Cosmic microwave background radiation

In cosmology, the cosmic microwave background radiation (CMB) is a form of electromagnetic radiation discovered in 1964 that radiates throughout the universe in the microwave range.

Features

The principal feature of the CMB is how closely it matches a black body spectrum. Although the temperature of the CMB varies from point to point (i.e. it contains small anisotropies), the spectrum in a particular direction almost exactly resembles a black body. The CMB radiation frequency ranges from 0.3 GHz to 630 GHz, and peaks at 160.4 GHz, corresponding to a temperature of 2.725 kelvins.

Related Topics:
Black body spectrum - Temperature - 2.725 kelvins

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There are however very small yet significant variations (anisotropies) from the black body spectrum. The most pronounced is the dipole anisotropy (180 degree scales) which is at a level of about 10 −3 of the monopole. This feature is consistent with the Earth moving at some 700 km/s relative to the CMB.

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Variations due to external physics also exist; the Sunyaev-Zel'dovich effect is one of the major factors here, in which a cloud of high energy electrons scatters the radiation, transferring some energy to the CMB photons.

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Even more interesting are anisotropies at a level of roughly 10 −5 on scales of roughly tens of arcminutes to several degrees. These very small variations are the result of the Sachs-Wolfe effect which causes photons from the cosmic microwave background to be gravitationally redshifted. According to inflationary theory, the origin of the variations is quantum fluctuations which expand during inflation and result in primordial fluctuations. The angular power spectrum of these variations (in terms of amplitudes of component multipole moments) can be calculated and produces a number of peaks and valleys. The location of these peaks and valleys can be correlated with cosmological parameters such as the Hubble constant, and the geometry of the universe.

Related Topics:
Anisotropies - Sachs-Wolfe effect - Photon - Inflationary theory - Quantum fluctuation - Primordial fluctuations - Multipole moments - Hubble constant - Geometry of the universe

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