NationMaster - Encyclopedia: Dark energy

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. ^[1] Assuming the existence of dark energy is the most popular way to explain recent observations that the universe appears to be expanding at an accelerating rate. In the standard model of cosmology, dark energy currently accounts for almost three-quarters of the total mass-energy of the universe. This article is about the physics subject. ... 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 deceleration parameter in cosmology is a dimensionless measure of the cosmic acceleration of the expansion of the universe. ... A pie chart indicating the proportional composition of different energy-density components of the universe. ...

Two proposed forms for dark energy are the cosmological constant, a constant energy density filling space homogeneously,^[2] and scalar fields such as quintessence or moduli, dynamic fields whose energy density can vary in time and space. In fact contributions from scalar fields which are constant in space are usually also included in the cosmological constant. The cosmological constant is thought to arise from the vacuum energy. Scalar fields which do change in space are hard to distinguish from a cosmological constant, because the change may be extremely slow. In physical cosmology, the cosmological constant (usually denoted by the Greek capital letter lambda: Î›) was proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a stationary universe. ... It has been suggested that quartic interaction be merged into this article or section. ... In physics, quintessence is a hypothetical form of dark energy postulated as an explanation of observations of an accelerating universe. ... In theoretical physics, moduli are scalar fields whose different values are equally good (each one such scalar field is called a modulus). ... It has been suggested that quartic interaction be merged into this article or section. ... In physical cosmology, the cosmological constant (usually denoted by the Greek capital letter lambda: Î›) was proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a stationary universe. ... In physical cosmology, the cosmological constant (usually denoted by the Greek capital letter lambda: Î›) was proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a stationary universe. ... Vacuum energy is an underlying background energy that exists in space even when devoid of matter (known as free space). ...

High-precision measurements of the expansion of the universe are required to understand how the speed of the expansion changes over time. The rate of expansion is parameterized by the cosmological equation of state. Measuring the equation of state of dark energy is one of the biggest efforts in observational cosmology today. 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. ... 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. ...

Adding the cosmological constant to cosmology's standard FLRW metric leads to the Lambda-CDM model, which has been referred to as the "standard model" of cosmology because of its precise agreement with observations. // 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. ... A pie chart indicating the proportional composition of different energy-density components of the universe. ...

Negative pressure

Strangely, dark energy causes expansion because it has strong negative pressure. Pressure is defined in terms of a force applied over an area. ...

A substance has positive pressure when it pushes outward on its surroundings. This is the usual situation for fluids. Negative pressure, or tension, exists when the substance instead pulls on its surroundings. A common example of negative pressure occurs when a solid is stretched to support a hanging weight.

According to the Friedmann-Lemaître-Robertson-Walker metric, which is an application of General Relativity to cosmology, the pressure within a substance contributes to its gravitational attraction for other things just as its mass density does. Negative pressure causes a gravitational repulsion. // 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. ... For a less technical and generally accessible introduction to the topic, see Introduction to general relativity. ...

The gravitational repulsive effect of dark energy's negative pressure is greater than the gravitational attraction caused by the energy itself. At the cosmological scale, it also overwhelms all other forms of gravitational attraction, resulting in the accelerating expansion of the universe.

One might wonder, how can pushing cause attraction? How can pulling cause repulsion? This sounds like a contradiction. The solution is:

Evidence for dark energy

In 1998, observations of type Ia supernovae ("one-A") by the Supernova Cosmology Project at the Lawrence Berkeley National Laboratory and the High-z Supernova Search Team suggested that the expansion of the universe is accelerating.^[3]^[4] Since then, these observations have been corroborated by several independent sources. Measurements of the cosmic microwave background, gravitational lensing, and the large scale structure of the cosmos as well as improved measurements of supernovae have been consistent with the Lambda-CDM model.^[5] Multiwavelength X-ray image of the remnant of Keplers Supernova, SN 1604. ... The Supernova Cosmology Project is one of two research teams that determined the likelihood of an accelerating universe and therefore a positive Cosmological constant. ... The Berkeley Lab is perched on a hill overlooking the Berkeley central campus and San Francisco Bay. ... The High-z Supernova Search Team is an international cosmology group which uses Type Ia Supernovae to chart the expansion of the universe. ... For other uses, see Universe (disambiguation). ... The deceleration parameter in cosmology is a dimensionless measure of the cosmic acceleration of the expansion of the universe. ... 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. ... 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. ... 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. ...

The type Ia supernovae provide the most direct evidence for dark energy. Measuring the scale factor at the time that light was emitted from an object is accomplished easily by measuring the redshift of the receding object. Finding the distance to an object is a more difficult problem, however. It is necessary to find standard candles: objects for which the actual brightness, what astronomers call the absolute magnitude, is known, so that it is possible to relate the observed brightness, or apparent magnitude, to the distance. Without standard candles, it is impossible to measure the redshift-distance relation of Hubble's law. Type Ia supernovae are the best known standard candles for cosmological observation because they are very bright and thus visible across billions of light years. The consistency in absolute magnitude for type Ia supernovae is explained by the favored model of an old white dwarf star which gains mass from a companion star and grows until it reaches the precisely defined Chandrasekhar limit. At this mass, the white dwarf is unstable to thermonuclear runaway and explodes as a type Ia supernova with a characteristic brightness. The observed brightness of the supernovae are plotted against their redshifts, and this is used to measure the expansion history of the universe. These observations indicate that the expansion of the universe is not decelerating, which would be expected for a matter-dominated universe, but rather is mysteriously accelerating. These observations are explained by postulating a kind of energy with negative pressure (see equation of state (cosmology) for a mathematical explanation): dark energy. Redshift of spectral lines in the optical spectrum of a supercluster of distant galaxies (right), as compared with that of the Sun (left). ... A standard candle is an astronomical object that has a known luminosity. ... In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standard luminosity distance away from us, in the absence of interstellar extinction. ... The apparent magnitude (m) of a star, planet or other celestial body is a measure of its apparent brightness as seen by an observer on Earth. ... Hubbles law is the statement in physical cosmology that the redshift in light coming from distant galaxies is proportional to their distance. ... This article or section does not adequately cite its references or sources. ... The Chandrasekhar limit, is the maximum mass possible for a white dwarf (one of the end stages of stars when they cool down) and is approximately 3 Ã— 1030 kg, around 1. ... This article or section does not adequately cite its references or sources. ... The deceleration parameter in cosmology is a dimensionless measure of the cosmic acceleration of the expansion of the 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. ...

The existence of dark energy, in whatever form, is needed to reconcile the measured geometry of space with the total amount of matter in the universe. Measurements of the cosmic microwave background (CMB), most recently by the WMAP satellite, indicate that the universe is very close to flat. For the shape of the universe to be flat, the mass/energy density of the Universe must be equal to a certain critical density. The total amount of matter in the Universe (including baryons and dark matter), as measured by the CMB, accounts for only about 30% of the critical density. This implies the existence of an additional form of energy to account for the remaining 70%.^[5] 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. ... 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 shape of the Universe is an informal name for a subject of investigation within physical cosmology. ... The flatness problem is a cosmological problem with the Big Bang theory, which is solved by hypothesising an inflationary universe. ... In cosmology, the Big Crunch is a hypothesis that states the universe will stop expanding and start to collapse upon itself; a counterpart to the Big Bang. ... In particle physics, the baryons are a family of subatomic particles including the proton and the neutron (collectively called Greek barys, meaning heavy, as they are heavier than the other main groups of particles. ... In 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. ...

The theory of large scale structure, which governs the formation of structure in the universe (stars, quasars, galaxies and galaxy clusters), also suggests that the density of matter in the universe is only 30% of the critical density. Astronomy and cosmology examine the universe to understand the large-scale structure of the cosmos. ... STAR is an acronym for: Organizations Society of Ticket Agents and Retailers], the self-regulatory body for the entertainment ticket industry in the UK. Society for Telescopy, Astronomy, and Radio, a non-profit New Jersey astronomy club. ... The introduction to this article provides insufficient context for those unfamiliar with the subject matter. ... For other uses, see Galaxy (disambiguation). ... Galaxy groups and clusters are super-structures in the spread of galaxies of the cosmos. ...

The most recent WMAP observations are consistent with a Universe made up of 74% dark energy, 22% dark matter, and 4% ordinary matter.

Nature of dark energy

The exact nature of this dark energy is a matter of speculation. It is known to be very homogeneous, not very dense and is not known to interact through any of the fundamental forces other than gravity. Since it is not very dense—roughly 10⁻²⁹ grams per cubic centimeter—it is hard to imagine experiments to detect it in the laboratory. Dark energy can only have such a profound impact on the universe, making up 70% of all energy, because it uniformly fills otherwise empty space. The two leading models are quintessence and the cosmological constant. Image File history File links Cosmological_composition. ... Image File history File links Cosmological_composition. ... For other uses, see Density (disambiguation). ... A fundamental interaction is a mechanism by which particles interact with each other, and which cannot be explained by another more fundamental interaction. ... Gravity is a force of attraction that acts between bodies that have mass. ...

Cosmological constant

The simplest explanation for dark energy is that it is simply the "cost of having space": that is, a volume of space has some intrinsic, fundamental energy. This is the cosmological constant, sometimes called Lambda (hence Lambda-CDM model) after the Greek letter Λ, the symbol used to mathematically represent this quantity. Since energy and mass are related by

E = m c 2

, Einstein's theory of general relativity predicts that it will have a gravitational effect. It is sometimes called a vacuum energy because it is the energy density of empty vacuum. In fact, most theories of particle physics predict vacuum fluctuations that would give the vacuum exactly this sort of energy. The cosmological constant is estimated by cosmologists to be on the order of 10⁻²⁹g/cm³, or about 10⁻¹²⁰ in reduced Planck units. A pie chart indicating the proportional composition of different energy-density components of the universe. ... For a less technical and generally accessible introduction to the topic, see Introduction to general relativity. ... Vacuum energy is an underlying background energy that exists in space even when devoid of matter (known as free space). ... Look up Vacuum in Wiktionary, the free dictionary. ... Thousands of particles explode from the collision point of two relativistic (100 GeV per nucleon) gold ions in the STAR detector of the Relativistic Heavy Ion Collider. ... In the description of the interaction between elementary particles in quantum field theory, a virtual particle is a temporary elementary particle, used to describe an intermediate stage in the interaction. ... // In physics, Planck units are physical units of measurement originally proposed by Max Planck. ...

The cosmological constant has negative pressure equal to its energy density and so causes the expansion of the universe to accelerate (see equation of state (cosmology)). The reason why a cosmological constant has negative pressure can be seen from classical thermodynamics; Energy must be lost from inside a container to do work on the container. A change in volume dV requires work done equal to a change of energy −p dV, where p is the pressure. But the amount of energy in a box of vacuum energy actually increases when the volume increases (dV is positive), because the energy is equal to ρV, where ρ (rho) is the energy density of the cosmological constant. Therefore, p is negative and, in fact, p = −ρ. The deceleration parameter in cosmology is a dimensionless measure of the cosmic acceleration of the expansion of the 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 major outstanding problem is that most quantum field theories predict a huge cosmological constant from the energy of the quantum vacuum, up to 120 orders of magnitude too large. This would need to be cancelled almost, but not exactly, by an equally large term of the opposite sign. Some supersymmetric theories require a cosmological constant that is exactly zero, which does not help. The present scientific consensus amounts to extrapolating the empirical evidence where it is relevant to predictions, and fine-tuning theories until a more elegant solution is found. Philosophically, our most elegant solution may be to say that if things were different, we would not be here to observe anything - the anthropic principle.^[6] Technically, this amounts to checking theories against macroscopic observations. Unfortunately, as the known error margin in the constant predicts the fate of the universe more than its present state, many such "deeper" questions remain unknown. This is a list of some of the unsolved problems in physics. ... Quantum field theory (QFT) is the quantum theory of fields. ... In the description of the interaction between elementary particles in quantum field theory, a virtual particle is a temporary elementary particle, used to describe an intermediate stage in the interaction. ... 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. ... This article or section is in need of attention from an expert on the subject. ... In mathematics, extrapolation is the process of constructing new data points outside a discrete set of known data points. ... A central concept in science and the scientific method is that all evidence must be empirical, or empirically based, that is, dependent on evidence or consequences that are observable by the senses. ... Fine Tuning is the name of XM Satellite Radios eclectic music channel. ... In physics and cosmology, the anthropic principle is an umbrella term for various dissimilar attempts to explain the structure of the universe by way of coincidentally balanced features that are necessary and relevant to the existence of observers (usually assumed to be carbon-based life or even specifically human beings). ... Many religions have postulated an end to the Universe. ...

Another problem arises with inclusion of the cosmic constant in the standard model which is appearance of solutions with regions of discontinuities (see classification of discontinuities for three examples) at low matter density.^[7] The discontinuity also affects the past sign of the vacuum energy, changing from the current negative pressure to attractive, as one looks back towards the early Universe. This finding should be considered a shortcoming of the standard model, but only when a term for vacuum energy is included. Continuous functions are of utmost importance in mathematics and applications. ...

In spite of its problems, the cosmological constant is in many respects the most economical solution to the problem of cosmic acceleration. One number successfully explains a multitude of observations. Thus, the current standard model of cosmology, the Lambda-CDM model, includes the cosmological constant as an essential feature. For the House television show episode called Occams Razor, see Occams Razor (House episode) Occams razor (sometimes spelled Ockhams razor) is a principle attributed to the 14th-century English logician and Franciscan friar William of Ockham. ... The deceleration parameter in cosmology is a dimensionless measure of the cosmic acceleration of the expansion of the universe. ...

Quintessence

Dark energy may become dark matter when buffeted by baryonic particles, thus leading to particle-like excitations in some type of dynamical field, referred to as quintessence. Quintessence differs from the cosmological constant in that it can vary in space and time. In order for it not to clump and form structure like matter, it must be very light so that it has a large Compton wavelength. In particle physics, the baryons are a family of subatomic particles including the proton and the neutron (collectively called nucleons), as well as a number of unstable, heavier particles (called hyperons). ... The Lorenz attractor is an example of a non-linear dynamical system. ... In mathematics and physics, a scalar field associates a scalar to every point in space. ... In physics, quintessence is a hypothetical form of dark energy postulated as an explanation of observations of an accelerating universe. ... Astronomy and cosmology examine the universe to understand the large-scale structure of the cosmos. ... The Compton wavelength of a particle is given by , where is the Planck constant, is the particles mass and is the speed of light. ...

No evidence of quintessence is yet available, but it has not been ruled out either. It generally predicts a slightly slower acceleration of the expansion of the universe than the cosmological constant. Some scientists think that the best evidence for quintessence would come from violations of Einstein's equivalence principle and variation of the fundamental constants in space or time. Scalar fields are predicted by the standard model and string theory, but an analogous problem to the cosmological constant problem (or the problem of constructing models of cosmic inflation) occurs: renormalization theory predicts that scalar fields should acquire large masses. In the physics of relativity, the equivalence principle is applied to several related concepts dealing with gravitation and the uniformity of physical measurements in different frames of reference. ... In the physics of relativity, the equivalence principle is applied to several related concepts dealing with gravitation and the uniformity of physical measurements in different frames of reference. ... In mathematics and physics, a scalar field associates a scalar to every point in space. ... The Standard Model of Fundamental Particles and Interactions For the Standard Model in Cryptography, see Standard Model (cryptography). ... Interaction in the subatomic world: world lines of pointlike particles in the Standard Model or a world sheet swept up by closed strings in string theory String theory is a model of fundamental physics whose building blocks are one-dimensional extended objects called strings, rather than the zero-dimensional point... 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. ... Figure 1. ...

The cosmic coincidence problem asks why the cosmic acceleration began when it did. If cosmic acceleration began earlier in the universe, structures such as galaxies would never have had time to form and life, at least as we know it, would never have had a chance to exist. Proponents of the anthropic principle view this as support for their arguments. However, many models of quintessence have a so-called tracker behavior, which solves this problem. In these models, the quintessence field has a density which closely tracks (but is less than) the radiation density until matter-radiation equality, which triggers quintessence to start behaving as dark energy, eventually dominating the universe. This naturally sets the low energy scale of the dark energy. The deceleration parameter in cosmology is a dimensionless measure of the cosmic acceleration of the expansion of the universe. ... The deceleration parameter in cosmology is a dimensionless measure of the cosmic acceleration of the expansion of the universe. ... For other uses, see Galaxy (disambiguation). ... In physics and cosmology, the anthropic principle is an umbrella term for various dissimilar attempts to explain the structure of the universe by way of coincidentally balanced features that are necessary and relevant to the existence of observers (usually assumed to be carbon-based life or even specifically human beings). ... For other uses, see Big Bang (disambiguation). ... In physics, energy scale is a particular value of energy determined with the precision of one order (or a few orders) of magnitude. ...

Some special cases of quintessence are phantom energy, in which the energy density of quintessence actually increases with time, and k-essence (short for kinetic quintessence) which has a non-standard form of kinetic energy. They can have unusual properties: phantom energy, for example, can cause a Big Rip. Phantom energy is a hypothetical form of dark energy with equation of state . ... The kinetic energy of an object is the extra energy which it possesses due to its motion. ... The Big Rip is a cosmological hypothesis about the Ultimate fate of the universe, in which the matter of the universe, from stars and galaxies to atoms and subatomic particles, are progressively torn apart by the expansion of the universe at a certain time in the future. ...

See main article on quintessence In physics, quintessence is a hypothetical form of dark energy postulated as an explanation of observations of an accelerating universe. ...

Alternative ideas

Some theorists think that dark energy and cosmic acceleration are a failure of general relativity on very large scales, larger than superclusters. It is a tremendous extrapolation to think that our law of gravity, which works so well in the solar system, should work without correction on the scale of the universe. Most attempts at modifying general relativity, however, have turned out to be either equivalent to theories of quintessence, or inconsistent with observations. The deceleration parameter in cosmology is a dimensionless measure of the cosmic acceleration of the expansion of the universe. ... For a less technical and generally accessible introduction to the topic, see Introduction to general relativity. ... Superclusters are large groupings of smaller galaxy groups and clusters, and are among the largest structures of the cosmos. ... This article is about the Solar System. ... In physics, quintessence is a hypothetical form of dark energy postulated as an explanation of observations of an accelerating universe. ...

Alternative ideas for dark energy have come from string theory, brane cosmology and the holographic principle, but have not yet proved as compelling as quintessence and the cosmological constant. Interaction in the subatomic world: world lines of pointlike particles in the Standard Model or a world sheet swept up by closed strings in string theory String theory is a model of fundamental physics whose building blocks are one-dimensional extended objects called strings, rather than the zero-dimensional point... Brane cosmology is a protoscience motivated by, but not rigorously derived from, superstring theory and M-theory. ... The holographic principle is a speculative conjecture about quantum gravity theories, proposed by Gerard t Hooft and improved and promoted by Leonard Susskind, claiming that all of the information contained in a volume of space can be represented by a theory which lives in the boundary of that region. ...

Yet another, "radically conservative" class of proposals aims to explain the observational data by a more refined use of established theories rather than through the introduction of dark energy, focusing, for example, on the gravitational effects of density inhomogeneities (assumed negligible in the standard Friedmann-Robertson-Walker approximation and confirmed negligible by studies of the anisotropies of the cosmic microwave background and statistics of large-scale structure) or on consequences of electroweak symmetry breaking in the early universe^[8]. // 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. ... 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. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... The Higgs mechanism, originally discovered by the British physicist Peter Higgs (building on a previous suggestion by Philip Anderson in condensed matter physics), is the mechanism that gives masses to all elementary particles in particle physics. ...

More insight as to dark energy might be deduced from LIGO I (with it's 10^-21 sensitivity), Virgo etc. non-detection of gravity waves; which might be interpreted as indicating that C_R pseudo-Riemannian spacetime continuum (manifold's) stiffness is not insignificant, rather than the assumption that g.w.s propagate long distance. Statistically LIGO I seems to have a large enough volume and sample size for inclusion of compact objects in NS and BH binary systems in tight orbits at least, even if not catching any coalescing events. However even for binary coalescence of BHs, generated {g.w.} might decay very rapidly. So resistance to deformation (normal stress: extension and compression, and even any shear stress) might not be insignificant. Such stiffness (resistance to deformation/distortion) may be considered as like inertia of C_R manifold. That is, {g.w.} have non-localized energy, but such energy is associated with deformation of manifold. Hence such {g.w.} energy might be considered as trying to overcome resistance to deformation (i.e. stiffness) of C_R manifold. Hence such inertia of manifold (resistance to deformation) would seem to represent a contribution to stress energy momentum tensor and it’s matrix representation; thus contributing not insignificantly to overall curvature. So if long range g.w.s are not detected, then LIGO I might actually be exploring a qualitative assessment (not limits) as to stiffness of C_R manifold. Thus C_R manifold may be quite robust to perturbation. Any such robustness would seem consistent with such manifold not breaking up (i.e. so no "foam"?) for near to, and at C_p Planck scale; hence also consistent with no quantization of manifold C_R. Also then less likely to have leakage of g.w.s propagating out of C_R manifold into another dimension i.e. brane. Also any such significant stiffness of C_R manifold would be less consistent with deformations associated with superstrings. And if the concept of inertia of manifold is descriptive, then any entertained recent new acceleration (i.e. resulting then in a strain or elasticity of manifold) of such C_R manifold would seem less likely. Also energy associated with resistance to deformation of manifold may represent a significant portion of energy required to approach flatness. That is, rather than a quest for so-called dark energy, perhaps an additional significant contribution is in the form of energy of C_R manifold; such stiffness of C_R manifold contributing to stress energy momentum tensor, and hence to curvature. So perhaps LIGO I already has made a great discovery - that is, the inertia of C_R manifold. So C_R manifold seems to have significant stiffness, and hence contributes a significant amount of energy to Tuv, and thus contributes significantly to curvature.[4] Image File history File links Broom_icon. ...

Implications for the fate of the universe

Cosmologists estimate that the acceleration began roughly 9 billion years ago. Before that, it is thought that the expansion was decelerating, due to the attractive influence of dark matter and baryons. The density of dark matter in an expanding universe disappears more quickly than dark energy, and eventually the dark energy dominates. Specifically, when the volume of the universe doubles, the density of dark matter is halved but the density of dark energy is nearly unchanged (it is exactly constant in the case of a cosmological constant). The deceleration parameter in cosmology is a dimensionless measure of the cosmic acceleration of the 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. ... Combinations of three u, d or s-quarks with a total spin of 3/2 form the so-called baryon decuplet. ... 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. ...

If the acceleration continues indefinitely, the ultimate result will be that galaxies outside the local supercluster will move beyond the cosmic horizon: they will no longer be visible, because their line-of-sight velocity becomes greater than the speed of light. This is not a violation of special relativity, and the effect cannot be used to send a signal between them. (Actually there is no way to even define "relative speed" in a curved spacetime. Relative speed and velocity can only be meaningfully defined in flat spacetime or in sufficiently small (infinitesimal) regions of curved spacetime). Rather, it prevents any communication between them and the objects pass out of contact. The Earth, the Milky Way and the Virgo supercluster, however, would remain virtually undisturbed while the rest of the universe recedes. In this scenario, the local supercluster would ultimately suffer heat death, just as was thought for the flat, matter-dominated universe, before measurements of cosmic acceleration. The Virgo Supercluster or Local Supercluster is the supercluster of galaxies that contains the Local Group and with it our galaxy, the Milky Way. ... For the science fiction film, see Event Horizon (film). ... Radial velocity is the velocity of an object in the direction of the line of sight. ... For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ... This article is about Earth as a planet. ... For other uses, see Milky Way (disambiguation). ... The Virgo Supercluster The Virgo Supercluster or Local Supercluster is the galactic supercluster that contains the Local Group, the latter which, in its turn, contains the Milky Way and Andromeda galaxies. ... The heat death is a possible final state of the universe, in which it has run down to a state of no free energy to sustain motion or life. ... The deceleration parameter in cosmology is a dimensionless measure of the cosmic acceleration of the expansion of the universe. ...

There are some very speculative ideas about the future of the universe. One suggests that phantom energy causes divergent expansion, which would imply that the effective force of dark energy continues growing until it dominates all other forces in the universe. Under this scenario, dark energy would ultimately tear apart all gravitationally bound structures, including galaxies and solar systems, and eventually overcome the electrical and nuclear forces to tear apart atoms themselves, ending the universe in a "Big Rip". On the other hand, dark energy might dissipate with time, or even become attractive. Such uncertainties leave open the possibility that gravity might yet rule the day and lead to a universe that contracts in on itself in a "Big Crunch". Some scenarios, such as the cyclic model suggest this could be the case. While these ideas are not supported by observations, they are not ruled out. Measurements of acceleration are crucial to determining the ultimate fate of the universe in big bang theory. Electromagnetism is the physics of the electromagnetic field: a field, encompassing all of space, composed of the electric field and the magnetic field. ... A Feynman diagram of a strong proton-neutron interaction mediated by a neutral pion. ... The Big Rip is a cosmological hypothesis about the Ultimate fate of the universe, in which the matter of the universe, from stars and galaxies to atoms and subatomic particles, are progressively torn apart by the expansion of the universe at a certain time in the future. ... This article is about the cosmological theory. ... The cyclic model is a brane cosmology model of the creation of the universe, derived from the earlier ekpyrotic model. ...

History

The cosmological constant was first proposed by Einstein as a mechanism to obtain a stable solution of the gravitational field equation that would lead to a static universe, effectively using dark energy to balance gravity. Not only was the mechanism an inelegant example of fine-tuning, it was soon realized that Einstein's static universe would actually be unstable because local inhomogeneities would ultimately lead to either the runaway expansion or contraction of the universe. The equilibrium is unstable: if the universe expands slightly, then the expansion releases vacuum energy, which causes yet more expansion. Likewise, a universe which contracts slightly will continue contracting. These sorts of disturbances are inevitable, due to the uneven distribution of matter throughout the universe. More importantly, observations made by Edwin Hubble showed that the universe appears to be expanding and not static at all. Einstein famously referred to his failure to predict the idea of a dynamic universe, in contrast to a static universe, as his greatest blunder. Following this realization, the cosmological constant was largely ignored as a historical curiosity. â€œEinsteinâ€ redirects here. ... In physics, the Einstein field equation or Einstein equation is a differential equation in Einsteins theory of general relativity. ... Fine Tuning is the name of XM Satellite Radios eclectic music channel. ... A dynamic equilibrium occurs when two reversible processes occur at the same rate. ... Edwin Powell Hubble (November 20, 1889 â€“ September 28, 1953) was an American astronomer. ...

Alan Guth proposed in the 1970s that a negative pressure field, similar in concept to dark energy, could drive cosmic inflation in the very early universe. Inflation postulates that some repulsive force, qualitatively similar to dark energy, resulted in an enormous and exponential expansion of the universe slightly after the Big Bang. Such expansion is an essential feature of most current models of the Big Bang. However, inflation must have occurred at a much higher energy density than the dark energy we observe today and is thought to have completely ended when the universe was just a fraction of a second old. It is unclear what relation, if any, exists between dark energy and inflation. Even after inflationary models became accepted, the cosmological constant was thought to be irrelevant to the current universe. Alan Harvey Guth (born February 27, 1947) is a physicist and cosmologist. ... The 1970s decade refers to the years from 1970 to 1979, also called The Seventies. ... 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. ... For other uses, see Big Bang (disambiguation). ...

The term "dark energy" was coined by Michael Turner in 1998.^[9] By that time, the missing mass problem of big bang nucleosynthesis and large scale structure was established, and some cosmologists had started to theorize that there was an additional component to our universe. The first direct evidence for dark energy came from supernova observations of accelerated expansion, in Riess et al^[4] and later confirmed in Perlmutter et al.^[3]. This resulted in the Lambda-CDM model, which as of 2006 is consistent with a series of increasingly rigorous cosmological observations, the latest being the 2005 Supernova Legacy Survey. First results from the SNLS reveal that the average behavior (i.e., equation of state) of dark energy behaves like Einstein's cosmological constant to a precision of 10 per cent.^[10] Recent results from the Hubble Space Telescope Higher-Z Team indicate that dark energy has been present for at least 9 billion years and during the period preceding cosmic acceleration. Turner (not pictured) is employed by the University of Chicago Michael S. Turner is a cosmologist who coined the term dark energy. ... 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. ... Astronomy and cosmology examine the universe to understand the large-scale structure of the cosmos. ... The deceleration parameter in cosmology is a dimensionless measure of the cosmic acceleration of the expansion of the universe. ... Adam Riess receiving the Shaw Prize for astronomy in 2006. ... Saul Perlmutter receiving the Shaw Prize for astronomy in 2006. ... A pie chart indicating the proportional composition of different energy-density components of the universe. ...

References

^ P. J. E. Peebles and Bharat Ratra (2003). "The cosmological constant and dark energy". Reviews of Modern Physics 75: 559–606.
^ Sean Carroll (2001). "The cosmological constant". Living Reviews in Relativity 4. Retrieved on 2006-09-28.
^ ^a ^b S. Perlmutter et al. (The Supernova Cosmology Project) (1999). "Measurements of Omega and Lambda from 42 high redshift supernovae". Astrophysical J. 517: 565–86.
^ ^a ^b Adam G. Riess et al. (Supernova Search Team) (1998). "Observational evidence from supernovae for an accelerating universe and a cosmological constant". Astronomical J. 116: 1009–38.
^ ^a ^b D. N. Spergel et al. (WMAP collaboration) (March 2006). "Wilkinson Microwave Anisotropy Probe (WMAP) three year results: implications for cosmology".
^ S. Weinberg, "Anthropic bound on the cosmological constant", Phys. Rev. Lett. 59, 2607 (1987).
^ A.M. Öztas and M.L. Smith (2006). "Elliptical Solutions to the Standard Cosmology Model with Realistic Values of Matter Density". International Journal of Theoretical Physics 45: 925-936.
^ Primordial inflation explains why the universe is accelerating today by Kolb, Matarrese, Notari and Riotto, which is disputed by [1], [2] and [3]
^ The first mention of the term "dark energy" is in the article with another cosmologist and Turner's student at the time, Dragan Huterer, "Prospects for Probing the Dark Energy via Supernova Distance Measurements", which was posted to the ArXiv.org e-print archive in August 1998 and published in Physical Review D in 1999 (Huterer and Turner, Phys. Rev. D 60, 081301 (1999)).
^ Pierre Astier et al. (Supernova Legacy Survey) (2006). "The Supernova legacy survey: Measurement of omega(m), omega(lambda) and W from the first year data set". Astronomy and Astrophysics 447: 31–48.

Sean B. Carroll is the author of Endless Forms Most Beautiful: The New Science of Evo Devo and the Making of the Animal Kingdom, the first popular summary narrative of Evolutionary Developmental Biology. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 271st day of the year (272nd in leap years) in the Gregorian calendar. ... Saul Perlmutter receiving the Shaw Prize for astronomy in 2006. ... The Supernova Cosmology Project is one of two research teams that determined the likelihood of an accelerating universe and therefore a positive Cosmological constant. ... Adam Riess receiving the Shaw Prize for astronomy in 2006. ... The High-z Supernova Search Team is an international cosmology group which uses Type Ia Supernovae to chart the expansion of the universe. ... arXiv. ... The Supernova Legacy Survey Program[1] is a project designed to investigate dark energy, by detecting and monitoring approximately 2000 high-redshift supernovae between 2003 and 2008, using MegaPrime, a large [CCD]] mosaic at the Canada-France-Hawaii Telescope. ... The deceleration parameter in cosmology is a dimensionless measure of the cosmic acceleration of the expansion of the universe. ... Sean M. Carroll is a senior research associate in the Department of Physics at the California Institute of Technology. ...

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