INSTRUCTIONS AND PROPHECIES OF THE Blessed MOTHER ALIPIA GOLOSEEVSKY, Kyiv...
Everything that we see around us (stars and galaxies) is no more than 4-5% of the total mass in the Universe!
According to modern cosmological theories, our Universe consists of only 5% of ordinary, so-called baryonic matter, which forms all observable objects; 25% of dark matter registered due to gravity; and dark energy, which makes up as much as 70% of the total.
The terms dark energy and dark matter are not entirely successful and represent a literal, but not semantic translation from English.
In the physical sense, these terms mean only that these substances do not interact with photons, and they could just as well be called invisible or transparent matter and energy.
Many modern scientists are convinced that research aimed at studying dark energy and matter will probably help answer the global question: what awaits our Universe in the future?
Clumps the size of a galaxy
Dark matter is a substance that most likely consists of new, still unknown particles in terrestrial conditions and has properties inherent in the most ordinary matter. For example, it is also capable, like ordinary substances, of gathering into clumps and participating in gravitational interactions. But the size of these so-called clumps can exceed an entire galaxy or even a cluster of galaxies.
Approaches and methods for studying dark matter particles
On the this moment scientists around the world are trying in every possible way to detect or obtain artificially in terrestrial conditions particles of dark matter, using specially designed super-technological equipment and many different research methods, but so far all the work has not been crowned with success.
One method involves conducting experiments at high-energy accelerators, commonly known as colliders. Scientists, believing that dark matter particles are 100-1000 times heavier than a proton, suggest that they will have to be generated by the collision of ordinary particles accelerated to high energies by means of a collider. The essence of another method is to register dark matter particles that are all around us. The main difficulty in registering these particles is that they exhibit very weak interaction with ordinary particles, which, in their essence, are, as it were, transparent to them. And yet, dark matter particles very rarely, but collide with the nuclei of atoms, and there is a certain hope, sooner or later, to register this phenomenon.
There are other approaches and methods for studying dark matter particles, and which of them will be the first to succeed, only time will tell, but in any case, the discovery of these new particles will be the most important scientific achievement.
Substance with antigravity
Dark energy is an even more unusual substance than the same dark matter. It does not have the ability to gather into clumps, as a result of which it is evenly distributed absolutely throughout the Universe. But its most unusual property at the moment is anti-gravity.
The nature of dark matter and black holes
Thanks to modern astronomical methods, it is possible to determine the rate of expansion of the Universe at the present time and to model the process of its change earlier in time. As a result, information was obtained that at the moment, just as in the recent past, our Universe is expanding, while the rate of this process is constantly increasing. That is why the hypothesis of antigravity of dark energy appeared, since the usual gravitational attraction would have a slowing down effect on the process of "recession of galaxies", restraining the rate of expansion of the Universe. This phenomenon does not contradict the general theory of relativity, but at the same time, dark energy must have a negative pressure - a property that none of the currently known substances has.
Candidates for the role of "Dark Energy"
The mass of galaxies in the Abel 2744 cluster is less than 5 percent of its total mass. This gas is so hot that it only shines in the X-ray range (red in this image). The distribution of invisible dark matter (which makes up about 75 percent of the mass of this cluster) is colored blue.
One of the proposed candidates for the role of dark energy is the vacuum, whose energy density remains unchanged during the expansion of the Universe and thus confirms the negative pressure of the vacuum. Another alleged candidate is the "quintessence" - a previously unknown super-weak field, allegedly passing through the entire Universe. There are also other possible candidates, but not one of them has so far contributed to obtaining an accurate answer to the question: what is dark energy? But it is already clear that dark energy is something completely supernatural, remaining the main mystery of the fundamental physics of the XXI century.
The first scientist who theoretically substantiated and calculated the possibility of the existence of hidden unknown matter was the Swiss astronomer of Bulgarian origin Fritz Zwicky. Using Doppler methods, the scientist calculated the speeds of eight galaxies located in the constellation Veronica. In scientific literature, another romantic name is sometimes found - Veronica's Hair.
dark matter and dark energy
History of the discovery of an unknown mass
The logic behind Zwicky's calculations was as follows. The gravitational field should keep the galaxies inside their cluster. Based on this position, the required mass is calculated. Galaxies emit light, so one more value for galactic mass can be calculated. These two values should have coincided, but this did not happen. The values differed greatly. A much larger value of mass was required in order for the gravitational field to prevent the galaxies from flying apart.
It is this missing part of it that Zwicky gave the name "dark matter"
As the calculations of the scientist showed, there is much less ordinary matter in the constellation than dark matter. Zwicky published his results in a not very famous journal. Helvetica Phisica Acta .
However, for the next 40 years, astrophysicists tried to ignore such a disturbing and outstanding result.
In 1970, Vera Rubin and W.C. Ford first studied rotational movements the mysterious Andromeda Nebula. A little later, the motion of more than 60 galaxies was studied. Studies have shown that the speed of rotation of galaxies is much greater than the speed provided by their apparent observable mass. The resulting complex of indisputable observed facts is proof of the existence of hidden unknown matter.
Dark matter. Anatoly Vladimirovich
General ideas about unknown particles of unknown matter
In their research, physicists sometimes use methods that are difficult for ordinary people to identify unknown objects in the universe. They delineate unknown phenomena with firmly established and experimentally verified models and begin to slowly "squeeze" the obstinate phenomenon, patiently waiting for the necessary information from it.
However, dark matter shows true gravitational courage to the scientific curiosity of physicists.
Hidden matter clusters in exactly the same way as ordinary matter, forming galaxies and their clusters. This, perhaps, is the only similarity between the well-known visible matter and the unknown mass, whose share is 25% in the energy "bank" of the Universe.
This unknown shareholder of our Universe has simple properties. Sufficiently cold hidden matter willingly interacts with its visible neighbor (in particular, with baryons) exclusively in gravitational language. It should be noted that the cosmic density of baryons is several times less than the density of hidden matter. Such superiority in density allows it to actually "lead" the gravitational potential of the Universe.
Scientists suggest that the material composition of matter are new unknown particles. But so far they have not been found. It is only known that they do not break up into even smaller elements of Nature. Otherwise, in the time interval of the life of the Universe, they would have already gone through the process of decay. Therefore, this fact eloquently speaks in favor of the fact that there is a place to be new law conservation, prohibiting the decay of particles. However, it has not been opened yet.
Further, the dark matter substance "does not like" to interact with known particles. Due to this circumstance, the composition of the hidden mass cannot be determined by terrestrial experiments. The nature of the particles remains unknown.
Frequency Keepers - Inhomogeneous Universe
What are the ways to search for particles of dark matter?
Let's list a few ways.
- There is an assumption that protons are lighter than unknown particles by 2-3 orders of magnitude. In this case, they can be created in collisions with visible particles if they are accelerated to very high energies in a collider.
- I got the impression that unknown particles are somewhere out there, in distant galaxies. No, not only there, but also next to us. It is assumed that in one cubic meter their number can reach 1000 pieces. However, they prefer to avoid collisions with the atomic nuclei of a known substance. Although such cases do happen, and scientists hope to register them.
- unknown particles hidden mass annihilate each other. Since ordinary matter is absolutely transparent for them, they can fall into and. One of the products of the annihilation process is a neutrino, which has the ability to freely penetrate through the entire thickness of the Sun and the Earth. The registration of such neutrinos may yield unknown particles.
What is the nature of the hidden mass?
Scientists have outlined three directions in the study of the nature of dark matter.
- baryon dark matter.
Under this assumption, all particles are well known. But their radiation manifests itself in such a way that it cannot be detected.
- ordinary matter, strongly scattered in the space between galaxies;
- massive astrophysical halo objects (MACHO).
These objects, surrounding galaxies, are relatively small in size. They have very weak radiation. These properties make it impossible to detect them.
Bodies can include the following objects:
- brown dwarfs;
- white dwarfs;
- black holes;
- neutron stars.
The search for the above objects is carried out using gravitational lenses.
- Non-baryonic dark matter.
The composition of the substance is unknown. There are two options:
- a cold mass that could include photinos, axions, and quark lumps;
- hot mass (neutrino).
- A new look at gravity.
Truthfulness of the theory
It is possible that intergalactic distances will force us to look at the time-honored theory of gravitation from a new angle of galactic vision.
Refers to "Theory of the Universe"Discoveries of the properties of secret matter are yet to come. Whether it is given to a person to know and what he will do with such wealth - only the future will answer these questions.
Dark matter and dark energy in the universe
V. A. Rubakov,
Institute for Nuclear Research RAS, Moscow, Russia
1. Introduction
Natural science is now at the beginning of a new, extraordinary interesting stage of its development. It is remarkable, first of all, by the fact that the science of the microworld - elementary particle physics - and the science of the Universe - cosmology - become a single science of the fundamental properties of the world around us. Using different methods, they answer the same questions: what kind of matter is the Universe filled with today? What was its evolution in the past? What processes that took place between elementary particles in the early Universe ultimately led to its current state? If relatively recently the discussion of such questions stopped at the level of hypotheses, then today there are numerous experimental and observational data that make it possible to obtain quantitative (!) answers to these questions. This is another feature of the current stage: cosmology has become an exact science over the past 10–15 years. Already today, the data of observational cosmology have high precision; even more information about the modern and early universe will be obtained in the coming years.
The recently obtained cosmological data require a cardinal addition to modern ideas about the structure of matter and about the fundamental interactions of elementary particles. Today we know everything or almost everything about those "bricks" that make up ordinary matter - atoms, atomic nuclei, protons and neutrons that make up the nuclei - and about how these "bricks" interact with each other at distances up to 1 /1000 of the size of the atomic nucleus (Fig. 1). This knowledge was obtained as a result of many years of experimental research, mainly on accelerators, and the theoretical understanding of these experiments. Cosmological data testify to the existence of new types of particles that have not yet been discovered in terrestrial conditions and that make up “dark matter” in the Universe. Most likely, we are talking about a whole layer of new phenomena in the physics of the microcosm, and it is quite possible that this layer of phenomena will be discovered in terrestrial laboratories in the near future.
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An even more surprising result of observational cosmology was the indication of the existence of a completely new form of matter - "dark energy".
What are the properties of dark matter and dark energy and? What cosmological data testify to their existence? What does it say from the point of view of the physics of the microworld? What are the prospects for studying dark matter and dark energy in terrestrial conditions as well? This lecture is devoted to these questions.
2. Expanding Universe
There are a number of facts that speak about the properties of the Universe today and in the relatively recent past.
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universe as a whole homogeneous: All areas in the universe look the same. Of course, this does not apply to small areas: there are areas where there are many stars - these are galaxies; there are areas where there are many galaxies - these are clusters of galaxies; there are also areas where there are few galaxies - these are giant voids. But regions of 300 million light-years or more all look the same. This is clearly evidenced by astronomical observations, as a result of which a "map" of the Universe was drawn up to distances of about 10 billion light years from us. It must be said that this “map” serves as a source of the most valuable information about the modern Universe, since it allows us to determine on a quantitative level exactly how matter is distributed in the Universe.
On the rice. 2 a fragment of this map is shown, covering a relatively small volume of the universe. It can be seen that in the Universe there are structures of a rather large size, but in general, galaxies are “scattered” in it uniformly.
Universe expands: galaxies are moving away from each other. Space is stretching in all directions, and the farther away a galaxy is from us, the faster it moves away from us. Today, the rate of this expansion is slow: all distances will double in about 15 billion years, but earlier the rate of expansion was much higher. The density of matter in the Universe decreases over time, and in the future the Universe will be more and more rarefied. On the contrary, the Universe used to be much denser than it is now. The expansion of the universe is directly evidenced by the “reddening” of light emitted by distant galaxies or bright stars: due to the general stretching of space, the wavelength of light increases during the time it flies to us. It was this phenomenon that was established by E. Hubble in 1927 and served as observational evidence of the expansion of the Universe, predicted three years earlier by Alexander Friedman.
It is remarkable that modern observational data make it possible to measure not only the rate of expansion of the Universe at the present time, but also to track the rate of its expansion in the past. The results of these measurements and the far-reaching conclusions that follow from them will be discussed later. Here we will say the following: the very fact of the expansion of the Universe, together with the theory of gravity - the general theory of relativity - indicates that in the past the Universe was extremely dense and expanded extremely rapidly. If we trace the evolution of the Universe back into the past, using the known laws of physics, then we will come to the conclusion that this evolution began with the moment of the Big Bang; at that moment, the matter in the universe was so dense, and the gravitational interaction so strong, that the known laws of physics were inapplicable. 14 billion years have passed since then, which is the age of the modern Universe.
The Universe is “warm”: it has electromagnetic radiation characterized by a temperature of T = 2.725 degrees Kelvin (cosmic microwave background photons, which today are radio waves). Of course, this temperature is low today (below the temperature of liquid helium), but this was far from the case in the past. In the process of expansion, the Universe cools down, so that in the early stages of its evolution, the temperature, as well as the density of matter, was much higher than today. In the past, the universe was hot, dense, and rapidly expanding.
The photo shown on rice. 3 led to several important and unexpected conclusions. First, he allowed us to establish that our three-dimensional space is Euclidean with a good degree of accuracy: the sum of the angles of a triangle in it is 180 degrees even for triangles with sides whose lengths are comparable to the size of the visible part of the Universe, i.e. comparable to 14 billion light years. Generally speaking, the general theory of relativity admits that space may not be Euclidean, but curved; observational data show that this is not the case (at least for our region of the universe). The method for measuring the "sum of the angles of a triangle" on cosmological scales of distances is as follows. It is possible to reliably calculate the characteristic spatial size of regions where the temperature differs from the average: at the time of the plasma-gas transition, this size is determined by the age of the Universe, i.e., it is proportional to 300 thousand light years. The observed angular size of these regions depends on the geometry of three-dimensional space, which makes it possible to establish that this geometry is Euclidean.
In the case of the Euclidean geometry of three-dimensional space, the general theory of relativity unambiguously links the rate of expansion of the Universe with the total density of all forms of energy and, just as in the Newtonian theory of gravity, the speed of the Earth's revolution around the Sun is determined by the mass of the Sun. The measured expansion rate corresponds to the total energy density and in the modern Universe
In terms of mass density (since energy is related to mass by E = mc 2 ) this number is
If the energy in the Universe were entirely determined by the rest energy of ordinary matter, then on average there would be 5 protons per cubic meter in the Universe. We will see, however, that there is much less ordinary matter in the universe.
Secondly, from the photograph rice. 3 it is possible to establish what magnitude(amplitude) inhomogeneities temperature and density in the early Universe - it was 10 -4 -10 -5 of the average values. It is from these density inhomogeneities that galaxies and clusters of galaxies arose: regions with more high density attracted the surrounding matter due to gravitational forces, became even denser and eventually formed galaxies.
Since the initial density inhomogeneities are known, the process of galaxy formation can be calculated and the result compared with the observed distribution of galaxies in the Universe. This calculation is consistent with observations only if we assume that in addition to ordinary matter in the Universe there is another type of matter - dark matter, whose contribution to the total energy density is still about 25%.
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Another stage in the evolution of the Universe corresponds to even earlier times, from 1 to 200 seconds (!) from the time of the Big Bang, when the temperature of the Universe reached billions of degrees. At this time in the universe there were thermonuclear reactions, similar to reactions occurring in the center of the Sun or in a thermonuclear bomb. As a result of these reactions, part of the protons associated with neutrons and formed light nuclei - the nuclei of helium, deuterium and lithium-7. The number of light nuclei formed can be calculated, while the only unknown parameter is the density of the number of protons in the Universe (the latter, of course, decreases due to the expansion of the Universe, but its values at different times are simply interconnected).
A comparison of this calculation with the observed amount of light elements in the universe is given in rice. four : the lines represent the results of a theoretical calculation depending on a single parameter, the density of ordinary matter (baryons), and the rectangles are observational data. Remarkably, there is agreement for all three light nuclei (helium-4, deuterium and lithium-7); there is also agreement with the data on cosmic microwave background radiation (shown vertical stripe in fig. 4, designated CMB - Cosmic Microwave Background). This agreement indicates that the general theory of relativity and the known laws of nuclear physics correctly describe the Universe at the age of 1–200 seconds, when the matter in it had a temperature of a billion degrees or more. It is important for us that all these data lead to the conclusion that the mass density of ordinary matter in the modern Universe is
i.e., ordinary matter contributes only 5% to the total energy density in the Universe as well.
4. Energy balance in the modern Universe
So, the share of ordinary matter (protons, atomic nuclei, electrons) in the total energy and in the modern Universe is only 5%. In addition to ordinary matter, there are also relic neutrinos in the Universe - about 300 neutrinos of all types per cubic centimeter. Their contribution to the total energy (mass) in the Universe is small, since the neutrino masses are small, and is obviously no more than 3%. The remaining 90–95% of the total energy is also in the Universe - "it is not known what". Moreover, this "unknown what" consists of two fractions - dark matter and dark energy, and, as depicted in rice. 5 .
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At the same time, the matter in the stars is even 10 times less; ordinary matter is found mostly in clouds of gas.
5. Dark matter
Dark matter is akin to ordinary matter in the sense that it can clump (the size of, say, a galaxy or a cluster of galaxies) and participate in gravitational interactions in the same way as ordinary matter. Most likely, it consists of new particles not yet discovered in terrestrial conditions.
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In addition to cosmological data, measurements of the gravitational field in galaxy clusters and in galaxies serve in favor of the existence of dark matter. There are several ways to measure the gravitational field in galaxy clusters, one of which is gravitational lensing, illustrated in rice. 6 .
The gravitational field of the cluster bends the rays of light emitted by the galaxy behind the cluster, i.e. the gravitational field acts as a lens. At the same time, several images of this distant galaxy sometimes appear; on the left half of Fig. 6 they are blue. The curvature of light depends on the distribution of mass in the cluster, regardless of which particles create this mass. The mass distribution restored in this way is shown in the right half of Fig. 6 in blue; it can be seen that it differs greatly from the distribution of the luminous matter. The masses of galaxy clusters measured in this way are consistent with the fact that dark matter contributes about 25% to the total energy density in the Universe as well. Recall that the same number is obtained from a comparison of the theory of the formation of structures (galaxies, clusters) with observations.
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Dark matter also exists in galaxies. This again follows from measurements of the gravitational field, now in galaxies and their environs. The stronger the gravitational field, the faster the stars and gas clouds revolve around the galaxy, so that measurements of rotation speeds depending on the distance to the center of the galaxy make it possible to reconstruct the mass distribution in it. This is illustrated in rice. 7 : as you move away from the center of the galaxy, the circulation velocities do not decrease, which indicates that in the galaxy, including far from its luminous part, there is non-luminous, dark matter. In our Galaxy in the vicinity of the Sun, the mass of dark matter is approximately equal to the mass of ordinary matter.
What are dark matter particles? It is clear that these particles must not decay into other, lighter particles, otherwise they would have decayed during the existence of the Universe. This fact itself indicates that in nature there is new not open yet conservation law, which prevents these particles from decaying. The analogy here is with the law of conservation of electric charge: an electron is the lightest particle with an electric charge, and that is why it does not decay into lighter particles (for example, neutrinos and photons). Further, dark matter particles interact extremely weakly with our matter, otherwise they would have already been detected in terrestrial experiments. Next comes the area of hypotheses. The most plausible (but by no means the only!) hypothesis seems to be that dark matter particles are 100–1000 times heavier than a proton, and that their interaction with ordinary matter is comparable in intensity to that of a neutrino. It is within the framework of this hypothesis that the modern density of dark matter finds a simple explanation: dark matter particles were intensively created and annihilated in the very early Universe at superhigh temperatures (of the order of 10 15 degrees), and some of them have survived to this day. With the specified parameters of these particles, their current number in the Universe is exactly what is needed.
Can we expect the discovery of dark matter particles in the near future under terrestrial conditions? Since we do not know the nature of these particles today, it is impossible to answer this question quite unambiguously. However, the outlook appears to be very optimistic.
There are several ways to search for dark matter particles. One of them is related to experiments at future high-energy accelerators and colliders. If dark matter particles are indeed 100–1000 times heavier than a proton, then they will be born in collisions of ordinary particles accelerated at colliders to high energies (the energies achieved at existing colliders are not enough for this). The immediate prospects here are associated with the Large Hadron Collider (LHC) under construction at the CERN International Center near Geneva, which will produce colliding beams of protons with an energy of 7x7 Teraelectronvolts. It must be said that according to the hypotheses popular today, dark matter particles are only one representative of a new family of elementary particles, so along with the discovery of dark matter particles, one can hope to discover a whole class of new particles and new interactions at accelerators. Cosmology suggests that the world of elementary particles is far from being exhausted by the known "bricks"!
Another way is to register dark matter particles that fly around us. There are by no means few of them: with a mass equal to 1000 masses of a proton, there should be 1000 of these particles in a cubic meter here and now. The problem is that they interact extremely weakly with ordinary particles, the substance is transparent to them. However, dark matter particles occasionally collide with atomic nuclei, and these collisions can hopefully be registered. Search in this direction
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Finally, another way is connected with the registration of the products of annihilation of dark matter particles with each other. These particles should accumulate in the center of the Earth and in the center of the Sun (substance is practically transparent for them, and they are able to fall into the Earth or the Sun). There, they annihilate each other, and in doing so, other particles are formed, including neutrinos. These neutrinos freely pass through the thickness of the Earth or the Sun, and can be registered by special installations - neutrino telescopes. One of these neutrino telescopes is located in the depths of Lake Baikal (NT-200, rice. eight ), another (AMANDA) - deep in the ice at the South Pole.
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As shown in rice. 9 , a neutrino coming, for example, from the center of the Sun, can, with a low probability, experience an interaction in water, as a result of which a charged particle (muon) is formed, the light from which is recorded. Since the interaction of neutrinos with matter is very weak, the probability of such an event is small, and very large volume detectors are required. The construction of a detector with a volume of 1 cubic kilometer has now begun at the South Pole.
There are other approaches to the search for dark matter particles, for example, the search for their annihilation products in the central region of our Galaxy. Which of these paths will be the first to succeed, time will tell, but in any case, the discovery of these new particles and the study of their properties will be a major scientific achievement. These particles will tell us about the properties of the Universe 10–9 s (one billionth of a second!) After the Big Bang, when the temperature of the Universe was 10 15 degrees, and dark matter particles interacted intensively with the cosmic plasma.
6. Dark energy
Dark energy is a much stranger substance than dark matter. To begin with, it does not gather into clumps, but is evenly “spilled” in the Universe. There is as much of it in galaxies and clusters of galaxies as outside of them. The most unusual thing is that dark energy in a certain sense does not experience antigravity. We have already said that modern astronomical methods can not only measure the current rate of expansion of the Universe, but also determine how it has changed over time. So, astronomical observations indicate that today (and in the recent past) the Universe is expanding with acceleration: the rate of expansion increases with time. This is the meaning of e and we can talk about antigravity: the usual gravitational attraction would slow down the recession of galaxies, but in our Universe, it turns out, the opposite is true.
Such a picture, generally speaking, does not contradict the general theory of relativity, however, for this, dark energy must have a special property - negative pressure. This sharply distinguishes it from ordinary forms of matter. It would not be an exaggeration to say that the nature of dark energy and is main riddle fundamental physics of the XXI century.
One of the candidates for the role of dark energy is vacuum. The energy density of the vacuum does not change with the expansion of the Universe, and this means the negative pressure of the vacuum. Another candidate is a new superweak field that permeates the entire Universe; the term "quintessence" is used for it. There are other candidates, but in any case, the dark energy of the self is something completely unusual.
Another way to explain the accelerated expansion of the universe is to assume that the very laws of gravity change over cosmological distances and cosmological times. Such a hypothesis is far from harmless: attempts to generalize the general theory of relativity in this direction encounter serious difficulties.
Apparently, if such a generalization is possible at all, then it will be associated with the idea of the existence of additional dimensions of space, in addition to the three dimensions that we perceive in everyday experience.
Unfortunately, there are currently no ways of direct experimental study of dark energy under terrestrial conditions. This, of course, does not mean that new brilliant ideas in this direction cannot appear in the future, but today the hopes for clarifying the nature of dark energy and (or, more generally, the reasons for the accelerated expansion of the Universe) are associated exclusively with astronomical observations and with obtaining new, more accurate cosmological data. We have to find out in detail exactly how the Universe expanded at a relatively late stage of its evolution, and this, hopefully, will allow us to make a choice between different hypotheses.
We are talking about observations of type 1a supernovae.
The change in energy and with a change in volume is determined by pressure, Δ E = -pΔ V. As the Universe expands, the vacuum energy grows together with the volume (energy density and is constant), which is possible only if the vacuum pressure is negative. Note that the opposite signs of pressure and energy and vacuum follow directly from the Lorentz invariance.
7. Conclusion
As is often the case in science, the spectacular advances in particle physics and cosmology have raised unexpected and fundamental questions. Today we do not know what constitutes the bulk of matter in the universe. We can only guess what phenomena occur at ultra-small distances, and what processes took place in the Universe at the earliest stages of its evolution. It is remarkable that many of these questions will be answered in the foreseeable future - within 10-15 years, and maybe even earlier. Our time is the time of a radical change in the view of nature, and the main discoveries here are yet to come.
DISCUSSION
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We are on the threshold of a discovery that can change the essence of our ideas about the World. We are talking about the nature of dark matter. In recent years, astronomy has made critical steps in the observational justification of dark matter, and today the existence of such matter in the Universe can be considered a firmly established fact. The peculiarity of the situation is that astronomers observe structures consisting of a substance unknown to physicists. So there was an identification problem. physical nature this matter.
1. "Bring something, I don't know what"
Modern elementary particle physics does not know particles that have the properties of dark matter. Requires an extension of the Standard Model. But how, in what direction to move, what and where to look for? The words from the well-known Russian fairy tale, put in the title of this section, reflect the current situation in the best possible way.
Physicists are looking for unknown particles, having only general ideas about the properties of observed matter. What are these properties?
We only know that dark matter interacts with luminous matter (baryons) in a gravitational manner and is a cold medium with a cosmological density several times higher than that of baryons. Due to such simple properties dark matter directly affects the development of the gravitational potential of the universe. The contrast of its density increased with time, leading to the formation of gravitationally bound systems of the dark matter halo.
It should be emphasized that this process of gravitational instability could be triggered in the Friedmann Universe only in the presence of seed density perturbations, the very existence of which is in no way related to dark matter, but is due to the physics of the Big Bang. Therefore, another important question arises about the origin of seed perturbations, from which the structure of dark matter developed.
The question of the generation of initial cosmological perturbations will be considered somewhat later. Now let's get back to dark matter.
Baryons are trapped in the gravitational wells of dark matter concentrations. Therefore, although dark matter particles do not interact with light, there is light where there is dark matter. This remarkable property of gravitational instability made it possible to study the quantity, state, and distribution of dark matter from observational data from the radio range to the X-ray range.
An independent confirmation of our conclusions about the properties of dark matter and about other parameters of the Universe is the data on the anisotropy and polarization of the cosmic microwave background radiation, on the abundance of light elements in the Universe, and on the distribution of absorption lines of matter in the spectra of distant quasars. An increasingly important role is played by numerical simulation, which has replaced experiment in cosmological studies. The most valuable information about the distribution of dark matter is contained in numerous observational data on gravitational lensing of distant sources by nearby matter clumps.
Rice. 1. Photograph of the sky in the direction of the galaxy cluster 0024 + 1654, taken with the Hubble telescope.
Figure 1 shows a section of the sky in the direction of one of these dark mass clumps ($\sim 10^(14)M_(odot)$). We see a cluster of galaxies captured by the gravitational field of this bunch, hot X-ray gas resting at the bottom of the gravitational potential well, and a multiple image of one of the background galaxies that appeared on the line of sight of the dark halo and was distorted by its gravitational field.
Table 1. Main cosmological parameters
Table 1 shows the average values of cosmological parameters obtained from astronomical observations (10% accuracy). Obviously, the total energy density of all types of particles in the Universe does not exceed 30% of the total critical density (the contribution of neutrinos is not more than a few percent). The remaining 70% are in a form that did not take part in the gravitational heaping of matter. Only the cosmological constant or its generalization, a medium with negative pressure ($|\varepsilon + p|\ll\varepsilon $), which is called "dark energy", has this property. Determining the nature of the latter is a long-term perspective for the development of physics.
This report is devoted to the issues of physical cosmology, the solution of which is expected in the coming years. First of all, this concerns the determination of the initial conditions for the formation of dark matter structures and the search for the unknown particles themselves.
2. Early Universe and Late Universe
The observed structure of the Universe is the result of the joint action of the starting conditions and the evolution of the density perturbation field. Modern observational data made it possible to determine the characteristics of the density perturbation field in different epochs of its development. Thus, it was possible to separate information about the initial conditions and about the conditions of development, which marked the beginning of an independent study of the physics of the early and late Universe.
The term "early Universe" in modern cosmology means the final stage of accelerated expansion followed by a transition to the hot phase of evolution. We do not know the parameters of the Big Bang, there are only upper limits (see Section 3, relations (12)). However, there is a well-developed theory of the generation of cosmological perturbations, according to which we can calculate the spectra of initial perturbations of the matter density and primary gravitational waves depending on the values of cosmological parameters.
The reasons for the absence of a generally accepted model of the early Universe lie in the stability of the predictions of the Big Bang inflationary paradigm - the proximity of the generated spectra to flat view, the relative smallness of the amplitude of cosmological gravitational waves, the three-dimensional Euclidean nature of the visible Universe, etc., which can be obtained in a wide class of model parameters. The moment of truth for building a model of the early Universe could be the discovery of cosmological gravitational waves, which seems possible in the event of a successful international space experiment "Planck", which should begin in 2008.
Our knowledge of the late universe is diametrically opposed. We have a fairly accurate model - we know the composition of matter, the laws of structure development, the values of cosmological parameters (see Table 1), but at the same time we do not have a generally accepted theory of the origin of matter components.
The known properties of the visible Universe allow us to describe its geometry in terms of perturbation theory. The small parameter ($10^(-5)$) is the amplitude of cosmological perturbations.
In order zero, the Universe is Friedmannian and is described by a single function of time - the scale factor $a(t)$. The first order is somewhat more complicated. The perturbations of the metric are the sum of three independent modes - scalar $S(k)$, vector $V(k)$ and tensor $T(k)$, each of which is characterized by its own spectral function of the wave number $k$. The scalar mode describes cosmological density perturbations, the vector mode is responsible for the vortex motions of matter, and the tensor mode is gravitational waves. Thus, the entire geometry is described using four functions: $a(t),~ S(k),~ V(k)$ and $T(k)$, of which only the first two are known to us today (in some domains of definition ).
The Big Bang was a catastrophic process of rapid expansion accompanied by an intense, rapidly changing gravitational field. In the course of the cosmological expansion, metric perturbations were spontaneously born parametrically from vacuum fluctuations, just as any massless degrees of freedom are born under the action of an external variable field. An analysis of the observational data indicates a quantum-gravitational mechanism for the generation of bare perturbations. Thus, the large-scale structure of the Universe is an example of the solution of the problem of measurability in quantum field theory.
Let us note the main properties of the generated perturbation fields: Gaussian statistics (random distributions in space), a distinguished time phase (the "growing" branch of perturbations), the absence of a distinguished scale in a wide range of wavelengths, and a nonzero amplitude of gravitational waves. The latter is of decisive importance for constructing a model of the early Universe, since, having the simplest connection with the background metric, gravitational waves carry direct information about the energy scale of the Big Bang.
As a result of the development of the scalar mode of perturbations, galaxies and other astronomical objects were formed. An important achievement recent years(the WMAP experiment (Wilkinson Microwave Anisotropy Probe)) became a serious refinement of our knowledge of the anisotropy and polarization of the cosmic microwave background radiation, which arose long before the appearance of galaxies as a result of the impact on the distribution of photons of all three modes of cosmological perturbations.
A joint analysis of observational data on the distribution of galaxies and the anisotropy of the cosmic microwave background radiation made it possible to separate the starting conditions and evolution. Using the condition that the sum $S+V+T\approx 10^(-10)$ is fixed by the CMB anisotropy, we can obtain an upper limit on the sum of the vortex and tensor modes of perturbations in the Universe (their detection is possible only with an increase in the accuracy of observations):
$$\frac(V+T)(S) If inequality (1) were violated, the magnitude of density perturbations would be insufficient to form the observed structure.
3. In the beginning there was a sound...
The effect of quantum-gravitational production of massless fields has been well studied. This is how particles of matter can be born (see, for example, ) (although, in particular, relic photons arose as a result of the decay of protomatter in the early Universe). In the same way, gravitational waves and density perturbations are generated, since these fields are also massless and their production is not prohibited by the threshold energy condition. The problem of generating vortex disturbances is still waiting for its researchers.
The theory of $S$- and $T$-modes of perturbations in the Friedmann Universe is reduced to the quantum-mechanical problem of independent oscillators $q_k(\eta)$ located in an external parametric field ($\alpha(\eta)$) in the Minkowski world with time coordinate $\eta=\int dt/a$. The action and Lagrangian of elementary oscillators depend on their spatial frequency $k \in (0, \infty)$:
$$S_k = \int L_kd\eta,~\;\;\;L_k=\frac(\alpha^2)(2k^3)(q'^2-\omega^2q^2)~\;\; \;\;\;\;\;\;\; (2)$$
where the prime denotes the time derivative $\eta$, $\omega=\beta$ is the frequency of the oscillator, $\beta$ is the perturbation propagation velocity in units of the speed of light in vacuum (hereinafter $c=\hbar =1$, index $k$ is omitted from field $q$); in the case of the $T$-mode, $q = q_T$ is the transverse traceless component of the metric tensor,
$$\alpha^2_T=\frac(a^2)(8\pi G)~\;\;\;\beta=1, ~\;\;\;\;\;\;\;\;\ ; (3)$$
and in the case of the $S$-mode $q = q_s$ - linear superposition of the longitudinal gravitational potential (perturbation of the scale factor) and the 3-velocity potential of the medium, multiplied by the Hubble parameter ,
$$\alpha^2_S=\frac(a^2\gamma)(4\pi G\beta^2),\;\;\gamma=\frac(\dot(H))(H^2),\ ;\;H=\frac(\dot(a))(a),~\;\;\;\;\;\;\;\;\; (4)$$
the dot means the time derivative $t$.
As can be seen from (3), the field $q_T$ is fundamental, since it is minimally related to the background metric and does not depend on the properties of matter (in the general theory of relativity, the speed of propagation of gravitational waves is equal to the speed of light). As for $q_S$, its connection with the external field (4) is more complicated: it includes both derivatives of the scale factor and some characteristics of the substance (for example, the velocity of propagation of perturbations in the medium). We know nothing about protomatter in the early Universe - there are only general approaches to this issue.
Usually, an ideal medium is considered with the energy-momentum tensor depending on the energy density $\epsilon$, the pressure $p$, and the 4-velocity of matter $u^\mu$. For the $S$-mode, the 4-velocity is potential and can be represented as a gradient of the 4-scalar $\phi$:
$$T_(\mu\nu)=(\epsilon + p)u_\mu u_\nu-pg_(\mu\nu),\;\;u_\mu=\frac(\phi_(,\mu)) (w),~\;\;\;\;\;\;\;\;\; (5)$$
where $w^2=\phi_(,\mu)\phi_(,\nu) g^(\mu\nu)$ is the normalization function, the subscript comma means the derivative with respect to the coordinate. The speed of sound is given using the "equation of state" as a proportionality factor between the accompanying perturbations of pressure and energy density of matter:
$$\delta p_c=\beta^2\delta\epsilon_c,~\;\;\;\;\;\;\;\;\; (6)$$
where $\delta X_c\equiv\delta X – v\dot(X)$, $v\equiv\delta\phi /w$ is the 3-velocity potential of the medium.
In the linear order of perturbation theory, the concept of an ideal medium is equivalent to the field concept, according to which the material field $\phi$ is assigned a Lagrangian density, $L=L(w,\phi)$. In the field approach, the propagation velocity of excitations is found from the equation
$$\beta^(-2)=\frac(\partial\ln|\partial L/\partial w|)(\partial\ln|w|),~\;\;\;\;\;\; \;\;\; (7)$$
which also corresponds to relation (6). Most models of the early Universe assume that $\beta\sim 1$ (in particular, at the radiation-dominated stage $\beta=1/\sqrt(3)$).
The evolution of elementary oscillators is described by the Klein-Gordon equation
$$\bar(q)''+(\omega^2-U) \bar(q)=0,~\;\;\;\;\;\;\;\;\; (8)$$
where
$$\bar(q)\equiv\alpha q,\;\;U\equiv\frac(\alpha "")(\alpha),~\;\;\;\;\;\;\;\; \; (9)$$
The solution of equation (8) has two asymptotic branches of behavior: adiabatic ($\omega^2>U$), when the oscillator is in free oscillation mode and its excitation amplitude decays ($|q|\sim(\alpha\sqrt(\beta ))^(-1)$), and parametric ($\omega^2
Quantitatively, the spectra of generated perturbations depend on the initial state of the oscillators:
$$T\equiv 2\langle q_T^2\rangle,\;\;\;S\equiv\langle q_S^2\rangle,~\;\;\;\;\;\;\;\;\; (10)$$
the coefficient 2 in the expression for the tensor mode takes into account two polarizations of gravitational waves. The $\langle\rangle$ state is considered to be the main state, i.e. corresponding to the minimum level of initial excitation of oscillators. This is the main hypothesis of the Big Bang theory. In the presence of an adiabatic zone, the ground (vacuum) state of elementary oscillators is the only one.
Thus, assuming that the function U increases with time and $\beta\sim 1$, we obtain a universal general result for the spectra $T(k)$ and $S(k)$:
$$T\approx\frac((1-\gamma/2)H^2)(M_P^2),\;\;\;\frac(T)(S)\approx4\gamma~\;\;\ ;\;\;\;\;\;\; (11)$$
where $k=\sqrt(U)\approx aH$ and $M_p\equiv G^(-1/2)$ is the Planck mass. As can be seen from (11), in the theory, the $T$ mode is not discriminated in any way with respect to the $S$ mode. It's all about the value of the $\gamma$ factor in the epoch of perturbation generation.
From the observed fact that the $T$-mode is small in our Universe (see Section 2, relation (1)), we obtain an upper bound on the energy scale of the Big Bang and on the $\gamma$ parameter in the early Universe:
$$H The last condition means that the Big Bang had an inflationary character ($\gamma) $ at the initial (adiabatic) and final (radiation-dominated, $a\propto n$) stages of evolution (see Fig. 2).
Rice. 2. Illustration of the solution of equation (8) in the formulation of the scattering problem
For each of the above asymptotics common decision has the form
$$\bar(q)=C_1\sin\omega\eta+C_2\cos\omega\eta,~\;\;\;\;\;\;\;\;\; (13)$$
where the operators $C_(1,2)$ define the amplitudes of the "growing" and "falling" branches of evolution. In the vacuum state, the initial time phase of the field is arbitrary: $\langle|C_1^((in))|\rangle=\langle|C_2^((in))|\rangle$. However, as a result of solving the evolution equations, it turns out that at the radiation-dominated stage, only the growing branch of sound perturbations remains to gain: $\langle|C_1^((out))|\rangle\gg\langle|C_2^((out))| \rangle$. By the time the radiation is detached from the matter in the recombination epoch, the radiation spectrum is modulated with the phase $k=n\pi\sqrt(3)/\eta_(rec)$, where $n$ is a natural number.
Rice. 3. Manifestation of sound modulation in the CMB anisotropy spectrum. (According to WMAP experiments, ACBAR (Arcminute Cosmology Bolometer Array Receiver), BOOMERANG (Ballon Observations Of Millimetric Extragalactic Radiation ANd Geophysics), CBI (Cosmic Background Imager), VSA (Very Small Array).)
It is these acoustic oscillations that are observed in the CMB anisotropy spectra (Fig. 3, large peak corresponds to $n = 1$) and density perturbations, which confirms the quantum gravitational origin of the $S$ mode. In the spectrum of density perturbations, the sound modulation is suppressed by the factor of smallness of the fraction of baryons relative to the total density of matter, which makes it possible to find this fraction independently of other cosmological tests. The scale of the oscillation itself serves as an example of a standard ruler by which the most important parameters of the Universe are determined. In this regard, it should be emphasized that the acute problem of the degeneration of cosmological parameters in observational data, which for many years prevented the construction of a real model of the Universe, has now been removed due to the abundance of independent and complementary observational tests.
Summing up, we can state that the problem of the formation of initial cosmological perturbations and the large-scale structure of the Universe has been solved in principle today. The theory of the quantum-gravitational origin of perturbations in the early Universe will be finally confirmed after the discovery of the $T$-mode, which may happen in the near future. Thus, the simplest Big Bang model (power-law inflation on a massive scalar field) predicts the value of the $T$-mode amplitude only 5 times less than the $S$-mode amplitude. Modern tools and technologies make it possible to solve the problem of registering such small signals from the data of observations of the anisotropy and polarization of the CMB.
4. Dark side of matter
There are several hypotheses about the origin of matter, but none of them has yet been confirmed. There are direct observational indications that the mystery of dark matter is closely related to the baryon asymmetry of the universe. However, there is no generally accepted theory of the origin of baryon asymmetry and dark matter today.
Where is dark matter located?
We know that the luminous component of matter is observed in the form of stars gathered into galaxies of different masses, and in the form of the X-ray gas of clusters. However most of ordinary matter (up to 90%) is in the form of a rarefied intergalactic gas with a temperature of several electron volts, as well as in the form of MACHO (Massive Compact Halo Object) - compact remnants of the evolution of stars and objects with low mass. Since these structures usually have a low luminosity, the name "dark baryons" has stuck to them.
Rice. 4. Upper limit on the mass fraction of the Galactic halo in the MACNO according to the EROS experiment (from French - Experience pour la Recherche d "Objets Sombres).
Several groups (MACHO, EROS, etc.) have been studying the number and distribution of compact dark objects in the halo of our Galaxy based on microlensing events. As a result of the joint analysis, an important limitation was obtained - no more than 20% of the total mass of the halo is concentrated in the MACNO in the range of values from the mass of the moon to the masses of stars (Fig. 4). The rest of the halo's dark matter is made up of particles of an unknown nature.
Where else is non-baryonic dark matter hidden?
The development of high technologies in the observational astronomy of the 20th century made it possible to obtain a clear answer to this question: non-baryonic dark matter is found in gravitationally bound systems (halos). Dark matter particles are non-relativistic and weakly interacting - their dissipative processes are not the same as those of baryons. Baryons, on the other hand, cool down by radiation, settle down and accumulate in the centers of the halo, reaching rotational equilibrium. dark matter remains distributed around the visible matter of galaxies with a characteristic scale of about 200 kpc. Thus, in the Local Group, which includes the Andromeda Nebula and Milky Way, more than half of all dark matter is concentrated in these two large galaxies. There are no particles with the required properties in the Standard Model of elementary particle physics. An important parameter that cannot be determined from observations due to the Equivalence Principle is the mass of the particle. Within the framework of possible extensions of the Standard Model, there are several candidates for dark matter particles. The main ones are listed in Table. 2 in ascending order of their rest mass.
Table 2. Candidates for non-baryonic dark matter particles
| Candidate | |
Gravitons |
|
"Sterile" neutrinos |
|
mirror substance |
|
massive particles |
|
supermassive particles |
$10^(13)$ GeV |
Monopoles and defects |
$10^(19)$ GeV |
Primordial black holes |
$(10^(-16)-10^(-17))M_(\odot)$ |
Today's main version of massive particles - the neutralino hypothesis - is associated with minimal supersymmetry. This hypothesis can be tested at the Large Hadron Accelerator at CERN, which is scheduled to be launched in 2008. The expected mass of such particles is $\sim$ 100 GeV, and their density in our Galaxy is one particle in the volume of a tea glass.
The search for dark matter particles is carried out around the world at many installations. It is interesting to note that the neutral hypothesis can be independently verified both in underground experiments on elastic scattering and by indirect data on neutralino annihilation in the Galaxy. So far, a positive response has been received only in one of the underground detectors of the DAMA project (DArk MAtter), where a signal of unknown origin of the "summer-winter" type has been observed for several years. However, the range of masses and cross sections associated with this experiment has not yet been confirmed on other facilities, which calls into question both the reliability and significance of the result.
An important property of neutralinos is the possibility of their indirect observation from the annihilation flux in the gamma region. In the process of hierarchical crowding, such particles could form a mini-halo with a characteristic size of the order of the size of the solar system and a mass of the order of the mass of the Earth, the remnants of which have survived to this day. The Earth itself with a high probability can be located inside such minihalos, where the density of particles increases by several tens of times. This increases the probability of both direct and indirect detection of dark matter in our galaxy. The existence of such different search methods inspires optimism and allows us to hope for an early determination of the physical nature of dark matter.
5. On the threshold of new physics
In our time, it has become possible to independently determine the properties of the early Universe and the late Universe from observational astronomical data. We understand how the initial cosmological density perturbations arose from which the structure of the Universe developed. We know the values of the most important cosmological parameters underlying the Standard Model of the Universe, which today has no serious competitors. However, the fundamental questions of the origin of the Big Bang and the main components of matter remain unsolved.
The observational determination of the tensor mode of cosmological perturbations is the key to constructing a model of the early Universe. Here we are dealing with a clear prediction of a theory that has been well tested in the case of the $S$ mode and has the possibility of experimental verification of the $T$ mode in the coming years.
Theoretical physics, having provided an extensive list of possible directions and methods for searching for dark matter particles, has exhausted itself. Now it's up to the experiment. The current situation is reminiscent of the one that preceded the great discoveries - the discovery of quarks, W- and Z-bosons, neutrino oscillations, anisotropy and polarization of the cosmic microwave background radiation.
One question arises, which, however, is beyond the scope of this overview report: why is Nature so generous to us and allows us to reveal its secrets?
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V.N. Lukash, E.V. Mikheev
Plays a decisive role in the development of the universe. However, little is known about this strange substance yet. Professor Matthias Bartelmann - Heidelberg Institute for Theoretical Astrophysics - explains how dark matter research has been done, answering a series of questions from journalists.
and how does it arise?
I have no idea! So far, no one. It probably consists of heavy elementary particles. But no one knows if they are really particles. In any case, they are very different from anything we have known before.
Is it like discovering a whole new animal species?
Yes, that's right, that's a good comparison.
Who discovered dark matter and when?
In 1933, Fritz Zwicky considered the motion of galaxies in galaxy clusters, which depends on the total mass of the cluster. The researcher noticed that galaxies, given their calculated mass, move very quickly. This was the first hint of dark matter. No known matter could explain why the stars in galaxies stick together: they must fly apart due to their high speed of circulation.
Gravitational lens Photo: Wissensschreiber
What other evidence is there?
Pretty good evidence is the gravitational lens effect. Distant galaxies appear distorted to us, as light rays deviate from matter on their way. It's like looking through fluted glass. And the effect is stronger than it would be if only visible matter existed.
What does dark matter look like?
It cannot be seen, since there is no interaction between dark matter and electromagnetic radiation. This means that it does not reflect light and does not emit any radiation.
How do you study dark matter then? What instruments are needed for research?
We are not studying dark matter specifically, but only its manifestations, for example, the effect of a gravitational lens. I am a theorist. As a matter of fact, I just need my computer, a pen and a sheet of paper. But I also use data from large telescopes in Hawaii and Chile.
Is it possible to depict dark matter?
Yes, you can create a kind of map of its distribution. Just as the lines of hills show on geographical map the contours of the mountain, here you can see by the density of lines, where there is especially a lot of dark matter.
When did she appear?
Dark matter arose either directly at the Big Bang, or 10,000-100,000 years later. But we are still studying this.
How much dark matter is there?
Nobody can say for sure. But based on recent research, we believe that there is about seven to eight times more dark matter in the universe than visible matter.
Computer modeling shows the distribution of dark matter in the form of a web, and we see its accumulation in the brightest areas.
Photo: Volker Springel
Is there a relationship between dark energy and dark matter?
Probably not. Dark energy ensures the accelerated expansion of the universe, while dark matter holds galaxies together.
Where did she come from?
Dark matter is probably everywhere, only it is not evenly distributed - just like visible matter, it forms clumps.
What is the significance of dark matter for us and our worldview?
For everyday life, it does not matter. But in astrophysics it is very important, as it plays a decisive role in the development of the Universe.
What is our universe made of? 4.9% visible matter, 26.8% dark matter, 68.3% dark energy Photo: Wissensschreiber
What will she bring about in the future?
Probably nothing more. Previously, for the development of the universe, it was very important. Today, it only still holds individual galaxies together. And as the universe continues to expand, it becomes increasingly difficult for new structures of dark matter to emerge.
Will it be possible in the future to directly image dark matter using instruments?
Yes it is possible. For example, one can measure the vibrations that occur when dark matter particles collide with atoms in a crystal. The same happens in a particle accelerator: if elementary particles seem to fly in an unexpected direction for no reason, then an unknown particle may be to blame. Then this would be another proof of the existence of dark matter. Imagine: you are standing on a football field and there is a ball in front of you. He suddenly flies away for no apparent reason. He must have been knocked down by something invisible.
What interests you the most in your work?
I am attracted by the assumption that visible matter is only a small fraction of everything, and we have no idea of the remainder.
Thank you for taking the time. We hope you will learn more about dark matter soon!
