- Translation
This is no longer a speculative theory, since four of them have been confirmed.
Scientific ideas should be simple, explanatory and predictive. And as far as we know today, the inflationary multiverse does not have such properties.
- Paul Steinhart, 2014
When we think of the Big Bang, we imagine the starting point of the universe: the hot, dense, expanding state from which everything emerged. By noticing and measuring the current expansion of the Universe - galaxies flying apart from each other, we can not only determine the fate of the Universe, but also its beginning.
But just this hot and dense state is fraught with many questions, including:
Why are very distant, different regions of space, which could not exchange information since the beginning of time, filled with the same density of matter and radiation of the same temperature?
Why would the Universe, which would recollapse if it had more substance, or would it expand to a state of nonexistence if it had less matter, so perfectly balanced?
And where, if the Universe used to be in a very hot and dense state, are all these high-energy relic particles (such as magnetic monopoles), which theoretically should be easy to detect today?
Answers to questions were found in late 1979, early 1980, when Alan Guth put forward the theory of cosmic inflation.
Assuming that the Big Bang was preceded by a state in which the Universe was not filled with matter and radiation, but only large quantity energy inherent in the fabric of the cosmos itself, Gut managed to solve all these problems. In addition, there were other developments in the 1980s that made it possible to find new classes of models that help inflationary models to reproduce the current universe:
Filled with substance and radiation
isotropic (the same in all directions),
homogeneous (the same at all points),
hot, dense and expanding in the initial state.
Such models were developed by Andrey Linde, Paul Steinhart, Andy Albrecht, and additional details were worked out by Henry Tai, Bruce Allen, Alexey Starobinsky, Michael Turner, David Schramm, Rocky Kolb and others.
We found something remarkable: two generic class models gave us everything we needed. There was a new inflation, with a potential flat at the top, from which the inflationary field could "slowly roll" to the bottom, and there was a chaotic inflation with a U-shaped potential, from which one could also slowly slide.
In both cases, space expanded exponentially, straightened out, its properties were the same everywhere, and when inflation ended, you returned to a Universe very similar to ours. In addition, you received five additional predictions for which there were no observations at that time.
1) Flat Universe. In the early 1980s, we completed survey studies of galaxies, galaxy clusters, and began to understand the large-scale structure of the universe. Based on what we saw, we were able to measure two indicators:
The critical density of the Universe, that is, the density of matter necessary for the ideal balance of the Universe between recollapse and eternal expansion.
real density matter in the Universe, not only luminous matter, gas, dust and plasma, but all sources, including dark matter, which has a gravitational effect.
We found that the second indicator was between 10% and 35% of the first, depending on the source of the data. In other words, the matter in the Universe was much less than the critical amount - which means that the Universe is open.
But inflation predicted a flat universe. It takes the universe of any shape and stretches it to a flat state, or, according to at least, to a state indistinguishable from flat. Many people have tried to build models of inflation that give the universe a negative curvature (open) but have not been successful.
With the advent of the dark energy era, the supernova observation in 1998 followed by the collection of data from the WMAP project, first released in 2003 (and the data from the Boomerang project, released a little earlier), we came to the conclusion that the universe is actually flat , and the reason for the low density of matter was the presence of this new, unexpected form of energy.
2) A universe with fluctuations on scales larger than light can overcome. Inflation - by causing the space of the universe to expand exponentially - inflates what happens on very small scales to very large ones. The universe of today has inherent uncertainty on quantum level, small energy fluctuations due to Heisenberg's uncertainty principle.
But during inflation, these small-scale fluctuations of energy should have been stretched out across the universe to gigantic macroscopic scales, stretching across its entire extent! (In general, and even further, since we cannot observe anything that lies outside the observable universe).
But looking at the fluctuations relic radiation on the largest scale that the COBE project was able to do to some extent in 1992, we found these fluctuations. And with the improved results from WMAP, we were able to measure their magnitude and see that they are in line with inflation predictions.
3) A universe with adiabatic fluctuations, that is, with the same entropy everywhere. Fluctuations can be different: adiabatic, constant curvature, or a mixture of both types. Inflation predicted 100% adiabatic fluctuations, which meant the presence of well-defined CMB parameters that could be measured in WMAP, and large-scale structures measured in the 2dF and SDSS projects. If the CMB and large-scale fluctuations are related to each other, they are adiabatic, and if not, they can be of constant curvature. If the universe had a different set of fluctuations, we wouldn't know about it until the year 2000!
But this point has been so taken for granted, thanks to the rest of the advances in the theory of inflation, that its confirmation has gone almost unnoticed. It was just a confirmation of what we already "know" when in fact it was just as revolutionary as any of the others.
4) A universe in which the spectrum of fluctuations was slightly smaller than that of a scale-invariant (n s< 1). Это серьёзное предсказание! Конечно, инфляция, в общем, предсказывает, что флуктуации должны быть масштабно-инвариантными. Но есть подвох, или уточнение: форма инфляционных потенциалов влияет на то, как спектр флуктуаций отличается от идеальной масштабной инвариантности.
Working models discovered in the 1980s predicted that the fluctuation spectrum (scalar spectral index, n s) should be slightly less than 1, somewhere between 0.92 and 0.98, depending on the model used.
When we got the observational data, we found that the measured amount, n s , was about 0.97, with an error (according to the CMB measurements by the BAO project) of 0.012. They were first noticed in WMAP, and this observation was not only confirmed, but also reinforced over time by others. It is indeed less than one, and only inflation made this prediction.
5) And, finally, the Universe with a certain spectrum of fluctuations of gravitational waves. This is the latest prediction, the only one of the big ones that has not yet been confirmed. Some models, such as Linde's chaotic inflation model, produce large gravity waves (which BICEP2 should have noticed), others, such as the Albrecht-Steinhard model, can produce very small gravity waves.
We know what spectrum they should have and how these waves interact with fluctuations in the CMB polarization. The uncertainty is only in their strength, which may be too small to observe, depending on which inflation model is correct.
Keep this in mind the next time you read an article about the speculative nature of the theory of inflation, or about how one of the founders of the theory doubts its veracity. Yes, people try to find holes in the best theories and look for alternatives; We scientists do this.
But inflation is not some theoretical monster detached from observation. She made five new predictions, four of which we confirmed! She may have predicted things we don't yet know how to test, like the multiverse, but that doesn't take away from her success.
The theory of cosmic inflation is no longer speculative. Thanks to observations of the CMB and large-scale structures of the universe, we were able to confirm her predictions. This is the very first of all events that happened in our universe. Cosmic inflation happened before big bang and prepared everything for his appearance. And maybe we can learn a lot more thanks to her!
In addition to the question of the origin of the universe, modern cosmologists face a number of other problems. In order for the standard to be able to predict the distribution of matter that we observe, its initial state must be characterized by a very high degree of organization. The question immediately arises: how could such a structure be formed?
Physicist Alan Guth of Massachusetts Institute of Technology proposed his own version, which explains the spontaneous emergence of this organization, eliminating the need to artificially introduce exact parameters into the equations describing the initial state of the Universe. His model has been called the "inflationary universe". Its essence is that inside a rapidly expanding, superheated Universe, a small area of space cools and begins to expand more strongly, just as supercooled water rapidly freezes, expanding at the same time. This phase of rapid expansion eliminates some of the problems inherent in standard big bang theories.
However, Guth's model is also not without flaws. In order for Guth's equations to correctly describe the inflationary Universe, he had to set the initial parameters for his equations very precisely. Thus, he faced the same problem as the creators of other theories. He hoped to get rid of the need to specify the exact parameters of the conditions of the big bang, but for this he had to introduce his own parameterization, which remained unexplained. Guth and his co-author P. Steingart admit that in their model “calculations lead to acceptable predictions only if the given initial parameters of the equations vary in a very narrow range. Most theorists (including ourselves) consider such initial conditions unlikely.” The authors go on to talk about their hopes that someday new mathematical theories will be developed that will allow them to make their model more plausible.
This dependency is not yet open theories is another shortcoming of the Guth model. Theory unified field, on which the model of the inflationary universe is based, is completely hypothetical and "poorly lends itself to experimental verification, since most its predictions cannot be quantitatively tested in the laboratory.” (The unified field theory is a rather dubious attempt by scientists to tie together some of the fundamental forces of the universe.)
Another shortcoming of Guth's theory is that it says nothing about the origin of superheated and expanding matter. Guth tested the compatibility of his inflationary theory with three hypotheses for the origin of the universe. He first considered the standard big bang theory. In this case, according to Gut, the inflationary episode should have occurred at one of the early stages of the evolution of the Universe. However, this model poses an unsolvable singularity problem. The second hypothesis postulates that the universe emerged from chaos. Some parts of it were hot, others cold, some expanding and others contracting. In this case, inflation should have started in an overheated and expanding region of the universe. True, Guth admits that this model cannot explain the origin of primary chaos.
The third possibility, favored by Guth, is that a superheated, expanding clump of matter emerges quantum-mechanically from the void. In an article that appeared in Scientific American in 1984, Guth and Steingart argued: “The inflationary model of the universe gives us an idea of possible mechanism, with the help of which the observable Universe could appear from an infinitesimal region of space. Knowing this, it's hard to resist the temptation to take it one step further and conclude that the universe literally came into existence out of nothing."
However attractive this idea may be for scientists who are ready to take up arms against any mention of the possibility of the existence of a higher consciousness that created the Universe, on closer examination it does not hold water. The "nothing" that Guth is talking about is a hypothetical quantum mechanical vacuum, described by the as yet undeveloped unified field theory, which should unify the equations quantum mechanics and the general theory of relativity. In other words, at the moment this vacuum cannot be described even theoretically.
It should be noted that physicists have described a simpler type of quantum mechanical vacuum, which is a sea of so-called "virtual particles", fragments of atoms that "almost exist". From time to time, some of these subatomic particles pass from the vacuum into the world. material reality. This phenomenon is called vacuum fluctuations. Vacuum fluctuations cannot be directly observed, but theories postulating their existence have been experimentally confirmed. According to these theories, particles and antiparticles arise from a vacuum for no reason and disappear almost immediately, annihilating each other. Guth and his colleagues assumed that at some point, instead of a tiny particle, an entire universe appeared from the vacuum, and instead of immediately disappearing, this universe somehow survived for billions of years. The authors of this model solved the singularity problem by postulating that the state in which the Universe emerges from vacuum is somewhat different from the singularity state.
However, this scenario has two major drawbacks. First, one can only be surprised at the boldness of the imagination of scientists who have disseminated a rather limited experience with subatomic particles to the whole universe. S. Hawking and G. Ellis wisely warn their overly enthusiastic colleagues: “The assumption that the laws of physics, discovered and studied in the laboratory, will be valid at other points in the space-time continuum is, of course, a very bold extrapolation.” Secondly, strictly speaking, the quantum mechanical vacuum cannot be called "nothing". Description of the quantum mechanical vacuum, even in the simplest of existing theories occupies many pages of highly abstract mathematical calculations. Such a system is undoubtedly “something”, and the same stubborn question immediately arises: “How did such a complexly organized “vacuum” arise?”
Let's go back to the original problem that Guth created the inflationary model to solve: the problem of accurately parameterizing the initial state of the universe. Without such a parametrization, it is impossible to obtain the observed distribution of matter in the Universe. As we have seen, Gut failed to solve this problem. Moreover, the very possibility that any version of the big bang theory, including Guth's version, can predict the observed distribution of matter in the universe is doubtful.
The highly organized initial state in Guth's model, in his own words, eventually turns into a "Universe" with a diameter of 10 centimeters, filled with a homogeneous, super-dense, superheated gas. It will expand and cool, but there is no reason to believe that it will ever turn into anything more than a homogeneous cloud of gas. In fact, all big bang theories lead to this result. If Guth had to resort to many tricks and make dubious assumptions in order to finally get the Universe in the form of a cloud of homogeneous gas, then one can imagine what the mathematical apparatus of the theory should be, leading to the Universe as we know it!
A good scientific theory makes it possible to predict many complex natural phenomena from a simple theoretical scheme. But in Guth's theory (and any other version), the opposite is true: as a result of complex mathematical calculations, we get an expanding bubble of a homogeneous gas. Despite this, scientific journals print enthusiastic articles about inflationary theory, accompanied by numerous colorful illustrations, which should give the reader the impression that Guth has finally achieved his cherished goal - he found an explanation for the origin of the universe. It would be more honest to simply open a permanent rubric in scientific journals to publish in it the theory of the origin of the universe, fashionable this month.
It is even difficult to imagine the complexity of the initial state and the conditions necessary for the emergence of our Universe with all the diversity of its structures and organisms. In the case of our universe, the degree of this complexity is such that it can hardly be explained by physical laws alone.
What would happen if, in the distant past, the space of the universe was in a state of false vacuum? If the density of matter in that era was less than required to balance the universe, then repulsive gravity would have dominated. This would cause the universe to expand, even if it did not initially expand.
To make our ideas more definite, we will assume that the Universe is closed. Then she puffs up like hot air balloon. As the volume of the Universe grows, matter becomes rarefied and its density decreases. However, the false vacuum mass density is a fixed constant; it always stays the same. So very quickly the density of matter becomes negligible, we are left with a uniform expanding sea of false vacuum.
The expansion is caused by the tension of the false vacuum, which is greater than the attraction associated with its mass density. Since none of these quantities change with time, the rate of expansion remains constant to a high degree of accuracy. This rate is characterized by the proportion in which the universe expands per unit of time (say, one second). In meaning, this value is very similar to the rate of inflation in the economy - the percentage increase in prices per year. In 1980, when Guth was teaching a seminar at Harvard, the US inflation rate was 14%. If this value remained unchanged, prices would double every 5.3 years. Similarly, a constant rate of expansion of the universe implies that there is a fixed interval of time during which the size of the universe doubles.
Growth that is characterized by a constant doubling time is called exponential growth. It is known to lead to gigantic numbers very quickly. If today a slice of pizza costs $1, then after 10 doubling cycles (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, 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 factor of a googol in one-thirtieth of a microsecond, 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 inflate to a size far 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 miraculously eliminates the horizon and flat geometry problems that are characteristic of Big Bang cosmology.
The essence 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 suggests 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 it should be, so if the regions cannot interact today, they certainly were not able to do so before. The root of the problem, therefore, is related to the attractive nature of gravity, due to which the expansion gradually slows down.
However, in a false vacuum universe, gravity is repulsive, and instead of slowing down 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 must have interacted in the past. The horizon problem is gone!
The problem of flat space is solved just as easily. It turns out that the Universe moves away from the critical density only if its expansion slows down. In the case of an accelerated inflationary expansion, the opposite is true: the Universe is approaching a critical density, which means it is becoming flatter. Because inflation enlarges the universe by a colossal factor, we only see a tiny fraction of it. This observable region appears flat, similar to our Earth, which also appears flat when viewed close to the surface.
So, a short period of inflation makes the universe large, hot, uniform, and flat, creating just the kind of initial conditions required for standard Big Bang cosmology.
The theory of inflation began to conquer the world. As for Gut himself, his postdoc status is over. He accepted an offer from his alma mater, the Massachusetts Institute of Technology, where he continues to work today.
Excerpt from A. Vilenkin's book "Many Worlds in One: The Search for Other Universes"
It seemed unlikely that an echo of the events that took place in the first milliseconds of the birth of the Universe could reach us. However, it 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 humanity. For the development of cosmology, and science in general, it is extremely important to understand the Universe as a whole. A special role is played by the experimental verification of abstract constructions, their confirmation by observational data, the comprehension and comparison of research results, and an adequate assessment of certain theories. Now we are in the middle of the path that leads from the solution of Einstein's equations to the knowledge of the secret of the birth and life of the Universe.
The next step on this path was made by the creator of the theory of chaotic inflation, a graduate of Moscow State University, now a professor at Stanford University, Andrey Dmitrievich Linde, who made a significant contribution to understanding the earliest stage in the development of the Universe. For many years he worked in one of the leading academic Russian institutions- Physical Institute. Lebedev Academy of Sciences (FIAN), dealt with 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 in early universe there were peculiar phase transitions, when the differences between different types interactions suddenly disappeared: strong and electroweak interactions merged into one single force. ( unified theory 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), created in the late 1960s. Steven Weinberg, Sheldon Glashow and Abdus Salam.) Subsequently, Linde focused on studying processes at even earlier stages of the development of the Universe, in the first 10–30 s after its birth. Previously, it seemed unlikely that an echo of events that took place in the first milliseconds of the birth of the Universe could reach us. However, in last years modern methods Astronomical observations have made it possible to look into the distant past.
Problems of cosmology
Considering the theory of the Big Bang, researchers were faced with 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 did not exist at one time. In Theoretical Physics by Landau and Lifshitz it is said that the solution of Einstein's equations cannot be continued into 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 excite all of us.
Do parallel lines intersect? At school they told us no. However, when it comes to cosmology, the answer is not so clear cut. For example, in a closed universe similar to 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 appear to be flat? Was she like this from the start? To answer these questions, it is necessary to establish what the Universe was like at a very early stage of development.
Why is the universe homogeneous? Actually this is not true. There are galaxies, stars and other inhomogeneities. If you look at that part of the universe that is within the range of view of modern telescopes, and analyze average density distribution 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 in different parts Does the same laws of physics apply to the universe? Why is the universe so big? Where did the energy needed to create it come from?
Doubts always arose, 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 they magnetic charge must be a multiple of some given value, which, in turn, is determined by the fundamental quantity electric charge. For almost half a century, this topic was practically forgotten, but in 1975 a sensational statement was made that magnetic monopole 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 elementary particle theories that arose in the 1970s, monopoles could appear in the early Universe as a result of phase transitions predicted by Kirzhnits and Linde. The mass of each monopole is a million billion times more mass proton. In 1978–1979 Zel'dovich, Khlopov and Preskill found that quite a lot of such monopoles were born, so that now there would be a monopole for each proton, which means that the Universe would be very heavy and would have to quickly collapse under its own weight. The fact that we still exist disproves that possibility.
Revisiting the theory of the early universe
The answer to most of these questions was obtained only after the emergence of inflationary theory.
The inflation theory has long history. The first theory of this type was proposed in 1979 by Aleksey Aleksandrovich Starobinsky, Corresponding Member of the Russian Academy of Sciences. His theory was quite complex. Unlike subsequent work, she did not try to explain why the universe is large, flat, homogeneous, isotropic. However, she had many important traits. inflationary cosmology.
In 1980, an employee of the Massachusetts Institute of Technology Alan Goose ( Alan Guth) in the article “The Inflating Universe: Possible Solution problems of horizon and flatness" outlined interesting scenario expanding 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 exceptionally high. Therefore, the expansion occurred faster than according to the Big Bang theory. This stage of exponentially rapid expansion was called inflation (inflation) of the Universe. Then the false vacuum disintegrated, and its energy passed into the energy of ordinary matter.
Goose's theory was based on the theory of phase transitions in the early universe developed by Kirzhnits and Linde. Unlike Starobinsky, Gus aimed to explain, using one simple principle, why the universe is large, flat, homogeneous, isotropic, and also why there are no monopoles. An inflation stage 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 a false vacuum, like boiling 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 be converted into the thermal energy of the Universe, it was necessary for the walls of huge bubbles to collide, and this should have led to a violation of the uniformity and isotropy of the Universe after inflation, which contradicts the problem posed.
Although the Gus 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 for an expanding 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 the 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 should change slowly to ensure inflation inside the bubble; secondly, for more late stages there must 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 supercooling and false vacuum, from which Alan Hus started. It was an emotional shock, because it was necessary to abandon the ideas about the hot Universe that were considered true, phase transitions and hypothermia. It was necessary to find new way problem solving. Then the theory of chaotic inflation was put forward.
Chaotic inflation
The idea underlying Linde's theory of chaotic inflation is very simple, but in order to explain it, we need to introduce the concept of a scalar field. There are directional fields - electromagnetic, electric, magnetic, gravitational, but there may be at least one more - scalar, which is not directed anywhere, but is simply a function of coordinates.
The closest (though not exact) analog of a scalar field is the electrostatic potential. The voltage in the electrical networks of the United States is 110 V, and in Russia it is 220 V. If a person held on to the American wire with one hand and the Russian one with the other, the potential difference would kill him. If the voltage were the same everywhere, there would be no potential difference and no current would 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 high density energy.
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 almost flat top, but later, in the scenario of chaotic inflation, it turned out that it is enough to take the usual parabola, and everything works.
Consider the simplest scalar field, the density potential energy 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 begin to fluctuate near its minimum. However, if the field is large enough, then it will roll down very slowly, accelerating the Universe due to 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 rate of expansion of the Universe. The high rate of expansion of the Universe prevents the field from falling and thus does not allow the potential energy density to decrease. BUT high density energy continues to accelerate the universe at an ever-increasing speed. This self-sustaining regime leads to inflation, the exponentially rapid expansion 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 the 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 - 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 for some reason the exponential expansion mode was not found. And I should have just written complete equation for a scalar field, which in the standard version (that is, without taking into account the expansion of the Universe) looked like an equation for a pendulum:
But some additional term intervened - the force of friction, 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 large, 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 rapid 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 by 2 times. Then its volume increased by 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 fell rapidly, and the rate of expansion of the universe rapidly decreased.
The same would be true for a scalar field. But as long as the field remained very large, it supported itself, like Baron Munchausen pulling himself out of the swamp by his pigtail. This was possible due to the friction force, which was significant at high field values. In accordance with the theories of a new type, the universe expanded rapidly, and the field remained almost unchanged; accordingly, the energy density did not change either. So the expansion was exponential.
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 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 an inflation stage, if at the end of this stage the Universe became hot anyway, as in the old Big Bang theory?
Exponential expansion
There are three simple 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 similar to the surface of a hyperboloid, and the closed universe is similar to 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 small as a ball. According to the Big Bang theory, it grew to a decent size, but still remained relatively small. And according to inflationary theory, a tiny ball resulting from an exponential explosion in a very a short time became huge. Being on it, the observer would see a flat surface.
Imagine the Himalayas, where there are many different ledges, crevices, abysses, hollows, boulders, i.e. heterogeneities. But suddenly, someone or something in an absolutely incredible way increased the mountains to gigantic proportions, or we shrunk, like Alice in Wonderland. Then, being at the top of Everest, we will see that it is completely flat - it has been stretched, as it were, and the inhomogeneities have ceased to have any significance. The mountains remain, but in order to climb at least one meter, you need to go incredibly far. Thus, the problem of homogeneity 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 cross and monopoles can exist, but only so far away that we can't see it.
The emergence of galaxies
The small universe became colossal, and everything became homogeneous. But what about galaxies? It turned out that during the exponential expansion of the Universe, small quantum fluctuations that always exist, even in empty space, due to the quantum mechanical uncertainty principle, stretched to colossal sizes and turned into galaxies. According to the inflationary theory, galaxies are the result of increased quantum fluctuations, i.e., enhanced and frozen quantum noise.
For the first time this amazing possibility was pointed out by FIAN researchers Vyacheslav Fedorovich Mukhanov and Gennady Vasil'evich Chibisov in a paper 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.
Dotted sky
Quantum fluctuations led not only to the birth of galaxies, but also to the appearance of anisotropy of the cosmic microwave background radiation with a temperature of approximately 2.7 K, coming to us from distant regions Universe.
Modern technologies help scientists to study the relic radiation. artificial satellites Earth. The most valuable data was obtained using the WMAP space probe ( Wilkinson Microwave Anisotropy Probe), named after astrophysicist David Wilkinson ( David Wilkinson). The resolution of its equipment is 30 times greater than that of its predecessor - spacecraft COBE.
The temperature of the sky was previously thought to be 2.7 K everywhere, but WMAP was able to measure it to within 10–5 K with high angular resolution. According to the data obtained for the first 3 years of observations, the sky turned out to be inhomogeneous: somewhere hot, and somewhere colder. The simplest models of inflationary theory predicted ripples in the sky. But until the telescopes fixed its spotting, only a three-degree radiation was observed, which served as the most powerful confirmation of the theory of a hot Universe. Now it turned out that the theory of a hot universe is not enough.
It was possible to obtain photographs of swollen quantum fluctuations, which appeared 10–30 s after the birth of the universe and have survived to this day. The researchers not only detected sky patchiness, but also studied the spectrum of patches, that is, the intensity of the signal in different angular directions.
The results of high-precision measurements of the polarization of radiation carried out using WMAP confirmed the theory of the expansion of the Universe and made it possible to establish when the ionization of intergalactic gas occurred, caused by the very first stars. 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 inflation theory prediction, and the black dots correspond to the WMAP experimental data. If the Universe were not flat, then 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 a region where the scalar field is small, it oscillates and the universe does not expand exponentially. In a region where the field is strong enough, it slowly falls off, and small fluctuations appear on it. At this time, there is an exponential expansion and there is a process of inflation. If the scalar field were even larger (marked in blue on the graph), then it would hardly decrease due to huge friction, quantum fluctuations would be huge, and the Universe could become fractal.
Imagine that the Universe is rapidly expanding, and at some point the scalar field, instead of rolling to the energy minimum, jumps up due to quantum fluctuations (see above). Where the field jumped, the universe is expanding exponentially faster. A low-lying field is unlikely to jump, but the higher it is, the greater the likelihood of such a development of events, and hence an exponentially larger volume. new area. In each of these flat areas, the field can also jump up, which leads to the creation of new exponentially growing parts of the universe. As a result of this, instead of looking like one huge growing ball, our world becomes like an ever-growing tree, consisting of many such balls.
The inflationary theory gives us the only explanation currently known 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 schematically shows how one inflating region of the Universe generates more and more of its parts. In this sense, it becomes eternal and self-regenerating.
Properties of space-time and laws of interaction of elementary particles with each other in different areas 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 for many lows with different physics, which is similar to water that can be found 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 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 constantly recreating swelling areas and quantum leaps from one vacuum state to another, sorting through different possibilities and dimensions.
Thus the Universe becomes eternal, infinite 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 singular. 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 plurality of worlds in time and space takes on a completely different meaning: the Universe can reproduce itself infinitely in all its possible states.
This claim, which was based on Linde's work in 1986, took on new meaning a few years ago when string theorists (the leading candidate for the theory of all fundamental forces) concluded that 10 100 -10 1000 are possible in this theory. various vacuum states. These states differ due to the extraordinary diversity of the possible structure of the world at ultra-small distances.
Together with the theory of a self-healing inflationary Universe, this means that the Universe during inflation breaks into infinitely many parts with an incredibly large number of different properties. Cosmologists call this scenario the eternal inflationary multiverse theory ( multiverse), and string theorists call it a string landscape.
25 years ago, inflationary cosmology looked like something in between physical theory and science fiction. Over time, many of the predictions of this theory have been tested, and it gradually acquired the features of a standard cosmological paradigm. But it's too early to calm down. This theory continues to evolve and change rapidly. The main problem is the development of inflationary cosmology models based on realistic versions of elementary particle theory and string theory. This issue may be the subject of a separate report.
After learning about the Big Bang theory, I asked myself the question, where did it come from that exploded?
The question of the origin of the Universe with all its known and yet unknown properties has been of concern to man since time immemorial. But only in the twentieth century, after the discovery of cosmological expansion, the question of the evolution of the universe began to gradually become clearer. Recent scientific data have led to the conclusion that our universe was born 15 million years ago as a result of the Big Bang. But what exactly exploded at that moment and what, in fact, existed before the Big Bang, still remained a mystery. The inflationary theory of the appearance of our world, created in the 20th century, made it possible to make significant progress in resolving these issues, the general picture of the first moments of the Universe is already well drawn today, although many problems are still waiting in the wings.
Until the beginning of the last century, there were only two views on the origin of our universe. Scientists believed that it is eternal and unchanging, and theologians said that the world was created and it will have an end. The twentieth century, having destroyed a lot of what had been created in previous millennia, managed to give its own answers to most of the questions that occupied the minds of scientists of the past. And perhaps one of greatest achievements of the past century is the clarification of the question of how the Universe in which we live arose, and what hypotheses exist about its future. A simple astronomical fact - the expansion of our Universe - has led to a complete revision of all cosmogonic concepts and the development new physics- physics of emerging and disappearing worlds. Just 70 years ago, Edwin Hubble discovered that light from more distant galaxies is "redder" than light from closer ones. Moreover, the recession speed turned out to be proportional to the distance from the Earth (Hubble's expansion law). This was discovered thanks to the Doppler effect (the dependence of the wavelength of light on the speed of the light source). Since more distant galaxies appear more "red", it was assumed that they are moving away at a faster rate. By the way, it is not stars and even individual galaxies that scatter, but clusters of galaxies. The nearest stars and galaxies are connected with each other by gravitational forces and form stable structures. Moreover, in whatever direction you look, clusters of galaxies scatter from the Earth at the same speed, and it may seem that our Galaxy is the center of the Universe, but this is not so. Wherever the observer is, he will everywhere see the same picture - all the galaxies are running away from him. But such expansion of matter must have a beginning. This means that all galaxies must have been born at the same point. Calculations show that this happened about 15 billion years ago. At the moment of such an explosion, the temperature was very high, and a lot of light quanta should have appeared. Of course, everything cools down over time, and the quanta scatter over the emerging space, but the echoes of the Big Bang should have survived to this day. The first confirmation of the fact of the explosion came in 1964, when American radio astronomers R. Wilson and A. Penzias discovered relic electromagnetic radiation with a temperature of about 3° Kelvin (–270°C). It was this discovery, unexpected for scientists, that convinced them that the Big Bang really took place and that the Universe was very hot at first. The Big Bang theory has helped explain many of the problems facing cosmology. But, unfortunately, or perhaps fortunately, it also raised a number of new questions. In particular: What happened before the Big Bang? Why does our space have zero curvature and why is Euclid's geometry, which is studied at school, correct? If the Big Bang theory is correct, then why is the current size of our universe so much larger than the 1 centimeter predicted by the theory? Why is the Universe surprisingly homogeneous, while in any explosion the matter scatters in different directions extremely unevenly? What led to the initial heating of the Universe to an unimaginable temperature of more than 10 13 K?
All this indicated that the Big Bang theory was incomplete. Long time it seemed that it was impossible to go any further. Only a quarter of a century ago, thanks to the work of Russian physicists E. Gliner and A. Starobinsky, as well as the American A. Gus, a new phenomenon was described - the superfast inflationary expansion of the Universe. The description of this phenomenon is based on well-studied sections theoretical physics- Einstein's general theory of relativity and quantum field theory. Today it is generally accepted that this period, called "inflation", preceded the Big Bang.
When trying to give an idea of the essence initial period The life of the Universe has to operate with such ultra-small and super-large numbers that our imagination hardly perceives them. Let's try to use some analogy to understand the essence of the process of inflation.
Imagine a snow-covered mountain slope interspersed with heterogeneous small objects - pebbles, branches and pieces of ice. Someone on top of this slope made a small snowball and let it roll down the mountain. Moving down, the snowball increases in size, as new layers of snow with all the inclusions stick to it. And than larger size snowball, the faster it will increase. Very soon, from a small snowball, it will turn into a huge lump. If the slope ends in an abyss, then he will fly into it with ever-increasing speed. Having reached the bottom, the lump will hit the bottom of the abyss and its components will scatter in all directions (by the way, part of the lump's kinetic energy will go to heat the environment and flying snow).
Let us now describe the main provisions of the theory using the above analogy. First of all, physicists had to introduce a hypothetical field, which was called "inflaton" (from the word "inflation"). This field filled the entire space (in our case, snow on the slope). Due to random fluctuations, it took different meanings in arbitrary spatial regions and at different points in time. Nothing significant happened until a homogeneous configuration of this field with a size of more than 10 -33 cm was accidentally formed. As for the Universe we observe, in the first moments of its life, apparently, it had a size of 10 -27 cm. It is assumed that on such scales the basic laws of physics known to us today are already valid, so it is possible to predict the further behavior of the system. It turns out that immediately after this, the spatial region occupied by the fluctuation (from the Latin fluctuatio - “fluctuation”, random deviations observed physical quantities from their average values), begins to increase very rapidly in size, and the inflaton field tends to take a position in which its energy is minimal (the snowball rolled). Such an expansion lasts only 10 -35 seconds, but this time is enough for the diameter of the Universe to increase at least 1027 times and by the end of the inflationary period our Universe has acquired a size of about 1 cm. Inflation ends when the inflaton field reaches a minimum of energy - there is nowhere else to fall. In this case, the accumulated kinetic energy is converted into the energy of particles born and expanding, in other words, the heating of the Universe occurs. It is this moment that is called today the Big Bang.
The mountain mentioned above can have a very complex relief - several different lows, valleys below and all sorts of hills and bumps. Snowballs (future universes) are continuously born at the top of the mountain due to field fluctuations. Each lump can slide into any of the minima, thus giving rise to its own universe with specific parameters. Moreover, the universes can differ significantly from each other. properties of our universe amazingly adapted to give rise to intelligent life. Other universes may not have been as fortunate.
Once again, I would like to emphasize that the described process of the birth of the Universe "practically from nothing" is based on strictly scientific calculations. Nevertheless, any person who first gets acquainted with the inflationary mechanism described above has many questions.
Today, our universe is made up of a large number of stars, not to mention hidden mass. And it might seem that the total energy and mass of the universe is enormous. And it is completely incomprehensible how all this could fit in the initial volume of 10-99 cm3. However, in the Universe there is not only matter, but also a gravitational field. It is known that the energy of the latter is negative and, as it turned out, in our Universe, the energy of gravity exactly compensates for the energy contained in particles, planets, stars and other massive objects. Thus, the law of conservation of energy is perfectly fulfilled, and the total energy and mass of our Universe are practically equal to zero. It is this circumstance that partly explains why the nascent Universe did not turn into a huge black hole immediately after its appearance. Its total mass was completely microscopic, and at first there was simply nothing to collapse. And only at later stages of development did local clumps of matter appear, capable of creating such gravitational fields near themselves, from which even light cannot escape. Accordingly, the particles from which the stars are "made" on initial stage development simply did not exist. Elementary particles began to be born at that period of the development of the Universe, when the inflaton field reached a minimum of potential energy and the Big Bang began.
The area occupied by the inflaton field grew at a speed much greater than the speed of light, but this does not in the least contradict Einstein's theory of relativity. faster than light only material bodies cannot move, and in this case the imaginary, non-material boundary of the region where the Universe was born was moving (an example superluminal motion is the movement of a light spot on the surface of the Moon during the rapid rotation of the laser illuminating it).
Moreover, the environment did not at all resist the expansion of the region of space, covered by an ever more rapidly growing inflaton field, since it seemed to not exist for the emerging World. General theory Relativity states that the physical picture that an observer sees depends on where he is and how he moves. So, the picture described above is valid for the "observer" located inside this area. Moreover, this observer will never know what is happening outside the region of space where he is. Another "observer", looking at this area from the outside, will not find any expansion at all. AT best case he will see only a small spark, which, according to his watch, will disappear almost instantly. Even the most sophisticated imagination refuses to perceive such a picture. And yet it appears to be true. At least, this is what modern scientists think, drawing confidence in the already discovered laws of Nature, the correctness of which has been repeatedly verified.
It must be said that this inflaton field still continues to exist and fluctuate. But only we, internal observers, are not able to see this - after all, for us, a small area has turned into a colossal Universe, the boundaries of which even light cannot reach.
So, immediately after the end of inflation, a hypothetical internal observer would see the Universe filled with energy in the form of material particles and photons. If all the energy that could be measured by an internal observer is converted into a mass of particles, then we will get approximately 10 80 kg. The distances between particles increase rapidly due to the general expansion. The gravitational forces of attraction between particles reduce their speed, so the expansion of the universe after the end of the inflationary period gradually slows down.
Immediately after birth, the universe continued to grow and cool. At the same time, cooling occurred, among other things, due to the banal expansion of space. Electromagnetic radiation characterized by a wavelength that can be associated with temperature - the more average length radiation waves, the lower temperature. But if space expands, then the distance between the two "humps" of the wave will increase, and, consequently, its length. This means that in expanding space, the radiation temperature must also decrease. Which strongly confirms low temperature modern relic radiation.
As it expands, the composition of the matter that fills our world also changes. Quarks unite into protons and neutrons, and the Universe is filled with already familiar to us elementary particles- protons, neutrons, electrons, neutrinos and photons. There are also antiparticles. The properties of particles and antiparticles are almost identical. It would seem that their number should be the same immediately after inflation. But then all particles and antiparticles would mutually annihilate and there would be no building material for galaxies and ourselves. And here again we are lucky. Nature made sure that there were a little more particles than antiparticles. It is thanks to this little difference and our world exists. And relic radiation is just a consequence of the annihilation (that is, mutual annihilation) of particles and antiparticles. Of course, at the initial stage, the energy of the radiation was very high, but due to the expansion of space and, as a result, the cooling of the radiation, this energy quickly decreased. Now the energy of relic radiation is about ten thousand times (104 times) less than the energy contained in massive elementary particles.
Gradually, the temperature of the universe dropped to 1010 K. By this time, the age of the universe was about 1 minute. Only now have protons and neutrons been able to combine into nuclei of deuterium, tritium and helium. This was due to nuclear reactions, which people have already studied well, detonating thermonuclear bombs and operating atomic reactors on Earth. Therefore, one can confidently predict how many and what elements can appear in such a nuclear pile. It turned out that the currently observed abundance of light elements is in good agreement with the calculations. This means that we know physical laws are the same in the entire observable part of the Universe and were so already in the first seconds after the appearance of our world. Moreover, about 98% of the helium existing in nature was formed precisely in the first seconds after the Big Bang.
Immediately after birth, the Universe went through an inflationary period of development - all distances rapidly increased (from the point of view of internal observer). However, the energy density at different points in space cannot be exactly the same - some inhomogeneities are always present. Suppose that in some area the energy is slightly greater than in neighboring ones. But since all sizes are growing rapidly, then the size of this area should also grow. After the end of the inflationary period, this expanded area will have slightly more particles than the space around it, and its temperature will be slightly higher.
Realizing the inevitability of the emergence of such areas, supporters of the inflationary theory turned to the experimenters: "it is necessary to detect temperature fluctuations ..." - they stated. And in 1992 this wish was fulfilled. Almost simultaneously, the Russian satellite "Relikt-1" and the American "COBE" detected the required fluctuations in the temperature of the cosmic microwave background radiation. As already mentioned, modern universe has a temperature of 2.7 K, and the temperature deviations found by scientists from the average were approximately 0.00003 K. It is not surprising that such deviations were difficult to detect before. So the inflationary theory received another confirmation.
With the discovery of temperature fluctuations, another exciting opportunity has emerged - to explain the principle of galaxy formation. After all, in order to gravitational forces compressed matter, the initial embryo is needed - an area with increased density. If matter is uniformly distributed in space, then gravity, like Buridan's donkey, does not know in which direction to act. But it is precisely the areas with an excess of energy that generate inflation. Now the gravitational forces know what to act on, namely the denser areas created during the inflationary period. Under the influence of gravity, these initially slightly denser regions will shrink and it is from them that stars and galaxies will form in the future.
The current moment of the evolution of the Universe is extremely well adapted for life, and it will last for many more billions of years. Stars will be born and die, galaxies will rotate and collide, and clusters of galaxies will fly farther and farther apart. Therefore, humanity has plenty of time for self-improvement. True, the very concept of "now" for such vast universe, like ours, is poorly defined. So, for example, the life of quasars observed by astronomers, remote from the Earth by 10-14 billion light years, is separated from our "now" just by those same 10-14 billion years. And the further into the depths of the Universe we look with the help of various telescopes, the more early period We are watching its development.
Today, scientists are able to explain most of the properties of our universe, from 10 -42 seconds to the present and beyond. They can also trace the formation of galaxies and predict the future of the universe with some confidence. Nevertheless, a number of "small" incomprehensibility still remains. First of all, this is the essence of the hidden mass (dark matter) and dark energy. In addition, there are many models that explain why our Universe contains many more particles than antiparticles, and we would like to decide in the end on the choice of one correct model.
As the history of science teaches us, it is usually "minor imperfections" that open further ways development, so that future generations of scientists will certainly have something to do. In addition, deeper questions are also already on the agenda of physicists and mathematicians. Why is our space three-dimensional? Why are all the constants in nature as if “fitted” so that intelligent life arises? And what is gravity? Scientists are already trying to answer these questions.
And of course, leave room for surprises. It should not be forgotten that such fundamental discoveries as the expansion of the Universe, the presence of relic photons and vacuum energy were made, one might say, by chance and were not expected by the scientific community.
