Relic light. How useful is cosmic microwave background radiation? Relic radiation speaks of the homogeneity of the universe

One of interesting discoveries associated with the electromagnetic spectrum is cosmic background radiation. It was discovered by accident, although the possibility of its existence was predicted.

The history of the discovery of relic radiation

Discovery history relic radiation started in 1964. American lab staff Bell Phone developed a communication system using an artificial Earth satellite. This system was supposed to work on waves with a length of 7.5 centimeters. Such short waves in relation to satellite radio communications have some advantages, but up to Arno Penzias and Robert Wilson no one has solved this problem.

They were pioneers in this area and had to make sure that there were no strong interference on the same wavelength, or that communications workers knew about such interference in advance. At that time, it was believed that only point objects like radio galaxies or stars.

Sources of radio waves

The scientists had at their disposal an extremely accurate receiver and a rotary horn antenna. With their help, scientists could listen to the entire vault of heaven similar to how a doctor listens to a patient's chest with a stethoscope.

Natural source signal

And as soon as the antenna was pointed at one of the points of the sky, a curved line danced on the oscilloscope screen. Typical signal natural source . Probably, the experts were surprised at their luck: at the very first measured point - a source of radio emission!

But wherever they pointed their antenna, the effect remained the same. Scientists again and again checked the health of the equipment, but it was in in perfect order. And finally, they realized that they had discovered a previously unknown phenomenon of nature: the whole universe was, as it were, filled with centimeter-length radio waves.

If we could see radio waves, the firmament would appear to us luminous from edge to edge.

Penzias and Wilson's discovery was published. And not only they, but also scientists from many other countries began to search for sources of mysterious radio waves that are captured by all antennas and receivers adapted for this purpose, wherever they are and no matter what point in the sky they aim at, and the intensity of radio emission at a wavelength of 7.5 centimeter at any point was exactly the same, it seemed to be spread evenly across the sky.

CMB radiation calculated by scientists

Soviet scientists A. G. Doroshkevich and I. D. Novikov, who predicted background radiation before its opening made the most difficult calculations.. They took into account all the sources of radiation available in our Universe, and took into account how the radiation of certain objects changed over time. And it turned out that in the region of centimeter waves, all these radiations are minimal and, therefore, they are in no way responsible for the detected skyglow.

Meanwhile, further calculations showed that the density of the smeared radiation is very high. Here is a comparison of photon jelly (as scientists called the mysterious radiation) with the mass of all matter in the universe.

If all the matter of all visible Galaxies is evenly “smeared” over the entire space of the Universe, then there will be only one hydrogen atom per three cubic meters of space (for simplicity, we will consider all the matter of stars as hydrogen). At the same time, each cubic centimeter of real space contains about 500 photons of radiation.

A lot, even if we compare not the number of units of matter and radiation, but directly their masses. Where did such intense radiation come from?

At one time, the Soviet scientist A. A. Fridman, solving the famous Einstein equations, discovered that our universe is in constant expansion. Soon confirmation of this was found.

American E. Hubble discovered recession of galaxies. Extrapolating this phenomenon into the past, one can calculate the moment when all the matter of the Universe was in a very small volume and its density was incomparably greater than now. In the course of the expansion of the Universe, the lengthening of the wavelength of each quantum also occurs in proportion to the expansion of the Universe; in this case, the quantum, as it were, “cools” - after all, the shorter the wavelength
quantum, the "hotter" it is.

Today's centimeter radiation has a brightness temperature of about 3 degrees Kelvin absolute. And ten billion years ago, when the Universe was incomparably smaller, and the density of its matter was very high, these quanta had a temperature of about 10 billion degrees.

Since then, our Universe has been “filled with” quanta of continuously cooling radiation. That is why centimeter radio emission “smeared” over the Universe got the name
relic radiation.

relics, as you know, are called the remains of the most ancient animals and plants that have survived to this day. Centimeter radiation quanta are by far the oldest of all possible relics. After all, their formation belongs to an era that is about 15 billion years away from us.

Knowledge about the universe brought cosmic microwave background radiation

Virtually nothing can be said about what matter was like at moment zero, when its density was infinitely high. But the phenomena and processes that took place in Universe, just a second after her birth and even earlier, up to 10 ~ 8 seconds, scientists already understand quite well. Information about this was brought by background radiation.

So, a second has passed since zero moment. The matter of our Universe had a temperature of 10 billion degrees and consisted of a kind of "porridge" relic quanta, electrodes, positrons, neutrinos and antineutrinos. The density of the "porridge" was huge - more than a ton for each cubic centimeter. In such "crampedness" collisions of neutrons and positrons with electrons continuously occurred, protons turned into neutrons and vice versa.

But most of all there were quanta here - 100 million times more than neutrons and protons. Of course, at such a density and temperature, no complex nuclei of matter could exist: they did not decay here.

One hundred seconds have passed. The expansion of the universe continued, its density continuously decreased, the temperature fell. Positrons almost disappeared, neutrons turned into protons.

The formation of atomic nuclei of hydrogen and helium began. Calculations carried out by scientists show that 30 percent of the neutrons combined to form helium nuclei, while 70 percent of them remained alone, becoming hydrogen nuclei. In the course of these reactions, new quanta arose, but their number could no longer be compared with the original, so we can assume that it did not change at all.

The expansion of the universe continued. The density of the "porridge", so steeply brewed by nature at the beginning, decreased in proportion to the cube of the linear distance. Years, centuries, millennia passed.

3 million years have passed. The temperature of the “porridge” by that moment had dropped to 3-4 thousand degrees, the density of the substance also approached the one known to us today, however, clots of matter from which stars and galaxies could form could not yet arise. At that time, the radiation pressure was too great, pushing any such formation apart. Even the atoms of helium and hydrogen remained ionized: electrons existed separately, protons and atomic nuclei - also separately.

Only towards the end of the three-million-year period did the first thickenings begin to appear in the cooling "porridge". There were very few of them at first. As soon as one thousandth of the "porridge" condensed into peculiar protostars, these formations began to "burn" similarly to modern stars.

And the photons and energy quanta emitted by them warmed up the “porridge” that had begun to cool down to temperatures at which the formation of new condensations again turned out to be impossible.

The periods of cooling and reheating of the “porridge” by outbursts of protostars alternated, replacing each other. And at some stage of the expansion of the Universe, the formation of new clumps became practically impossible, if only because the once so thick "porridge" was too "thinned".

Approximately 5 percent of the matter managed to unite, and 95 percent scattered in the space of the expanding Universe. This is how the once-hot quanta, which formed the relic radiation, "scattered" as well. This is how the nuclei of hydrogen and helium atoms, which were part of the "porridge", scattered.

The hypothesis of the formation of the Universe

Planetary systems formed around some of these stars, at least on one of these planets, life arose, which in the course of evolution gave rise to intelligence. How often stars are found in the vastness of space, surrounded by a round dance of planets, scientists do not yet know. Nor can they say anything about how often.

And the question of how often the plant of life blossoms into a lush flower of the mind remains open. The hypotheses known to us today that treat all these questions are more like unsubstantiated guesses.

But today science is developing like an avalanche. More recently, scientists had no idea how ours began. The relic radiation, discovered about 70 years ago, made it possible to draw that picture. Today, mankind lacks facts, based on which it can answer the questions formulated above.

Penetration into outer space, visits to the Moon and other planets, bring new facts. And the facts are no longer followed by hypotheses, but by strict conclusions.

Relic radiation speaks of the homogeneity of the universe

What else did the relic rays, these witnesses of the birth of our Universe, tell scientists?

A. A. Fridman solved one of the equations given by Einstein, and on the basis of this solution discovered the expansion of the Universe. In order to solve the Einstein equations, it was necessary to set the so-called initial conditions.

Friedman proceeded from the assumption that The universe is homogeneous and isotropic, meaning that matter is evenly distributed in it. And during the 5-10 years that have passed since the discovery of Friedman, the question of whether this assumption was correct remained open.

It has now essentially been removed. The isotropy of the Universe is evidenced by the amazing uniformity of the relict radio emission. The second fact testifies to the same - the distribution of the matter of the Universe between the Galaxies and the intergalactic gas.

After all, intergalactic gas, which makes up the main part of the matter of the Universe, is distributed over it as evenly as relict quanta..

The discovery of relic radiation makes it possible to look not only into the ultra-distant past - beyond such limits of time when there was neither our Earth, nor our Sun, nor our Galaxy, nor even the Universe itself.

Like an amazing telescope that can be pointed in any direction, the discovery of the cosmic microwave background allows you to look into the ultra-distant future. Such an ultra-distant, when there will be no Earth, no Sun, no Galaxy.

The phenomenon of the expansion of the Universe will help here, as the stars that make it up, Galaxies, clouds of dust and gas scatter in space. Is this process eternal? Or will the expansion slow down, stop, and then be replaced by compression? And are not the successive contractions and expansions of the Universe a kind of pulsations of matter, indestructible
and eternal?

The answer to these questions depends primarily on how much matter is contained in the universe. If its general gravity is sufficient to overcome the inertia of expansion, then the expansion will inevitably be replaced by contraction, in which the Galaxies will gradually approach each other. Well, if the forces of gravity are not enough to slow down and overcome the inertia of the expansion, our Universe is doomed: it will dissipate in space!

CMB radiation-cosmic electromagnetic radiation with a high degree of isotropy and with a spectrum characteristic of a black body with temperature? 2.725 K. CMB radiation was predicted by G. Gamow, R. Alfer and R. Herman in 1948 on the basis of the first Big Bang theory they created. Alfer and Herman were able to establish that the temperature of the cosmic microwave background should be 5 K, and Gamow gave a prediction in 3 K. Although some estimates of the temperature of space existed before this, they had several drawbacks. Firstly, these were measurements of only the effective temperature of space, it was not assumed that the radiation spectrum obeys Planck's law. Secondly, they were dependent on our special location at the edge of the Galaxy and did not assume that the radiation is isotropic. Moreover, they would give completely different results if the Earth were somewhere else in the universe. Neither G. Gamow himself, nor many of his followers raised the question of the experimental detection of relic radiation. Apparently, they believed that this radiation could not be detected, since it "sinks" in the energy fluxes brought to the earth by the radiation of stars and cosmic rays.

The possibility of detecting relic radiation against the background of radiation from galaxies and stars in the region of centimeter radio waves was substantiated by the calculations of A.G. Doroshkevich and I.D. Novikov, made at the suggestion of Ya.B. Zeldovich in 1964, i.e. a year before the discovery by A. Pepzias and R. Wilson.

In 1965, Arno Penzias and Robert Woodrow Wilson built the Dicke radiometer, which they intended to use not for CMB searches, but for experiments in radio astronomy and satellite communications. When calibrating the device, it turned out that the antenna has an excess temperature of 3.5 K which they could not explain. A small noise background did not change either from the direction or from the time of work. At first they decided that this was noise inherent in the equipment. The radio telescope was dismantled, and its "stuffing" was tested again and again. The pride of the engineers was hurt, and therefore the check went to the last detail, to the last soldering. Eliminated everything. Gathered again - the noise resumed. After much thought, theorists came to the conclusion that this radiation could be nothing more than a constant background of cosmic radio emission that fills the Universe with an even stream. Upon receiving the call from Holdmdale, Dicke quipped, "We hit the jackpot, boys." A meeting between the Princeton and Holmdale groups determined that this antenna temperature was caused by the CMB. The astrophysicists have calculated that the noise corresponds to a temperature of about 3 degrees Kelvin and “is heard at various frequencies. In 1978, Penzias and Wilson received the Nobel Prize for their discovery. One can imagine how happy the supporters of the "hot" model were when this message arrived. This discovery not only strengthened the position of the "hot" model. The relic radiation made it possible to descend from the quasar time step (8-10 billion years) to the step corresponding to 300 thousand years from the very "beginning". At the same time, the idea was confirmed that the Universe once had a density a billion times higher than it is now. It is known that a heated substance always emits photons. According to the general laws of thermodynamics, this is a manifestation of the desire for an equilibrium state at which saturation is achieved: the birth of new photons is compensated by the reverse process, the absorption of photons by matter, so that the total number of photons in the medium does not change. This "photon gas" evenly fills the entire universe. The temperature of the photon gas is close to absolute zero - about 3 kelvins, but the energy contained in it is greater than the light energy emitted by all stars during their lifetime. For every cubic centimeter of space in the Universe, there are approximately five hundred quanta of radiation, and the total number of photons within the visible Universe is several billion times greater. full number particles of matter, i.e. atoms, nuclei, electrons that make up planets, stars and galaxies. This general background radiation of the universe is called light hand I.S. Shklovsky, relic, i.e. residual, which is a residue, a relic of dense and hot initial state Universe. Assuming that the substance early universe was hot, G. Gamow predicted that photons, which were then in thermodynamic equilibrium with matter, should be preserved in modern era. These photons were directly detected in 1965. Having experienced a general expansion and cooling associated with it, the gas of photons now forms the background radiation of the Universe, which comes to us uniformly from all sides. The quantum of relic radiation does not have a rest mass, like any quantum of electromagnetic radiation, but it has energy, and therefore, according to the famous Einstein formula E=Ms?, and the mass corresponding to this energy. For most relic quanta, this mass is very small: much less than the mass of the hydrogen atom, the most common element in stars and galaxies. Therefore, despite a significant predominance in the number of particles, the cosmic microwave background radiation is inferior to stars and galaxies in terms of its contribution to the total mass of the Universe. In the modern era, the radiation density is 3*10 -34 g/cm 3 , which is about a thousand times less than the average density of the matter of galaxies. But this was not always the case - in the distant past of the Universe, photons made the main contribution to its density. The fact is that in the course of cosmological expansion, the radiation density falls faster than the density of matter. In this process, not only the concentration of photons decreases (at the same rate as the concentration of particles), but the average energy of one photon also decreases, since the temperature of the photon gas decreases during expansion. During the subsequent expansion of the Universe, the temperature of the plasma and radiation fell. The interaction of particles with photons no longer had time to noticeably affect the emission spectrum during the characteristic expansion time. However, even in the complete absence of interaction between radiation and matter, during the expansion of the Universe, the black-body radiation spectrum remains black-body, and only the radiation temperature decreases. As long as the temperature exceeded 4000 K, the primary matter was completely ionized, the range of photons from one scattering event to another was much less than the horizon of the Universe. At T ? 4000K there was a recombination of protons and electrons, the plasma turned into a mixture of neutral atoms of hydrogen and helium, the Universe became completely transparent to radiation. In the course of its further expansion, the temperature of the radiation continued to fall, but the black-body nature of the radiation was preserved as a relic, as a "memory" of the early period of the evolution of the world. This radiation was discovered first at a wavelength of 7.35 cm, and then at other wavelengths (from 0.6 mm to 50 cm).

No stars and radio galaxies, no hot intergalactic gas, no re-emission of visible light interstellar dust cannot produce radiation approaching microwave background radiation in properties: the total energy of this radiation is too high, and its spectrum is not similar to either the spectrum of stars or the spectrum of radio sources. This, as well as the almost complete absence of intensity fluctuations over the celestial sphere (small-scale angular fluctuations), proves the cosmological, relic origin of the microwave background radiation.

Background radiation is isotropic only in the coordinate system associated with "receding" galaxies, in the so-called. comoving frame of reference (this frame is expanding along with the Universe). In any other coordinate system, the radiation intensity depends on the direction. This fact opens up the possibility of measuring the speed of the Sun relative to the coordinate system associated with the microwave background radiation. Indeed, due to the Doppler effect, photons propagating towards a moving observer have a higher energy than those catching up with him, despite the fact that in the system associated with the M.F. i.e., their energies are equal. Therefore, the radiation temperature for such an observer turns out to be direction dependent. The dipole anisotropy of the cosmic microwave background radiation, associated with the motion of the solar system relative to the field of this radiation, has now been firmly established: in the direction of the Leo constellation, the temperature of the cosmic microwave background radiation is 3.5 mK higher than the average, and in the opposite direction (the constellation of Aquarius) is by the same amount below the average . Consequently, the Sun (together with the Earth) moves relative to the mf. and. at a speed of about 400 km / s towards the constellation Leo. The accuracy of observations is so high that experimenters fix the speed of the Earth around the Sun, which is 30 km/s. Accounting for the speed of the Sun's motion around the center of the Galaxy makes it possible to determine the speed of the motion of the Galaxy relative to the background radiation. It is ~600 km/s. Far Spectrophotometer infrared radiation(FIRAS) on NASA's Cosmic Background Explorer (COBE) satellite has made precise measurements of the CMB spectrum. These measurements have become the most accurate blackbody spectrum measurements to date. The most detailed map of the relic radiation was built as a result of the work of the American spacecraft wmap.

The spectrum of the relic radiation filling the Universe corresponds to the radiation spectrum of an absolutely black body with a temperature of 2.725 K. Its maximum falls at a frequency of 160.4 GHz, which corresponds to a wavelength of 1.9 mm. It is isotropic with an accuracy of 0.001% - standard deviation temperature is approximately 18 µK. This value does not take into account the dipole anisotropy (the difference between the coldest and hottest region is 6.706 mK) caused by the Doppler shift of the emission frequency due to our own velocity relative to the CMB frame. Dipole anisotropy corresponds to the movement of the solar system towards the constellation Virgo with a speed? 370 km/s.

CMB radiation

The extragalactic microwave background radiation falls in the frequency range from 500 MHz to 500 GHz, which corresponds to wavelengths from 60 cm to 0.6 mm. This background radiation carries information about the processes that took place in the Universe before the formation of galaxies, quasars, and other objects. This radiation, called relic, was discovered in 1965, although it was predicted back in the 40s by Georgy Gamow and studied by astronomers for decades.

In the expanding Universe, the average density of matter depends on time - in the past it was greater. However, during expansion, not only the density changes, but also the thermal energy of matter, which means that at the early stage of expansion the Universe was not only dense, but also hot. As a consequence, in our time there should be observed residual radiation, the spectrum of which is the same as the spectrum of absolutely solid body, and this radiation should be in the highest degree isotropically. In 1964, A.A. Penzias and R. Wilson, testing a sensitive radio antenna, discovered a very weak background microwave radiation, which they could not get rid of in any way. Its temperature turned out to be 2.73 K, which is close to the predicted value. From experiments on the study of isotropy, it was shown that the source of microwave background radiation cannot be located inside the Galaxy, since then a concentration of radiation towards the center of the Galaxy would have to be observed. The source of radiation could not be located inside the solar system, as well. a diurnal variation in the radiation intensity would be observed. Because of this, a conclusion was drawn about the extragalactic nature of this background radiation. Thus, the hypothesis of a hot Universe received an observational basis.

To understand the nature of the CMB, it is necessary to turn to the processes that took place in the early stages of the expansion of the Universe. Let us consider how the physical conditions in the Universe changed during the expansion process.

Now each cubic centimeter of space contains about 500 cosmic microwave background photons, and there is much less substance in this volume. Since the ratio of the number of photons to the number of baryons in the process of expansion is preserved, but the energy of photons decreases with time due to the expansion of the Universe due to redshift, we can conclude that at some time in the past the energy density of radiation was more density the energy of the particles of matter. This time is called the radiation stage in the evolution of the Universe. The radiation stage was characterized by the equality of the temperature of matter and radiation. In those days, radiation completely determined the nature of the expansion of the Universe. Approximately one million years after the start of the expansion of the Universe, the temperature dropped to several thousand degrees and the recombination of electrons, which were previously free particles, took place with protons and helium nuclei, i.e. the formation of atoms. The Universe has become transparent to radiation, and it is this radiation that we now capture and call relict. True, since that time, due to the expansion of the Universe, photons have reduced their energy by about 100 times. Figuratively speaking, relic radiation quanta "imprinted" the era of recombination and carry direct information about the distant past.

After recombination, the matter for the first time began to evolve independently, regardless of radiation, and densifications began to appear in it - the embryos of future galaxies and their clusters. That is why experiments on studying the properties of relic radiation - its spectrum and spatial fluctuations - are so important for scientists. Their efforts were not in vain: in the early 90s. The Russian space experiment "Relikt-2" and the American "Kobe" discovered differences in the temperature of the relict radiation of neighboring sections of the sky, and the deviation from the average temperature is only about a thousandth of a percent. These temperature variations carry information about the deviation of the matter density from the average value during the recombination epoch. After recombination, the matter in the Universe was distributed almost evenly, and where the density was at least slightly above average, the attraction was stronger. It was density variations that subsequently led to the formation of large-scale structures observed in the Universe, clusters of galaxies and individual galaxies. By modern ideas, the first galaxies must have formed at an epoch that corresponds to redshifts 4 to 8.

Is there any chance to look even further into the era preceding recombination? Until the moment of recombination, it was the pressure of electromagnetic radiation that mainly created the gravitational field, which slowed down the expansion of the Universe. At this stage, the temperature varied in inverse proportion to the square root of the time elapsed since the start of expansion. Let us consider successively different stages of the expansion of the early Universe.

At a temperature of approximately 1013 Kelvin, pairs of various particles and antiparticles were born and annihilated in the Universe: protons, neutrons, mesons, electrons, neutrinos, etc. When the temperature dropped to 5 * 1012 K, almost all protons and neutrons annihilated, turning into radiation quanta; only those for which there were “not enough” antiparticles remained. It is from these "excess" protons and neutrons that the substance of the modern observable Universe mainly consists.

At Т= 2*1010 K all-penetrating neutrinos ceased to interact with the matter – from that moment the “relic background of neutrinos” should have remained, which may be detected in the course of future neutrino experiments.

Everything that has just been said took place under super high temperatures in the first second after the beginning of the expansion of the universe. A few seconds after the moment of the “birth” of the Universe, the era of primary nucleosynthesis began, when the nuclei of deuterium, helium, lithium and beryllium were formed. It lasted approximately three minutes, and its main result was the formation of helium nuclei (25% of the mass of the entire matter of the Universe). The remaining elements, heavier than helium, made up a negligible part of the substance - about 0.01%.

After the epoch of nucleosynthesis and before the epoch of recombination (about 106 years), there was a calm expansion and cooling of the Universe, and then - hundreds of millions of years after the beginning - the first galaxies and stars appeared.

In recent decades, the development of cosmology and elementary particle physics has made it possible to theoretically consider the very initial, “superdense” period of the expansion of the Universe. It turns out that at the very beginning of the expansion, when the temperature was incredibly high (more than 1028 K), the Universe could be in a special state in which it expanded with acceleration, and the energy per unit volume remained constant. This stage of expansion was called inflationary. Such a state of matter is possible under one condition - negative pressure. The stage of ultrafast inflationary expansion covered a tiny period of time: it ended by the time of about 10–36 s. It is believed that the real "birth" of elementary particles of matter in the form in which we know them now occurred just after the end of the inflationary stage and was caused by the collapse of the hypothetical field. After that, the expansion of the universe continued by inertia.

The inflationary universe hypothesis answers a number of important issues cosmology, which until recently were considered inexplicable paradoxes, in particular to the question of the cause of the expansion of the universe. If in its history the Universe really went through an era when there was a large negative pressure, then gravity would inevitably have to cause not attraction, but mutual repulsion of material particles. And that means that the Universe began to expand rapidly, explosively. Of course, the model of the inflationary Universe is only a hypothesis: even an indirect verification of its positions requires such instruments, which are simply not yet created at present. However, the idea of ​​accelerated expansion of the Universe at the earliest stage of its evolution has become firmly established in modern cosmology.

Speaking about the early Universe, we are suddenly transported from the largest cosmic scales to the region of the microcosm, which is described by the laws quantum mechanics. The physics of elementary particles and superhigh energies is closely intertwined in cosmology with the physics of giant astronomical systems. The biggest and the smallest merge here with each other. This is the amazing beauty of our world, full of unexpected interconnections and deep unity.

The manifestations of life on Earth are extremely diverse. Life on Earth is represented by nuclear and pre-nuclear, unicellular and multicellular beings; multicellular, in turn, are represented by fungi, plants and animals. Any of these kingdoms unites various types, classes, orders, families, genera, species, populations and individuals.

In all the seemingly endless variety of living things, several different levels of organization of living things can be distinguished: molecular, cellular, tissue, organ, ontogenetic, population, species, biogeocenotic, biospheric. The listed levels are highlighted for ease of study. If we try to identify the main levels, which reflect not so much the levels of study as the levels of organization of life on Earth, then the main criteria for such a selection should be recognized as the presence of specific elementary, discrete structures and elementary phenomena. With this approach, it turns out to be necessary and sufficient to single out the molecular-genetic, ontogenetic, population-species and biogeocenotic levels (N.V. Timofeev-Resovsky and others).

Molecular genetic level. In the study of this level, apparently, the greatest clarity has been achieved in the definition of the basic concepts, as well as in the identification of elementary structures and phenomena. The development of the chromosomal theory of heredity, the analysis of the mutation process, and the study of the structure of chromosomes, phages, and viruses revealed the main features of the organization of elementary genetic structures and the phenomena associated with them. It is known that the main structures at this level (codes of hereditary information transmitted from generation to generation) are DNA, differentiated in length into code elements - triplets of nitrogenous bases that form genes.

Genes at this level of life organization represent elementary units. The main elementary phenomena associated with genes can be considered their local structural changes (mutations) and the transfer of information stored in them to intracellular control systems.

Covariant reduplication occurs according to the matrix principle by breaking hydrogen bonds double helix DNA with the participation of the enzyme DNA polymerase. Then each of the strands builds a corresponding thread for itself, after which the new strands are complementaryly connected to each other. The pyrimidine and purine bases of the complementary strands are hydrogen-bonded to each other by DNA polymerase. This process is very fast. Thus, the self-assembly of Escherichia coli DNA, which consists of about 40 thousand base pairs, requires only 100 s. Genetic information is transferred from the nucleus by mRNA molecules to the cytoplasm to the ribosomes and is involved in protein synthesis there. A protein containing thousands of amino acids is synthesized in a living cell in 5–6 minutes, while in bacteria it is faster.

The main control systems, both in convariant reduplication and in intracellular information transfer, use the "matrix principle", i.e. are matrices, next to which the corresponding specific macromolecules are built. At present, the structure embedded in the structure is being successfully decrypted. nucleic acids a code that serves as a matrix in the synthesis of specific protein structures in cells. Reduplication based on matrix copying retains not only the genetic norm, but also deviations from it, i.e. mutations (the basis of the evolutionary process). Sufficiently accurate knowledge of the molecular-genetic level is a necessary prerequisite for a clear understanding of life phenomena occurring at all other levels of life organization.

The content of the article

RELICT RADIATION, cosmic electromagnetic radiation that comes to Earth from all sides of the sky with approximately the same intensity and has a spectrum characteristic of black body radiation at a temperature of about 3 K (3 degrees Celsius). absolute scale Kelvin, which corresponds to -270 ° C). At this temperature, the main part of the radiation falls on the radio waves of the centimeter and millimeter ranges. The energy density of the relic radiation is 0.25 eV/cm 3 .

Experimental radio astronomers prefer to call this radiation the "cosmic microwave background" (CMB). Theoretical astrophysicists often call it “relic radiation” (the term was proposed by the Russian astrophysicist I.S. Shklovsky), since, in the framework of the theory of the hot Universe generally accepted today, this radiation arose at an early stage of the expansion of our world, when its substance was practically homogeneous and very hot. Sometimes in the scientific and popular literature you can also find the term "three-degree cosmic radiation." In what follows, we will call this radiation "relic".

The discovery in 1965 of the relic radiation was of great importance for cosmology; it became one of major achievements natural sciences of the 20th century. and, by far, the most important for cosmology after the discovery of redshift in the spectra of galaxies. Weak relic radiation brings us information about the first moments of the existence of our Universe, about that distant era when the entire Universe was hot and there were no planets, no stars, no galaxies yet. Held in last years detailed measurements of this radiation with the help of ground, stratospheric and space observatories lift the veil over the mystery of the very birth of the Universe.

hot universe theory.

In 1929, the American astronomer Edwin Hubble (1889-1953) discovered that most galaxies are moving away from us, and the faster the farther away the galaxy is (Hubble's law). This has been interpreted as a general expansion of the universe that began about 15 billion years ago. The question arose of how the universe looked in the distant past, when the galaxies had just begun to move away from each other, and even earlier. Although mathematical apparatus, based on general theory Einstein's theory of relativity and describing the dynamics of the universe, was created back in the 1920s by Willem de Sitter (1872–1934), Alexander Friedmann (1888–1925) and Georges Lemaitre (1894–1966), about physical condition Nothing was known to the universe in the early epoch of its evolution. There was not even a certainty that there was a certain moment in the history of the universe that could be considered the "beginning of expansion."

Development nuclear physics in the 1940s allowed the development of theoretical models evolution of the Universe in the past, when its substance was supposed to be compressed to high density at which nuclear reactions were possible. These models, first of all, were supposed to explain the composition of the matter of the Universe, which by that time had already been quite reliably measured from observations of the spectra of stars: on average, they consist of 2/3 of hydrogen and 1/3 of helium, and all other chemical elements taken together make up no more than 2%. Knowledge of the properties of intranuclear particles - protons and neutrons - made it possible to calculate options for the beginning of the expansion of the Universe, differing in the initial content of these particles and the temperature of the substance and the radiation that is in thermodynamic equilibrium with it. Each of the variants gave its own composition of the initial substance of the Universe.

If we omit the details, then there are two fundamentally different possibilities for the conditions under which the beginning of the expansion of the Universe proceeded: its substance could be either cold or hot. The consequences of nuclear reactions are fundamentally different from each other. Although the idea of ​​the possibility of a hot past of the Universe was expressed in his early works by Lemaitre, historically, the possibility of a cold beginning was first considered in the 1930s.

In the first assumptions, it was believed that all the matter of the Universe existed at first in the form of cold neutrons. Later it turned out that such an assumption contradicts observations. The fact is that a neutron in a free state decays on average 15 minutes after its occurrence, turning into a proton, an electron and an antineutrino. In an expanding universe, the resulting protons would begin to combine with the remaining neutrons, forming the nuclei of deuterium atoms. Further, a chain of nuclear reactions would lead to the formation of nuclei of helium atoms. More complex atomic nuclei, as calculations show, practically do not arise in this case. As a result, all matter would turn into helium. Such a conclusion is in sharp contradiction with observations of stars and interstellar matter. The prevalence of chemical elements in nature rejects the hypothesis of the beginning of the expansion of matter in the form of cold neutrons.

In 1946 in the United States, a "hot" version of the initial stages of the expansion of the Universe was proposed by the physicist of Russian origin Georgy Gamov (1904-1968). In 1948, the work of his collaborators Ralph Alfer and Robert Herman was published, which considered nuclear reactions in hot matter at the beginning of cosmological expansion in order to obtain the currently observed ratio between the number of various chemical elements and their isotopes. In those years, the desire to explain the origin of all chemical elements by their synthesis in the first moments of the evolution of matter was natural. The fact is that at that time they erroneously estimated the time that had elapsed since the beginning of the expansion of the Universe as only 2–4 billion years. This was due to the overestimated value of the Hubble constant, which followed in those years from astronomical observations.

Comparing the age of the Universe at 2-4 billion years with the estimated age of the Earth - about 4 billion years - it was necessary to assume that the Earth, the Sun and stars were formed from primary matter with a ready-made chemical composition. It was believed that this composition did not change in any significant way, since the synthesis of elements in stars is a slow process and there was no time for its implementation before the formation of the Earth and other bodies.

The subsequent revision of the scale of extragalactic distances also led to a revision of the age of the Universe. The theory of stellar evolution successfully explains the origin of all heavy elements(heavier than helium) by their nucleosynthesis in stars. There was no need to explain the origin of all elements, including heavy ones, at an early stage of the expansion of the Universe. However, the essence of the hot universe hypothesis turned out to be correct.

On the other hand, the abundance of helium in stars and interstellar gas is about 30% by mass. This is much more than can be explained by nuclear reactions in stars. This means that helium, unlike heavy elements, should be synthesized at the beginning of the expansion of the Universe, but at the same time - in a limited amount.

The main idea of ​​Gamow's theory is precisely that the high temperature of matter prevents the transformation of all matter into helium. At the moment 0.1 sec after the beginning of the expansion, the temperature was about 30 billion K. In such a hot substance there are many photons of high energy. The density and energy of photons are so high that light interacts with light, leading to the creation of electron-positron pairs. The annihilation of pairs can, in turn, lead to the production of photons, as well as to the production of pairs of neutrinos and antineutrinos. In this "boiling cauldron" is ordinary matter. At very high temperatures, complex atomic nuclei cannot exist. They would be instantly broken by the surrounding energetic particles. Therefore, heavy particles of matter exist in the form of neutrons and protons. Interactions with energetic particles cause neutrons and protons to quickly turn into each other. However, the reactions of combining neutrons with protons do not take place, since the resulting deuterium nucleus is immediately broken up by particles of high energy. So, because of the high temperature at the very beginning, the chain leading to the formation of helium breaks.

It is not until the expansion of the universe cools below a billion kelvins that some of the resulting deuterium is already stored and leads to the fusion of helium. Calculations show that the temperature and density of matter can be adjusted so that by this time the fraction of neutrons in the matter is about 15% by weight. These neutrons combine with the same number of protons to form about 30% helium. The remaining heavy particles remained in the form of protons - the nuclei of hydrogen atoms. Nuclear reactions end after the first five minutes after the beginning of the expansion of the Universe. In the future, as the Universe expands, the temperature of its matter and radiation decreases. From the works of Gamow, Alfer and Herman in 1948, it followed: if the theory of the hot Universe predicts the emergence of 30% helium and 70% hydrogen as the main chemical elements of nature, then modern universe must inevitably be filled with a remnant (“relic”) of primordial hot radiation, and the modern temperature of this relict radiation must be about 5 K.

However, the analysis of different variants of the beginning of the cosmological expansion did not end with the Gamow hypothesis. In the early 1960s, an ingenious attempt to return to the cold version was made by Ya.B. Zel'dovich, who suggested that the original cold matter consisted of protons, electrons and neutrinos. As Zel'dovich showed, such a mixture transforms into pure hydrogen. Helium and other chemical elements, according to this hypothesis, were synthesized later, when stars formed. Note that by this time, astronomers already knew that the Universe was several times older than the Earth and most of the stars around us, and the data on the abundance of helium in prestellar matter were still very uncertain in those years.

Seemingly, decisive test to choose between cold and hot models of the universe could be the search for cosmic microwave background radiation. But for some reason, for many years after the prediction of Gamow and his colleagues, no one consciously tried to detect this radiation. It was discovered quite by accident in 1965 by radio physicists from the American company "Bell" R. Wilson and A. Penzias, who were awarded the Nobel Prize in 1978.

On the way to the discovery of relic radiation.

In the mid-1960s, astrophysicists continued to theoretically study the hot model of the universe. The calculation of the expected characteristics of the CMB was performed in 1964 by A.G. Doroshkevich and I.D. Novikov in the USSR and independently by F. Hoyle and R.J. Taylor in Great Britain. But these works, like the earlier work of Gamow and his colleagues, did not attract attention. But they have already convincingly shown that relic radiation can be observed. Despite the extreme weakness of this radiation in our era, it fortunately lies in that region of the electromagnetic spectrum where all other cosmic sources as a whole radiate even weaker. Therefore, a targeted search for the cosmic microwave background should have led to its discovery, but radio astronomers did not know about it.

Here is what A. Penzias said in his Nobel lecture: “The first published recognition of the cosmic microwave background as a detectable phenomenon in the radio range appeared in the spring short article A.G. Doroshkevich and I.D. Novikov, entitled Average density radiation in the Metagalaxy and some questions of relativistic cosmology. Although an English translation appeared in the same year, but somewhat later, in the well-known journal Sovetskaya Fizika - Doklady, the article apparently did not attract the attention of other specialists in this field. This remarkable article not only displays the spectrum of the cosmic microwave background as a black body wave phenomenon, but also clearly focused on the twenty-foot horn reflector of the Bell Laboratory at Crawford Hill, as the most suitable tool for detecting it! (quoted by: Sharov A.S., Novikov I.D. The Man Who Discovered the Explosion of the Universe: The Life and Work of Edwin Hubble. M., 1989).

Unfortunately, this article went unnoticed by either theorists or observers; it did not stimulate the search for cosmic microwave background radiation. Historians of science are still wondering why for many years no one tried to consciously look for radiation from the hot Universe. It is curious that past this discovery - one of the largest by the 20th century. – scientists passed several times without noticing it.

For example, relic radiation could have been discovered as early as 1941. Then the Canadian astronomer E. McKellar analyzed the absorption lines caused in the spectrum of the star Zeta Ophiuchus by interstellar cyanide molecules. He came to the conclusion that these lines in the visible region of the spectrum can only appear when light is absorbed by rotating cyan molecules, and their rotation must be excited by radiation with a temperature of about 2.3 K. Of course, no one could have thought then that the excitation of the rotational levels of these molecules caused by relic radiation. Only after its discovery in 1965 were the works of I.S. Shklovsky, J. Field and others published, in which it was shown that the excitation of the rotation of interstellar cyan molecules, whose lines are clearly observed in the spectra of many stars, is caused precisely by relict radiation.

An even more dramatic story took place in the mid-1950s. Then the young scientist T.A. Shmaonov, under the guidance of the famous Soviet radio astronomers S.E. Khaikin and N.L. Kaidanovsky, measured radio emission from space at a wavelength of 32 cm. These measurements were made using a horn antenna similar to the one used many years later by Penzias and Wilson. Shmaonov carefully studied the possible interference. Of course, at that time he did not have at his disposal such sensitive receivers as the Americans later had. The results of Shmaonov's measurements were published in 1957 in his Ph.D. thesis and in the journal Devices and Experimental Technique. The conclusion from these measurements was as follows: "It turned out that the absolute value of the effective temperature of the background radio emission ... is equal to 4 ± 3 K." Shmaonov noted the independence of the radiation intensity from the direction in the sky and from time. Although the measurement errors were large and there is no need to talk about any reliability of the figure 4, it is now clear to us that Shmaonov measured precisely the cosmic microwave background radiation. Unfortunately, neither he nor other radio astronomers knew anything about the possibility of the existence of cosmic microwave background radiation and did not attach due importance to these measurements.

Finally, around 1964, the well-known experimental physicist from Princeton (USA) Robert Dicke consciously approached this problem. Although his reasoning was based on the theory of an "oscillating" universe that repeatedly experiences expansion and contraction, Dicke clearly understood the need to search for the CMB. On his initiative, in early 1965, the young theorist F.J.A. To search for background radiation, it is not necessary to use large radio telescopes, since the radiation comes from all directions. Nothing is gained from the fact that a large antenna focuses the beam on a smaller area of ​​the sky. But Dicke's group did not have time to make the planned discovery: when their equipment was already ready, they only had to confirm the discovery, accidentally made by others the day before.

Discovery of relic radiation.

In 1960, an antenna was built in Crawford Hill, Holmdel (New Jersey, USA) to receive radio signals reflected from the Echo balloon satellite. By 1963, this antenna was no longer needed for satellite work, and radio physicists Robert Woodrow Wilson (b. 1936) and Arno Elan Penzias (b. 1933) from the Bell Telephone laboratory decided to use it for radio astronomy observations. The antenna was a 20-foot horn. Together with the latest receiving device, this radio telescope was at that time the most sensitive instrument in the world for measuring radio waves coming from wide platforms in the sky. First of all, it was supposed to measure the radio emission interstellar medium of our Galaxy at a wavelength of 7.35 cm. Arno Penzias and Robert Wilson did not know about the theory of the hot Universe and were not going to look for cosmic microwave background radiation.

To accurately measure the radio emission of the Galaxy, it was necessary to take into account all possible interference caused by the radiation of the earth's atmosphere and the surface of the Earth, as well as interference occurring in the antenna, electrical circuits and receivers. Preliminary testing of the receiving system showed slightly more noise than expected, but it seemed plausible that this was due to a slight excess of noise in the amplifying circuits. To get around these problems, Penzias and Wilson used a device known as a "cold load" in which the signal coming from the antenna is compared with the signal from artificial source, cooled with liquid helium at a temperature of about four degrees above absolute zero(4K). In both cases, the electrical noise in the amplifying circuits must be the same, and therefore the difference obtained by comparison gives the power of the signal coming from the antenna. This signal contains contributions only from the antenna device, the earth's atmosphere, and an astronomical source of radio waves that enters the antenna's field of view.

Penzias and Wilson expected the antenna arrangement to produce very little electrical noise. However, to test this assumption, they began their observations at relatively short wavelengths of 7.35 cm, at which the radio noise from the Galaxy should be negligible. Naturally, some radio noise was expected at such a wavelength from the Earth's atmosphere, but this noise should have a characteristic dependence on direction: it should be proportional to the thickness of the atmosphere in the direction in which the antenna is looking: a little less towards the zenith, a little more towards direction of the horizon. It was expected that after subtracting the atmospheric term from characteristic dependence no significant signal from the antenna will remain from the direction and this will confirm that the electrical noise produced by the antenna device is negligible. After that, it will be possible to begin studying the Galaxy itself at large wavelengths - about 21 cm, where the radiation Milky Way is of significant importance. (Note that radio waves with lengths of centimeters or decimeters, up to 1 m, are commonly referred to as "microwave radiation". This name is given because these wavelengths are smaller than those ultrashort waves used in radars at the beginning of World War II. .)

To their surprise, Penzias and Wilson discovered in the spring of 1964 that they were picking up quite a noticeable amount of direction-independent microwave noise at 7.35 cm. They found that this "static background" did not change with the time of day, and later found that it did not depend on the season either. Consequently, this could not be the radiation of the Galaxy, because in this case its intensity would change depending on whether the antenna looks along the plane of the Milky Way or across. In addition, if this were the radiation of our Galaxy, then the large spiral galaxy M 31 in Andromeda, similar in many respects to ours, would also have to radiate strongly at a wavelength of 7.35 cm, but this was not observed. The absence of any variation in the observed microwave noise with direction strongly suggested that these radio waves, if they do exist, do not come from the Milky Way, but from a much larger volume of the universe.

It was clear to the researchers that they needed to test again to see if the antenna itself might be producing more electrical noise than expected. In particular, it was known that a pair of pigeons nested in the mouthpiece of the antenna. They were caught, mailed to Bell's Vippani property, released, rediscovered a few days later in their position in the antenna, recaptured, and finally pacified by more drastic means. However, while renting the premises, the pigeons coated the inside of the antenna with what Penzias called a "white dielectric substance" that, at room temperature, could be a source of electrical noise. At the beginning of 1965 the antenna horn was removed and all the dirt was cleaned out, but this, like all other tricks, gave very little reduction in the observed noise level.

When all sources of interference were carefully analyzed and accounted for, Penzias and Wilson were forced to conclude that the radiation comes from space, and from all directions with the same intensity. It turned out that space radiates as if it were heated to a temperature of 3.5 kelvin (more precisely, the accuracy achieved allowed us to conclude that the "temperature of space" was from 2.5 to 4.5 kelvin). It should be noted that this is a very subtle experimental result: for example, if an ice cream block was placed in front of the antenna horn, it would shine in the radio range, 22 million times brighter than the corresponding part of the sky. Pondering over the unexpected result of their observations, Penzias and Wilson were in no hurry to publish. But events developed already against their will.

It so happened that Penzias called his friend Bernard Burke from Massachusetts on a completely different occasion. Institute of Technology. Shortly before this, Burke had heard from his colleague Ken Tsrner of the Carnegie Institution about a talk he had heard at Johns Hopkins University by the Princeton theorist Phil Peebleslem, who worked under Robert Dicke. In this talk, Peebles argued that there must be background radio noise left over from the early universe that now has an equivalent temperature of about 10 K.

Penzias called Dicke and the two research teams met. It became clear to Robert Dicke and his colleagues F.Peebles, P.Roll and D.Wilkinson that A.Penzias and R.Wilson had discovered the relic radiation of the hot Universe. The scientists decided to simultaneously publish two letters in the prestigious Astrophysical Journal. In the summer of 1965, both works were published: by Penzias and Wilson on the discovery of cosmic microwave background radiation and by Dicke and colleagues with his explanation using the theory of the hot Universe. Apparently not entirely convinced of the cosmological interpretation of their discovery, Penzias and Wilson gave their note a modest title: Antenna Excess Temperature Measurement at 4080 MHz. They simply announced that "measurements of the effective zenith noise temperature ... gave a value 3.5 K higher than expected", and avoided any mention of cosmology, except for the phrase that "a possible explanation for the observed excess noise temperature is given by Dicke, Peebles , Roll, and Wilkinson in an accompanying letter in the same issue of the magazine.

In subsequent years, numerous measurements were carried out at various wavelengths from tens of centimeters to fractions of a millimeter. Observations have shown that the CMB spectrum corresponds to Planck's formula, as it should be for radiation with a certain temperature. This temperature was confirmed to be approximately 3 K. It was done wonderful discovery, which proves that the Universe was hot at the beginning of the expansion.

Such is the complex interweaving of events that culminated in the discovery of a hot Universe by Penzias and Wilson in 1965. The establishment of the fact of superhigh temperature at the beginning of the expansion of the Universe was the starting point major research, leading to the disclosure of not only astrophysical secrets, but also the secrets of the structure of matter.

The most accurate measurements of cosmic microwave background radiation have been carried out from space: these are the Relikt experiment on the Soviet Prognoz-9 satellite (1983–1984) and the DMR (Differential Microwave Radiometer) experiment on the American COBE satellite (Cosmic Background Explorer, November 1989–1993). the latter made it possible to most accurately determine the temperature of the relic radiation: 2.725 ± 0.002 K.

Microwave background as "new ether".

So, the spectrum of relic radiation with very high precision corresponds to black body radiation (i.e., described by the Planck formula) with a temperature T = 2.73 K. However, there are small (about 0.1%) deviations from this average temperature, depending on which direction the measurement is taken in the sky . The fact is that the cosmic microwave background radiation is isotropic only in the coordinate system associated with the entire system of receding galaxies, in the so-called "comoving reference frame", which expands along with the Universe. In any other coordinate system, the radiation intensity depends on the direction. First of all, this is caused by the movement of the measuring device relative to the cosmic microwave background: the Doppler effect leads to the "blueness" of photons flying towards the device, and to the "reddening" of photons catching up with it.

In this case, the measured temperature compared to the average (T 0) depends on the direction of movement: T \u003d T 0 (1 + (v / c) cos i), where v is the speed of the device in the coordinate system associated with the background radiation; c is the speed of light, i is the angle between the velocity vector and the direction of observation. Against the background of a uniform temperature distribution, two "poles" appear - warm in the direction of movement and cool in the opposite direction. Therefore, such a deviation from uniformity is called "dipole". The dipole component in the distribution of cosmic microwave background radiation was discovered even during ground-based observations: in the direction of the constellation Leo, the temperature of this radiation turned out to be 3.5 mK higher than the average, and in the opposite direction (the constellation of Aquarius) it was the same lower than the average. Therefore, we are moving relative to the background radiation at a speed of about 400 km / s. The measurement accuracy turned out to be so high that even annual variations in the dipole component were found, caused by the Earth's revolution around the Sun at a speed of 30 km/s.

Measurements with artificial satellites The Earth significantly refined these data. According to COBE data, after taking into account the orbital motion of the Earth, it turns out that the solar system moves in such a way that the amplitude of the dipole component of the CMB temperature is D T = 3.35 mK; this corresponds to the speed of movement V = 366 km/s. The Sun moves relative to the radiation in the direction of the border of the constellations Leo and the Chalice, to the point with equatorial coordinates a = 11 h 12 m and d = –7.1° (epoch J2000); which corresponds to the galactic coordinates l = 264.26° and b = 48.22°. Accounting for the motion of the Sun itself in the Galaxy shows that, relative to all galaxies in the Local Group, the Sun moves at a speed of 316 ± 5 km/s in the direction l 0 = 93 ± 2° and b 0 = –4 ± 2° . Therefore, the motion of the Local Group itself relative to the cosmic microwave background occurs at a speed of 635 km/s in the direction of about l= 269° and b= +29°. This is approximately at an angle of 45° relative to the direction to the center of the cluster of galaxies in Virgo (Virgo).

Studying the movements of galaxies on an even larger scale shows that the collection of nearby clusters of galaxies (119 clusters from the Abel catalog within 200 Mpc from us) moves as a whole relative to the CMB at a speed of about 700 km/s. Thus, our neighborhood of the Universe is floating in the sea of ​​cosmic microwave background radiation at a noticeable speed. Astrophysicists have repeatedly paid attention to the fact that the very fact of the existence of relict radiation and the selected reference system associated with it assigns to this radiation the role of a "new ether". But there is nothing mystical in this: everything physical measurements in this reference system are equivalent to measurements in any other inertial system reference. (Discussion of the problem of the "new ether" in connection with the Mach principle can be found in the book: Zel'dovich Ya.B., Novikov I.D. Structure and evolution of the Universe. M., 1975).

Anisotropy of relic radiation.

The temperature of the CMB is only one of its parameters that describe the early Universe. In the properties of this radiation, other obvious traces of very early era evolution of our world. Astrophysicists find these traces by analyzing the spectrum and spatial inhomogeneity (anisotropy) of the CMB.

According to the theory of the hot Universe, after about 300 thousand years after the start of expansion, the temperature of matter and the radiation associated with it decreased to 4000 K. At this temperature, photons could no longer ionize hydrogen and helium atoms. Therefore, in that epoch corresponding to the redshift z = 1400, hot plasma recombination occurred, as a result of which the plasma turned into a neutral gas. Of course, there were no galaxies and stars back then. They arose much later.

Having become neutral, the gas filling the Universe turned out to be practically transparent to the relic radiation (although in that era it was not radio waves, but light in the visible and near infrared ranges). Therefore, the ancient radiation reaches us almost unhindered from the depths of space and time. But still, along the way, it experiences some influences, and how archaeological site bears traces of historical events.

For example, during the epoch of recombination, atoms emitted many photons with an energy of the order of 10 eV, which is tens of times higher than average energy photons of the equilibrium radiation of that era (at T = 4000 K, there are very few such energetic photons, about one billionth of their total number). Therefore, the recombination radiation would have to strongly distort the Planck spectrum of the cosmic microwave background radiation in the wavelength range of about 250 μm. True, calculations have shown that the strong interaction of radiation with matter will lead to the fact that the released energy will mainly “dissipate” over a wide region of the spectrum and will not distort it much, but future accurate measurements will be able to notice this distortion as well.

And much later, in the era of the formation of galaxies and the first generation of stars (at z ~ 10), when a huge mass of almost cooled matter again experienced significant heating, the CMB spectrum could change again, because, scattering on hot electrons, low-energy photons increase their energy (the so-called "inverse Compton effect"). Both effects described above distort the spectrum of the cosmic microwave background radiation in its short-wavelength region, which has so far been the least studied.

Although in our era most of ordinary matter is densely packed in stars, and those in galaxies, nevertheless, even near us, the cosmic microwave background radiation can experience a noticeable distortion of the spectrum if its rays pass through a large cluster of galaxies on their way to the Earth. Typically, such clusters are filled with a rarefied but very hot intergalactic gas with a temperature of about 100 million K. Scattering on fast electrons of this gas, low-energy photons increase their energy (still the same inverse Compton effect) and pass from the low-frequency, Rayleigh-Jeans region of the spectrum into the high-frequency, guilty region. This effect was predicted by R.A. Sunyaev and Ya.B. Zeldovich and discovered by radio astronomers in the direction of many clusters of galaxies in the form of a decrease in the radiation temperature in the Rayleigh-Jeans region of the spectrum by 1–3 mK. The Sunyaev-Zel'dovich effect was the first to be discovered among the effects that create the anisotropy of the relic radiation. A comparison of its magnitude with the X-ray luminosity of galaxy clusters made it possible to independently determine the Hubble constant (H = 60 ± 12 km/s/Mpc).

Let's go back to the era of recombination. At an age of less than 300,000 years, the Universe was an almost homogeneous plasma, shuddering from sound, or rather, infrasonic waves. Cosmologists' calculations say that these waves of compression and expansion of matter also generated fluctuations in the radiation density in an opaque plasma, and therefore now they should be detected as a slightly noticeable "swell" in an almost uniform cosmic microwave background radiation. Therefore, today it should come to Earth from different directions with slightly different intensity. In this case, we are not talking about a trivial dipole anisotropy caused by the motion of the observer, but about intensity variations that are actually inherent in the radiation itself. Their amplitude should be extremely small: approximately one hundred thousandth of the radiation temperature itself, i.e. about 0.00003 K. They are very difficult to measure. The first attempts to determine the magnitude of these small fluctuations depending on the direction in the sky were made immediately after the discovery of the relic radiation itself in 1965. Later they did not stop, but the discovery took place only in 1992 using equipment taken outside the Earth. In our country, such measurements were carried out in the Relikt experiment, but these small fluctuations were more confidently recorded from the American COBE satellite (Fig. 1).

Recently, many experiments have been carried out and planned to measure the amplitude of fluctuations of the cosmic microwave background radiation in various angular scales, from degrees to seconds of arc. Various physical phenomena, which occurred in the very first moments of the life of the Universe, should have left their characteristic imprint in the radiation coming to us. The theory predicts a certain relationship between the sizes of cold and hot spots in the CMB intensity and their relative brightness. The dependence is very peculiar: it contains information about the processes of the birth of the Universe, about what happened immediately after birth, as well as about the parameters of today's Universe.

The angular resolution of the first observations - in the Relict-2 and COBE experiments - was very poor, about 7°, so information about the fluctuations of the CMB was incomplete. In subsequent years, the same observations were carried out with the help of both ground-based radio telescopes (in our country, the RATAN-600 instrument with an unfilled aperture 600 m in diameter is used for this purpose) and radio telescopes that climbed balloons into the upper layers of the atmosphere.

A fundamental step in the study of the anisotropy of cosmic microwave background radiation was the Boomerang experiment (BOOMERANG), performed by scientists from the USA, Canada, Italy, England and France using a NASA (USA) unmanned balloon with a volume of 1 million cubic meters, which from December 29, 1998 to January 9, 1999 made circle at an altitude of 37 km around the South Pole and, having flown about 10 thousand km, dropped the gondola with instruments on a parachute 50 km from the launch site. The observations were carried out with a submillimeter telescope with a main mirror 1.2 m in diameter, at the focus of which was a system of bolometers cooled to 0.28 K, which measured the background in four frequency channels (90, 150, 240, and 400 GHz) with an angular resolution of 0.2–0 .3 degrees. During the flight, observations covered about 3% celestial sphere.

The temperature inhomogeneities of the relic radiation with a characteristic amplitude of 0.0001 K registered in the Boomerang experiment confirmed the correctness of the "acoustic" model and showed that the four-dimensional space-time geometry of the Universe can be considered flat. The information obtained also made it possible to judge the composition of the Universe: it was confirmed that ordinary baryonic matter, which stars, planets and interstellar gas consist of, makes up only about 4% of the mass; and the remaining 96% are contained in yet unknown forms of matter.

The Boomerang experiment was perfectly complemented by a similar MAXIMA (Millimeter Anisotropy eXperiment IMaging Array) experiment, mainly performed by scientists in the USA and Italy. Their equipment, which flew into the stratosphere in August 1998 and June 1999, explored less than 1% of the celestial sphere, but with a high angular resolution: about 5 ". The balloon made night flights over the continental United States. The main mirror of the telescope had a diameter of 1.3 m. The receiving part of the equipment consisted of 16 detectors covering 3 frequency ranges.The secondary mirrors were cooled to cryogenic temperature, and the bolometers even low temperature it was possible to maintain up to 40 hours, which limited the duration of the flight.

The MAXIMA experiment revealed a small "ripple" in the angular distribution of the CMB temperature. Its data were supplemented by observations from a ground-based observatory using the DASI (Degree Angular Scale Interferometer) interferometer installed by radio astronomers at the University of Chicago (USA) at south pole. This 13-element cryogenic interferometer observed in ten frequency channels in the range of 26-36 GHz and revealed even smaller fluctuations in the CMB, and the dependence of their amplitude on the angular size well confirms the theory of acoustic oscillations inherited from the young Universe.

In addition to measurements of the intensity of relic radiation from the Earth's surface, space experiments are also planned. In 2007, it is planned to launch the Planck radio telescope (European Space Agency) into space. Its angular resolution will be significantly higher and its sensitivity about 30 times better than in the COBE experiment. Therefore, astrophysicists hope that many facts about the beginning of the existence of our Universe will be clarified (see Fig. 1).

Vladimir Surdin

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Cosmology: Theory and Observations. M., 1978
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Sunyaev R.A. Microwave background radiation. - In the book: Space Physics: Little Encyclopedia. M., 1986
Dolgov A.D., Zeldovich Ya.B., Sazhin M.V. Cosmology of the early universe. M., 1988
Novikov I.D. Evolution of the Universe. M., 1990