Planck character of the spectrum of the CMB is the evidence of the last state of local thermodynamic equilibrium (LTE) between quanta and cosmic plasma. This condition allows you to build a detailed thermal history of the early Universe with the indication of the characteristic stages, when there was a change of qualitative structure of matter due to interconversion of different kinds of elementary particles.

However, the closer to a modern condition of a balance between the plasma and radiation must inevitably collapse, because the expansion of the Universe is both a source of cooling substances.

Cooling space plasma leads to irreversible changes in its composition, the free electrons are trapped protons to form neutral hydrogen atoms. This process plays a crucial role in the dynamics of formation of the anisotropy of relic radiation, as a sharp decrease in the concentration of free charge carriers (electrons and protons) "off" relic radiation from interaction with matter. The spectrum of the CMB "can" information about the properties of the surface of last scattering quanta free charge carriers. What are the properties of this "surface" ?

This question, despite its seeming simplicity, for almost 30 years determined the vector of development of one of the most rapidly advancing areas of extragalactic astronomy, stimulating both theoretical and experimental research. The fact that the properties of the surface of last scattering quantums to electrons are the key to solving the most important problems of astrophysics, and all natural Sciences - how and why in the expanding Universe has arisen various structural forms of self-organization of matter?

The roots of this problem lie deep in the history of astronomy and physics, to the epoch of Galileo Galilei and Isaac Newton, when the first, using a simple telescope, significantly expanded the horizons of exploring space, and the second by opening the law of gravity, showed that the heavenly bodies move (and exist) due to the gravity of the matter.

The next step in solving made James jeans, published in 1902 famous work on gravitational instability dust-like matter. In short, the statement of the problem and main results of this work was the following.

Imagine that the space is filled uniformly distributed substance, the pressure of which can be ignored. Will create in this matter weak spherically symmetric density inhomogeneity (fluctuation). Suppose for definiteness, this will be an area thickening agents. Then the surplus substances will automatically create the excess of the gravitational field, which in turn will cause the gravitational acceleration of particles and sent to the center configuration. This matter is moving to the center, in turn, leads to the compression of a substance, and therefore to increase its density. Then the circle is closed. Increasing the density increases gravity, gravity increases the velocity field, the speed increases the degree of compaction, etc. Exact calculation shows that if in the moment of creation of the initial fluctuations of the density contrast was arbitrarily small, but finite, then over time it will grow very quickly.

In relation to the galaxies, elementary calculations based on the idea of jeans, show that during about 3-10 billion years microscopic amplitude fluctuations of the density of time to rise to a modern level and to form galaxies. At first glance, the key to solving the problem of the origin of the structures in the Universe is found, as in any system of a large number of particles, there are always small fluctuations in the distribution of the density (the so-called statistical fluctuations). And, if for the given system the main interaction between particles is the gravitational interaction, it is necessary to wait for a relatively short period of time, as the whole system will break down into bunches!

However, there is one small detail that spoil all the impression of simplicity and elegance of the solution. The thing is that we don't accidentally drew attention to the year of publication James jeans - 1902. Before the opening of the Hubble rouzbehani galaxies remained almost 27 years.

What will the effect of expansion of the Universe? Qualitatively the answer to this question is clear - extension leads to a restructuring of the velocity field of a substance in the zone inhomogeneity and instead of sealing configuration we will get the opposite effect - the heterogeneity in the distribution of gravitating matter should disciplinati (smoothed). It would seem that after 1929 effective mechanism of gravitational instability can "to write off the scrap heap of history". But, fortunately, it was not so.

In 1946, Soviet physics E.M. Lifshitz thoroughly examined the question of the pace of gravitational instability in an expanding Universe. The main conclusions of his work was the following.

Indeed, the cosmological expansion leads to a decrease in the rate of increase of the amplitude of inhomogeneities. But the average density of matter decreases in time even faster. Therefore, contrast density is still growing, though more slowly compared to the naive result, based on the idea J.. Men jeans.

At first glance, a purely quantitative difference - instead of strong only relatively weak growth rate of fluctuations. However, this difference are the fundamental physical consequence. And, first of all the structure in the Universe is not a product of strengthening normal statistical fluctuations in the density of matter! Hence the conclusion - for the development of structures in the expanding Universe, the level of statistical fluctuations are not enough, therefore, in primary cosmic plasma should be small nonequilibrium fluctuations, the level of which, however, exceeds the natural equilibrium background on tens of orders of magnitude! Recall that this is the year of 1946. Before the discovery of relict radiation even need to wait for almost 20 years, and experimental detection of these fluctuations is almost all 50!.

Thus, for various directions on the sky corresponding to the intensity fluctuations of the background radiation on the surface of last scattering should be variations in the signal level. Their value is called the level of the angular anisotropy of relic radiation. This anisotropy "authorized" in the emission spectrum in the era of the hydrogen recombination and is preserved up to the present point in time, and the mechanism of its generation, caused by quantum scattering on moving matter, briefly called the Doppler effect.

In addition anisotropy generated by the irregularities in the surface of last scattering, a significant role in formation of the intensity distribution of the background radiation in the sky plays the gravitational shift of the frequency of quanta in the process of distribution from the epoch of recombination of hydrogen to the observer. Passing through the zones of high and low density, which correspond to the gravitational potential, the quanta of radiation feel "the blue shift", when you enter the zone of high density, and is "red shift" - at the exit.

The influence of the Doppler effect and gravitational displacement divided naturally. The first significant in scale L1 degrees).

Thus, the extent corresponding to the current large-scale structure in the distribution of matter, form the background radiation anisotropy on small angles under the influence of quantum dispersion on moving matter. At angular scales larger than 1 degree ( and L>200 IPS) heterogeneity in the Universe have not had time to form any structure you want "wait" a certain period of time exceeding the modern age of the Universe dozens of times, that at those scales there were new forms of self-organization of matter.