What are the cosmological models of the Universe? The future of the Universe. Various cosmological scenarios are proposed to describe the future of the Universe. Origin and evolution of the Universe

Introduction

For a long time, human thought has been trying to solve the problem of the origin of our world, the emergence and further fate of the universe. This question is one of the eternal questions, and will probably never cease to excite people’s minds. At different times, various solutions to this problem were proposed. According to one of them, the world was created and once began to exist; according to others, the world is eternal and has no beginning. There are also known points of view according to which the universe periodically arises and is destroyed.

Origin and evolution of the Universe

The Universe arose approximately 20 billion years ago from some dense and hot proto-matter. Today we can only guess what this ancestral substance of the Universe was like, how it was formed, what laws it obeyed, and what processes led it to expansion. There is a point of view that from the very beginning protomatter began to expand at a gigantic speed. At the initial stage, this dense substance scattered, scattered in all directions and was a homogeneous seething mixture of unstable particles that constantly disintegrated during collisions. Cooling and interacting over millions of years, this entire mass of matter scattered in space was concentrated into large and small gas formations, which over the course of hundreds of millions of years, approaching and merging, turned into huge complexes. In them, in turn, denser areas arose - stars and even entire galaxies subsequently formed there. As a result of gravitational instability, dense “protostellar formations” with masses close to the mass of the Sun can form in different zones of the formed galaxies. The compression process that has begun will accelerate under the influence of its own gravitational field. This process accompanies the free fall of cloud particles towards its center - gravitational compression occurs. In the center of the cloud a compaction forms, consisting of molecular hydrogen and helium. An increase in density and temperature in the center leads to the disintegration of molecules into atoms, ionization of atoms and the formation of a dense protostar core. There is a hypothesis about the cyclical state of the Universe. Having once arisen from a super-dense clot of matter. The Universe may have already generated billions of star systems and planets within itself already in the first cycle. But then, inevitably, the Universe begins to tend to the state from which the history of the cycle began, the red shift gives way to violet, the radius of the Universe gradually decreases, and in the end the matter of the Universe returns to its original super-dense state, mercilessly destroying all life along the way. And this is repeated every time, in every cycle for eternity! By the early 1930s, it was believed that the main components of the Universe were galaxies, each of which on average consisted of 100 billion stars. The Sun, together with the planetary system, is part of our Galaxy, the bulk of whose stars we observe in the form of the Milky Way. Except stars and planets. The galaxy contains a significant amount of rarefied gases and cosmic dust. Is the Universe finite or infinite, what is its geometry - these and many other questions are related to the evolution of the Universe, in particular to the observed expansion. If, as is currently believed, the speed of “expansion” of galaxies will increase by 75 km/s for every million parsecs, then extrapolation to the past leads to an amazing result: approximately 10–20 billion years ago the entire Universe was concentrated in a very small area . Many scientists believe that at that time the density of the Universe was the same as that of an atomic nucleus. Simply put, the Universe was then one giant “nuclear blob.” For some reason, this “drop” became unstable and exploded. We are now observing the consequences of this explosion as systems of galaxies. The most serious blow to the inviolability of the Universe was dealt by the results of measurements of the speeds of removal of galaxies obtained by the famous American scientist E. Hubble. He found that any galaxy is moving away from us on average at a speed proportional to the distance to it. This discovery finally destroyed the idea of ​​a static, unshakable Universe that had existed since the time of Aristotle, which, however, had already been shaken in connection with the discovery of the evolution of stars. This means that galaxies are not at all cosmic lanterns suspended at equal distances from each other, and, moreover, since they are moving away, then at some time in the past they must have been closer to us. About 20 billion years ago, all the galaxies, apparently, were concentrated at one point, from which the rapid expansion of the Universe began to its present size. But where is this point? Answer: nowhere and at the same time everywhere; it is impossible to indicate its location; this would contradict the basic principle of cosmology. Another comparison may help to understand this statement. According to the general theory of relativity, the presence of matter in space leads to its curvature. If there is a sufficient amount of matter, it is possible to construct a model of curved space. Moving along the earth in one direction, we must ultimately return to our starting point after traveling 40,000 km. In the curved Universe the same thing will happen, but after 40 billion light years; in addition, the “wind rose” is not limited to the four parts of the world, but also includes up and down directions. So, the Universe resembles an inflatable ball on which galaxies are drawn and, like on a globe, parallels and meridians are marked to determine the position of points; but in the case of the Universe, to determine the position of galaxies it is necessary to use not two, but three dimensions. The expansion of the Universe resembles the process of inflating this balloon: the relative position of various objects on its surface does not change, there are no designated points on the balloon. To estimate the total amount of matter in the Universe, we simply need to count all the galaxies around us. By doing this, we will receive less substance than is necessary to, according to Einstein, close the “balloon” of the Universe. There are models of the open Universe, the mathematical interpretation of which is equally simple and which explain the lack of matter. On the other hand, it may turn out that the Universe contains not only matter in the form of galaxies, but also invisible matter in the amount necessary for the Universe to be closed; The controversy on this issue still does not subside.

The creative role of the physical vacuum

When we pronounce the word “vacuum,” we usually imagine an extremely rarefied environment, which is either studied in special laboratories or observed in outer space. However, vacuum is not emptiness, but something completely different: a special, unobservable state of matter in everyday life, called physical vacuum.

Of course, there are no ordinary (real) particles in an empty volume, but quantum theory predicts the existence of many other particles, called virtual ones. Such particles are capable of turning into real ones under certain conditions.

The lifetime for particles with mass me is about

With. This value is very small and they speak not so much about “life” as about a short-term burst of life of very strange particles and fields associated with them.

So, a sea of ​​unobservable particles, ready under certain conditions to turn into ordinary particles.

The state of a physical vacuum can be characterized by the lowest energy value of quantum fields such as a scalar field that must exist in a vacuum. This field is associated with the hypothetical Higgs particle (named after the scientist Higgs who proposed it), which is an example of a superheavy boson, the mass of which is perhaps

times the mass of a proton. Such particles can be born at a temperature of K. There are projects of huge accelerators, where, by observing the interaction of particles, scientists hope to confirm the reality of the existence of Higgs.

American engineers and physicists plan to implement one of the projects at the end of the century. This will be a very powerful colliding beam accelerator, and superconducting magnets will be used to reduce energy consumption in a ring installation with a circumference of 84 km. The future accelerator is called the SSC superconducting super collider.

One of the amazing properties of the physical vacuum is due to the fact that it creates negative pressure and, therefore, can be a source of repulsive forces in nature. This property plays an extremely important role in the “inflating universe” scenario.

Paradoxes of a stationary Universe

In 1744, Swiss astronomer Jean Philippe de Chézeau discovered a photometric paradox associated with the supposed infinity of the universe. Its essence is this: if there are countless stars in the infinite universe, then in any direction the gaze of an earthly observer would certainly encounter some star, and then the sky would have a brightness comparable to the brightness of the sun, which is not actually observed. In 1826, the German astronomer Heinrich Olbers independently came to the same conclusions. Since then, the photometric paradox has been called the Chezo-Olbers paradox. Scientists have tried in various ways to eliminate this paradox, suggesting the uneven distribution of stars or the absorption of light by gas and dust interstellar clouds, as Chezo and Olbers tried to do. However, as was later shown, the gas and dust clouds had to heat up and themselves re-emit the absorbed rays, and this fact did not allow us to avoid the photometric paradox.

In 1895, German astronomer Hugo Seeliger discovered the gravitational paradox, also related to the supposed infinity of the universe. Its essence is this: if in an infinite universe there are countless evenly distributed stars (mass), then their gravitational force acting on any body becomes either infinitely large or indefinite (depending on the method of calculation), which is not observed. And in this case, attempts were made to avoid the gravitational paradox by assuming a different formula for the gravitational force in the law of gravity, or by considering that the mass density in the universe is close to zero. But accurate observations of the movements of the planets of the solar system refuted these assumptions. The paradox remained in force.

Not a single physicist today disputes the special theory of relativity, and only a few dispute the basic tenets of the general theory of relativity. True, the general theory of relativity leaves many important problems unresolved. There is also no doubt that observations and experiments supporting this theory are few and not always convincing. But even if there were no evidence at all, general relativity would still be extremely attractive because of the great simplifications it introduces into physics.

Simplifications? It may seem strange to use this word in relation to a theory that uses mathematics so advanced that someone once said that no more than twelve people in the whole world could understand it (incidentally, this number was clearly underestimated even at the time when This opinion was generally accepted).

The mathematical apparatus of the theory of relativity is indeed complex, but this complexity is compensated by the extraordinary simplification of the overall picture. For example, reducing gravity and inertia to the same phenomenon is enough to make the general theory of relativity the most fruitful direction in forming a view of the world.

Einstein expressed this idea in 1921 when he lectured on relativity at Princeton University: “ The ability to explain the numerical equality of inertia and gravity by the unity of their nature gives the general theory of relativity, in my opinion, such advantages over the concepts of classical mechanics that, in comparison, all the difficulties encountered here should be considered small...»

In addition, the theory of relativity has what mathematicians like to call “elegance.” This is a kind of artistic work. “Every lover of beauty,” Lorenz once said, “must wish that it turns out to be correct.”

In this chapter, the firmly established aspects of the theory of relativity will be set aside and the reader will be plunged into an area of ​​intense debate, an area where viewpoints are little more than conjectures to be accepted or rejected on the basis of scientific evidence.

What is the Universe as a whole? We know that the Earth is the third planet from the Sun in a system of nine planets and that the Sun is one of the approximately one hundred billion stars that make up our Galaxy. We know that in the region of space that can be probed by the most powerful telescopes, there are other galaxies scattered about, the number of which must also number in the billions. Does this continue indefinitely?

Is the number of galaxies infinite? Or does space still have finite dimensions? (Perhaps we should say “our space”, because if our space is limited, then who is to say that there are not other limited spaces?)

Astronomers are working hard to answer these questions. They construct so-called models of the Universe - imaginary pictures of the world, if it is considered as a whole. In the early nineteenth century, many astronomers assumed that the universe was limitless and contained an infinite number of suns. The space was considered Euclidean. Direct showers went off to infinity in all directions. If a spaceship were to set out in any direction and move in a straight line, its journey would last forever, and it would never reach the border. This view dates back to the ancient Greeks. They liked to say that if a warrior threw his spear further and further into space, he would never be able to reach the end; If such an end was imagined, then the warrior could stand there and throw the spear even further!

There is one important objection to this view. The German astronomer Heinrich Olbers noted in 1826 that if the number of suns was infinite and these suns were randomly distributed in space, then a straight line drawn from the Earth in any direction would eventually pass through some star. This would mean that the entire night sky would have been one continuous surface, emitting blinding starlight. We know this is not true. Some explanation for the darkness of the night sky must be invented to explain what is now called Albers' paradox. Most astronomers of the late nineteenth and early twentieth centuries believed that the number of suns was limited. Our galaxy, they argued, contains all the suns there are. What's outside the galaxy? Nothing! (It was only in the mid-twenties of this century that irrefutable evidence emerged that there were millions of galaxies at enormous distances from ours.) Other astronomers assumed that light from distant stars could be absorbed by clusters of interstellar dust.

The most ingenious explanation was given by the Swedish mathematician W. K. Charlier. Galaxies, he said, are grouped into associations, associations into super-associations, super-associations into super-super-associations, and so on ad infinitum. At each stage of unification, the distances between groups grow faster than the sizes of the groups. If this is correct, then the further a straight line continues from our galaxy, the less likely it is that it will encounter another galaxy. At the same time, this hierarchy of associations is infinite, so we can still say that the Universe contains an infinite number of stars. There is nothing wrong with Charlier's explanation of the Albers paradox, except that there is the following simpler explanation.

The first model of the Universe, based on the theory of relativity, was proposed by Einstein himself in a paper published in 1917. It was an elegant and beautiful model, although Einstein was later forced to abandon it. It was already explained above that gravitational fields are curvatures of the space-time structure produced by the presence of large masses of matter. Inside each galaxy, therefore, there are many similar twists and bends of space-time. What about the vast regions of empty space between galaxies? One point of view is that the greater the distance from galaxies, the flatter (more Euclidean) space becomes. If the Universe were free of all matter, then space would be completely flat; some, however, believe that in this case it would be meaningless to say that it has any structure at all. In both cases, the Universe of space-time extends unlimitedly in all directions.

Einstein made one tempting counter-offer. Suppose, he said, that the amount of matter in the universe is large enough to provide an overall positive curvature. Space would then close on itself in all directions. This cannot be fully understood without delving into four-dimensional non-Euclidean geometry, but the meaning can be grasped quite easily using a two-dimensional model. Let's imagine a flat country called Ploskovia, where two-dimensional creatures live. They consider their country to be a Euclidean plane that extends limitlessly in all directions. True, the suns of Ploskovia cause various bulges to appear on this plane, but these are local bulges that do not affect the overall smoothness. There is, however, another possibility that astronomers in this country can imagine. Perhaps each local convexity produces a slight curvature of the entire plane in such a way that the total action of all the suns will lead to the deformation of this plane into something similar to the surface of a lumpy sphere. Such a surface would nevertheless be limitless in the sense that you could move in any direction forever and never reach the boundary. A warrior of Ploskovia could not find a place beyond which he would have nowhere to throw his flat spear. However, the surface of the country would be finite. A traveler traveling in a "straight line" for long enough would eventually arrive back where he started.

Mathematicians say that such a surface is “closed.” It is, of course, not limitless. Like infinite Euclidean space, its center is everywhere, the periphery does not exist. This “closedness,” a topological property of such a surface, can be easily verified by the inhabitants of this country. One criterion has already been mentioned: movement around the sphere in all directions. Another way to check would be to paint this surface. If an inhabitant of this country, starting from a certain place, began to draw larger and larger circles, he would eventually enclose himself inside a spot on the opposite side of the sphere. However, if this sphere is large and the inhabitants occupy a small part of it, they will not be able to perform such topological tests.

Einstein proposed that our space is the three-dimensional “surface” of a huge hypersphere (four-dimensional sphere). Time in his model remains uncurved; it is a direct coordinate stretching back infinitely into the past and extending infinitely forward into the future. If this model is thought of as a four-dimensional space-time structure, it resembles a hypercylinder more than a hypersphere. For this reason, such a model is usually called the “cylindrical universe” model. At any given time, we see space as a kind of three-dimensional cross section of a hypercylinder. Each cross section represents the surface of a hypersphere.

Our Galaxy occupies only a small part of this surface, so it is not yet possible to perform a topological experiment that would prove its closedness. But there is a fundamental possibility of proving closure. By placing a sufficiently powerful telescope in one direction, you can focus it on a particular galaxy, and then, turning the telescope in the opposite direction, see the far side of that same galaxy. If there were spaceships with a speed close to the speed of light, they could circle the Universe, moving in any direction in the straightest line possible.

The Universe cannot be “colored” in the literal sense of the word, but essentially the same thing can be done by making spherical maps of the Universe of larger and larger sizes. If the cartographer does this long enough, he may find that he is inside the sphere he is mapping. This sphere will become smaller and smaller as he continues his occupation, like the circle that becomes smaller when a Ploskovian encloses himself within a spot.

In some respects, Einstein's non-Euclidean model is simpler than the classical model, in which space is not curved. It is simpler in the same sense in which a circle can be said to be simpler than a straight line. A straight line extends to infinity in both directions, and infinity in mathematics is a very difficult thing! The convenience of a circle is that it is limited. It has no ends, no one has to worry about what will happen to this line in infinity. In a neat Einsteinian Universe, no one has to worry about all the loose ends at infinity, what cosmologists like to call “boundary conditions.” In Einstein's cozy universe there are no boundary problems because it has no boundaries.

Other cosmological models, fully consistent with general relativity, were discussed in the twenties. Some of them have properties even more unusual than Einstein's cylindrical Universe. Dutch astronomer Billem de Sitter developed a model of a closed, limited Universe in which time is curved in the same way as space. The further you look through de Sitter space, the slower the clock appears to move. If you look far enough, you can see areas where time has completely stopped, “like at a tea party at the madman Shlyapochkin’s,” Eddington writes, “where it is always six o’clock in the evening.”

“There is no need to think that there is some kind of boundary,” explains Bertrand Russell in “The ABCs of Relativity.” “People living in the country, which our observer considers the country of lotophages, live in exactly the same hustle and bustle as the observer himself, and it seems to them that he himself is frozen in eternal stillness. In fact, you would never know about this land of lotivores, since it would take an infinitely long time for the light to reach you from it. You could find out about places located not far from it, but it itself would always remain behind the horizon.” Of course, if you were to travel to this area in a spaceship, keeping it under constant observation with a telescope, you would see that the passage of time there slowly accelerates as you approach it. When you arrive there, everything will move at normal speed. The land of the lot eaters will now be on the edge of a new horizon.

Have you noticed that when a plane flies low above you and takes off sharply, the pitch of the sound from its engines immediately decreases slightly? This is called the Doppler effect, named after the Austrian physicist Christian Johann Doppler, who discovered the effect in the mid-nineteenth century. It's easy to explain. When a plane approaches, the sound waves from its engines vibrate your eardrum more frequently than they would if the plane were stationary. This increases the pitch of the sound. As the plane moves away, the shocks your ears feel from the sound vibrations are less frequent. The sound gets lower.

Absolutely the same thing happens when a light source moves quickly towards or away from you. In this case, the speed of light (which is always constant), but not its wavelength, should remain unchanged. If you and a light source move towards each other, the Doppler effect shortens the light's wavelength, shifting the color toward the violet end of the spectrum. If you and the light source move away from each other, the Doppler effect produces a similar shift toward the red end of the spectrum.

At one of his lectures, Georgy Gamow told a story (no doubt anecdotal) about the Doppler effect, which is too good not to be cited here. This seems to have happened to the famous American physicist from Johns Hopkins University, Robert Wood, who was detained in Baltimore for running a red light. In front of the judge, Wood brilliantly explained, using the Doppler effect, that his high speed had caused the red light to shift to the violet end of the spectrum, causing him to perceive it as green. The judge was inclined to acquit Wood, but one of Wood's students, whom Wood had recently failed, happened to be at the trial. He quickly calculated the speed required for the traffic light to turn from red to green. The judge threw out the original charge and fined Wood for speeding.

Doppler thought that the effect he discovered explained the apparent color of distant stars: reddish stars should move away from the Earth, bluish stars - towards the Earth. As it turned out, this was not the case (these colors were explained by other reasons); in the twenties of our century it was discovered that the light from distant galaxies exhibits a clear red shift, which cannot be explained convincingly except by assuming that these galaxies are moving from the Earth. Moreover, this displacement increases on average in proportion to the distance from the galaxy to the Earth. If galaxy A is twice as far away as galaxy B, then the redshift from A is approximately twice the redshift from B. According to the English astronomer Fred Hoyle, the redshift for the association of galaxies in the constellation Hydra indicates that this the association is moving away from the Earth at an enormous speed of approximately 61,000 km/sec.

Various attempts have been made to explain the red shift by some other method than the Doppler effect. According to the theory of “light fatigue”, the longer light travels, the lower its oscillation frequency. (This is a perfect example of a hypothesis ad hoc, i.e., a hypothesis associated only with this particular phenomenon, since there is no other evidence in its favor.) Another explanation is that the passage of light through cosmic dust leads to the appearance of a displacement. In de Sitter's model, this displacement clearly follows from the curvature of time.

But the simplest explanation, the one that fits best with other known facts, is that the redshift does indicate the real movement of galaxies. Based on this assumption, a new series of "expanding universe" models were soon developed.

However, this expansion does not mean that the galaxies themselves are expanding or that (as is now believed) the distances between galaxies in galaxy associations are increasing. Apparently, this expansion entails an increase in the distances between associations. Imagine a giant ball of dough interspersed with several hundred raisins. Each raisin represents an association of galaxies. If this dough is placed in the oven, it expands evenly in all directions, but the size of the raisins remains the same. The distance between the raisins increases. None of the highlights can be called the center of expansion. From the point of view of any single raisin, all other raisins appear to move away from it.

The greater the distance to the raisin, the greater the apparent speed of its removal.

Einstein's model of the Universe is static. This is because he developed this model before astronomers discovered the expansion of the Universe. To prevent the contraction of his Universe by gravitational forces and its death, Einstein was forced to assume in his model that there was another force (he introduced it into the model using the so-called “cosmological constant”), the role of which is to repel and hold stars at a certain distance from each other.

Calculations performed later showed that Einstein's model was unstable, like a coin standing on its edge. The slightest push will cause it to fall either on the front or on the back side, the first corresponding to the expanding, the second to the contracting Universe. The discovery of the redshift showed that the Universe is in any case not contracting; cosmologists turned to models of an expanding universe.

All kinds of models of the expanding Universe were constructed. Soviet scientist Alexander Friedman and Belgian abbot Georges Lemaitre developed the two most famous models. In some of these models, space is assumed to be closed (positive curvature), in others - open (negative curvature), in others, the question of whether space is closed remains open.

One of the models was proposed by Eddington, who described it in a fascinating book, The Expanding Universe. His model is essentially very similar to Einstein's; it is closed, like a huge four-dimensional ball, and expands uniformly across all three of its spatial dimensions. At present, however, astronomers are not sure that space is closed on itself. Apparently, the density of matter in space is not sufficient to lead to positive curvature. Astronomers favor an open or infinite Universe with an overall negative curvature, resembling the surface of a saddle.

The reader should not think that if the surface of a sphere has positive curvature, then from the inside this surface will have negative curvature. The curvature of a spherical surface is positive regardless of which side you look at it from - from the outside or from the inside. The negative curvature of the seat surface is caused by the fact that at any point this surface is curved differently. It is concave if you move your hand along it from back to front, and convex if you move your hand from one edge to the other. One curvature is expressed as a positive number, while the other is expressed as a negative number. To get the curvature of this surface at a given point, these two numbers must be multiplied. If this number is negative at all points, as it should be when the surface is curved differently at any point, then this surface is said to have negative curvature. The surface surrounding a hole in a torus (donut) is another well-known example of a surface of negative curvature. Of course, such surfaces are only rough models of three-dimensional space of negative curvature.

Perhaps, with the advent of more powerful telescopes, it will be possible to resolve the question of whether the curvature of the Universe is positive, negative or equal to zero. The telescope allows you to see galaxies only in a certain spherical volume. If galaxies are distributed randomly and if space is Euclidean (zero curvature), the number of galaxies inside such a sphere should always be proportional to the cube of the radius of that sphere. In other words, if you build a telescope that can look twice as far as any previous telescope, then the number of visible galaxies should increase with n before 8n. If this jump turns out to be smaller, it will mean that the curvature of the Universe is positive; if it is larger, it will be negative.

You might think that it should be the other way around, but consider the case of two-dimensional surfaces with positive and negative curvature. Let us assume that a circle is cut from a flat sheet of rubber.

Raisins are glued onto it at distances of half a centimeter from one another. In order to give this rubber the shape of a spherical surface, it must be compressed, and many of the raisins will come together. In other words, if on a spherical surface the raisins must remain half a centimeter apart from each other, then fewer raisins will be needed. If rubber is applied to the surface of the saddle, then the raisins will move apart to greater distances, i.e., in order to maintain half a centimeter distance between the raisins on the surface of the saddle, more raisins will be required. The moral of all this can be put in a humorous way: when you buy a bottle of beer, be sure to tell the seller that you want a bottle containing space curved negatively rather than positively?

Models of the expanding Universe do not require Einstein's cosmological constant, which leads to the hypothetical repulsion of stars.

(Einstein later considered the concept of a cosmological constant to be the biggest mistake he had ever made.) With the advent of these models, the issue of Albers' paradox about the brightness of the night sky immediately became clearer. Einstein's static model was of little help in this regard. True, it contains only a finite number of suns, but due to the closed space in the model, the light from these suns is forced to forever go around the Universe, bending its trajectory in accordance with the local curvatures of space-time. The result is that the night sky is as brightly illuminated as it would be if there were an infinite number of suns, unless we assume that the Universe is so young that light could only make a limited number of circular orbits.

The concept of an expanding universe eliminates this paradox very simply. If distant galaxies move away from Earth at speeds proportional to their distances, then the total amount of light reaching Earth should decrease. If any galaxy is far enough away, its speed can exceed the speed of light, then the light from it will never reach us at all. Now many astronomers seriously believe that if the Universe were not expanding, then there would be literally no difference between night and day.

The fact that the speed of distant galaxies relative to the Earth can exceed the speed of light would seem to be a violation of the principle that no material body can move faster than light. But, as we saw in Chap. 4, this provision is valid only under conditions that meet the requirements of the special theory of relativity. In general relativity, it should be rephrased as follows: no signals can be transmitted faster than light. But an important question still remains controversial: whether distant galaxies can actually overcome the light barrier and, becoming invisible, disappear forever from the field of view of a person, even if he has the most powerful telescopes imaginable. Some experts believe that the speed of light really is the limit and that the most distant galaxies will simply become dimmer, without ever becoming completely invisible (provided, of course, that people have sensitive enough instruments to observe them).

Old galaxies, as someone once noted, never die. They just gradually disappear. It is important to understand, however, that no galaxy disappears in the sense that its matter disappears from the Universe. It simply reaches such a speed that it becomes impossible or almost impossible to detect it with telescopes on Earth. A vanishing galaxy continues to be visible from all galaxies closer to it. Each galaxy has an “optical horizon,” a spherical boundary beyond which its telescopes cannot penetrate. These spherical horizons do not coincide for any two galaxies. Astronomers have calculated that the point at which galaxies will begin to disappear from our “field of view” is approximately twice as far as the range of any modern optical telescope. If this assumption is correct, then about one-eighth of all the galaxies that will someday be observable are now visible.

If the Universe is expanding (it doesn't matter whether space is flat, open or closed), then this tricky question arises. What was the Universe like before? There are two different ways to answer this question, two modern models of the Universe. Both models are discussed in the next chapter.

Notes:

Book character Lewis Kzrrol"Alice in Wonderland". - Note translation.

A land of plenty and idleness, see The Odyssey. - Note translation.

Formulated in the form of models of the origin and development of the Universe. This is due to the fact that in cosmology it is impossible to carry out reproducible experiments and derive any laws from them, as is done in other natural sciences. In addition, each cosmic phenomenon is unique. Therefore, cosmology operates with models. As new knowledge about the surrounding world accumulates, new cosmological models are refined and developed.

Classical cosmological model

Advances in cosmology and cosmogony in the 18th-19th centuries. culminated in the creation of a classical polycentric picture of the world, which became the initial stage in the development of scientific cosmology.

This model is quite simple and understandable.

1. The Universe is considered infinite in space and time, in other words, eternal.

2. The basic law governing the movement and development of celestial bodies is the law of universal gravitation.

3. Space is in no way connected with the bodies located in it, playing the passive role of a container for these bodies.

4. Time also does not depend on matter, being the universal duration of all natural phenomena and bodies.

5. If all bodies suddenly disappeared, space and time would remain unchanged. The number of stars, planets and star systems in the Universe is infinitely large. Each celestial body goes through a long life path. The dead, or rather extinguished, stars are being replaced by new, young luminaries.

Although the details of the origin and death of celestial bodies remained unclear, basically this model seemed harmonious and logically consistent. In this form, the classical polycentric model existed in science until the beginning of the 20th century.

However, this model of the universe had several flaws.

The law of universal gravitation explained the centripetal acceleration of the planets, but did not say where the desire of the planets, as well as any material bodies, to move uniformly and rectilinearly came from. To explain the inertial motion, it was necessary to assume the existence of a divine “first push” in it, which set all material bodies in motion. In addition, God's intervention was also allowed to correct the orbits of cosmic bodies.

The appearance within the framework of the classical model of the so-called cosmological paradoxes - photometric, gravitational, thermodynamic. The desire to resolve them also prompted scientists to search for new consistent models.

Thus, the classical polycentric model of the Universe was only partially scientific in nature; it could not provide a scientific explanation of the origin of the Universe and therefore was replaced by other models.

Relativistic model of the Universe

A new model of the Universe was created in 1917 by A. Einstein. It was based on the relativistic theory of gravity - the general theory of relativity. Einstein abandoned the postulates of absoluteness and infinity of space and time, but retained the principle of stationarity, the immutability of the Universe in time and its finitude in space. The properties of the Universe, according to Einstein, are determined by the distribution of gravitational masses in it. The Universe is limitless, but at the same time closed in space. According to this model, space is homogeneous and isotropic, i.e. has the same properties in all directions, matter is distributed evenly in it, time is infinite, and its flow does not affect the properties of the Universe. Based on his calculations, Einstein concluded that world space is a four-dimensional sphere.

At the same time, one should not imagine this model of the Universe in the form of an ordinary sphere. Spherical space is a sphere, but a four-dimensional sphere that cannot be visually represented. By analogy, we can conclude that the volume of such space is finite, just as the surface of any ball is finite; it can be expressed in a finite number of square centimeters. The surface of any four-dimensional sphere is also expressed in a finite number of cubic meters. Such a spherical space has no boundaries, and in this sense it is limitless. Flying in such space in one direction, we will eventually return to the starting point. But at the same time, a fly crawling along the surface of the ball will nowhere find boundaries or barriers that prohibit it from moving in any chosen direction. In this sense, the surface of any ball is limitless, although finite, i.e. limitlessness and infinity are different concepts.

So, from Einstein’s calculations it followed that our world is a four-dimensional sphere. The volume of such a Universe can be expressed, although very large, but still by a finite number of cubic meters. In principle, you can fly around the entire closed Universe, moving all the time in one direction. Such an imaginary journey is similar to earthly trips around the world. But the Universe, finite in volume, is at the same time limitless, just as the surface of any sphere has no boundaries. Einstein's Universe contains, although a large, but still finite number of stars and stellar systems, and therefore the photometric and gravitational paradoxes are not applicable to it. At the same time, the specter of heat death looms over Einstein’s Universe. Such a Universe, finite in space, inevitably comes to its end in time. Eternity is not inherent in it.

Thus, despite the novelty and even revolutionary nature of the ideas, Einstein in his cosmological theory was guided by the usual classical ideological attitude of the static nature of the world. He was more attracted to a harmonious and stable world than to a contradictory and unstable world.

Expanding Universe Model

Einstein's model of the Universe became the first cosmological model based on the conclusions of the general theory of relativity. This is due to the fact that it is gravity that determines the interaction of masses over large distances. Therefore, the theoretical core of modern cosmology is the theory of gravity - the general theory of relativity. Einstein assumed in his cosmological model the presence of a certain hypothetical repulsive force, which was supposed to ensure the stationarity and immutability of the Universe. However, the subsequent development of natural science made significant adjustments to this idea.

Five years later, in 1922, the Soviet physicist and mathematician A. Friedman, based on rigorous calculations, showed that Einstein’s Universe cannot be stationary and unchanging. At the same time, Friedman relied on the cosmological principle he formulated, which is based on two assumptions: the isotropy and homogeneity of the Universe. The isotropy of the Universe is understood as the absence of distinguished directions, the sameness of the Universe in all directions. The homogeneity of the Universe is understood as the sameness of all points of the Universe: we can conduct observations at any of them and everywhere we will see an isotropic Universe.

Friedman, based on the cosmological principle, proved that Einstein’s equations have other, non-stationary solutions, according to which the Universe can either expand or contract. At the same time, we were talking about expanding the space itself, i.e. about the increase in all the distances in the world. Friedman's universe resembled an inflating soap bubble, with both its radius and surface area continuously increasing.

Initially, the model of the expanding Universe was hypothetical and did not have empirical confirmation. However, in 1929, the American astronomer E. Hubble discovered the effect of “red shift” of spectral lines (shift of lines towards the red end of the spectrum). This was interpreted as a consequence of the Doppler effect - a change in oscillation frequency or wavelength due to the movement of the wave source and observer relative to each other. "Redshift" was explained as a consequence of galaxies moving away from each other at a rate that increases with distance. According to recent measurements, the increase in expansion rate is approximately 55 km/s for every million parsecs.

As a result of his observations, Hubble substantiated the idea that the Universe is a world of galaxies, that our Galaxy is not the only one in it, that there are many galaxies separated by enormous distances. At the same time, Hubble came to the conclusion that intergalactic distances do not remain constant, but increase. Thus, the concept of an expanding Universe appeared in natural science.

What kind of future awaits our Universe? Friedman proposed three models for the development of the Universe.

In the first model, the Universe expands slowly so that due to the gravitational attraction between different galaxies, the expansion of the Universe slows down and eventually stops. After this, the Universe began to shrink. In this model, space bends, closing on itself, forming a sphere.

In the second model, the Universe expanded infinitely, and space was curved like the surface of a saddle and at the same time infinite.

In Friedman's third model, space is flat and also infinite.

Which of these three options follows the evolution of the Universe depends on the ratio of gravitational energy to the kinetic energy of the expanding matter.

If the kinetic energy of the expansion of matter prevails over the gravitational energy that prevents the expansion, then gravitational forces will not stop the expansion of galaxies, and the expansion of the Universe will be irreversible. This version of the dynamic model of the Universe is called the open Universe.

If gravitational interaction predominates, then the rate of expansion will slow down over time until it stops completely, after which the compression of matter will begin until the Universe returns to its original state of singularity (a point volume with an infinitely high density). This version of the model is called the oscillating, or closed, Universe.

In the limiting case, when the gravitational forces are exactly equal to the energy of the expansion of matter, the expansion will not stop, but its speed will tend to zero over time. Several tens of billions of years after the expansion of the Universe begins, a state will occur that can be called quasi-stationary. Theoretically, a pulsation of the Universe is also possible.

When E. Hubble showed that distant galaxies are moving away from each other at an ever-increasing speed, an unambiguous conclusion was made that our Universe is expanding. But an expanding Universe is a changing Universe, a world with all its history, having a beginning and an end. The Hubble constant allows us to estimate the time during which the process of expansion of the Universe continues. It turns out that it is no less than 10 billion and no more than 19 billion years. The most probable lifetime of the expanding Universe is considered to be 15 billion years. This is the approximate age of our Universe.

Scientist's opinion

There are other, even the most exotic, cosmological (theoretical) models based on the general theory of relativity. Here's what Cambridge University mathematics professor John Barrow says about cosmological models:

“The natural task of cosmology is to understand as best as possible the origin, history and structure of our own Universe. At the same time, general relativity, even without borrowing from other branches of physics, makes it possible to calculate an almost unlimited number of very different cosmological models. Of course, their selection is made on the basis of astronomical and astrophysical data, with the help of which it is possible not only to test various models for compliance with reality, but also to decide which of their components can be combined for the most adequate description of our world. This is how the current standard model of the Universe arose. So even for this reason alone, the historical diversity of cosmological models has been very useful.

But it's not only that. Many models were created when astronomers had not yet accumulated the wealth of data they have today. For example, the true degree of isotropy of the Universe was established thanks to space equipment only during the last two decades. It is clear that in the past space modelers had many fewer empirical constraints. In addition, it is possible that even models that are exotic by today’s standards will be useful in the future for describing those parts of the Universe that are not yet accessible to observation. And finally, the invention of cosmological models may simply stimulate the desire to find unknown solutions to the general relativity equations, and this is also a powerful incentive. In general, the abundance of such models is understandable and justified.

The recent union of cosmology and particle physics is justified in the same way. Its representatives consider the earliest stage of the life of the Universe as a natural laboratory, ideally suited for studying the basic symmetries of our world, which determine the laws of fundamental interactions. This union has already laid the foundation for a whole fan of fundamentally new and very deep cosmological models. There is no doubt that in the future it will bring no less fruitful results.”

Did you know that the Universe we observe has fairly definite boundaries? We are used to associating the Universe with something infinite and incomprehensible. However, modern science, when asked about the “infinity” of the Universe, offers a completely different answer to such an “obvious” question.

According to modern concepts, the size of the observable Universe is approximately 45.7 billion light years (or 14.6 gigaparsecs). But what do these numbers mean?

The first question that comes to the mind of an ordinary person is how can the Universe not be infinite? It would seem that it is indisputable that the container of all that exists around us should have no boundaries. If these boundaries exist, what exactly are they?

Let's say some astronaut reaches the boundaries of the Universe. What will he see in front of him? A solid wall? Fire barrier? And what is behind it - emptiness? Another Universe? But can emptiness or another Universe mean that we are on the border of the universe? After all, this does not mean that there is “nothing” there. Emptiness and another Universe are also “something”. But the Universe is something that contains absolutely everything “something”.

We arrive at an absolute contradiction. It turns out that the boundary of the Universe must hide from us something that should not exist. Or the boundary of the Universe should fence off “everything” from “something”, but this “something” should also be part of “everything”. In general, complete absurdity. Then how can scientists declare the limiting size, mass and even age of our Universe? These values, although unimaginably large, are still finite. Does science argue with the obvious? To understand this, let's first trace how people came to our modern understanding of the Universe.

Expanding the boundaries

Since time immemorial, people have been interested in what the world around them is like. There is no need to give examples of the three pillars and other attempts of the ancients to explain the universe. As a rule, in the end it all came down to the fact that the basis of all things is the earth's surface. Even in the times of antiquity and the Middle Ages, when astronomers had extensive knowledge of the laws of planetary movement along the “fixed” celestial sphere, the Earth remained the center of the Universe.

Naturally, even in Ancient Greece there were those who believed that the Earth revolves around the Sun. There were those who spoke about the many worlds and the infinity of the Universe. But constructive justifications for these theories arose only at the turn of the scientific revolution.

In the 16th century, Polish astronomer Nicolaus Copernicus made the first major breakthrough in knowledge of the Universe. He firmly proved that the Earth is only one of the planets revolving around the Sun. Such a system greatly simplified the explanation of such a complex and intricate movement of planets in the celestial sphere. In the case of a stationary Earth, astronomers had to come up with all sorts of clever theories to explain this behavior of the planets. On the other hand, if the Earth is accepted as moving, then an explanation for such intricate movements comes naturally. Thus, a new paradigm called “heliocentrism” took hold in astronomy.

Many Suns

However, even after this, astronomers continued to limit the Universe to the “sphere of fixed stars.” Until the 19th century, they were unable to estimate the distance to the stars. For several centuries, astronomers have tried to no avail to detect deviations in the position of stars relative to the Earth’s orbital movement (annual parallaxes). The instruments of those times did not allow such precise measurements.

Finally, in 1837, the Russian-German astronomer Vasily Struve measured parallax. This marked a new step in understanding the scale of space. Now scientists could safely say that the stars are distant similarities to the Sun. And our luminary is no longer the center of everything, but an equal “resident” of an endless star cluster.

Astronomers have come even closer to understanding the scale of the Universe, because the distances to the stars turned out to be truly monstrous. Even the size of the planets’ orbits seemed insignificant in comparison. Next it was necessary to understand how the stars are concentrated in .

Many Milky Ways

The famous philosopher Immanuel Kant anticipated the foundations of the modern understanding of the large-scale structure of the Universe back in 1755. He hypothesized that the Milky Way is a huge rotating star cluster. In turn, many of the observed nebulae are also more distant “milky ways” - galaxies. Despite this, until the 20th century, astronomers believed that all nebulae are sources of star formation and are part of the Milky Way.

The situation changed when astronomers learned to measure distances between galaxies using . The absolute luminosity of stars of this type strictly depends on the period of their variability. By comparing their absolute luminosity with the visible one, it is possible to determine the distance to them with high accuracy. This method was developed in the early 20th century by Einar Hertzschrung and Harlow Scelpi. Thanks to him, the Soviet astronomer Ernst Epic in 1922 determined the distance to Andromeda, which turned out to be an order of magnitude greater than the size of the Milky Way.

Edwin Hubble continued Epic's initiative. By measuring the brightness of Cepheids in other galaxies, he measured their distance and compared it with the redshift in their spectra. So in 1929 he developed his famous law. His work definitively disproved the established view that the Milky Way is the edge of the Universe. Now it was one of many galaxies that had once been considered part of it. Kant's hypothesis was confirmed almost two centuries after its development.

Subsequently, the connection discovered by Hubble between the distance of a galaxy from an observer relative to the speed of its removal from him, made it possible to draw a complete picture of the large-scale structure of the Universe. It turned out that the galaxies were only an insignificant part of it. They connected into clusters, clusters into superclusters. In turn, superclusters form the largest known structures in the Universe—threads and walls. These structures, adjacent to huge supervoids (), constitute the large-scale structure of the currently known Universe.

Apparent infinity

It follows from the above that in just a few centuries, science has gradually fluttered from geocentrism to a modern understanding of the Universe. However, this does not answer why we limit the Universe today. After all, until now we were talking only about the scale of space, and not about its very nature.

The first who decided to justify the infinity of the Universe was Isaac Newton. Having discovered the law of universal gravitation, he believed that if space were finite, all its bodies would sooner or later merge into a single whole. Before him, if anyone expressed the idea of ​​​​the infinity of the Universe, it was exclusively in a philosophical vein. Without any scientific basis. An example of this is Giordano Bruno. By the way, like Kant, he was many centuries ahead of science. He was the first to declare that stars are distant suns, and planets also revolve around them.

It would seem that the very fact of infinity is quite justified and obvious, but the turning points of science of the 20th century shook this “truth”.

Stationary Universe

The first significant step towards developing a modern model of the Universe was taken by Albert Einstein. The famous physicist introduced his model of a stationary Universe in 1917. This model was based on the general theory of relativity, which he had developed a year earlier. According to his model, the Universe is infinite in time and finite in space. But, as noted earlier, according to Newton, a Universe with a finite size must collapse. To do this, Einstein introduced a cosmological constant, which compensated for the gravitational attraction of distant objects.

No matter how paradoxical it may sound, Einstein did not limit the very finitude of the Universe. In his opinion, the Universe is a closed shell of a hypersphere. An analogy is the surface of an ordinary three-dimensional sphere, for example, a globe or the Earth. No matter how much a traveler travels across the Earth, he will never reach its edge. However, this does not mean that the Earth is infinite. The traveler will simply return to the place from which he began his journey.

On the surface of the hypersphere

In the same way, a space wanderer, traversing Einstein’s Universe on a starship, can return back to Earth. Only this time the wanderer will move not along the two-dimensional surface of a sphere, but along the three-dimensional surface of a hypersphere. This means that the Universe has a finite volume, and therefore a finite number of stars and mass. However, the Universe has neither boundaries nor any center.

Einstein came to these conclusions by connecting space, time and gravity in his famous theory. Before him, these concepts were considered separate, which is why the space of the Universe was purely Euclidean. Einstein proved that gravity itself is a curvature of space-time. This radically changed early ideas about the nature of the Universe, based on classical Newtonian mechanics and Euclidean geometry.

Expanding Universe

Even the discoverer of the “new Universe” himself was not a stranger to delusions. Although Einstein limited the Universe in space, he continued to consider it static. According to his model, the Universe was and remains eternal, and its size always remains the same. In 1922, Soviet physicist Alexander Friedman significantly expanded this model. According to his calculations, the Universe is not static at all. It can expand or contract over time. It is noteworthy that Friedman came to such a model based on the same theory of relativity. He managed to apply this theory more correctly, bypassing the cosmological constant.

Albert Einstein did not immediately accept this “amendment.” This new model came to the aid of the previously mentioned Hubble discovery. The recession of galaxies indisputably proved the fact of the expansion of the Universe. So Einstein had to admit his mistake. Now the Universe had a certain age, which strictly depends on the Hubble constant, which characterizes the rate of its expansion.

Further development of cosmology

As scientists tried to solve this question, many other important components of the Universe were discovered and various models of it were developed. So in 1948, George Gamow introduced the “hot Universe” hypothesis, which would later turn into the big bang theory. The discovery in 1965 confirmed his suspicions. Now astronomers could observe the light that came from the moment when the Universe became transparent.

Dark matter, predicted in 1932 by Fritz Zwicky, was confirmed in 1975. Dark matter actually explains the very existence of galaxies, galaxy clusters and the Universal structure itself as a whole. This is how scientists learned that most of the mass of the Universe is completely invisible.

Finally, in 1998, during a study of the distance to, it was discovered that the Universe is expanding at an accelerating rate. This latest turning point in science gave birth to our modern understanding of the nature of the universe. The cosmological coefficient, introduced by Einstein and refuted by Friedman, again found its place in the model of the Universe. The presence of a cosmological coefficient (cosmological constant) explains its accelerated expansion. To explain the presence of a cosmological constant, the concept of a hypothetical field containing most of the mass of the Universe was introduced.

Modern understanding of the size of the observable Universe

The modern model of the Universe is also called the ΛCDM model. The letter "Λ" means the presence of a cosmological constant, which explains the accelerated expansion of the Universe. "CDM" means that the Universe is filled with cold dark matter. Recent studies indicate that the Hubble constant is about 71 (km/s)/Mpc, which corresponds to the age of the Universe 13.75 billion years. Knowing the age of the Universe, we can estimate the size of its observable region.

According to the theory of relativity, information about any object cannot reach an observer at a speed greater than the speed of light (299,792,458 m/s). It turns out that the observer sees not just an object, but its past. The farther an object is from him, the more distant the past he looks. For example, looking at the Moon, we see as it was a little more than a second ago, the Sun - more than eight minutes ago, the nearest stars - years, galaxies - millions of years ago, etc. In Einstein’s stationary model, the Universe has no age limit, which means its observable region is also not limited by anything. The observer, armed with increasingly sophisticated astronomical instruments, will observe increasingly distant and ancient objects.

We have a different picture with the modern model of the Universe. According to it, the Universe has an age, and therefore a limit of observation. That is, since the birth of the Universe, no photon could have traveled a distance greater than 13.75 billion light years. It turns out that we can say that the observable Universe is limited from the observer to a spherical region with a radius of 13.75 billion light years. However, this is not quite true. We should not forget about the expansion of the space of the Universe. By the time the photon reaches the observer, the object that emitted it will be already 45.7 billion light years away from us. years. This size is the horizon of particles, it is the boundary of the observable Universe.

Over the horizon

So, the size of the observable Universe is divided into two types. Apparent size, also called the Hubble radius (13.75 billion light years). And the real size, called the particle horizon (45.7 billion light years). The important thing is that both of these horizons do not at all characterize the real size of the Universe. Firstly, they depend on the position of the observer in space. Secondly, they change over time. In the case of the ΛCDM model, the particle horizon expands at a speed greater than the Hubble horizon. Modern science does not answer the question of whether this trend will change in the future. But if we assume that the Universe continues to expand with acceleration, then all those objects that we see now will sooner or later disappear from our “field of vision”.

Currently, the most distant light observed by astronomers is the cosmic microwave background radiation. Peering into it, scientists see the Universe as it was 380 thousand years after the Big Bang. At this moment, the Universe cooled down enough that it was able to emit free photons, which are detected today with the help of radio telescopes. At that time, there were no stars or galaxies in the Universe, but only a continuous cloud of hydrogen, helium and an insignificant amount of other elements. From the inhomogeneities observed in this cloud, galaxy clusters will subsequently form. It turns out that precisely those objects that will be formed from inhomogeneities in the cosmic microwave background radiation are located closest to the particle horizon.

True Boundaries

Whether the Universe has true, unobservable boundaries is still a matter of pseudoscientific speculation. One way or another, everyone agrees on the infinity of the Universe, but interprets this infinity in completely different ways. Some consider the Universe to be multidimensional, where our “local” three-dimensional Universe is only one of its layers. Others say that the Universe is fractal - which means that our local Universe may be a particle of another. We should not forget about the various models of the Multiverse with its closed, open, parallel Universes, and wormholes. And there are many, many different versions, the number of which is limited only by human imagination.

But if we turn on cold realism or simply step back from all these hypotheses, then we can assume that our Universe is an infinite homogeneous container of all stars and galaxies. Moreover, at any very distant point, be it billions of gigaparsecs from us, all the conditions will be exactly the same. At this point, the particle horizon and the Hubble sphere will be exactly the same, with the same relict radiation at their edge. There will be the same stars and galaxies around. Interestingly, this does not contradict the expansion of the Universe. After all, it is not just the Universe that is expanding, but its space itself. The fact that at the moment of the Big Bang the Universe arose from one point only means that the infinitely small (practically zero) dimensions that were then have now turned into unimaginably large ones. In the future, we will use precisely this hypothesis in order to clearly understand the scale of the observable Universe.

Visual representation

Various sources provide all sorts of visual models that allow people to understand the scale of the Universe. However, it is not enough for us to realize how big the cosmos is. It is important to imagine how concepts such as the Hubble horizon and the particle horizon actually manifest themselves. To do this, let's imagine our model step by step.

Let's forget that modern science does not know about the “foreign” region of the Universe. Discarding versions of multiverses, the fractal Universe and its other “varieties”, let’s imagine that it is simply infinite. As noted earlier, this does not contradict the expansion of its space. Of course, let's take into account that its Hubble sphere and particle sphere are respectively 13.75 and 45.7 billion light years.

Scale of the Universe

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First, let's try to understand how large the Universal scale is. If you have traveled around our planet, you can well imagine how big the Earth is for us. Now imagine our planet as a grain of buckwheat moving in orbit around a watermelon-Sun the size of half a football field. In this case, Neptune’s orbit will correspond to the size of a small city, the area will correspond to the Moon, and the area of ​​​​the boundary of the influence of the Sun will correspond to Mars. It turns out that our Solar System is as much larger than the Earth as Mars is larger than buckwheat! But this is just the beginning.

Now let’s imagine that this buckwheat will be our system, the size of which is approximately equal to one parsec. Then the Milky Way will be the size of two football stadiums. However, this will not be enough for us. The Milky Way will also have to be reduced to centimeter size. It will somewhat resemble coffee foam wrapped in a whirlpool in the middle of coffee-black intergalactic space. Twenty centimeters from it there is the same spiral “crumb” - the Andromeda Nebula. Around them there will be a swarm of small galaxies of our Local Cluster. The apparent size of our Universe will be 9.2 kilometers. We have come to an understanding of the Universal dimensions.

Inside the universal bubble

However, it is not enough for us to understand the scale itself. It is important to realize the Universe in dynamics. Let's imagine ourselves as giants, for whom the Milky Way has a centimeter diameter. As noted just now, we will find ourselves inside a ball with a radius of 4.57 and a diameter of 9.24 kilometers. Let’s imagine that we are able to float inside this ball, travel, covering entire megaparsecs in a second. What will we see if our Universe is infinite?

Of course, countless galaxies of all kinds will appear before us. Elliptical, spiral, irregular. Some areas will be teeming with them, others will be empty. The main feature will be that visually they will all be motionless while we are motionless. But as soon as we take a step, the galaxies themselves will begin to move. For example, if we are able to discern a microscopic Solar System in the centimeter-long Milky Way, we will be able to observe its development. Moving 600 meters away from our galaxy, we will see the protostar Sun and the protoplanetary disk at the moment of formation. Approaching it, we will see how the Earth appears, life arises and man appears. In the same way, we will see how galaxies change and move as we move away from or approach them.

Consequently, the more distant galaxies we look at, the more ancient they will be for us. So the most distant galaxies will be located further than 1300 meters from us, and at the turn of 1380 meters we will already see relict radiation. True, this distance will be imaginary for us. However, as we get closer to the cosmic microwave background radiation, we will see an interesting picture. Naturally, we will observe how galaxies will form and develop from the initial cloud of hydrogen. When we reach one of these formed galaxies, we will understand that we have covered not 1.375 kilometers at all, but all 4.57.

Zooming out

As a result, we will increase in size even more. Now we can place entire voids and walls in the fist. So we will find ourselves in a rather small bubble from which it is impossible to get out. Not only will the distance to objects at the edge of the bubble increase as they get closer, but the edge itself will shift indefinitely. This is the whole point of the size of the observable Universe.

No matter how big the Universe is, for an observer it will always remain a limited bubble. The observer will always be at the center of this bubble, in fact he is its center. Trying to get to any object at the edge of the bubble, the observer will shift its center. As you approach an object, this object will move further and further from the edge of the bubble and at the same time change. For example, from a shapeless hydrogen cloud it will turn into a full-fledged galaxy or, further, a galactic cluster. In addition, the path to this object will increase as you approach it, since the surrounding space itself will change. Having reached this object, we will only move it from the edge of the bubble to its center. At the edge of the Universe, relict radiation will still flicker.

If we assume that the Universe will continue to expand at an accelerated rate, then being in the center of the bubble and moving time forward by billions, trillions and even higher orders of years, we will notice an even more interesting picture. Although our bubble will also increase in size, its changing components will move away from us even faster, leaving the edge of this bubble, until each particle of the Universe wanders separately in its lonely bubble without the opportunity to interact with other particles.

So, modern science does not have information about the real size of the Universe and whether it has boundaries. But we know for sure that the observable Universe has a visible and true boundary, called respectively the Hubble radius (13.75 billion light years) and the particle radius (45.7 billion light years). These boundaries depend entirely on the observer's position in space and expand over time. If the Hubble radius expands strictly at the speed of light, then the expansion of the particle horizon is accelerated. The question of whether its acceleration of the particle horizon will continue further and whether it will be replaced by compression remains open.

In the beginning, the Universe was an expanding clump of emptiness. Its collapse led to the Big Bang, in the fire-breathing plasma of which the first chemical elements were forged. Then gravity compressed the cooling gas clouds for millions of years. And then the first stars lit up, illuminating a grandiose Universe with trillions of pale galaxies... This picture of the world, supported by the greatest astronomical discoveries of the 20th century, stands on a solid theoretical foundation. But there are specialists who don’t like it. They persistently look for weak points in it, hoping that a different cosmology will replace the current one.

In the early 1920s, St. Petersburg scientist Alexander Friedman, assuming for simplicity that matter uniformly fills all space, found a solution to the equations of general relativity (GTR), which describe the non-stationary expanding Universe. Even Einstein did not take this discovery seriously, believing that the Universe must be eternal and unchanging. To describe such a Universe, he even introduced a special “anti-gravity” lambda term into the general relativity equations. Friedman soon died of typhoid fever, and his decision was forgotten. For example, Edwin Hubble, who worked on the world's largest 100-inch telescope at Mount Wilson Observatory, had not heard anything about these ideas.

By 1929, Hubble had measured the distances to several dozen galaxies and, comparing them with previously obtained spectra, unexpectedly discovered that the farther away a galaxy is, the more redshifted its spectral lines are. The easiest way to explain the red shift was the Doppler effect. But then it turned out that all the galaxies were quickly moving away from us. It was so strange that astronomer Fritz Zwicky put forward a very bold hypothesis of “tired light”, according to which it is not galaxies that are moving away from us, but light quanta during a long journey experiencing some resistance to their movement, gradually losing energy and turning red. Then, of course, they remembered the idea of ​​expanding space, and it turned out that no less strange new observations fit well into this strange forgotten theory. Friedman’s model also benefited from the fact that the origin of the red shift in it looks very similar to the usual Doppler effect: even today, not all astronomers understand that the “scattering” of galaxies in space is not at all the same as the expansion of space itself with “frozen” ones. galaxies into it.

The “tired light” hypothesis quietly faded from the scene by the end of the 1930s, when physicists noted that a photon loses energy only by interacting with other particles, and in this case the direction of its movement necessarily changes at least slightly. So the images of distant galaxies in the “tired light” model should blur, as if in a fog, but they are visible quite clearly. As a result, the Friedmann model of the Universe, an alternative to generally accepted ideas, has recently won everyone’s attention. (However, until the end of his life, in 1953, Hubble himself admitted that the expansion of space could only be an apparent effect.)

Twice alternative standard

But since the Universe is expanding, it means it was denser before. Mentally reversing its evolution, Friedman's student, nuclear physicist Georgi Gamow, concluded that the early Universe was so hot that thermonuclear fusion reactions took place in it. Gamow tried to explain with them the observed prevalence of chemical elements, but he managed to “cook” only a few types of light nuclei in the primary cauldron. It turned out that, in addition to hydrogen, the world should contain 23-25% helium, a hundredth of a percent of deuterium and a billionth of lithium. The theory of the synthesis of heavier elements in stars was later developed with his colleagues by Gamow’s competitor, astrophysicist Fred Hoyle.

In 1948, Gamow also predicted that an observable trace should remain from the hot Universe - cooled microwave radiation with a temperature of several degrees Kelvin, coming from all directions in the sky. Alas, Gamow’s prediction repeated the fate of Friedman’s model: no one was in a hurry to look for its radiation. The theory of a hot Universe seemed too extravagant to carry out expensive experiments to test it. In addition, parallels were seen in it with divine creation, from which many scientists distanced themselves. It ended with Gamow abandoning cosmology and switching to genetics, which was emerging at that time.

In the 1950s, a new version of the theory of a stationary Universe, developed by the same Fred Hoyle together with astrophysicist Thomas Gold and mathematician Hermann Bondi, gained popularity in the 1950s. Under pressure from Hubble's discovery, they accepted the expansion of the Universe, but not its evolution. According to their theory, the expansion of space is accompanied by the spontaneous creation of hydrogen atoms, so that the average density of the Universe remains unchanged. This, of course, is a violation of the law of conservation of energy, but an extremely insignificant one - no more than one hydrogen atom per billion years per cubic meter of space. Hoyle called his model “the theory of continuous creation” and introduced a special C-field (from the English creation - creation) with negative pressure, which forced the Universe to inflate, while maintaining a constant density of matter. In defiance of Gamow, Hoyle explained the formation of all elements, including light ones, by thermonuclear processes in stars.

The cosmic microwave background predicted by Gamow was accidentally noticed almost 20 years later. Its discoverers received the Nobel Prize, and the hot Friedmann-Gamow Universe quickly supplanted competing hypotheses. Hoyle, however, did not give up and, defending his theory, argued that the microwave background was generated by distant stars, the light of which was scattered and re-emitted by cosmic dust. But then the glow of the sky should be spotty, but it is almost perfectly uniform. Gradually, data was accumulated on the chemical composition of stars and cosmic clouds, which were also consistent with Gam’s model of primary nucleosynthesis.

Thus, the twice-alternative theory of the Big Bang became generally accepted, or, as it is fashionable to say today, turned into the scientific mainstream. And now schoolchildren are taught that Hubble discovered the explosion of the Universe (and not the dependence of the red shift on distance), and cosmic microwave radiation, with the light hand of the Soviet astrophysicist Joseph Samuilovich Shklovsky, becomes a relict radiation. The model of the hot Universe is “stitched” into people’s minds literally at the level of language.

Four Causes of Redshift

Which one should you choose to explain Hubble's law - the dependence of redshift on distance?

	Laboratory tested	Not laboratory tested
Frequency change	1. Doppler effect Occurs when the source of radiation is removed. Its light waves arrive at our receiver a little less often than they are emitted by the source. The effect is widely used in astronomy to measure the speed of movement of objects along the line of sight.	3. Expansion of space According to the general theory of relativity, the properties of space itself can change over time. If this results in an increase in the distance between the source and the receiver, then the light waves are stretched in the same way as in the Doppler effect.
Energy Change	2. Gravitational redshift When a quantum of light escapes from a gravitational well, it expends energy to overcome the forces of gravity. A decrease in energy corresponds to a decrease in the frequency of radiation and its shift to the red side of the spectrum.	4. Light fatigue Perhaps the movement of a light quantum in space is accompanied by a kind of “friction,” that is, a loss of energy proportional to the path traveled. This was one of the first hypotheses put forward to explain the cosmological redshift.

Digging under the foundations

But human nature is such that as soon as another undeniable idea takes hold in society, there are immediately people who want to argue. Criticism of standard cosmology can be divided into conceptual, pointing out the imperfection of its theoretical foundations, and astronomical, citing specific facts and observations that are difficult to explain.

The main target of conceptual attacks is, of course, the general theory of relativity (GR). Einstein gave a surprisingly beautiful description of gravity, identifying it with the curvature of space-time. However, from general relativity it follows the existence of black holes, strange objects in the center of which matter is compressed into a point of infinite density. In physics, the appearance of infinity always indicates the limits of applicability of a theory. At ultra-high densities, general relativity must be replaced by quantum gravity. But all attempts to introduce the principles of quantum physics into general relativity have failed, which forces physicists to look for alternative theories of gravity. Dozens of them were built in the 20th century. Most did not withstand experimental testing. But a few theories still hold. Among them, for example, is the field theory of gravity by Academician Logunov, in which there is no curved space, no singularities arise, which means there are no black holes or the Big Bang. Wherever the predictions of such alternative theories of gravity can be tested experimentally, they agree with those of general relativity, and only in extreme cases - at ultra-high densities or at very large cosmological distances - do their conclusions differ. This means that the structure and evolution of the Universe must be different.

New cosmography

Once upon a time, Johannes Kepler, trying to theoretically explain the relationships between the radii of planetary orbits, nested regular polyhedra into each other. The spheres described and inscribed in them seemed to him the most direct path to unraveling the structure of the universe - “The Cosmographic Mystery,” as he called his book. Later, based on the observations of Tycho Brahe, he discarded the ancient idea of ​​​​the celestial perfection of circles and spheres, concluding that the planets move in ellipses.

Many modern astronomers are also skeptical about the speculative constructions of theorists and prefer to draw inspiration by looking at the sky. And there you can see that our Galaxy, the Milky Way, is part of a small cluster called the Local Group of galaxies, which is attracted to the center of a huge cloud of galaxies in the constellation Virgo, known as the Local Supercluster. Back in 1958, astronomer George Abel published a catalog of 2,712 galaxy clusters in the northern sky, which, in turn, are grouped into superclusters.

Agree, it does not look like a Universe uniformly filled with matter. But without homogeneity in the Friedman model it is impossible to obtain an expansion regime consistent with Hubble's law. And the amazing smoothness of the microwave background cannot be explained either. Therefore, in the name of the beauty of the theory, the homogeneity of the Universe was declared a Cosmological principle, and observers were expected to confirm it. Of course, at small distances by cosmological standards—a hundred times the size of the Milky Way—the attraction between galaxies dominates: they move in orbit, collide and merge. But, starting from a certain distance scale, the Universe simply must become homogeneous.

In the 1970s, observations did not yet allow us to say with certainty whether structures larger than a couple of tens of megaparsecs existed, and the words “large-scale homogeneity of the Universe” sounded like a protective mantra of Friedmann’s cosmology. But by the beginning of the 1990s the situation had changed dramatically. On the border of the constellations Pisces and Cetus, a complex of superclusters measuring about 50 megaparsecs was discovered, which includes the Local Supercluster. In the constellation Hydra, they first discovered the Great Attractor with a size of 60 megaparsecs, and then behind it a huge Shapley supercluster three times larger. And these are not isolated objects. At the same time, astronomers described the Great Wall, a complex 150 megaparsecs long, and the list continues to grow.

By the end of the century, the production of 3D maps of the Universe was put on stream. In one telescope exposure, spectra of hundreds of galaxies are obtained. To do this, a robotic manipulator places hundreds of optical fibers in the focal plane of the wide-angle Schmidt camera at known coordinates, transmitting the light of each individual galaxy to the spectrographic laboratory. The largest SDSS survey to date has already determined the spectra and redshifts of a million galaxies. And the largest known structure in the Universe remains the Great Wall of Sloan, discovered in 2003 according to the previous CfA-II survey. Its length is 500 megaparsecs, which is 12% of the distance to the horizon of the Friedmann Universe.

Along with concentrations of matter, many deserted regions of space have also been discovered - voids, where there are no galaxies or even mysterious dark matter. Many of them exceed 100 megaparsecs in size, and in 2007 the American National Radio Astronomy Observatory reported the discovery of a Great Void with a diameter of about 300 megaparsecs.

The very existence of such grandiose structures challenges standard cosmology, in which inhomogeneities develop due to the gravitational crowding of matter from tiny density fluctuations left over from the Big Bang. At the observed natural speeds of motion of galaxies, they cannot travel more than a dozen or two megaparsecs during the entire lifetime of the Universe. And how then can we explain the concentration of a substance measuring hundreds of megaparsecs?

Dark Entities

Strictly speaking, Friedman’s model “in its pure form” does not explain the formation of even small structures - galaxies and clusters, unless we add to it one special unobservable entity, invented in 1933 by Fritz Zwicky. While studying the Coma cluster, he discovered that its galaxies were moving so fast that they should easily fly away. Why doesn't the cluster disintegrate? Zwicky suggested that its mass was much greater than estimated from luminous sources. This is how hidden mass appeared in astrophysics, which today is called dark matter. Without it, it is impossible to describe the dynamics of galactic disks and galaxy clusters, the bending of light when passing by these clusters, and their very origin. It is estimated that there is 5 times more dark matter than normal luminous matter. It has already been established that these are not dark planetoids, not black holes, and not any known elementary particles. Dark matter probably consists of some heavy particles that participate only in weak interactions.

Recently, the Italian-Russian satellite experiment PAMELA detected a strange excess of energetic positrons in cosmic rays. Astrophysicists do not know a suitable source of positrons and suggest that they may be the products of some kind of reaction with dark matter particles. If so, then Gamow’s theory of primordial nucleosynthesis may be at risk, because it did not assume the presence of a huge number of unknown heavy particles in the early Universe.

The mysterious dark energy had to be urgently added to the standard model of the Universe at the turn of the 20th and 21st centuries. Not long before this, a new method for determining distances to distant galaxies was tested. The “standard candle” in it was the explosions of supernovae of a special type, which at the very height of the outbreak always have almost the same luminosity. Their apparent brightness is used to determine the distance to the galaxy where the cataclysm occurred. Everyone expected that measurements would show a slight slowdown in the expansion of the Universe under the influence of self-gravity of its matter. With great surprise, astronomers discovered that the expansion of the Universe, on the contrary, is accelerating! Dark energy was invented to provide the universal cosmic repulsion that inflates the Universe. In fact, it is indistinguishable from the lambda term in Einstein's equations and, what is funnier, from the C-field from the Bondi-Gold-Hoyle theory of a stationary universe, in the past the main competitor of the Friedmann-Gamow cosmology. This is how artificial speculative ideas migrate between theories, helping them survive under the pressure of new facts.

If Friedman’s original model had only one parameter determined from observations (the average density of matter in the Universe), then with the advent of “dark entities” the number of “tuning” parameters increased noticeably. These are not only the proportions of the dark “ingredients”, but also their arbitrarily assumed physical properties, such as the ability to participate in various interactions. Isn't it true that all this is reminiscent of Ptolemy's theory? More and more epicycles were added to it, too, to achieve consistency with observations, until it collapsed under the weight of its own overcomplicated design.

DIY Universe

Over the past 100 years, a great variety of cosmological models have been created. If earlier each of them was perceived as a unique physical hypothesis, now the attitude has become more prosaic. To build a cosmological model, you need to deal with three things: the theory of gravity, on which the properties of space depend, the distribution of matter, and the physical nature of the redshift, from which the dependence is derived: distance - redshift R(z). This sets the cosmography of the model, which makes it possible to calculate various effects: how the brightness of a “standard candle,” the angular size of a “standard meter,” the duration of a “standard second,” and the surface brightness of a “reference galaxy” change with distance (or rather, with redshift). All that remains is to look at the sky and understand which theory gives the correct predictions.

Imagine that in the evening you are sitting in a skyscraper by the window, looking at the sea of ​​city lights stretching below. There are fewer of them in the distance. Why? Perhaps there are poor outskirts there, or even development has completely ended. Or maybe the light from the lanterns is dimmed by fog or smog. Or the curvature of the Earth’s surface affects it, and distant lights simply go beyond the horizon. For each option, you can calculate the dependence of the number of lights on the distance and find a suitable explanation. This is how cosmologists study distant galaxies, trying to choose the best model of the Universe.

For the cosmological test to work, it is important to find “standard” objects and take into account the influence of all interference that distorts their appearance. Observational cosmologists have been struggling with this for eight decades. Take, say, the angular size test. If our space is Euclidean, that is, not curved, the apparent size of galaxies decreases in inverse proportion to the redshift z. In Friedmann's model with curved space, the angular sizes of objects decrease more slowly, and we see galaxies slightly larger, like fish in an aquarium. There is even a model (Einstein worked with it in the early stages), in which galaxies first decrease in size as they move away, and then begin to grow again. The problem, however, is that we see distant galaxies as they were in the past, and during the course of evolution their sizes can change. In addition, at a great distance, foggy spots appear smaller - due to the fact that it is difficult to see their edges.

It is extremely difficult to take into account the influence of such effects, and therefore the result of a cosmological test often depends on the preferences of a particular researcher. In a huge array of published works, one can find tests that both confirm and refute a variety of cosmological models. And only the professionalism of the scientist determines which of them to believe and which not. Here are just a couple of examples.

In 2006, an international team of three dozen astronomers tested whether distant supernova explosions stretched out over time, as required by Friedmann's model. They received complete agreement with the theory: flashes lengthen exactly as many times as the frequency of light coming from them decreases - time dilation in general relativity has the same effect on all processes. This result could have been another final nail in the coffin of the theory of a stationary Universe (the first one 40 years ago was named by Stephen Hawking as the cosmic microwave background), but in 2009, American astrophysicist Eric Lerner published exactly the opposite results obtained by a different method. He used the surface brightness test for galaxies, invented by Richard Tolman back in 1930, specifically to make a choice between an expanding and a static universe. In the Friedmann model, the surface brightness of galaxies falls very quickly with increasing redshift, and in Euclidean space with “tired light” the decay is much slower. At z = 1 (where, according to Friedman, galaxies are about half as young as those near us), the difference is 8-fold, and at z = 5, which is close to the limit of the Hubble Space Telescope's capabilities, it is more than 200-fold. The test showed that the data almost perfectly coincides with the “tired light” model and strongly diverges from Friedman’s.

Ground for doubt

Observational cosmology has accumulated a lot of data that cast doubt on the correctness of the dominant cosmological model, which, after adding dark matter and energy, began to be called LCDM (Lambda - Cold Dark Matter). A potential problem for LCDM is the rapid increase in record redshifts of detected objects. Masanori Iye, an employee of the Japanese National Astronomical Observatory, studied how the record open redshifts of galaxies, quasars and gamma-ray bursts (the most powerful explosions and the most distant beacons in the observable Universe) grew. By 2008, all of them had already overcome the z = 6 threshold, and the record z of gamma-ray bursts grew especially rapidly. In 2009, they set another record: z = 8.2. In Friedman's model, this corresponds to an age of about 600 million years after the Big Bang and fits to the limit with existing theories of galaxy formation: any more, and they simply will not have time to form. Meanwhile, progress in z indicators does not seem to be stopping - everyone is waiting for data from the new Herschel and Planck space telescopes, launched in the spring of 2009. If objects with z = 15 or 20 appear, it will become a full-blown LCDM crisis.

Another problem was noticed back in 1972 by Alan Sandage, one of the most respected observational cosmologists. It turns out that Hubble's law holds all too well in the immediate vicinity of the Milky Way. Within a few megaparsecs from us, matter is distributed extremely inhomogeneously, but the galaxies do not seem to notice this. Their redshifts are exactly proportional to their distances, except for those that are very close to the centers of large clusters. The chaotic speeds of galaxies seem to be dampened by something. Drawing an analogy with the thermal motion of molecules, this paradox is sometimes called the anomalous coldness of the Hubble flow. There is no comprehensive explanation for this paradox in LCDM, but it receives a natural explanation in the “tired light” model. Alexander Raikov from the Pulkovo Observatory hypothesized that the redshift of photons and the damping of the chaotic velocities of galaxies may be a manifestation of the same cosmological factor. And the same reason may explain the anomaly in the movement of the American interplanetary probes Pioneer 10 and Pioneer 11. As they left the solar system, they experienced a small, inexplicable slowdown, just the right amount numerically to explain the coldness of the Hubble stream.

A number of cosmologists are trying to prove that matter in the Universe is distributed not uniformly, but fractally. This means that no matter what scale we consider the Universe, it will always reveal an alternation of clusters and voids of the corresponding level. The first to raise this topic was the Italian physicist Luciano Piotroneiro in 1987. And a few years ago, St. Petersburg cosmologist Yuri Baryshev and Pekka Teerikorpi from Finland published an extensive monograph “The Fractal Structure of the Universe.” A number of scientific articles claim that in redshift surveys, the fractal nature of the distribution of galaxies is confidently revealed up to a scale of 100 megaparsecs, and heterogeneity is traced up to 500 megaparsecs and more. And recently, Alexander Raikov, together with Viktor Orlov from St. Petersburg State University, discovered signs of a fractal distribution in the catalog of gamma-ray bursts on scales up to z = 3 (that is, according to the Friedmann model in most of the visible Universe). If this is confirmed, cosmology is in for a major shake-up. Fractality generalizes the concept of homogeneity, which, for reasons of mathematical simplicity, was taken as the basis of 20th-century cosmology. Today, fractals are actively studied by mathematicians, and new theorems are regularly proven. The fractality of the large-scale structure of the Universe can lead to very unexpected consequences, and who knows whether radical changes in the picture of the Universe and its development await us ahead?

Cry from the heart

And yet, no matter how inspired cosmological “dissidents” are by such examples, today there is no coherent and well-developed theory of the structure and evolution of the Universe that differs from the standard LCDM. What is collectively called alternative cosmology consists of a number of claims that are rightly raised by proponents of the generally accepted concept, as well as a set of promising ideas of varying degrees of sophistication that may be useful in the future if a strong alternative research program emerges.

Many proponents of alternative views tend to overemphasize individual ideas or counterexamples. They hope that by demonstrating the difficulties of the standard model, it can be abandoned. But, as the philosopher of science Imre Lakatos argued, neither experiment nor paradox can destroy a theory. Only a new, better theory kills a theory. There is nothing to offer for an alternative cosmology yet.

But where will new serious developments come from, the “alternatives” complain, if all over the world, in grant committees, in the editorial offices of scientific journals and in commissions on the distribution of observation time of telescopes, the majority are supporters of standard cosmology. They, they say, simply block the allocation of resources to work that lies outside the cosmological mainstream, considering it a useless waste of funds. Several years ago, tensions reached such a height that a group of cosmologists wrote a very harsh “Open Letter to the Scientific Community” in New Scientist magazine. It announced the establishment of the international public organization Alternative Cosmology Group (www. cosmology. info), which has since periodically held its own conferences, but has not yet been able to significantly change the situation.

The history of science knows many cases when a powerful new research program was unexpectedly formed around ideas that were considered deeply alternative and of little interest. And, perhaps, the current disparate alternative cosmology carries within itself the germ of a future revolution in the picture of the world.