According to the theory of cosmic inflation, the early universe began to expand exponentially, just after the Big Bang. Cosmologists put forward this theory in 1981 to explain several important problems in cosmology.
One such problem is the horizon problem. Suppose for a moment that the universe is not expanding. Now imagine that in the very early universe, a photon was released that flew freely before it hit the Earth's North Pole. Now imagine that at the same time a photon is fired, this time in the opposite direction to the first. He would have to hit the South Pole of the Earth.
Can two given photons exchange any information that occurred during their creation? Obviously not. Because the time required to transfer data from one photon to another, in this case, will be two ages of the Universe. The photons are isolated. They are beyond each other's horizon.
However, observations show that photons coming from opposite directions interacted in some way. Since the background microwave cosmic radiation has almost identical temperatures in all points of our sky.
This problem can be solved by accepting the assumption that some time after the Big Bang, the universe expanded exponentially. Up to this point, the universe could have had casual contact and a balanced overall temperature. Regions that are now at great distances from each other were very close in the early universe. This explains why photons coming from different directions almost always have the same temperature.
A simple model for understanding the expansion of the universe is like inflating a balloon. To an observer on either side of the ball, it may appear that he is in the center of the expansion, as all neighboring points get farther away.
When the balloon is inflated, the distance between objects on the surface of the balloon is about e60 = 1026. This is a number with twenty-six zeros. It transcends the normal political and economic debate about inflation.
Quantum fluctuations
Let's imagine that before the balloon began to inflate, an inscription was written on it. So small that it was impossible to read it. Inflating the balloon made the message readable. This means that inflation acts as a microscope that shows what was written on the original ball.
Likewise, we can consider the quantum fluctuations that were generated at the start of inflation. The expansion of space during the inflationary era acts as a huge microscope that shows quantum fluctuations. This leaves imprints in the background microwave cosmic radiation (hotter and colder regions) and in the expansion of galaxies.
When using classical physics, the evolution of the inflationary Universe is homogeneous - each point in space develops identically. However, quantum physics introduces some uncertainty in the initial conditions for different points in space.
These variations act like seeds in the formation of the structure. After a period of inflation, when the fluctuations intensify, the distribution of matter will differ slightly from place to place in the universe. The force of gravity forms denser regions, which leads to the formation of galaxies.
What would happen if in the distant past the space of the Universe was in a state of a false vacuum? If the density of matter at that epoch was less than is required to balance the universe, then repulsive gravity would dominate. This would cause the universe to expand, even if it had not originally expanded.
To make our ideas more definite, we will assume that the Universe is closed. Then it inflates like a balloon. With the growth of the volume of the Universe, matter becomes rarefied, and its density decreases. However, the mass density of the false vacuum is a fixed constant; it always remains the same. So very quickly the density of matter becomes negligible, we are left with a homogeneous expanding sea of false vacuum.
The expansion is caused by the tension of the false vacuum, which exceeds the attraction associated with the density of its mass. Since none of these quantities change over time, the expansion rate remains constant with high precision. This rate is characterized by the proportion in which the universe expands per unit of time (say, one second). In terms of meaning, this value is very similar to the rate of inflation in the economy - the percentage increase in prices for the year. In 1980, when Guth was teaching a seminar at Harvard, the inflation rate in the United States was 14%. If this value remained unchanged, prices would double every 5.3 years. Likewise, a constant rate of expansion of the universe implies that there is a fixed time interval during which the size of the universe doubles.
Growth that is characterized by a constant doubling time is called exponential. It is known to lead to gigantic numbers very quickly. If today a slice of pizza costs $ 1, then after 1o cycles of doubling (53 years in our example) its price will be $ 10 ^ (24) $ dollars, and after 330 cycles it will reach $ 10 ^ (100) $ dollars. This colossal number, the one followed by 100 zeros, has a special name - googol. Guth suggested using the term inflation in cosmology to describe the exponential expansion of the universe.
The doubling time for a universe filled with a false vacuum is incredibly short. And the higher the vacuum energy, the shorter it is. In the case of an electroweak vacuum, the universe will expand by a googol once in one-thirty microseconds, and in the presence of a Grand Unification vacuum, this will happen $ 10 ^ (26) $ times faster. In such a short fraction of a second, a region the size of an atom will swell to a size much larger than the entire observable universe today.
Because the false vacuum is unstable, it eventually disintegrates and its energy ignites a fireball of particles. This event marks the end of inflation and the beginning of normal cosmological evolution. Thus, from a tiny initial embryo, we get a huge hot expanding Universe. And as an added bonus, this scenario surprisingly removes the horizon and flat geometry problems that are characteristic of the Big Bang cosmology.
The crux of the horizon problem is that the distances between some parts of the observable universe are such that they seem to have always been greater than the distance traveled by light since the Big Bang. This assumes that they never interacted with each other, and then it is difficult to explain how they achieved almost exact equality of temperatures and densities. In the standard Big Bang theory, the path traveled by light grows in proportion to the age of the universe, while the distance between regions increases more slowly, as cosmic expansion is slowed down by gravity. Areas that cannot interact today will be able to influence each other in the future, when the light finally covers the distance separating them. But in the past, the distance traveled by light becomes even shorter than necessary, so if the regions cannot interact today, they were all the more unable to do so before. The root of the problem is thus related to the attractive nature of gravity, due to which the expansion is gradually slowing down.
However, in a universe with a false vacuum, gravity is repulsive, and instead of slowing expansion, it speeds it up. In this case, the situation is reversed: areas that can exchange light signals will lose this opportunity in the future. And, more importantly, those areas that are inaccessible to each other today should have interacted in the past. The horizon problem disappears!
The flat space problem is just as easy to solve. It turns out that the universe moves away from critical density only if its expansion slows down. In the case of accelerated inflationary expansion, the opposite is true: the Universe approaches the critical density, which means it becomes flatter. Since inflation increases the Universe by a colossal number of times, we only see a tiny fraction of it. This observable area looks flat like our Earth, which also appears flat when viewed from near the surface.
So a short period of inflation makes the Universe big, hot, homogeneous and flat, creating just the initial conditions required for standard Big Bang cosmology.
The theory of inflation began to conquer the world. As for Guth himself, his post-doc status is over. He accepted an offer from his alma mater, MIT, where he continues to work today.
Excerpt from A. Vilenkin's book "Many Worlds in One: The Search for Other Universes"
In which he briefly describes the emergence and development of the theory of the inflationary universe, which gives a new explanation for the Big Bang and predicts the existence of many other universes along with ours.
Cosmology is in some way akin to philosophy. First, in terms of the vastness of its subject of research, it is the entire Universe as a whole. Secondly, due to the fact that some of the premises in it are accepted by scientists as admissible without the possibility of conducting any verification experiment. Third, the predictive power of many cosmological theories will only work if we can get into other universes - which is not to be expected.
However, it does not at all follow from this that modern cosmology is such a hand-waving and not entirely scientific field, where, like the ancient Greeks, you can lie in the shadow of trees and hypothesize about the number of dimensions of space-time - ten or eleven? Cosmological models are based on observational data from astronomy, and the more of this data, the more material for cosmological models - which should link and agree these data with each other. The difficulty is that in cosmology fundamental questions are raised that require some initial assumptions, which are chosen by the authors of the models based on their personal ideas about the harmony of the universe. In this, in general, there is nothing exceptional: when building any theory, you need to take some reference points. It's just that for cosmology, which operates on the largest scales of space and time, it is especially difficult to choose them.
First, a few important definitions.
Cosmology is a science that studies the properties of our Universe as a whole. However, it does not yet have any unified theory that would describe everything that happens and has ever happened. Now there are four main cosmological models that try to describe the origin and evolution of the universe, and each of them has its pluses and minuses, its adherents and opponents. The Lambda-CDM model is considered the most authoritative, although not undeniable. It is important to understand that cosmological models do not necessarily compete with each other. They just can describe fundamentally different stages of evolution. For example, the Labmda-CDM does not address the issue of the Big Bang at all, although it perfectly explains everything that happened after it.
Multiverse structure with mini-universe bubbles within it.
Pattern: Andrei Linde
The surprising thing about this is that the cosmological constant (that is, the energy of the vacuum) does not change in time as the universe expands, while the density of matter just changes quite predictably and depends on the volume of space. It turns out that in the early universe the density of matter was much higher than the density of the vacuum; in the future, as galaxies expand, the density of matter will decrease. So why exactly now, when we can measure them, are they so close in value to each other?
The only known way to explain such an incredible coincidence, without attracting any unscientific hypotheses, is possible only with the help of the anthropic principle and the inflationary model - that is, from a multitude of existing universes, life originated in one where the cosmological constant at a given moment in time turned out to be equal to the density of matter (this in turn determines the time elapsed since the beginning of inflation, and gives just enough time for the formation of galaxies, the formation of heavy elements and the development of life).
Another turning point in the development of the inflationary model was the publication in 2000 of an article by Busso and Polchinski, in which they proposed using string theory to explain a large set of different types of vacuum, in each of which the cosmological constant could take on different values. And when one of the founders of string theory itself, Leonard Susskind, joined the work on the unification of string theory and the inflationary model, it not only helped to compose a more complete picture of what is now called the "anthropic landscape of string theory", but also in some way added the weight of the entire model in the scientific world. The number of articles on inflation increased over the year from four to thirty-two.
The inflationary model claims to not only explain the fine-tuning of fundamental constants, but also help discover some of the fundamental parameters that determine the magnitude of these constants. The fact is that today there are 26 parameters in the Standard Model (the cosmological constant was the last one to be discovered), which determine the magnitude of all the constants that you have ever encountered in a physics course. This is quite a lot, and Einstein already believed that their number could be reduced. He proposed a theorem, which, according to him, cannot currently be more than a belief, that there are no arbitrary constants in the world: it is so wisely constructed that there must be some logical connections between seemingly completely different quantities. In the inflationary model, these constants can be just an environmental parameter that seems to us to be locally unchanged due to the effect of inflation, although it will be completely different in another part of the universe and is determined by not yet identified, but certainly existing truly fundamental parameters.
At the end of the article, Linde writes that criticism of the inflationary model is often based on the fact that we will not be able to penetrate other universes in the foreseeable future. Therefore, it is impossible to test the theory, and we still do not have answers to the most basic questions: Why is the universe so big? Why is it homogeneous? Why is it isotropic and does not rotate like our galaxy? However, if you look at these questions from a different angle, it turns out that even without travel to other mini-universes, we have a lot of experimental data. Such as size, plane, isotropy, homogeneity, the value of the cosmological constant, the ratio of the masses of the proton and neutron, and so on. And today the only reasonable explanation for this and many other experimental data is given within the framework of the multiverse theory and, therefore, the inflationary cosmology model.
, 1990. Andrey Linde
"The Anthropic landscape of string theory" 2003. Leonard Susskind
Marat Musin
It seemed unlikely that the echo of the events that took place in the first milliseconds of the birth of the universe could reach us. However, this turned out to be possible.
Cosmology, the structure of the Universe, the past, present and future of our world - these questions have always occupied the best minds of mankind. For the development of cosmology, and science as a whole, it is extremely important to understand the Universe as a whole. A special role is played by experimental verification of abstract constructions, their confirmation by observational data, comprehension and comparison of research results, adequate assessment of certain theories. We are now in the middle of the path that leads from solving Einstein's equations to knowing the mystery of the birth and life of the Universe.
The next step on this path was taken by the creator of the theory of chaotic inflation, a graduate of Moscow State University, now a professor at Stanford University, Andrei Dmitrievich Linde, who made a significant contribution to understanding the earliest stage of the development of the Universe. For many years he worked in one of the leading academic Russian institutes - the Physics Institute named after Lebedev Academy of Sciences (FIAN), studied the consequences of modern theories of elementary particles, working together with Professor David Abramovich Kirzhnits.
In 1972 Kirzhnits and Linde came to the conclusion that peculiar phase transitions took place in the early Universe, when the differences between different types of interactions suddenly disappeared: strong and electroweak interactions merged into one single force. (A unified theory of weak and electromagnetic interactions carried out by quarks and leptons through the exchange of massless photons (electromagnetic interaction) and heavy intermediate vector bosons (weak interaction) was developed in the late 1960s by Steven Weinberg, Sheldon Glashow, and Abdus Salam.) Linde focused on the study of processes at even earlier stages of the development of the Universe, in the first 10 –30 s after its birth. Earlier it seemed unlikely that the echo of events that took place in the first milliseconds of the birth of the Universe could reach us. However, in recent years, modern methods of astronomical observations have made it possible to look into the distant past.
Cosmology problems
In considering the Big Bang theory, researchers faced problems that were previously perceived as metaphysical. However, questions invariably arose and demanded answers.
What happened when there was nothing? If the Universe was born from a singularity, then it once did not exist. In "Theoretical Physics" by Landau and Lifshitz it is said that the solution of Einstein's equations cannot be continued in the region of negative time, and therefore, within the framework of the general theory of relativity, the question "What was before the birth of the Universe?" doesn't make sense. However, this question continues to worry all of us.
Do parallel lines intersect? At school we were told no. However, when it comes to cosmology, the answer is not so straightforward. For example, in a closed universe like the surface of a sphere, lines that were parallel at the equator intersect at the north and south poles. So is Euclid right? Why does the universe seem flat? Was she like this from the start? To answer these questions, it is necessary to establish what the universe was like at the earliest stage of development.
Why is the universe homogeneous? Actually this is not true. There are galaxies, stars and other irregularities. If you look at that part of the Universe, which is within sight of modern telescopes, and analyze the average distribution density of matter on a cosmic scale, it turns out that it is the same in all directions with an accuracy of 10 -5. Why is the universe homogeneous? Why do the same laws of physics operate in different parts of the Universe? Why is the universe so big? Where did the energy needed for its emergence come from?
Doubts have always arisen, and the more scientists learned about the structure and history of the existence of our world, the more questions remained unanswered. However, people tried not to think about them, perceiving a large homogeneous Universe and non-intersecting parallel lines as a given, not subject to discussion. The last straw that forced physicists to reconsider their attitude to the theory of the early Universe was the problem of relic monopoles.
The existence of magnetic monopoles was proposed in 1931 by the English theoretical physicist Paul Dirac. If such particles really exist, then their magnetic charge must be a multiple of some given value, which, in turn, is determined by the fundamental value of the electric charge. For almost half a century, this topic was practically forgotten, but in 1975 a sensational statement was made that a magnetic monopole was discovered in cosmic rays. The information was not confirmed, but the message reawakened interest in the problem and contributed to the development of a new concept.
According to a new class of theories of elementary particles that arose in the 70s, monopoles could have appeared in the early Universe as a result of phase transitions predicted by Kirzhnits and Linde. Each monopole has a million billion times the mass of a proton. In 1978-1979. Zeldovich, Khlopov and Preskill found that quite a lot of such monopoles were born, so now there would be a monopole for each proton, which means that the Universe would be very heavy and had to quickly collapse under its own weight. The fact that we still exist disproves such a possibility.
Revision of the theory of the early universe
The answer to most of the above questions was obtained only after the emergence of the inflationary theory.
Inflationary theory has a long history. The first theory of this type was proposed in 1979 by RAS Corresponding Member Alexei Alexandrovich Starobinsky. His theory was quite complex. Unlike subsequent works, she did not try to explain why the Universe is large, flat, homogeneous, isotropic. However, it had many important features of inflationary cosmology.
In 1980, an employee of the Massachusetts Institute of Technology Alan Goose ( Alan guth) in the article "The Swelling Universe: A Possible Solution to the Horizon and Flatness Problem" he outlined an interesting scenario of the swelling Universe. Its main difference from the traditional theory of the Big Bang was the description of the birth of the universe in the period from 10 -35 to 10 -32 s. Gus suggested that at this time the universe was in a state of the so-called "false" vacuum, in which its energy density was extremely high. Therefore, the expansion proceeded faster than according to the Big Bang theory. This stage of exponentially fast expansion was called inflation (inflation) of the Universe. Then the false vacuum disintegrated, and its energy passed into the energy of ordinary matter.
Gus's theory was based on the theory of phase transitions in the early Universe developed by Kirzhnits and Linde. Unlike Starobinsky, Gus set himself the goal of using one simple principle to explain why the Universe is large, flat, homogeneous, isotropic, and also why there are no monopoles. The stage of inflation could solve these problems.
Unfortunately, after the collapse of the false vacuum in the Goos model, the universe turned out to be either very inhomogeneous or empty. The fact is that the decay of the false vacuum, like the boiling of water in a kettle, occurred due to the formation of bubbles of a new phase. In order for the energy released in this case to pass into the thermal energy of the Universe, it was necessary to collide the walls of huge bubbles, and this should lead to a violation of the homogeneity and isotropy of the Universe after inflation, which contradicts the set task.
Although Goos' model did not work, it stimulated the development of new scenarios for an inflating universe.
New inflationary theory
In mid-1981, Linde proposed the first version of a new scenario of an inflating universe, based on a more detailed analysis of phase transitions in the Grand Unification model. He came to the conclusion that in some theories the exponential expansion does not end immediately after the formation of bubbles, so that inflation can go not only before the phase transition with the formation of bubbles, but also after, already inside them. In this scenario, the observable part of the Universe is considered to be contained within a single bubble.
In the new scenario, Linde showed that heating after inflation occurs due to the creation of particles during oscillations of the scalar field (see below). Thus, the collisions of the walls of the bubbles, generating inhomogeneities, became unnecessary, and thus the problem of large-scale homogeneity and isotropy of the Universe was solved.
The new scenario contained two key points: first, the properties of the physical state inside the bubbles must change slowly to ensure inflation inside the bubble; secondly, at later stages, there should be processes that ensure the heating of the Universe after the phase transition. A year later, the researcher revised his approach, proposed in the new inflationary theory, and came to the conclusion that phase transitions are not needed at all, as well as hypothermia and the false vacuum with which Alan Goose started. It was an emotional shock, since it was necessary to abandon the ideas that were considered true about the hot Universe, phase transitions and hypothermia. It was necessary to find a new way to solve the problem. Then the theory of chaotic inflation was put forward.
Chaotic inflation
The idea behind Linde's theory of chaotic inflation is very simple, but in order to explain it, you need to introduce the concept of a scalar field. There are directed fields - electromagnetic, electric, magnetic, gravitational, but there can be at least one more - scalar, which is not directed anywhere, but is simply a function of coordinates.
The closest (although not accurate) analogue of a scalar field is the electrostatic potential. The voltage in the US electrical networks is 110 V, and in Russia - 220 V. If a person were to hold on to the American wire with one hand and the Russian one with the other, the potential difference would kill him. If the voltage was the same everywhere, there would be no potential difference and the current would not flow. So in a constant scalar field there is no potential difference. Therefore, we cannot see a constant scalar field: it looks like a vacuum, which in some cases can have a high energy density.
It is believed that without fields of this type it is very difficult to create a realistic theory of elementary particles. In recent years, almost all particles predicted by the theory of electroweak interactions, except for the scalar one, have been discovered. The search for such particles is one of the main goals of the huge accelerator currently under construction at CERN, Switzerland.
The scalar field was present in almost all inflationary scenarios. Gus suggested exploiting the potential with several deep lows. Linde's new inflationary theory needed a potential with an almost flat top, but later, in a chaotic inflation scenario, it turned out that it was enough to take an ordinary parabola and everything worked.
Consider the simplest scalar field, the potential energy density of which is proportional to the square of its magnitude, just as the energy of a pendulum is proportional to the square of its deviation from the equilibrium position:
A small field will know nothing about the Universe and will oscillate near its minimum. However, if the field is large enough, then it will roll down very slowly, accelerating the Universe at the expense of its energy. In turn, the speed of the Universe (and not any particles) will slow down the fall of the scalar field.
Thus, a large scalar field leads to a high expansion rate of the Universe. The high expansion rate of the Universe prevents the field from decreasing and thereby prevents the potential energy density from decreasing. And the high energy density continues to accelerate the Universe at an ever greater speed. It is this self-sustaining regime that leads to inflation, an exponentially rapid inflation of the Universe.
To explain this amazing effect, it is necessary to jointly solve the Einstein equation for the scale factor of the Universe:
and the equation of motion for a scalar field:
Here H is the so-called Hubble constant, proportional to the energy density of the scalar field of mass m (this constant actually depends on time); G is the gravitational constant.
Researchers have already considered how the scalar field will behave in the vicinity of a black hole and during the collapse of the universe. But somehow the exponential expansion mode was not found. And it was only necessary to write the complete equation for the scalar field, which in the standard version (that is, without taking into account the expansion of the Universe) looked like the equation for a pendulum:
But some additional term intervened - the friction force, which was associated with geometry; no one took it into account at first. It is the product of the Hubble constant and the speed of the field:
When the Hubble constant was large, the friction was also great, and the scalar field decreased very slowly. Therefore, the Hubble constant, which is a function of the scalar field, remained almost unchanged for a long time. The solution to the Einstein equation with a slowly varying Hubble constant describes an exponentially rapidly expanding universe.
This stage of the exponentially fast expansion of the Universe is called inflation.
How does this regime differ from the usual expansion of the Universe filled with ordinary matter? Let's assume that the Universe filled with dust has expanded 2 times. Then its volume increased 8 times. This means that in 1 cm 3 there is 8 times less dust. If we solve the Einstein equation for such a Universe, it turns out that after the Big Bang, the density of matter dropped rapidly, and the rate of expansion of the Universe was rapidly decreasing.
The same would be the case with a scalar field. But while the field remained very large, it supported itself, like Baron Munchausen pulling himself out of the swamp by the pigtail. This was possible due to the friction force, which was significant at high field values. In accordance with the theories of the new type, the universe was expanding rapidly, and the field remained almost unchanged; accordingly, the energy density did not change either. Hence, the expansion proceeded exponentially.
Gradually, the field decreased, the Hubble constant also decreased, the friction became small, and the field began to oscillate, generating elementary particles. These particles collided, exchanged energy and gradually came to a state of thermodynamic equilibrium. As a result, the universe became hot.
It used to be thought that the universe was hot from the start. This conclusion was reached by studying microwave radiation, which was interpreted as a consequence of the Big Bang and subsequent cooling. Then they began to think that at first the Universe was hot, then inflation occurred, and after it the Universe became hot again. However, in the theory of chaotic inflation, the first hot stage turned out to be unnecessary. But why do we need the stage of inflation, if at the end of this stage the universe still became hot, as in the old theory of the Big Bang?
Exponential expansion
There are three simplest models of the universe: flat, open, and closed. A flat universe is like the surface of a flat table; parallel lines in such a universe always remain parallel. The open universe is like the surface of a hyperboloid, and the closed universe is like the surface of a ball. Parallel lines in such a universe intersect at its north and south poles.
Let's assume that we live in a closed universe, which at first was as small as a ball. According to the Big Bang theory, it grew to a decent size, but still remained relatively small. And according to the inflationary theory, a tiny ball has become huge as a result of an exponential explosion in a very short time. While on it, the observer would see a flat surface.
Imagine the Himalayas, where there are many different ledges, crevices, abysses, hollows, boulders, that is, inhomogeneities. But suddenly someone or something in a completely incredible way increased the mountains to gigantic proportions, or we shrank, like Alice in Wonderland. Then, being on the top of Everest, we will see that it is completely flat - it was as if stretched, and the heterogeneities ceased to have any meaning. The mountains remain, but in order to climb at least one meter, you need to go incredibly far. Thus, the homogeneity problem can be solved. This also explains why the universe is flat, why parallel lines do not intersect, and why monopoles do not exist. Parallel lines can intersect and monopoles can exist, but only so far away from us that we cannot see it.
The emergence of galaxies
The small universe became colossal and everything became homogeneous. But what about galaxies? It turned out that in the course of the exponential expansion of the Universe, small quantum fluctuations, which always exist, even in empty space, due to the quantum mechanical principle of uncertainty, stretched to colossal sizes and turned into galaxies. According to inflationary theory, galaxies are the result of amplified quantum fluctuations, i.e. amplified and frozen quantum noise.
For the first time, this striking possibility was pointed out by FIAN employees Vyacheslav Fedorovich Mukhanov and Gennady Vasilievich Chibisov in a work based on the model proposed in 1979 by Starobinsky. Shortly thereafter, a similar mechanism was discovered in the new inflationary scenario and in the theory of chaotic inflation.
Speckled sky
Quantum fluctuations led not only to the birth of galaxies, but also to the anisotropy of the relict radiation with a temperature of about 2.7 K, coming to us from the distant regions of the Universe.
Modern artificial satellites of the Earth help scientists to study the relic radiation. The most valuable data was obtained using the WMAP space probe ( Wilkinson Microwave Anisotropy Probe), named after astrophysicist David Wilkinson ( David Wilkinson). Its hardware resolution is 30 times greater than that of its predecessor, the COBE spacecraft.
Previously it was believed that the temperature of the sky is everywhere equal to 2.7 K, but WMAP was able to measure it with an accuracy of 10 -5 K with high angular resolution. According to the data obtained in the first 3 years of observations, the sky turned out to be heterogeneous: somewhere hot, and somewhere colder. The simplest models of inflationary theory predicted ripples in the sky. But until the telescopes recorded its spotting, only three-degree radiation was observed, which served as a powerful confirmation of the theory of a hot universe. Now it turned out that the theory of a hot universe is not enough.
We managed to obtain photographs of inflated quantum fluctuations that appeared 10-30 s after the birth of the universe and have survived to this day. The researchers not only found the patchiness of the sky, but also studied the spectrum of the spots, that is, the signal intensity in different angular directions.
The results of high-precision measurements of radiation polarization carried out with the help of WMAP confirmed the theory of the expansion of the Universe and made it possible to establish when the ionization of intergalactic gas, caused by the very first stars, took place. The information received from the satellite confirmed the position of the inflationary theory that we live in a large flat Universe.
In the figure, the red line shows the prediction of the inflationary theory, and the black dots correspond to the experimental data of WMAP. If the universe were not flat, the peak of the graph would be to the right or to the left.
Eternal and endless
Let's look again at the figure showing the simplest potential of a scalar field (see above). In the region where the scalar field is small, it oscillates, and the Universe does not expand exponentially. In the region where the field is large enough, it slowly decreases, and small fluctuations appear on it. At this time, there is an exponential expansion and inflation. If the scalar field were even larger (marked in blue on the graph), then due to tremendous friction it would hardly decrease, quantum fluctuations would be huge, and the Universe could become fractal.
Imagine that the Universe is expanding rapidly, and in some place the scalar field, instead of rolling to a minimum of energy, jumps up due to quantum fluctuations (see above). At the point where the field jumped, the universe is expanding exponentially faster. A low-lying field is unlikely to bounce, but the higher it is, the more likely such a development of events is, and hence the exponentially larger volume of the new area. In each of these even areas, the field can also jump upward, which leads to the creation of new exponentially growing parts of the Universe. As a result, instead of looking like one huge growing ball, our world becomes like an ever-growing tree, consisting of many such balls.
Inflationary theory provides us with the only currently known explanation for the homogeneity of the observable part of the Universe. Paradoxically, the same theory predicts that on an extremely large scale, our Universe is absolutely inhomogeneous and looks like a huge fractal.
The figure shows schematically how one swelling region of the Universe generates more and more new parts of it. In this sense, it becomes eternal and self-healing.
The properties of space-time and the laws of interaction of elementary particles with each other in different regions of the Universe can be different, as well as the dimensions of space and the types of vacuum.
This fact deserves a more detailed explanation. According to the simplest theory with one potential energy minimum, the scalar field rolls down to this minimum. However, more realistic versions allow many minima with different physics, which resembles water, which can be in different states: liquid, gaseous and solid. Different parts of the Universe can also be in different phase states; this is possible in inflationary theory even without taking into account quantum fluctuations.
The next step, based on the study of quantum fluctuations, is the theory of a self-healing universe. This theory takes into account the process of constant reconstruction of swelling regions and quantum jumps from one vacuum state to another, enumerating different possibilities and dimensions.
So the Universe becomes eternal, endless and diverse. The entire universe will never collapse. However, this does not mean that there are no singularities. On the contrary, a significant part of the physical volume of the Universe is always in a state close to a singular one. But since different volumes pass it at different times, there is no single end of space-time, after which all regions disappear. And then the question of the multiplicity of worlds in time and space takes on a completely different sound: the Universe can reproduce itself indefinitely in all its possible states.
This claim, which was based on Linde's 1986 work, took on a new dimension a few years ago when string theorists (a leading candidate for the theory of all fundamental interactions) concluded that 10 100 –10 1000 various vacuum states. These states differ due to the extraordinary diversity of the possible structure of the world at ultra-short distances.
Taken together with the theory of a self-healing inflationary universe, this means that during inflation, the universe breaks up into infinitely many parts with an incredibly large number of different properties. Cosmologists call this scenario the theory of the eternal inflationary multiverse ( multiverse), and string theorists call it the string landscape.
Inflationary cosmology 25 years ago looked like something intermediate between physical theory and science fiction. Since then, many of the predictions of this theory have been tested, and it has gradually acquired the features of the standard cosmological paradigm. But it's too early to calm down. This theory continues to develop and change rapidly even now. The main problem is the development of models of inflationary cosmology based on realistic versions of the theory of elementary particles and string theory. This question can be the topic of a separate report.
Immediately after its inception, the universe expanded at an incredible rate.
Since the 30s of the XX century, astrophysicists already knew that, according to Hubble's law, the universe is expanding, which means that it had its beginning at a certain moment in the past. The task of astrophysicists, thus, outwardly looked simple: to trace all the stages of the Hubble expansion in reverse chronology, applying the corresponding physical laws at each stage, and, having gone this way to the end - more precisely, to the very beginning - to understand exactly how everything happened.
In the late 1970s, however, several fundamental problems related to the early universe remained unresolved, namely:
- Antimatter problem. According to the laws of physics, matter and antimatter have an equal right to exist in the Universe ( cm. Antiparticles), but the universe is almost entirely made up of matter. Why did it happen?
- Horizon problem. According to the background cosmic radiation ( cm. Big Bang), we can determine that the temperature of the Universe is approximately the same everywhere, but its individual parts (clusters of galaxies) could not be in contact (as they say, they were outside the horizon each other). How did it happen that thermal equilibrium was established between them?
- The problem of straightening space. The universe appears to have exactly the mass and energy needed to slow down and stop the Hubble expansion. Why, of all possible masses, does the Universe have exactly this?
The key to solving these problems was the idea that immediately after its birth, the universe was very dense and very hot. All matter in it was a red-hot mass of quarks and leptons ( cm. Standard Model), which had no way of combining into atoms. The various forces acting in the modern Universe (such as electromagnetic and gravitational forces) then corresponded to a single field of force interaction ( cm. Universal theories). But when the Universe expanded and cooled down, the hypothetical unified field disintegrated into several forces ( cm. Early Universe).
In 1981, the American physicist Alan Guth realized that the separation of strong interactions from a single field, which happened about 10 -35 seconds after the birth of the Universe (just think - these are 34 zeros and ones after the decimal point!), Was a turning point in its development. Happened phase transition matter from one state to another on the scale of the Universe is a phenomenon similar to the transformation of water into ice. And just as when water freezes, its randomly moving molecules suddenly "grab" and form a strict crystalline structure, so under the influence of the released strong interactions, an instant restructuring took place, a kind of "crystallization" of matter in the Universe.
Anyone who has seen how water pipes or pipes of a car radiator burst in severe frost, as soon as the water in them turns into ice, he knows from his own experience that water expands when it freezes. Alan Guth was able to show that when the strong and weak interactions were separated, something similar happened in the Universe - a discontinuous expansion. This is an extension called inflationary, is many times faster than the usual Hubble extension. In about 10 -32 seconds, the Universe expanded by 50 orders of magnitude - it was smaller than a proton, and became the size of a grapefruit (for comparison: water expands by only 10% when it freezes). And this rapid inflationary expansion of the Universe removes two of the above three problems, directly explaining them.
Solution space straightening problems The following example most clearly demonstrates: Imagine a coordinate grid drawn on a thin elastic map, which is then crumpled at random. If we now take and strongly shake this crumpled elastic map, it will again take a flat form, and the coordinate lines on it will be restored, no matter how much we deform it when we crumpled it. Similarly, no matter how curved the space of the Universe was at the time of the beginning of its inflationary expansion, the main thing is that after the completion of this expansion, space was completely flattened. And since we know from the theory of relativity that the curvature of space depends on the amount of matter and energy in it, it becomes clear why there is exactly as much matter in the Universe as is necessary to balance the Hubble expansion.
Explains the inflationary model and horizon problem though not so straightforward. From the theory of black body radiation, we know that the radiation emitted by a body depends on its temperature. Thus, we can determine their temperature from the emission spectra of distant parts of the Universe. Such measurements gave stunning results: it turned out that at any observed point in the Universe, the temperature (with an error of measurement of up to four decimal places) is the same. If we proceed from the model of the usual Hubble expansion, then the matter immediately after the Big Bang must have scattered too far for the temperatures to equalize. According to the inflationary model, the matter of the Universe until the moment t = 10 -35 seconds remained much more compact than during the Hubble expansion. This extremely short period was quite enough for the establishment of thermal equilibrium, which was not disturbed at the stage of inflationary expansion and has been preserved to this day.
American physicist, specialist in the field of elementary particles and cosmology. Born in New Brunswick, New Jersey. He received his doctorate from the Massachusetts Institute of Technology, where he returned in 1986, becoming a professor of physics. Guth developed his theory of the inflationary expansion of the Universe at Stanford University, studying the theory of elementary particles. He is known for his review of the Universe as “an endless self-assembled tablecloth”.