Cosmic radiation background, definition and study. A-Z index of Cognitio.

In cosmology, the underlying cosmic radiation, abbreviated in CMB, is the electromagnetic radiation permeating the universe, interpreted as a residual of that produced by the Big Bang.

Cosmology, definition and study. A-Z index of Cognitio.


Despite the space between stars and galaxies appearing black with a conventional optical telescope, a radio telescope can detect a weak isotropic radiation that is not associated with any star, galaxy or other celestial body with greater intensity in the electromagnetic spectrum microwave region .

Cosmic space, definition and study. A-Z index of Cognitio.

Cosmic space

The background radiation is definable as the residual radiation from the early stages of the universe’s birth and its discovery is considered a key confirmation of the Big Bang model. In the early stages of life, before the formation of stars and planets, the universe had dimensions much smaller than the present ones, it was much warmer and permeated by uniform radiation in close interaction with hydrogen plasma. High photon energy prevented electrons from attaching to protons, preventing the formation of atoms. With the expansion of the universe, both plasma and radiation began to cool down to a temperature at which the least energy of the photons was no longer able to prevent the formation of the first stable atoms. They could no longer absorb the thermal radiation, so that the universe, which until then had been a kind of opaque fog, became transparent to radiation. The photons that existed at that time began to propagate, becoming less energetic, as they went to fill a larger universe. Precise measurements of cosmic background radiation are fundamental to cosmology, since any proposed universe model must be able to explain this radiation. Although many different processes can produce the general shape of a black body spectrum, no model other than the Big Bang has so far fluctuated.

Big Bang, definition and study. A-Z index of Cognitio.

Big Bang

That is why most cosmologists believe the Big Bang model is the one that gives the best interpretation of the background radiation. The fundamental cosmic radiation measurements made the Big Bang inflationary theory the standard model of the origins of the universe. This theory assumes that the initial conditions for the universe are of a random nature (that is, they are not able to go back to the previous moments). The underlying cosmic radiation and the shift towards cosmological red are considered the best evidence available for the Big Bang theory. Background radiation provides a snapshot of the universe when, according to standard cosmology, the temperature had dropped enough to allow the formation of hydrogen atoms by electrons and protons, making the universe transparent to radiation. When this happened, about 380,000 years after the Big Bang, the temperature of the Universe was about 3,000 K. In 2004, astronomers identified a large region of the sky in the map of the cosmic radiation background, which was about 500 million light-years, where the temperature was significantly lower than the mean value: the term Cold Spot was attributed to it. On average, the typical fluctuation of the cosmic background radiation temperature is in the order of 10-5, while the “cold spot” is 70 μK colder than the average temperature of the CMB.



The standard cosmological model of the Big Bang predicts the existence of regions of various sizes, which may be colder or warmer than the average value of the space temperature, but a region of such size was a surprise. If this particular region of the sky originated from the Big Bang, it could be the signal of a more exotic physics than the standard cosmology can not explain. If, instead, the “cold spot” was caused by a background structure between us and the CMB, then it could be an indication that there would be a very large, cosmic, large-scale structure that would be distinguished from the average distribution of the material present Universe.

Cosmic radiation background, definition and study. A-Z index of Cognitio.



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Cosmic radiation background, definition and study. A-Z index of Cognitio.

Cosmic radiation background