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 larger 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, we take into account that its Hubble sphere and particle sphere are respectively 13.75 and 45.7 billion light years.

Scale of the Universe

Press the START button and discover a new, unknown world!
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.

Models of a stationary Universe. The uniqueness of the Universe does not allow experimental verification of the hypotheses put forward and raising them to the level of theories, therefore the evolution of the Universe can only be considered within the framework of models.

After the creation of classical mechanics, the scientific picture of the world was based on Newtonian ideas about space, time and gravity and described a constant in time, i.e. stationary, infinite Universe created by the Creator.

In the 20th century new theoretical foundations have emerged for the creation of new cosmological models.

First of all, we must mention the cosmological postulate, according to which the physical laws established in a limited part of the Universe are valid for the entire Universe. In addition, the homogeneity and isotropy of the large-scale distribution of matter in the Universe is considered an axiom. In this case, the evolutionary model must correspond to the so-called anthropic principle, i.e. provide for the possibility of an observer (a reasonable person) appearing at a certain stage of evolution.

Since it is gravity that determines the interaction of masses at large distances, the theoretical core of twentieth-century cosmology. became the relativistic theory of gravity and space-time - the general theory of relativity. According to this theory, the distribution and movement of matter determine the geometric properties of space-time and at the same time themselves depend on them. The gravitational field manifests itself as a “curvature” of space-time. In Einstein's first cosmological model, created on the basis of general relativity in 1916, the Universe is also stationary. It is limitless, but closed and has finite dimensions. Space closes on itself.

Friedman models of a non-stationary Universe. Einstein's model of a stationary Universe was refuted in the works of the Russian scientist A.A. Friedman (1888 - 1925), who in 1922 showed that curved space cannot be stationary: it must either expand or contract. Three different models of changes in the radius of curvature of the Universe are possible, depending on the average density of matter in it, and in two of them the Universe expands infinitely, and in the third, the radius of curvature changes periodically (the Universe pulsates).

Although E. Hubble’s discovery of the law of the dependence of the speed of removal of galaxies on the distance to them confirmed the expansion of the Universe, at present, a comparison of the experimentally estimated density of matter with the critical value of this parameter, which determines the transition from expansion to pulsation, does not make it possible to unambiguously select a scenario for further evolution. These two values ​​turned out to be close, but the experimental data were not reliable enough.

The expansion of the Universe is currently a well-founded and generally accepted fact that allows us to estimate the age of the Universe. According to the most common estimates, it is 10 18 s (18 billion years). Therefore, modern models assume a “beginning” of the Universe. How did its evolution begin?

Model of a hot Universe. The basis of modern ideas about the initial stages of the evolution of the Universe is the model of the “hot Universe”, or “Big Bang”, the foundations of which were laid in the 40s of the 20th century. Russian scientist working in the USA, G.A. Gammov (1904 – 1968). In the simplest version of this model, it appears that the Universe arose spontaneously as a result of an explosion from a super-dense and super-hot state with infinite curvature of space (singularity state). The “hotness” of the initial singular state is characterized by the predominance of electromagnetic radiation in it over matter. This is confirmed by the experimental discovery in 1965 of isotropic electromagnetic “relict radiation” by American astrophysicists Penzias (born 1933) and Wilson (born 1936). Modern physical theories make it possible to describe the evolution of matter starting from the moment of time t= 10 -43 s. The very beginning moments of the evolution of the Universe are still behind the physical barrier. Only starting from the moment t= 10 -10 s after the Big Bang, our ideas about the state of matter in the early Universe and the processes occurring in it can be tested experimentally and described theoretically.

As the Universe expands, the density of matter in it decreases and the temperature drops. In this case, processes of qualitative transformations of particles of matter occur. At 10 -10 s, matter consists of free quarks, leptons and photons (see section III). As the Universe cools, hadrons are formed, then nuclei of light elements appear - isotopes of hydrogen, helium, lithium. The synthesis of helium nuclei stops at the moment t= 3 min. Only after hundreds of thousands of years do nuclei combine with electrons to form hydrogen and helium atoms, and from that moment on the substance ceases to interact with electromagnetic radiation. “Relict” radiation arose precisely during this period. When the size of the Universe was about 100 times smaller than in the present era, gas clumps arose from inhomogeneities of hydrogen and helium gas, which fragmented and led to the emergence of stars and galaxies.

The question of the exclusivity of the Universe as an object of cosmology remains open. Along with the widespread point of view that the entire Universe is our Metagalaxy, there is an opposite opinion that the Universe can consist of many metagalaxies, and the idea of ​​​​the uniqueness of the Universe is historically relative, determined by the level of science and practice.

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.

Hypothesis of a multi-leaf model of the Universe

Preface by the site author: For the attention of readers of the site "Knowledge is Power" we offer fragments from the 29th chapter of Andrei Dmitrievich Sakharov's book "Memoirs". Academician Sakharov talks about the work in the field of cosmology, which he carried out after he began to actively engage in human rights activities - in particular, in Gorky’s exile. This material is of undoubted interest on the topic “The Universe”, discussed in this chapter of our site. We will get acquainted with the hypothesis of a multi-leaf model of the Universe and other problems of cosmology and physics. ...And, of course, let's remember our recent tragic past.

Academician Andrei Dmitrievich SAKHAROV (1921-1989).

In Moscow in the 70s and in Gorky, I continued my attempts to study physics and cosmology. During these years I was unable to put forward significantly new ideas, and I continued to develop those directions that were already presented in my works of the 60s (and described in the first part of this book). This is probably the lot of most scientists when they reach a certain age limit for them. However, I do not lose hope that perhaps something else will “shine” for me. At the same time, I must say that simply observing the scientific process, in which you yourself do not take part, but know what is what, brings deep inner joy. In this sense, I am “not greedy.”

In 1974, I did and in 1975 published a paper in which I developed the idea of ​​a zero Lagrangian of the gravitational field, as well as the calculation methods that I had used in previous works. At the same time, it turned out that I came to the method proposed many years ago by Vladimir Aleksandrovich Fok, and then by Julian Schwinger. However, my conclusion and the very path of construction, the methods were completely different. Unfortunately, I could not send my work to Fok - he died just then.

I subsequently discovered some errors in my article. It left unclarified the question of whether “induced gravity” (the modern term used instead of the term “zero Lagrangian”) gives the correct sign of the gravitational constant in any of the options that I considered.<...>

Three works - one published before my expulsion and two after my expulsion - are devoted to cosmological problems. In the first paper, I discuss the mechanisms of baryon asymmetry. Of some interest, perhaps, are general considerations about the kinetics of reactions leading to the baryon asymmetry of the Universe. However, specifically in this work, I reason within the framework of my old assumption about the existence of a “combined” conservation law (the sum of the numbers of quarks and leptons is conserved). I already wrote in the first part of my memoirs how I came to this idea and why I now consider it wrong. Overall, this part of the work seems to me unsuccessful. I like much more the part of the job where I write about multi-leaf model of the Universe . This is an assumption that the cosmological expansion of the Universe is replaced by compression, then a new expansion in such a way that the cycles of compression - expansion are repeated an infinite number of times. Such cosmological models have long attracted attention. Different authors called them "pulsating" or "oscillating" models of the Universe. I like the term better "multi-leaf model" . It seems more expressive, more in line with the emotional and philosophical meaning of the grandiose picture of the repeated repetition of the cycles of existence.

As long as conservation was assumed, the multileaf model encountered, however, an insurmountable difficulty following from one of the fundamental laws of nature - the second law of thermodynamics.

Retreat. In thermodynamics, a certain characteristic of the state of bodies is introduced, called. My dad once remembered an old popular science book called “The Queen of the World and Her Shadow.” (Unfortunately, I forgot who the author of this book is.) The queen is, of course, energy, and the shadow is entropy. Unlike energy, for which there is a conservation law, for entropy the second law of thermodynamics establishes the law of increase (more precisely, non-decrease). Processes in which the total entropy of bodies does not change are called (considered) reversible. An example of a reversible process is mechanical movement without friction. Reversible processes are an abstraction, a limiting case of irreversible processes accompanied by an increase in the total entropy of bodies (during friction, heat transfer, etc.). Mathematically, entropy is defined as a quantity whose increase is equal to the heat influx divided by the absolute temperature (it is additionally assumed - more precisely, it follows from general principles - that the entropy at absolute zero temperature and the entropy of vacuum are equal to zero).

Numerical example for clarity. A certain body having a temperature of 200 degrees transfers 400 calories during heat exchange to a second body having a temperature of 100 degrees. The entropy of the first body decreased by 400/200, i.e. by 2 units, and the entropy of the second body increased by 4 units; The total entropy increased by 2 units, in accordance with the requirement of the second law. Note that this result is a consequence of the fact that heat is transferred from a hotter body to a colder one.

An increase in total entropy during nonequilibrium processes ultimately leads to heating of the substance. Let's turn to cosmology, to multi-leaf models. If we assume that the number of baryons is fixed, then the entropy per baryon will increase indefinitely. The substance will heat up indefinitely with each cycle, i.e. conditions in the Universe will not be repeated!

The difficulty is eliminated if we abandon the assumption of conservation of baryon charge and consider, in accordance with my idea of ​​1966 and its subsequent development by many other authors, that the baryon charge arises from "entropy" (i.e. neutral hot matter) in the early stages of cosmological expansion of the Universe. In this case, the number of baryons formed is proportional to the entropy at each expansion-compression cycle, i.e. the conditions for the evolution of matter and the formation of structural forms can be approximately the same in each cycle.

I first coined the term "multi-leaf model" in a 1969 paper. In my recent articles I use the same term in a slightly different sense; I mention this here to avoid misunderstandings.

The first of the last three articles (1979) examined a model in which space is assumed to be flat on average. It is also assumed that Einstein's cosmological constant is not zero and is negative (although very small in absolute value). In this case, as the equations of Einstein's theory of gravity show, cosmological expansion inevitably gives way to compression. Moreover, each cycle completely repeats the previous one in terms of its average characteristics. It is important that the model is spatially flat. Along with flat geometry (Euclidean geometry), the following two works are also devoted to the consideration of Lobachevsky geometry and the geometry of a hypersphere (a three-dimensional analogue of a two-dimensional sphere). In these cases, however, another problem arises. An increase in entropy leads to an increase in the radius of the Universe at the corresponding moments of each cycle. Extrapolating into the past, we find that each given cycle could have been preceded by only a finite number of cycles.

In “standard” (one-sheet) cosmology there is a problem: what was there before the moment of maximum density? In multi-sheet cosmologies (except for the case of a spatially flat model), this problem cannot be avoided - the question is transferred to the moment of the beginning of the expansion of the first cycle. One can take the view that the beginning of the expansion of the first cycle or, in the case of the standard model, the only cycle is the Moment of the Creation of the World, and therefore the question of what happened before that lies beyond the scope of scientific research. However, perhaps, just as - or, in my opinion, more - justified and fruitful is an approach that allows for unlimited scientific research of the material world and space-time. At the same time, apparently, there is no place for the Act of Creation, but the basic religious concept of the divine meaning of Being is not affected by science and lies beyond its boundaries.

I am aware of two alternative hypotheses related to the problem under discussion. One of them, it seems to me, was first expressed by me in 1966 and was subject to a number of clarifications in subsequent works. This is the “turning of the arrow of time” hypothesis. It is closely related to the so-called reversibility problem.

As I already wrote, completely reversible processes do not exist in nature. Friction, heat transfer, light emission, chemical reactions, life processes are characterized by irreversibility, a striking difference between the past and the future. If we film some irreversible process and then play the movie in the opposite direction, we will see on the screen something that cannot happen in reality (for example, a flywheel rotating by inertia increases its rotation speed, and the bearings cool). Quantitatively, irreversibility is expressed in a monotonic increase in entropy. At the same time, the atoms, electrons, atomic nuclei, etc. that are part of all bodies. move according to the laws of mechanics (quantum, but this is unimportant here), which are completely reversible in time (in quantum field theory - with simultaneous CP reflection, see in the first part). The asymmetry of the two directions of time (the presence of the “arrow of time,” as they say) with the symmetry of the equations of motion has long attracted the attention of the creators of statistical mechanics. Discussion of this issue began in the last decades of the last century and was sometimes quite heated. The solution that more or less satisfied everyone was the hypothesis that the asymmetry was due to the initial conditions of motion and the position of all atoms and fields “in the infinitely distant past.” These initial conditions must be “random” in some well-defined sense.

As I suggested (in 1966 and more explicitly in 1980), in cosmological theories that have a designated point in time, these random initial conditions should be attributed not to the infinitely distant past (t -> - ∞), but to this selected point (t = 0).

Then automatically at this point the entropy has a minimum value, and when moving forward or backward from it in time, the entropy increases. This is what I called “the turning of the arrow of time.” Since when the arrow of time turns, all processes, including informational processes (including life processes), reverse, no paradoxes arise. The above ideas about the reversal of the arrow of time, as far as I know, have not received recognition in the scientific world. But they seem interesting to me.

The rotation of the arrow of time restores the symmetry of the two directions of time inherent in the equations of motion in the cosmological picture of the world!

In 1966-1967 I assumed that at the turning point of the arrow of time, CPT reflection occurs. This assumption was one of the starting points of my work on baryon asymmetry. Here I will present another hypothesis (Kirzhnitz, Linde, Guth, Turner and others had a hand; I only have the remark here that there is a turning of the arrow of time).

Modern theories assume that vacuum can exist in various states: stable, with an energy density equal to zero with great accuracy; and unstable, having a huge positive energy density (effective cosmological constant). The latter state is sometimes called a "false vacuum".

One of the solutions to the equations of general relativity for such theories is as follows. The Universe is closed, i.e. at each moment represents a “hypersphere” of finite volume (a hypersphere is a three-dimensional analogue of the two-dimensional surface of a sphere; a hypersphere can be imagined “embedded” in four-dimensional Euclidean space, just as a two-dimensional sphere is “embedded” in three-dimensional space). The radius of the hypersphere has a minimum finite value at some point in time (let us denote it t = 0) and increases with distance from this point, both forward and backward in time. Entropy is zero for a false vacuum (as for any vacuum in general) and when moving away from the point t = 0 forward or backward in time, it increases due to the decay of the false vacuum, turning into a stable state of true vacuum. Thus, at the point t = 0 the arrow of time rotates (but there is no cosmological CPT symmetry, which requires infinite compression at the point of reflection). Just as in the case of CPT symmetry, all conserved charges here are also equal to zero (for a trivial reason - at t = 0 there is a vacuum state). Therefore, in this case it is also necessary to assume the dynamic occurrence of the observed baryon asymmetry, caused by the violation of CP invariance.

An alternative hypothesis about the prehistory of the Universe is that in fact there is not one Universe or two (as - in some sense of the word - in the hypothesis of the turning of the arrow of time), but many radically different from each other and arising from some “primary” space (or its constituent particles; this may just be a different way of saying it). Other Universes and primary space, if it makes sense to talk about it, may, in particular, have, in comparison with “our” Universe, a different number of “macroscopic” spatial and temporal dimensions - coordinates (in our Universe - three spatial and one temporal dimension; in In other Universes, everything may be different!) I ask you not to pay special attention to the adjective “macroscopic” enclosed in quotation marks. It is associated with the “compactization” hypothesis, according to which most dimensions are compactified, i.e. closed on itself on a very small scale.

Structure of the “Mega-Universe”

It is assumed that there is no causal connection between different Universes. This is precisely what justifies their interpretation as separate Universes. I call this grandiose structure the “Mega Universe.” Several authors have discussed variations of such hypotheses. In particular, the hypothesis of multiple births of closed (approximately hyperspherical) Universes is defended in one of his works by Ya.B. Zeldovich.

The Mega Universe ideas are extremely interesting. Perhaps the truth lies precisely in this direction. For me, in some of these constructions there is, however, one ambiguity of a somewhat technical nature. It is quite acceptable to assume that conditions in different regions of space are completely different. But the laws of nature must necessarily be the same everywhere and always. Nature cannot be like the Queen in Carroll's Alice in Wonderland, who arbitrarily changed the rules of the game of croquet. Existence is not a game. My doubts relate to those hypotheses that allow a break in the continuity of space - time. Are such processes acceptable? Are they not a violation of the laws of nature at the breaking points, and not the “conditions of being”? I repeat, I am not sure that these are valid concerns; Maybe, again, as in the question of conservation of the number of fermions, I am starting from too narrow a point of view. In addition, hypotheses where the birth of Universes occurs without breaking continuity are quite conceivable.

The assumption that the spontaneous birth of many, and perhaps an infinite number of Universes differing in their parameters, and that the Universe surrounding us is distinguished among many worlds precisely by the condition for the emergence of life and intelligence, is called the “anthropic principle” (AP). Zeldovich writes that the first consideration of AP known to him in the context of an expanding Universe belongs to Idlis (1958). In the concept of a multi-leaf Universe, the anthropic principle can also play a role, but for the choice between successive cycles or their regions. This possibility is discussed in my work “Multiple Models of the Universe”. One of the difficulties of multi-sheet models is that the formation of “black holes” and their merging breaks the symmetry at the compression stage so much that it is completely unclear whether the conditions of the next cycle are suitable for the formation of highly organized structures. On the other hand, in sufficiently long cycles the processes of baryon decay and black hole evaporation occur, leading to the smoothing out of all density inhomogeneities. I assume that the combined action of these two mechanisms - the formation of black holes and the alignment of inhomogeneities - leads to a successive change of “smoother” and more “disturbed” cycles. Our cycle was supposed to be preceded by a “smooth” cycle during which no black holes were formed. To be specific, we can consider a closed Universe with a “false” vacuum at the turning point of the arrow of time. The cosmological constant in this model can be considered equal to zero; the change from expansion to compression occurs simply due to the mutual attraction of ordinary matter. The duration of the cycles increases due to the increase in entropy with each cycle and exceeds any given number (tends to infinity), so that the conditions for the decay of protons and the evaporation of “black holes” are met.

Multileaf models provide an answer to the so-called large number paradox (another possible explanation is the hypothesis of Guth et al., which involves a long "inflation" stage, see Chapter 18).

A planet on the outskirts of a distant globular star cluster. Artist © Don Dixon

Why is the total number of protons and photons in a Universe of finite volume so enormously large, although finite? And another form of this question, relating to the “open” version, is why is the number of particles so large in that region of Lobachevsky’s infinite world, the volume of which is of the order of A 3 (A is the radius of curvature)?

The answer given by the multileaf model is very simple. It is assumed that many cycles have already passed since t = 0; during each cycle, entropy (i.e., the number of photons) increased and, accordingly, an increasing baryon excess was generated in each cycle. The ratio of the number of baryons to the number of photons in each cycle is constant, since it is determined by the dynamics of the initial stages of the expansion of the Universe in a given cycle. The total number of cycles since t = 0 is just such that the observed number of photons and baryons is obtained. Since their number grows exponentially, for the required number of cycles we will not even get such a large value.

A by-product of my 1982 work is a formula for the probability of gravitational coalescence of black holes (the estimate in the book by Zeldovich and Novikov was used).

Another intriguing possibility, or rather a dream, is associated with multi-leaf models. Maybe a highly organized mind, developing billions of billions of years during a cycle, finds a way to transmit in encoded form some of the most valuable part of the information it has to its heirs in subsequent cycles, separated from this cycle in time by a period of a super-dense state?.. Analogy - transmission by living beings from generation to generation of genetic information, “compressed” and encoded in the chromosomes of the nucleus of a fertilized cell. This possibility, of course, is absolutely fantastic, and I did not dare to write about it in scientific articles, but on the pages of this book I gave myself free rein. But regardless of this dream, the hypothesis of a multi-leaf model of the Universe seems to me important in a philosophical worldview.

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Introduction. The structure of the Universe in Antiquity

3Heliocentric model of the Universe. Cosmological models of the Universe

1Cosmology

2Stationary model of the Universe

3Non-stationary model of the Universe

4Modern studies of cosmological models of the Universe. Nobel Prize for the discovery of the accelerated expansion of the Universe

5Dark matter

6Dark energy

Conclusion

Literature

Introduction

The Universe as a whole is the subject of a special astronomical science - cosmology, which has an ancient history. Its origins go back to antiquity. Cosmology has long been significantly influenced by the religious worldview, being not so much a subject of knowledge as a matter of faith.

Since the 19th century. Cosmological problems are not a matter of faith, but a subject of scientific knowledge. They are solved with the help of scientific concepts, ideas, theories, as well as instruments and instruments that allow us to understand what the structure of the universe is and how it was formed. In the 20th century Significant progress has been made in the scientific understanding of the nature and evolution of the Universe as a whole. Of course, the understanding of these problems is still far from complete, and, undoubtedly, the future will lead to new great revolutions in the currently accepted views on the picture of the universe. However, it is important to note that here we are dealing specifically with science, with rational knowledge, and not with beliefs and religious beliefs.

The relevance of this work is due, on the one hand, to the great interest in the structure of the Universe in modern science, on the other hand, to its insufficient development, as well as attention to the Universe in the modern world.

Object of study: Universe.

Subject of research: models of the structure of the Universe.

Purpose of the work: to consider modern cosmological models of the Universe.

To achieve this goal, it is necessary to solve the following tasks:

)Analyze the literature on the course of general physics and astronomy, in connection with the choice of subject of study.

)Trace the history of cosmological research.

)Consider modern cosmological models.

)Select illustrative material.

The course work consists of an introduction, three chapters, a conclusion and a bibliography. Chapter 1 is devoted to the history of the structure of the Universe, Chapter 2 examines cosmological models of the Universe, Chapter 3 opens modern studies of cosmological models, and in conclusion sums up the work done.

Chapter 1. The structure of the Universe in Antiquity

.1 Pyrocentric model of the Universe

The path to understanding the position of our planet and humanity living on it in the Universe was very difficult and sometimes very dramatic. In ancient times, it was natural to believe that the Earth was stationary, flat and at the center of the world. It seemed that the whole world was created for the sake of man. Such ideas are called anthropocentrism (from the Greek anthropos - man). Many ideas and thoughts that were later reflected in modern scientific ideas about nature, in particular in astronomy, originated in Ancient Greece, several centuries before our era. It is difficult to list the names of all the thinkers and their brilliant guesses. The outstanding mathematician Pythagoras (6th century BC) was convinced that “number rules the world.” It is believed that it was Pythagoras who first expressed the idea that the Earth, like all other celestial bodies, has a spherical shape and is located in the Universe without any support. The Pythagoreans proposed a pyrocentric model of the Universe, in which the stars, the Sun, the Moon and six planets revolve around a Central Fire (Hestia). To make the sacred number - ten - of spheres in total, the sixth planet was declared to be the Counter-Earth (Antichthon). Both the Sun and the Moon, according to this theory, shone with the reflected light of Hestia. This was the first mathematical system of the world - the rest of the ancient cosmogonists worked more with imagination than logic. The distances between the spheres of the luminaries among the Pythagoreans corresponded to musical intervals in the scale; when they rotate, the “music of the spheres” sounds, inaudible to us. The Pythagoreans believed that the Earth was spherical and rotating, which is why the change of day and night occurs. The Pythagoreans first arose the concept of ether. This is the uppermost, clean and transparent layer of air, the place of residence of the gods.

1.2 Geocentric model of the Universe

Another equally famous scientist of antiquity, Democritus - the founder of the concept of atoms, who lived 400 years BC - believed that the Sun is many times larger than the Earth, that the Moon itself does not glow, but only reflects sunlight, and the Milky Way consists of a huge number of stars. Summarize all the knowledge that had been accumulated by the 4th century. BC e., was able to the outstanding philosopher of the ancient world Aristotle (384-322 BC).

Rice. 1. Geocentric system of the world of Aristotle-Ptolemy.

His activities covered all natural sciences - information about the sky and Earth, about the patterns of movement of bodies, about animals and plants, etc. Aristotle's main merit as an encyclopedist scientist was the creation of a unified system of scientific knowledge. For almost two thousand years, his opinion on many issues was not questioned. According to Aristotle, everything heavy tends to the center of the Universe, where it accumulates and forms a spherical mass - the Earth. The planets are placed on special spheres that revolve around the Earth. Such a system of the world was called geocentric (from the Greek name for the Earth - Gaia). It was not by chance that Aristotle proposed to consider the Earth as the immovable center of the world. If the Earth moved, then, according to Aristotle’s fair opinion, a regular change in the relative positions of the stars on the celestial sphere would be noticeable. But none of the astronomers observed anything like this. Only at the beginning of the 19th century. The displacement of stars (parallax) resulting from the movement of the Earth around the Sun was finally discovered and measured. Many of Aristotle's generalizations were based on conclusions that could not be verified by experience at that time. Thus, he argued that the movement of a body cannot occur unless a force acts on it. As you know from your physics course, these ideas were refuted only in the 17th century. during the times of Galileo and Newton.

1.3 Heliocentric model of the Universe

Among ancient scientists, Aristarchus of Samos, who lived in the 3rd century, stands out for the boldness of his guesses. BC e. He was the first to determine the distance to the Moon and calculate the size of the Sun, which, according to his data, turned out to be more than 300 times larger than the Earth in volume. Probably, these data became one of the grounds for the conclusion that the Earth, along with other planets, moves around this largest body. Nowadays, Aristarchus of Samos has come to be called the “Copernicus of the ancient world.” This scientist introduced something new into the study of the stars. He believed that they were immeasurably further from the Earth than the Sun. For that era, this discovery was very important: from a cozy little home, the Universe was turning into an immense giant world. In this world, the Earth with its mountains and plains, with forests and fields, with seas and oceans became a tiny speck of dust, lost in a grandiose empty space. Unfortunately, the works of this remarkable scientist have practically not reached us, and for more than one and a half thousand years, humanity was sure that the Earth was the immovable center of the world. To a large extent, this was facilitated by the mathematical description of the visible movement of the luminaries, which was developed for the geocentric system of the world by one of the outstanding mathematicians of antiquity - Claudius Ptolemy in the 2nd century. AD The most difficult task was to explain the loop-like motion of the planets.

Ptolemy, in his famous work “Mathematical Treatise on Astronomy” (better known as “Almagest”) argued that each planet moves uniformly along an epicycle - a small circle, the center of which moves around the Earth along a deferent - a large circle. Thus, he was able to explain the special nature of the movement of the planets, which distinguished them from the Sun and Moon. The Ptolemaic system gave a purely kinematic description of the motion of the planets - the science of that time could not offer anything else. You have already seen that using a model of the celestial sphere to describe the movement of the Sun, Moon and stars allows you to carry out many calculations useful for practical purposes, although in reality such a sphere does not exist. The same is true for epicycles and deferents, on the basis of which the positions of the planets can be calculated with a certain degree of accuracy.

Rice. 2. Movement of the Earth and Mars.

However, over time, the requirements for the accuracy of these calculations constantly increased, and more and more new epicycles had to be added for each planet. All this complicated the Ptolemaic system, making it unnecessarily cumbersome and inconvenient for practical calculations. Nevertheless, the geocentric system remained unshakable for about 1000 years. After all, after the heyday of ancient culture in Europe, a long period began during which not a single significant discovery was made in astronomy and many other sciences. Only during the Renaissance did a rise in the development of sciences begin, in which astronomy became one of the leaders. In 1543, a book by the outstanding Polish scientist Nicolaus Copernicus (1473-1543) was published, in which he substantiated a new - heliocentric - system of the world. Copernicus showed that the daily motion of all the stars can be explained by the rotation of the Earth around its axis, and the loop-like motion of the planets by the fact that all of them, including the Earth, revolve around the Sun.

The figure shows the movement of the Earth and Mars during the period when, as it seems to us, the planet is describing a loop in the sky. The creation of the heliocentric system marked a new stage in the development of not only astronomy, but also all natural science. A particularly important role was played by Copernicus’s idea that behind the visible picture of occurring phenomena, which seems true to us, we must look for and find the essence of these phenomena, inaccessible to direct observation. The heliocentric system of the world, substantiated but not proven by Copernicus, was confirmed and developed in the works of such outstanding scientists as Galileo Galilei and Johannes Kepler.

Galileo (1564-1642), one of the first to point a telescope at the sky, interpreted the discoveries made as evidence in favor of the Copernican theory. Having discovered the change of phases of Venus, he came to the conclusion that such a sequence can only be observed if it revolves around the Sun.

Rice. 3. Heliocentric system of the world.

The four satellites of the planet Jupiter that he discovered also refuted the idea that the Earth is the only center in the world around which other bodies can rotate. Galileo not only saw mountains on the Moon, but even measured their height. Along with several other scientists, he also observed sunspots and noticed their movement across the solar disk. On this basis, he concluded that the Sun rotates and, therefore, has the kind of motion that Copernicus attributed to our planet. Thus, it was concluded that the Sun and Moon have a certain similarity with the Earth. Finally, observing many faint stars in and outside the Milky Way, inaccessible to the naked eye, Galileo concluded that the distances to the stars are different and that no “sphere of fixed stars” exists. All these discoveries became a new stage in understanding the position of the Earth in the Universe.

Chapter 2. Cosmological models of the Universe

.1 Cosmology

Translated from Greek, cosmology means “description of the world order.” This is a scientific discipline designed to find the most general laws of the movement of Matter and build an understanding of the Universe as a harmonious whole. Ideally, there should be no place for randomness in it (in cosmological theory), but all phenomena observed in the Cosmos should appear as manifestations of the general laws of motion of Matter. Thus, cosmology is the keys to understanding everything that happens in both the macrocosm and the microcosm.

Cosmology is a branch of astronomy and astrophysics that studies the origin, large-scale structure and evolution of the Universe. Data for cosmology are mainly obtained from astronomical observations. To interpret them, the general theory of relativity of A. Einstein (1915) is currently used. The creation of this theory and the carrying out of corresponding observations made it possible in the early 1920s to place cosmology among the exact sciences, whereas before that it was rather a field of philosophy. Now two cosmological schools have emerged: empiricists limit themselves to the interpretation of observational data, without extrapolating their models into unexplored areas; theorists try to explain the observable universe using some hypotheses selected for simplicity and elegance. The cosmological model of the Big Bang is now widely known, according to which the expansion of the Universe began some time ago from a very dense and hot state; The stationary model of the Universe is also discussed, in which it exists forever and has neither beginning nor end.

2.2 Stationary model of the Universe

The beginning of a new theory of the origin of the Universe was laid by the publication in 1916 of Albert Einstein's work “Fundamentals of the General Theory of Relativity.”

This work is the basis of the Relativistic Theory of Gravity, which, in turn, is the basis of modern cosmology. The general theory of relativity applies to all reference systems (and not just to those moving at a constant speed relative to each other) and looks mathematically much more complicated than the special one (which explains the eleven-year gap between their publication). It includes as a special case the special theory of relativity (and therefore Newton's laws). At the same time, the general theory of relativity goes much further than all its predecessors. In particular, it gives a new interpretation of gravity. The general theory of relativity makes the world four-dimensional: time is added to the three spatial dimensions. All four dimensions are inseparable, so we are no longer talking about the spatial distance between two objects, as is the case in the three-dimensional world, but about the space-time intervals between events, which combine their distance from each other - both in time and in space . That is, space and time are considered as a four-dimensional space-time continuum or, simply, space-time. Already in 1917, Einstein himself proposed a model of space, derived from his field equations, now known as the Einstein Model of the Universe. At its core, it was a stationary model. In order not to conflict with staticity, Einstein modified his theory by introducing the so-called cosmological constant into the equations. He introduced a new “anti-gravity” force, which, unlike other forces, was not generated by any source, but was embedded in the very structure of space-time. Einstein argued that space-time itself is always expanding and this expansion exactly balances the attraction of all other matter in the Universe, so that as a result the Universe turns out to be static.

Taking into account the cosmological constant, Einstein’s equations have the form:

Where ? - cosmological constant, g ab - metric tensor, R ab - Ricci tensor, R - scalar curvature, T ab - energy-momentum tensor, c - speed of light, G - Newton's gravitational constant.

“The universe, as depicted by Einstein's theory of relativity, is like an inflating soap bubble. She is not his insides, but a film. The surface of a bubble is two-dimensional, but the bubble of the Universe has four dimensions: three spatial and one temporal,” wrote the once prominent English physicist James Jeans. This modern scientist (he died in 1946) seemed to revive the old idea of ​​​​the followers of Plato and Pythagoras that everything around is pure mathematics, and the god who created this mathematical Universe was himself a great mathematician.

But Einstein was also a great mathematician. His formulas allow us to calculate the radius of this Universe. Since its curvature depends on the mass of the bodies that compose it, it is necessary to know the average density of matter. Astronomers have spent years studying the same small patches of sky and painstakingly counting the amount of matter in them. It turned out that the density is approximately 10 -30 g/cm 3 . If we substitute this figure into Einstein’s formulas, then, firstly, we get a positive value for curvature, that is, our Universe is closed! - and, secondly, its radius is 35 billion light years. This means that although the Universe is finite, it is huge - a ray of light, rushing along the Great Cosmic Circle, will return to the same point after 200 billion Earth years!

This is not the only paradox of Einstein's universe. It is not only finite, but limitless, it is also impermanent. Albert Einstein formulated his theory in the form of ten very complex, so-called nonlinear differential equations. However, not all scientists treated them as ten commandments, allowing only one interpretation. This is not surprising - after all, modern mathematics cannot accurately solve such equations, and there can be many approximate solutions.

2.3 Non-stationary model of the Universe

The first fundamentally new revolutionary cosmological consequences of the general theory of relativity were revealed by the outstanding Soviet mathematician and theoretical physicist Alexander Alexandrovich Friedman (1888-1925).

The fundamental equations of general relativity are Einstein's “world equations,” which describe the geometric properties, or metric, of four-dimensional curved spacetime.

Solving them allows us, in principle, to construct a mathematical model of the Universe. The first such attempt was made by Einstein himself. Considering the radius of curvature of space to be constant (that is, based on the assumption that the Universe as a whole is stationary, which seemed most reasonable), he came to the conclusion that the Universe should be spatially finite and have the shape of a four-dimensional cylinder. In 1922-1924. Friedman criticized Einstein's conclusions. He showed the groundlessness of his initial postulate - about the stationarity, immutability in time of the Universe. Having analyzed the world equations, Friedman came to the conclusion that their solution under no circumstances can be unambiguous and cannot answer the question about the shape of the Universe, its finiteness or infinity.

Based on the opposite postulate - about the possible change in the radius of curvature of world space in time, Friedman found non-stationary solutions to the “world equations”. As an example of such solutions, he constructed three possible models of the Universe. In two of them, the radius of curvature of space increases monotonically, and the Universe expands (in one model - from a point, in the other - starting from a certain finite volume). The third model painted a picture of a pulsating Universe with a periodically changing radius of curvature.

Friedman's model is based on the idea of ​​an isotropic, homogeneous and non-stationary state of the Universe:

Ø Isotropy indicates that there are no distinct directional points in the Universe, that is, its properties do not depend on direction.

Ø The homogeneity of the Universe characterizes the distribution of matter in it. This uniform distribution of matter can be justified by counting the number of galaxies up to a given apparent magnitude. According to observations, the density of matter in the part of space we see is on average the same.

Ø Nonstationarity means that the Universe cannot be in a static, unchanging state, but must either expand or contract

In modern cosmology, these three statements are called cosmological postulates. The combination of these postulates is the fundamental cosmological principle. The cosmological principle directly follows from the postulates of the general theory of relativity. A. Friedman, on the basis of the postulates he put forward, created a model of the structure of the Universe in which all galaxies are moving away from each other. This model is similar to a uniformly inflating rubber ball, all points of which move away from each other. The distance between any two points increases, but neither of them can be called the center of expansion. Moreover, the greater the distance between the points, the faster they move away from each other. Friedman himself considered only one model of the structure of the Universe, in which space changes according to a parabolic law. That is, at first it will slowly expand, and then, under the influence of gravitational forces, the expansion will be replaced by compression to its original size. His followers showed that there are at least three models for which all three cosmological postulates are satisfied. The parabolic model of A. Friedman is one of the possible options. A slightly different solution to the problem was found by the Dutch astronomer W. de Sitter. The space of the Universe in his model is hyperbolic, that is, the expansion of the Universe occurs with increasing acceleration. The expansion rate is so high that gravitational influence cannot interfere with this process. He actually predicted the expansion of the Universe. The third option for the behavior of the Universe was calculated by the Belgian priest J. Lemaitre. In his model, the Universe will expand to infinity, but the rate of expansion will constantly decrease - this dependence is logarithmic. In this case, the expansion rate is just sufficient to avoid contraction to zero. In the first model, space is curved and closed on itself. It is a sphere, so its dimensions are finite. In the second model, space is curved differently, in the form of a hyperbolic paraboloid (or saddle), the space is infinite. In the third model with a critical expansion rate, space is flat, and therefore also infinite.

Initially, these hypotheses were perceived as an incident, including by A. Einstein. However, already in 1926, an epoch-making event in cosmology occurred, which confirmed the correctness of the calculations of Friedmann - De Sitter - Lemaitre. Such an event, which influenced the construction of all existing models of the Universe, was the work of the American astronomer Edwin P. Hubble. In 1929, while conducting observations with the largest telescope at that time, he found that light coming to Earth from distant galaxies is shifted towards the long-wavelength part of the spectrum. This phenomenon, called the “Redshift Effect,” is based on a principle discovered by the famous physicist K. Doppler. The Doppler effect says that in the spectrum of a radiation source approaching the observer, the spectral lines are shifted to the short-wave (violet) side, while in the spectrum of a source moving away from the observer, the spectral lines are shifted to the red (long-wave) side.

The redshift effect indicates that galaxies are moving away from the observer. With the exception of the famous Andromeda Nebula and several star systems closest to us, all other galaxies are moving away from us. Moreover, it turned out that the speed of expansion of galaxies is not the same in different parts of the Universe. The further away they are located, the faster they move away from us. In other words, the redshift value turned out to be proportional to the distance to the radiation source - this is the strict formulation of the open Hubble law. The natural relationship between the speed of removal of galaxies and the distance to them is described using the Hubble constant (N, km/sec per 1 megaparsec of distance).

V = Hr ,

where V is the speed of removal of galaxies, H is the Hubble constant, r is the distance between them.

The value of this constant has not yet been definitively established. Various scientists define it in the range of 80 ± 17 km/sec for each megaparsec of distance. The phenomenon of red shift was explained in the phenomenon of “galaxy recession”. In this regard, the problems of studying the expansion of the Universe and determining its age based on the duration of this expansion come to the fore.

Most modern cosmologists understand this expansion as the expansion of the entire conceivable and existing Universe... Unfortunately, his early death did not allow the brilliant theorist of the Universe A. A. Friedman, whose ideas have guided the thought of cosmologists for more than half a century, to take part in the further revolutionary development of the process himself updating the cosmological picture of the world. The experience of the history of the development of knowledge about the world suggests, however, that the modern relativistic cosmological picture of the world, being the result of extrapolation of knowledge about a limited part of the Universe to the entire conceivable “whole,” is inevitably inaccurate. Therefore, one can think that it rather reflects the properties of a limited part of the Universe (which can be called the Metagalaxy), and, perhaps, only one of the stages of its development (which relativistic cosmology allows and which can become clearer with clarification of the average density of matter in the Metagalaxy). At present, however, at this point the picture of the world remains uncertain.

Chapter 3. Modern research into cosmological models of the Universe

.1 Nobel Prize for the discovery of the accelerated expansion of the Universe

Modern cosmology is a complex, integrated and rapidly developing system of natural scientific (astronomy, physics, chemistry, etc.) and philosophical knowledge about the Universe as a whole, based on both observational data and theoretical conclusions related to the part of the universe covered by astronomical observations .

Quite recently, in the field of modern cosmology, a discovery was made that in the future could change our ideas about the origin and evolution of our Universe. Scientists who made a huge contribution to the development of this discovery were awarded the Nobel Prize for their work.

The Nobel Prize was awarded to the American Saul Perlmutter, the Australian Brian Schmidt and the American Adam Rees for their discovery of the accelerated expansion of the Universe.

In 1998, scientists discovered that the Universe is expanding at an accelerating rate. The discovery was made through the study of Type Ia supernovae. Supernovae are stars that flash brightly in the sky from time to time and then dim fairly quickly. Because of their unique properties, these stars are used as markers to determine how cosmological distances change over time. A supernova is a moment in the life of a massive star when it experiences a catastrophic explosion. Supernovae come in different types depending on the specific circumstances preceding the cataclysm. During observations, the type of flare is determined by the spectrum and shape of the light curve. Supernovae, designated Ia, occur in the thermonuclear explosion of a white dwarf whose mass has exceeded a threshold of ~1.4 solar masses, called the Chandrasekhar limit. As long as the white dwarf's mass is below a threshold value, the star's gravitational force is balanced by the pressure of the degenerate electron gas. But if in a close binary system matter flows onto it from a neighboring star, then at a certain moment the electron pressure turns out to be insufficient and the star explodes, and astronomers record another type Ia supernova explosion. Since the threshold mass and the reason why a white dwarf explodes are always the same, such supernovae at maximum brightness should have the same, and very high, luminosity and can serve as a “standard candle” for determining intergalactic distances. If we collect data on many such supernovae and compare the distances to them with the redshifts of the galaxies in which the explosions occurred, we can determine how the expansion rate of the Universe has changed in the past and select an appropriate cosmological model.

By studying distant supernovae, scientists have found that they are at least a quarter dimmer than theory predicts - meaning the stars are too far away. Having thus calculated the parameters of the expansion of the Universe, scientists have established that this process is accelerating.

3.2 Dark matter

Dark matter is similar to ordinary matter in the sense that it can clump together (the size of, say, a galaxy or cluster of galaxies) and participates in gravitational interactions in the same way as ordinary matter. Most likely, it consists of new particles that have not yet been discovered under terrestrial conditions.

In addition to cosmological data, measurements of the gravitational field in galaxy clusters and in galaxies support the existence of dark matter. There are several ways to measure the gravitational field in galaxy clusters, one of which is gravitational lensing, illustrated in Fig. 4.

Rice. 4. Gravitational lensing.

The gravitational field of the cluster bends the rays of light emitted by the galaxy located behind the cluster, i.e. the gravitational field acts like a lens. In this case, sometimes several images of this distant galaxy appear; on the left half of Fig. 7 they are blue. The bending of light depends on the distribution of mass in the cluster, regardless of which particles create that mass. The mass distribution restored in this way is shown on the right half of Fig. 7 in blue; it is clear that it is very different from the distribution of the luminous substance. The masses of galaxy clusters measured in this way are consistent with the fact that dark matter contributes about 25% of the total energy density in the Universe. Let us recall that this same number is obtained from comparing the theory of formation of structures (galaxies, clusters) with observations.

Dark matter also exists in galaxies. This again follows from measurements of the gravitational field, now in galaxies and their environs. The stronger the gravitational field, the faster the stars and clouds of gas rotate around the galaxy, so measuring rotation rates depending on the distance to the center of the galaxy makes it possible to reconstruct the distribution of mass in it.

What are dark matter particles? It is clear that these particles should not decay into other, lighter particles, otherwise they would decay during the existence of the Universe. This fact itself indicates that a new, not yet discovered conservation law operates in nature, prohibiting these particles from decaying. The analogy here is with the law of conservation of electric charge: an electron is the lightest particle with an electric charge, and that is why it does not decay into lighter particles (for example, neutrinos and photons). Further, dark matter particles interact extremely weakly with our matter, otherwise they would have already been discovered in earthly experiments. Then the area of ​​hypotheses begins. The most plausible (but far from the only!) hypothesis seems to be that dark matter particles are 100-1000 times heavier than a proton, and that their interaction with ordinary matter is comparable in intensity to the interaction of neutrinos. It is within the framework of this hypothesis that the modern density of dark matter finds a simple explanation: dark matter particles were intensively born and annihilated in the very early Universe at ultra-high temperatures (about 1015 degrees), and some of them have survived to this day. With the indicated parameters of these particles, their current number in the Universe turns out to be exactly what is needed.

Can we expect the discovery of dark matter particles in the near future under terrestrial conditions? Since today we do not know the nature of these particles, it is impossible to answer this question completely unambiguously. However, the outlook seems very optimistic.

There are several ways to search for dark matter particles. One of them is associated with experiments at future high-energy accelerators - colliders. If dark matter particles are really 100-1000 times heavier than a proton, then they will be born in collisions of ordinary particles accelerated at colliders to high energies (the energies achieved at existing colliders are not enough for this). The immediate prospects here are connected with the Large Hadron Collider (LHC), which is being built at the international center CERN near Geneva, which will produce colliding beams of protons with an energy of 7x7 Teraelectronvolts. It must be said that, according to today's popular hypotheses, dark matter particles are only one representative of a new family of elementary particles, so that along with the discovery of dark matter particles, one can hope for the discovery of a whole class of new particles and new interactions at accelerators. Cosmology suggests that the world of elementary particles is far from being exhausted by the “building blocks” known today!

Another way is to detect dark matter particles flying around us. There are by no means a small number of them: with a mass equal to 1000 times the mass of a proton, there should be 1000 of these particles here and now per cubic meter. The problem is that they interact extremely weakly with ordinary particles; the substance is transparent to them. However, dark matter particles occasionally collide with atomic nuclei, and these collisions can hopefully be detected. The search in this direction is carried out using a number of highly sensitive detectors placed deep underground, where the background from cosmic rays is sharply reduced.

Finally, another way is associated with recording the products of annihilation of dark matter particles among themselves. These particles should accumulate in the center of the Earth and in the center of the Sun (the matter is almost transparent to them, and they are able to fall into the Earth or the Sun). There they annihilate each other, and in the process other particles are formed, including neutrinos. These neutrinos pass freely through the thickness of the Earth or the Sun, and can be recorded by special installations - neutrino telescopes. One of these neutrino telescopes is located in the depths of Lake Baikal, the other (AMANDA) is located deep in the ice at the South Pole. There are other approaches to searching for dark matter particles, for example, searching for the products of their annihilation in the central region of our Galaxy. Time will tell which of all these paths will lead to success first, but in any case, the discovery of these new particles and the study of their properties will be the most important scientific achievement. These particles will tell us about the properties of the Universe 10-9 s (one billionth of a second!) after the Big Bang, when the temperature of the Universe was 1015 degrees, and dark matter particles intensively interacted with cosmic plasma.

3.3 Dark energy

Dark energy is a much stranger substance than dark matter. To begin with, it does not gather in clumps, but is evenly “spread” throughout the Universe. There is as much of it in galaxies and galaxy clusters as outside them. The most unusual thing is that dark energy, in a certain sense, experiences anti-gravity. We have already said that modern astronomical methods can not only measure the current rate of expansion of the Universe, but also determine how it has changed over time. So, astronomical observations indicate that today (and in the recent past) the Universe is expanding at an accelerating rate: the rate of expansion is increasing with time. In this sense, we can talk about antigravity: ordinary gravitational attraction would slow down the retreat of galaxies, but in our Universe, it turns out that the opposite is true.

heliocentric universe cosmological gravitational

Rice. 5. Illustration of dark energy.

This picture, generally speaking, does not contradict the general theory of relativity, but for this, dark energy must have a special property - negative pressure. This sharply distinguishes it from ordinary forms of matter. It is no exaggeration to say that the nature of dark energy is the main mystery of fundamental physics of the 21st century.

One of the candidates for the role of dark energy is vacuum. The vacuum energy density does not change as the Universe expands, and this means negative vacuum pressure. Another candidate is a new super-weak field that permeates the entire Universe; the term “quintessence” is used for it. There are other candidates, but in any case, dark energy is something completely unusual.

Another way to explain the accelerated expansion of the Universe is to assume that the laws of gravity themselves change over cosmological distances and cosmological times. This hypothesis is far from harmless: attempts to generalize the general theory of relativity in this direction face serious difficulties. Apparently, if such a generalization is possible at all, it will be associated with the idea of ​​the existence of additional dimensions of space, in addition to the three dimensions that we perceive in everyday experience.

Unfortunately, there are currently no visible ways to directly experimentally study dark energy under terrestrial conditions. This, of course, does not mean that new brilliant ideas in this direction cannot appear in the future, but today hopes for clarifying the nature of dark energy (or, more broadly, the reasons for the accelerated expansion of the Universe) are associated exclusively with astronomical observations and with obtaining new, more accurate cosmological data. We have to learn in detail exactly how the Universe expanded at a relatively late stage of its evolution, and this, hopefully, will allow us to make a choice between different hypotheses.

Conclusion

In this course work I examined cosmological models of the Universe. Having analyzed the literature on the course of general physics and astronomy, I traced the history of cosmological research, examined modern cosmological models of the Universe and selected illustrative material for the research topic. Having proved the relevance of the chosen topic, I summed up the work done.

Literature

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.Veselovsky I.N. Aristarchus of Samos - Copernicus of the ancient world. Historical and astronomical research. - M.: Nauka, 1961. Issue 7, p. 44.

.Efremov Yu.N., Pavlovskaya E.D. Determining the epoch of observation of the Almagest star catalog using the proper motions of stars. -- Historical and astronomical research. M.: Nauka, 1989, issue 18.

.I. G. Kolchinsky, A. A. Korsun, M. G. Rodriguez. Astronomers. 2nd ed., Kyiv, 1986.

.Karpenkov S.Kh. The concept of modern natural science: Textbook for universities / M.: Academic prospect, 2001.

.Klimishin I.A. Discovery of the Universe. - M.: Nauka, 1987.

.Matvievskaya G.P. As-Sufi. - Historical and astronomical research. M.: Nauka, 1983, issue 16, pp. 93--138.

.Pannekoek A. History of astronomy. - M.: Nauka, 1966.

.S. Shapiro, S. Tyukalski. Black holes, white dwarfs and neutron stars. Moscow, Mir, 1985

.Samygina S.I. “Concepts of modern natural science”/Rostov n/D: “Phoenix”, 1997.

.Physics of space: A small encyclopedia. M.: Sov. encyclopedia, 1986.

.Hawking S. A Brief History of Time: From the Big Bang to Black Holes. M.: Mir, 1990.

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