of particles. ... The axion is a hypothetical exotic particle postulated by Peccei-Quinn theory to resolve the strong-CP problem in quantum chromodynamics (QCD). ... Massive compact halo object, or MACHO, is a general name for any kind of astronomical body that might explain the apparent presence of dark matter in galaxy halos. ... Wikipedia does not yet have an article with this exact name. ... Brane cosmology is a protoscience motivated by, but not rigorously derived from, superstring theory and M-theory. ...

The physics at the center of galaxies (see active galactic nuclei, supermassive black hole) may give some clues about the nature of dark matter. An active galaxy is a galaxy where a significant fraction of the energy output is not emitted by the normal components of a galaxy: stars, dust and interstellar gas. ... Top: artists conception of a supermassive black hole drawing material from a nearby star. ...

Dark energy

If the universe is to be flat, there must be an additional component making up 71% (in addition to the 25% dark matter and 4% baryons) of the density of the universe. This is called dark energy. In order not to interfere with big bang nucleosynthesis and the cosmic microwave background, it must not cluster in haloes like baryons and dark matter. There is strong observational evidence for dark energy, as the total mass of the universe is known, since it is measured to be flat, but the amount of clustering matter is tightly measured, and is much less than this. The case for dark energy was strengthened in 1999, when measurements demonstrated that the expansion of the universe is accelerating, much like the more rapid acceleration during cosmic inflation. In cosmology, dark energy is a hypothetical form of energy which permeates all of space and has strong negative pressure. ...

However, apart from its density and its clustering properties, nothing is known about dark energy. Quantum field theory predicts a cosmological constant much like dark energy, but 120 orders of magnitude too large. Steven Weinberg and a number of string theorists (see string landscape) have used this as evidence for the anthropic principle, which suggests that the cosmological constant is so small because life (and thus physicists, to make observations) cannot exist in a universe with a large cosmological constant, but many people find this an unsatisfying explantion. Other possible explanations for dark energy include quintessence or a modification of gravity on the largest scales. The effect on cosmology of the dark energy that these models describe is given by the dark energy's equation of state, which varies depending upon the theory. The nature of dark energy is one of the most challenging problems in cosmology. Quantum field theory (QFT) is the application of quantum mechanics to fields. ... The cosmological constant (usually denoted by the Greek capital letter lambda: Î›) occurs in Einsteins theory of general relativity. ... An order of magnitude is the class of scale or magnitude of any amount, where each class contains values of a fixed ratio to the class preceding it. ... Steven Weinberg at Harvard University Steven Weinberg (born May 3, 1933) is an American physicist. ... The string landscape is an idea to implement the anthropic principle, in particular Steven Weinbergs proposal for anthropic selection of the vacuum density, in string theory. ... In cosmology, the anthropic principle in its most basic form states the truism that any valid theory of the universe must be consistent with our existence as carbon-based human beings at this particular time and place in the universe. ... In physics, quintessence is a hypothetical form of dark energy postulated as an explanation of observations of an accelerating 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. ...

A better understanding of dark energy is likely to solve the problem of the ultimate fate of the universe. In the current cosmological epoch, the accelerated expansion due to dark energy is preventing structures larger than superclusters from forming. It is not known whether the acceleration will continue indefinitely, perhaps even increasing and cause a big rip, or whether it will eventually reverse. To meet Wikipedias quality standards, this article or section may require cleanup. ... The Big Rip is a cosmological hypothesis about the ultimate fate of the Universe. ...

Other areas of inquiry

A primordial black hole is a hypothetical type of black hole that is formed not by the gravitational collapse of a star but by the extreme densities of matter present during early universe. ... The Greisen-Zatsepin-Kuzmin limit (GZK limit) is a theoretical upper limit on the energy of cosmic rays from distant sources. ... Special relativity (SR) or the special theory of relativity is the physical theory published in 1905 by Albert Einstein in his article On the Electrodynamics of Moving Bodies. It replaced Newtonian notions of space and time and incorporated electromagnetism as represented by Maxwells equations. ... THERE IS NO SUCH THING< MWAHAHAHAHAHAHAHA> In relativity, the equivalence principle is applied to several related concepts dealing with gravitation and the uniformity of physical measurements in different frames of reference. ...

References

Contents

History of physical cosmology

Areas of study

The very early universe

Big bang nucleosynthesis

Cosmic microwave background

Formation and evolution of large-scale structure

Dark matter

Dark energy

Other areas of inquiry

References

Popular reading

Textbooks

External references

From groups

From individuals

Contents

History of physical cosmology GA_googleFillSlot("encyclopedia_square");

Areas of study

The very early universe

Big bang nucleosynthesis

Cosmic microwave background

Formation and evolution of large-scale structure

Dark matter

Dark energy

Other areas of inquiry

References

Popular reading

Textbooks

External references

From groups

From individuals

History of physical cosmology