What is relic radiation? Changing the temperature of the relict radiation with time Experimental detection of relict radiation confirmed.

One of the interesting discoveries related to 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

The history of the discovery of 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 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 of the sky, a curved line danced on the oscilloscope screen. Typical natural source signal. 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 serviceability of the equipment, but it was 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.
Radio waves of the Universe. 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; at the same time, the quantum is, as it were, "cooled" - after all, the shorter the wavelength of the 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 the centimeter radio emission “smeared” over the Universe was called 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 enormous - more than a ton for every 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

Here is one of them: most of the matter in our Universe is, by no means, part of the planets, stars and Galaxies, but forms an 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 usual for us, ordinary unfolding spiral galaxies, ordinary stars, the most familiar of which is ours. 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.
Round dance of planets. 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! The coming fate of our entire universe! Is there a bigger problem? The study of relic radiation gave science the opportunity to deliver it. And it is possible that further research will solve it.

Despite the use of modern instruments and the latest methods for studying the Universe, the question of its appearance is still open. This is not surprising, given its age: according to the latest data, it is from 14 to 15 billion years. It is obvious that since then there has been very little evidence of the once grandiose processes of the Universal scale. Therefore, no one dares to assert anything, limiting himself to hypotheses. However, one of them has recently received a very significant argument - relic radiation.

In 1964, two employees of a well-known laboratory performing radio monitoring of the Echo satellite, having access to the appropriate ultra-sensitive equipment, decided to test some of their theories regarding the intrinsic radio emission of certain space objects.

In order to weed out possible interference from ground 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 these radio interference or the time of day. Neither R. Wilson nor A. Penzias even guessed that they had discovered the cosmic microwave background radiation.

Since none of them expected this, attributing the “background” to the features of the equipment (suffice it to recall that the microwave antenna used was the most sensitive at that time), almost a whole year passed before it became obvious that the recorded noise is part of the Universe itself. The intensity of the captured radio signal turned out to be almost identical to the intensity of radiation at a temperature of 3 Kelvin (1 Kelvin is equal to -273 degrees Celsius). For comparison: zero according to Kelvin corresponds to the temperature of an object of motionless atoms. is in the range 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 found out about lectures on this topic, contacted the university and reported that the cosmic microwave background was registered.

Based on the Big Bang theory, all matter arose as a result of a colossal explosion. For the first 300 thousand years after that, space was a combination of elementary particles and radiation. Subsequently, due to the expansion, temperatures began to fall, which made it possible for atoms to appear. Registered relic radiation is an echo of those distant times. As long as the universe had boundaries, the particle density was so high that the radiation was "coupled" because the mass of the particles reflected any kind of wave, preventing them from propagating. And only after the beginning of the formation of atoms, the space became "transparent" for waves. It is believed that the relic radiation appeared in this way. At the moment, each cubic centimeter of space contains about 500 initial quanta, although their energy has decreased by almost 100 times.

Relic radiation in different parts of the universe has different temperatures. This is due to the location of the primary matter in the expanding universe. Where the density of future matter atoms was higher, the proportion of radiation, and hence its temperature, was reduced. It was in these directions that large objects (galaxies and their clusters) subsequently formed.

The study of relic radiation lifts the veil of uncertainty over many processes occurring at the beginning of time.

Relic radiation is the background microwave radiation, which is the same in all directions and has a spectrum characteristic of a blackbody at a temperature of ~ 2.7 K.

It is believed that this radiation can be used to find out the answer to the question: where did it come from? In fact, the relic radiation is what remains of the "construction of the Universe", when it only began to emerge after the expansion of dense hot plasma. In order to make it easier to understand what relic radiation is, let's compare it with the remnants of human activity. For example, a person invents something, others buy it, use it and throw away waste. So garbage (the very result of human life) - this is an analogue of relic radiation. From the garbage you can find out everything - where a person was at a certain period of time, what he ate, what he was wearing, and even what he was talking about. Also, relic radiation. According to its properties, scientists are trying to build a picture of the moment of the big bang, which may give an answer to the question: how did the Universe appear? But still, the laws of conservation of energy create certain disagreements about the origin of the universe, because nothing is taken from nowhere and does not go anywhere. The dynamics of our universe is transitions, changes in properties and states. This can be observed even on our planet. For example, ball lightning appears in a clot of a cloud of water particles?! How? How can that be? No one can explain the origin of certain laws. There are only moments of discovery of these laws, as well as the history of the discovery of relic radiation.

Historical facts of the study of relic radiation

For the first time, Georgy Antonovich Gamov (George Gamow) mentioned the CMB when he tried to explain the Big Bang theory. He assumed that some kind of residual radiation fills the space of an ever-expanding universe. In 1941, while studying the absorption of one of the stars in the Ophiuchi cluster, Andrew McKellar noticed spectral absorption lines of light that corresponded to a temperature of 2.7 K. In 1948, Georgy Gamow, Ralph Alfert and Robert German set the temperature of the cosmic microwave background radiation at 5 K. Later Georgy Gamow suggested a temperature less than known at 3 K. But this was only a superficial study of this fact, at that time unknown to anyone. In the early 1960s, Robert Dicke and Yakov Zel'dovich obtained the same results as Gamow, fixing waves whose radiation intensity did not depend on time. The inquisitive mind of scientists had to create a special radio telescope for more accurate registration of relic radiation. In the early 1980s, with the development of the space industry, relic radiation began to be studied more carefully from onboard a spacecraft. It was possible to establish the isotropy property of the relict radiation (the same properties in all directions, for example, 5 steps to the north in 10 seconds and 5 steps to the south will also be in 10 seconds). To date, studies of the properties of relic studies and the history of its occurrence are continuing.

What are the properties of relic radiation?

CMB spectrum from data obtained with the FIRAS instrument aboard the COBE satellite

The CMB spectrum is 2.75 Kelvin, which is similar to soot cooled to this temperature. Such a substance always absorbs the radiation (light) falling on it, no matter how you influence it. At least put it in a magnetic coil, at least throw a nuclear bomb, at least shine with a searchlight. Such a body also emits small radiation. But this only proves the fact that nothing is absolute. It is always possible to deduce an ideal law for an infinitely long time, to achieve the maximum of a certain property of something, but there will always remain a small fraction of inertia.

Interesting facts related to the study of relic radiation

The maximum frequency of the relic radiation was registered at 160.4 GHz, which is equal to 1.9 mm wave. And the density of such radiation is 400-500 photons per cm 3. CMB radiation is the oldest, most ancient radiation that can be observed at all in the universe. Each particle traveled 400,000 years to reach Earth. Not kilometers, but years! According to the observations of the satellite and mathematical calculations, the cosmic background radiation seems to stand still, and all galaxies and constellations move relative to it at a tremendous speed, of the order of hundreds of kilometers per second. It's like watching through the window of a moving train. The temperature of the background radiation in the direction of the constellation is 0.1% higher, and in the opposite direction 0.1% lower. This explains the movement of the Sun in the direction of this constellation relative to the background background.

What gives us the study of relic radiation?

The early universe was cold, very cold. Why was the universe so cold, and what happened when the expansion of the universe began? It can be assumed that, due to the big bang, a huge amount of clots of energy was thrown out of the universe, then the Universe cooled down, almost froze, but over time, the energy began to gather into clots again, and a certain reaction arose that started the process of expansion of the universe. Then where did dark matter come from and does it interact with the cosmic microwave background? Perhaps the CMB is the result of the decomposition of dark matter, which is more logical than the residual radiation of the big bang. Since dark energy can be antimatter and particles of dark matter, colliding with particles of matter, form radiation in the material and antimaterial world like relic radiation. To date, this is the most recent, unexplored area of ​​​​science in which success can be achieved and imprinted in the history of science and society.

What does "relic" radiation indicate?

Relic called background cosmic radiation, the spectrum of which corresponds to the spectrum of a completely black body with a temperature of about 3 degrees Kelvin. This radiation is observed at wavelengths from a few millimeters to tens of centimeters; it is almost isotropic. The discovery of relic radiation was a decisive confirmation of the theory of the hot Universe, according to which in the past the Universe had a much higher density of matter and a very high temperature than now. The relic radiation recorded today is information about long-past events, when the age of the Universe was only 300-500 thousand years, and the density was about 1000 atoms per cubic centimeter. It was then that the temperature of the original Universe dropped to about 3000 degrees Kelvin, elementary particles formed atoms of hydrogen and helium, and the sudden disappearance of free electrons led to radiation, which we today call relict.

The first theoretical estimates of the expected temperature of the relic radiation are contained in the works of Gamow and Alfer, carried out in the 50s. They indicated a figure of about 5 K. Can this radiation be observed against the background of the electromagnetic radiation of stars and radio galaxies? In the work of the Soviet astrophysicist A.G. Doroshkevich and the author in 1964, it was for the first time specifically calculated how much the intensity of the cosmic microwave background radiation (if it exists, of course) should exceed the radiation intensity of radio galaxies and other sources in the centimeter region of the spectrum. The possibility of setting up a decisive experiment to search for relic radiation, on which the choice between hot and cold models of the Universe depended, became clear. But this theoretical work went unnoticed by observers.

Relic radiation was discovered quite by accident in 1965 by Penzias and Wilson, employees of the American company Bell, while debugging a horn radio antenna designed to observe the Echo satellite. They found a weak background radio noise coming from space, independent of the direction of the antenna. Dicke, Peebles, Roll and Wilkinson immediately gave a cosmological explanation for Penzias and Wilson's measurements as evidence for a hot model of the universe. At that time, Dicke and his collaborators were themselves preparing equipment for searching for the radio background from cosmic microwave background radiation at a wavelength of 3 cm. Penzias and Wilson's first observations were made at 7.35 cm. They showed that the temperature of the radiation is about 3° of the absolute Kelvin scale. 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 emission spectrum is in equilibrium, as predicted by the theory of the hot Universe. It corresponds to Planck's formula for equilibrium radiation with a temperature of 2.7 K. In fig. 21 shows the entire spectrum of electromagnetic radiation in space from meter radio waves to ultraviolet radiation * .

* (Of course, this is the spectrum of radiation that exists on average in the Universe far from stars and other sources.)

At meter wavelengths, the so-called radio galaxies radiate, which were discussed in § 3 of Ch. 1. They have powerful magnetic fields and energetic electrons. The movement of electrons in magnetic fields causes radio emission. In the visible region, the stars radiate; in the infrared region, probably, mainly dust heated by starlight shines. Other sources of infrared radiation are also possible. Between these two regions, radio waves and visible light (and infrared sources), is the region of the spectrum where the CMB dominates.

It is interesting to note that astronomers discovered the first manifestation of the cosmic microwave background back in 1941. It was then that the astrophysicist McKellar noted that cyanide radicals are observed in the interstellar gas in an excited rotational state corresponding to an excitation temperature of about 2.3 K. What excites the molecules then remained unclear. After the discovery of cosmic microwave background radiation, IS Shklovsky and independently Field, Wulff, Tadeusz and other scientists explained this by the excitation of molecules by cosmic microwave background radiation. Observation of the corresponding molecular lines in the CN spectrum helped to calculate the temperature of the cosmic microwave background radiation λ ≈ 0.26 cm.

If we measure at the same wavelength the intensity of the relic radiation coming to us from different directions, then within the measurement accuracy it turns out to be the same. The measurement accuracy is tenths of a percent. This circumstance is an important proof that the expansion of the Universe is isotropic not only now, but also in the distant past, when the density of matter was thousands of times greater than today. After all, the Universe is now practically transparent to relic radiation, and it comes to us from great distances. We will talk about this in more detail in Section 8 of Chap. 3. Only for the very early stages of expansion is there a possibility for the universe to disobey Friedmann's theory!

The relic radiation did not originate in any sources like the light of stars or radio waves born in radio galaxies. CMB radiation has existed since the very beginning of the expansion of the Universe. It was in that hot matter of the Universe, which was expanding from the singularity.

If we calculate the total amount of energy density that is contained in the CMB today, then it will be 30 times greater than the energy density in radiation from stars, radio galaxies and other sources combined. You can count the number of CMB photons in each cubic centimeter of the universe. It turns out that the concentration of these photons:

Recall that the average density of ordinary matter in the Universe is about 10 -30 (g / cm 3) (see Chap. 1). This means that if we "smeared" all the matter evenly in space, then there would be only 1 atom in one cubic meter (recall that the mass of a hydrogen atom, the most common element of the Universe, is about 10 -24 g). At the same time, a cubic meter contains about a billion photons of relic radiation.

Thus, the quanta of electromagnetic waves, these peculiar particles, are much more common in nature than ordinary matter. In § 2 ch. 3 it was said that the ratio of the number of quanta of electromagnetic waves to the number of heavy particles characterizes the entropy of the Universe. In our case, this ratio is *

* (Note that the number of photons per unit volume is well known from measurements, but the density of ordinary matter, as we saw in Chap. 1 is much less known. Therefore, the ratio (6) can vary numerically depending on the refinement of the density of the substance, So, if this density is equal to ρ crit, then S = 10 8 .)

Thus, the entropy of the universe is enormous. Relation (6), as we said, practically does not change during the evolution of the Universe.

The discovery of relic radiation is a grandiose achievement of modern science. It allows us to say that in the early stages of expansion the Universe was hot. The prediction of relic radiation was made within the framework of the theory of the expanding Universe, so its discovery once again shows the correctness and fruitfulness for cosmology of the path indicated by the works of A. A. Fridman.