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The cosmic microwave background (CMB) is electromagnetic radiation as a remnant from an early stage of the universe in Big Bang
Big Bang
cosmology. In older literature, the CMB
CMB
is also variously known as cosmic microwave background radiation (CMBR) or "relic radiation". The CMB
CMB
is a faint cosmic background radiation filling all space that is an important source of data on the early universe because it is the oldest electromagnetic radiation in the universe, dating to the epoch of recombination. With a traditional optical telescope, the space between stars and galaxies (the background) is completely dark. However, a sufficiently sensitive radio telescope shows a faint background noise, or glow, almost isotropic, that is not associated with any star, galaxy, or other object. This glow is strongest in the microwave region of the radio spectrum. The accidental discovery of the CMB
CMB
in 1964 by American radio astronomers Arno Penzias
Arno Penzias
and Robert Wilson[1][2] was the culmination of work initiated in the 1940s, and earned the discoverers the 1978 Nobel Prize
Nobel Prize
in Physics. The discovery of CMB
CMB
is landmark evidence of the Big Bang
Big Bang
origin of the universe. When the universe was young, before the formation of stars and planets, it was denser, much hotter, and filled with a uniform glow from a white-hot fog of hydrogen plasma. As the universe expanded, both the plasma and the radiation filling it grew cooler. When the universe cooled enough, protons and electrons combined to form neutral hydrogen atoms. Unlike the uncombined protons and electrons, these newly conceived atoms could not absorb the thermal radiation, and so the universe became transparent instead of being an opaque fog.[3] Cosmologists
Cosmologists
refer to the time period when neutral atoms first formed as the recombination epoch, and the event shortly afterwards when photons started to travel freely through space rather than constantly being scattered by electrons and protons in plasma is referred to as photon decoupling. The photons that existed at the time of photon decoupling have been propagating ever since, though growing fainter and less energetic, since the expansion of space causes their wavelength to increase over time (and wavelength is inversely proportional to energy according to Planck's relation). This is the source of the alternative term relic radiation. The surface of last scattering refers to the set of points in space at the right distance from us so that we are now receiving photons originally emitted from those points at the time of photon decoupling. Precise measurements of the CMB
CMB
are critical to cosmology, since any proposed model of the universe must explain this radiation. The CMB has a thermal black body spectrum at a temperature of 7000272548000000000♠2.72548±0.00057 K.[4] The spectral radiance dEν/dν peaks at 160.23 GHz, in the microwave range of frequencies, corresponding to a photon energy of about 6.626 × 10−4 eV. Alternatively, if spectral radiance is defined as dEλ/dλ, then the peak wavelength is 1.063 mm (282 GHz, 1.168 x 10−3 eV photons). The glow is very nearly uniform in all directions, but the tiny residual variations show a very specific pattern, the same as that expected of a fairly uniformly distributed hot gas that has expanded to the current size of the universe. In particular, the spectral radiance at different angles of observation in the sky contains small anisotropies, or irregularities, which vary with the size of the region examined. They have been measured in detail, and match what would be expected if small thermal variations, generated by quantum fluctuations of matter in a very tiny space, had expanded to the size of the observable universe we see today. This is a very active field of study, with scientists seeking both better data (for example, the Planck spacecraft) and better interpretations of the initial conditions of expansion. Although many different processes might produce the general form of a black body spectrum, no model other than the Big Bang
Big Bang
has yet explained the fluctuations. As a result, most cosmologists consider the Big Bang
Big Bang
model of the universe to be the best explanation for the CMB. The high degree of uniformity throughout the observable universe and its faint but measured anisotropy lend strong support for the Big Bang model in general and the ΛCDM ("Lambda Cold Dark Matter") model in particular. Moreover, the fluctuations are coherent on angular scales that are larger than the apparent cosmological horizon at recombination. Either such coherence is acausally fine-tuned, or cosmic inflation occurred.[5][6]

Contents

1 Features 2 History 3 Relationship to the Big Bang

3.1 Primary anisotropy 3.2 Late time anisotropy

4 Polarization

4.1 E-modes 4.2 B-modes

4.2.1 Primordial gravitational waves 4.2.2 Gravitational lensing

5 Microwave
Microwave
background observations 6 Data reduction and analysis

6.1 CMBR dipole anisotropy 6.2 Low multipoles and other anomalies

7 Future evolution 8 Timeline of prediction, discovery and interpretation

8.1 Thermal (non-microwave background) temperature predictions 8.2 Microwave
Microwave
background radiation predictions and measurements

9 In popular culture 10 See also 11 References 12 Further reading 13 External links

Features[edit]

Graph of cosmic microwave background spectrum measured by the FIRAS instrument on the COBE, the most precisely measured black body spectrum in nature.[7] The error bars are too small to be seen even in an enlarged image, and it is impossible to distinguish the observed data from the theoretical curve.

The cosmic microwave background radiation is an emission of uniform, black body thermal energy coming from all parts of the sky. The radiation is isotropic to roughly one part in 100,000: the root mean square variations are only 18 µK,[8] after subtracting out a dipole anisotropy from the Doppler shift
Doppler shift
of the background radiation. The latter is caused by the peculiar velocity of the Earth relative to the comoving cosmic rest frame as the planet moves at some 371 km/s towards the constellation Leo. The CMB
CMB
dipole as well as aberration at higher multipoles have been measured, consistent with galactic motion.[9] In the Big Bang
Big Bang
model for the formation of the universe, inflationary cosmology predicts that after about 10−37 seconds[10] the nascent universe underwent exponential growth that smoothed out nearly all irregularities. The remaining irregularities were caused by quantum fluctuations in the inflaton field that caused the inflation event.[11] Before the formation of stars and planets (after 10−6 seconds), the early universe was smaller, much hotter, and filled with a uniform glow from its white-hot fog of interacting plasma of photons, electrons, and baryons. As the universe expanded, adiabatic cooling caused the energy density of the plasma to decrease until it became favorable for electrons to combine with protons, forming hydrogen atoms. This recombination event happened when the temperature was around 3000 K or when the universe was approximately 379,000 years old.[12] As photons did not interact with these electrically neutral atoms, the former began to travel freely through space, resulting in the decoupling of matter and radiation.[13] The color temperature of the ensemble of decoupled photons has continued to diminish ever since; now down to 7000272600000000000♠2.7260±0.0013 K,[4] it will continue to drop as the universe expands. The intensity of the radiation also corresponds to black-body radiation at 2.726 K because red-shifted black-body radiation is just like black-body radiation at a lower temperature. According to the Big Bang
Big Bang
model, the radiation from the sky we measure today comes from a spherical surface called the surface of last scattering. This represents the set of locations in space at which the decoupling event is estimated to have occurred[14] and at a point in time such that the photons from that distance have just reached observers. Most of the radiation energy in the universe is in the cosmic microwave background,[15] making up a fraction of roughly 6995600000000000000♠6×10−5 of the total density of the universe.[16] Two of the greatest successes of the Big Bang
Big Bang
theory are its prediction of the almost perfect black body spectrum and its detailed prediction of the anisotropies in the cosmic microwave background. The CMB
CMB
spectrum has become the most precisely measured black body spectrum in nature.[7] Density of energy for CMB
CMB
is 6986400544121750000♠0.25 eV/cm3[17] (6986400499999999999♠4.005×10−14 J/m3) or (400–500 photons/cm3[18]). History[edit] See also: Discovery of cosmic microwave background radiation The cosmic microwave background was first predicted in 1948 by Ralph Alpher and Robert Herman.[19][20][21][22] Alpher and Herman were able to estimate the temperature of the cosmic microwave background to be 5 K, though two years later they re-estimated it at 28 K. This high estimate was due to a mis-estimate of the Hubble constant
Hubble constant
by Alfred Behr, which could not be replicated and was later abandoned for the earlier estimate. Although there were several previous estimates of the temperature of space, these suffered from two flaws. First, they were measurements of the effective temperature of space and did not suggest that space was filled with a thermal Planck spectrum. Next, they depend on our being at a special spot at the edge of the Milky Way
Milky Way
galaxy and they did not suggest the radiation is isotropic. The estimates would yield very different predictions if Earth happened to be located elsewhere in the universe.[23]

The Holmdel Horn Antenna
Holmdel Horn Antenna
on which Penzias and Wilson discovered the cosmic microwave background

The 1948 results of Alpher and Herman were discussed in many physics settings through about 1955, when both left the Applied Physics Laboratory at Johns Hopkins University. The mainstream astronomical community, however, was not intrigued at the time by cosmology. Alpher and Herman's prediction was rediscovered by Yakov Zel'dovich
Yakov Zel'dovich
in the early 1960s, and independently predicted by Robert Dicke
Robert Dicke
at the same time. The first published recognition of the CMB
CMB
radiation as a detectable phenomenon appeared in a brief paper by Soviet astrophysicists A. G. Doroshkevich and Igor Novikov, in the spring of 1964.[24] In 1964, David Todd Wilkinson
David Todd Wilkinson
and Peter Roll, Dicke's colleagues at Princeton University, began constructing a Dicke radiometer to measure the cosmic microwave background.[25] In 1964, Arno Penzias
Arno Penzias
and Robert Woodrow Wilson
Robert Woodrow Wilson
at the Crawford Hill
Crawford Hill
location of Bell Telephone Laboratories
Bell Telephone Laboratories
in nearby Holmdel Township, New Jersey had built a Dicke radiometer that they intended to use for radio astronomy and satellite communication experiments. On 20 May 1964 they made their first measurement clearly showing the presence of the microwave background,[26] with their instrument having an excess 4.2K antenna temperature which they could not account for. After receiving a telephone call from Crawford Hill, Dicke said "Boys, we've been scooped."[1][27][28] A meeting between the Princeton and Crawford Hill groups determined that the antenna temperature was indeed due to the microwave background. Penzias and Wilson received the 1978 Nobel Prize in Physics for their discovery.[29] The interpretation of the cosmic microwave background was a controversial issue in the 1960s with some proponents of the steady state theory arguing that the microwave background was the result of scattered starlight from distant galaxies.[30] Using this model, and based on the study of narrow absorption line features in the spectra of stars, the astronomer Andrew McKellar wrote in 1941: "It can be calculated that the 'rotational temperature' of interstellar space is 2 K."[31] However, during the 1970s the consensus was established that the cosmic microwave background is a remnant of the big bang. This was largely because new measurements at a range of frequencies showed that the spectrum was a thermal, black body spectrum, a result that the steady state model was unable to reproduce.[32] Harrison, Peebles, Yu and Zel'dovich realized that the early universe would have to have inhomogeneities at the level of 10−4 or 10−5.[33][34][35] Rashid Sunyaev
Rashid Sunyaev
later calculated the observable imprint that these inhomogeneities would have on the cosmic microwave background.[36] Increasingly stringent limits on the anisotropy of the cosmic microwave background were set by ground based experiments during the 1980s. RELIKT-1, a Soviet cosmic microwave background anisotropy experiment on board the Prognoz 9 satellite (launched 1 July 1983) gave upper limits on the large-scale anisotropy. The NASA COBE mission clearly confirmed the primary anisotropy with the Differential Microwave
Microwave
Radiometer instrument, publishing their findings in 1992.[37][38] The team received the Nobel Prize
Nobel Prize
in physics for 2006 for this discovery. Inspired by the COBE results, a series of ground and balloon-based experiments measured cosmic microwave background anisotropies on smaller angular scales over the next decade. The primary goal of these experiments was to measure the scale of the first acoustic peak, which COBE did not have sufficient resolution to resolve. This peak corresponds to large scale density variations in the early universe that are created by gravitational instabilities, resulting in acoustical oscillations in the plasma.[39] The first peak in the anisotropy was tentatively detected by the Toco experiment
Toco experiment
and the result was confirmed by the BOOMERanG and MAXIMA experiments.[40][41][42] These measurements demonstrated that the geometry of the universe is approximately flat, rather than curved.[43] They ruled out cosmic strings as a major component of cosmic structure formation and suggested cosmic inflation was the right theory of structure formation.[44] The second peak was tentatively detected by several experiments before being definitively detected by WMAP, which has also tentatively detected the third peak.[45] As of 2010, several experiments to improve measurements of the polarization and the microwave background on small angular scales are ongoing. These include DASI, WMAP, BOOMERanG, QUaD, Planck spacecraft, Atacama Cosmology
Cosmology
Telescope, South Pole Telescope and the QUIET
QUIET
telescope. Relationship to the Big Bang[edit]

Nature
Nature
timeline

view • discuss • edit

-13 — – -12 — – -11 — – -10 — – -9 — – -8 — – -7 — – -6 — – -5 — – -4 — – -3 — – -2 — – -1 — – 0 —

cosmic expansion

Earliest light

cosmic speed-up

Solar System

water

Single-celled life

photosynthesis

Multicellular life

Land life

Earliest gravity

Dark energy

Dark matter

Earliest universe (−13.80)

Earliest stars

Earliest galaxy

Earliest quasar/sbh

Omega Centauri
Omega Centauri
forms

Andromeda Galaxy
Andromeda Galaxy
forms

Milky Way
Milky Way
Galaxy spiral arms form

Alpha Centauri
Alpha Centauri
forms

Earliest Earth (−4.54)

Earliest life

Earliest oxygen

Atmospheric oxygen

Earliest sexual reproduction

Cambrian explosion

Earliest humans

L i f e

P r i m o r d i a l

Axis scale: billion years Also see: Human
Human
timeline and Life timeline

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The cosmic microwave background radiation and the cosmological redshift-distance relation are together regarded as the best available evidence for the Big Bang
Big Bang
theory. Measurements of the CMB
CMB
have made the inflationary Big Bang
Big Bang
theory the Standard Cosmological Model.[46] The discovery of the CMB
CMB
in the mid-1960s curtailed interest in alternatives such as the steady state theory.[47] The CMB
CMB
essentially confirms the Big Bang
Big Bang
theory. In the late 1940s Alpher and Herman reasoned that if there was a big bang, the expansion of the universe would have stretched and cooled the high-energy radiation of the very early universe into the microwave region of the electromagnetic spectrum, and down to a temperature of about 5 K. They were slightly off with their estimate, but they had exactly the right idea. They predicted the CMB. It took another 15 years for Penzias and Wilson to stumble into discovering that the microwave background was actually there.[48] The CMB
CMB
gives a snapshot of the universe when, according to standard cosmology, the temperature dropped enough to allow electrons and protons to form hydrogen atoms, thereby making the universe nearly transparent to radiation because light was no longer being scattered off free electrons. When it originated some 380,000 years after the Big Bang—this time is generally known as the "time of last scattering" or the period of recombination or decoupling—the temperature of the universe was about 3000 K. This corresponds to an energy of about 0.26 eV,[49] which is much less than the 13.6 eV ionization energy of hydrogen.[50] Since decoupling, the temperature of the background radiation has dropped by a factor of roughly 1,100[51] due to the expansion of the universe. As the universe expands, the CMB
CMB
photons are redshifted, causing them to decrease in energy. The temperature of this radiation stays inversely proportional to a parameter that describes the relative expansion of the universe over time, known as the scale length. The temperature Tr of the CMB
CMB
as a function of redshift, z, can be shown to be proportional to the temperature of the CMB
CMB
as observed in the present day (2.725 K or 0.2348 meV):[52]

Tr = 2.725(1 + z)

For details about the reasoning that the radiation is evidence for the Big Bang, see Cosmic background radiation
Cosmic background radiation
of the Big Bang. Primary anisotropy[edit]

The power spectrum of the cosmic microwave background radiation temperature anisotropy in terms of the angular scale (or multipole moment). The data shown comes from the WMAP
WMAP
(2006), Acbar (2004) Boomerang (2005), CBI (2004), and VSA (2004) instruments. Also shown is a theoretical model (solid line).

The anisotropy, or directional dependency, of the cosmic microwave background is divided into two types: primary anisotropy, due to effects that occur at the last scattering surface and before; and secondary anisotropy, due to effects such as interactions of the background radiation with hot gas or gravitational potentials, which occur between the last scattering surface and the observer. The structure of the cosmic microwave background anisotropies is principally determined by two effects: acoustic oscillations and diffusion damping (also called collisionless damping or Silk damping). The acoustic oscillations arise because of a conflict in the photon–baryon plasma in the early universe. The pressure of the photons tends to erase anisotropies, whereas the gravitational attraction of the baryons, moving at speeds much slower than light, makes them tend to collapse to form overdensities. These two effects compete to create acoustic oscillations, which give the microwave background its characteristic peak structure. The peaks correspond, roughly, to resonances in which the photons decouple when a particular mode is at its peak amplitude. The peaks contain interesting physical signatures. The angular scale of the first peak determines the curvature of the universe (but not the topology of the universe). The next peak—ratio of the odd peaks to the even peaks—determines the reduced baryon density.[53] The third peak can be used to get information about the dark-matter density.[54] The locations of the peaks also give important information about the nature of the primordial density perturbations. There are two fundamental types of density perturbations called adiabatic and isocurvature. A general density perturbation is a mixture of both, and different theories that purport to explain the primordial density perturbation spectrum predict different mixtures.

Adiabatic density perturbations In an adiabatic density perturbation, the fractional additional number density of each type of particle (baryons, photons ...) is the same. That is, if at one place there is a 1% higher number density of baryons than average, then at that place there is also a 1% higher number density of photons (and a 1% higher number density in neutrinos) than average. Cosmic inflation
Cosmic inflation
predicts that the primordial perturbations are adiabatic. Isocurvature density perturbations In an isocurvature density perturbation, the sum (over different types of particle) of the fractional additional densities is zero. That is, a perturbation where at some spot there is 1% more energy in baryons than average, 1% more energy in photons than average, and 2% less energy in neutrinos than average, would be a pure isocurvature perturbation. Cosmic strings would produce mostly isocurvature primordial perturbations.

The CMB
CMB
spectrum can distinguish between these two because these two types of perturbations produce different peak locations. Isocurvature density perturbations produce a series of peaks whose angular scales (l values of the peaks) are roughly in the ratio 1:3:5:..., while adiabatic density perturbations produce peaks whose locations are in the ratio 1:2:3:...[55] Observations are consistent with the primordial density perturbations being entirely adiabatic, providing key support for inflation, and ruling out many models of structure formation involving, for example, cosmic strings. Collisionless damping is caused by two effects, when the treatment of the primordial plasma as fluid begins to break down:

the increasing mean free path of the photons as the primordial plasma becomes increasingly rarefied in an expanding universe, the finite depth of the last scattering surface (LSS), which causes the mean free path to increase rapidly during decoupling, even while some Compton scattering
Compton scattering
is still occurring.

These effects contribute about equally to the suppression of anisotropies at small scales and give rise to the characteristic exponential damping tail seen in the very small angular scale anisotropies. The depth of the LSS refers to the fact that the decoupling of the photons and baryons does not happen instantaneously, but instead requires an appreciable fraction of the age of the universe up to that era. One method of quantifying how long this process took uses the photon visibility function (PVF). This function is defined so that, denoting the PVF by P(t), the probability that a CMB
CMB
photon last scattered between time t and t + dt is given by P(t) dt. The maximum of the PVF (the time when it is most likely that a given CMB
CMB
photon last scattered) is known quite precisely. The first-year WMAP
WMAP
results put the time at which P(t) has a maximum as 372,000 years.[56] This is often taken as the "time" at which the CMB
CMB
formed. However, to figure out how long it took the photons and baryons to decouple, we need a measure of the width of the PVF. The WMAP
WMAP
team finds that the PVF is greater than half of its maximal value (the "full width at half maximum", or FWHM) over an interval of 115,000 years. By this measure, decoupling took place over roughly 115,000 years, and when it was complete, the universe was roughly 487,000 years old. Late time anisotropy[edit] Since the CMB
CMB
came into existence, it has apparently been modified by several subsequent physical processes, which are collectively referred to as late-time anisotropy, or secondary anisotropy. When the CMB photons became free to travel unimpeded, ordinary matter in the universe was mostly in the form of neutral hydrogen and helium atoms. However, observations of galaxies today seem to indicate that most of the volume of the intergalactic medium (IGM) consists of ionized material (since there are few absorption lines due to hydrogen atoms). This implies a period of reionization during which some of the material of the universe was broken into hydrogen ions. The CMB
CMB
photons are scattered by free charges such as electrons that are not bound in atoms. In an ionized universe, such charged particles have been liberated from neutral atoms by ionizing (ultraviolet) radiation. Today these free charges are at sufficiently low density in most of the volume of the universe that they do not measurably affect the CMB. However, if the IGM was ionized at very early times when the universe was still denser, then there are two main effects on the CMB:

Small scale anisotropies are erased. (Just as when looking at an object through fog, details of the object appear fuzzy.) The physics of how photons are scattered by free electrons (Thomson scattering) induces polarization anisotropies on large angular scales. This broad angle polarization is correlated with the broad angle temperature perturbation.

Both of these effects have been observed by the WMAP
WMAP
spacecraft, providing evidence that the universe was ionized at very early times, at a redshift more than 17.[clarification needed] The detailed provenance of this early ionizing radiation is still a matter of scientific debate. It may have included starlight from the very first population of stars (population III stars), supernovae when these first stars reached the end of their lives, or the ionizing radiation produced by the accretion disks of massive black holes. The time following the emission of the cosmic microwave background—and before the observation of the first stars—is semi-humorously referred to by cosmologists as the dark age, and is a period which is under intense study by astronomers (see 21 centimeter radiation). Two other effects which occurred between reionization and our observations of the cosmic microwave background, and which appear to cause anisotropies, are the Sunyaev–Zel'dovich effect, where a cloud of high-energy electrons scatters the radiation, transferring some of its energy to the CMB
CMB
photons, and the Sachs–Wolfe effect, which causes photons from the Cosmic Microwave
Microwave
Background to be gravitationally redshifted or blueshifted due to changing gravitational fields. Polarization[edit]

This artist's impression shows how light from the early universe is deflected by the gravitational lensing effect of massive cosmic structures forming B-modes
B-modes
as it travels across the universe.

The cosmic microwave background is polarized at the level of a few microkelvin. There are two types of polarization, called E-modes and B-modes. This is in analogy to electrostatics, in which the electric field (E-field) has a vanishing curl and the magnetic field (B-field) has a vanishing divergence. The E-modes arise naturally from Thomson scattering in a heterogeneous plasma. The B-modes
B-modes
are not produced by standard scalar type perturbations. Instead they can be created by two mechanisms: the first one is by gravitational lensing of E-modes, which has been measured by the South Pole Telescope
South Pole Telescope
in 2013;[57] the second one is from gravitational waves arising from cosmic inflation. Detecting the B-modes
B-modes
is extremely difficult, particularly as the degree of foreground contamination is unknown, and the weak gravitational lensing signal mixes the relatively strong E-mode signal with the B-mode signal.[58] E-modes[edit] E-modes were first seen in 2002 by the Degree Angular Scale Interferometer
Interferometer
(DASI). B-modes[edit] Cosmologists
Cosmologists
predict two types of B-modes, the first generated during cosmic inflation shortly after the big bang,[59][60][61] and the second generated by gravitational lensing at later times.[62] Primordial gravitational waves[edit] Primordial gravitational waves are gravitational waves that could be observed in the polarisation of the cosmic microwave background and having their origin in the early universe. Models of cosmic inflation predict that such gravitational waves should appear; thus, their detection supports the theory of inflation, and their strength can confirm and exclude different models of inflation. It is the result of three things: inflationary expansion of space itself, reheating after inflation, and turbulent fluid mixing of matter and radiation. [63] On 17 March 2014 it was announced that the BICEP2 instrument had detected the first type of B-modes, consistent with inflation and gravitational waves in the early universe at the level of r = 6999200000000000000♠0.20+0.07 −0.05, which is the amount of power present in gravitational waves compared to the amount of power present in other scalar density perturbations in the very early universe. Had this been confirmed it would have provided strong evidence of cosmic inflation and the Big Bang,[64][65] [66][67] [68][69][70] but on 19 June 2014, considerably lowered confidence in confirming the findings was reported[69][71][72] and on 19 September 2014 new results of the Planck experiment reported that the results of BICEP2 can be fully attributed to cosmic dust.[73][74] Gravitational lensing[edit] The second type of B-modes
B-modes
was discovered in 2013 using the South Pole Telescope with help from the Herschel Space Observatory.[75] This discovery may help test theories on the origin of the universe. Scientists are using data from the Planck mission by the European Space Agency, to gain a better understanding of these waves.[76][77][78] In October 2014, a measurement of the B-mode polarization at 150 GHz was published by the POLARBEAR
POLARBEAR
experiment.[79] Compared to BICEP2, POLARBEAR
POLARBEAR
focuses on a smaller patch of the sky and is less susceptible to dust effects. The team reported that POLARBEAR's measured B-mode polarization was of cosmological origin (and not just due to dust) at a 97.2% confidence level.[80] Microwave
Microwave
background observations[edit] Main article: List of cosmic microwave background experiments Subsequent to the discovery of the CMB, hundreds of cosmic microwave background experiments have been conducted to measure and characterize the signatures of the radiation. The most famous experiment is probably the NASA
NASA
Cosmic Background Explorer
Cosmic Background Explorer
(COBE) satellite that orbited in 1989–1996 and which detected and quantified the large scale anisotropies at the limit of its detection capabilities. Inspired by the initial COBE results of an extremely isotropic and homogeneous background, a series of ground- and balloon-based experiments quantified CMB
CMB
anisotropies on smaller angular scales over the next decade. The primary goal of these experiments was to measure the angular scale of the first acoustic peak, for which COBE did not have sufficient resolution. These measurements were able to rule out cosmic strings as the leading theory of cosmic structure formation, and suggested cosmic inflation was the right theory. During the 1990s, the first peak was measured with increasing sensitivity and by 2000 the BOOMERanG experiment
BOOMERanG experiment
reported that the highest power fluctuations occur at scales of approximately one degree. Together with other cosmological data, these results implied that the geometry of the universe is flat. A number of ground-based interferometers provided measurements of the fluctuations with higher accuracy over the next three years, including the Very Small Array, Degree Angular Scale Interferometer
Interferometer
(DASI), and the Cosmic Background Imager
Cosmic Background Imager
(CBI). DASI made the first detection of the polarization of the CMB
CMB
and the CBI provided the first E-mode polarization spectrum with compelling evidence that it is out of phase with the T-mode spectrum.

All-sky mollweide map of the CMB, created from 9 years of WMAP
WMAP
data

Comparison of CMB
CMB
results from COBE, WMAP
WMAP
and Planck (March 21, 2013)

In June 2001, NASA
NASA
launched a second CMB
CMB
space mission, WMAP, to make much more precise measurements of the large scale anisotropies over the full sky. WMAP
WMAP
used symmetric, rapid-multi-modulated scanning, rapid switching radiometers to minimize non-sky signal noise.[51] The first results from this mission, disclosed in 2003, were detailed measurements of the angular power spectrum at a scale of less than one degree, tightly constraining various cosmological parameters. The results are broadly consistent with those expected from cosmic inflation as well as various other competing theories, and are available in detail at NASA's data bank for Cosmic Microwave Background (CMB) (see links below). Although WMAP
WMAP
provided very accurate measurements of the large scale angular fluctuations in the CMB
CMB
(structures about as broad in the sky as the moon), it did not have the angular resolution to measure the smaller scale fluctuations which had been observed by former ground-based interferometers. A third space mission, the ESA (European Space Agency) Planck Surveyor, was launched in May 2009 and performed an even more detailed investigation until it was shut down in October 2013. Planck employed both HEMT
HEMT
radiometers and bolometer technology and measured the CMB
CMB
at a smaller scale than WMAP. Its detectors were trialled in the Antarctic Viper telescope
Viper telescope
as ACBAR (Arcminute Cosmology
Cosmology
Bolometer Array Receiver) experiment—which has produced the most precise measurements at small angular scales to date—and in the Archeops balloon telescope. On 21 March 2013, the European-led research team behind the Planck cosmology probe released the mission's all-sky map (565x318 jpeg, 3600x1800 jpeg) of the cosmic microwave background.[81][82] The map suggests the universe is slightly older than researchers thought. According to the map, subtle fluctuations in temperature were imprinted on the deep sky when the cosmos was about 370,000 years old. The imprint reflects ripples that arose as early, in the existence of the universe, as the first nonillionth of a second. Apparently, these ripples gave rise to the present vast cosmic web of galaxy clusters and dark matter. Based on the 2013 data, the universe contains 4.9% ordinary matter, 26.8% dark matter and 68.3% dark energy. On 5 February 2015, new data was released by the Planck mission, according to which the age of the universe is 13.799 ± 0.021 billion years old and the Hubble constant
Hubble constant
was measured to be 67.74 ± 0.46 (km/s)/Mpc.[83] Additional ground-based instruments such as the South Pole Telescope in Antarctica and the proposed Clover Project, Atacama Cosmology Telescope and the QUIET telescope
QUIET telescope
in Chile will provide additional data not available from satellite observations, possibly including the B-mode polarization. Data reduction and analysis[edit] Raw CMBR data, even from space vehicles such as WMAP
WMAP
or Planck, contain foreground effects that completely obscure the fine-scale structure of the cosmic microwave background. The fine-scale structure is superimposed on the raw CMBR data but is too small to be seen at the scale of the raw data. The most prominent of the foreground effects is the dipole anisotropy caused by the Sun's motion relative to the CMBR background. The dipole anisotropy and others due to Earth's annual motion relative to the Sun and numerous microwave sources in the galactic plane and elsewhere must be subtracted out to reveal the extremely tiny variations characterizing the fine-scale structure of the CMBR background. The detailed analysis of CMBR data to produce maps, an angular power spectrum, and ultimately cosmological parameters is a complicated, computationally difficult problem. Although computing a power spectrum from a map is in principle a simple Fourier transform, decomposing the map of the sky into spherical harmonics, in practice it is hard to take the effects of noise and foreground sources into account. In particular, these foregrounds are dominated by galactic emissions such as Bremsstrahlung, synchrotron, and dust that emit in the microwave band; in practice, the galaxy has to be removed, resulting in a CMB map that is not a full-sky map. In addition, point sources like galaxies and clusters represent another source of foreground which must be removed so as not to distort the short scale structure of the CMB
CMB
power spectrum. Constraints on many cosmological parameters can be obtained from their effects on the power spectrum, and results are often calculated using Markov Chain Monte Carlo
Markov Chain Monte Carlo
sampling techniques. CMBR dipole anisotropy[edit] From the CMB
CMB
data it is seen that the Local Group
Local Group
(the galaxy group that includes the Milky Way
Milky Way
galaxy) appears to be moving at 7005627000000000000♠627±22 km/s relative to the reference frame of the CMB
CMB
(also called the CMB
CMB
rest frame, or the frame of reference in which there is no motion through the CMB) in the direction of galactic longitude l = 7000481710873550436♠276°±3°, b = 6999523598775598300♠30°±3°.[84][85] This motion results in an anisotropy of the data ( CMB
CMB
appearing slightly warmer in the direction of movement than in the opposite direction).[86] From a theoretical point of view, the existence of a CMB
CMB
rest frame breaks Lorentz invariance even in empty space far away from any galaxy.[87] The standard interpretation of this temperature variation is a simple velocity red shift and blue shift due to motion relative to the CMB, but alternative cosmological models can explain some fraction of the observed dipole temperature distribution in the CMB.[88] Low multipoles and other anomalies[edit] With the increasingly precise data provided by WMAP, there have been a number of claims that the CMB
CMB
exhibits anomalies, such as very large scale anisotropies, anomalous alignments, and non-Gaussian distributions.[89][90][91] The most longstanding of these is the low-l multipole controversy. Even in the COBE map, it was observed that the quadrupole (l = 2, spherical harmonic) has a low amplitude compared to the predictions of the Big Bang. In particular, the quadrupole and octupole (l = 3) modes appear to have an unexplained alignment with each other and with both the ecliptic plane and equinoxes,[92][93][94] A number of groups have suggested that this could be the signature of new physics at the greatest observable scales; other groups suspect systematic errors in the data.[95][96][97] Ultimately, due to the foregrounds and the cosmic variance problem, the greatest modes will never be as well measured as the small angular scale modes. The analyses were performed on two maps that have had the foregrounds removed as far as possible: the "internal linear combination" map of the WMAP
WMAP
collaboration and a similar map prepared by Max Tegmark
Max Tegmark
and others.[45][51][98] Later analyses have pointed out that these are the modes most susceptible to foreground contamination from synchrotron, dust, and Bremsstrahlung
Bremsstrahlung
emission, and from experimental uncertainty in the monopole and dipole. A full Bayesian analysis
Bayesian analysis
of the WMAP
WMAP
power spectrum demonstrates that the quadrupole prediction of Lambda-CDM cosmology is consistent with the data at the 10% level and that the observed octupole is not remarkable.[99] Carefully accounting for the procedure used to remove the foregrounds from the full sky map further reduces the significance of the alignment by ~5%.[100][101][102][103] Recent observations with the Planck telescope, which is very much more sensitive than WMAP
WMAP
and has a larger angular resolution, record the same anomaly, and so instrumental error (but not foreground contamination) appears to be ruled out.[104] Coincidence is a possible explanation, chief scientist from WMAP, Charles L. Bennett
Charles L. Bennett
suggested coincidence and human psychology were involved, "I do think there is a bit of a psychological effect; people want to find unusual things." [105] See also: Cosmological principle, Axis of evil (cosmology), and CMB cold spot Future evolution[edit] Assuming the universe keeps expanding and it does not suffer a Big Crunch, a Big Rip, or another similar fate, the cosmic microwave background will continue redshifting until it will no longer be detectable,[106] and will be overtaken first by the one produced by starlight, and later by the background radiation fields of processes that are assumed will take place in the far future of the universe.[107], §VD. Timeline of prediction, discovery and interpretation[edit] Thermal (non-microwave background) temperature predictions[edit]

1896 – Charles Édouard Guillaume
Charles Édouard Guillaume
estimates the "radiation of the stars" to be 5.6K.[108] 1926 – Sir Arthur Eddington
Arthur Eddington
estimates the non-thermal radiation of starlight in the galaxy "... by the formula E = σT4 the effective temperature corresponding to this density is 3.18° absolute ... black body"[109] 1930s – Cosmologist
Cosmologist
Erich Regener
Erich Regener
calculates that the non-thermal spectrum of cosmic rays in the galaxy has an effective temperature of 2.8 K 1931 – Term microwave first used in print: "When trials with wavelengths as low as 18 cm. were made known, there was undisguised surprise+that the problem of the micro-wave had been solved so soon." Telegraph & Telephone Journal XVII. 179/1 1934 – Richard Tolman
Richard Tolman
shows that black-body radiation in an expanding universe cools but remains thermal 1938 – Nobel Prize
Nobel Prize
winner (1920) Walther Nernst
Walther Nernst
reestimates the cosmic ray temperature as 0.75K 1946 – Robert Dicke
Robert Dicke
predicts "... radiation from cosmic matter" at <20 K, but did not refer to background radiation [110] 1946 – George Gamow
George Gamow
calculates a temperature of 50 K (assuming a 3-billion year old universe),[111] commenting it "... is in reasonable agreement with the actual temperature of interstellar space", but does not mention background radiation.[112] 1953 – Erwin Finlay-Freundlich
Erwin Finlay-Freundlich
in support of his tired light theory, derives a blackbody temperature for intergalactic space of 2.3K [113] with comment from Max Born
Max Born
suggesting radio astronomy as the arbitrator between expanding and infinite cosmologies.

Microwave
Microwave
background radiation predictions and measurements[edit]

1941 – Andrew McKellar detected the cosmic microwave background as the coldest component of the interstellar medium by using the excitation of CN doublet lines measured by W. S. Adams in a B star, finding an "effective temperature of space" (the average bolometric temperature) of 2.3 K[31][114] 1946 – George Gamow
George Gamow
calculates a temperature of 50 K (assuming a 3-billion year old universe),[111] commenting it "... is in reasonable agreement with the actual temperature of interstellar space", but does not mention background radiation. 1948 – Ralph Alpher
Ralph Alpher
and Robert Herman estimate "the temperature in the universe" at 5 K. Although they do not specifically mention microwave background radiation, it may be inferred.[115] 1949 – Ralph Alpher
Ralph Alpher
and Robert Herman re-re-estimate the temperature at 28 K. 1953 – George Gamow
George Gamow
estimates 7 K.[110] 1956 – George Gamow
George Gamow
estimates 6 K.[110] 1955 – Émile Le Roux of the Nançay Radio Observatory, in a sky survey at λ = 33 cm, reported a near-isotropic background radiation of 3 kelvins, plus or minus 2.[110] 1957 – Tigran Shmaonov reports that "the absolute effective temperature of the radioemission background ... is 4±3 K".[116] It is noted that the "measurements showed that radiation intensity was independent of either time or direction of observation ... it is now clear that Shmaonov did observe the cosmic microwave background at a wavelength of 3.2 cm"[117][118] 1960s – Robert Dicke
Robert Dicke
re-estimates a microwave background radiation temperature of 40 K[110][119] 1964 – A. G. Doroshkevich and Igor Dmitrievich Novikov publish a brief paper suggesting microwave searches for the black-body radiation predicted by Gamow, Alpher, and Herman, where they name the CMB radiation phenomenon as detectable.[120] 1964–65 – Arno Penzias
Arno Penzias
and Robert Woodrow Wilson
Robert Woodrow Wilson
measure the temperature to be approximately 3 K. Robert Dicke, James Peebles, P. G. Roll, and D. T. Wilkinson interpret this radiation as a signature of the big bang. 1966 – Rainer K. Sachs and Arthur M. Wolfe theoretically predict microwave background fluctuation amplitudes created by gravitational potential variations between observers and the last scattering surface (see Sachs-Wolfe effect) 1968 – Martin Rees
Martin Rees
and Dennis Sciama
Dennis Sciama
theoretically predict microwave background fluctuation amplitudes created by photons traversing time-dependent potential wells 1969 – R. A. Sunyaev
R. A. Sunyaev
and Yakov Zel'dovich
Yakov Zel'dovich
study the inverse Compton scattering of microwave background photons by hot electrons (see Sunyaev-Zel'dovich effect) 1983 – Researchers from the Cambridge Radio Astronomy Group and the Owens Valley Radio Observatory
Owens Valley Radio Observatory
first detect the Sunyaev-Zel'dovich effect from clusters of galaxies 1983 – RELIKT-1
RELIKT-1
Soviet CMB
CMB
anisotropy experiment was launched. 1990 – FIRAS on the Cosmic Background Explorer
Cosmic Background Explorer
(COBE) satellite measures the black body form of the CMB
CMB
spectrum with exquisite precision, and shows that the microwave background has a nearly perfect black-body spectrum and thereby strongly constrains the density of the intergalactic medium. January 1992 – Scientists that analysed data from the RELIKT-1 report the discovery of anisotropy in the cosmic microwave background at the Moscow astrophysical seminar.[121] 1992 – Scientists that analysed data from COBE DMR report the discovery of anisotropy in the cosmic microwave background.[122] 1995 – The Cosmic Anisotropy
Anisotropy
Telescope performs the first high resolution observations of the cosmic microwave background. 1999 – First measurements of acoustic oscillations in the CMB anisotropy angular power spectrum from the TOCO, BOOMERANG, and Maxima Experiments. The BOOMERanG experiment
BOOMERanG experiment
makes higher quality maps at intermediate resolution, and confirms that the universe is "flat". 2002 – Polarization discovered by DASI.[123] 2003 – E-mode polarization spectrum obtained by the CBI.[124] The CBI and the Very Small Array
Very Small Array
produces yet higher quality maps at high resolution (covering small areas of the sky). 2003 – The Wilkinson Microwave Anisotropy Probe
Wilkinson Microwave Anisotropy Probe
spacecraft produces an even higher quality map at low and intermediate resolution of the whole sky ( WMAP
WMAP
provides no high-resolution data, but improves on the intermediate resolution maps from BOOMERanG). 2004 – E-mode polarization spectrum obtained by the CBI.[125] 2004 – The Arcminute Cosmology Bolometer Array Receiver
Arcminute Cosmology Bolometer Array Receiver
produces a higher quality map of the high resolution structure not mapped by WMAP. 2005 – The Arcminute Microkelvin Imager
Arcminute Microkelvin Imager
and the Sunyaev-Zel'dovich Array begin the first surveys for very high redshift clusters of galaxies using the Sunyaev-Zel'dovich effect. 2005 – Ralph A. Alpher
Ralph A. Alpher
is awarded the National Medal of Science
National Medal of Science
for his groundbreaking work in nucleosynthesis and prediction that the universe expansion leaves behind background radiation, thus providing a model for the Big Bang
Big Bang
theory. 2006 – The long-awaited three-year WMAP
WMAP
results are released, confirming previous analysis, correcting several points, and including polarization data. 2006 – Two of COBE's principal investigators, George Smoot
George Smoot
and John Mather, received the Nobel Prize in Physics
Nobel Prize in Physics
in 2006 for their work on precision measurement of the CMBR. 2006-2011 – Improved measurements from WMAP, new supernova surveys ESSENCE and SNLS, and baryon acoustic oscillations from SDSS and WiggleZ, continue to be consistent with the standard Lambda-CDM model. 2010 – The first all-sky map from the Planck telescope is released. 2013 – An improved all-sky map from the Planck telescope is released, improving the measurements of WMAP
WMAP
and extending them to much smaller scales. 2014 – On March 17, 2014, astrophysicists of the BICEP2 collaboration announced the detection of inflationary gravitational waves in the B-mode power spectrum, which if confirmed, would provide clear experimental evidence for the theory of inflation.[64][65][66][67][69][126] However, on 19 June 2014, lowered confidence in confirming the cosmic inflation findings was reported.[69][71][72] 2015 – On January 30, 2015, the same team of astronomers from BICEP2 withdrew the claim made on the previous year. Based on the combined data of BICEP2 and Planck, the European Space Agency
European Space Agency
announced that the signal can be entirely attributed to dust in the Milky Way.[127]

In popular culture[edit]

In the Stargate Universe
Universe
TV series, an Ancient spaceship, Destiny, was built to study patterns in the CMBR which indicate that the universe as we know it might have been created by some form of sentient intelligence. In Wheelers, a novel by Ian Stewart & Jack Cohen, CMBR is explained as the encrypted transmissions of an ancient civilization. This allows the Jovian "blimps" to have a society older than the currently-observed age of the universe. In The Three-Body Problem, a novel by Liu Cixin, a probe from an alien civilization compromises instruments monitoring the CMBR in order to deceive a character into believing the civilization has the power to manipulate the CMBR itself. The Swiss 20 francs bill lists several astronomical objects with their distances – the CMB
CMB
is mentioned with 430 · 1015 light-seconds.

See also[edit]

Wikimedia Commons has media related to Cosmic microwave background.

Computational packages for Cosmologists Cosmic neutrino background Cosmic gravitational wave background Cosmological perturbation theory Axis of evil (cosmology) Gravitational wave
Gravitational wave
background Heat death of the universe Lambda-CDM model Observational cosmology Observation history of galaxies Physical cosmology

References[edit]

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Big Bang
signal". BBC News. Retrieved June 20, 2014.  ^ Planck Collaboration Team (9 February 2016). "Planck intermediate results. XXX. The angular power spectrum of polarized dust emission at intermediate and high Galactic latitudes". Astronomy & Astrophysics. 586: A133. arXiv:1409.5738 . Bibcode:2016A&A...586A.133P. doi:10.1051/0004-6361/201425034.  ^ Overbye, Dennis (22 September 2014). "Study Confirms Criticism of Big Bang
Big Bang
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Nature
News & Comment.  ^ ESA Planck (Oct 22, 2013). "Planck Space Mission". Retrieved Oct 23, 2013.  ^ NASA/Jet Propulsion Laboratory (October 22, 2013). "Long-sought pattern of ancient light detected". ScienceDaily. Retrieved October 23, 2013.  ^ Hanson, D.; et al. (Sep 30, 2013). "Detection of B-Mode Polarization in the Cosmic Microwave
Microwave
Background with Data from the South Pole Telescope". Physical Review Letters. 14. 111. arXiv:1307.5830 . Bibcode:2013PhRvL.111n1301H. doi:10.1103/PhysRevLett.111.141301.  ^ The Polarbear Collaboration (October 2014). "A Measurement of the Cosmic Microwave
Microwave
Background B-Mode Polarization Power Spectrum at Sub-Degree Scales with POLARBEAR" (PDF). The Astrophysical Journal. 794: 171. arXiv:1403.2369 . Bibcode:2014ApJ...794..171T. doi:10.1088/0004-637X/794/2/171. Retrieved November 16, 2014.  ^ " POLARBEAR
POLARBEAR
project offers clues about origin of universe's cosmic growth spurt". Christian Science Monitor. October 21, 2014.  ^ Clavin, Whitney; Harrington, J.D. (21 March 2013). "Planck Mission Brings Universe
Universe
Into Sharp Focus". NASA. Retrieved 21 March 2013.  ^ Staff (21 March 2013). "Mapping the Early Universe". New York Times. Retrieved 23 March 2013.  ^ Planck Collaboration (2015). "Planck 2015 results. XIII. Cosmological parameters (See Table 4 on page 31 of pfd)". Astronomy & Astrophysics. 594: A13. arXiv:1502.01589 . Bibcode:2016A&A...594A..13P. doi:10.1051/0004-6361/201525830.  ^ Kogut, A.; Lineweaver, C.; Smoot, G. F.; Bennett, C. L.; Banday, A.; Boggess, N. W.; Cheng, E. S.; De Amici, G.; Fixsen, D. J.; Hinshaw, G.; Jackson, P. D.; Janssen, M.; Keegstra, P.; Loewenstein, K.; Lubin, P.; Mather, J. C.; Tenorio, L.; Weiss, R.; Wilkinson, D. T.; Wright, E. L. (1993). " Dipole
Dipole
Anisotropy
Anisotropy
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Microwave
Background Anomalies: The Effect of a Cosmological Constant". Astrophysical Journal. 664 (2): 650–659. arXiv:astro-ph/0612347 . Bibcode:2007ApJ...664..650I. doi:10.1086/517603.  ^ Rossmanith, G.; Räth, C.; Banday, A. J.; Morfill, G. (2009). "Non-Gaussian Signatures in the five-year WMAP
WMAP
data as identified with isotropic scaling indices". Monthly Notices of the Royal Astronomical Society. 399 (4): 1921–1933. arXiv:0905.2854 . Bibcode:2009MNRAS.399.1921R. doi:10.1111/j.1365-2966.2009.15421.x.  ^ Bernui, A.; Mota, B.; Rebouças, M. J.; Tavakol, R. (2005). "Mapping the large-scale anisotropy in the WMAP
WMAP
data". Astronomy and Astrophysics. 464 (2): 479–485. arXiv:astro-ph/0511666 . Bibcode:2007A&A...464..479B. doi:10.1051/0004-6361:20065585.  ^ Jaffe, T.R.; Banday, A. J.; Eriksen, H. K.; Górski, K. M.; Hansen, F. K. (2005). "Evidence of vorticity and shear at large angular scales in the WMAP
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CMB
fluctuations in WMAP". Physical Review D. 69 (6): 063516. arXiv:astro-ph/0307282 . Bibcode:2004PhRvD..69f3516D. doi:10.1103/PhysRevD.69.063516.  ^ Schwarz, D. J.; Starkman, Glenn D.; et al. (2004). "Is the low-l microwave background cosmic?". Physical Review Letters. 93 (22): 221301. arXiv:astro-ph/0403353 . Bibcode:2004PhRvL..93v1301S. doi:10.1103/PhysRevLett.93.221301.  ^ Bielewicz, P.; Gorski, K. M.; Banday, A. J. (2004). "Low-order multipole maps of CMB
CMB
anisotropy derived from WMAP". Monthly Notices of the Royal Astronomical Society. 355 (4): 1283–1302. arXiv:astro-ph/0405007 . Bibcode:2004MNRAS.355.1283B. doi:10.1111/j.1365-2966.2004.08405.x.  ^ Liu, Hao; Li, Ti-Pei (2009). "Improved CMB
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Microwave
Anisotropy
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data: a cut-sky analysis". Astrophysical Journal. 635 (2): 750–60. arXiv:astro-ph/0507186 . Bibcode:2005ApJ...635..750B. doi:10.1086/497263.  ^ Copi, C.J.; Huterer, Dragan; Schwarz, D. J.; Starkman, G. D. (2006). "On the large-angle anomalies of the microwave sky". Monthly Notices of the Royal Astronomical Society. 367: 79–102. arXiv:astro-ph/0508047 . Bibcode:2006MNRAS.367...79C. doi:10.1111/j.1365-2966.2005.09980.x.  ^ de Oliveira-Costa, A.; Tegmark, M. (2006). " CMB
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24, series 2, p. 234, cited in "History of the 2.7 K Temperature Prior to Penzias and Wilson" (PDF) ^ Eddington, A., The Internal Constitution of the Stars, cited in "History of the 2.7 K Temperature Prior to Penzias and Wilson" (PDF) ^ a b c d e Kragh, H. (1999). Cosmology
Cosmology
and Controversy: The Historical Development of Two Theories of the Universe. ISBN 0-691-00546-X.  "In 1946, Robert Dicke
Robert Dicke
and coworkers at MIT tested equipment that could test a cosmic microwave background of intensity corresponding to about 20K in the microwave region. However, they did not refer to such a background, but only to 'radiation from cosmic matter'. Also, this work was unrelated to cosmology and is only mentioned because it suggests that by 1950, detection of the background radiation might have been technically possible, and also because of Dicke's later role in the discovery". See also Dicke, R. H.; et al. (1946). "Atmospheric Absorption Measurements with a Microwave
Microwave
Radiometer". Physical Review. 70 (5–6): 340–348. Bibcode:1946PhRv...70..340D. doi:10.1103/PhysRev.70.340.  ^ a b George Gamow, The Creation Of The Universe
Universe
p.50 (Dover reprint of revised 1961 edition) ISBN 0-486-43868-6 ^ Gamow, G. (2004) [1961]. Cosmology
Cosmology
and Controversy: The Historical Development of Two Theories of the Universe. Courier Dover Publications. p. 40. ISBN 978-0-486-43868-9.  ^ Erwin Finlay-Freundlich, "Ueber die Rotverschiebung der Spektrallinien" (1953) Contributions from the Observatory, University of St. Andrews ; no. 4, p. 96–102. Finlay-Freundlich also gave two extreme values of 1.9K and 6.0K in Finlay-Freundlich, E.: 1954, "Red shifts in the spectra of celestial bodies", Phil. Mag., Vol. 45, pp. 303–319. ^ Weinberg, S. (1972). Oxford Astronomy Encyclopedia. John Wiley & Sons. p. 514. ISBN 0-471-92567-5.  ^ Helge Kragh, Cosmology
Cosmology
and Controversy: The Historical Development of Two Theories of the Universe
Universe
(1999) ISBN 0-691-00546-X. "Alpher and Herman first calculated the present temperature of the decoupled primordial radiation in 1948, when they reported a value of 5 K. Although it was not mentioned either then or in later publications that the radiation is in the microwave region, this follows immediately from the temperature ... Alpher and Herman made it clear that what they had called "the temperature in the univerese" the previous year referred to a blackbody distributed background radiation quite different from sunliight". ^ Shmaonov, T. A. (1957). "Commentary". Pribory i Tekhnika Experimenta (in Russian). 1: 83. doi:10.1016/S0890-5096(06)60772-3.  ^ It is noted that the "measurements showed that radiation intensity was independent of either time or direction of observation ... it is now clear that Shmaonov did observe the cosmic microwave background at a wavelength of 3.2cm" ^ Naselsky, P. D.; Novikov, D.I.; Novikov, I. D. (2006). The Physics of the Cosmic Microwave
Microwave
Background. ISBN 0-521-85550-0.  ^ Helge Kragh, Cosmology
Cosmology
and Controversy: The Historical Development of Two Theories of the Universe ^ Doroshkevich, A. G.; Novikov, I.D. (1964). "Mean Density of Radiation
Radiation
in the Metagalaxy and Certain Problems in Relativistic Cosmology". Soviet Physics Doklady. 9 (23): 4292–4298. Bibcode:1999EnST...33.4292W. doi:10.1021/es990537g.  ^ Nobel Prize
Nobel Prize
In Physics: Russia's Missed Opportunities, RIA Novosti, Nov 21, 2006 ^ Sanders, R.; Kahn, J. (13 October 2006). "UC Berkeley, LBNL cosmologist George F. Smoot
George F. Smoot
awarded 2006 Nobel Prize
Nobel Prize
in Physics". UC Berkeley News. Retrieved 2008-12-11.  ^ Kovac, J.M.; et al. (2002). "Detection of polarization in the cosmic microwave background using DASI". Nature. 420 (6917): 772–787. arXiv:astro-ph/0209478 . Bibcode:2002Natur.420..772K. doi:10.1038/nature01269. PMID 12490941.  ^ Readhead, A. C. S.; et al. (2004). "Polarization Observations with the Cosmic Background Imager". Science. 306 (5697): 836–844. arXiv:astro-ph/0409569 . Bibcode:2004Sci...306..836R. doi:10.1126/science.1105598. PMID 15472038.  ^ A. Readhead et al., "Polarization observations with the Cosmic Background Imager", Science 306, 836-844 (2004). ^ http://www.math.columbia.edu/~woit/wordpress/?p=6865 ^ Cowen, Ron (2015-01-30). " Gravitational waves
Gravitational waves
discovery now officially dead". nature. doi:10.1038/nature.2015.16830. 

Further reading[edit]

Balbi, Amedeo (2008). The music of the big bang : the cosmic microwave background and the new cosmology. Berlin: Springer. ISBN 3540787267.  Evans, Rhodri (2015). The Cosmic Microwave
Microwave
Background: How It Changed Our Understanding of the Universe. Springer. ISBN 9783319099279. 

External links[edit]

Student Friendly Intro to the CMB
CMB
A pedagogic, step-by-step introduction to the cosmic microwave background power spectrum analysis suitable for those with an undergraduate physics background. More in depth than typical online sites. Less dense than cosmology texts. CMBR Theme on arxiv.org Audio: Fraser Cain and Dr. Pamela Gay – Astronomy Cast. The Big Bang and Cosmic Microwave
Microwave
Background – October 2006 Visualization of the CMB
CMB
data from the Planck mission Copeland, Ed. "CMBR: Cosmic Microwave
Microwave
Background Radiation". Sixty Symbols. Brady Haran
Brady Haran
for the University of Nottingham. 

v t e

Cosmic microwave background radiation
Cosmic microwave background radiation
(CMB)

Discovery of CMB
CMB
radiation Timeline of CMB
CMB
astronomy

Effects

Cosmic variance Diffusion damping Recombination Sachs–Wolfe effect Sunyaev–Zel'dovich effect Thomson scattering

9-year WMAP
WMAP
image (2012) of the CMB.

Experiments

Space

COBE Planck RELIKT-1 WMAP

Balloon

Archeops ARCADE BOOMERanG EBEX MAXIMA QMAP Spider TopHat

Ground

ABS ACBAR ACT AMI AMiBA APEX ATCA BICEP BICEP2 BICEP3 BIMA CAPMAP CAT CBI CLASS COSMOSOMAS DASI Keck Array MAT OVRO POLARBEAR QUaD QUBIC QUIET QUIJOTE Saskatoon SPT SZA Tenerife VSA

v t e

Radio astronomy

Concepts

Astronomical interferometer
Astronomical interferometer
(History) Very Long Baseline Interferometry
Interferometry
(VLBI) Radio telescope
Radio telescope
(Radio window) Astronomical radio source Units (watt and jansky)

Radio telescopes (List)

Individual telescopes

RATAN-600
RATAN-600
Radio Telescope (Russia) 500 m Aperture Spherical Telescope (FAST, China) Arecibo Observatory
Arecibo Observatory
(Puerto Rico, US) Caltech Submillimeter Observatory
Caltech Submillimeter Observatory
(CSO, US) Effelsberg Telescope (Germany) Large Millimeter Telescope
Large Millimeter Telescope
(Mexico) Yevpatoria RT-70 (Ukraine) Galenki RT-70 (Russia) Suffa RT-70 (Uzbekistan) Green Bank Telescope
Green Bank Telescope
(West Virginia, US) Lovell Telescope
Lovell Telescope
(UK) Ooty Telescope (India) UTR-2 decameter radio telescope (Ukraine) Sardinia Radio Telescope
Sardinia Radio Telescope
(Italy) Usuda Telescope (Japan) Qitai Radio Telescope
Qitai Radio Telescope
(China)

Southern Hemisphere HartRAO (South Africa) Parkes Observatory
Parkes Observatory
(Australia) Warkworth Radio Astronomical Observatory
Warkworth Radio Astronomical Observatory
(NZ)

Interferometers

Allen Telescope Array
Allen Telescope Array
(ATA, California, US) Atacama Large Millimeter Array
Atacama Large Millimeter Array
(ALMA, Chile) Australia Telescope Compact Array
Australia Telescope Compact Array
(ATCA, Australia) Australian Square Kilometre Array Pathfinder
Australian Square Kilometre Array Pathfinder
(ASKAP, Australia) Canadian Hydrogen
Hydrogen
Intensity Mapping Experiment (CHIME, Canada) Combined Array for Research in Millimeter-wave Astronomy
Combined Array for Research in Millimeter-wave Astronomy
(CARMA, California, US) European VLBI Network
European VLBI Network
(Europe) Event Horizon Telescope
Event Horizon Telescope
(EHT) Green Bank Interferometer
Interferometer
(GBI, West Virginia, US) Giant Metrewave Radio Telescope
Giant Metrewave Radio Telescope
(GMRT, India) Korean VLBI Network
Korean VLBI Network
(KVN, South Korea) Low-Frequency Array (LOFAR, Netherlands) MeerKAT
MeerKAT
(South Africa) Large Latin American Millimeter Array
Large Latin American Millimeter Array
(LLAMA, Argentina/Brazil) Murchison Widefield Array
Murchison Widefield Array
(MWA, Australia) Multi-Element Radio Linked Interferometer
Interferometer
Network (MERLIN, UK) Molonglo Observatory Synthesis Telescope
Molonglo Observatory Synthesis Telescope
(MOST, Australia) Northern Cross Radio Telescope
Northern Cross Radio Telescope
(Italy) Northern Extended Millimeter Array
Northern Extended Millimeter Array
(France) One-Mile Telescope
One-Mile Telescope
(UK) Primeval Structure Telescope
Primeval Structure Telescope
(PaST, China) Square Kilometre Array
Square Kilometre Array
(SKA, Australia, South Africa) Submillimeter Array
Submillimeter Array
(SMA, US) Very Large Array (VLA, New Mexico, US) Very Long Baseline Array
Very Long Baseline Array
(VLBA, US) Westerbork Synthesis Radio Telescope
Westerbork Synthesis Radio Telescope
(WSRT, Netherlands)

Space-based telescopes

Spektr-R
Spektr-R
(Russia) HALCA (Japan)

Observatories

Algonquin Radio Observatory
Algonquin Radio Observatory
(Canada) Haystack Observatory
Haystack Observatory
(US) Jodrell Bank Observatory
Jodrell Bank Observatory
(UK) Mullard Radio Astronomy Observatory
Mullard Radio Astronomy Observatory
(UK) National Radio Astronomy Observatory
National Radio Astronomy Observatory
(US) Onsala Space Observatory
Onsala Space Observatory
(Sweden) Special
Special
Astrophysical Observatory of the Russian Academy of Science (SAORAS, Russia) Warkworth Radio Astronomical Observatory Pushchino Radio Astronomy Observatory
Pushchino Radio Astronomy Observatory
(PRAO ASC LPI, Russia)

Multi-use

PARL (Canada) DRAO (Canada) ESA New Norcia (Australia)

People

Elizabeth Alexander John G. Bolton Edward George Bowen Ronald Bracewell Jocelyn Bell Burnell Arthur Covington Frank Drake Antony Hewish Karl Guthe Jansky (Unit: jansky) Kenneth Kellermann Frank J. Kerr John D. Kraus Bernard Lovell Jan Oort Joseph Lade Pawsey Ruby Payne-Scott Arno Penzias Govind Swarup Grote Reber Martin Ryle Gart Westerhout Paul Wild Robert Wilson

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Cosmic microwave background
Cosmic microwave background
radiation SETI Interferometry Radio propagation Aperture synthesis Wow! signal Radio signal from HD 164595 Pulsar timing array

Optical astronomy Submillimetre astronomy Infrared astronomy High-energy astronomy Gravitational-wave astronomy

v t e

Cosmology

Background

Age of the universe Big Bang Chronology of the universe Universe

History of cosmological theories

Discovery of cosmic microwave background History of the Big Bang
Big Bang
theory Religious interpretations of the Big Bang Timeline of cosmological theories

Past universe

Cosmic microwave background Gravitational wave
Gravitational wave
background Neutrino background Inflation Nucleosynthesis Habitable epoch

Present universe

FLRW metric Friedmann equations Hubble's law Metric expansion of space Redshift

Future universe

Future of an expanding universe Ultimate fate of the universe

Components

Dark energy Dark fluid Dark matter Lambda-CDM model

Structure formation

Galaxy filament Galaxy formation Large quasar group Large-scale structure Reionization Shape of the universe Structure formation

Experiments

2dF BOOMERanG COBE Illustris project Observational cosmology Planck SDSS WMAP

Cosmology
Cosmology
portal

v t e

Relativity

Special relativity

Background

Principle of relativity Special
Special
relativity Doubly special relativity

Foundations

Frame of reference Speed of light Hyperbolic orthogonality Rapidity Maxwell's equations

Formulation

Galilean relativity Galilean transformation Lorentz transformation

Consequences

Time dilation Relativistic mass Mass–energy equivalence Length contraction Relativity of simultaneity Relativistic Doppler effect Thomas precession Relativistic disks

Spacetime

Light cone World line Spacetime
Spacetime
diagram Biquaternions Minkowski space

General relativity

Background

Introduction Mathematical formulation

Fundamental concepts

Special
Special
relativity Equivalence principle World line Riemannian geometry Minkowski diagram Penrose diagram

Phenomena

Black hole Event horizon Frame-dragging Geodetic effect Lenses Singularity Waves Ladder paradox Twin paradox Two-body problem BKL singularity

Equations

ADM formalism BSSN formalism Einstein field equations Geodesic equation Friedmann equations Linearized gravity Post-Newtonian formalism Raychaudhuri equation Hamilton–Jacobi–Einstein equation Ernst equation Tolman–Oppenheimer–Volkoff equation

Advanced theories

Brans–Dicke theory Kaluza–Klein Mach's principle Quantum gravity

Solutions

Schwarzschild (interior) Reissner–Nordström Gödel Kerr Kerr–Newman Kasner Friedmann–Lemaître–Robertson–Walker Taub–NUT Milne pp-wave van Stockum dust Weyl−Lewis−Papapetrou

Scientists

Einstein Lorentz Hilbert Poincaré Schwarzschild de Sitter Reissner Nordström Weyl Eddington Friedmann Milne Zwicky Lemaître Gödel Wheeler Robertson Bardeen Walker Kerr Chandrasekhar Ehlers Penrose Hawking Taylor Hulse Stockum Taub Newman Yau Thorne Weiss Bondi Misner others

Cosmology
Cosmology
por

.