The universe is everything that exists. From the smallest dust particles and atoms to huge accumulations of the matter of stellar worlds and star systems. Therefore, it will not be a mistake to say that any science, one way or another, studies the Universe, more precisely, one way or another of its aspects. Exists scientific discipline, the object of study of which is the Universe itself. This is a special branch of astronomy, the so-called cosmology.

Cosmology is the study of the universe as a whole, including the theory of the entire astronomical observations regions as parts of the universe.

With the development of science, more and more revealing physical processes occurring in the world around us, most scientists gradually moved to materialistic ideas about the infinity of the universe. Here great value had the discovery by I. Newton (1643 - 1727) of the law gravity published in 1687. One of the important consequences of this law was the assertion that in finite universe all its substance in a limited period of time must be drawn together into a single close system, whereas in infinite universe matter under the action of gravity is collected in some limited volumes (according to the ideas of that time - in the stars), evenly filling the universe.

Great value for development contemporary ideas about the structure and development of the universe has a general theory of relativity, created by A. Einstein (1879 - 1955). It generalizes Newton's theory of gravity to large masses and speeds comparable to the speed of light. Indeed, a colossal mass of matter is concentrated in galaxies, and the speeds of distant galaxies and quasars are comparable to the speed of light.

One of the significant consequences general theory relativity is the conclusion about continuous movement matter in the universe - the non-stationarity of the universe. This conclusion was reached in the 20s of our century Soviet mathematician A.A. Fridman (1888 - 1925). He showed that, depending on the average density of matter, the universe must either expand or contract. With the expansion of the Universe, the speed of the recession of galaxies should be proportional to the distance to them - a conclusion confirmed by Hubble by the discovery of redshift in the spectra of galaxies.

The critical value of the average density of a substance, on which the nature of its movement depends,

where G is the gravitational constant, and H=75 km/s*Mpc is the Hubble constant. Substituting desired values, we obtain that the critical value of the average density of the substance P k = 10 -29 g/cm 3 .

If the average density of matter in the Universe is greater than the critical one, then in the future expansion of the universe will be replaced by compression, and at an average density equal to or less than the critical one, the expansion will not stop. One thing is clear, that over time, the expansion led to a significant decrease in the density of matter, and at a certain stage of the expansion, galaxies and stars began to form.

In the 20s. XX century outstanding Soviet physicist A. A. Friedman established that from the equations of the general theory of relativity it follows that the Universe cannot be unchanged, it must evolve. Our world must shrink or expand. From the point of view of the observer (regardless of where he is: after all, the world is homogeneous and at each point everything happens the same way as at all the others), all distant objects move away from him (or approach him) with that more speed the further they are located. This changes the average density of matter in the universe. In observations, the expansion of the Universe is manifested in the fact that in the spectra of distant galaxies, the absorption lines are shifted to the red side of the spectrum. This is called redshift.

Redshift easily removes the photometric paradox. After all, when moving to more and more distant objects, the brightness of the star decreases also because the quantum energy decreases due to the red shift. When the speed of removal approaches the speed of light, the star becomes invisible.

In Friedman's theory, a quantity called the critical density appears; it can be expressed in terms of the Hubble constant:

ρ to = 3 H 2/8π G,

where H is the Hubble constant; G- gravitational constant.

space-time

The general theory of relativity allows us to interpret the Hubble constant as the reciprocal of the time elapsed since the origin of the Universe:

H = 1 / T.

Indeed, if we go back on the time scale, then it turns out that for about 15-20 billion years the Universe had zero dimensions and infinite density. Such a state is commonly called a singularity. It appears in all variants of the Friedman model. It is clear that here lies the limit of applicability of the theory and it is necessary to go beyond the framework of this model. For sufficiently short times quantum effects(OTO purely classical theory) become decisive.

It follows from Friedman's theory that various scenarios for the evolution of the Universe are possible: unlimited expansion, alternation of contractions and expansions, and even a trivial steady state. Which of these scenarios is realized depends on the ratio between the critical and actual density of matter in the Universe at each stage of evolution. In order to estimate the values ​​of these densities, let us first consider how astrophysicists imagine the structure of the Universe.

It is currently believed that matter in the universe exists in three forms: ordinary matter, background radiation and so-called "dark" matter. Ordinary matter is concentrated mainly in stars, of which there are about a hundred billion in our Galaxy alone. The size of our Galaxy is 15 kiloparsecs (1 parsec = 30.8 x 1012 km). It is assumed that in the Universe there are up to a billion different galaxies, the average distance between which is on the order of one megaparsec. These galaxies are distributed extremely unevenly, forming clusters. However, if we consider the Universe in a very large scale, for example, "breaking" it into "cells" with a linear size exceeding 300 megaparsecs, then the uneven structure of the Universe will no longer be observed. Thus, on very large scales, the universe is homogeneous and isotropic. Here, for such a uniform distribution of the substance, one can calculate the density rv, which is ~ 3×10-31 g / cm3.

The density equivalent to relict radiation is rr ~ 5×10-34 g/cm3, which is much less than rv and, therefore, may not be taken into account when calculating the total density of matter in the Universe.

Observing the behavior of galaxies, scientists suggested that in addition to the luminous, "visible" matter of the galaxies themselves, in the space around them there are, apparently, significant masses of matter that cannot be directly observed. These "hidden" masses manifest themselves only as gravity, which affects the motion of galaxies in groups and clusters. Based on these signs, the density rt associated with this "dark" matter is also estimated, which, according to calculations, should be approximately 30 times greater than rv. As will be seen from what follows, it is "dark" matter that is ultimately "responsible" for one or another "scenario" of the evolution of the Universe 1.

To verify this, let us estimate the critical density of matter, starting from which the "pulsating" scenario of evolution is replaced by a "monotonous" one. Such an estimate, although rather rough, can be made on the basis of classical mechanics, without involving the general theory of relativity. From modern astrophysics, we need only Hubble's law.

Let's calculate the energy of some galaxy with mass m, which is located at a distance L from the "observer" (Fig. 1.1). The energy E of this galaxy is the sum of the kinetic energy T = mv2/2 = mH2L2/2 and the potential energy U = - GMm / L, which is associated with gravitational interaction galaxy m with matter of mass M located inside a ball of radius L (it can be shown that matter outside the ball does not contribute to potential energy). Expressing the mass M in terms of the density r, M = 4pL3r/3, and taking into account the Hubble law, we write the expression for the energy of the galaxy:

E \u003d T - G 4/3 pmr v2 / H2 \u003d T (1-G 8pr / 3H2) (1.1).

Fig.1.1.

It can be seen from this expression that, depending on the value of the density r, the energy E can be either positive (E > 0) or negative (E< 0). В первом случае рассматриваемая галактика обладает достаточной kinetic energy to overcome gravitational attraction mass M and go to infinity. This corresponds to an unlimited monotonous expansion of the Universe (the "open" Universe model).

In the second case (E< 0) расширение Вселенной в какой-то момент прекратится и сменится сжатием (модель "замкнутой" Вселенной). Критическое значение плотности соответствует условию Е = 0, так что из (1.1) получаем:

rk = 3Н2 / 8pG (1.2).

Substituting into this expression known values H = 15 ((km/s)/106 light years) and G = 6.67×10-11 m3/kg s2, we obtain the value of the critical density rk ~ 10-29 g/cm3. Thus, if the Universe consisted only of ordinary "visible" matter with a density rv ~ 3 × 10-31 g/cm3, then its future would be associated with unlimited expansion. However, as mentioned above, the presence of "dark" matter with a density rt > rv can lead to a pulsating evolution of the Universe, when the period of expansion is replaced by a period of contraction (collapse) (Fig. 1.2). True, in recent times scientists are increasingly coming to the conclusion that the density of all matter in the universe, including "dark" energy, is exactly equal to the critical one. Why is it so? There is no answer to this question yet.

Fig.1.2.

At the heart of the concept big bang lies the assumption that the beginning of the evolution of the Universe (t = 0) corresponded to a state with an infinite density r = Ґ ( singular state universe) 1. From this moment on, the Universe expands2, and its average density r decreases with time according to the law:

r ~ 1 / G t2 (1.3)

where G is the gravitational constant 3 .

The second postulate of the Big Bang theory is the recognition of the decisive role light radiation on the processes that took place at the beginning of the expansion4. The energy density e of such radiation, on the one hand, is related to the temperature T famous formula Stefan-Boltzmann:

where s = 7.6 10-16 J/m3deg4 is the Stefan-Boltzmann constant, and on the other hand, with the mass density r:

r = e / с2 = sТ4/с2 (1.5)

where c is the speed of light.

Substituting (1.6) into (1.4), taking into account numerical values G and s we get:

T ~ 1010 t-1/2 (1.6)

where time is in seconds and temperature is in kelvins.

At very high temperatures(T > 1013 K, t< 10-6 с) Вселенная была абсолютно непохожа на то, что мы видим сегодня. В той Вселенной не было ни галактик, ни звезд, ни атомов... Как в "кипящем котле" в ней непрерывно рождались и исчезали кварки, лептоны и кванты fundamental interactions, first of all, photons (g). In a collision of two photons, for example, a pair of electron (e-) - positron (e +) could be born, which almost immediately annihilated (self-destructed), again giving birth to light quanta:

g + g "e- + e+ (1.7)

Annihilation of an electron-positron pair could lead to the birth of other particle-antiparticle pairs, for example, neutrino (n) and antineutrino (n)

e- + e+ "n + `n (1.8)

Similar reversible reactions were also carried out with the participation of hadrons, in particular, nucleons (protons, neutrons and their antiparticles).

However, it should be borne in mind that the creation of a particle-antiparticle pair in a collision of photons is possible only if the photon energy Wg exceeds the rest energy W0 = m0c2 of the generated particles. Average energy photons in a state of thermodynamic equilibrium is determined by the temperature:

where k is Boltzmann's constant.

Therefore, the reversible nature of processes involving photons took place only at temperatures exceeding quite certain value for each type elementary particles T~m0c2/k.

For example, for nucleons, m0c2 ~ 1010 eV, which means Tnucl ~ 1013 K. So, at T > Tnucleon, the continuous appearance of nucleon-antinucleon pairs and their almost instantaneous annihilation with the production of photons could and did occur. But as soon as the temperature T became less than T nucleon, nucleons and antinucleons for a very a short time vanished into light. And if this were the case for all nucleons and antinucleons, then the Universe would be left without stable hadrons, which means that there would be no substance from which galaxies, stars and others were subsequently formed. space objects. But it turns out that on average there was one (!) "extra" particle for every billion nucleon-antinucleon pairs. It is from these "extra" nucleons that the substance of our Universe is built.

A similar process of annihilation of electrons and positrons occurred later, at t ~ 1 s, when the temperature of the Universe dropped to ~ 1010 K and the photon energy was not enough to produce electron-positron pairs. As a result, a relatively small number of electrons remained in the Universe - just enough to compensate for the positive electric charge"extra" protons.

The protons and neutrons remaining after global self-destruction for some time reversibly passed into each other in accordance with the reaction formulas:

p + e-" n + `n;

p + n " n + e+ .

And here the decisive role was played little difference rest masses of protons and neutrons, which, in the end, led to the fact that the concentrations of neutrons and protons turned out to be different. The theory says that by the end of the fifth minute, there were about 15 neutrons for every hundred protons. It was at this time that the temperature of the Universe dropped to ~ 1010 K, and conditions were created for the formation of stable nuclei, primarily hydrogen (H) and helium (He). If we neglect the nuclei of other elements (and then they really almost did not arise), then, taking into account the above ratio of protons and neutrons, ~ 70% of hydrogen nuclei and ~ 30% of helium nuclei should have been formed in the Universe. It is this ratio of these elements that is observed in the intergalactic medium and in the stars of the first generation, thus confirming the concept of the Big Bang.

After the formation of H and He nuclei for a long time (about a million years), almost nothing worthy of attention happened in the Universe. It was still hot enough for the nuclei to hold on to electrons, as the photons immediately ripped them off. Therefore, the state of the Universe during this period is called photon plasma.

This continued until the temperature dropped to ~ 4000 K, which happened ~ 1013 s or almost a million years after the Big Bang. At this temperature, hydrogen and helium nuclei begin to intensively capture electrons and turn into stable nuclei. neutral atoms(photon energy is no longer enough to break these atoms). Astrophysicists call this process recombination.

Only from this moment the matter of the Universe becomes transparent to radiation and suitable for the formation of clots, from which galaxies later turned out. The radiation, called relic, has since led an independent existence, traveling through the Universe in all directions. Now the quanta of this radiation come to us on Earth, which flew almost rectilinearly over a huge distance, equal to the product the speed of light c by the time tp that has passed since the moment of recombination: L = tp. But after all, as a result of the expansion of the Universe, we actually "run away" from these relic radiation quanta at a speed v = НL ~ tр/t0, where t0 = 1/Н is the time that has passed since the Big Bang. And this means that the wavelengths of the relic radiation received by us due to the Doppler effect should be many (~ t0 / tp) times greater than that of the one that was at the time of recombination at T ~ 4000 K. Calculations show that the relic The radiation registered on the Earth must be the same as if it were emitted by a body heated to a temperature T ~ 3 K1. It was these properties that the radiation possessed, which was recorded in 1965 by A. Penzias and R. Wilson.

Smirnov O.G., Candidate of Technical Sciences

ON THE CRITICAL DENSITY OF MATTER IN THE UNIVERSE

The problems of determining the average density of matter in the Universe are considered.

1. Critical Density matter in the Universe is estimated by the formula

where - H is the Hubble constant, O is the gravitational constant.

An estimate of the masses of matter in galaxies and clusters of galaxies gives average density~10-27kg/m3. It follows from this that we are dealing with an infinitely expanding Universe (!). Is it so?

2. The first mistake is that in the observable Universe all cosmic objects (stars, galaxies, clusters of galaxies...) have a higher matter density in the center than on the outskirts. This should also be expected from the distribution of matter in the Universe. We observe only a small part of the Universe and talk about uniform distribution matter in the universe is clearly incorrect.

In , calculations were made, according to which our Galaxy is located on the outskirts of the Universe and, according to recent observations, is moving towards single center together with large groups other galaxies. The movement occurs with acceleration in the direction of a massive object located outside the observable Universe between the constellations Centaurus and Parus (according to US astrophysicists). According to our version, this is the core of the Universe. The foregoing suggests that there is no need to introduce the concept of "dark energy".

It is also assumed that processes occur inside the Universe that cause matter to continuously move from the depths to the boundaries (explosive processes) and back (movement of galaxies).

where TV, Yav, g - mass, radius and distance from the center of the Universe.

On the outskirts of the Universe (r=Jav)

P(*v) = -tb (3)

But we are interested in the average density included in formula (1).

She is equal

Thus, the average density of the Universe is three times greater than at its outskirts. Being on the outskirts of the Universe, we observe a small part of the substance from the half, which moves towards the center of the Universe. Therefore, the average density of matter in the Universe will be no less than 6 . 10-27 kg/m3.

3. Travel speed remote space objects(stars, galaxies...) are determined by "redshift". B , non-linear the quantum physics gives formulas according to which the speeds turn out to be approximately twice as large, which means that the mass is four times greater (mass is proportional to the square of the speed). Along the way, the need to introduce the concept of " dark matter».

Now the average density of matter in the Universe should be taken equal to ~ 6 4 "10" = 2.4 10-26 kg/m3, which is 2.4 times greater than the critical one.

We come to important conclusion that the infinitely expanding universe should be excluded from consideration.

The substance, moving to the outskirts of the universe, reduces its temperature to absolute zero, enlarges into galaxies and begins to move back to the center of the universe.

The "retreat" of galaxies just speaks of their movement towards a single center with acceleration, and the Hubble constant is actually a variable ranging from 100 km/(s-Mpc) to 50 km/(s-Mpc). The decrease is towards the center of the universe. The inverse value gives the time of the beginning of the movement of our Galaxy to the center of the Universe. It is a minimum of 9.75 billion years (H=100 km/(s-Mpc)), or a maximum of 13.9 billion years (H=70 km/(s-Mpc))

The foregoing allows us to get out of the impasse in which modern cosmology has entered.

Literature

1. Kononovich E.V., Moroz V.I. General course astronomy. Ed. 2nd. URSS.2004-544s.

2. Smirnov O.G. Knowledge of the Universe and discoveries of the third millennium. "APSN", No. 5, 2010.-pp.73-84.

3. Smirnov O.G. Universe physics and " global energy". 6th ed., add.-M .: Sputnik + Publishing House, 2010. - 611s.

4. Smirnov O.G. Nonlinear physics. - M.: Sputnik + Publishing House, 2010. - 289 p.

THE CRITICAL DENSITY OF THE UNIVERSE- the value of the density of matter in universe, defined by the expression where H is the Hubble constant (cf. Hubble law), G is Newton's constant of gravity. In homogeneous isotropic models of the Universe (see Cosmological models)With zero cosmological constant value r With is critical. value separating the model of the closed Universe where r - real cf. density of all kinds of matter) from the open universe model

If the gravity of matter is strong enough, it greatly slows down the expansion of the Universe, and in the future its expansion should be replaced by contraction. 3D space in the models under consideration for has positive. curvature, closed, its volume is finite.

When gravity is not enough to stop the expansion, and the Universe under these conditions expands indefinitely in the future. The three-dimensional space in the considered models has a negative value. curvature, its volume is infinite (in the simplest topology).

Hubble constant H known from astronomical observations with mean. uncertainty: H - (50-100) km/(s*Mpc). Hence, there is an uncertainty in the meaning of K. p. V. r c\u003d (5 * 10 -30 -2 * 10 -29) g / cm 3. On the other hand, observations show that the average density of the matter that makes up galaxies is apparently much less than the C.p.V. hidden masses. Qty