Physical Cosmology

Physical Cosmology

Universe · Big Bang Age of the universe Timeline of the Big Bang... Ultimate fate of the Universe Image File history File links Download high resolution version (2198x1274, 1278 KB)WMAP map of CMB anisotropy, from NASA.gov File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Physical cosmology, as a branch of astrophysics, is the study of the large-scale structure of the universe and is concerned with fundamental questions about its formation and evolution. ... Universe is a word derived from the Old French univers, which in turn comes from the Latin roots unus (one) and versus (a form of vertere, to turn). Based on observations of the observable universe, physicists attempt to describe the whole of space-time, including all matter and energy and... According to the Big Bang theory, the universe emerged from an extremely dense and hot state (singularity). ... The age of the universe, according to the Big Bang theory, is the time elapsed between the Big Bang and the present day. ... A graphical timeline is available here: Graphical timeline of the Big Bang This timeline of the Big Bang describes the events that have occurred and will occur according to the scientific theory of the Big Bang, using the cosmological time parameter of comoving coordinates. ... The ultimate fate of the universe is a topic in physical cosmology. ...

Early universe

Inflation · Nucleosynthesis Cosmic gravitational waves Cosmic microwave background In cosmology, Big Bang nucleosynthesis (or primordial nucleosynthesis) refers to the production of nuclei other than H-1, the normal, light hydrogen, during the early phases of the universe, shortly after the Big Bang. ... This article or section is in need of attention from an expert on the subject. ... In cosmology, the cosmic microwave background radiation (most often abbreviated CMB but occasionally CMBR, CBR or MBR, also referred as relic radiation) is a form of electromagnetic radiation discovered in 1965 that fills the entire universe. ...

Expanding universe

Redshift · Hubble's law Metric expansion of space Friedmann equations · FLRW metric Redshift of spectral lines in the optical spectrum of a supercluster of distant galaxies (right), as compared with that of the Sun (left). ... Hubbles law is the statement in physical cosmology that the redshift in light coming from distant galaxies is proportional to their distance. ... The metric expansion of space is a key part of sciences current understanding of the universe, whereby space itself is described by a metric which changes over time. ... The Friedmann equations relate various cosmological parameters within the context of general relativity. ... // The Friedmann-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. ...

Structure formation

Shape of the universe Structure formation Galaxy formation Large-scale structure The shape of the Universe is an informal name for a subject of investigation within physical cosmology. ... It has been suggested that this article or section be merged into Large-scale structure of the cosmos. ... In astrophysics, the questions of galaxy formation and evolution are: How, from a homogeneous universe, did we obtain the very heterogeneous one we live in? How did galaxies form? How do galaxies change over time? A spectacular head-on collision between two galaxies is seen in this NASA Hubble Space... Astronomy and cosmology examine the universe to understand the large-scale structure of the cosmos. ...

Components

Lambda-CDM model Dark energy · Dark matter A pie chart indicating the proportional composition of different energy-density components of the universe. ... In physical cosmology, dark energy is a hypothetical form of energy that permeates all of space and has strong negative pressure. ... In astrophysics and cosmology, dark matter is matter of unknown composition that does not emit or reflect enough electromagnetic radiation to be observed directly, but whose presence can be inferred from gravitational effects on visible matter. ...

History

Timeline of cosmology... This lists a timeline of cosmological theories and discoveries. ...

Cosmology experiments

Observational cosmology 2dF · SDSS CoBE · BOOMERanG · WMAP Observational cosmology is the study of the structure, the evolution and the origin of the universe through observation, using instruments such as telescopes and cosmic ray detectors. ... In astronomy, the 2dF Galaxy Redshift Survey (Two-degree-Field Galaxy Redshift Gurvey), or 2dFGRS is a redshift survey conducted by the Anglo-Australian Observatory in the 1990s. ... SDSS Logo The Sloan Digital Sky Survey or SDSS is a major multi-filter imaging and spectroscopic redshift survey using a dedicated 2. ... The Cosmic Background Explorer (COBE), also referred to as Explorer 66, was the first satellite built dedicated to cosmology. ... The Telescope being readied for launch The BOOMERanG experiment (Balloon Observations Of Millimetric Extragalactic Radiation and Geophysics) measured the cosmic microwave background radiation of a part of the sky during three sub-orbital (high altitude) balloon flights. ... Artist depiction of the WMAP satellite at the L2 point The Wilkinson Microwave Anisotropy Probe (WMAP) is a NASA satellite whose mission is to survey the sky to measure the temperature of the radiant heat left over from the Big Bang. ...

Scientists

Einstein · Friedman · Lemaître Hubble · Penzias · Wilson Gamow · Dicke · Zel'dovich Mather · Smoot · others Albert Einstein( ) (March 14, 1879 – April 18, 1955) was a German-born theoretical physicist who is widely considered to have been one of the greatest physicists of all time. ... Alexander Alexandrovich Friedman or Friedmann (Александр Александрович Фридман) (June 16, 1888 – September 16, 1925) was a Russian cosmologist and mathematician. ... Father Georges-Henri Lemaître (July 17, 1894 – June 20, 1966) was a Belgian Roman Catholic priest, honorary prelate, professor of physics and astronomer. ... // For the politician, see Edwin N. Hubbell. ... 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 partial list of persons who have made major contributions to the development of standard mainstream Cosmology. ...

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See universe for a general discussion of the universe.

The observable universe (also called the Hubble Volume) is a term used in Big Bang cosmology to describe the region of space bounded by a sphere, centred on the observer, that is small enough that we might observe objects in it, i.e. there has been sufficient time for light emitted by an object to arrive at the observer. Every position has its own observable universe which may or may not overlap with the one centered around the Earth. Universe is a word derived from the Old French univers, which in turn comes from the Latin roots unus (one) and versus (a form of vertere, to turn). Based on observations of the observable universe, physicists attempt to describe the whole of space-time, including all matter and energy and... According to the Big Bang theory, the universe emerged from an extremely dense and hot state (singularity). ...

The word observable used in this sense has nothing to do with whether modern technology actually permits us to detect radiation from an object in this region. It simply means that it is possible for light or other radiation from the object to reach an observer on earth. In practice, we can only observe objects as far as the surface of last scattering, when the universe became transparent. However, it may be possible to infer information from before this time through the detection of gravitational waves. By the mid 20th century humans had achieved a mastery of technology sufficient to leave the surface of the Earth for the first time and explore space. ... Radiation as used in physics, is energy in the form of waves or particles. ... When any patch of the sky is observed where no individual sources can be discerned, and the effects of interplanetary dust, and interstellar matter are taken into account, there is still radiation. ... The ASCII codes for the word Wikipedia represented in binary, the numeral system most commonly used for encoding computer information. ... In physics, a gravitational wave is a fluctuation in the curvature of spacetime which propagates as a wave, traveling outward from a moving object or system of objects. ...

The universe versus the observable universe

Both popular and professional research articles in cosmology often use the term "universe" to mean "observable universe". This can be justified on the grounds that we can never know anything about any part of the universe that is causally disconnected from us. No one believes, however, that the observable universe is precisely the entire universe; that would imply that the Earth is exactly at the center of the universe, violating a fundamental assumption of astronomy (and indeed all of science). It is likely that the galaxies within our visible universe represent only a minuscule fraction of the galaxies in the universe. The total number of galaxies may even be infinite. Although causality, the relationship between causes and effects, is often examined in the fields of philosophy, computer science, and statistics, it has a place in the study of physics as well. ... A giant Hubble mosaic of the Crab Nebula, a supernova remnant Astronomy is the science of celestial objects (such as stars, planets, comets, and galaxies) and phenomena that originate outside the Earths atmosphere (such as auroras and cosmic background radiation). ... Part of a scientific laboratory at the University of Cologne. ... NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 17,000 parsecs in diameter and approximately 20 million parsecs distant. ...

It is also possible that the universe is smaller than the observable universe. In this case, what we take to be very distant galaxies are actually duplicate images of nearby galaxies, formed by light that has circumnavigated the universe. It is difficult to test this hypothesis experimentally because different images of a galaxy would show different eras in its history, and consequently might appear quite different. A 2004 paper ^[1] claims to establish a lower bound of 24 gigaparsecs (78 billion^[2] light-years) on the diameter of the universe, based on matching-circle analysis of the WMAP data. However, other sources have stated that the outer boundary is 93 billion light-years distant^[3]. 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... Stellar parallax motion The parsec (symbol pc) is a unit of length used in astronomy. ... One thousand million (1,000,000,000) is the natural number following 999,999,999 and preceding 1,000,000,001. ... A light-year, symbol ly, is the distance light travels in one year: exactly 9. ... 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. ...

Hubble limit

The Hubble Limit^[4] is a concept in physical cosmology that is related to the Big Bang Theory. It refers to the limit where objects receding from the observer are receding at the speed of light. It is named after the astronomer Edwin Hubble, who was the first to discover that objects on a galactic scale are moving away from us. In the aftermath of the Big Bang everything in the universe is flying apart, and due to the fact that the speed of light is constant, farther objects appear to be receding at a higher velocity. Eventually an object will appear to have a velocity which is the speed of light, and an object at this point is known to be at the Hubble Limit. Physical cosmology, as a branch of astrophysics, is the study of the large-scale structure of the universe and is concerned with fundamental questions about its formation and evolution. ... According to the Big Bang theory, the universe originated in an infinitely dense and physically paradoxical singularity. ... A line showing the speed of light on a scale model of Earth and the Moon 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. It is the speed of all electromagnetic radiation... An astronomer or astrophysicist is a person whose area of interest is astronomy or astrophysics. ... // For the politician, see Edwin N. Hubbell. ... In mathematics and the mathematical sciences, a constant is a fixed, but possibly unspecified, value. ...

Size

The comoving distance from the Earth to the edge of the visible universe is about 46.5 billion light-years in any direction; this is the comoving radius of the visible universe. It is sometimes quoted as a diameter of 92-94 billion light-years^[3]. Since the visible universe is a perfect sphere and space is roughly flat, this size corresponds to a comoving volume of about 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. ... Circle illustration In classical geometry, a radius (plural: radii) of a circle or sphere is any line segment from its center to its boundary. ... DIAMETER is an AAA protocol (Authentication, Authorization and Accounting) succeeding its predecessor RADIUS. // The name is a pun on the RADIUS protocol, which is the predecessor (a diameter is twice the radius). ... A sphere is a perfectly symmetrical geometrical object. ... Around 300 BC, the Greek mathematician Euclid laid down the rules of what has now come to be called Euclidean geometry, which is the study of the relationships between angles and distances in space. ...

or 3.4×10⁸⁰ cubic meters.

The figures quoted above are distances now (in cosmological time), not distances at the time the light was emitted. For example, the cosmic microwave background radiation that we see right now was emitted about 13.7 billion years ago by matter that has, in the intervening time, condensed into galaxies. Those galaxies are now about 46 billion light-years from us, but at the time the light was emitted, that matter was only about 40 million light-years away from the matter that would eventually become the Earth. See comoving coordinates. A graphical timeline is available here: Graphical timeline of the Big Bang This timeline of the Big Bang describes the events that have occurred and will occur according to the scientific theory of the Big Bang. ... In cosmology, the cosmic microwave background radiation (most often abbreviated CMB but occasionally CMBR, CBR or MBR, also referred as relic radiation) is a form of electromagnetic radiation discovered in 1965 that fills the entire universe. ... This article or section does not adequately cite its references or sources. ... 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. ...

Misconceptions

Many secondary sources have reported a wide variety of incorrect figures for the size of the visible universe. Some of these are listed below.

• 13.7 billion light-years. The age of the universe is about 13.7 billion years. While it is commonly understood that nothing travels faster than light, it is a common misconception that the radius of the observable universe must therefore amount to only 13.7 billion light-years. This would make sense in the flat spacetime of special relativity. But in the real universe spacetime is highly curved at cosmological scales (general relativity), and light does not move rectilinearly. If a distance is obtained from the product of the speed of light times a cosmological time interval, it has no direct physical significance. ^[5]

• 15.8 billion light-years. This is obtained in the same way as the 13.7 billion light-year figure, but starting from an incorrect age of the universe which was reported in the popular press in mid-2006 (e.g. [2] [3] [4]). For an analysis of this claim and the paper that prompted it, see ^[6].

• 27 billion light-years. This is a diameter obtained from the (incorrect) radius of 13.7 billion light-years.

• 78 billion light-years. This figure, as mentioned above, is a lower bound on the diameter of the whole universe. It yields a lower bound on the radius of 39 billion light-years, which is less than the comoving radius of 46.5 billion light-years. For the 39 billion light-year radius to be correct, light must have circumnavigated the universe, and some regions of space would be visible twice, in opposite directions. This has yet to be proven.

• 156 billion light-years. This figure was obtained by doubling 78 billion light-years on the assumption that it is a radius. Since 78 billion light-years is already a diameter (or rather a circumference), the doubled figure is meaningless even in its original context. This figure was very widely reported (e.g. [5] [6] [7]).

• 180 billion light-years. This estimate accompanied the age estimate of 15.8 billion years in some sources; it was obtained by incorrectly adding 15% to the incorrect figure of 156 billion light-years.

The age of the universe, according to the Big Bang theory, is the time elapsed between the Big Bang and the present day. ... The special theory of relativity was proposed in 1905 by Albert Einstein in his article On the Electrodynamics of Moving Bodies. Some three centuries earlier, Galileos principle of relativity had stated that all uniform motion was relative, and that there was no absolute and well-defined state of rest... General relativity (GR) [also called the general theory of relativity (GTR) and general relativity theory (GRT)] is the geometrical theory of gravitation published by Albert Einstein in 1915/16. ... For the Manfred Mann album, see 2006 (album). ...

Matter content

The observable universe contains about 3 to 5 × 10²² stars, organized in around 80 billion galaxies, which themselves form clusters and superclusters. STAR is an acronym for: Organizations Society for Telescopy, Astronomy, and Radio, a non-profit New Jersey astronomy club. ... NGC 4414, a typical spiral galaxy in the constellation Coma Berenices, is about 17,000 parsecs in diameter and approximately 20 million parsecs distant. ... Galaxy groups and clusters are super-structures in the spread of galaxies of the cosmos. ... Superclusters are large groupings of smaller galaxy groups and clusters, and are among the largest structures of the cosmos. ...

Two back-of-envelope calculations give the number of atoms in the observable universe to be around 10⁸⁰. The phrase back-of-the-envelope refers to rough calculations that, while not rigorous, test or support a point. ... Properties In chemistry and physics, an atom (Greek ἄτομος or átomos meaning indivisible) is the smallest particle still characterizing a chemical element. ...

1. The critical density of the universe is 3H² / 8πG, which works out to be 1×10⁻²⁹ grams/cubic centimeter or about 5×10⁻⁶ atoms of hydrogen/cc. It is believed that only 4 percent of the critical density is in the form of normal atoms, so this leaves 2×10⁻⁷ hydrogen atoms/cc. Multiplying this by the volume of the visible universe, you get about 7×10⁷⁹ hydrogen atoms.
2. A typical star has a mass of about 2×10³³ grams, which is about 1×10⁵⁷ atoms of hydrogen per star. A typical galaxy has about 400 billion stars so that means each galaxy has 1×10⁵⁷ × 4×10¹¹ = 4×10⁶⁸ hydrogen atoms. There are possibly 80 billion galaxies in the Universe, so that means that there are about 4×10⁶⁸ × 8×10¹⁰ = 3×10⁷⁹ hydrogen atoms in the observable Universe. But this is definitely a lower limit calculation, and ignores many possible atom sources. ^[7]

In physics, density is mass m per unit volume V. For the common case of a homogeneous substance, it is expressed as: where, in SI units: ρ (rho) is the density of the substance, measured in kg·m-3 m is the mass of the substance, measured in kg V is... STAR is an acronym for: Organizations Society for Telescopy, Astronomy, and Radio, a non-profit New Jersey astronomy club. ... BIC pen cap, about 1 gram. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ...

See also

• Mass of the observable universe (for slightly different estimates)
• Particle horizon
• Causality (physics)
• Observation
• Universe
• Nine million bicycles (for an example of popular use of a mistaken estimate)

The mass of the observable universe can be estimated using estimations for its density and size. ... It has been suggested that this article or section be merged into Observable universe. ... Although causality, the relationship between causes and effects, is often examined in the fields of philosophy, computer science, and statistics, it has a place in the study of physics as well. ... Observation is an activity of a sapient or sentient living being (e. ... Universe is a word derived from the Old French univers, which in turn comes from the Latin roots unus (one) and versus (a form of vertere, to turn). Based on observations of the observable universe, physicists attempt to describe the whole of space-time, including all matter and energy and... Nine Million Bicycles is a song written and produced by Mike Batt for Georgian-born singer Katie Meluas second album, Piece by Piece. ...

References

Scientific American is a popular-science magazine, published (first weekly and later monthly) since August 28, 1845, making it the oldest continuously published magazine in the United States. ... 2007 (MMVII) is the current year, a common year starting on Monday of the Gregorian calendar and the Anno Domini (common) era. ... March 5 is the 64th day of the year in the Gregorian calendar (65th in leap years). ...

External links

• Cosmology FAQ
• Hubble, VLT and Spitzer Capture Galaxy Formation in the Early Universe