Big universe online magazine posts. Scientists have proven that the universe could not have been born without a big bang. Observations of non-evolved objects
On the edge of the world
When they want to talk about something that is very far from us, they often say: Where is this the end of the world? Probably, over the many centuries that have passed since the birth of this saying, the idea of the end of the world has changed more than once. For ancient Greeks outside the ecumene - the inhabited earth - there was a tiny region. Behind the Pillars of Hercules, “terra incognita”, an unknown land, had already begun for them. They had no idea about China. The Age of the Greats showed that the Earth has no edge, and Copernicus, (more details:), who discovered, threw the edge of the world beyond the sphere of fixed stars.
Nicolaus Copernicus - discovered the solar system. , who formulated it, pushed it back to infinity altogether. But Einstein, whose brilliant equations were solved by the Soviet scientist A. A. Friedman, created the doctrine of our Small Universe and made it possible to more accurately determine the edge of the world. It turned out to be about 12-15 billion light years away from us. 
Isaac Newton - discovered the law of universal gravitation. Einstein's followers clearly stated that no material body can leave the limits of the Small Universe, closed by the force of universal gravity, and we will never know what lies beyond its boundaries. It seemed that human thought had reached the extreme possible limits, and itself comprehended their inevitability. And that means you shouldn’t push further. 
Albert Einstein - created the doctrine of our Small Universe. And for more than half a century, human thought tried not to cross the established extreme line, especially since even within the limits outlined by Einstein’s equations there were quite a lot of mysterious and mysterious things that made sense to think about. Even science fiction writers, whose bold flight of thoughts no one ever put obstacles in, were apparently satisfied with the areas allotted to them, which contained an uncountable number of worlds of the most diverse classes and categories: planets and stars, galaxies and quasars. What is the Big Universe
And only in the twentieth century did theoretical physicists first raise the question of what lies beyond our Small Universe, what is the Big Universe, into which the expanding boundaries of our Universe are continuously moving at the speed of light? We have to do the most long journey. We follow the thoughts of the scientists who made this journey with the help of mathematical formulas. We will accomplish it on the wings of dreams. Countless science fiction writers are following us along this same path, for whom those 12-15 billion light years of the radius of our Universe, measured by scientists according to Einstein’s formulas, will become cramped... So, let’s go! We are quickly picking up speed. Here, of course, today's space technologies are insufficient. Speeds even ten times faster will barely be sufficient to study our solar system. The speed of light will not be enough for us; we cannot spend tens of billions of years just to overcome the space of our Universe!
Planets of the solar system. No, we must cover this section of the path in ten seconds. And here we are at the borders of the Universe. The gigantic fires of quasars, which are always located almost at its outermost borders, blaze unbearably. Now they are left behind and seem to be winking at us: after all, the radiation of quasars pulsates and changes periodically. We fly at the same fantastic speed and suddenly find ourselves surrounded by complete darkness. No sparks from distant stars, no colored milk from mysterious nebulae. Maybe the Big Universe is absolute emptiness? We turn on all possible devices. No, there are some hints of the presence of matter. Occasionally, quanta from various parts of the electromagnetic spectrum are encountered. It was possible to detect several meteoric dust particles - matter. And further. Quite a dense cloud of gravitons; we clearly feel the action of many gravitational masses. But where are these same gravitating bodies? Neither various telescopes nor various locators can show them to us. So, maybe these are all already “burnt-out” pulsars and “black holes”, the final stages of the development of stars, when matter, collected in giant formations, cannot resist its own gravitational field and, having tightly swaddled itself, plunges into a long, almost endless sleep ? Such a formation cannot be seen through a telescope - it does not emit anything. It cannot be detected by a radar either: it irreversibly absorbs any rays that fall on it. And only the gravitational field betrays its presence. 
Well, the Big Universe is infinite not only in space, but also in time. 15 billion years of existence of the Small Universe compared to the eternity of the existence of the Big Universe is not even an instant, not a second compared to a millennium; we can calculate how many seconds are included in a millennium and we will get, although large, a finite figure. How many billions of years are included in eternity? Infinite quantity! Eternity is simply incommensurate with billions of years! So, during these innumerable times, any, the most economically burning star fires managed to “burn out”, they managed to go through all the stages of stellar life, they managed to go out and cool down almost to absolute zero. By the way, the temperature of a body that finds itself in the space of the Big Universe does not differ by a thousandth of a degree from absolute zero on the Kelvin scale. Meanwhile, a thermometer placed at any point in the Small Universe will show several degrees of positive temperature: after all, the light of the most distant stars carries some energy. In our Small Universe it is not only light, but also warm! Yes, it’s not very comfortable in the Big Universe! We slow down the speed of our flight to values usual in the Small Universe - tens and hundreds of kilometers per second. Objects inhabiting the Big Universe
Let's look at some of the inhabiting Big Universe objects. Here a gigantic (judging by the size of its gravitational field) mass of matter flies past. We peer into the superlocator screen. It turns out that the powerful field gives rise to a tiny formation, its diameter is only about ten kilometers. Neutron star! We examine its surface; it is perfectly smooth, as if it had been thoroughly polished in a good workshop. Suddenly there was an instantaneous flash on this surface: attracted by a powerful attraction, a meteorite, a piece of a substance common to us, crashed into our dead star. No, he did not remain lying on the surface of the star corpse. It somehow very quickly spread over its surface like a puddle of solid matter, and then was absorbed without a trace into the ground... Jokes are bad with such powerful dwarfs! After all, their almighty gravity will in the same way completely absorb the starship, its crew, and instruments and turn everything into a neutron liquid, from which, after time, hydrogen and helium of the new Small Universe will arise. And of course, in this remelting all the events that happened to substances in our days will be forgotten, just as after remelting a metal it is impossible to restore the previous contours of machine parts that have gone to scrap.What space of the Big Universe
Yes, there are many things here that are different from those in our Small Universe. Well, what Big Universe space? What are its properties? We carry out experiments. The space is the same as ours, three-dimensional. Like ours, it is curved in places by the gravitational field. Yes, being one of the forms of existence of matter, space is tightly connected with the matter that fills it. This connection is especially pronounced here, where gigantic masses of matter are concentrated into tiny formations. We have already seen some of them - “black holes” and neutron stars. These formations, which are a natural result of the development of stars, have already been found in our Universe.
A black hole in the big Universe. But there are also material formations here that are much smaller in size - only meters, centimeters or even microns in diameter, but their mass is quite large, they also consist of super-densified matter. Such bodies cannot arise by themselves; their own gravity is not enough to swaddle themselves tightly. But they can exist steadily if an outside force has squeezed them to such a state. What kind of power is this? Or maybe these are fragments of larger blocks of super-dense matter that collapsed for some reason? These are the plankeons of K. P. Stanyukovich. In the Big Universe, matter is also found in its usual form. No, these are not stars, they are smaller than stars. In our Small Universe, these formations could be small planets or satellites of planets. Maybe they ever were in some Small Universe unknown to us, but the stars around which they revolved went out and shrank, some accident tore them away from the central stars, and since their “small” ones disintegrated universes,” they wander through the infinity of the Big Universe “without a rudder and without sails.” Rogue Planets
Maybe among these wandering planets Are there any that were inhabited by intelligent beings? Of course, in the conditions of the Big Universe, life cannot exist on them for long. These completely frozen planets are deprived of energy sources. Their reserves of radioactive substances have long since decayed to the last molecule; they have no energy from wind, water, or fossil fuels: after all, all these energy sources have their primary source in the rays of the central star, and they went out a long time ago. But if the inhabitants of these worlds knew how to foresee their upcoming fate, they could seal letters in these planets to those who, after unknown times, would visit them and be able to read and understand. However, is the possibility of their long-term existence in the endless space of this Universe, so hostile to living things, really likely? The Big Universe is filled with matter approximately as “loosely” as our Small Universe. At the same time, we must remember that the abundance of stars that we observe on a moonless night in the sky is not typical for the Small Universe. It’s just that our Sun, and therefore the Earth, are part of a swarm of stars - our Galaxy.Intergalactic space
More typical intergalactic space, from which only a few Galaxies would be visible, like light, slightly luminous clouds falling on the black velvet of the sky. Stars and galaxies close to each other move relative to each other at speeds of tens and hundreds of kilometers per second.
Stars of intergalactic space. As you can see, these speeds are low. But they are such that they prevent the fall of some celestial bodies onto others. When, say, two stars come together, their trajectories will be slightly bent, but the stars will each fly their own path. The probability of collisions or convergence of stars is practically zero, even in densely populated star cities like our Galaxy. The probability of collision of material bodies in the Big Universe is approximately the same. And letters sealed for ultra-distant descendants, taking into account the ultra-low temperatures that stopped even the thermal movement of molecules, will also be able to exist indefinitely for a long time. Could this not serve as excellent material for a fantastic story called “Letter from Eternity”? So, in the Big Universe we have not found a space dissimilar to our three-dimensional one. In all likelihood, spaces of four and many dimensions are a bare mathematical abstraction that has no real embodiments, unless, of course, we consider time as the fourth dimension. But it differs sharply from the first three dimensions (forward-backward, left-right, up-down) by its very character. Formation of the Small Universe
Well, how did ours arise in the Big Universe? Small Universe? Some scientists believe that as a result of the collision of two supermassive formations of matter, which was in a certain “pre-stellar” form, all the matter that makes up our Universe was released in one fell swoop. It began to rapidly expand at the speed of light in all directions, forming a kind of luminous bubble in the infinite body of the Big Universe.Big Bang Theory of the Universe
The author of the proposed hypothesis of the structure of the Big Universe, professor, doctor of physical and mathematical sciences K. P. Stanyukovich believes that this initial explosion is of a slightly different nature.
Kirill Petrovich Stanyukovich is the author of the big bang theory of the Universe. It's hard to say why this started big bang of the universe. Perhaps when two plankeons collided, perhaps a random fluctuation in the density of one plankeon caused the first sparks of this explosion to appear. It could have been very modest in scale, but it released a gravitational wave, and when it reached the nearest planckeons, they also “entered a reaction” - the release of matter bound by gravity began, accompanied by huge emissions of both substances and quanta of electromagnetic radiation. Small plankeons carried out this transformation immediately, but large ones, which subsequently formed the cores of galaxies, spent billions of years on this process. And today astronomers are still surprised by the never-ending generosity of the nuclei of some Galaxies, throwing out violent streams of gases, rays, and clusters of stars. This means that the process of transformation of prestellar matter into stellar matter has not been completed in them... The sparks of the great gravitational fire fly further and further and more and more new planckeons flare up, set on fire by these sparks. Quasars
Astronomers know of several relatively young fires that are likely to blossom into luxurious galaxies in the future. These are the so-called quasars. All of them are very far from us, at the very “edge” of our Small Universe. This is the very beginning of the burning of the cores of future galaxies. Billions of years will pass, and the substance released from the flames of these fires will form into streams of stars and planets, which form beautiful spiral crowns around these cores. They will become remarkably similar to the existing spiral galaxies. But, unfortunately, in those days our Galaxies will already burn out and scatter into space in handfuls of cooled dead bodies, probably in many ways similar in the nature of the matter that composes them to prestellar matter. For them, the cycle will close until a new “fire of matter” occurs. And in the Galaxies formed by the combustion of today's quasars, planets will appear suitable for development and life, and, perhaps, intelligence. And their sages will look at their starry skies and wonder why they are so alone in the Universe? Will the minds of people live in those ultra-distant times? Will he pass through the unimaginable abysses of time? Or will all the creations of our culture be melted down in some plankeon without a trace, so that only one matter will remain - eternal and indestructible? There is no answer to all these questions, and it is not known when science will answer them. But, once it has arisen, intelligent life, if it passes the first risky stages of its development, will increasingly strengthen its position. What could threaten the culture of earthlings when it spreads to a group of planetary systems of nearby stars? Space disaster? The explosion of the Sun, which suddenly turned out to be a supernova? Will this cause no more damage to the culture of mankind than today’s tsunami wave that washed away a couple of islands? Yes, intelligent life that has reached such a milestone will be as indestructible as matter itself. And she will not be afraid of either the gigantic chasms of time or the immeasurable gaps of space. And yet, our journey into the Big Universe should be considered unscientific fiction, an absurd fiction. No, the point is not that the space of the Big Universe we imagine will turn out to be different, that its “population” we imagine will turn out to be different. No, in all these questions we firmly adhered to the scientific facts known to us, and followed the roads already trodden by the hypotheses of scientists. The point is different.Travel to the Big Universe is impossible
The fact is that journey to the Big Universe may turn out to be for us, the people of Earth impossible,unfeasible. Remember the basic properties of our Universe. After all, it is “expanding”. At the same time, its “expanding” faces move at the maximum speed possible in our Universe - at the speed of light in emptiness. But such a speed is impossible for any material body. Indeed, as the speed increases, approaching the speed of light, the mass of this body will continuously increase. Very soon it will exceed all possible values - the masses of planets, stars, quasars, galaxies, our entire Universe.
Journey to the Big Universe. The mass of our accelerating body will become infinitely large. Well, acceleration can be imparted to an infinitely large mass only by an infinitely large force. It is easy to understand that we have reached a dead end. We will not be able to move our interstellar ship, which has an infinitely large mass. And humanity will never be able to catch up with the ray of light. But we are not talking about the speed of light, but about incomparably high speeds that would allow us to cross our entire Universe in a matter of minutes. This method of space travel was extracted from volumes of non-science fiction. More often than not, the corresponding author reports that his interstellar ship is moving in "subspace", "piercing the fourth dimension", without saying anything substantive about "subspace" and the "fourth dimension". Such modesty is understandable: it is impossible to say anything concrete about the terms invented by science fiction writers. For any statement about speeds higher than the speed of light today is unscientific and fantastic. And from a modern point of view, talking about super-fast travel is nonsense. Of course, it is unacceptable in popular science books. Unless only in a specially noted case, when it is obvious that this is a simple invention, made for “official purposes” in order to more clearly show the main thing. So, travel to prove the existence of the Big Universe is impossible...
28.02.1993 15:16
| A. D. Chernin /The Universe and We
The starry sky has always occupied the imagination of people. Why do stars light up? How many of them shine in the night? Are they far from us? Does the stellar universe have boundaries? Since ancient times, man has been thinking about this, striving to understand and comprehend the structure of the big world in which he lives.
The earliest ideas of people about the starry world were preserved in tales and legends. Centuries and millennia passed before the science of the Universe arose and received deep substantiation and development, revealing to us the remarkable simplicity and amazing order of the universe. It is not for nothing that in ancient Greece the Universe was called Cosmos: this word originally meant order and beauty.
Picture of the world
In the ancient Indian book called "Rigveda", which means "Book of Hymns", one can find one of the very first descriptions in the history of mankind of the entire Universe as a single whole. It contains, first of all, the Earth. It appears as a boundless flat surface - “vast space”. This surface is covered on top by the sky - a blue vault dotted with stars. Between the sky and the Earth is “luminous air.”
The early ideas about the world among the ancient Greeks and Romans are very similar to this picture - also a flat Earth under the dome of the sky.
This was very far from science. But something else is important here. The daring goal itself is remarkable and grandiose - to embrace the entire Universe with thought. This is where our confidence originates that the human mind is capable of comprehending, understanding, unraveling the structure of the Universe, and creating a complete picture of the world in its imagination.
Celestial Spheres
The scientific picture of the world took shape as the most important knowledge about the Earth, Sun, Moon, planets, and stars accumulated.
Back in the 6th century. BC. the great mathematician and philosopher of antiquity Pythagoras taught that the Earth is spherical. Proof of this is, for example, the round shadow of our planet falling on the Moon during lunar eclipses.
Another great scientist of the ancient world, Aristotle, considered the entire Universe to be spherical, spherical. This idea was suggested not only by the rounded appearance of the sky, but also by the circular daily movements of the luminaries. He placed the Earth at the center of his picture of the Universe. Around it were the Sun, the Moon and the five planets known at that time. Each of these bodies corresponded to its own sphere revolving around our planet. The body is “attached” to its sphere and therefore also moves around the Earth. The eighth sphere was considered the most distant sphere, encompassing all the others. The stars are “attached” to it. It also revolved around the Earth in accordance with the observed daily movement of the sky.
Aristotle believed that celestial bodies, like their spheres, are made of a special “heavenly” material - ether, which does not have the properties of gravity and lightness and performs eternal circular motion in world space.
This picture of the world reigned in the minds of people for two millennia - right up to the era of Copernicus. In the 2nd century AD, this picture was improved by Ptolemy, the famous astronomer and geographer who lived in Alexandria. He gave a detailed mathematical theory of planetary motion. Ptolemy could accurately calculate the visible positions of the luminaries - where they are now, where they were before and where they will be later.
True, five spheres were not enough to reproduce all the subtle details of the movement of planets across the sky. New ones had to be added to the five circular movements, and the old ones had to be rebuilt. For Ptolemy, each planet participated in several circular movements, and their addition gave the visible movement of the planets across the sky.
Later, in the Middle Ages, Aristotle’s doctrine of the celestial spheres, which then became generally accepted, was attempted to be developed in a completely different direction. For example, the spheres were proposed to be considered crystal. Why? Probably because crystal is transparent and, moreover, a crystal sphere is beautiful! And yet such additions did not at all improve the picture of the universe.
The world of Copernicus.
Copernicus' book, published in the year of his death (1543), bore the modest title "On the Revolutions of the Celestial Spheres." But this was a complete overthrow of the Aristotelian view of the world. The complex colossus of hollow transparent crystal spheres did not immediately become a thing of the past. From this time on, a new era began in our understanding of the Universe. It continues to this day.
Thanks to Copernicus, we learned that the Sun occupies its proper position at the center of the planetary system. The Earth is not the center of the world, but one of the ordinary planets revolving around the Sun. So everything fell into place. The structure of the solar system was finally solved.
Further discoveries by astronomers expanded the family of planets. There are nine of them: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto. In this order they occupy their orbits around the Sun. Many small bodies of the Solar System have been discovered - asteroids and comets. But this did not change the Copernican picture of the world. On the contrary, all these discoveries only confirm and clarify it.
Now we understand that we live on a small planet, shaped like a ball. The Earth revolves around the Sun in an orbit not too different from a circle. The radius of this orbit is close to 150 million kilometers.
The distance from the Sun to Saturn, the farthest planet known at the time of Copernicus, is approximately ten times the radius of the Earth's orbit. This distance was completely correctly determined by Copernicus. The distance from the Sun to the most distant known planet (Pluto) is almost four times greater and is approximately six billion kilometers.
This is the picture of the Universe in our immediate environment. This is the world according to Copernicus.
But the Solar System is not the whole Universe. We can say that this is only our small world. What about distant stars? Copernicus did not dare to express any opinion about them. He simply left them in the same place, on the distant sphere, where Aristotle had them, and only said - and quite correctly - that the distance to them is many times greater than the size of the planetary orbits. Like ancient scientists, he imagined the Universe as a closed space, limited to this sphere.
How many stars are there in the sky?
Everyone will answer this question: oh, a lot. But how much - a hundred or a thousand?
Much more, a million or a billion.
This answer can be heard often.
Indeed, the sight of the starry sky gives us the impression of countless stars. As Lomonosov said in his famous poem: “An abyss has opened, it’s full of stars, the stars have no number...”
But in reality, the number of stars visible to the naked eye is not at all so large. If you do not succumb to the impression, but try to count them, it will turn out that even on a clear moonless night, when nothing interferes with observation, a person with acute vision will see no more than two to three thousand flickering dots in the sky.
In the list compiled in the 2nd century BC. by the famous ancient Greek astronomer Hipparchus and later supplemented by Ptolemy, there are 1022 stars. Hevelius, the last astronomer to make such calculations without the help of a telescope, brought their number to 1533.
But already in ancient times they suspected the existence of a large number of stars invisible to the naked eye. Democritus, the great scientist of antiquity, said that the whitish strip stretching across the entire sky, which we call the Milky Way, is actually a combination of light from many individually invisible stars. Disputes about the structure of the Milky Way have continued for centuries. The solution - in favor of Democritus's guess - came in 1610, when Galileo reported the first discoveries made in the sky using a telescope. He wrote with understandable excitement and pride that he had now succeeded in “making available to the eye stars that had never been visible before and whose number is at least ten times greater than the number of stars known from ancient times.”
Sun and stars
But this great discovery still left the world of stars mysterious. Are all of them, visible and invisible, really concentrated in a thin spherical layer around the Sun?
Even before Galileo’s discovery, a remarkably bold idea, unexpected at that time, was expressed. It belongs to Giordano Bruno, whose tragic fate is known to everyone. Bruno put forward the idea that our Sun is one of the stars of the Universe. Just one of a great many, and not the center of the Universe.
If Copernicus pointed out the place of the Earth - not at all in the center of the world, then Bruno and the Sun deprived this privilege.
Bruno's idea gave rise to many striking consequences. From it followed an estimate of the distances to the stars. Indeed, the Sun is a star, like others, but only the one closest to us. That's why it's so big and bright. How far should the star be moved so that it looks like, for example, the star Sirius? The answer to this question was given by the Dutch astronomer Huygens (1629-1695). He compared the brilliance of these two celestial bodies, and this is what it turned out: Sirius is hundreds of thousands of times farther from us than the Sun.
To better imagine how great the distance to the star is, let's say this: a ray of light that travels three hundred thousand kilometers in one second takes several years to travel from us to Sirius. Astronomers speak in this case of a distance of several light years. According to modern updated data, the distance to Sirius is 8.7 light years. And the distance from us to the Sun is only 8 1/3 light minutes.
Of course, different stars differ in themselves from the Sun and from each other (this is taken into account in the modern estimate of the distance to Sirius). Therefore, determining the distances to them even now often remains a difficult, sometimes simply unsolvable task for astronomers, although many new methods have been invented for this since the time of Huygens.
Bruno's remarkable idea and Huygens' calculation based on it became a very important step in the science of the Universe. Thanks to this, the boundaries of our knowledge about the world have expanded greatly, they have gone beyond the solar system and reached the stars.
Galaxy
Since the 17th century, the most important goal of astronomers has been to study the Milky Way - this gigantic collection of stars that Galileo saw through his telescope. The efforts of many generations of astronomer-observers were aimed at finding out what the total number of stars in the Milky Way is, determining its actual shape and boundaries, and estimating its size. Only in the 19th century was it possible to understand that this is a single system containing all visible and many invisible stars. Our Sun, and with it the Earth and planets, are included in this system on equal terms with everyone. Moreover, they are located far from the center, but on the outskirts of the Milky Way system. 
It took many more decades of careful observation and deep thought before the structure of the Galaxy could be elucidated. This is how they began to call the star system, which we see from the inside as a strip of the Milky Way. (The word "galaxy" is derived from the modern Greek "galaktos", which means "milky").
It turned out that the Galaxy has a fairly regular structure and shape, despite the visible raggedness of the Milky Way and the disorder with which, as it seems to us, the stars are scattered across the sky. It consists of a disk, a halo and a crown. As can be seen from the schematic drawing, the disk looks like two plates folded at the edges. It is formed by stars that move within this volume in almost circular orbits around the center of the Galaxy.
The diameter of the disk has been measured to be approximately one hundred thousand light years. This means that it takes light one hundred thousand years to cross the disk from end to end in diameter. And the number of stars in the disk is approximately one hundred billion.
There are ten times fewer stars in the halo. (The word “halo” means “round.”) They fill a slightly flattened spherical volume and move not in circular, but in highly elongated orbits. The planes of these orbits pass through the center of the Galaxy. They are distributed more or less evenly in different directions.
The disk and surrounding halo are embedded in the corona. If the radii of the disk and halo are comparable in size, then the radius of the corona is five, and maybe ten times larger. Why maybe"? Because the crown is invisible - no light comes from it. How did astronomers know about it then?
Hidden mass
All bodies in nature create gravity and experience its effects. Newton's well-known law speaks about this. They learned about the crown not by the light, but by the gravity created by it. It affects visible stars, luminous clouds of gas. Observing the movement of these bodies, astronomers discovered that in addition to the disk and halo, something else was acting on them. A detailed study eventually made it possible to discover a corona, which creates additional gravity. It turned out to be very massive - several times greater than the total mass of all the stars included in the disk and halo. This is the information obtained by the Estonian astronomer J. Einasto and his collaborators at the Tartu Observatory, and then by other astronomers.
Of course, studying the invisible corona is difficult. Because of this, estimates of its size and mass are not yet very accurate. But the main mystery of the crown is different: we don’t know what it consists of. We don’t know if there are stars in it, even if they are some unusual ones that don’t emit light at all.
Now many people assume that its mass is not composed of stars at all, but of elementary particles - for example, neutrinos. These particles have been known to physicists for a long time, but they themselves also remain mysterious. What is not known about them, one might say, is the most important thing: whether they have a rest mass, that is, the mass that the particle has in a state when it is not moving. Many elementary particles (electron, proton, neutron), from which all atoms are made, have such a mass. But a photon, a particle of light, does not have it. Photons exist only in motion. Neutrinos could serve as material for the corona, but only if they have rest mass.
It is easy to imagine how impatiently astronomers await news from physics laboratories, where special experiments are being carried out to find out whether neutrinos have rest mass. Theoretical physicists, meanwhile, are considering other options for elementary particles, not necessarily just neutrinos, that could act as carriers of hidden mass.
Star worlds.
By the beginning of our century, the boundaries of the Universe had expanded so much that they included the Galaxy. Many, if not all, thought then that this huge star system was the entire Universe.
But in the twenties, the first large telescopes were built, and new and unexpected horizons opened up for astronomers. It turned out that the world does not end outside the Galaxy. Billions of star systems, galaxies, both similar to ours and different from it, are scattered here and there across the expanses of the Universe.
Photos of galaxies taken with the largest telescopes are striking in their beauty and variety of shapes. These are mighty whirlwinds of star clouds, and regular balls or ellipsoids; other star systems do not exhibit a correct structure; they are ragged and shapeless. All these types of galaxies - spiral, elliptical, irregular, named after their appearance in photographs, were discovered and described by the American astronomer Edwin Hubble in the 20-30s of our century.
If we could see our Galaxy from the side and from afar, then it would appear to us completely different from the schematic drawing by which we became acquainted with its structure. We would not see either the disk, or the halo, or, of course, the corona, which is generally invisible. From great distances, only the brightest stars would be visible. And all of them, as it turned out, are collected in wide stripes, which extend in arcs from the central region of the Galaxy. The brightest stars form its spiral pattern. Only this pattern would be visible from afar. Our Galaxy in a photograph taken by an astronomer from some other galaxy would look very similar to the Andromeda Nebula as it appears to us from photographs.
Research recent years showed that many large galaxies (not just ours) have extended and massive invisible coronas. And this is very important: after all, if so, then it means that in general almost the entire mass of the Universe, or, in any case, its overwhelming part, is a mysterious, invisible, but gravitating “hidden” mass.
Chains and voids
Many, and perhaps almost all, galaxies are collected in various groups, which are called groups, clusters and superclusters - depending on how many of them there are. A group may contain only 3 or 4 galaxies, but a supercluster may contain tens of thousands. Our Galaxy, the Andromeda Nebula and more than a thousand similar objects are included in the Local Supercluster. It does not have a clearly defined shape and overall looks rather flattened.
Other superclusters that lie far from us, but are quite clearly visible with the help of modern large telescopes, look approximately the same.
Until recently, astronomers believed that superclusters were the largest formations in the Universe and that there were simply no other larger systems. It turned out, however, that this was not the case.
A few years ago, astronomers compiled an amazing map of the Universe. On it, each galaxy is represented by just a dot. At first glance, they are scattered randomly on the map. If you look closely, you can find groups, clusters and superclusters, the latter being represented by chains of dots. The map reveals that some of these chains connect and intersect, forming some kind of mesh or cellular pattern, reminiscent of lace or perhaps a honeycomb with a cell size of 100-300 million light years.
Whether such “grids” cover the entire Universe remains to be seen. But several individual cells outlined by superclusters were studied in detail. There are almost no galaxies inside them; they are all collected in “walls” that limit huge voids, which are now called “voids” (i.e., “emptiness”).
Cell and Void are the preliminary working names for the largest formation in the Universe. Larger systems in nature are unknown to us. Therefore, we can say that scientists have now solved one of the most ambitious problems in astronomy - the entire sequence, or, as they also say, the hierarchy of astronomical systems, is now completely known.
Universe
More than anything else, the Universe itself, which embraces and includes all the planets, stars, galaxies, clusters, superclusters and cells with voids. The range of modern telescopes reaches several billion light years. This is the size of the observable Universe.
All celestial bodies and systems amaze with their diversity of properties and complexity of structure. How is the entire Universe structured, the Universe as a whole? It turns out that it is extremely monotonous and simple!
Its main property is homogeneity. This can be said more precisely. Let's imagine that we have mentally identified a very large cubic volume in the Universe with an edge, say, five hundred million light years. Let's count how many galaxies there are in it. Let's make the same calculations for other, but equally gigantic volumes located in different parts of the Universe. If you do all this and compare the results, it turns out that each of them, no matter where you take them, contains the same number of galaxies. The same will happen when counting clusters and even cells.
So, if we ignore such “details” as clusters, superclusters, cells, and look at the Universe more broadly, mentally taking in the entire multitude of stellar worlds at once, then it will appear before us the same everywhere - “solid” and homogeneous.
You couldn't imagine a simpler device. It must be said that people have suspected this for a long time. For example, the wonderful thinker Pascal (1623-1662) said that the world is a circle, the center of which is everywhere, and the circumference is nowhere. So, with the help of a visual geometric image, he spoke about the homogeneity of the world.
In a homogeneous world, all “places,” one might say, have equal rights and any of them can claim to be the Center of the world. And if so, then it means that there is no center of the world at all.
Extension
The Universe has one more thing most important property, but no one even guessed about it until the end of the 20s of our century. The Universe is in motion - it is expanding. The distance between clusters and superclusters is constantly increasing. They seem to run away from each other. And the network of the cellular structure is stretched.
At all times, people preferred to consider the Universe eternal and unchanging. This point of view prevailed until the 20s. It was believed that the Universe is limited by the size of our Galaxy. And although individual stars of the Milky Way may be born and die, the Galaxy still remains the same - just as a forest remains unchanged, in which trees are replaced generation after generation.
A real revolution in the science of the Universe was made in 1922-24. works of St. Petersburg mathematician Alexander Alexandrovich Friedman. Based on the general theory of relativity that Einstein had just created at that time, he mathematically proved that the world is not something frozen and unchanging. As a single whole, it lives its own dynamic life, changes over time, expanding or contracting according to strictly defined laws.
Friedman discovered the non-stationary nature of the Universe. This was a theoretical prediction. It was possible to finally decide whether the Universe is expanding or contracting only on the basis of astronomical observations. Such observations in 1928-29. Hubble managed to do it.
He discovered that distant galaxies and entire groups of them are scattering from us in all directions. According to Friedman's predictions, this is exactly what the overall expansion of the Universe should look like.
If the Universe is expanding, it means that in the distant past clusters and superclusters were closer to each other. Moreover, from Friedman’s theory it follows that 15-20 billion years ago neither stars nor galaxies existed yet and all matter was mixed and compressed to a colossal density. This substance then had a monstrously high temperature. 
Big Bang
The hypothesis about the high temperature of cosmic matter in that distant era was put forward by Georgy Antonovich Gamov (1904-1968), who began his studies in cosmology at Leningrad University under the guidance of Professor A. A. Friedman. Gamow argued that the expansion of the Universe began with the Big Bang, which occurred simultaneously and everywhere in the world. The Big Bang filled space with hot matter and radiation.
The initial goal of Gamow's research was to determine the origin of the chemical elements that make up all the bodies in the Universe - galaxies, stars, planets and ourselves.
Astronomers have long established that the most abundant element in the Universe is hydrogen, number one on the periodic table. It accounts for approximately 3/4 of all “ordinary” (not hidden) matter in the Universe. About 1/4 is helium (element N2), and all other elements (carbon, oxygen, calcium, silicon, iron, etc.) account for very little, up to 2% (by mass). This is the chemical composition of the Sun and most stars.
How did the universal chemical composition of cosmic matter develop, how did the “standard” ratio between hydrogen and helium arise in the first place?
In search of an answer to this question, astronomers and physicists first turned to the interior of stars, where reactions of transformation of atomic nuclei occur intensively. It soon became clear, however, that under the conditions that exist in the central regions of stars like the Sun, no elements heavier than helium could be formed in any significant quantities.
What if chemical elements appeared not in stars, but throughout the entire Universe at the very first stages of cosmological expansion? The versatility of the chemical composition is automatically ensured. As for physical conditions, in the early Universe the matter was undoubtedly very dense, in any case, much denser than in the depths of stars. The high density guaranteed by Friedmann's cosmology is an indispensable condition for the occurrence of nuclear reactions of the synthesis of elements. These reactions also require a high temperature of the substance. The early Universe was, according to Gamow's idea, the “cauldron” in which the synthesis of all chemical elements took place.
As a result of many years of collective activity of scientists different countries, initiated by Gamow, in the 40-60s. It became apparent that the cosmic abundance of the two main elements - hydrogen and helium - could indeed be explained by nuclear reactions in the hot matter of the early Universe. Heavier elements must apparently be synthesized in a different way (during supernova explosions).
The synthesis of elements is possible, as already mentioned, only at high temperatures; but in a heated substance, according to the general laws of thermodynamics, there must always be radiation that is in thermal equilibrium with it. After the era of nucleosynthesis (which, by the way, lasted only a few minutes), the radiation does not disappear anywhere and continues to move along with matter during the general evolution of the expanding Universe. It should be preserved to the present era, only its temperature should be - due to significant expansion - much lower than at the beginning. Such radiation should create a general background of the sky in the short radio wave range.
The largest event in all of natural science, a real triumph of Friedmann-Gamow cosmology, was the discovery in 1965 of cosmic radio emission predicted by this theory. This was the most important observational discovery in cosmology since the discovery of the general recession of galaxies.
How galaxies formed
Observations have shown that cosmic radiation comes to us from all directions in space extremely uniformly. This fact has been established with a record accuracy for cosmology: up to hundredths of a percent. It is with this precision that we can now speak about the general uniformity, the homogeneity of the Universe itself as a whole.
So, observations reliably confirmed not only the idea of a hot beginning of the Universe, but also the ideas about the geometric properties of the world embedded in cosmology.
But that's not all. Quite recently, very weak, less than a thousandth of a percent, deviations from complete and ideal uniformity were found in the cosmic background. Cosmologists rejoiced at this discovery almost more than they once rejoiced at the discovery of radiation itself. This was a long-awaited discovery.
For a long time, theorists predicted that there should be small “ripples” in cosmic radiation that arose in it in early times life of the Universe, when there were no stars or galaxies in it. Instead, there were only very weak concentrations of matter, from which modern star systems were subsequently “born.” These condensations gradually became denser due to their own gravity and at a certain epoch were able to “disconnect” from the general cosmological expansion. After this, they turned into observable galaxies, their groups, clusters and superclusters. The presence of pre-galactic inhomogeneities in the early Universe left its clear imprint on the cosmic background radiation: because of them, it cannot be perfectly uniform, which was discovered in 1992 (see “Astronomy News” on page 14 - Ed.).
This was reported by two groups of observational astronomers - from the Space Research Institute in Moscow and from the Goddard Space Center near Washington. Their research was carried out at orbital stations equipped with special, very sensitive radio wave receivers. The cosmic radiation predicted by Gamow thereby provided a new service to astronomy.
The hidden masses, it must be assumed, were also born in a single grandiose event Big Bang. They were collected into future coronas, inside which the “ordinary” matter continued to compress and disintegrate into relatively small but dense fragments - gas clouds. Those, in turn, continued to compress even more under the influence of their own gravity and were divided into protostars, which eventually turned into stars when thermonuclear reactions “turned on” in their densest and hottest regions.
The release of large energy in the reactions of conversion of hydrogen into helium, and then into heavier elements, is the source of luminosity of both the very first stars and stars of subsequent generations. Now astronomers can directly observe the birth of young stars in the disk of the Galaxy: it is happening before our eyes. The physical nature of stars, the reason why these physical bodies emit their light, and even their very origin are no longer an insoluble mystery.
Why is it expanding?
It is much more difficult for science to advance in the study of the early, prestellar, pregalactic stages of the evolution of the world, which cannot be observed directly. Cosmic background radiation has told us a lot about the past of the Universe. But the main questions of cosmology remain open. This is primarily a question about the reason for the general expansion of matter, which continues for 15-20 billion years.
For now, one can only build hypotheses, put forward theoretical assumptions, and make guesses about the physical nature of this most grandiose natural phenomenon. One of these hypotheses has now won big number passionate supporters.
Its initial idea is that at the very beginning of the Universe, even before the era of nucleosynthesis, it was not universal gravity that reigned in the world, but universal antigravity. The general theory of relativity, on which cosmology is based, does not exclude such a possibility in principle. This idea was, in fact, suggested by Einstein himself many years ago.
If we accept this idea, then it is not difficult to guess that, due to anti-gravity, all bodies in the world should not attract, but, on the contrary, repel and fly away from each other. This expansion does not stop and continues by inertia even after anti-gravity is replaced at some point by the universal gravitation familiar to us.
This bright and fruitful hypothesis is now actively developing in theoretical terms, but it must still undergo strict observational testing in order to, if successful, turn into a convincing concept, as happened earlier with the theories of Friedmann and Gamow. In the meantime, this is just one of the interesting areas of scientific research in cosmology. The solution to the most amazing secrets of the Big Universe is yet to come.
And its characteristic features, as well as the precise structure and organization of the Universe, give us reason to assume that someone is worth it. Book - Think and Grow Rich!
Our awe-inspiring universe
For thousands of years, people have admired the starry sky. On a clear night, the beautiful stars stand out like sparkling precious stones, on black
background of outer space. The night in all its beauty floods the earth with moonlight.
People thinking about such a spectacle often have questions: “What, after all, is there in space? How does it all work? Can we figure out how this all came about? The answers to these questions will undoubtedly help explain why the Earth and all life on it came to be, and what the future holds.
Centuries ago, it was believed that the universe consisted of several thousand stars that were visible to the naked eye. But now, thanks to powerful instruments that carefully scan the sky, scientists know that there are many more of them.
In fact, what can be observed today is much more awe-inspiring than anyone could have imagined before. Immeasurable
the scale and complexity of it all boggles the human imagination.
According to National Geographic magazine, the knowledge that man is currently acquiring about the universe is “stunning.”
Awe-inspiring dimensions
In previous centuries, astronomers scanning the sky with early telescopes noticed vague cloud-like formations.
They suggested that these were nearby gas clouds. But in the 1920s, when larger and more powerful telescopes began to be used, these “gases” turned out to be a much larger and more significant phenomenon - galaxies.
A galaxy is a huge collection of stars, gases and other matter orbiting around a central core. Galaxies are called island universes because each one itself resembles a universe.
Consider, for example, the galaxy in which we live called the Milky Way. Our solar system, that is, the Sun, Earth and other planets with their satellites, is part of this galaxy. But it is just a tiny part of it, since our Milky Way consists of more than 100
billion stars!
Some scientists estimate that there are at least 200 to 400 billion stars. One science editor even stated: "It is possible that in the Milky Way
The path contains between five and ten trillion stars."
The diameter of our Galaxy is so large that even if you could travel at the speed of light (299,793 kilometers per second), it would take you 100,000 years to cross it! How many kilometers is this?
Since light travels about ten trillion (10000000000000) kilometers per year, you will get your answer by multiplying this number by 100000: diameter
Our Milky Way is approximately one quintillion (10000000000000000000) kilometers!
The average distance between stars within our Galaxy is estimated to be about six light years, or about 60 trillion kilometers.
Such dimensions and distances are almost impossible to comprehend by the human mind. And yet, our Galaxy is only the beginning of what is in outer space! There is something even more amazing: so many galaxies have been discovered so far that they are now considered “as commonplace as blades of grass in a meadow.”
There are about ten billion galaxies within the visible universe! But there is much more beyond the sight of modern telescopes. Some astronomers believe that the universe contains 100 billion galaxies! And each galaxy may consist of hundreds of billions of stars!
Galaxy clusters
But that is not all. These awe-inspiring galaxies are not scattered haphazardly throughout space. On the contrary, they are usually located in certain groups, so-called clusters, like berries in a bunch of grapes. Thousands of these galaxy clusters have already been observed and photographed.
Some clusters contain relatively few galaxies. The Milky Way, for example, is part of a cluster of about twenty galaxies.
As part of this local group, there is one galaxy “neighboring” to us, which can be seen on a clear night without a telescope. We are talking about the Andromeda Galaxy, which, like our Galaxy, has a spiral structure.
Other galaxy clusters consist of many dozens and perhaps hundreds or even thousands of galaxies. It is estimated that one such cluster contains about 10,000 galaxies!
The distance between galaxies within a cluster can average one million light years. However, the distance from one galaxy cluster to another can be a hundred times greater. And there is even evidence that the clusters themselves are arranged in “super clusters,” like clusters on a grapevine. What a colossal size and what a brilliant organization!
Similar organization
Returning back to our solar system, we find a similar, superbly organized arrangement. The sun is a medium-sized star -
is the “core” around which the Earth and other planets along with their satellites move in precisely specified orbits.
From year to year they move with such mathematical inevitability that astronomers can accurately predict where they will be at one time or another.
We find the same accuracy when looking at the infinitesimal world of atoms. The atom is a miracle of order, like a miniature solar system. An atom consists of a nucleus made of protons and neutrons and tiny electrons surrounding the nucleus. All matter is made up of these building blocks
details.
One substance differs from another in the number of protons and neutrons in the nucleus, as well as the number and arrangement of electrons rotating around it. There is an ideal order in all this, since all the elements that make up matter can be brought into a neat system, according to the available number of these building parts.
What explains this organization?
As we have noted, the size of the universe is truly awe-inspiring. The same can be said about its wonderful design. From the infinitely large to the infinitely small, from clusters of galaxies to atoms, the universe is characterized by a magnificent organization.
Discover magazine said: “We are surprised to sense order, and our cosmologists and physicists continue to find new, surprising facets of this order...
We are used to saying that it is a miracle, and we still allow ourselves to talk about the whole universe as a miracle.” The ordered structure is confirmed even by the use of the word that denotes the universe in astronomy: “cosmos”.
One reference manual defines the word as “a coherent, organized system, as opposed to chaos, a disorderly accumulation of matter.”
Former astronaut John Glenn drew attention to the “order in the entire universe around us” and that galaxies “all move in
established orbits in a certain ratio to each other.”
So he asked, “Could this have just happened by chance? Was it
Is it an accident that drifting objects suddenly began to move along these orbits on their own?”
His conclusion was: “I can’t believe it... Some Force brought all these objects into orbit and is keeping them there.”
Indeed, the universe is so precisely organized that man can use the celestial bodies as a basis for measuring time. But any
a well-constructed watch is obviously the product of an orderly mind capable of design. It's orderly
Only a rational person can have a thinking mind capable of design.
How then to consider the much more complex design and reliability that is found throughout the universe? Doesn't it indicate
also this is on the designer, on the creator, on the plan - on the intellect? And do you have any reason to believe that the intellect can exist separately from the personality?
One thing we can't help but recognize is that a great organization requires a great organizer. In our life experience there is not one
an incident that would indicate the random occurrence of something organized. On the contrary, all our life experience shows that any organization must have an organizer.
Every machine, computer, building, even pencil and piece of paper had a maker, an organizer. It is logical that the much more complex and awe-inspiring organization of the universe should also have an organizer.
The law requires a legislator
In addition, the entire universe, from atoms to galaxies, is governed by certain physical laws. For example, there are laws governing heat, light, sound and gravity.
Physicist Stephen W. Hawking said: “The more we study the universe, the clearer it becomes that it is not random at all, but obeys certain well-established laws that operate in different areas.
The supposition that there are some universal principles, so that all laws are part of some larger law, seems quite reasonable."
Rocket scientist Wernher von Braun went even further when he stated: “The laws of nature in the universe are so precise that we have no difficulty in
construction spaceship for a flight to the Moon, and we can time the flight to within a fraction of a second.
These laws had to be made by someone.” Scientists who wish to successfully place a rocket into orbit around the Earth or Moon must act in accordance with these universal laws.
When we think about laws, we realize that they must come from the legislature. Behind the stop sign there is certainly a person or group of people who made that law.
What then can be said about the all-encompassing laws that govern the material universe? Such brilliantly calculated laws undoubtedly indicate a highly intelligent legislator.
Organizer and Legislator
After commenting on the many special conditions that are so obvious in the universe, characterized by order and regularity, in Science News
(Science News) noted: “Thinking about this worries cosmologists because it seems that such exceptional and precise conditions could hardly have been created by chance.
One way to solve this problem is to assume that everything was invented and attribute it to God's Providence."
Many people, including many scientists, are reluctant to accept this possibility. But others are ready to admit what the facts persistently convince us of - reason. They recognize that such colossal size, precision and pattern, found throughout the universe, could never have been formed simply by chance. All this must be the result of activity beyond reason.
This is precisely the conclusion expressed by one of the Bible writers who said regarding the material heavens: “Lift up your eyes to the heights of the heavens, and see who created them? Who brings out the army by counting them? He calls them all by name." “He” is none other than “he who created the heavens and their spaces” (Isaiah 40:26; 42:5).
Energy source
Existing matter is subject to universal laws. But where did all this matter come from? In the book Cosmos, Carl Sagan says: “In the beginning
the existence of this universe there were no galaxies, no stars or planets, no life or civilizations.”
He calls the transition from this state to the modern universe “the most spectacular transformation of matter and energy that we have had the honor of imagining.”
This is the key to understanding how the universe could begin to exist: there must have been a transformation of energy and matter.
This relationship is confirmed by Einstein's famous formula E=mc2 (energy equals mass times the square of the speed of light). From this formula
the conclusion follows that matter can be created from energy, just as colossal energy can be obtained from matter.
The proof of the latter was the atomic bomb. Therefore, astrophysicist Josip Kleczek said: “Most of the elementary particles, and perhaps all
they can be created by materializing energy.”
Therefore, the assumption that a source of unlimited energy would have the raw material to create the matter of the universe has scientific proof.
The previously quoted Bible writer noted that this source of energy is a living, thinking person, saying: “By the abundance of power and
Because of His great power, nothing (not one of the celestial bodies) fails.”
Thus, from a biblical point of view, behind what is described in Genesis 1:1 with the words “In the beginning God created the heavens and the earth” lies this source
inexhaustible energy.
The beginning wasn't chaotic
Scientists now generally accept that the universe had a beginning. One famous theory that attempts to describe this beginning is called the “Big Bang” theory. "Almost all recent discussions about the origin of the universe are based on the '' theory," notes Francis Crick.
Jastrow speaks of this cosmic "explosion" as a "literal moment of creation." Scientists, as astrophysicist John Gribbin admitted in New magazine
Scientist (New Scientist) "claim that they are, by and large, able to describe in some detail" what happened after this "moment", but
For what reason this “instant of creation” occurred remains a mystery.
“It’s possible that God did it after all,” he noted thoughtfully.
However, most scientists are unwilling to connect this “moment” with God. Therefore, an "explosion" is usually described as something chaotic, like an explosion
atomic bomb. But does such an explosion lead to improved organization of anything? Do bombs dropped on cities during
wars, beautifully constructed buildings, streets and road signs?
On the contrary, such explosions cause death, disorder, chaos and destruction. And when a nuclear weapon explodes, the disruption is total, like
the Japanese cities of Hiroshima and Nagasaki experienced this in 1945.
No, a simple “explosion” could not create our awe-inspiring universe with its amazing order, purposeful structure and laws.
Only a powerful organizer and legislator could direct the enormous forces at work so that the result would be a magnificent organization and excellent laws.
Therefore, scientific evidence and logic provide a solid basis for the Bible's following statement: “The heavens declare the glory of God, and the firmament declares the work of His hands” (Psalm 19:2).
So the Bible comes to grips with questions that evolutionary theory has not been able to answer convincingly. Instead of leaving us in the dark about the origin of everything, the Bible gives us a simple and clear answer.
It confirms scientific as well as our own observations that nothing is created by itself.
Although we were not personally present when the universe was erected, it is obvious that it required a master designer, according to the reasoning of the Bible: “Every house is built by someone; and he who created all things is God” (Hebrews 3:4).
MOSCOW, June 15 - RIA Novosti. The Universe could only be born as a result of the Big Bang, since all alternative scenarios for its formation lead to the immediate collapse of the newborn Universe and its destruction, says an article published in the journal Physical Review D.
“All these theories were developed in order to explain the initial “smooth” structure of the Universe at the moment of its birth and to “grope” for the primary conditions of its formation. We showed that in fact they give rise to the opposite picture - powerful disturbances arise in them, which ultimately lead to the collapse of the entire system,” write Jean-Luc Lehners from the Institute of Gravitational Physics in Potsdam (Germany) and his colleagues.
Most cosmologists believe that the Universe was born from a singularity that began to rapidly expand in the first moments after the Big Bang. Another group of astrophysicists believes that the birth of our Universe was preceded by the death of its “progenitor,” which probably occurred during the so-called “Big Rip.”
The main problem of these theories is that they are incompatible with the theory of relativity - at the moment when the Universe was a dimensionless point, it should have had an infinite energy density and space curvature, and powerful quantum fluctuations should have arisen inside it, which is impossible from the point of view vision of Einstein's brainchild.
To solve this problem, scientists have developed several alternative theories over the past 30 years, in which the Universe is born under different, less extreme conditions. For example, Stephen Hawking and James Hartle suggested 30 years ago that the Universe was a point not only in space, but also in time, and before its birth, time, in our understanding of the word, simply did not exist. When time appeared, space was already relatively “flat” and homogeneous so that a “normal” Universe with “classical” laws of physics could arise.
In turn, Soviet-American physicist Alexander Vilenkin believes that our Universe represents a kind of “bubble” of false vacuum inside an eternal and constantly expanding giant multi-Universe, where similar bubbles constantly appear as a result of quantum fluctuations of the vacuum, being born literally out of nothing.
Both of these theories avoid the issue of the “beginning of time” and the incompatibility of the conditions of the Big Bang with Einsteinian physics, but at the same time they pose a new question - are such variants of the expansion of the Universe capable of giving rise to it in the form in which it now exists?
As calculations by Lehners and his colleagues show, in fact, such scenarios for the birth of the Universe cannot work in principle. In most cases, they do not lead to the birth of a “flat” and calm Universe like ours, but to the appearance of powerful disturbances in its structure, which will make such “alternative” Universes unstable. Moreover, the probability of the birth of such an unstable Universe is much higher than its stable counterparts, which calls into question the ideas of Hawking and Vilenkin.
Accordingly, the Big Bang cannot be avoided - scientists, as Lehners and his colleagues conclude, will have to find a way to reconcile quantum mechanics and the theory of relativity, and also understand how quantum fluctuations were suppressed by extremely high matter densities and the curvature of space-time.
Large-scale structure of the Universe as it appears in 2.2 µm infrared - 1,600,000 galaxies recorded in the Extended Source Catalog as a result of the Two Micron All-Sky Survey. The brightness of galaxies is shown in color from blue (brightest) to red (dimmer). The dark stripe along the diagonal and edges of the picture is the location of the Milky Way, the dust of which interferes with observations
The Universe is a concept in astronomy and philosophy that does not have a strict definition. It is divided into two fundamentally different entities: speculative(philosophical) and material observable at present or in the foreseeable future. If the author distinguishes between these entities, then, following tradition, the first is called the Universe, and the second - the astronomical Universe or Metagalaxy (in Lately this term has almost fallen into disuse). The Universe is the subject of study of cosmology.
Historically, various words have been used to denote "all space", including equivalents and variants from various languages, such as "cosmos", "world", "celestial sphere". The term "macrocosm" has also been used, although it is intended to define large-scale systems, including their subsystems and parts. Likewise, the word microcosm is used to refer to small-scale systems.
Any research, any observation, be it a physicist observing how the nucleus of an atom splits, a child observing a cat, or an astronomer observing a distant planet - all this is an observation of the Universe, or rather, of its individual parts. These parts serve as the subject of study of individual sciences, and the Universe on the largest possible scale, and even the Universe as a single whole, is studied by astronomy and cosmology; in this case, the Universe is understood either as the region of the world covered by observations and space experiments, or as the object of cosmological extrapolations - the physical Universe as a whole.
The subject of the article is knowledge about the observable Universe as a single whole: observations, their theoretical interpretation and history of formation.
Among the clearly interpretable facts regarding the properties of the Universe, we present here the following:
The theoretical explanations and descriptions of these phenomena are based on the cosmological principle, the essence of which is that observers, regardless of the location and direction of observation, on average detect the same picture. The theories themselves seek to explain and describe the origin of chemical elements, the course of development and the cause of expansion, and the emergence of large-scale structure.
The first significant push towards modern ideas about the Universe was made by Copernicus. The second largest contributions were made by Kepler and Newton. But truly revolutionary changes in our ideas about the Universe occur only in the 20th century.
Etymology
In Russian, the word “Universe” is a borrowing from the Old Slavonic “vselena”, which is a calque of the ancient Greek word “oikoumene” (ancient Greek οἰκουμένη), from the verb οἰκέω “I inhabit, inhabit” and in the first meaning it meant only the inhabited part of the world . Therefore, the Russian word “Universe” is related to the noun “vseleniya” and is only consonant with the attributive pronoun “everything”. The most common definition for the "Universe" among ancient Greek philosophers, beginning with the Pythagoreans, was τὸ πᾶν (All), which included both all matter (τὸ ὅλον) and the entire cosmos (τὸ κενόν).
The Shape of the Universe
Imagining the Universe as a whole the world, we immediately make it unique and unique. And at the same time, we deprive ourselves of the opportunity to describe it in terms of classical mechanics: because of its uniqueness, the Universe cannot interact with anything, it is a system of systems, and therefore in its relation such concepts as mass, shape, size lose their meaning. Instead, we have to resort to the language of thermodynamics, using concepts such as density, pressure, temperature, and chemical composition.
Expansion of the Universe
However, the Universe bears little resemblance to ordinary gas. Already on the largest scales we are faced with the expansion of the Universe and the relict background. The nature of the first phenomenon is the gravitational interaction of all existing objects. It is its development that determines the future of the Universe. The second phenomenon is a legacy of early eras, when the light of the hot Big Bang practically stopped interacting with matter and separated from it. Now, due to the expansion of the Universe, most of the photons emitted then have moved from the visible range to the microwave radio range.
Hierarchy of scales in the Universe
When moving to scales smaller than 100 Mpc, a clear cellular structure is revealed. Inside the cells there is emptiness - voids. And the walls are formed from superclusters of galaxies. These superclusters are the top level of the whole hierarchy, then there are clusters of galaxies, then local groups of galaxies, and the lowest level (scale 5-200 kpc) is a huge variety of very different objects. Of course, they are all galaxies, but they are all different: they are lenticular, irregular, elliptical, spiral, with polar rings, with active nuclei, etc.
Of these, it is worth mentioning separately, characterized by a very high luminosity and such a small angular size that for several years after their discovery they could not be distinguished from “point sources” -. The bolometric luminosity of quasars can reach 10 46 - 10 47 erg/s.
Moving on to the composition of the galaxy, we find: dark matter, cosmic rays, interstellar gas, globular clusters, open clusters, double stars, larger star systems, supermassive and stellar-mass black holes, and, finally, single stars of various populations.
Their individual evolution and interaction with each other gives rise to many phenomena. Thus, it is assumed that the source of energy for the already mentioned quasars is the accretion of interstellar gas onto a supermassive central black hole.
It is worth mentioning separately about gamma-ray bursts - these are sudden short-term localized increases in the intensity of cosmic gamma radiation with an energy of tens and hundreds of keV. From estimates of the distances to gamma-ray bursts, we can conclude that the energy emitted by them in the gamma-ray range reaches 10 50 erg. For comparison, the luminosity of the entire galaxy in the same range is “only” 10 38 erg/s. Such bright flares are visible from the most distant corners of the Universe, so GRB 090423 has a redshift z = 8.2.
The most complex complex, which includes many processes, is the evolution of the galaxy:
The course of evolution has little dependence on what happens to the entire galaxy as a whole. However, total number newly formed stars and their parameters are subject to significant external influence. Processes whose scales are comparable or larger size galaxies, change the morphological structure, the rate of star formation, and therefore the rate of chemical evolution, the spectrum of the galaxy, and so on.
Observations
The variety described above gives rise to a whole range of observational problems. One group can include the study of individual phenomena and objects, and this is:
Expansion phenomenon. And to do this, you need to measure distances and redshifts of as distant objects as possible. Upon closer examination, this results in a whole set of problems called the distance scale.
Relic background.
Individual distant objects such as quasars and gamma-ray bursts.
Distant and old objects emit little light and require giant telescopes such as the Keck Observatory, VLT, BTA, Hubble and the E-ELT and James Webb under construction. In addition, specialized tools are needed to complete the first task, such as Hipparcos and the currently under development Gaia.
As was said, the CMB radiation lies in the microwave wavelength range, therefore, to study it, radio observations and, preferably, space telescopes such as WMAP and Planck are needed.
The unique features of gamma-ray bursts require not only on-orbit gamma-ray laboratories like SWIFT, but also unusual telescopes - robot telescopes - whose field of view is larger than the above-mentioned SDSS instruments and capable of automatic observation. Examples of such systems are the telescopes of the Russian Master network and the Russian-Italian Tortora project.
The previous tasks are work on individual objects. A completely different approach is required for:
Studying the large-scale structure of the Universe.
Study of the evolution of galaxies and its component processes. Thus, observations of objects as old as possible and in as many numbers as possible are needed. On the one hand, massive, survey observations are needed. This forces the use of wide-field telescopes, such as those in the SDSS project. On the other hand, detail is required that is orders of magnitude greater than the needs of most tasks of the previous group. And this is only possible with the help of VLBI observations, with a base in diameter, or even larger, like the Radioastron experiment.
Separately, it is worth highlighting the search for relic neutrinos. To solve it, it is necessary to use special telescopes - neutrino telescopes and neutrino detectors - such as the Baksan Neutrino Telescope, the Baikal Underwater Telescope, IceCube, KATRIN.
One study of gamma-ray bursts and the relict background indicates that only the optical part of the spectrum cannot be used here. However, the Earth's atmosphere has only two windows of transparency: in the radio and optical range, and therefore it is impossible to do without space observatories. Among those currently operating, we will cite Chandra, Integral, XMM-Newton, and Herschel as examples. Spektr-UV, IXO, Spektr-RG, Astrosat and many others are in development.
Distance scale and cosmological redshift
Measuring distance in astronomy is a multi-step process. And the main difficulty is that the best accuracies in different methods are achieved at different scales. Therefore, to measure more and more distant objects, a longer and longer chain of methods is used, each of which is based on the results of the previous one.
All these chains are based on the trigonometric parallax method - the basic one, the only one where the distance is measured geometrically, with minimal use of assumptions and empirical laws. Other methods, for the most part, use a standard candle - a source with known luminosity - to measure distance. And the distance to it can be calculated:
where D is the required distance, L is the luminosity, and F is the measured luminous flux.
Scheme of the occurrence of annual parallax
Trigonometric parallax method:Parallax is the angle resulting from the projection of a source onto the celestial sphere. There are two types of parallax: annual and group.
Annual parallax is the angle at which the average radius of the Earth's orbit would be visible from the center of mass of the star. Due to the movement of the Earth in its orbit, the apparent position of any star on the celestial sphere is constantly shifting - the star describes an ellipse, the semi-major axis of which turns out to be equal to the annual parallax. According to the known parallax from the laws of Euclidean geometry, the distance from the center of the earth’s orbit to the star can be found as:
,
where D is the required distance, R is the radius of the earth's orbit, and the approximate equality is written for a small angle (in radians). This formula clearly demonstrates the main difficulty of this method: with increasing distance, the parallax value decreases along a hyperbola, and therefore measuring distances to distant stars is associated with significant technical difficulties.
The essence of group parallax is as follows: if a certain star cluster has a noticeable speed relative to the Earth, then, according to the laws of projection, the apparent directions of motion of its members will converge at one point, called the radiant of the cluster. The position of the radiant is determined from the proper motions of the stars and the shift of their spectral lines resulting from the Doppler effect. Then the distance to the cluster is found from the following relation:
where μ and V r are, respectively, the angular (in arcseconds per year) and radial (in km/s) velocity of the cluster star, λ is the angle between the straight lines -star and radiant star, and D is the distance, expressed in parsecs. Only the Hyades have a noticeable group parallax, but until the launch of the Hipparcos satellite, this is the only way to calibrate the distance scale for old objects.
Method for determining distance from Cepheids and RR Lyrae stars
On Cepheids and RR Lyrae stars, the single distance scale diverges into two branches - the distance scale for young objects and for old ones. Cepheids are located mainly in regions of recent star formation and are therefore young objects. type RR Lyrae gravitate towards old systems, for example, there are especially many of them in globular star clusters in the halo of our Galaxy.
Both types of stars are variable, but if Cepheids are recently formed objects, then RR Lyrae stars have left the main sequence - spectral giants classes A-F, located mainly on the horizontal branch of the color-magnitude diagram for globular clusters. However, the ways to use them as standard candles are different:
Determining distances using this method is associated with a number of difficulties:
It is necessary to select individual stars. Within the Milky Way this is not particularly difficult, but the greater the distance, the smaller the angle separating the stars.
It is necessary to take into account the absorption of light by dust and the heterogeneity of its distribution in space.
In addition, for Cepheids, it remains a serious problem to accurately determine the zero point of the pulsation period-luminosity relationship. Throughout the 20th century, its meaning constantly changed, which means that the distance estimate obtained in this way also changed. The luminosity of RR Lyrae stars, although almost constant, still depends on the concentration of heavy elements.
Method for determining distance from type Ia supernovae:
Light curves of various supernovae.
A colossal explosive process occurring throughout the entire body of the star, with the released energy ranging from 10 50 - 10 51 erg. Type Ia supernovae also have the same luminosity at maximum brightness. Together, this makes it possible to measure distances to very distant galaxies.
It was thanks to them that in 1998 two groups of observers discovered the acceleration of the expansion of the Universe. Today, the fact of acceleration is almost beyond doubt, however, it is impossible to unambiguously determine its magnitude from supernovae: errors are still extremely large for large z.
Typically, in addition to those common to all photometric methods, the disadvantages and open problems include:
The K-correction problem. The essence of this problem is that it is not the bollometric intensity (integrated over the entire spectrum) that is measured, but in a certain spectral range of the receiver. This means that for sources with different redshifts, the intensity is measured in different spectral ranges. To take this difference into account, a special correction is introduced, called the K-correction.
The shape of the distance versus redshift curve is measured by different observatories on different instruments, which creates problems with flux calibrations, etc.
Previously, it was believed that all Ia supernovae are those exploding in a close binary system, where the second component is. However, evidence has emerged that at least some of them may arise from the merger of two white dwarfs, which means this subclass is no longer suitable for use as a standard candle.
Dependence of supernova luminosity on the chemical composition of the predecessor star.
Geometry of gravitational lensing:
Geometry of gravitational lensing
Passing near a massive body, a beam of light is deflected. Thus, a massive body is capable of collecting a parallel beam of light at a certain focus, building an image, and there may be several of them. This phenomenon is called gravitational lensing. If the lensed object is variable, and several images of it are observed, this opens up the possibility of measuring distances, since there will be different time delays between images due to the propagation of rays in different parts of the gravitational field of the lens (an effect similar to the Shapiro effect in ).
If, as a characteristic scale for image coordinates ξ and source η (see figure) in the corresponding planes take ξ 0 =D l and η 0 =ξ 0 D s/ D l (where D- angular distance), then you can record the time delay between images number i And j in the following way:
Where x=ξ /ξ 0 and y=η /η 0 - angular positions of the source and image, respectively, With- speed of light, z l is the redshift of the lens, and ψ - deviation potential depending on the choice of model. It is believed that in most cases the real potential of the lens is well approximated by a model in which the matter is distributed radially symmetrically, and the potential turns to infinity. Then the delay time is determined by the formula:
However, in practice, the sensitivity of the method to the type of galactic halo potential is significant. So, the measured value H 0 for the SBS 1520+530 galaxy, depending on the model, ranges from 46 to 72 km/(s Mpc).
Method for determining distance from red giants:
The brightest red giants have the same absolute magnitude -3.0 m ±0.2 m, which means they are suitable for the role of standard candles. Sandage was the first to discover this effect observationally in 1971. It is assumed that these stars are either at the top of the first rise of the red giant branch of low-mass (less than solar) stars, or lie on the asymptotic giant branch.
The main advantage of the method is that red giants are located far from regions of star formation and high dust concentrations, which greatly facilitates the accounting of absorption. Their luminosity also depends extremely weakly on the metallicity of both the stars themselves and their environment. The main problem of this method is identifying red giants from observations of the stellar composition of the galaxy. There are two ways to solve it:
- Classic - method of highlighting the edges of images. In this case, a Sobel filter is usually used. The beginning of the failure is the desired turning point. Sometimes, instead of a Sobel filter, a Gaussian is taken as an approximating function, and the edge selection function depends on photometric observation errors. However, as the star weakens, so do the method errors. As a result, the maximum measured brightness is two magnitudes worse than what the equipment allows.
where a is a coefficient close to 0.3, m is the observed magnitude. The main problem is the divergence in some cases of the series resulting from the maximum likelihood method. The main problem is the divergence in some cases of the series resulting from the maximum likelihood method.
Issues and contemporary discussions:
One of the problems is the uncertainty in the value of the Hubble constant and its isotropy. One group of researchers argues that the value of the Hubble constant fluctuates on scales of 10-20°. Possible reasons There are several reasons for this phenomenon:
A real physical effect - in this case, the cosmological model must be radically revised;
The standard error averaging procedure is incorrect. This also leads to a revision of the cosmological model, but perhaps not as significant. In turn, many other surveys and their theoretical interpretation do not show anisotropy exceeding that locally caused by the growth of inhomogeneity, which includes our Galaxy, in an overall isotropic Universe.
CMB spectrum
Study of the relict background:The information that can be obtained by observing the CMB is extremely diverse: the very fact of the existence of the CMB is noteworthy. If the Universe existed forever, then the reason for its existence is unclear - we do not observe mass sources capable of creating such a background. However, if the lifetime of the Universe is finite, then it is obvious that the reason for its occurrence lies in the initial stages of its formation.
Today, the dominant opinion is that the cosmic microwave background radiation is radiation released at the moment of formation of hydrogen atoms. Before this, the radiation was locked in matter, or rather, in what it was then - dense hot plasma.
The method of analyzing the relict background is based on this assumption. If you mentally trace the path of each photon, it turns out that the surface of the last scattering is a sphere, then temperature fluctuations can be conveniently expanded into a series according to spherical functions:
where are the coefficients, called multipole, and are the spherical harmonics. The resulting information is quite varied.
- Various information is also contained in deviations from blackbody radiation. If the deviations are large-scale and systematic, then the Sunyaev-Zeldovich effect is observed, while small fluctuations are caused by fluctuations of matter in the early stages of the development of the Universe.
- Particularly valuable information about the first seconds of the life of the Universe (in particular, about the stage of inflationary expansion) is provided by the polarization of the relict background.
Sunyaev-Zeldovich effect
If CMB photons encounter the hot gas of galaxy clusters on their way, then during scattering due to the inverse Compton effect, the photons will heat up (that is, increase the frequency), taking away some of the energy from the hot electrons. Observationally, this will be manifested by a decrease in the flux of cosmic microwave background radiation in the direction of large clusters of galaxies in the long-wavelength region of the spectrum.
Using this effect you can get information:
about the pressure of hot intergalactic gas in the cluster, and, possibly, about the mass of the cluster itself;
about the speed of the cluster along the line of sight (from observations at different frequencies);
on the value of the Hubble constant H0, using observations in the gamma-ray range.
With a sufficient number of observed clusters, the total density of the Universe Ω can be determined.
CMB polarization map according to WMAP data
Polarization of the cosmic microwave background radiation could only arise in the era of enlightenment. Since Thompson scattering, the CMB radiation is linearly polarized. Accordingly, the Stokes parameters Q and U, which characterize the linear parameters, are different, and the parameter V is equal to zero. If intensity can be expanded into scalar harmonics, then polarization can be expanded into so-called spin harmonics:
The E-mode (gradient component) and B-mode (rotor component) are distinguished.
The E-mode can appear when radiation passes through an inhomogeneous plasma due to Thompson scattering. The B-mode, whose maximum amplitude reaches only , arises only when interacting with gravitational waves.
The B-mode is a sign of inflation of the Universe and is determined by the density of primary gravitational waves. Observing the B-mode is challenging due to the unknown noise level for this component of the CMB, and also due to the fact that the B-mode is mixed by weak gravitational lensing with the stronger E-mode.
To date, polarization has been discovered, its magnitude is at a level of several (microkelvins). The B-mode has not been observed for a long time. It was first discovered in 2013, and confirmed in 2014.
CMB fluctuations
After removing the background sources, the constant component of the dipole and quadrupole harmonics, only fluctuations scattered across the sky remain, the amplitude spread of which lies in the range from −15 to 15 μK.
For comparison with theoretical data, the raw data are reduced to a rotationally invariant quantity:
The “spectrum” is constructed for the value l(l+1)Cl/2π, from which conclusions important for cosmology are obtained. For example, by the position of the first peak one can judge the total density of the Universe, and by its value one can judge the baryon content.
Thus, from the coincidence of the cross-correlation between anisotropy and the E-mode of polarization with the theoretical predictions for small angles (θ<5°) и значительного расхождения в области больших можно сделать о наличии эпохи рекомбинации на z ≈ 15-20.
Since the fluctuations are Gaussian, the Markov chain method can be used to construct a maximum likelihood surface. In general, processing data on the cosmic microwave background is a whole complex of programs. However, both the final result and the assumptions and criteria used give rise to debate. Various groups have shown the difference between the fluctuation distribution and the Gaussian one, and the dependence of the distribution map on the algorithms for processing it.
An unexpected result was an anomalous distribution on large scales (from 6° and more). The quality of the latest confirmatory data obtained from the Planck Space Observatory excludes measurement errors. Perhaps they are caused by a phenomenon that has not yet been discovered and investigated.
Observing distant objects
Lyman alpha forest
In the spectra of some distant objects, one can observe a large accumulation of strong absorption lines in a small part of the spectrum (the so-called forest of lines). These lines are identified as Lyman series lines, but having different redshifts.
Neutral hydrogen clouds effectively absorb light at wavelengths from Lα(1216 Å) to the Lyman limit. Radiation, initially short-wavelength, on its way to us due to the expansion of the Universe is absorbed where its wavelength is compared with this “forest”. The interaction cross section is very large and calculations show that even a small fraction of neutral hydrogen is sufficient to create large absorption in the continuous spectrum.
With a large number of clouds of neutral hydrogen in the path of light, the lines will be located so close to each other that a dip will form over a fairly wide interval in the spectrum. The long-wavelength boundary of this interval is determined by Lα, and the short-wavelength boundary depends on the nearest redshift, closer to which the medium is ionized and there is little neutral hydrogen. This effect is called the Hahn-Peterson effect.
The effect is observed in quasars with a redshift z > 6. From here it is concluded that the epoch of ionization of intergalactic gas began at z ≈ 6.
Gravity-lensed objects
Among the effects that can also be observed for any object (it doesn’t even matter if it is distant), it is necessary to include the effect of gravitational lensing. In the last section it was indicated that using gravitational lensing a distance scale is constructed; this is a variant of the so-called strong lensing, when the angular separation of source images can be directly observed. However, there is also weak lensing, which can be used to explore the potential of the object being studied. Thus, with its help, it was established that clusters of galaxies ranging in size from 10 to 100 Mpc are gravitationally bound, thereby being the largest stable systems in the Universe. It also turned out that this stability is ensured by a mass that manifests itself only in gravitational interaction - dark mass or, as it is called in cosmology, dark matter.
Nature of the quasar
A unique property of quasars is large concentrations of gas in the region of radiation. According to modern concepts, the accretion of this gas onto a black hole provides such a high luminosity of objects. A high concentration of a substance also means a high concentration of heavy elements, and therefore more noticeable absorption lines. Thus, water lines were discovered in the spectrum of one of the lensed quasars.
A unique advantage is the high luminosity in the radio range; against its background, the absorption of part of the radiation by cold gas is more noticeable. In this case, the gas may belong to both the quasar’s home galaxy and a random cloud of neutral hydrogen in the intergalactic medium, or a galaxy that accidentally fell into the line of sight (there are often cases when such a galaxy is not visible - it is too dim for our telescopes). The study of interstellar matter in galaxies using this method is called “transmission study”; for example, the first galaxy with supersolar metallicity was discovered in a similar way.
Another important result of using this method, although not in the radio range, but in the optical range, is the measurement of the primary abundance of deuterium. The current value of deuterium abundance obtained from such observations is 
.
Using quasars, unique data on the temperature of the relict background at z ≈ 1.8 and at z = 2.4 were obtained. In the first case, the lines of the hyperfine structure of neutral carbon were studied, for which quanta with T ≈ 7.5 K (the estimated temperature of the relict background at that time) play the role of pumping, providing an inverse population of levels. In the second case, lines of molecular hydrogen H2, hydrogen deuteride HD, and also a molecule of carbon monoxide CO were discovered, the intensity of the spectrum of which was used to measure the temperature of the relict background; it coincided with the expected value with good accuracy.
Another achievement made possible by quasars is the estimation of the rate of star formation at large z. First, by comparing the spectra of two different quasars, and then by comparing individual sections of the spectrum of the same quasar, they discovered a strong dip in one of the UV sections of the spectrum. Such a strong failure could only be caused by a high concentration of dust absorbing radiation. Previously, they tried to detect dust using spectral lines, but it was not possible to identify specific series of lines proving that it was dust and not an admixture of heavy elements in the gas. It was the further development of this method that made it possible to estimate the rate of star formation at z from ~ 2 to ~ 6.
Observations of gamma-ray bursts
Popular model for the occurrence of a gamma-ray burst
Gamma-ray bursts are a unique phenomenon, and there is no generally accepted opinion about their nature. However, the vast majority of scientists agree with the statement that the progenitor of a gamma-ray burst is objects of stellar mass.
The unique possibilities of using gamma-ray bursts to study the structure of the Universe are as follows:
Since the progenitor of a gamma-ray burst is an object of stellar mass, gamma-ray bursts can be traced over a greater distance than quasars, both because of the earlier formation of the progenitor itself and because of the small mass of the quasar’s black hole, and therefore less luminosity for that period of time. The spectrum of a gamma-ray burst is continuous, that is, it does not contain spectral lines. This means that the most distant absorption lines in the gamma-ray burst spectrum are the lines of the interstellar medium of the host galaxy. From the analysis of these spectral lines, one can obtain information about the temperature of the interstellar medium, its metallicity, degree of ionization and kinematics.
Gamma-ray bursts provide almost an ideal way to study the intergalactic medium before the epoch of reionization, since their influence on the intergalactic medium is 10 orders of magnitude less than quasars, due to the short lifetime of the source. If the afterglow of a gamma-ray burst in the radio range is strong enough, then from the 21 cm line one can judge the state of various structures of neutral hydrogen in the intergalactic medium near the progenitor galaxy of the gamma-ray burst. A detailed study of the processes of star formation in the early stages of the development of the Universe using gamma-ray bursts strongly depends on the chosen model of the nature of the phenomenon, but if you collect sufficient statistics and construct distributions of the characteristics of gamma-ray bursts depending on the redshift, then, while remaining within the framework of fairly general provisions, it is possible to estimate the rate of star formation and the mass function of the stars being born.
If we accept the assumption that a gamma-ray burst is a population III supernova explosion, then we can study the history of the enrichment of the Universe with heavy metals. Also, a gamma-ray burst can serve as a pointer to a very faint dwarf galaxy, which is difficult to detect during “mass” observation of the sky.
A serious problem for observing gamma-ray bursts in general and their applicability for studying the Universe, in particular, is their sporadic nature and short time, when the afterglow of the burst, by which only the distance to it can be determined, can be observed spectroscopically.
Study of the evolution of the Universe and its large-scale structure
Study of large-scale structure
Large-scale 2df survey structure data
The first way to study the large-scale structure of the Universe, which has not lost its relevance, was the so-called “star count” method or the “star scoop” method. Its essence is to count the number of objects in different directions. Used by Herschel at the end of the 18th century, when the existence of distant space objects was only guessed at, and the only objects available for observation were stars, hence the name. Today, of course, they count not stars, but extragalactic objects (quasars, galaxies), and in addition to the selected direction, they construct distributions along z.
The largest sources of data on extragalactic objects are individual observations of specific objects, surveys such as SDSS, APM, 2df, as well as compilation databases such as Ned and Hyperleda. For example, in the 2df survey, the sky coverage was ~5%, the mean z was 0.11 (~500 Mpc), and the number of objects was ~220,000.
The dominant opinion is that when moving to scales of hundreds of megaparsecs, the cells add up and average, and the distribution of visible matter becomes uniform. However, clarity on this issue has not yet been achieved: using various methods, some researchers come to the conclusion that there is no uniformity in the distribution of galaxies up to the largest scales studied. At the same time, inhomogeneities in the distribution of galaxies do not negate the fact of the high homogeneity of the Universe in the initial state, which is derived from the high degree of isotropy of the cosmic microwave background radiation.
At the same time, it has been established that the distribution of the number of galaxies by redshift is complex. The dependency is different for different objects. However, all of them are characterized by the presence of several local maxima. What this is connected with is not yet entirely clear.
Until recently, it was not clear how the large-scale structure of the Universe evolves. However, recent work shows that large galaxies formed first, and only then small ones (the so-called downsizing effect).
Observations of star clusters
Population of white dwarfs in the globular star cluster NGC 6397. Blue squares are helium white dwarfs, purple circles are “normal” high-carbon white dwarfs.
The main property of globular clusters for observational cosmology is that there are many stars of the same age in a small space. This means that if the distance to one member of the cluster is measured in some way, then the difference in the distance to other members of the cluster is negligible.
The simultaneous formation of all stars in a cluster makes it possible to determine its age: based on the theory of stellar evolution, isochrones are constructed, that is, curves of equal ages for stars of different masses. By comparing them with the observed distribution of stars in the cluster, its age can be determined.
The method has a number of difficulties. Trying to solve them, different teams, in different time received different ages for the oldest clusters, from ~8 billion years to ~25 billion years.
In galaxies, globular clusters that are part of the old spherical subsystem of galaxies contain many white dwarfs - the remnants of evolved red giants of relatively small mass. White dwarfs are deprived of their own sources of thermonuclear energy and radiate solely due to the emission of heat reserves. White dwarfs have approximately the same mass of their predecessor stars, and therefore approximately the same temperature dependence on time. Having determined from the spectrum of a white dwarf its absolute magnitude at this moment and knowing the time-luminosity relationship during cooling, one can determine the age of the dwarf.
However, this approach is associated with great technical difficulties - white dwarfs are extremely faint objects - extremely sensitive instruments are needed to observe them. The first and so far the only telescope that can solve this problem is the space telescope named after. Hubble. The age of the oldest cluster, according to the team that worked with it: billions of years, however, the result is disputed. Opponents point out that additional sources of error, their billion-year estimate, were not taken into account.
Observations of non-evolved objects
NGC 1705 is a BCDG galaxy
Objects actually consisting of primordial matter have survived to our time due to the extremely low rate of their internal evolution. This makes it possible to study the primary chemical composition of elements, and also, without going into too much detail and based on the laboratory laws of nuclear physics, to estimate the age of such objects, which will give a lower limit on the age of the Universe as a whole.
This type includes: low-mass stars with low metallicity (the so-called G-dwarfs), low-metallicity HII regions, as well as dwarf irregular galaxies of the BCDG class (Blue Compact Dwarf Galaxy).
According to modern ideas, lithium should have been formed during primary nucleosynthesis. The peculiarity of this element is that nuclear reactions with its participation begin at temperatures that are not very high, on a cosmic scale. And during stellar evolution, the original lithium had to be almost completely recycled. It could only remain with massive population type II stars. Such stars have a calm, non-convective atmosphere, allowing lithium to remain on the surface without the risk of burning up in the hotter inner layers of the star.
During measurements, it was discovered that in most of these stars the abundance of lithium is:
However, there are a number of stars, including ultra-low metal stars, whose abundance is significantly lower. What this is connected with is not entirely clear; it is assumed that it is somehow connected with processes in the atmosphere.
For the star CS31082-001, a member of the Type II stellar population, lines were detected and atmospheric concentrations of thorium and uranium were measured. These two elements have different half-lives, so their ratio changes over time, and if you somehow estimate the initial ratio of abundances, you can determine the age of the star. It can be assessed in two ways: from the theory of r-processes, confirmed by both laboratory measurements and observations of the Sun; or you can cross the curve of changes in concentrations due to decay and the curve of changes in the content of thorium and uranium in the atmospheres of young stars due to the chemical evolution of the Galaxy. Both methods gave similar results: 15.5±3.2 billion years were obtained by the first method, billion years by the second.
Weakly metallic BCDG galaxies (there are ~10 of them in total) and HII zones are sources of information on the primary abundance of helium. For each object, the metallicity (Z) and He concentration (Y) are determined from its spectrum. By extrapolating the Y-Z diagram to Z=0 in a certain way, an estimate of primary helium is obtained.
The final value of Yp varies from one group of observers to another and from one observation period to another. Thus, one, consisting of the most authoritative specialists in this field: Izotova and Thuan (Thuan) obtained the value Yp = 0.245 ± 0.004 for BCDG galaxies, for HII zones at the moment (2010) they settled on the value Yp = 0.2565 ± 0.006. Another authoritative group led by Peimbert also received different meanings Yp, from 0.228±0.007 to 0.251±0.006.
Theoretical models
Of the entire set of observational data for constructing and confirming theories, the following are key:
Their interpretation begins with a postulate that states that each observer at the same moment in time, regardless of the place and direction of observation, discovers on average the same picture. That is, on large scales the Universe is spatially homogeneous and isotropic. Note that this statement does not prohibit heterogeneity in time, that is, the existence of selected sequences of events accessible to all observers.
Proponents of stationary Universe theories sometimes formulate the “perfect cosmological principle”, according to which four-dimensional space-time should have the properties of homogeneity and isotropy. However, the evolutionary processes observed in the Universe do not appear to be consistent with such a cosmological principle.
In general, the following theories and branches of physics are used to build models:
Equilibrium statistical physics, its basic concepts and principles, as well as the theory of relativistic gas.
The theory of gravity, usually general relativity. Although its effects have been tested only on the scale of the Solar System, its use on the scale of galaxies and the Universe as a whole can be questioned.
Some information from the physics of elementary particles: a list of basic particles, their characteristics, types of interaction, conservation laws. Cosmological models would be much simpler if the proton were not a stable particle and would decay, which modern experiments in physical laboratories do not confirm. At the moment, a complex of models, the best way explaining observational data is:
The Big Bang Theory. Describes the chemical composition of the Universe.
Inflation stage theory. Explains the reason for the expansion.
Friedman's expansion model. Describes the extension.
Hierarchical theory. Describes large-scale structure.
Expanding Universe Model
The expanding Universe model describes the very fact of expansion. In general, it is not considered when and why the Universe began to expand. Most models are based on general relativity and its geometric view of the nature of gravity.
If an isotropically expanding medium is considered in a coordinate system rigidly related to matter, then the expansion of the Universe formally reduces to a change in the scale factor of the entire coordinate grid, at the nodes of which the galaxies are “planted.” Such a coordinate system is called comoving. The origin of reference is usually attached to the observer.
There is no single point of view on whether the Universe is truly infinite or finite in space and volume. However, the observable Universe is finite because the speed of light is finite and there was a Big Bang.
Friedman model
| Stage | Evolution | Hubble parameter |
|---|---|---|
| Inflationary |  |
|
| Radiation dominance p=ρ/3 |
||
| Dust stage p=const |
||
| -dominance |  |
Within the framework of general relativity, the entire dynamics of the Universe can be reduced to simple differential equations for the scale factor.
In a homogeneous, isotropic four-dimensional space with constant curvature, the distance between two infinitely approximate points can be written as follows:
,
where k takes the value:
- k=0 for a three-dimensional plane
- k=1 for a three-dimensional sphere
- k=-1 for a three-dimensional hypersphere
x - three-dimensional radius vector in quasi-Cartesian coordinates: .
If we substitute the expression for the metric into the general relativity equations, we obtain the following system of equations:
- Energy equation
- Equation of motion
- Continuity equation
where Λ is the cosmological constant, ρ is the average density of the Universe, P is pressure, c is the speed of light.
The given system of equations allows for many solutions, depending on the selected parameters. In fact, the values of the parameters are fixed only at the current moment and evolve over time, so the evolution of the expansion is described by a set of solutions.
Hubble's Law Explained
Suppose there is a source located in the accompanying system at a distance r 1 from the observer. The observer's receiving equipment registers the phase of the incoming wave. Let's consider two intervals between points with the same phase:
On the other hand, for a light wave in the accepted metric the following equality holds:
If we integrate this equation and remember that in accompanying coordinates r does not depend on time, then, provided that the wavelength is small relative to the radius of curvature of the Universe, we obtain the relation:
If we now substitute it into the original ratio:
After expanding the right-hand side into a Taylor series, taking into account the term of the first order of smallness, we obtain a relation that exactly coincides with Hubble’s law. Where the constant H takes the form:
ΛCDM
As already mentioned, Friedmann's equations admit of many solutions, depending on the parameters. AND modern modelΛCDM is a Friedman model with generally accepted parameters. Usually in the work of observers they are given in terms related to critical density:
If we express the left-hand side from Hubble’s law, then after reduction we get the following form:
,where Ω m =ρ/ρ cr, Ω k = -(kc 2)/(a 2 H 2), Ω Λ =(8πGΛc 2)/ρ cr. From this record it is clear that if Ω m + Ω Λ = 1, i.e. the total density of matter and dark energy is equal to critical, then k = 0, i.e. the space is flat, if more, then k = 1, if less than k= -1
In the modern generally accepted expansion model, the cosmological constant is positive and significantly different from zero, that is, antigravity forces arise on large scales. The nature of such forces is unknown; theoretically, a similar effect could be explained by the action of a physical vacuum, but the expected energy density turns out to be many orders of magnitude greater than the energy corresponding to the observed value of the cosmological constant - cosmological constant problem.
The remaining options are currently only of theoretical interest, but this may change as new experimental data become available. Modern history cosmology already knows such examples: models with zero cosmological constant dominated unconditionally (apart from a brief surge of interest in other models in the 1960s) from the discovery of cosmological redshift by Hubble until 1998, when data on Type Ia supernovae convincingly refuted them.
Further evolution of the expansion
The further course of expansion in the general case depends on the values of the cosmological constant Λ, space curvature k and the equation of state P(ρ). However, the evolution of expansion can be assessed qualitatively based on fairly general assumptions.
If the value of the cosmological constant is negative, then only attractive forces act and nothing else. The right-hand side of the energy equation will be non-negative only for finite values of R. This means that for a certain value of R c the Universe will begin to contract for any value of k and regardless of the form of the equation of state.
If the cosmological constant is zero, then the evolution at a given value of H 0 depends entirely on the initial density of matter:
If , then the expansion continues indefinitely, in the limit with a speed asymptotically tending to zero. If the density is greater than critical, then the expansion of the Universe slows down and gives way to compression. If it is less, then the expansion continues indefinitely with a non-zero limit H.
If Λ>0 and k≤0, then the Universe expands monotonically, but unlike the case with Λ=0, at large values of R the expansion rate increases:
When k=1, the highlighted value is . In this case, there is a value of R at which and , that is, the Universe is static.
For Λ>Λ c, the expansion rate decreases up to a certain point, and then begins to increase without limit. If Λ slightly exceeds Λ c, then for some time the expansion rate remains practically unchanged.
In the case of Λ<Λ c всё зависит от начального значения R, с которого началось расширения. В зависимости от этого значения Вселенная либо будет расширяться до какого-то размера, а потом сожмётся, либо будет неограниченно расширяться.
Big Bang theory (hot universe model)
The Big Bang theory is the theory of primordial nucleosynthesis. Answers the question - how were chemical elements formed and why their prevalence is exactly what it is now. It is based on extrapolation of the laws of nuclear and quantum physics, under the assumption that when moving into the past, the average energy of particles (temperature) increases.
The limit of applicability is the region of high energies, above which the studied laws cease to work. In this case, there is no longer any substance as such, but there is practically pure energy. If we extrapolate Hubble's law at that time, it turns out that the visible region of the Universe was located in a small volume. Small volume and high energy are the characteristic state of matter after an explosion, hence the name of the theory - the Big Bang theory. At the same time, the answer to the question remains outside the scope: “What caused this explosion and what is its nature?”
Also, the Big Bang theory predicted and explained the origin of the cosmic microwave background radiation - this is a legacy of the moment when all matter was still ionized and could not resist the pressure of light. In other words, the relict background is the remnant of the “photosphere of the Universe.”
Entropy of the Universe
The main argument confirming the theory of a hot Universe is the value of its specific entropy. It is equal, up to a numerical coefficient, to the ratio of the concentration of equilibrium photons n γ to the concentration of baryons n b.
Let us express n b in terms of the critical density and the fraction of baryons:
where h 100 is the modern Hubble value, expressed in units of 100 km/(s Mpc), and, taking into account that for cosmic microwave background radiation with T = 2.73 K
cm−3,
we get:
The reciprocal value is the specific entropy value.
The first three minutes. Primary nucleosynthesis
Presumably, from the beginning of birth (or at least from the end of the inflationary stage) and for as long as the temperature remains at least 10 16 GeV (10 −10 s), all known elementary particles are present, and all of them have no mass. This period is called the Great Unification period, when the electroweak and strong forces are unified.
At the moment it is impossible to say exactly what particles are present at that moment, but something is still known. The value η is not only an indicator of specific entropy, but also characterizes the excess of particles over antiparticles:
At the moment when the temperature drops below 10 15 GeV, X- and Y-bosons with the corresponding masses are probably released.
The era of the Great Unification is replaced by the era of electroweak unification, when electromagnetic and weak interactions represent a single whole. During this era, the X- and Y-bosons are annihilated. At the moment when the temperature drops to 100 GeV, the era of electroweak unification ends, quarks, leptons and intermediate bosons are formed.
The hadron era is coming, the era of active creation and annihilation of hadrons and leptons. During this era, the moment of quark-hadron transition or the moment of quark confinement is noteworthy, when the fusion of quarks into hadrons became possible. At this moment the temperature is 300-1000 MeV, and the time from the birth of the Universe is 10 −6 s.
The era of the hadron era is succeeded by the lepton era - at the moment when the temperature drops to the level of 100 MeV, and the clock is 10 −4 s. During this era, the composition of the Universe begins to resemble the modern one; the main particles are photons, besides them there are only electrons and neutrinos with their antiparticles, as well as protons and neutrons. During this period, one important event occurs: the substance becomes transparent to neutrinos. Something like a relict background appears, but for neutrinos. But since the separation of neutrinos occurred before the separation of photons, when some types of particles had not yet annihilated, giving up their energy to others, they cooled down more. By now the neutrino gas should have cooled to 1.9 K if neutrinos have no mass (or their masses are negligible).
At a temperature of T≈0.7 MeV, the thermodynamic equilibrium between protons and neutrons that existed before is disrupted and the ratio of the concentration of neutrons and protons freezes at a value of 0.19. The synthesis of deuterium, helium, and lithium nuclei begins. ~200 seconds after the birth of the Universe, the temperature drops to values at which nucleosynthesis is no longer possible, and the chemical composition of matter remains unchanged until the birth of the first stars.
Problems with the Big Bang Theory
Despite significant advances, the theory of a hot Universe faces a number of difficulties. If the Big Bang caused the expansion of the Universe, then in the general case a strong inhomogeneous distribution of matter could arise, which is not observed. The Big Bang theory also does not explain the expansion of the Universe; it accepts it as a fact.
The theory also suggests that the ratio of particles to antiparticles in the original stage was such that it resulted in the present predominance of matter over antimatter. It can be assumed that at the beginning the Universe was symmetrical - there was the same amount of matter and antimatter, but then, to explain the baryon asymmetry, some mechanism of baryogenesis is necessary, which should lead to the possibility of proton decay, which is also not observed.
Various theories of the Grand Unification suggest the birth in the early Universe of a large number of magnetic monopoles, which have also not been discovered until now.
Inflation model
The goal of inflation theory is to answer the questions that expansion theory and the Big Bang theory left behind: “Why is the Universe expanding? And what is the Big Bang? To do this, the expansion is extrapolated to the zero point in time and the entire mass of the Universe ends up at one point, forming a cosmological singularity, often called the Big Bang. Apparently, the general theory of relativity was no longer applicable at that time, which leads to numerous, but so far, alas, only purely speculative attempts to develop a more general theory (or even “new physics”) that would solve this problem of cosmological singularity.
The main idea of the inflationary stage is that if you drive a scalar field called the inflanton, the influence of which is large in the initial stages (starting from about 10 −42 s), but quickly decreases with time, then the flat geometry of space can be explained, while the Hubble expansion becomes a movement due to inertia due to the large kinetic energy accumulated during inflation, and the origin from a small initially causally related region explains the homogeneity and isotropy of the Universe.
However, there are a great many ways to define inflaton, which in turn gives rise to a whole variety of models. But most are based on the assumption of a slow decline: the inflaton potential slowly decreases to a value equal to zero. The specific type of potential and the method of setting the initial values depend on the chosen theory.
Inflation theories are also divided into infinite and finite in time. In a theory with infinite inflation, there are regions of space - domains - that began to expand, but due to quantum fluctuations returned to their original state, in which conditions for repeated inflation arise. Such theories include any theory with infinite potential and Linde's chaotic theory of inflation.
Theories with a finite inflation time include a hybrid model. There are two types of fields in it: the first is responsible for high energies (and therefore for the rate of expansion), and the second for small ones, which determine the moment of completion of inflation. In this case, quantum fluctuations can only affect the first field, but not the second, which means the inflation process itself is finite.
Unsolved problems of inflation include temperature fluctuations over a very wide range, at some point it drops almost to absolute zero. At the end of inflation, the substance is reheated to high temperatures. “Parametric resonance” is proposed as a possible explanation for such strange behavior.
Multiverse
“Multiverse”, “Big Universe”, “Multiverse”, “Hyperverse”, “Superverse”, “Multiverse”, “Omniverse” - various translations of the English term multiverse. It appeared during the development of the theory of inflation.
Regions of the Universe separated by distances greater than the size of the particle horizon evolve independently of each other. Any observer sees only those processes that occur in a domain equal in volume to a sphere with a radius equal to the distance to the particle horizon. In the era of inflation, two expansion areas separated by a distance of the order of the horizon do not intersect.
Such domains can be considered as separate universes like ours: they are just as homogeneous and isotropic on large scales. A conglomerate of such formations is the Multiverse.
The chaotic theory of inflation assumes an infinite variety of Universes, each of which may have physical constants different from other Universes. In another theory, universes differ in quantum dimensions. By definition, these assumptions cannot be tested experimentally.
Alternatives to inflation theory
The cosmic inflation model is quite successful, but is not necessary for considering cosmology. She has opponents, including Roger Penrose. Their argument is that the solutions offered by the inflation model leave behind missing details. For example, this theory does not offer any fundamental justification for the fact that density disturbances at the pre-inflationary stage should be exactly so small that the observed degree of homogeneity arises after inflation. The situation is similar with spatial curvature: it decreases very strongly during inflation, but nothing prevented it from being so important before inflation that it still manifests itself at the present stage of development of the Universe. In other words, the problem of initial values is not solved, but only skillfully draped.
As an alternative, exotic theories such as string theory and brane theory, as well as cyclic theory, are proposed. The basic idea of these theories is that all the necessary initial values are formed before the Big Bang.
String theory requires adding a few more dimensions to the usual four-dimensional space-time, which would have played a role in the early stages of the Universe, but are now in a compactified state. To the inevitable question of why these dimensions are compactified, the answer is the following: superstrings have T-duality, due to which the string “wraps” around additional dimensions, limiting their size.
In brane theory (M-theory), everything starts with a cold, static five-dimensional space-time. The four spatial dimensions are bounded by three-dimensional walls or three-branes; one of these walls is the space in which we live, while the second brane is hidden from perception. There is another three-brane, “lost” somewhere between the two boundary branes in four-dimensional space. According to the theory, when this brane collides with ours, a large amount of energy is released, thereby creating the conditions for the Big Bang to occur.
Cyclic theories postulate that the Big Bang is not unique in its kind, but implies a transition of the Universe from one state to another. Cyclic theories were first proposed in the 1930s. The stumbling block for such theories was the second law of thermodynamics, according to which entropy can only increase. This means that previous cycles would have been much shorter and the matter in them would have been much hotter than at the time of the last Big Bang, which is unlikely. At the moment, there are two cyclic theories that have managed to solve the problem of ever-increasing entropy: the Steinhardt-Turok theory and the Baum-Frampton theory.
Theory of evolution of large-scale structures
An artist's impression of the formation and collapse of protogalactic clouds.
As data on the cosmic microwave background show, at the moment of separation of radiation from matter, the Universe was virtually homogeneous, fluctuations of matter were extremely small, and this represents a significant problem. The second problem is the cellular structure of superclusters of galaxies and at the same time the spherical structure of clusters of smaller sizes. Any theory attempting to explain the origin of the large-scale structure of the Universe must necessarily solve these two problems (and also correctly model the morphology of galaxies).
The modern theory of the formation of a large-scale structure, as well as individual galaxies, is called the “hierarchical theory”. The essence of the theory boils down to the following: at first the galaxies were small in size (about the size of the Magellanic Cloud), but over time they merge, forming ever larger galaxies.
Recently, the fidelity of the theory has been called into question, and downsizing has contributed to this to a large extent. However, in theoretical studies this theory is dominant. The most striking example of such research is Millennium simulation (Millennium run).
General provisions
The classical theory of the emergence and evolution of fluctuations in the early Universe is the Jeans theory against the background of the expansion of a homogeneous isotropic Universe:
Where u s- speed of sound in the medium, G is the gravitational constant, and ρ is the density of the undisturbed medium, is the magnitude of the relative fluctuation, Φ is the gravitational potential created by the medium, v is the velocity of the medium, p(x,t) is the local density of the medium and is considered in the accompanying coordinate system.
The above system of equations can be reduced to one, which describes the evolution of inhomogeneities:
,where a is the scale factor and k is the wave vector. From it, in particular, it follows that fluctuations whose size exceeds:
In this case, the growth of the disturbance is linear or weaker, depending on the evolution of the Hubble parameter and energy density.
This model adequately describes the collapse of disturbances in a nonrelativistic medium if their size is much smaller than the current event horizon (including for dark matter during the radiation-dominated stage). For opposite cases, it is necessary to consider exact relativistic equations. Energy-momentum tensor of an ideal fluid taking into account small density perturbations
is covariantly conserved, from which the hydrodynamic equations generalized for the relativistic case follow. Together with the general relativity equations, they represent the original system of equations that determine the evolution of fluctuations in cosmology against the background of the Friedman solution.
The era before recombination
A highlighted moment in the evolution of the large-scale structure of the Universe can be considered the moment of hydrogen recombination. Until this moment, some mechanisms operate, after which - completely different ones.
The initial density waves are larger than the event horizon and do not affect the density of matter in the Universe. But as the horizon expands, the size of the horizon is compared with the length of the disturbance wave, as they say “the wave leaves under the horizon” or “enters under the horizon.” After this, the process of its expansion is the propagation of a sound wave against an expanding background.
During this epoch, waves with a wavelength for the current epoch of no more than 790 Mpc enter the horizon. Waves important for the formation of galaxies and their clusters enter at the very beginning of this stage.
At this time, the substance is a multicomponent plasma, in which there are many different effective mechanisms for the attenuation of all sound disturbances. Perhaps the most effective among them in cosmology is the Silk damping. After all sound disturbances are suppressed, only adiabatic disturbances remain.
For some time, the evolution of ordinary and dark matter proceeds synchronously, but due to interaction with radiation, the temperature of ordinary matter drops more slowly. There is a kinematic and thermal separation of dark matter and baryonic matter. It is assumed that this moment occurs at 10 5.
The behavior of the baryon-photon component after separation and up to the end of the radiation stage is described by the equation:
,
where k is the momentum of the wave under consideration, η is the conformal time. From his solution it follows that at that epoch the amplitude of perturbations in the density of the baryon component did not increase or decrease, but experienced acoustic oscillations:
.At the same time, dark matter did not experience such oscillations, since neither the pressure of light nor the pressure of baryons and electrons affects it. Moreover, the amplitude of its disturbances increases:
.After recombination
After recombination, the pressure of photons and neutrinos on matter is already negligible. Consequently, the systems of equations describing the disturbances of dark and baryonic matter are similar:
,
.
Already from the similarity of the form of the equations, one can assume and then prove that the difference in fluctuations between dark and baryonic matter tends to a constant. In other words, ordinary matter rolls into potential holes formed by dark matter. The growth of disturbances immediately after recombination is determined by the solution
,where C i are constants depending on the initial values. As can be seen from the above, at long times density fluctuations grow in proportion to the scale factor:
.
All growth rates of disturbances given in this paragraph and in the previous one grow with wave number k, therefore, with an initial flat spectrum of disturbances, disturbances of the smallest spatial scales reach the collapse stage earlier, that is, objects with a lower mass are formed first.
For astronomy, objects with a mass of ~10 5 M ʘ are of interest. The fact is that during the collapse of dark matter, a protohalo is formed. Hydrogen and helium, tending to its center, begin to emit, and with masses less than 10 5 M ʘ, this radiation throws the gas back to the outskirts of the protostructure. At higher masses, the process of formation of the first stars begins.
An important consequence of the initial collapse is that high-mass stars emerge, emitting in the hard part of the spectrum. The emitted hard quanta, in turn, meet neutral hydrogen and ionize it. Thus, immediately after the first burst of star formation, secondary ionization of hydrogen occurs.
Dark energy dominance stage
Let us assume that the pressure and density of dark energy does not change with time, that is, it is described by a cosmological constant. Then from the general equations for fluctuations in cosmology it follows that the disturbances evolve as follows:
.
Considering that the potential is inversely proportional to the scale factor a, this means that the disturbances do not grow and their size remains unchanged. This means that the hierarchical theory does not allow structures greater than those currently observed.
In the era of dark energy dominance, the last two important events for large-scale structures occur: the appearance of galaxies like the Milky Way - this happens at z~2, and a little later - the formation of clusters and superclusters of galaxies.
Problems of theory
The hierarchical theory, which logically follows from modern, proven ideas about the formation of stars and uses a large arsenal of mathematical tools, has recently encountered a number of problems, both theoretical and, more importantly, observational in nature:
The biggest theoretical problem lies where thermodynamics and mechanics meet: without introducing additional nonphysical forces, it is impossible to force two dark matter halos to merge.
Voids are formed closer to our time than to recombination, however, the recently discovered absolutely empty spaces with dimensions of 300 Mpc come into dissonance with this statement.
Also, giant galaxies are born at the wrong time; their number per unit volume at large z is much greater than what the theory predicts. Moreover, it remains unchanged when, according to theory, it should grow very quickly.
Data from the oldest globular clusters do not want to accept the burst of formation of stars with a mass of about 100 Mʘ and prefer stars like our Sun. And this is only part of the problems that the theory faces.
If you extrapolate Hubble's law back in time, you end up with a point, a gravitational singularity, called a cosmological singularity. This is a big problem, since the entire analytical apparatus of physics becomes useless. And although, following Gamow’s path, proposed in 1946, it is possible to reliably extrapolate until the moment when modern laws of physics are operational, it is not yet possible to accurately determine this moment of the onset of “new physics”.
The question of the shape of the Universe is an important open question in cosmology. In mathematical terms, we are faced with the problem of finding a three-dimensional topology of the spatial section of the Universe, that is, a figure that best represents the spatial aspect of the Universe. The general theory of relativity as a local theory cannot give a complete answer to this question, although it also introduces some restrictions.
First, it is unknown whether the Universe is globally spatially flat, that is, whether the laws of Euclidean geometry apply at the largest scales. Currently, most cosmologists believe that the observable Universe is very close to being spatially flat, with local folds where massive objects distort space-time. This view has been confirmed by recent WMAP data looking at "acoustic oscillations" in the temperature variations of the CMB.
Secondly, it is not known whether the Universe is simply connected or multiply connected. According to the standard expansion model, the Universe has no spatial boundaries, but may be spatially finite. This can be understood using a two-dimensional analogy: the surface of a sphere has no boundaries, but has a limited area, and the curvature of the sphere is constant. If the Universe is truly spatially limited, then in some models of it, moving in a straight line in any direction, you can get to the starting point of the journey (in some cases this is impossible due to the evolution of space-time).
Thirdly, there are suggestions that the Universe was originally born rotating. The classic idea of origin is that the Big Bang is isotropic, that is, energy spreads equally in all directions. However, a competing hypothesis has emerged and received some support: a team of researchers from the University of Michigan, led by physics professor Michael Longo, found that spiral arms of galaxies twisting counterclockwise are 7% more common than galaxies with “opposite orientation” which may indicate the presence of an initial moment of rotation of the Universe. This hypothesis should also be tested by observations in the Southern Hemisphere.