The Microwave Background

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 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... 

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... 

As far as we can see into the Universe, we don t observe any primordial antimatter. Within the limits of our present observational horizon the Universe is seen to contain only matter and no antimatter. The presence of cosmic antimatter would lead to observable traces of annihilation however the measurements of the extragalactic 7 ray flux indicate an absence of annihilation radiation, and the microwave background spectrum lacks a corresponding distortion. These findings preclude the existence of a significant amount of antimatter within tens of Megaparsecs, which is the scale of super-clusters of galaxies. 

Fig. 20 shows the observed interstellar molecular lines of various isotopic species of formaldehyde, H2CO, as detected by Gardner et al., 1971. This particular line, the lowest asymmetry-doublet transition 110 — lu, is seen in absorption in the continuum radiation of the strong radio source Sgr B2, which is located behind the molecular gas cloud. Frequency is plotted along the abscissa and the ordinate is intensity, expressed in the ratio of line-to-continuum antenna temperatures. For all three formaldehyde isotopes the continuum temperature is Tc T >b Tex- This is the case because the formaldehyde molecules are in approximate equilibrium with the microwave background... 

Clearly, the viability of all of the speculative ideas above relies at this point on the confirmation or refutation of time-varying constants of nature. Most recently, Barrow (2005) has shown that the isotropy of the microwave background imposes very stringent bounds on spatial variations of physical constants. 

The temperature of the present universe, derived from the microwave background, T = 2.7K, predicts that the radiation should be homogeneous over a radius of 6km. However, the radiation is observed uniform in temperature to within 10 on a cosmological scale of about 10 cm. 

The dominant component is the microwave background produced by the primordial Universe at recombination (z 1089). The second most important is the FIR background, produced by galaxies in the young Universe. The third is the optical background dominated by evolved stars/galaxies and AGN (Dole et al. 2006). The first and third of these components have now been mapped in detail over the entire sky, while virtually no sky has been imaged in the FIR to any reasonable depth. 

US astrophysicists Arno Penzias (1933- ) and Robert Wilson (1936- ) discover the microwave background radiation. 

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