Cosmological diffuse Fund

The cosmological diffuse bottom is a electromagnetic Rayonnement coming from the Univers, and which strikes the Ground in a quasi uniform way in all the directions.

He is regarded as being a remainder of the dense time and heat which knew the Universe there is approximately 13 billion years, in accordance with the predictions of the models of Big Bang (see below).

This weak radiation is also known under the name of fossil radiation or radiation to 3 K (in reference to its temperature). It should be noted that none of these names corresponds exactly to its English translation of Cosmic Microwave Background Radiation or from now on Cosmic Microwave Background ( litt. “(radiation) basic cosmic microwave”).

Discovered

In 1964, the radio astronomers Penzias and Wilson, laboratories of the company Beautiful Telephone, have an antenna which was used initially for the communication with the satellites ECHO then TELSTAR 1. They wished to transform this antenna into radio telescope to measure the radiation in the field radio of the Milky Way. With this intention, they needed to gauge the antenna correctly, and in particular to know the background noise generated by this one like by the terrestrial atmosphere. They thus accidentally discover an additional noise of unknown origin during observations made over the wavelength 7,35 cm. This noise, converted into Temperature of antenna, corresponded to a temperature of the sky of 2,7 K, did not present seasonal variations, and its possible fluctuations according to the direction did not exceed 10 %. It could thus be a question of the signal emitted by the Milky Way only they sought to discover.

Penzias and Wilson did not know work of the cosmologists of their time, and it is almost by chance that they discover them. Penzias fortuitously mentions its discovery with the radio astronomer Bernie Burke, who tells him knowledge of Ken Turner that James Peebles predicted the existence of a radiation of some Kelvins, and that a team made up of Dicke, Roll and Wilkinson of the university of Princeton is building an antenna to detect it. Penzias then contacts Dicke to inform him of its results. They then decide to jointly publish two articles, one signed of Penzias and Wilson describing the discovery of the cosmological diffuse bottom, the other signed by Peebles and the team of Dicke by describing the cosmological consequences. The history tells that when Dicke learned the discovery from Penzias, there says to his collaborators a sentence remained famous: Well servant boys, we cuts been scooped (litt. “The guy, we were made precede”). It is not known well if the latter could indeed have detected this radiation with the means of which they laid out but that seems probable. They in any case detected the cosmological diffuse bottom with the wavelength of 3 cm in the current of the year 1965.

Penzias and Wilson will receive each one 1/4 of the Nobel Prize of physique 1978 for their discovery.

It was sometimes known as that the joint publications of Penzias and Wilson and the team of Dicke resulted from an attempt at the latter to acquire the benefit of discovered and to obtain the Nobel Prize. That seems not very probable, Penzias and Wilson having declared thereafter that they preferred to publish their measurement with share, with the reason “that their measurement was exact, whereas the interpretation of Peebles was only one interpretation which could prove to be false.” In fact, Wilson was even at the time partisan of the theory of the stationary state, it was thus undoubtedly reticent.

It is with George Gamow that one allots the prediction of the cosmological diffuse bottom. Gamow actually predicted the existence of a radiation resulting from Big Bang, but the spectrum of black Corps of it had not predicted. It is A.G. Dorochkevitch and I.D. Novikov which in 1964 are the first to predict that the spectrum of the radiation must be that of a black body and thus located in the microwave field. In fact, these authors go even until quoting the antenna of the Bell laboratories like the best tool to detect this radiation! In 1961, E.A. Ohm had written an internal report describing the performances of this antenna. But, basing itself on this report/ratio, Dorochkevitch and Novikov conclude that this radiation was not observed. It was however about a mistake in interpretation of their share: the report/ratio of Ohm mentioned a quantity $T_ {\ rm sky}$ , measured with 2,3 K, representing the contribution of the terrestrial atmosphere. Dorochkevitch and Novikov seem to have interpreted this quantity as the sum of the atmospheric contribution and the bottom of the sky. The figure of 2,3 K corresponding indeed well to the atmospheric contribution such as it was estimated at the time, Dorochkevitch and Novikov then concluded that the contribution of the bottom sky was to be limited to a fraction of 2,3 K, in dissension with the predictions from Gamow.

Sources (in English) of this part

Nobel Site: Speech of Arno A. Penzias, '' The origin off elements '', 1978
Brazilian Company of physics, '' History off 2.7 [[Kelvin|K] Temperature Prior to Penzias and Wilson , 1995]

University of Cincinnati, Course of astrophysics, CH. 23 - Cosmology Leaves 2

Science Magazine, '' The Afterglow off '' Creation, Marcus L6th

Cambridge University Close, Cambridge University Close, '' The Cosmological Background Radiation '', Marc Lachièze-Rey and Edgard Gunzid

Astrophysics and Cosmology, '' Cosmic Microwave Background Timeline ''

Michigan State University, Cours '' Radiation from the Big Bang ''

American Scientific Affiliation, '' Arno A. Penzias: Astrophysicist, Nobel Prize winner '', Jerry Bergman

not-official Site Stephen Jay Gould, various Quotations on Big Bang

Characteristics

Spectrum

The cosmological diffuse bottom seems a black Corps perfect within the limit of the precision of the measuring instruments. Its Température was measured fine 1989 by the satellite COBE with 2,728±0,002 K, uncertainty coming from the difficulty in precisely gauging a black body of reference embarked on the satellite. The maximum of energy is radiated with a Fréquence near to 160 GHz (Wavelength slightly lower than 2 mm, field of the Microwave S).

Dipole

Because of the displacement of the Ground in the Solar system and more generally of the displacement of this last compared to the surface of emission of the cosmological diffuse bottom, the temperature of the cosmological diffuse bottom presents a variation according to the direction, consequence of simple a Doppler effect. If one removes the contribution due to the earthmoving around the Sun, then the amplitude of the Dipôle observed is of 3,358±0,001 mK, corresponding at a speed of the Sun of 369 km/S of this one compared to the zone of emission of the radiation. The direction of this dipole is, in galactic Coordonnées, L =264,31°±0,20°, B =48,05°±0,11°, that is to say 11:00 11min 57s±23s and -7,22°±0,08° in term of Right ascension and variation. This direction is almost opposite with that of the solar apex, i.e. contrary to the direction towards which moves the Sun within the Milky Way. By taking account of the displacement of the Sun within the Milky Way, one calculates the dipole of the cosmological diffuse bottom compared to the Milky Way. Its direction is modified little, L =276°±3°, B =30°±2° but its amplitude increases significantly because of speed of the Sun compared to the galactic center, to reach 5,70 mK, corresponding at a speed of 627 km/s.

This order of magnitude speed is typical dispersion speed which one observes in the Galaxy cluster, which reinforces the interpretation of the dipole as being due for a local kinematic purpose. There remains however difficult to be certain about it because the zone of the dipole is very close to the galactic plane and of this fact it is difficult to chart there all the concentrations of masses which would explain why the Milky Way moves in this direction. This direction remains relatively close (45°) Attractile Grand and also near to several other concentrations of matter close to the local Groupe (less than 30 Mpc), in particular the Amas of Hydre and Pneumatic Machine.

Variation with the black body

A crucial question is to know (see below) if this radiation is a radiation of black body or not. In the paramount universe, the interactions between baryon Matter and Photon S made it possible the latter to be thermalized, i.e. to acquire a spectrum of black body. However, as the universe dilate and cool, the interactions between matter and photons decrease and thermal balance is not assured any more. The photons can thus preserve a spectrum of black body, but this one can be destroyed in the event of phenomenon which would produce energy in the form of radiation electromagnetic (because of Désintégration of unstable particles, for example). The presence or not of distortions to the black body in the cosmological diffuse content thus makes it possible to force all the phenomena injecting of energy in the form of radiation.

an injection of energy at one late time (Z ≤ 10) results in a depopulation of the low frequencies to the profit of the high frequencies (effect Compton '' there '').
an injection of energy at older times (10 ≤ Z ≤ 10) results in a transformation of a spectrum of black body into Specter of Bump-Einstein), i.e. a chemical Potentiel not no one for the photons.
Of the interactions between the radiation and the intergalactic hot matter at times much more recent (Z ≤ 10) can also deform the spectrum (Distortion free-free).

None of these distortions was for the time being detected, with very constraining higher limits on the majority of them.

Other anisotropies

The cosmological models are based on the idea that the Universe was in the past extremely homogeneous and that the structures which one observes little by little (Galaxie S, Amas, Superamas) are little by little formed by mechanism of gravitational Instabilité (or instability of Jean). So that this mechanism operates, it is necessary however that there are small fluctuations of density in the paramount universe. It is thus predicted that these fluctuations of density are found in the form of fluctuation of temperature in the cosmological diffuse content. Conversely, the detection and the fine comprehension of these fluctuations inform us about the state of the Universe at the time when it emitted this radiation, like on various processes being unrolled before and after this time. The study of these fluctuations at present represents (2006) the principal tool for the Cosmologie.

The fluctuations of the cosmological diffuse bottom were detected for the first time by the satellite of NASA COBE in 1992. A great number of experiments on the ground, in stratospheric balloons were carried out since with an aim of improving quality of the observations. The most outstanding experiments were BOOMERANG and Archeops. In 2001, NASA launched a second satellite, WMAP which considerably improved quality of the observations, and distinguished a cold Point. End 2007 or beginning 2008, the European space agency will launch the satellite Planck Surveyor, in order to still improve the data.

Cosmological diffuse Fund and Big Bang

Origin of the FDC

According to this theory, the state of energy of the paramount Univers - from its Density and its Temperature - caused the creation of pairs of particle S Antiparticule S. the annihilation of those (about 1 minute after Big Bang) created a considerable flood of highly energy photons at each point of the paramount universe, emitted in all the directions.

The expansion of the universe then considerably lengthened the Wavelength of these photons, bringing them of the field of the gamma rays highly energy towards the field of the Micro-onde S in which they are observed today.

Although these photons were created in the first minute of the Universe, this one became transparent only: 300000 years after Big Bang. Indeed, when the temperature is higher than the temperature of Ionization of the Hydrogène (that is to say about ten electronvolt S), the photons are continuously in interaction with the matter which absorbs or emits light. Just like in a plasma, the Libre range of the photons before this time of decoupling was very short and these photons could not reach us. The bottom observed today thus corresponds to the " Surface of last diffusion " , at the moment when the Universe sufficiently cooled so that the matter left this state of plasma and that the mean free path of the photons becomes sufficiently large (what amounts saying that the Universe becomes transparent), so that they can cross the considerable distances necessary to be observed nowadays.

Observation of the FDC

The theory of the Big Bang explains why we can observe the FDC today, whereas the creation of the FDC is a temporally specific event. How is it made that the photons of the FDC reach the Earth precisely today so that we can observe them?

The explanation is that the creation of the photons took place in any point of the paramount Universe and that this one, although denser than the current Universe, was also very wide spatially (the question of knowing if the universe is or is not spatially infinite is not solved yet at present). Under these conditions, there exists always, centered around our planet (and of course around any planet), a sphere of x-ray light-years (X being the age of the Universe) where photons FDC were created there is X years. This is why radiation FDC was always, and will be always, observable.

An image can be useful to include/understand that. We in the center of an huge crowd imagine; and that this whole crowd pushes a great cry, at the same time at a given moment. It will be then always possible to hear this cry: at every moment we would hear the sound coming from a circle of people, increasingly distant.

Fluctuations of the cosmological diffuse bottom

See too

cosmological Big Bang
Parameters
Model ΛCDM
cosmological Fund of neutrinos
Not cold

Observational means

Cosmic Background To explore - COBE (1992)
Boomerang (2001)
Archeops (2002)
Wilkinson Microwave Anisotropy Honest - WMAP (2003)
Satellite Planck (launching envisaged at the summer 2008)

External bonds

Missions

Site of mission COBE
Site of the mission Archeops
Site of the mission BOOMERANG
Site of mission WMAP

Results

The Cosmic Microwave Spectrum Background, by George F. Smoot
The CMB Dipole: The Most Recent Measurement And Summons History, by Charles H. Lineweaver
The Cosmic Microwave Background Anisotropy Experiments (pre BOOMERANG) by George F. Smoot

Cosmological aspects

the physics of the anisotropies of the bottom microwaves

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