Background microwave

By the formula E = aT the effective temperature corresponding to this density is 

The existence of this heat bath at a temperature of 2.3K was inferred from the observed rotational spectrum of interstellar cyanogen, CN, as early as 1941, and confirmed many times since then (Sciama, 1971). It only became big news when it was linked to the big bang, although there was nothing left to explain. Fred Hoyle (1997) lamented  

A surprising property of the background radiation is its remarkable homogeneity in temperature over the entire visible universe. A signal emitted longer than time t ago cannot be observed further than a distance ct away 

In an expanding universe 2ct defines the particle horizon that limits the independent region over which a homogeneous equilibrium state can develop at time t. The radius of the initial homogeneous region, at a temperature of 

The rate of expansion, as a function of temperature, has been calculated as V = Tin/Tfin- At the time of recombination, T = 4000K, and hence 

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R. W. Wilson, The cosmic microwave background radiation, pp. 113-33 in I.es Prix Nobel 1978. Almqvist Wiksell International, Stockholm 1979. A. A. Penzias, The origin of the elements, pp. 93-106 in Les Prix Nobel 1978 (also in Science 105, 549-54 (1979)). 

A. A. Penzias and R. W- Wilson (Holm-del) discovery of cosmic microwave background radiation. 

The primordial Li abundance was sought primarily because of its ability to constrain the baryon to photon ratio in the Universe, or equivalently the baryon contribution to the critical density. In this way, Li was able to complement estimates from 4He, the primordial abundance of which varied only slightly with baryon density. Li also made up for the fact that the other primordial isotopes, 2H (i.e. D) and 3He, were at that time difficult to observe and/or interpret. During the late 1990 s, however, measurements of D in damped Lyman alpha systems (high column-density gas believed to be related to galaxy discs) provided more reliable constraints on the baryon density than Li could do (e.g. [19]). Even more recently, the baryon density has been inferred from the angular power spectrum of the cosmic microwave background radiation, for example from the WMAP measurements [26]. We consider the role of Li plateau observations post WMAP. 

The measurement of the cosmic microwave background. Far infrared astronomers were the first to develop thermal detectors. Some of the resulting technologies, such as neutron transmutation doping (NTD) [3], have been transferred to particle detection sensors and have allowed many groups (e.g., ref. [4-11] to make rapid progress). 

We shall now describe an infrared bolometer operating at 0.3 K, built by Lange et al. in 1992 [80], We chose this example because such composite bolometer can be easily described from a cryogenic point of view, whereas the analysis of more recent devices would be quite complicated. Nevertheless the bolometer performances are very good, the NEP being less than 10-16 W/(Hz)1/2 and the time constant r = 11ms. It was used for the measurement of the cosmic microwave background (CMB) in an experiment on board of a stratospheric balloon [81]. 

The main goal of the Planck instrument is to improve the accuracy of the measurement of the cosmic microwave background (CMB), in order to extract cosmological parameters that remain poorly constrained after the results of WMAP (Wilkinson microwave anisotropy probe) and of the best ground-based experiments. The basic idea of HFI-Planck is to use all the information contained in the CMB radiation, i.e. to perform a radiometric measurement limited by the quantum fluctuations of the CMB radiation itself. In these conditions, the accuracy is only limited by the number of detectors and by the duration of the observation. 

Black bodies emit radiation at all wavelengths. Using the spreadsheet, calculate the contribution to the visible spectrum from the cosmic microwave background in the visible region of the spectrum. 

Cosmic microwave background radiation Fossil radiation surviving form the Big Bang with a black body temperature of 2.725 K. 

The microwave background radiation has very precisely the spectrum of a black body with a temperature... 

Fig. 4.1. Schematic thermal history of the Universe showing some of the major episodes envisaged in the standard model. GUTs is short for grand unification theories and MWB is short for (the last scattering of) the microwave background radiation. The Universe is dominated by radiation and relativistic particles up to a time a little before that of MWB and by matter (including non-baryonic matter) thereafter, with dark energy eventually taking over.

The upper end of the range in t] is in excellent agreement with what has been deduced from WMAP measurements of the angular fluctuation spectrum of the cosmic microwave background (see Fig. 4.3 and Section 4.9). 

The two error terms refer to Yp and the regression slope respectively. In contrast to some earlier work, based on less homogeneous data sets and apparently affected by underlying absorption lines, notably in I Zw 18, this result, together with a similar one by Peimbert, Luridiana and Peimbert (2007), gives a primordial helium abundance in excellent agreement with the one predicted theoretically on the basis of the microwave background fluctuations and the lower estimates of deuterium abundance (see Fig. 4.3), a comparatively small value of about 2 for AT/AZ and no... 

COBE observations confirm black-body character of microwave background. 

In consequence, the statistical characteristic temperature of relic radiation is fully determined in terms of relativistic invariant spectrum of the cosmic microwave background radiation and the distribution velocity function of radiating particles, i.e., is described with the following expression (compare with the results of reference (Einstein, 1965))... 

Like some other spectacular discoveries such as the cosmic microwave background, gamma-ray bursts (GRBs) were discovered by accident. Meant to monitor the outer space treaty , the American VELA satellites detected in July 1967 an intense flash of gamma-rays of unknown origin. It took until 1973 before the first detected GRBs were published for the scientific community (Klebesadel et al. 1973). 

On the other hand, we must somehow close the Universe, or more precisely, find some way of giving it the critical density, since this is what inflation demands. Indeed, it is required not only by inflationary theory, but also by close scrutiny of the leopard skin p attern that constitutes the microwave background, radiative relic from the B ig B ang. We... 

Anisotropic effects of the recorded frequency of cosmic microwave background radiation have been proposed for photon rest mass determination [20]. 

With reference to Table I, the energy usually flows frum higher levels to luwer levels—in a direction such ihut the entropy increases. Thus, cosmic microwave background radiation is defined as the ultimate heai sink. i,e il represents the ultimate in energy degradation with no lower form in which to be convened. 

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