Physical cosmology

Key topics

Universe · Big Bang Age of the universe Timeline of the Big Bang Ultimate fate of the universe

Early universe

Inflation · Nucleosynthesis GWB · Neutrino Background Cosmic microwave background Expanding universe Redshift · Hubble's law Metric expansion of space Friedmann equations FLRW metric Structure formation Shape of the universe Structure formation Galaxy formation Large-scale structure Components Lambda-CDM model Dark energy · Dark matter History Timeline of cosmology... Cosmology experiments Observational cosmology 2dF · SDSS CoBE · BOOMERanG · WMAP Scientists Einstein · Hawking . Friedman · Lemaître · Hubble · Penzias · Wilson · Gamow · Dicke · Zel'dovich · Mather · Smoot · others

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Hubble's law is a statement in physical cosmology which states that the redshift in light coming from distant galaxies is proportional to their distance. The law was first formulated by Edwin Hubble and Milton Humason in 1929^[1] after nearly a decade of observations. It is considered the first observational basis for the expanding space paradigm and today serves as one of the most often cited pieces of evidence in support of the Big Bang. The most recent calculation of the proportionality constant, using the satellite WMAP began in 2003, yielding a value of 71 ± 4 (km/s)/megaparsec. In August, 2006, a less accurate figure was obtained independently using data from NASA's orbital Chandra X-ray Observatory: 77 (km/s)/Mpc with an uncertainty of ± 15%.^[2] This article is about the physics subject. ... Image File history File links Size of this preview: 800 × 411 pixelsFull resolution‎ (1,237 × 635 pixels, file size: 1. ... For other uses, see Universe (disambiguation). ... For other uses, see Big Bang (disambiguation). ... The age of the universe, in Big Bang cosmology, refers to the time elapsed between the Big Bang and the present day. ... A graphical timeline is available here: Graphical timeline of the Big Bang This box:      This timeline of the Big Bang describes the events that have occurred and will occur according to the scientific theory of the Big Bang, using the cosmological time parameter of comoving coordinates. ... This box:      The ultimate fate of the universe is a topic in physical cosmology. ... In cosmology, Big Bang nucleosynthesis (or primordial nucleosynthesis) refers to the production of nuclei other than H-1, the normal, light hydrogen, during the early phases of the universe, shortly after the Big Bang. ... This article or section is in need of attention from an expert on the subject. ... The Cosmic Neutrino Background (CNB) is the background particle radiation composed of neutrinos. ... CMB redirects here. ... This article is about the physical phenomenon. ... The metric expansion of space is a key part of sciences current understanding of the universe, whereby space itself is described by a metric which changes over time. ... The Friedmann equations relate various cosmological parameters within the context of general relativity. ... // The Friedmann-Lemaître-Robertson-Walker (FLRW) metric is an exact solution of the Einstein field equations of general relativity and which describes a homogeneous, isotropic expanding/contracting universe. ... The shape of the Universe is an informal name for a subject of investigation within physical cosmology. ... It has been suggested that this article or section be merged into Large-scale structure of the cosmos. ... In astrophysics, the questions of galaxy formation and evolution are: How, from a homogeneous universe, did we obtain the very heterogeneous one we live in? How did galaxies form? How do galaxies change over time? A spectacular head-on collision between two galaxies is seen in this NASA Hubble Space... Astronomy and cosmology examine the universe to understand the large-scale structure of the cosmos. ... A pie chart indicating the proportional composition of different energy-density components of the universe. ... In physical cosmology, dark energy is a hypothetical form of energy that permeates all of space and tends to increase the rate of expansion of the universe. ... For other uses, see Dark matter (disambiguation). ... This lists a timeline of cosmological theories and discoveries. ... Observational cosmology is the study of the structure, the evolution and the origin of the universe through observation, using instruments such as telescopes and cosmic ray detectors. ... In astronomy, the 2dF Galaxy Redshift Survey (Two-degree-Field Galaxy Redshift Gurvey), or 2dFGRS is a redshift survey conducted by the Anglo-Australian Observatory in the 1990s. ... SDSS Logo The Sloan Digital Sky Survey or SDSS is a major multi-filter imaging and spectroscopic redshift survey using a dedicated 2. ... The Cosmic Background Explorer (COBE), also referred to as Explorer 66, was the first satellite built dedicated to cosmology. ... The Telescope being readied for launch The BOOMERanG experiment (Balloon Observations Of Millimetric Extragalactic Radiation and Geophysics) measured the cosmic microwave background radiation of a part of the sky during three sub-orbital (high altitude) balloon flights. ... Artist depiction of the WMAP satellite at the L2 point The Wilkinson Microwave Anisotropy Probe (WMAP) is a NASA satellite whose mission is to survey the sky to measure the temperature of the radiant heat left over from the Big Bang. ... “Einstein” redirects here. ... Stephen William Hawking, CH, CBE, FRS, FRSA, (born 8 January 1942) is a British theoretical physicist. ... Alexander Alexandrovich Friedman or Friedmann (Александр Александрович Фридман) (June 16, 1888 – September 16, 1925) was a Russian cosmologist and mathematician. ... Monsignor Georges Lemaître, priest and scientist. ... Edwin Powell Hubble (November 20, 1889 – September 28, 1953) was an American astronomer. ... Arno Allan Penzias (born April 26, 1933) is an American physicist and winner of the 1978 Nobel Prize in physics. ... Robert Woodrow Wilson Robert Woodrow Wilson (born January 10, 1936) is an American physicist. ... George Gamow (pronounced GAM-off) (March 4, 1904 – August 19, 1968) , born Georgiy Antonovich Gamov (Георгий Антонович Гамов) was a Ukrainian born physicist and cosmologist. ... Robert Henry Dicke (May 6, 1916 – March 4, 1997) was an American experimental physicist, who made important contributions to the fields of astrophysics, atomic physics, cosmology and gravity. ... Yakov Borisovich Zeldovich (Russian:Яков Борисович Зельдович) (March 8, 1914 – December 2, 1987) was a prolific Soviet physicist. ... John Cromwell Mather (b. ... George Fitzgerald Smoot III (born February 20, 1945) is an American astrophysicist and cosmologist awarded the 2006 Nobel Prize in Physics with John C. Mather for their discovery of the black body form and anisotropy of the cosmic microwave background radiation. This work helped cement the big-bang theory of... This is a list of cosmologists. ... This article is about the physics subject. ... This article is about the physical phenomenon. ... For other uses, see Galaxy (disambiguation). ... This article is about proportionality, the mathematical relation. ... Edwin Powell Hubble (November 20, 1889 – September 28, 1953) was an American astronomer. ... Milton Lasell Humason (August 19, 1891 – June 18, 1972) was as American astronomer. ... For other uses, see Observation (disambiguation). ... 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. ... For other uses, see Big Bang (disambiguation). ... Artist depiction of the WMAP satellite at the L2 point The Wilkinson Microwave Anisotropy Probe (WMAP) is a NASA satellite whose mission is to survey the sky to measure the temperature of the radiant heat left over from the Big Bang. ... A kilometer (Commonwealth spelling: kilometre), symbol: km is a unit of length in the metric system equal to 1,000 metres (from the Greek words χίλια (khilia) = thousand and μέτρο (metro) = count/measure). ... This article is about the unit of time. ... The megaparsec (abbreviated Mpc) is a unit of distance used in astronomy, equal to one million parsecs. ... The Chandra X-ray Observatory is a satellite launched on STS-93 by NASA on July 23, 1999. ... A kilometer (Commonwealth spelling: kilometre), symbol: km is a unit of length in the metric system equal to 1,000 metres (from the Greek words χίλια (khilia) = thousand and μέτρο (metro) = count/measure). ... This article is about the unit of time. ... The megaparsec (abbreviated Mpc) is a unit of distance used in astronomy, equal to one million parsecs. ...

Discovery

A decade before Hubble made his observations, a number of physicists and mathematicians had established a consistent theory of the relationship between space and time by using Einstein's field equations of general relativity. Applying the most general principles to the nature of the universe yielded a dynamic solution that conflicted with the then prevailing notion of a static Universe. Many famous physicists of the 20th and 21st century are found on the list of recipients of the Nobel Prize in physics. ... To meet Wikipedias quality standards, this article or section may require cleanup. ... For other uses of this term, see Spacetime (disambiguation). ... For other topics related to Einstein see Einstein (disambig) Introduction In physics, the Einstein field equation or Einstein equation is a tensor equation in the Einsteins theory of general relativity. ... For a less technical and generally accessible introduction to the topic, see Introduction to general relativity. ... For other uses, see Big Bang (disambiguation). ... For other uses, see Universe (disambiguation). ... In physics, dynamics is the branch of classical mechanics that is concerned with the effects of forces on the motion of objects. ...

In 1922, Alexander Friedmann derived his Friedmann equations from the Einstein field equations, showing that the universe might expand at a rate calculable by the equations.^[3] The parameter used by Friedmann is known today as the scale factor which can be considered as a scale invariant form of the proportionality constant of Hubble's Law. Georges Lemaître independently found a similar solution in 1927. The Friedmann equations are derived by inserting the metric for a homogeneous and isotropic universe into Einstein's field equations for a fluid with a given density and pressure. This idea of an expanding spacetime would eventually lead to the Big Bang and Steady State theories of cosmology. Alexander Alexandrovich Friedman (June 16, 1888 – September 16, Russian cosmologist and mathematician. ... The Friedmann equations relate various cosmological parameters within the context of general relativity. ... The Einstein field equations (EFE) or Einsteins equations are a set of ten equations in Einsteins theory of general relativity in which the fundamental force of gravitation is described as a curved spacetime caused by matter and energy. ... The scale factor, parameter of Friedmann-Lemaître-Robertson-Walker model, is a function of time which represents the relative expansion of the universe. ... In physics, scale invariance is the feature of physical objects of laws that do not change if the space is magnified, i. ... The word proportionality may have one of a number of meanings: In mathematics, proportionality is a mathematical relation between two quantities. ... Monsignor Georges Lemaître, priest and scientist. ... // The Friedmann-Lemaître-Robertson-Walker (FLRW) metric is an exact solution of the Einstein field equations of general relativity and which describes a homogeneous, isotropic expanding/contracting universe. ... For other uses, see Density (disambiguation). ... This article is about pressure in the physical sciences. ... For other uses, see Big Bang (disambiguation). ... HELLO EVERYONE!! Steady state is a more general situation than Dynamic equilibrium. ...

Before the advent of modern cosmology, there was considerable talk about the size and shape of the universe. In 1920, the famous Shapley-Curtis debate took place between Harlow Shapley and Heber D. Curtis over this issue. Shapley argued for a small universe the size of the Milky Way galaxy and Curtis argued that the universe was much larger. The issue would be resolved in the coming decade with Hubble's improved observations. For other uses, see Big Bang (disambiguation). ... For other uses, see Universe (disambiguation). ... The shape of the Universe is an informal name for a subject of investigation within physical cosmology. ... For other uses, see Universe (disambiguation). ... The Great Debate was between astronomers Harlow Shapley and Heber Curtis and concerned the nature of spiral nebulae and the size of the universe. ... Harlow Shapley in his earlier years. ... Heber Doust Curtis (June 27, 1872 – January 9, 1942) was an American astronomer. ... The Milky Way (a translation of the Latin Via Lactea, in turn derived from the Greek Galaxia Kuklos; or simply the Galaxy) is a barred spiral galaxy in the Local Group, and has special significance to humanity as the location of the solar system, which is located near the Orion...

Edwin Hubble did most of his professional astronomical observing work at Mount Wilson Observatory, the world's most powerful telescope at the time. His observations of Cepheid variable stars in spiral nebulae enabled him to calculate the distances to these objects. Surprisingly, these objects were discovered to be at distances which placed them well outside the Milky Way. The nebulae were first described as "island universes" and it was only later that the moniker "galaxy" would be applied to them. The Mount Wilson Observatory (MWO) is an astronomical observatory in Los Angeles County, California. ... Cepheid in the Spiral Galaxy M100 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. ... The Triangulum Emission Nebula NGC 604 lies in a spiral arm of Galaxy M33, 2. ... For other uses, see Milky Way (disambiguation). ...

Combining his measurements of galaxy distances with Vesto Slipher's measurements of the redshifts associated with the galaxies, Hubble discovered a rough proportionality of the objects' distances. Though there was considerable scatter (now known to be caused by peculiar velocities), Hubble was able to plot a trend line from the 46 galaxies he studied and obtain a value for the Hubble constant of 500 km/s/Mpc (much higher than the currently accepted value due to errors in his distance calibrations). (See cosmic distance ladder for details.) Vesto Melvin Slipher (November 11, 1875 – November 8, 1969) was an American astronomer. ... This article is about the light phenomenon. ... This article is about mathematics. ... The term peculiar velocity refers to the components of a receding galaxys velocity that cannot be explained by Hubbles law. ... The cosmic distance ladder is the succession of methods by which astronomers determine the distances to celestial objects. ...

In 1958, the first good estimate of H₀, 75 km/s/Mpc, was published by Allan Sandage^[4], but it would be decades before a consensus was achieved. Allan Rex Sandage (Born June 18, 1926) is an American astronomer. ...

After Hubble's discovery was published, Albert Einstein abandoned his work on the cosmological constant (which he had designed to allow for a static solution to his equations). He would later term this work his "greatest blunder" since the belief of a static universe prevented him from predicting the expanding universe. Einstein would make a famous trip to Mount Wilson in 1931 to thank Hubble for providing the observational basis for modern cosmology. “Einstein” redirects here. ... In physical cosmology, the cosmological constant (usually denoted by the Greek capital letter lambda: Λ) was proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a stationary universe. ...

Interpretation

The discovery of the linear relationship between redshift, interpreted as recessional velocity, and distance yields a straightforward mathematical expression for Hubble's Law as follows: This article is about the physical phenomenon. ... Recessional Velocity is a term used to describe the rate at which an object is moving away, typically from Earth. ...

where v is the recessional velocity, typically expressed in km/s. H₀ is Hubble's constant and corresponds to the value of H (often termed the Hubble parameter which is a value that is time dependent) in the Friedmann equations taken at the time of observation denoted by the subscript 0. This value is the same throughout the universe for a given comoving time. D is the comoving distance from the galaxy to the observer, measured in megaparsecs (Mpc), in the 3-space defined by given cosmological time. (Recession velocity is just v = dD/dt). As the formula implies, in very distant objects, v can be greater than c. This is not a violation of special relativity, because the rules of special relativity only apply precisely within a small region: a special-relativistic description of two widely-separated galaxies would in general be incorrect. (Thus special relativity strictly says, not that no speed can be faster than light, but that nothing can move past another object at a speed faster than light). A time-variant system is a system, that is not time-invariant(TIV). ... This box:      In standard cosmology, comoving distance and proper distance are two closely related distance measures used by cosmologists to define distances between objects. ... The comoving distance or conformal distance of two objects in the universe is the distance divided by a time-varying scale factor representing the expansion of the universe. ... For other uses, see Galaxy (disambiguation). ... mega- (symbol M) is an SI prefix in the SI system of units denoting a factor of 106, i. ... A parsec is the distance from the Earth to an astronomical object which has a parallax angle of one arcsecond. ... For a less technical and generally accessible introduction to the topic, see Introduction to special relativity. ...

Strictly speaking, neither v nor D in the formula are directly observable, because they are properties now of a galaxy, whereas our observations refer to the galaxy in the past, at the time that the light we currently see left it. For relatively nearby galaxies (redshift z much less than unity), v and D will not have changed much, and v can be estimated using the formula v = zc where c is the speed of light. This gives the empirical relation found by Hubble. For distant galaxies, v (or D) cannot be calculated from z without specifying a detailed model for how H changes with time. The redshift is not even directly related to the recession velocity at the time the light set out, but it does have a simple interpretation: (1+z) is the factor by which the universe has expanded while the photon was travelling towards the observer. This article is about the physical phenomenon. ... The speed of light in a vacuum is an important physical constant denoted by the letter c for constant or the Latin word celeritas meaning swiftness.[1] It is the speed of all electromagnetic radiation, including visible light, in a vacuum. ...

In using Hubble's law to determine distances, only the velocity due to the expansion of the universe can be used. Since gravitationally interacting galaxies move relative to each other independent of the expansion of the universe, these relative velocities, called peculiar velocities, need to be accounted for in the application of Hubble's law. The Finger of God effect is one result of this phenomenon discovered in 1938 by Benjamin Kenneally. In systems that are gravitationally bound, such as galaxies or our planetary system, the expansion of space is (more than) annihilated by the attractive force of gravity. Fingers of God in a portion of the Sloan Digital Sky Survey; image from the Cosmus Open Source Science Outreach project [1]. Fingers of God is an effect in cosmology that causes clusters of galaxies to be elongated in redshift space, with an axis of elongation pointed toward the observer... In mechanics, the virial theorem provides a general equation relating the average total kinetic energy of a system with its average total potential energy , where angle brackets represent the average of the enclosed quantity. ...

The mathematical derivation of an idealized Hubble's Law for a uniformly expanding universe is a fairly elementary theorem of geometry in 3-dimensional Cartesian/Newtonian coordinate space, which, considered as a metric space, is entirely homogeneous and isotropic (properties do not vary with location or direction). Simply stated the theorem is this: Cartesian means of or relating to the French philosopher and mathematician René Descartes. ... In mathematics, a metric space is a set where a notion of distance between elements of the set is defined. ... 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. ...

Any two points which are moving away from the origin, each along straight lines and with speed proportional to distance from the origin, will be moving away from each other with a speed proportional to their distance apart.

In fact this applies to non-Cartesian spaces as long as they are locally homogeneous and isotropic; specifically to the negatively- and positively-curved spaces frequently considered as cosmological models (see shape of the universe). The shape of the Universe is an informal name for a subject of investigation within physical cosmology. ...

The ultimate fate of the universe and the age of the universe can both be determined by measuring the Hubble constant today and extrapolating with the observed value of the deceleration parameter, uniquely characterized by values of density parameters (Ω). A so-called "closed universe" (Ω>1) comes to an end in a Big Crunch and is considerably younger than its Hubble age. An "open universe" (Ω≤1) expands forever and has an age that is closer its Hubble age. For the accelerating universe that we inhabit, the age of the universe is coincidentally very close to the Hubble age.

The value of Hubble parameter changes over time either increasing or decreasing depending on the sign of the so-called deceleration parameter q which is defined by Image File history File links Universes. ... Image File history File links Universes. ... This box:      The ultimate fate of the universe is a topic in physical cosmology. ... The age of the universe, in Big Bang cosmology, refers to the time elapsed between the Big Bang and the present day. ... This article is about the cosmological theory. ... The accelerating universe is the observation that the universe appears to be expanding at an accelerated rate. ... The deceleration parameter in cosmology is a dimensionless measure of the cosmic acceleration of the expansion of the universe. ...

In a universe with a deceleration parameter equal to zero, it follows that H = 1/t, where t is the time since the Big Bang. A non-zero, time-dependent value of q simply requires integration of the Friedmann equations backwards from the present time to the time when the comoving horizon size was zero. This article is about the concept of integrals in calculus. ... It has been suggested that this article or section be merged into Observable universe. ...

It was long thought that q was positive, indicating that the expansion is slowing down due to gravitational attraction. This would imply an age of the universe less than 1/H (which is about 14,000 million years). For instance, a value for q of 1/2 (once favoured by most theorists) would give the age of the universe as 2/(3H). The discovery in 1998 that q is apparently negative means that the universe could actually be older than 1/H. In fact, estimates of the age of the universe are, by coincidence, very close to 1/H. The age of the universe, in Big Bang cosmology, refers to the time elapsed between the Big Bang and the present day. ...

Olbers' paradox

Main article: Olbers' paradox

The expansion of space summarized by the Big Bang interpretation of Hubble's Law is relevant to the old conundrum known as Olbers' paradox: if the Universe were infinite, static, and filled with a uniform distribution of stars (notice that this also requires an infinite number of stars), then every line of sight in the sky would end on a star, and the sky would be as bright as the surface of a star. However, the night sky is largely dark. Since the 1600s, astronomers and other thinkers have proposed many possible ways to resolve this paradox, but the currently accepted resolution depends in part upon the Big Bang theory and in part upon the Hubble expansion. In a universe that exists for a finite amount of time, only the light of finitely many stars has had a chance to reach us yet, and the paradox is resolved. Additionally, in an expanding universe distant objects recede from us which cause the light emanating from them to be redshifted and diminished in brightness. Both effects contribute (the redshift being the more important of the two; remember the original paradox was couched in terms of a static universe). The darkness of the night sky, then, provides a kind of confirmation for the Hubble expansion of the universe. ^[5] Olbers paradox, described by the German astronomer Heinrich Wilhelm Olbers in 1826 and earlier by Johannes Kepler in 1610 and Halley and Cheseaux in the 18th century, is the paradoxical observation that the night sky is dark, when in a static infinite universe the night sky ought to be bright. ... Olbers paradox, described by the German astronomer Heinrich Wilhelm Olbers in 1826 and earlier by Johannes Kepler in 1610 and Halley and Cheseaux in the 18th century, is the paradoxical observation that the night sky is dark, when in a static infinite universe the night sky ought to be bright. ... Infinity is a word carrying a number of different meanings in mathematics, philosophy, theology and everyday life. ... Basic description The theory of a static universe is the rival theory to an expanding universe and all of its subvarieties. ... This article is about the astronomical object. ... When viewing a scene, as in optics, photography, or even hunting, the line of sight is the straight line between the observer and the target. ... Brightness is an attribute of visual perception in which a source appears to emit a given amount of light. ... For other uses, see Big Bang (disambiguation). ... Hubbles law is the statement in astronomy that the redshift in light coming from distant galaxies is proportional to their distance. ... Recessional Velocity is a term used to describe the rate at which an object is moving away, typically from Earth. ... This article is about the physical phenomenon. ...

Determining the Hubble constant

The value of the Hubble constant is estimated by measuring the redshift of distant galaxies and then determining the distances to the same galaxies (by some other method than Hubble's law). Uncertainties in the physical assumptions used to determine these distances have caused varying estimates of the Hubble constant. This article is about the physical phenomenon. ... The cosmic distance ladder is the succession of methods by which astronomers determine the distances to celestial objects. ...

For most of the second half of the 20th century the value of H₀ was estimated to be between 50 and 90 (km/s)/Mpc. The value of the Hubble constant was the topic of a long and rather bitter controversy between Gérard de Vaucouleurs who claimed the value was around 100 and Allan Sandage who claimed the value was near 50. In 1996, a debate moderated by John Bahcall between Gustav Tammann and Sidney van den Bergh was held in similar fashion to the earlier Shapley-Curtis debate over these two competing values. This difference was partially resolved with the introduction of the Lambda-CDM model of the Universe in the late 1990s. With this model observations of high-redshift clusters at X-ray and microwave wavelengths using the Sunyaev-Zel'dovich effect, measurements of anisotropies in the cosmic microwave background radiation, and optical surveys all gave a value of around 70 for the constant. In particular the Hubble Key Project (led by Dr. Wendy L. Freedman, Carnegie Observatories) gave the most accurate optical determination in May 2001 with its final estimate of 72±8 (km/s)/Mpc, consistent with a measurement of H₀ based upon Sunyaev-Zel'dovich effect observations of many galaxy clusters having a similar accuracy. The most precise cosmic microwave background radiation determinations were 71±4 (km/s)/Mpc, by WMAP in 2003, and 70.4^+1.5_−1.6 (km/s)/Mpc, for measurements up to 2006.^[6] These values arise from fitting a combination of WMAP and other cosmological data to the simplest version of the Lambda-CDM model. If the data is fitted with more general versions, H₀ tends to be smaller and more uncertain: typically around 67±4 (km/s)/Mpc although some models allow values near 63 (km/s)/Mpc.^[7] Gérard Henri de Vaucouleurs (April 25, 1918–October 7, 1995) was a French-American astronomer. ... Allan Rex Sandage (Born June 18, 1926) is an American astronomer. ... John N. Bahcall (born December 30, 1934) is an American astrophysicist. ... Dr. Gustav Tammann was the director of the Astronomical Institute of the University of Basel, Switzerland, European Space Agency member of the Space Telescope Advisory Team and Member of Council of the European Southern Observatory. ... Sidney van den Bergh (born 1929) is a Canadian astronomer. ... The Great Debate was between astronomers Harlow Shapley and Heber Curtis and concerned the nature of spiral nebulae and the size of the universe. ... A pie chart indicating the proportional composition of different energy-density components of the universe. ... 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. ... CMB redirects here. ... The Hubble Space Telescope (HST) is a telescope in orbit around the Earth, named after astronomer Edwin Hubble. ... 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. ... Galaxy groups and clusters are super-structures in the spread of galaxies of the cosmos. ... CMB redirects here. ... Artist depiction of the WMAP satellite at the L2 point The Wilkinson Microwave Anisotropy Probe (WMAP) is a NASA satellite whose mission is to survey the sky to measure the temperature of the radiant heat left over from the Big Bang. ...

In August 2006, using NASA's Chandra X-ray Observatory, a team from NASA's Marshall Space Flight Center (MSFC) found the Hubble constant to be 77 (km/s)/Mpc, with an uncertainty of about 15%. ^[8] The consistency of the measurements from all these methods lends support to both the measured value of H₀ and the Lambda-CDM model. August 2006 is the eighth month of that year, and has yet to occur. ... The Chandra X-ray Observatory is a satellite launched on STS-93 by NASA on July 23, 1999. ... Aerial view of the test area at Marshall Space Flight Center The George C. Marshall Space Flight Center (MSFC) is a lead NASA center for propulsion, Space Shuttle propulsion, external fuel tank, crew training and payloads, International Space Station (ISS) design and construction, for computers, networks, and information management. ... A pie chart indicating the proportional composition of different energy-density components of the universe. ...

(In the metric system, H₀ is about 2.3×10⁻¹⁸ s⁻¹; this should not be written as Hertz since the quantity is not a frequency). The International System of Units (symbol: SI) (for the French phrase Syst me International dUnit s) is the most widely used system of units. ... This article is about the SI unit of frequency. ...

A value for q measured from standard candle observations of Type Ia supernovae, which was determined in 1998 to be negative, surprised many astronomers with the implication that the expansion of the universe is currently "accelerating" (although the Hubble factor is still decreasing with time; see the articles on dark energy and the Lambda-CDM model). A standard candle is an astronomical object that has a known luminosity. ... Multiwavelength X-ray image of the remnant of Keplers Supernova, SN 1604. ... 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. ... A pie chart indicating the proportional composition of different energy-density components of the universe. ...

Derivation of the Hubble parameter

Start with the Friedman equation: The Friedmann equations relate various cosmological parameters within the context of general relativity. ...

where H is the Hubble parameter, a is the scale factor, G is the gravitational constant, k is the geometry of the universe and equal to −1, 0, or +1, and Λ is the cosmological constant. The scale factor, parameter of Friedmann-Lemaître-Robertson-Walker model, is a function of time which represents the relative expansion of the universe. ... According to the law of universal gravitation, the attractive force between two bodies is proportional to the product of their masses and inversely proportional to the square of the distance between them. ... In physical cosmology, the cosmological constant (usually denoted by the Greek capital letter lambda: Λ) was proposed by Albert Einstein as a modification of his original theory of general relativity to achieve a stationary universe. ...

Matter-dominated universe (with a cosmological constant)

If the universe is matter dominated then the energy density of the universe ρ can just be taken to include matter so The Matter-Dominated Era is the era in which we currently reside within our universe, as opposed to the Radiation-Dominated Era. ...

where ρ_m is the density of matter today. We know for nonrelativistic particles their energy density decreases proportional to the volume of the universe so the equation above must be true. We can also define (see density parameter for Ω_m) Alexander Friedmann The Friedmann equations are a set of equations in cosmology that govern the expansion of space in homogeneous and isotropic models of the universe within the context of general relativity. ...

so ρ = ρ_cΩ_m / a³. Also by definition,

and

where the subscript nouht refers to the values today, and a₀ = 1. Substituting all this in into the Friedman equation at the start of this section and replacing a with a = 1 / (1 + z) gives

Matter- and darkenergy-dominated universe

If the universe is both matter dominated and dark energy dominated then the above equation for the Hubble parameter will also be a function of the equation of state of dark energy. So now: The Matter-Dominated Era is the era in which we currently reside within our universe, as opposed to the Radiation-Dominated Era. ... In physical cosmology, dark energy is a hypothetical form of energy that permeates all of space and tends to increase the rate of expansion of the universe. ... In 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. ...

where ρ_de is the energy density of the dark energy. By definition an equation of state in cosmology is P = wρ, and if we substitute this into the fluid equation, which describes how the density of the universe evolves with time,

If w is constant,

Therefore for dark energy with a constant equation of state w, . If we substitute this into the Friedman equation in a similar way as before, but this time set k = 0 which is assuming we live in a flat universe, (see Shape of the Universe) The shape of the Universe is an informal name for a subject of investigation within physical cosmology. ...

If dark energy does not have a constant equation-of-state w, then

and to solve this we must parametrize w(a), for example if w(a) = w₀ + w_a(1 − a), giving

Units derived from the Hubble constant

Hubble time

The Hubble constant H₀ has units of inverse time. We can therefore define “Hubble time” as 1 / H₀. The value of Hubble time in the standard cosmological model is 4.35×10¹⁷ s or 13.8 billion years, somewhat longer than the current age of the universe. A pie chart indicating the proportional composition of different energy-density components of the universe. ...

Hubble length

The Hubble length is a unit of distance in cosmology, defined as c / H₀—the speed of light multiplied by the Hubble time. It is equivalent to 4228 million parsecs or 13.8 billion lightyears. (The numerical value of the Hubble length in lightyears is, by definition, equal to that of the Hubble time in years.)

Hubble volume

The Hubble volume is sometimes defined as a volume of the universe with a comoving size of c / H₀. The exact definition varies: it is sometimes defined as the volume of a sphere with radius c / H₀, or alternatively, a cube of side c / H₀. Some cosmologists even use the term Hubble volume to refer to the volume of the observable universe, although this has a radius approximately 3 times larger. The comoving distance or conformal distance of two objects in the universe is the distance divided by a time-varying scale factor representing the expansion of the universe. ... See universe for a general discussion of the universe. ...

See also

• Age of the universe
• Shape of the universe
  • Hyperbolic geometry (crinkly due to expansion)
  • Euclidean geometry (flat due to a balance)
  • Elliptic geometry (round due to gravity)

The age of the universe, in Big Bang cosmology, refers to the time elapsed between the Big Bang and the present day. ... The shape of the Universe is an informal name for a subject of investigation within physical cosmology. ... Lines through a given point P and asymptotic to line l. ... Euclid Euclidean geometry is a mathematical system attributed to the Greek mathematician [[Euclid]] of Alexandria. ... Elliptic geometry (sometimes known as Riemannian geometry) is a non-Euclidean geometry, in which, given a line L and a point p outside L, there exists no line parallel to L passing through p. ...

Notes

Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ... is the 220th day of the year (221st in leap years) in the Gregorian calendar. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 66th day of the year (67th in leap years) in the Gregorian calendar. ... John Huchra discovered the Great Wall (astronomy) in 1989, with Margaret Geller based on redshift survey data from the CfA Redshift Survey. ... Year 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the AD/CE era in the 21st century. ... is the 277th day of the year (278th in leap years) in the Gregorian calendar. ... Isaac Asimov (January 2?, 1920?[1] – April 6, 1992), pronounced , originally Исаак Озимов but now transcribed into Russian as Айзек Азимов [1], was a Russian-born American author and professor of biochemistry, a highly successful writer, best known for his works of science fiction and for his popular science books. ... The National Aeronautics and Space Administration (NASA) (IPA [ˈnæsə]) is an agency of the United States government, responsible for the nations public space program. ...

References

• Kutner, Marc (2003). Astronomy: A Physical Perspective. Cambridge University Press. ISBN 0-521-52927-1. 
• Hubble, E.P.., The Observational Approach to Cosmology (Oxford, 1937)
• Final Results from the Hubble Space Telescope Key Project to Measure the Hubble Constant. Freedman et al. The Astrophysical Journal, Volume 553, Issue 1, pp. 47-72.

The Astrophysical Journal is one of the foremost research journals devoted to recent developments, discoveries, and theories in astronomy and astrophysics. ...

External links

• The Hubble Key Project
• The Hubble Diagram Project