One of the components of the general background of space. email mag. radiation. R. and. uniformly distributed over the celestial sphere and in intensity corresponds to the thermal radiation of an absolutely black body at a temperature of approx. 3 K, detected by Amer. scientists A. Penzias and ... Physical encyclopedia
CMB radiation, filling the Universe, cosmic radiation, the spectrum of which is close to the spectrum of an absolutely black body with a temperature of about 3 K. Observed at waves from several mm to tens of cm, almost isotropically. Origin... ... Modern encyclopedia
Background cosmic radiation, the spectrum of which is close to the spectrum of a completely black body with a temperature of approx. 3 K. Observed at waves from several mm to tens of cm, almost isotropically. The origin of the cosmic microwave background radiation is associated with the evolution... Big Encyclopedic Dictionary
cosmic microwave background radiation- Background cosmic radio emission, which was formed in the early stages of the development of the Universe. [GOST 25645.103 84] Topics, conditions, physical space. space EN relict radiation… Technical Translator's Guide
Background cosmic radiation, the spectrum of which is close to the spectrum of an absolutely black body with a temperature of about 3°K. Observed at waves from several millimeters to tens of centimeters, almost isotropically. Origin of cosmic microwave background radiation... ... encyclopedic Dictionary
Electromagnetic radiation that fills the observable part of the Universe (See Universe). R. and. existed already in the early stages of the expansion of the Universe and played an important role in its evolution; is a unique source of information about her past... Great Soviet Encyclopedia
CMB radiation- (from Latin relicium remnant) cosmic electromagnetic radiation associated with the evolution of the Universe, which began its development after the “big bang”; background cosmic radiation, the spectrum of which is close to the spectrum of an absolutely black body with... ... The beginnings of modern natural science
Background space radiation, the spectrum of which is close to the spectrum of an absolutely black body with a temperature of approx. 3 K. Observed at waves from several. mm to tens of cm, almost isotropic. Origin of R. and. associated with the evolution of the Universe, to paradise in the past... ... Natural science. encyclopedic Dictionary
Thermal background cosmic radiation, the spectrum of which is close to the spectrum of an absolutely black body with a temperature of 2.7 K. Origin of radiation. associated with the evolution of the Universe, which in the distant past had high temperature and radiation density... ... Astronomical Dictionary
Cosmology Age of the Universe Big Bang Converging distance CMB Cosmological equation of state Dark energy Hidden mass Friedmann's Universe Cosmological principle Cosmological models Formation ... Wikipedia
Books
- Cosmology, Steven Weinberg, Nobel laureate Steven Weinberg's monumental monograph summarizes the progress made in modern cosmology over the past two decades. It is unique in… Category: Astronomy Publisher: Librocom,
- A new look at some fundamental concepts and experimental facts of physics, Emelyanov A.V. , The book is devoted to the analysis of three interrelated problems of physics: 1. The physical nature of inertial forces, which Newton began to solve, but did not solve. This complex problem leads to the conclusion that... Category: General questions. History of physics Series: Publisher:
Despite the use of modern instruments and the latest methods for studying the Universe, the question of its appearance still remains open. This is not surprising given its age: according to the latest data, it ranges from 14 to 15 billion years. It is obvious that since then there has been very little evidence of the grandiose processes of the Universal scale that once took place. Therefore, no one dares to assert anything, limiting themselves to hypotheses. However, one of them has recently received a very significant argument - cosmic microwave background radiation.
In 1964, two employees of a well-known laboratory, carrying out radio observations of the Echo satellite, having access to the appropriate ultra-sensitive equipment, decided to test some of their theories regarding the own radio emission of certain space objects.
In order to filter out possible interference from ground-based sources, it was decided to use 7.35 cm. However, after turning on and tuning the antenna, a strange phenomenon was recorded: a certain noise, a constant background component, was recorded throughout the Universe. It did not depend on the position of the Earth relative to other planets, which immediately eliminated the assumption of radio interference from these or on the time of day. Neither R. Wilson nor A. Penzias even realized that they had discovered the cosmic microwave background radiation of the universe.
Since none of them assumed this, attributing the “background” to the peculiarities of the equipment (suffice it to remember that the microwave antenna used was the most sensitive at that time), almost a whole year passed until it became obvious that the recorded noise was part of the Universe itself. The intensity of the detected radio signal turned out to be almost identical to the intensity of radiation with a temperature of 3 Kelvin (1 Kelvin is equal to -273 degrees Celsius). For comparison, zero Kelvin corresponds to the temperature of an object made of motionless atoms. ranges from 500 MHz to 500 GHz.
At this time, two theorists from Princeton University - R. Dicke and D. Pibbles, based on new models of the development of the Universe, mathematically calculated that such radiation should exist and permeate all space. Needless to say, Penzias, who accidentally learned about lectures on this topic, contacted the university and reported that the cosmic microwave background radiation had been registered.
Based on the Big Bang theory, all matter arose as a result of a colossal explosion. For the first 300 thousand years after this, space was a combination of elementary particles and radiation. Subsequently, due to expansion, temperatures began to fall, which made it possible for atoms to appear. The detected relict radiation is an echo of those distant times. While the universe had boundaries, the density of particles was so high that the radiation was “bound”, since the mass of particles reflected any kind of waves, preventing them from propagating. And only after the formation of atoms began, space became “transparent” for waves. It is believed that this is how the cosmic microwave background radiation appeared. At the moment, each cubic centimeter of space contains about 500 initial quanta, although their energy has decreased by almost 100 times.
CMB radiation has different temperatures in different parts of the Universe. This is due to the location of the primary matter in the expanding Universe. Where the density of atoms of future matter was higher, the share of radiation, and therefore its temperature, was reduced. It was in these directions that large objects (galaxies and their clusters) subsequently formed.
The study of cosmic microwave background radiation lifts the veil of uncertainty over many processes occurring at the beginning of time.
One of the interesting discoveries related to the electromagnetic spectrum is cosmic microwave background radiation. It was discovered by accident, although the possibility of its existence was predicted.
History of the discovery of cosmic microwave background radiation
History of the discovery of cosmic microwave background radiation started in 1964. American laboratory staff Bell Phone developed a communication system using an artificial Earth satellite. This system was supposed to work on waves 7.5 centimeters long. Such short waves have some advantages in relation to satellite radio communications, but Arno Penzias And Robert Wilson no one solved this problem. They were pioneers in this field and had to ensure that there was no strong interference on the same wavelength, or that the telecom workers knew about such interference in advance. At that time, it was believed that the source of radio waves coming from space could only be point objects like radio galaxies or stars. Sources of radio waves. The scientists had at their disposal an exceptionally accurate receiver and a rotating horn antenna. With their help, scientists could listen to the entire firmament in much the same way as 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 in the sky, a curved line danced on the oscilloscope screen. Typical natural source signal. The experts were probably surprised by their luck: at the very first measured point there was a source of radio emission! But no matter where they pointed their antenna, the effect remained the same. Scientists checked the equipment over and over again, but it was in perfect order. And finally they realized that they had discovered a previously unknown natural phenomenon: the entire Universe seemed to be filled with radio waves of centimeter length. If we could see radio waves, the firmament would appear to us glowing from edge to edge.
Radio waves of the Universe. Penzias and Wilson's discovery was published. And not only they, but also scientists from many other countries began searching for sources of mysterious radio waves, picked up by all antennas and receivers adapted for this purpose, no matter where they are and no matter what point in the sky they are aimed at, and the intensity of radio emission at wavelength 7.5 centimeter at any point was absolutely the same, it seemed to be smeared evenly across the entire sky. CMB radiation calculated by scientists
Soviet scientists A. G. Doroshkevich and I. D. Novikov, who predicted cosmic microwave background radiation before it opens, made complex calculations. They took into account all the sources of radiation available in our Universe, and also 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, are in no way responsible for the detected sky glow. Meanwhile, further calculations showed that the density of smeared radiation is very high. Here is a comparison of photon jelly (that’s what scientists called the mysterious radiation) with the mass of all matter in the Universe. If all the matter of all visible Galaxies is “spread” evenly throughout 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 to be hydrogen). And at the same time, every cubic centimeter of real space contains about 500 photons of radiation. Quite 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. Friedman, solving Einstein’s famous equations, discovered that our Universe is in constant expansion. Confirmation of this was soon found. American E. Hubble discovered galaxy recession phenomenon. By extrapolating this phenomenon into the past, we 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. During the expansion of the Universe, the wavelength of each quantum increases in proportion to the expansion of the Universe; in this case, the quantum seems to “cool” - after all, the shorter the wavelength of the quantum, the “hotter” it is. Today's centimeter-scale radiation has a brightness temperature of about 3 degrees absolute Kelvin. 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 “buried” with quanta of continuously cooling radiation. That is why the centimeter radio emission “smeared” throughout the Universe is called cosmic microwave background radiation. Relics, as you know, are the names of the remains of the most ancient animals and plants that have survived to this day. Quanta of centimeter radiation are certainly the most ancient of all possible relics. After all, their formation dates back to an era approximately 15 billion years distant from us.Knowledge about the Universe brought cosmic microwave background radiation
Almost nothing can be said about what matter was like at the zero moment, when its density was infinitely large. But the phenomena and processes that occurred during Universe, just a second after her birth and even earlier, up to 10~8 seconds, scientists already imagine quite well. Information about this was brought precisely cosmic microwave background radiation. So, a second has passed since the 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 enormous - more than a ton per cubic centimeter. In such “crowded conditions,” 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. A hundred seconds passed. The expansion of the Universe continued, its density continuously decreased, and its temperature dropped. 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 and became hydrogen nuclei. In the course of these reactions, new quanta appeared, but their number could no longer be compared with the original one, 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 this moment had dropped to 3-4 thousand degrees, the density of matter also approached what we know today, but clumps of matter from which stars and galaxies could be formed could not yet arise. The radiation pressure was too great at that time, pushing away any such formation. Even the atoms of helium and hydrogen remained ionized: electrons existed separately, protons and nuclei of atoms also existed separately. Only towards the end of the three-million-year period did the first condensations 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 heated the “porridge” that had begun to cool down to temperatures at which the formation of new condensations again turned out to be impossible. Periods of cooling and reheating of the “porridge” by flares of protostars alternated, replacing each other. And at some stage of the expansion of the Universe, the formation of new condensations became almost impossible because the once-so-thick “porridge” had become too “liquefied.” Approximately 5 percent of the matter managed to unite, and 95 percent was scattered in the space of the expanding Universe. This is how the once hot quanta that formed the relict radiation “dissipated”. This is how the nuclei of hydrogen and helium atoms, which were part of the “porridge,” were scattered.Hypothesis of the formation of the Universe
Here is one of them: most of the matter in our Universe is not located in the composition of planets, stars and galaxies, but forms intergalactic gas - 70 percent hydrogen and 30 percent helium, one hydrogen atom per cubic meter of space. Then the development of the Universe passed the stage of protostars and entered the stage of matter that is ordinary for us, ordinary unfolding spiral Galaxies, ordinary stars, the most familiar of which is ours. Planetary systems formed around some of these stars, and on at least one of these planets, life arose, which in the course of evolution gave rise to intelligence. Scientists do not yet know how often stars surrounded by a circle of planets are found in the vastness of space. They can't say anything about how often.
Round dance of the planets. And the question of how often the plant of life blossoms into the lush flower of reason remains open. The hypotheses known to us today that interpret all these issues are more like unfounded guesses. But today science is developing like an avalanche. More recently, scientists had no idea how ours began. The cosmic microwave background radiation, discovered about 70 years ago, made it possible to paint that picture. Today, humanity does not have enough 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 facts are no longer followed by hypotheses, but by strict conclusions. CMB radiation indicates the homogeneity of the Universe
What else did the relict rays, these witnesses to the birth of our Universe, tell scientists? A. A. Friedman solved one of the equations given by Einstein, and based on this solution he discovered the expansion of the Universe. In order to solve Einstein's 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 the substance in it is distributed evenly. And during the 5-10 years that have passed since Friedman’s discovery, the question of whether this assumption was correct remained open. Now it has essentially been removed. The isotropy of the Universe is evidenced by the amazing uniformity of the relict radio emission. The second fact indicates the same thing - the distribution of the matter of the Universe between Galaxies and intergalactic gas.
After all, intergalactic gas, which makes up the bulk of the matter of the Universe, is distributed throughout it as evenly as relic quanta. The discovery of cosmic microwave background radiation makes it possible to look not only into the ultra-distant past - beyond the 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 CMB allows us to peer into the ultra-distant future. So super-distant, when there will be no Earth, no Sun, no Galaxy. The phenomenon of the expansion of the Universe will help here, how its constituent stars, galaxies, clouds of dust and gas scatter in space. Is this process eternal? Or will the expansion slow down, stop, and then give way to compression? And aren’t the successive compressions 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 total gravity is sufficient to overcome the inertia of expansion, then the expansion will inevitably give way to compression, in which the Galaxies will gradually come closer together. Well, if the gravitational forces are not enough to slow down and overcome the inertia of expansion, our Universe is doomed: it will dissipate in space! The future fate of our entire Universe! Is there a bigger problem? The study of cosmic microwave background radiation gave science the opportunity to pose it. And it is possible that further research will solve it. CMB radiation
Extragalactic microwave background radiation occurs in the frequency range from 500 MHz to 500 GHz, corresponding 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 the cosmic microwave background radiation, was discovered in 1965, although it was predicted back in the 40s by George Gamow and has been studied by astronomers for decades.
In the expanding Universe, the average density of matter depends on time - in the past it was higher. However, during expansion, not only the density, but also the thermal energy of the substance changes, 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 a residual radiation, the spectrum of which is the same as the spectrum of an absolutely solid body, and this radiation should be highly isotropic. In 1964, A.A. Penzias and R. Wilson, testing a sensitive radio antenna, discovered 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 isotropy experiments it was shown that the source of the microwave background radiation cannot be located inside the Galaxy, since then a concentration of radiation towards the center of the Galaxy should be observed. The source of radiation could not be located inside the Solar system, because There would be a daily variation in radiation intensity. Because of this, a conclusion was made 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 cosmic microwave background radiation, 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 every cubic centimeter of space contains about 500 relict photons, and there is much less matter per volume. Since the ratio of the number of photons to the number of baryons during expansion is maintained, but the energy of photons during the expansion of the Universe decreases over time due to the red shift, we can conclude that at some time in the past the energy density of radiation was greater than the energy density of matter particles. This time is called the radiation stage in the evolution of the Universe. The radiation stage was characterized by equality of temperature of the substance and radiation. At that time, radiation completely determined the nature of the expansion of the Universe. About a million years after the expansion of the Universe began, the temperature dropped to several thousand degrees and a recombination of electrons, which were previously free particles, took place with protons and helium nuclei, i.e. formation of atoms. The Universe has become transparent to radiation, and it is this radiation that we now detect and call relict radiation. True, since that time, due to the expansion of the Universe, photons have decreased their energy by about 100 times. Figuratively speaking, cosmic microwave background quanta “imprinted” the era of recombination and carry direct information about the distant past.
After recombination, matter began to evolve independently for the first time, regardless of radiation, and densities began to appear in it - the embryos of future galaxies and their clusters. This is why experiments to study the properties of cosmic microwave background 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 cosmic microwave background radiation of neighboring areas 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 density of matter from the average value during the recombination epoch. After recombination, 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, galaxy clusters and individual galaxies observed in the Universe. According to modern ideas, the first galaxies should have formed in an epoch that corresponds to redshifts from 4 to 8.
Is there a chance to look even further into the era before recombination? Until the moment of recombination, it was the pressure of electromagnetic radiation that mainly created the gravitational field that 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 expansion began. Let us consider successively the various stages of 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 were 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 matter of the modern observable Universe mainly consists.
At T = 2*1010 K, all-penetrating neutrinos stopped interacting with matter - from that moment a “relict neutrino background” should have remained, which may be able to be detected during future neutrino experiments.
Everything that has just been discussed happened at ultra-high temperatures in the first second after the expansion of the Universe began. A few seconds after the “birth” of the Universe, the era of primary nucleosynthesis began, when 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 all matter in the Universe). The remaining elements, heavier than helium, made up a negligible part of the substance - about 0.01%.
After the era of nucleosynthesis and before the era of recombination (about 106 years), a quiet expansion and cooling of the Universe occurred, 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 ultra-rapid inflationary expansion covered a tiny period of time: it ended at 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 decay of a hypothetical field. After this, the expansion of the Universe continued by inertia.
The inflationary universe hypothesis answers a number of important questions in cosmology that until recently were considered inexplicable paradoxes, in particular 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 inevitably should have caused not attraction, but mutual repulsion of material particles. And this 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 provisions requires instruments that simply have not yet been created. However, the idea of the accelerated expansion of the Universe at the earliest stage of its evolution has firmly entered into modern cosmology.
Speaking about the early Universe, we are suddenly transported from the largest cosmic scales to the region of the microworld, which is described by the laws of quantum mechanics. The physics of elementary particles and ultra-high energies is closely intertwined in cosmology with the physics of giant astronomical systems. The largest and the smallest are connected here with each other. This is the amazing beauty of our world, full of unexpected connections and deep unity.
The manifestations of life on Earth are extremely diverse. Life on Earth is represented by nuclear and prenuclear, single- and multicellular creatures; 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 diversity of living things, several different levels of organization of living things can be distinguished: molecular, cellular, tissue, organ, ontogenetic, population, species, biogeocenotic, biosphere. The listed levels are highlighted for ease of study. If we try to identify the main levels, reflecting not so much the levels of study as the levels of organization of life on Earth, then the main criteria for such identification should be the presence of specific elementary, discrete structures and elementary phenomena. With this approach, it turns out to be necessary and sufficient to distinguish molecular genetic, ontogenetic, population-species and biogeocenotic levels (N.V. Timofeev-Resovsky and others).
Molecular genetic level. When studying this level, apparently, the greatest clarity was achieved in the definition of 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 related phenomena. It is known that the main structures at this level (codes of hereditary information transmitted from generation to generation) are DNA differentiated by 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.
Convariant reduplication occurs according to the template principle by breaking the hydrogen bonds of the DNA double helix with the participation of the enzyme DNA polymerase. Then each of the strands builds a corresponding strand, after which the new strands are complementarily connected to each other. The pyrimidine and purine bases of the complementary strands are held together by hydrogen bonds by DNA polymerase. This process is carried out very quickly. Thus, the self-assembly of Escherichia coli DNA, consisting of approximately 40 thousand nucleotide pairs, requires only 100 s. Genetic information is transferred from the nucleus by mRNA molecules to the cytoplasm to ribosomes and there participates in protein synthesis. A protein containing thousands of amino acids is synthesized in a living cell in 5–6 minutes, and faster in bacteria.
The main control systems, both during convariant reduplication and during intracellular information transfer, use the “matrix principle”, i.e. are matrices next to which the corresponding specific macromolecules are built. Currently, the code embedded in the structure of nucleic acids, which serves as a matrix for the synthesis of specific protein structures in cells, is being successfully deciphered. Reduplication, based on matrix copying, preserves 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.
Cosmic electromagnetic radiation coming to Earth from all sides of the sky with approximately the same intensity and having a spectrum characteristic of black body radiation at a temperature of about 3 K (3 degrees on the absolute Kelvin scale, which corresponds to -270 ° C). At this temperature, the main share of radiation comes from radio waves in the centimeter and millimeter ranges. The energy density of the cosmic microwave background radiation is 0.25 eV/cm 3 .
Experimental radio astronomers prefer to call this radiation “cosmic microwave background” (CMB). Theoretical astrophysicists often call it “relict radiation” (the term was proposed by the Russian astrophysicist I.S. Shklovsky), since, within the framework of the generally accepted theory of the hot Universe today, this radiation arose at the early stage of the expansion of our world, when its matter was almost homogeneous and very hot. Sometimes in scientific and popular literature you can also find the term “three-degree cosmic radiation”. Below we will call this radiation “relict radiation”.
The discovery of the cosmic microwave background radiation in 1965 was of great importance for cosmology; it became one of the most important achievements of natural science of the 20th century. and, of course, the most important for cosmology after the discovery of the redshift in the spectra of galaxies. Weak relict 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 no planets, no stars, no galaxies existed in it. Detailed measurements of this radiation carried out in recent years using ground-based, stratospheric and space observatories lift the curtain on the mystery of the very birth of the Universe.
Hot Universe theory. In 1929, American astronomer Edwin Hubble (1889-1953) discovered that most galaxies are moving away from us, and the faster the further the galaxy is located (Hubble's law). This was interpreted as a general expansion of the Universe, which began approximately 15 billion years ago. The question arose about what the Universe looked like in the distant past, when galaxies just began to move away from each other, and even earlier. Although the mathematical apparatus, based on Einstein’s general theory of relativity and describing the dynamics of the Universe, was created back in the 1920s by Willem de Sitter (1872-1934), Alexander Friedman (1888-1925) and Georges Lemaitre (1894-1966), about the physical nothing was known about the state of the Universe in the early era of its evolution. It was not even certain that there was a certain moment in the history of the Universe that could be considered the “beginning of expansion.”
The development of nuclear physics in the 1940s allowed the development of theoretical models for the evolution of the Universe in the past, when its matter was believed to be compressed to a 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 measured quite reliably 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 account for 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 options gave its own composition of the original substance of the Universe.
If we omit the details, then there are two fundamentally different possibilities for the conditions in which the beginning of the expansion of the Universe took place: its matter 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 by Lemaitre in his early works, historically it was the first to consider the possibility of a cold beginning in the 1930s.
In the first assumptions, it was believed that all matter in the Universe first existed in the form of cold neutrons. It later turned out that this 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, electron and 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. This conclusion is in sharp contradiction with observations of stars and interstellar matter. The prevalence of chemical elements in nature rejects the hypothesis that the expansion of matter begins in the form of cold neutrons.
In 1946 in the USA, a “hot” version of the initial stages of the expansion of the Universe was proposed by Russian-born physicist Georgy Gamow (1904-1968). In 1948, the work of his collaborators, Ralph Alpher and Robert Herman, was published, which examined nuclear reactions in hot matter at the beginning of cosmological expansion in order to obtain the currently observed relationships between the amounts 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 mistakenly 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 resulted from astronomical observations in those years.
Comparing the age of the Universe at 2-4 billion years with the estimate of the age of the Earth - about 4 billion years - we had to assume that the Earth, Sun and stars were formed from primary matter with a ready-made chemical composition. It was believed that this composition did not change any significantly, 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 extragalactic distance scale 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 is no longer any need to explain the origin of all elements, including heavy ones, at the 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 helium content of 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 limited quantities.
The main idea of Gamow's theory is precisely that the high temperature of a substance prevents the transformation of all the substance into helium. At the moment of 0.1 seconds after the start of expansion, the temperature was about 30 billion K. Such hot matter contains many high-energy photons. 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 emergence of neutrino and antineutrino pairs. In this “seething cauldron” there is an ordinary substance. At very high temperatures, complex atomic nuclei cannot exist. They would be instantly smashed 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 rapidly transform into each other. However, the reactions of combining neutrons with protons do not occur, since the resulting deuterium nucleus is immediately broken up by high-energy particles. Thus, due to the high temperature, the chain leading to the formation of helium breaks at the very beginning.
Only when the Universe, expanding, cools to a temperature below a billion kelvins, some amount of the resulting deuterium is already stored and leads to the synthesis of helium. Calculations show that the temperature and density of a substance can be adjusted so that by this moment the proportion of neutrons in the substance is about 15% by mass. These neutrons, combining with the same number of protons, form about 30% of 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 expansion of the Universe begins. Subsequently, as the Universe expands, the temperature of its matter and radiation decreases. From the works of Gamow, Alpher 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 the modern Universe must inevitably be filled with a remnant (“relic”) of the primordial hot radiation, and the modern temperature This CMB should be around 5 K.
However, the analysis of different options for the beginning of cosmological expansion did not end with Gamow’s hypothesis. In the early 1960s, an ingenious attempt to return to the cold version was made by Ya.B. Zeldovich, who suggested that the original cold matter consisted of protons, electrons and neutrinos. As Zeldovich showed, such a mixture, upon expansion, turns 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 is several times older than the Earth and most of the stars around us, and data on the abundance of helium in prestellar matter was still very uncertain in those years.
It would seem that the decisive test for choosing between the 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 Bell company R. Wilson and A. Penzias, who were awarded the Nobel Prize in 1978.
On the way to detecting cosmic microwave background radiation. In the mid-1960s, astrophysicists continued to theoretically study the hot model of the Universe. The calculation of the expected characteristics of the cosmic microwave background radiation was carried out in 1964 by A.G. Doroshkevich and I.D. Novikov in the USSR and independently by F. Hoyle and R. J. Taylor in the UK. But these works, like the earlier works of Gamow and his colleagues, did not attract attention. But they have already convincingly shown that cosmic microwave background 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 generally emit even weaker radiation. Therefore, a targeted search for the cosmic microwave background radiation should have led to its discovery, but radio astronomers did not know about it.
This is what A. Penzias said in his Nobel lecture: “The first published recognition of cosmic microwave background radiation as a detectable phenomenon in the radio range appeared in the spring of 1964 in a short article by A.G. Doroshkevich and I.D. Novikov, entitled Average radiation density in the Metagalaxy and some issues of relativistic cosmology. Although an English translation appeared the same year, somewhat later, in the widely known journal Soviet Physics - Reports, the article apparently did not attract the attention of other specialists in the field. This remarkable paper not only deduces the spectrum of the CMB as a black-body wave phenomenon, but also clearly focuses on the twenty-foot horn reflector at Bell Laboratory at Crawford Hill as the most suitable instrument for detecting it!” (quoted from: 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 both theorists and observers; it did not stimulate the search for cosmic microwave background radiation. Historians of science are still wondering why no one tried to consciously search for radiation from the hot Universe for many years. It is curious that past this discovery - one of the largest in the 20th century. - The scientists walked by several times without noticing him.
For example, cosmic microwave background radiation could have been discovered back in 1941. Then the Canadian astronomer E. McKellar analyzed the absorption lines caused by interstellar cyanogen molecules in the spectrum of the star Zeta Ophiuchi. He came to the conclusion that these lines in the visible region of the spectrum can only arise when light is absorbed by rotating cyanogen molecules, and their rotation should be excited by radiation with a temperature of about 2.3 K. Of course, no one could have thought then that the excitation of rotational levels of these molecules caused by cosmic microwave background 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 cyanogen molecules, the lines of which are clearly observed in the spectra of many stars, is caused precisely by relict radiation.
An even more dramatic story occurred in the mid-1950s. Then the young scientist T.A. Shmaonov, under the guidance of famous Soviet radio astronomers S.E. Khaikin and N.L. Kaidanovsky, carried out measurements of radio emission from space at a wavelength of 32 cm. These measurements were made using a horn antenna similar to the one that was used many years later by Penzias and Wilson. Shmaonov carefully examined possible interference. Of course, at that time he did not yet have at his disposal such sensitive receivers as the Americans later acquired. The results of Shmaonov’s measurements were published in 1957 in his candidate’s thesis and in the journal “Instruments and Experimental Techniques”. The conclusion from these measurements was as follows: “It turned out that the absolute value of the effective temperature of 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 number 4, it is now clear to us that Shmaonov measured precisely the cosmic microwave background radiation. Unfortunately, neither he himself 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 famous experimental physicist from Princeton (USA), Robert Dicke, consciously approached this problem. Although his reasoning was based on the theory of an “oscillating” Universe, which repeatedly experiences expansion and contraction, Dicke clearly understood the need to search for cosmic microwave background radiation. On his initiative, in early 1965, the young theorist F. J. E. Peebles carried out the necessary calculations, and P. G. Roll and D. T. Wilkinson began building a small low-noise antenna on the roof of the Palmer Physical Laboratory in Princeton. It is not necessary to use large radio telescopes to search for background radiation, since the radiation comes from all directions. Nothing is gained from having a large antenna focus the beam onto 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 that others had accidentally made the day before.
