V.V.Kazyutinsky

Inflationary cosmology: theory and scientific picture of the world*

Now there is a new radical revision of knowledge about the Universe as a whole, i.e. the largest fragment of the world whole that science is able to isolate with the means available at a given time. This revision concerns two conceptual levels: 1) the construction of new cosmological theories; 2) changes in the “world as a whole” block in the scientific picture of the world (SPM).

Modern changes in cosmology make an extremely large, but so far insufficiently appreciated contribution to modern NCM, not to mention the ideological interest they represent. Their essence is a return to the ideas expressed in the language of non-classical physics of an infinite number of worlds, the infinity of space and time, the infinity of processes of evolution and self-organization in the Universe (Metaverse), some of which were considered forever rejected from the standpoint of science.

The expanding universe theory has been an extremely effective research program. It made it possible to solve a number of problems related to the structure and evolution of our Metagalaxy, including the early stages of its development. For example, an outstanding achievement was the theory of the “hot Universe” by G. A. Gamov, confirmed by the discovery of cosmic microwave background radiation in 1965. Numerous alternatives to Friedmann's cosmology have proven unconvincing.

At the same time, the theory of the expanding Universe itself faced a number of serious problems. Some of them were, so to speak, “technical” in nature. Let's say, it is somewhat discouraging that, despite intensive research, it has still not been possible to build a sufficiently adequate model of the expanding Metagalaxy within the framework of the theory of A.A. Friedman, since known facts, necessary to build such a model, are either not accurate enough or contradictory. Other problems are more fundamental. The “paradox of mass” has long been hanging over cosmologists as a “sword of Damocles”, according to which 90-95% of the mass of the Metagalaxy should be in an invisible state, the nature of which is still unclear. The modern development of the theory of an expanding Universe has given rise to a number of even more serious problems, which, in essence, clearly show the limitations of the theory, its inability to cope with these problems without significant conceptual shifts. The problem that gave the theory a lot of trouble was the problem of the most initial stages evolution of the Universe. The problem of singularity is well known: when the radius of the Universe inverts, i.e. of our Metagalaxy, to zero many parameters became infinite. It turned out to be unclear physical meaning question: what was “before” the singularity (sometimes this question itself was declared meaningless, since time, as Augustine argued, arose along with the Universe. (But answers like: “before” there was no time and, therefore, the question itself is posed incorrectly , many cosmologists were not very satisfied.) The theory in its non-quantum version could not explain the reason that caused the Big Bang, the expansion of the Universe. In addition, there is an impressive list of more than a dozen other problems that A. A. Friedman's theory could not cope with Here are just a few of them: 1) The problem of flatness (or spatial Euclideanity) of the Universe: the proximity of the curvature of space to zero, which is orders of magnitude different from “theoretical expectations”; 2) the problem of the size of the Universe: it would be more natural, from a theoretical point of view, to expect that our Universe contains no more than a few elementary particles, and not 10 88 according to modern estimates - another huge discrepancy between theoretical expectations and observations! 3) the horizon problem: sufficiently distant points in our Universe have not yet had time to interact and cannot have common parameters (such as

density, temperature, etc.). But our Universe, the Metagalaxy, on a large scale remains surprisingly homogeneous, despite the impossibility of causal connections between its distant regions.

Now, after inflationary cosmology has been able to solve most of these problems, the difficulties of relativistic cosmology are often listed, and even somehow very willingly. But in the 60-70s, even their mentions were very restrained and measured, especially in the face of Nefridman’s research programs. Firstly, many still had in their memory tragic fate relativistic cosmology, which was subjected to ideological attacks not only in our country. Secondly, there was a general understanding that near the “beginning” quantum effects begin to play a decisive role. It followed that further translation of new knowledge from elementary particle physics and quantum field theory was necessary. Discussion of cosmological problems at the NCM level led to interesting conclusions. Two fundamental principles were put forward that caused a strong "progressive shift" in cosmology.

1) The principle of the quantum birth of the Universe. Cosmological singularity is an irreducible feature of the conceptual structure of non-quantum cosmology. But in quantum cosmology this is only a rough approximation, which must be replaced by the concept of spontaneous fluctuations of the vacuum (Tryon, 1973).

2) The principle of inflation, according to which, soon after the expansion of the Universe began, the process of its exponential inflation occurred. It lasted about 10 -35 s, but during this time the swelling area should reach, in the words of A.D. Linde, “unimaginable dimensions.” According to some inflation models, the scale of the Universe (in cm) will reach 10 to the power of 10 12, i.e. magnitudes that are many orders of magnitude greater than the distances to the most distant objects of the observable Universe.

The first version of inflation was considered by A.A. Starobinsky in 1979, then three scenarios of an inflating Universe appeared successively: the scenario of A. Gus (1981), the so-called new script(A.D. Linde, A. Albrecht, P.J. Steinhardt, 1982), chaotic inflation scenario (A.D. Linde, 1986). The chaotic inflation scenario assumes that the mechanism generating the rapid inflation of the early Universe is determined by scalar fields, which play a key role as

in particle physics and cosmology. Scalar fields in the early Universe can take on arbitrary values; hence the name, chaotic bloat.

Inflation explains many properties of the Universe that created intractable problems for Friedmann's cosmology. For example, the reason for the expansion of the Universe is the action of anti-gravitational forces in a vacuum. According to inflationary cosmology, the Universe should be flat. A.D. Linde even considers this fact as a prediction of inflationary cosmology, confirmed by observations. Synchronizing the behavior of remote regions of the Universe is also not a problem.

The theory of an inflating Universe introduces (at a hypothetical level for now) serious changes to the “world as a whole” block of the NCM.

1. In full accordance with the philosophical analysis of the concept of “the Universe as a whole,” which led to the conclusion that it is “everything that exists” from the point of view of a given cosmological theory or model (and not in some absolute sense), the theory has made an unprecedented expansion of volume this concept in comparison with relativistic cosmology. The generally accepted point of view that our Metagalaxy is the entire Universe was abandoned. In inflationary cosmology, the concept of the Metauniverse was introduced, while for regions on the scale of the Metagalaxy the term “miniuniverses” was proposed. Now the Metaverse is considered as “everything that exists” from the point of view of inflationary cosmology, and the Metagalaxy is considered as its local region. But it is possible that if a unified theory of physical interactions (EFT, GUT) is created, then the scope of the concept of the Universe as a whole will again be significantly expanded (or changed).

2. Friedman's theory was based on the principle of homogeneity of the Universe (Metagalaxy). Inflationary cosmology, explaining the fact of large-scale homogeneity of the Universe using the inflation mechanism, simultaneously introduces new principle- extreme heterogeneity of the Metaverse. Quantum fluctuations associated with the emergence of miniuniverses lead to differences in physical laws and conditions, the dimensions of space-time, the properties of elementary particles and other extra-metagalactic objects. Should we remind you that the principle of the infinite variety of the material world, in particular its physical forms, is a rather old philosophical idea, which is now finding new confirmation in cosmology.

3. The metaverse as a collection of many mini-universes arising from fluctuations of space-time “foam” is obviously infinite, has no beginning and end in time (I.D. Novikov called it the “eternally young Universe”, not suspecting that this metaphor is still in at the beginning of the 20th century was invented by K.E. Tsiolkovsky, criticizing the theory of the thermal death of the Universe).

4. The theory of an inflating Universe considers the processes of cosmic evolution in a significantly different way than Friedman’s. She rejects the idea that the entire Universe arose 10 9 years ago from a singular state. This is only the age of our mini-universe, the Metagalaxy, which emerged from the vacuum “foam”. Consequently, “before” the beginning of the expansion of the Metagalaxy there was a vacuum, which modern science considers as one of the physical forms of matter. But even before this conclusion was made in a cosmological context, relativity, and not absoluteness, and the completely natural, and not transcendental nature of expansion, were justified from philosophical considerations. Thus, the concept of “creation of the world”, which appears once in the texts of A.A. Friedman, and countless times - in theological, philosophical, and indeed cosmological works throughout most of the 20th century, turns out to be nothing more than a metaphor that does not follow from the essence of inflationary cosmology. The metaverse, according to the theory, may generally turn out to be stationary, although the evolution of the miniuniverses included in it is described by the big bang theory.

A.D. Linde introduced the concept of eternal inflation, which describes the evolutionary process that continues as a chain reaction. If the Metaverse contains at least one bloating region, it will continually spawn new bloating regions. A branching structure of mini-universes appears, similar to a fractal.

5. Inflationary cosmology has made it possible to provide a completely new understanding of the problem of singularity. The concept of singularity, irreducible within the framework of the standard relativistic model based on the classical method of description and explanation, significantly changes its meaning in the quantum method of description and explanation used in inflationary cosmology. It turns out that it is not at all necessary to assume that there was some kind of single beginning of the world, although this assumption encounters some difficulties. But, according to A.D. Linde, in scenarios of chaotic inflation of the Universe “it is especially clearly visible that

Instead of the tragedy of the birth of the entire world from a singularity, before which nothing existed, and its subsequent transformation into nothing, we are dealing with an endless process of interconversion of phases in which quantum fluctuations of the metric are small or, conversely, large.” It follows that the recently unshakable conclusion about the existence of a general cosmological singularity at the beginning of expansion loses its credibility. There is no need to say that all parts of the Universe began to expand simultaneously. The singularity is replaced in the theory of an expanding universe by a quantum fluctuation of the vacuum.

6. Inflationary cosmology on modern stage its development revises previous ideas about the thermal death of the Universe. A.D. Linde speaks of a “self-reproducing inflating Universe,” i.e. process of endless self-organization. Miniverses arise and disappear, but there is no single end to these processes.

7. In both relativistic and inflationary cosmology, the anthropic principle (AP) plays a significant role. It connects the fundamental parameters of our universe, the Metagalaxy, the parameters of elementary particles and the fact of human existence in the Metagalaxy. The cosmological conditions necessary for the emergence of man include the following: The Universe (Metagalaxy) must be sufficiently large, flat, and homogeneous. It is these properties that follow from the theory of an inflating Universe. Without involving the inflation process in the early Universe, it is impossible to explain the uniformity of its structure and properties within the region covered by observations.

It is not difficult to notice that the philosophical foundations of inflationary cosmology intertwine individual ideas and images transmitted from different philosophical systems. For example, the idea of ​​an infinite number of worlds has a long philosophical tradition dating back to the times of Leucippus, Democritus, Epicurus, and Lucretius. It was developed especially deeply by Nikolai Kuzansky and Giordano Bruno. The idea of ​​Aristotelian metaphysics about the transformation of the potentially possible into the actual influenced not only the quantum method of description and explanation used by inflationary cosmology, but it also turns out - in a paradoxical way! - the predecessor of the evolutionary ideas of this theory. Paradoxical because Aristotle himself considered the Universe to be unique and, considering creation and destruction as earthly processes, attributed to the sky immutability in

time and isolation in space. But the ideas he expressed about potential and actual being were transferred, contrary to Aristotle’s own views, to the infinite Metaverse. The influence of Plato's ideas is also found in the philosophical foundations of inflationary cosmology. It can be traced, in any case, through the Neoplatonists of the Renaissance.

Some researchers (for example, A.N. Pavlenko) believe that inflationary cosmology should be considered as a new stage of the modern revolution in the science of the Universe, since it not only creates a new NCM, but also leads to a revision of some ideals and norms of knowledge (for example, the ideals evidence of knowledge, which are reduced to intratheoretical factors). As a forecast or expert assessment, such a point of view is acceptable if we take into account, however, the following circumstances.

Of course, the development of a theory that causes a major shift in our knowledge of the world and serious ideological consequences is a necessary sign of a certain stage of a scientific revolution. This feature must, however, be supplemented by the justification of the new theory and its recognition in the scientific community, which is also part of the structure of the revolutionary shift. In terms of the degree of radicality with which inflationary cosmology (especially the version of chaotic inflation) revises the picture of the world as a whole, it clearly surpasses the theory of A.A. Friedman. In the community of cosmologists she began to enjoy great influence, which was not established immediately, however. In the first half of the 80s, various scenarios for the quantum birth of the Universe from vacuum were considered competitive, inflationary cosmology being one of them. This was due to the significant shortcomings of the first inflation scenarios. It was only after the emergence of the chaotic inflation scenario that there was a breakthrough in the recognition of the new cosmology. Nevertheless, the problem of substantiating this cosmological theory remains open, precisely because it does not correspond to the currently accepted ideals and norms of evidence of knowledge (other Universes are fundamentally unobservable). Hopes for changing these ideals in the foreseeable future (excluding the obligation of “external justification”) are still low. Strictly speaking, the revolution potentially contained in inflationary cosmology may or may not take place. For now we can only hope for its deployment, without completely excluding other unexpected and as yet unforeseen turns in this area.

The sociocultural assimilation of inflationary cosmology contains an interesting point. Being extremely revolutionary in its essence, the new cosmological theory did not cause much of a “boom”. About 20 years have passed since the appearance of the first version of this theory, but it almost did not go beyond a rather narrow circle of specialists, did not become a source of ideological discussions, even remotely reminiscent of the fierce battles around the theory of Copernicus, which excited minds even before the publication of his immortal treatise, or around the theory of A.A. Friedman. This astonishing circumstance requires explanation.

It is possible that the main reason is, alas, a decline in interest in scientific, in particular, physical and mathematical knowledge, which is being intensively replaced by various kinds of surrogates, often causing immeasurably greater excitement than the most first-class scientific achievements. Now only a few discoveries of science resonate, which reveal a direct connection with the problems of human existence.

Further, inflationary cosmology is an extremely complex theory, not very clear even to specialists from neighboring fields of physics, and even more so to non-specialists, and for this reason alone, is outside the scope of these interests.

Finally, the idea of ​​a unique and finite universe in time has taken too deep roots in culture and has had too strong an influence on it to easily give way to a theory that clearly resembles long-rejected cosmological models.

However, progress in cosmology continues and the coming years will likely lead to more confident estimates of the theory of an inflating universe.

Literature

1. Linde A.D. Particle physics and inflationary cosmology. M., 1990.

2. Kazyutinsky V.V. The concept of “Universe” // Infinity and the Universe. M., 1969.

3. Kazyutinsky V.V. Idea of ​​the Universe // Philosophy and ideological problems modern science. M., 1981.

In which he briefly describes the emergence and development of the theory of the inflationary universe, which provides a new explanation for the Big Bang and predicts the existence of many other universes along with ours.

Cosmology is in some ways akin to philosophy. Firstly, in terms of the vastness of its subject of research - it is the entire Universe as a whole. Secondly, because some premises in it are accepted by scientists as acceptable without the possibility of conducting any testing experiment. Third, the predictive power of many cosmological theories will only work if we can get to other universes - which is not to be expected.

However, it does not at all follow from all this that modern cosmology is such a hand-waving and not entirely scientific field where you can, like the ancient Greeks, lie in the shade of trees and hypothesize about the number of dimensions of space-time - are there ten or eleven? Cosmological models are based on observational data from astronomy, and the more data there is, the more material there is for cosmological models - which must connect and harmonize these data with each other. The difficulty is that cosmology deals with fundamental issues 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 general, there is nothing exceptional in this: when constructing 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, there is still no single theory that would describe everything that is happening 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 own pros and cons, its adherents and opponents. The Lambda-CDM model is considered the most authoritative, although not indisputable. It is important to understand that cosmological models are not necessarily in competition with each other. They can simply describe fundamentally different stages of evolution. For example, Labmda-CDM does not consider the Big Bang at all, although it perfectly explains everything that happened after it.

The structure of a multiverse with bubbles of mini-universes inside it.

Drawing: Andrei Linde

The surprising thing about this is that the cosmological constant (that is, the vacuum energy) does not change over time as the universe expands, while the density of matter changes completely predictably and depends on the volume of space. It turns out that in the early universe the density of matter far exceeded the density of vacuum; in the future, as galaxies fly apart, the density of matter will decrease. So why, now that we can measure them, are they so close in value to each other?

The only one in a known way It is possible to explain such an incredible coincidence, without resorting to some unscientific hypotheses, only with the help of the anthropic principle and the inflationary model - that is, from the many existing universes, life arose in the one where the cosmological constant is this moment time turned out to be equal to the density of matter (this in turn determines the time that has passed since the beginning of inflation, and provides 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 inflation model was the publication of a paper in 2000 by Busso and Polchinski, in which they proposed using string theory to explain the large set different types vacuum, in each of which the cosmological constant could take its own values. And when one of the creators of string theory itself, Leonard Susskind, got involved in the work on combining string theory and the inflationary model, it not only helped to create a more complete picture, which is now called the “anthropic landscape of string theory,” but also in some way added weight to the entire model V scientific world. The number of articles on inflation increased over the year from four to thirty-two.

The inflation model purports to not only explain the fine-tuning of fundamental constants, but also to help discover some of the fundamental parameters that determine the magnitude of these constants. The fact is that in the Standard Model today there are 26 parameters (the cosmological constant was the last to be discovered), which determine the value 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 structured that there should be some logical connections between seemingly completely different quantities. In an inflationary model, these constants may simply be an environmental parameter that appears to us locally unchanged due to the effect of inflation, although it will be completely different in another part of the universe and is determined by yet to be identified, but certainly existing truly fundamental parameters.

In the conclusion 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 into 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 we look at these questions from a different angle, it turns out that even without traveling to other mini-universes we have a lot of experimental data. Such as size, flatness, isotropy, homogeneity, the value of the cosmological constant, the ratio of proton and neutron masses, and so on. And the only reasonable explanation to date for these and many other experimental data is given within the framework of the theory of multiverses and, consequently, the model of inflationary cosmology.

, 1990. Andrey Linde

“The Anthropic landscape of string theory” 2003. Leonard Susskind

Marat Musin

One of the fragments of the first microsecond of the life of the universe played a huge role in its further evolution.

The conceptual breakthrough became possible thanks to a very beautiful hypothesis, born in attempts to find a way out of three serious problems with the Big Bang theory - the problem of a flat Universe, the problem of the horizon and the problem of magnetic monopoles.

Rare particle

Since the mid-1970s, physicists began working on theoretical models of the Grand Unification of the three fundamental forces - strong, weak and electromagnetic. Many of these models concluded that very massive particles carrying a single magnetic charge must have been produced in abundance shortly after the Big Bang. When the age of the Universe reached 10^-36 seconds (according to some estimates, even somewhat earlier), the strong interaction separated from the electroweak interaction and became independent. At the same time, point topological defects with a mass 10^15 –10^16 greater than the mass of the then non-existent proton were formed in vacuum. When, in turn, the electroweak interaction was divided into weak and electromagnetic and true electromagnetism appeared, these defects acquired magnetic charges and began new life- in the form of magnetic monopoles.

This beautiful model presented cosmology with an unpleasant problem. “Northern” magnetic monopoles annihilate when they collide with “southern” ones, but otherwise these particles are stable. Due to their huge nanogram-scale mass by the standards of the microcosm, soon after birth they were obliged to slow down to non-relativistic speeds, disperse throughout space and survive until our times. According to the standard Big Bang model, their current density should be approximately the same as that of protons. But in this case, the total density of cosmic energy would be at least a quadrillion times higher than the real one.

All attempts to discover monopoles have so far failed. As the search for monopoles in iron ores and sea water has shown, the ratio of their number to the number of protons does not exceed 10^-30. Either these particles are not present at all in our region of space, or there are so few of them that instruments are unable to register them, despite a clear magnetic signature. This is also confirmed by astronomical observations: the presence of monopoles should affect the magnetic fields of our Galaxy, but this has not been detected.

Of course, we can assume that monopoles never existed at all. Some models of the unification of fundamental interactions do not actually prescribe their appearance. But the problems of the horizon and a flat Universe remain. It so happened that in the late 1970s, cosmology faced serious obstacles, which clearly required new ideas to overcome.

Negative pressure

And these ideas were not slow to appear. The main one was the hypothesis according to which in outer space, in addition to matter and radiation, there is a scalar field (or fields) that creates negative pressure. This situation seems paradoxical, but it occurs in Everyday life. A positive pressure system, such as compressed gas, loses energy and cools as it expands. An elastic band, on the contrary, is in a state of negative pressure, because, unlike gas, it tends not to expand, but to contract. If such a tape is quickly stretched, it will heat up and thermal energy will increase. As the Universe expands, a field with negative pressure accumulates energy, which, when released, can generate particles and quanta of light.

Negative pressure can have different values. But there is a special case when it is equal to the density of cosmic energy with the opposite sign. In this situation, this density remains constant as space expands, since negative pressure compensates for the growing “rarefaction” of particles and light quanta. From the Friedmann–Lemaitre equations it follows that the Universe in this case expands exponentially.

Flat Universe

The expanding sphere demonstrates a solution to the problem of a flat Universe within the framework of inflationary cosmology. As the radius of the sphere increases, the selected area of ​​its surface becomes more and more flat. In exactly the same way, the exponential expansion of space-time during inflation has led to the fact that our Universe is now almost flat.

The exponential expansion hypothesis solves all three problems above. Suppose that the Universe arose from a tiny “bubble” of highly curved space, which underwent a transformation that endowed space with negative pressure and thereby caused it to expand according to an exponential law. Naturally, after this pressure disappears, the Universe will return to its previous “normal” expansion.

Problem solving

Let us assume that the radius of the Universe before entering the exponential phase was only several orders of magnitude greater than the Planck length, 10^-35 m. If in the exponential phase it grows, say, 10^50 times, then by its end it will reach thousands of light years. Whatever the difference in the space curvature parameter from unity before the expansion begins, by the end of the expansion it will decrease by 10^–100 times, that is, the space will become perfectly flat!

The problem of monopoles is solved in a similar way. If the topological defects that became their predecessors arose before or even during the process of exponential expansion, then by its end they should move away from each other at gigantic distances. Since then, the Universe has expanded considerably, and the density of monopoles has dropped to almost zero. Calculations show that even if you examine a cosmic cube with an edge of a billion light years, then with the highest degree of probability there will not be a single monopole.

The cosmological inflation model, which solves many of the problems with the Big Bang theory, states that in a very short time the size of the bubble from which our Universe was formed increased by 10^50 times. After this, the Universe continued to expand, but much more slowly.

The exponential expansion hypothesis also suggests a simple way out of the horizon problem. Let us assume that the size of the embryonic “bubble” that laid the foundation for our Universe did not exceed the path that light managed to travel after the Big Bang. In this case, thermal equilibrium could be established in it, ensuring equality of temperatures throughout the entire volume, which was preserved during exponential expansion. A similar explanation is present in many cosmology textbooks, but you can do without it.

From one bubble

At the turn of the 1970s and 1980s, several theorists, the first of whom was the Soviet physicist Alexei Starobinsky, considered models of the early evolution of the Universe with a short stage of exponential expansion. In 1981, American Alan Guth published a paper that brought this idea to widespread attention. He was the first to understand that such an expansion (most likely completed at the age mark of 10^-34 s) eliminates the problem of monopoles, which he initially dealt with, and points the way to resolving problems with flat geometry and the horizon. Guth beautifully called this expansion cosmological inflation, and the term became generally accepted.

But Guth's model still had a serious drawback. It allowed for the emergence of many inflationary areas colliding with each other. This led to the formation of a highly disordered cosmos with an inhomogeneous density of matter and radiation, which is completely different from real outer space. However, soon Andrei Linde from the Physical Institute of the Academy of Sciences (FIAN), and a little later Andreas Albrecht and Paul Steinhardt from the University of Pennsylvania showed that if you change the equation of the scalar field, then everything falls into place. This led to a scenario in which our entire observable Universe arose from a single vacuum bubble, separated from other inflationary regions by unimaginably large distances.

Chaotic inflation

In 1983, Andrei Linde made another breakthrough by developing the theory of chaotic inflation, which made it possible to explain both the composition of the Universe and the homogeneity of the cosmic microwave background radiation. During inflation, any previous inhomogeneities in the scalar field are stretched so much that they practically disappear. At the final stage of inflation, this field begins to rapidly oscillate near the minimum of its potential energy. At the same time, particles and photons are born in abundance, which intensively interact with each other and reach an equilibrium temperature. So at the end of inflation, we have a flat, hot Universe, which then expands according to the Big Bang scenario. This mechanism explains why today we observe cosmic microwave background radiation with tiny temperature fluctuations, which can be attributed to quantum fluctuations in the first phase of the existence of the Universe. Thus, the theory of chaotic inflation resolved the horizon problem without the assumption that before the onset of exponential expansion, the embryonic Universe was in a state of thermal equilibrium.

Lost connection

The cosmic microwave background radiation that we now see from Earth comes from a distance of 46 billion light years (on the accompanying scale), having traveled just under 14 billion years. However, when this radiation began its journey, the age of the Universe was only 300,000 years. During this time, the light could travel only 300,000 light years (small circles), and the two points in the illustration simply could not communicate with each other - their cosmological horizons do not intersect.

According to Linde's model, the distribution of matter and radiation in space after inflation simply must be almost perfectly homogeneous, with the exception of traces of primary quantum fluctuations. These fluctuations gave rise to local fluctuations in density, which eventually gave rise to galaxy clusters and the cosmic voids separating them. It is very important that without inflationary “stretching” the fluctuations would be too weak and would not be able to become the embryos of galaxies. In general, the inflationary mechanism has an extremely powerful and universal cosmological creativity - if you like, it appears as a universal demiurge. So the title of this article is by no means an exaggeration.

Flat problem

Astronomers have long been convinced that if the current outer space is deformed, it is quite moderate.

Geometry of space

The local geometry of the Universe is determined by a dimensionless parameter: if it is less than one, the Universe will be hyperbolic (open), if more - spherical (closed), and if exactly equal to one - flat. Even very small deviations from unity can lead to a significant change in this parameter over time. The illustration in blue shows a graph of the parameter for our Universe.

Friedmann and Lemaitre's models allow us to calculate what the curvature of space was shortly after the Big Bang. Curvature is estimated using a dimensionless parameter equal to the ratio of the average density of cosmic energy to its value at which this curvature becomes zero, and the geometry of the Universe, accordingly, becomes flat. About 40 years ago there was no longer any doubt that if this parameter differs from unity, it would be no more than ten times in one direction or another. It follows that one second after the Big Bang it differed from unity up or down by only 10^-14! Is such a fantastically precise “tuning” accidental or due to physical reasons? This is exactly how American physicists Robert Dicke and James Peebles formulated the problem in 1979.

On scales of the order of hundredths of the size of the Universe (now hundreds of megaparsecs), its composition was and remains homogeneous and isotropic. However, on the scale of the entire cosmos, homogeneity disappears. Inflation stops in one area and begins in another, and so on ad infinitum. This is a self-reproducing endless process that generates a branching set of worlds - the Multiverse. The same fundamental physical laws can be realized there in different guises - for example, intranuclear forces and the charge of an electron in other universes may turn out to be different from ours. This fantastic picture is currently being discussed in all seriousness by both physicists and cosmologists.

Struggle of ideas

“The main ideas of the inflationary scenario were formulated three decades ago,” Andrei Linde, one of the authors of inflationary cosmology, Stanford University professor, explains to PM. - After that main task began the development of realistic theories based on these ideas, but only the criteria for realism changed more than once. In the 1980s, the dominant view was that inflation could be understood using Grand Unified models. Then hopes faded, and inflation began to be interpreted in the context of the theory of supergravity, and later - the theory of superstrings. However, this path turned out to be very difficult. Firstly, both of these theories use extremely complex mathematics, and secondly, they are designed in such a way that it is very, very difficult to implement an inflationary scenario with their help. Therefore, progress here has been rather slow. In 2000, three Japanese scientists, with considerable difficulty, obtained, within the framework of the theory of supergravity, a model of chaotic inflation, which I had come up with almost 20 years earlier. Three years later, we at Stanford did work that showed the fundamental possibility of constructing inflationary models using superstring theory and, on its basis, explaining the four-dimensionality of our world. Specifically, we found that this way we can obtain a vacuum state with a positive cosmological constant, which is necessary to trigger inflation. Our approach was successfully developed by other scientists, and this greatly contributed to the progress of cosmology. It is now clear that superstring theory allows for the existence of a gigantic number of vacuum states, giving rise to the exponential expansion of the Universe.

There, beyond the horizon

The horizon problem is related to the cosmic microwave background radiation. No matter what point on the horizon it comes from, its temperature is constant with an accuracy of 0.001%.

Normal expansion at speeds lower than the speed of light leads to the fact that the entire Universe will sooner or later be inside our event horizon. Inflationary expansion at speeds significantly exceeding the speed of light has led to the fact that only a small part of the Universe formed during the Big Bang is accessible to our observation. This allows us to solve the horizon problem and explain the same temperature of the relict radiation coming from different points in the sky.

In the 1970s, this data was not yet available, but astronomers even then believed that the fluctuations did not exceed 0.1%. This was the mystery. Microwave radiation quanta scattered throughout space approximately 400,000 years after the Big Bang. If the Universe was evolving all the time according to Friedmann-Lemaitre, then the photons that came to Earth from parts of the celestial sphere separated by an angular distance of more than two degrees were emitted from regions of space that then could not have anything in common with each other. Between them lay distances that light simply would not have had time to overcome during the entire existence of the Universe at that time - in other words, their cosmological horizons did not intersect. Therefore, they did not have the opportunity to establish thermal equilibrium with each other, which would almost exactly equalize their temperatures. But if these regions were not connected in the early moments of formation, how did they end up being almost equally heated? If this is a coincidence, it is too strange.

Now we should take one more step and understand the structure of our Universe. This work is underway, but is encountering enormous technical difficulties, and what the result will be is not yet clear. My colleagues and I have been working for the last two years on a family of hybrid models that rely on both superstrings and supergravity. There is progress; we are already able to describe many really existing things. For example, we are close to understanding why the vacuum energy density is now so low, which is only three times higher than the density of particles and radiation. But we need to move on. We look forward to the results of observations from the Planck space observatory, which measures the spectral characteristics of the cosmic microwave background radiation at very high resolution. It is possible that the readings from its instruments will put entire classes of inflation models under the knife and give impetus to the development of alternative theories.”

Inflationary cosmology boasts many remarkable achievements. She predicted the flat geometry of our Universe long before astronomers and astrophysicists confirmed this fact. Until the end of the 1990s, it was believed that with full consideration of all matter in the Universe, the numerical value of the parameter does not exceed 1/3. It took the discovery of dark energy to make sure that this value is practically equal to unity, as follows from the inflationary scenario. Fluctuations in the temperature of the cosmic microwave background radiation were predicted and their spectrum was calculated in advance. There are many similar examples. Attempts to refute the inflation theory have been made repeatedly, but no one has succeeded. In addition, according to Andrei Linde, in recent years the concept of a plurality of universes has emerged, the formation of which can well be called a scientific revolution: “Despite its incompleteness, it is becoming part of the culture of a new generation of physicists and cosmologists.”

On par with evolution

“The inflationary paradigm is now implemented in many variants, among which there is no recognized leader,” says Alexander Vilenkin, director of the Institute of Cosmology at Tufts University. - There are many models, but no one knows which one is correct. Therefore, I would not talk about any dramatic progress achieved in recent years. Yes, and there are still enough difficulties. For example, it is not entirely clear how to compare the probabilities of events predicted by a particular model. In an eternal universe, any event must occur countless times. So to calculate probabilities you need to compare infinities, and this is very difficult. There is also the unresolved problem of the onset of inflation. Most likely, you cannot do without it, but it is not yet clear how to get to it. And yet the inflationary picture of the world has no serious competitors. I would compare it with Darwin's theory, which at first also had many inconsistencies. However, she never had an alternative, and in the end she won the recognition of scientists. It seems to me that the concept of cosmological inflation will cope perfectly with all the difficulties.”

The theory, which is the basis of all modern cosmology, may contain deep contradictions. A universe without an inflationary stage? The concept of the rapid inflation of the early Universe (marked in yellow) in the era following the Big Bang may be revised.

About 30 years ago, Alan Guth, while still a PhD candidate, gave a series of seminars at the Stanford Accelerator Center in which he introduced the word “inflation” into the lexicon of cosmology. This term refers to the era of rapid exponential expansion of the Universe, which took place in the early stages of its development, in the first moments after the Big Bang. One of Guth's seminars took place at Harvard, where he made a strong impression on many specialists in the field of astrophysics, relativity and particle physics, including the author of this article, also then a young and enthusiastic candidate of science. The modern theory of inflation is one of the areas of the most active activity of cosmologists and a source of interesting discoveries and theories.

BASIC POINTS

The idea of ​​cosmological inflation is so deeply rooted in the minds of scientists that it is accepted as proven. According to this concept, the early Universe underwent a sharp exponential expansion, which determined the global homogeneity and flatness of our modern world.

However, the founders and some developers of inflation theory believe that the concept may be inherently flawed. For inflation to begin, the Universe must have unlikely conditions. Moreover, inflation goes on forever, producing an infinite number of different worlds, which implies that this theory cannot produce accurate predictions.

There is active scientific debate. The proposals range from amendments to the theory of inflation to replacing it with another concept.

The rational basis of the inflation theory is to identify weak sides in the Big Bang theory. The main idea of ​​the Big Bang model is that our Universe is slowly expanding (decelerating) and cooling from the moment of its birth, i.e. approximately 13.7 billion years. This process of expansion and cooling can explain many details in the structure of the present-day Universe, if it began its evolution under strictly defined conditions. One of the most important of them is that our Universe should have been almost completely homogeneous - with the exception of very small inhomogeneities in mass and energy. Besides. The universe had to be geometrically flat (three-dimensional Euclidean - Translator's note), which means that light rays and the paths of moving objects were not bent by the fabric of space-time.

But why was the early Universe so uniform and flat? Such special initial conditions seem very unlikely. Reasoning about this problem gave rise to Guth's concept. Even if the Universe at the very beginning of its existence had large inhomogeneities of masses and energies, then the subsequent sharp exponential expansion could smooth them out. After the end of the inflationary period, the Universe could continue to expand by inertia, in full agreement with the Big Bang theory and already possessing necessary conditions for the formation of stars and galaxies, in order to develop, to give rise to the state we observe today.

The proposed idea was so simple and tempting that scientists around the world perceived it as practically already proven. However, over the almost 30-year period of its development, the theory of inflation has undergone changes. Along with her supporters, her opponents also appeared. Most take the theory of inflation as a starting point for their own research, not caring about the fundamental justification of this theory and hoping that its apparent contradictions will soon be resolved. However, the problems of inflation theory stubbornly continue to resist all the efforts of the scientific community.

The author of this article, who has contributed to the development of both the theory of inflation and its competing theories, will try to give some objective assessment of the state of inflation theory today, giving arguments for and against it.

In defense of the theory of cosmological inflation

The theory of cosmological inflation is so well known that it makes sense to dwell only on some of its features and important details. Inflation is generated by a special type of inflationary energy, which, together with gravitational forces, caused the early Universe to expand rapidly in a very short period of time. The extremely high density of inflationary energy has an unusual property - it practically does not change during expansion. Its most amazing property is that the gravitational field of inflationary energy does not have attraction, but repulsion, which determines such a rapid expansion of our world.

Many sources of such inflationary energy can be proposed. The main version is the existence of a certain scalar field, in the case of inflation called “inflaton”. Scalar fields are widely known in particle physics: for example, the famous Higgs boson, which they are trying to obtain at the Large Hadron Collider at CERN, is the carrier of one of the scalar fields predicted by the theory.

CLASSIC DESCRIPTION OF THE THEORY OF INFLATION: THE LATEST GROWTH Spurt

According to astronomical observations, our Universe has been expanding for 13.7 billion years. But what happened in the early Universe, still inaccessible to our observations, in the first moments after its birth? The main theory describing this earliest stage is the theory of cosmological inflation. During inflation, the Universe expands exponentially and sharply increases in size. Such a rapid expansion can almost completely smooth out all previously existing inhomogeneities in space-time and, thus, well explain the Universe observed today. Small inhomogeneities remaining after the inflationary stage served as the basis for the formation of stars and galaxies

Like all fields, the inflaton field has a certain intensity at every point in space-time. This tension determines how the inflaton interacts with other fields. During the inflationary expansion phase, the inflaton field strength is almost constant throughout. Depending on the strength of this field, it has a certain amount of potential energy. The relationship between field strength and energy can be illustrated by a graph, which for the inflaton field is a curve: first almost horizontal (plateau), then bending down and rising again. If the initial field strength takes on a value that belongs to a plateau, then as you move along the curve, the field strength and energy will fall. The equations for the evolution of the field are the same as the equations for the motion of a ball rolling down a slope into a hole; slope profile - potential energy curve.

Potential energy of the inflaton field - possible reason accelerated expansion of our Universe. In the process of such expansion, the inhomogeneities in the distribution of matter in the Universe are smoothed out, and it becomes flat. For a time equal to $10^(-33)$, the field maintains a constant value, and the Universe manages to “inflate” $10^(25)$ times in all directions. The stage of inflationary expansion ends when the magnitude of the inflaton field moves from the horizontal part of the curve to the inclined one. As the field “rolls”, its energy decreases. At the bottom point of such a roll-off, all the potential energy of the inflaton field transforms into forms of energy familiar to us: dark matter, ordinary matter with high kinetic energy, and radiation that fill the modern Universe, which enters the stage of expansion due to inertia. At this stage, a large-scale structure is formed.

NOT VERY GOOD

It is believed that inflation created a huge space in which the structures observed today naturally arise. However, if the inflation energy curve does not have a very characteristic profile (obtained by fitting one or many model parameters, further denoted by lambda), then the result of such inflation may be “bad”, i.e. As a result, a very large volume of space may receive too high an energy density, hence the distribution of galaxies that does not correspond to observations. Looking through all possible values ​​of $\lambda$, scientists concluded that “bad inflation” is more likely than “good”

Inflation smooths out initial irregularities, but not completely. Due to quantum effects, small inhomogeneities are preserved. According to the laws of quantum physics, the inflaton field cannot have the same intensity everywhere in space; there are random fluctuations of this field. Their presence leads to the fact that the stage of inflationary expansion ends in different parts The universe does not appear at the same time, and the temperature of different regions of the universe also varies slightly. These inhomogeneities served as the seeds for the formation of stars and galaxies - in an absolutely homogeneous Universe no structures could have formed. A prediction of inflation theory is that such discontinuities exhibit scale invariance. In other words, they do not depend on the size of the areas in which they are formed; they are the same at all scales.

The concept of inflation can be briefly formulated in three main points. First, inflation is inevitable. Since Guth's time, numerous studies in theoretical physics have only strengthened scientists in the idea of ​​the existence of scalar fields in the early Universe that were “responsible” for inflationary expansion. A huge number of such fields appear in all sorts of options theories of unification of all physical interactions, for example in superstring theories. It is believed that in the chaotic early Universe, at least one of these fields would have to have the conditions necessary for inflation.

IT HAD TO BE THIS WAY

It is believed that inflation occurs regardless of the initial conditions in which the Universe was located. Recent theoretical studies have shown otherwise. Of all the possible initial conditions, only a tiny fraction could lead to the homogeneous, flat Universe we observe. The overwhelming majority of the latter do not require the inflation stage to implement the indicated observed conditions. Thus, an insignificantly small part of all possible initial conditions for the development of the Universe leads to a homogeneous and flat world through inflationary expansion

Secondly, the inflation hypothesis can explain the observed homogeneity and flatness of the modern Universe. Nobody knows which ones exactly geometric parameters and what degree of homogeneity the Universe had immediately after the Big Bang. Inflation has made these issues irrelevant, since whatever the initial conditions, inflationary expansion can smooth them out in a manner consistent with observations. Third, and the strongest argument, the inflation hypothesis predicts observations well. For example, a large number of observations of the cosmic microwave background (CMB) and data on the distribution of galaxies confirm that spatial variations in the energy of the early Universe were practically scale-invariant.

Against the theory of cosmological inflation

The first signals that all is not well with the inflation theory are small differences between the predictions of this theory and actual observational data. The existence of differences undermines the very logical basis of the entire theory. Does the theory really work in perfect accordance with observational data, as was stated in the 80s? last century? Can the predictions of the inflation theory of those years be regarded as predictions of the modern theory of inflation? The answer to both of these questions is: no.

Let us give the reasoning for such answers. Consider the statement that the inflationary stage in the Universe is inevitable. If this is indeed the case, then a logical thought arises: after all, the realization of “bad inflation” is more likely than “good inflation”. By the first term we will understand such a period of accelerated expansion of the early Universe, whose consequences in the modern Universe are in clear contradiction with observational data. For example, too large variations in temperature are unacceptable. For a theory to agree well with observational data, the differences, for example, between “good” and “bad” theoretical values ​​on the exact observational potential energy curve must be very small. Theoretical values ​​are controlled large set model parameters. In a typical inflation model, this difference should be about $10^(-15) - zero with 15 decimal places. A worse-fitting inflation model, zero with 12, or ten, or eight decimal places, may already be “bad inflation,” in which the rate of acceleration is the same (or greater), but the temperature differences are greater than observed.

We can ignore the problems with “bad inflation” models since they are clearly incompatible with, for example, the origin of life in the Universe. In other words, even if large temperature changes may occur somewhere, we will still never be able to observe them. An appeal to such reasoning is generated by the so-called anthropic principle. However, in this case such arguments are not applicable. Larger temperature differences could affect more stars and galaxies, and the Universe could be more populated than observed. Indirect consequences tell us that there were no large temperature differences in the Universe after all.

Not only is “bad inflation” more likely than “good inflation,” but a world without inflation is more likely than a world with any inflation. This idea was first expressed by Roger Penrose in the 80s. last century. The scientist applied thermodynamic principles, similar to those intended to describe the configurations of atoms and molecules of gas, to calculate all possible initial configurations of the inflaton field and gravitational fields. Some of these initial data lead to the presence of inflationary expansion with the formation of an almost uniform distribution of matter in flat space-time. Other initial conditions lead to a homogeneous and flat universe - without inflationary expansion. Moreover, both sets of such initial conditions are small - in other words, the chances of getting a flat, homogeneous universe are small in any case. Also, getting a flat universe without inflation is much more likely than getting a flat universe through inflationary expansion.

Risk of eternal inflation

Another method of studying the early Universe, which leads to similar results, is based on extrapolating the history of the Universe from its present state back in time using known physical laws. The results of this method may vary, i.e. extrapolation is not the only one: taking as initial conditions the modern Universe, flat and homogeneous on average, we can obtain different chains of events in the past. According to modeling carried out in 2008 by Gary Gibbons of Cambridge and Neil Turok of the Institute for Theoretical Physics in Ontario, the vast majority of event sequences extrapolated into the past do not have an inflationary stage, which is consistent with Penrose's findings. On the one hand, both scenarios for the possible development of our Universe without inflation seem to go against intuition, because a flat and smoothed Universe is unlikely, and inflation is exactly the mechanism that is necessary for the implementation of such a state. On the other hand, these advantages of inflation turn out to be greatly undermined by its own unlikely initial conditions. Thus, if we take into account as much as possible all the factors available to us, it turns out that the Universe more likely came to its current state without an inflationary stage.

Many physicists and cosmologists consider these arguments to be untenable. Real observations and experiments are always more powerful than any theoretical reasoning, and the version of the inflationary theory formulated in the 1980s is in accordance with today's cosmological observations. However, the first versions of the inflationary theory were imperfect in many ways, providing scientists with, by and large, only a qualitative picture of the expansion of the Universe, and to today Inflation models have been revised several times. Which model ultimately fits best with the observational data?

A change in worldview came after Andrei Linde introduced the concept of “eternal inflation” into cosmology - once it begins, it will never end. This concept is based on the combination of the laws of quantum physics and the laws of the accelerated expansion of the Universe. When inflation comes to an end, quantum fluctuations lag a little. If in some region of space such fluctuations are small enough, then inflation in this region ends. However, since fluctuations are random, there will be areas where fluctuations are large enough to introduce a significant delay in the end of the inflationary stage. The latter areas are extremely rare, so the reader may wonder if they should be ignored altogether. The answer is no, because these areas expand inflationarily, continue to grow rapidly and in a matter of moments stop the expansion of those areas in which inflation has already ended. The result is a gigantic expanse of inflationary-expanding world, in which tiny islands float, filled with hot matter and radiation. Moreover, inflationary growing areas give rise to inflationary growing areas, each of which represents its own own world, a closed universe. If you are not yet confused by this picture, don't worry, it will get worse.

The islands of matter are not the same. According to the laws of quantum theory, some of them are very heterogeneous, others, on the contrary, are too smooth. The heterogeneity is similar to the “bad inflation” scenario mentioned above, but the reasons for the appearance of such heterogeneities are different. “Bad inflation” occurs because the parameters that control the shape of the potential energy curve are too large. Now, heterogeneity can arise due to eternal inflation and random quantum fluctuations, regardless of the values ​​of the parameters describing the model.

For more accurate quantitative estimates the word "some" should be replaced with "infinite number". In a world with eternal inflation, an infinite number of islands will have the properties that we observe, but an infinite number will not have them. This idea was well formulated by the creator of inflation theory, Alan Guth: “In a world with eternal inflation, everything that can happen happens, and happens an infinite number of times.”

Is our Universe the rule or the exception? With an infinite number of islands, each of which is a separate universe, this question is difficult to answer. Imagine that you have a box containing white and black balls, and you take them out one at a time. If you know how many white and how many black balls there were initially, then you can always definitely say which one you are more likely to draw. However, if there is an infinite number of them, then the situation changes dramatically. So, when you take out the balls, you can sort them so that one black corresponds to one white, and then it will seem to you that there are equal numbers of both in the box. But you can sort them so that there are ten white balls per black ball - and then your intuition will tell you that there are more white balls. Set theory gives the answer that in the case of comparing two infinities, both assumptions are false. Thus, it is impossible to say which ball will be more likely to appear. For this reason, it is impossible to guess which universe would be the most likely, “typical” one. Now is the time to really confuse you. What does it mean to say that inflation theory makes accurate predictions - for example, that our Universe is homogeneous or that it has scale-invariant fluctuations - since everything that should happen will still happen someday and will happen an infinite number of times? And if a theory does not make testable predictions, how can cosmologists claim that the theory agrees with observations, which they have consistently done until now?

The measure of our mistakes

Theorists suspect such problems, but despite a quarter of a century of active work since the advent of the theory of inflation, scientists have not lost hope of solving all the problems and preserving this fruitful concept.

Theories alternative to eternal inflation are proposed - for example, to completely deprive the evolution of the universe of any infinities. However, infinity is a natural consequence of inflation and quantum physics. To avoid infinities, the model of the Universe must be very sensitive to the initial special conditions, and the field that generates inflation has a special equation of state. Inflation must occur in such a way that it ends everywhere in space before quantum fluctuations have a chance to continue it. However, such requirements violate the very concept of inflation, which is poorly sensitive to the conditions that existed before it began.

THE ABYSS OF INFINITY

The theory of inflation is believed to make accurate predictions about the structure of our Universe, confirmed by observations. Is this really true? Once started, inflation continues due to the evolution of quantum fluctuations. As soon as inflation ends, a closed world like ours is born, which continues to expand. Our world is not typical; there are a large number of younger universes. In fact, an infinite number of worlds with an infinite variety of properties are formed. Everything that can be realized is realized in one of the worlds. A theory that predicts everything predicts nothing

Another alternative strategy implies that islands of matter and radiation similar to our Universe act as the most preferable outcome of inflation. Defenders of this model introduce the so-called measure, a special rule according to which each world has a probabilistic weight that determines which of them is preferable. The analogy with black and white balls is such that we are obliged, for example, for every three white balls to take five black balls. The concept of a measure is an unfounded assumption that inflation itself does not explain or predict anything.

Worse, measures that are theoretically equivalent lead to different conclusions. For example, a volume measure according to which island universes should have a probability weight according to their size. At first glance, this parameter is reasonable. The intuitive idea behind inflation is that inflationary expansion explains the observed homogeneity and flatness by creating extra-large volumes of space. Unfortunately, the introduction of such a volume measure is erroneous. Indeed, imagine two types of regions: island universes like ours, and other islands that formed later, after inflation increased. Based on the rate of exponential growth, later areas will occupy significantly larger volumes. Thus, younger universes than ours are most preferable. According to the volume measure, the birth of our Universe turns out to be very unlikely.

Enthusiasts of using measures do not give up: before using the measures they come up with, they test them so that as a result the probability of the formation of our Universe would become acceptably large. Even if one day success will be achieved. However, then you will have to introduce another principle to check why this measure is preferable to all others, then the next principle to choose such a principle, etc.

An alternative approach is to invoke the anthropic principle. When choosing a measure, it is assumed that our Universe is a typical island in an inflationary sea. The anthropic principle, on the contrary, believes that we live in a very atypical world that has minimal conditions for the existence of life. The meaning of the anthropic principle is that the conditions in all typical island universes are incompatible with the formation of galaxies, stars or other structures that are necessary for the origin of life. Even if typical island universes occupy much larger volumes than worlds like ours, they should be ignored, because we are only interested in those areas that can be inhabited by humans. Unfortunately, within the framework of this idea, the conditions in our Universe for human habitation should be at least minimally favorable, but this is not the case: our Universe is flatter, smoother and scale-invariant than is required for life. More typical islands, such as those younger than our world, are almost equally habitable and much more numerous.

Let those who hesitate pay

In light of the proposed arguments, the idea that observational data in cosmology tests the basic predictions of inflationary theory is erroneous. All we can say is that modern observational evidence confirms the predictions of the simplest inflationary model proposed in 1983, but this theory is not the same as modern inflationary cosmology. The simplest theory suggests that inflation, based only on classical physics, predicts the evolution of the Universe. However, the correct picture is that inflation is formed according to the laws of quantum physics and everything that can happen, happens. But if inflation theory cannot make accurate predictions, what is its point?

The problem is that the regime of postponing the end of inflation is not only not “unprofitable”, but on the contrary, it is even preferable. Areas in which the end of the inflationary stage is delayed continue accelerated exponential expansion. In an ideal situation, any such area will expand slowly or even contract. The remainder of space would then consist of regions where inflation had ended, and thus our observable Universe would be one of them.

As an alternative to inflationary cosmology, the author of the article and his colleagues proposed a theory called cyclic. According to this theory, the Big Bang is not the beginning of space and time (see: Veneziano G. The Myth of the Beginning of Time, VMN, No. 8, 2004), but only a “rebound” of the previous compression phase during the transition to a new expansion phase, accompanied by the birth substances and radiation. The theory is cyclical, because after billions of years the Universe will contract again and there will be a new rebound. The key idea of ​​this theory is that smoothing occurred before the Big Bang, during the compression era of the previous phase. All lagging regions continue to contract, while other regions are already rebounding and beginning to expand - thus, the first regions are relatively small and can be neglected.

Compression smoothing has observational implications. During any smooth phase, whether inflationary or cyclic, quantum fluctuations generate small, randomly propagated distortions of spacetime known as cosmological gravitational waves, which can leave a trace in the anisotropy of the background microwave background radiation. The amplitude of these waves is proportional to the energy density. Inflation could begin when the Universe was at its maximum density, and the equivalent process in a cyclic Universe could occur when the Universe was practically empty - so the predicted observational signatures of the two theories should be significantly different. Of course, cyclical theory is relatively new and may have many of its own problems, but it shows that in principle there are alternatives that do not have the problems of eternal inflation.

So, the arguments for and against the theory of inflation have been presented. Some scholars believe that the arguments against it undermine its foundations and that it requires radical revision. Others believe that only refinement of the original theory of inflation is required.

The final decision on the fate of inflation theory will be given by the results of observations. In the next few years, data on gravitational waves obtained from studies of the anisotropy of the cosmic microwave background radiation will be made public: the detection of gravitational waves could support the theory of inflation. Many researchers are gravitating toward alternative concepts like cyclic theory, which predicts an unobservably small signal from gravitational waves. The future will show which theory is correct and what fate awaits our Universe.

Paul Steinhardt - director of the Center for Theoretical Science at Princeton, member of the National Academy of Sciences, winner of the. P. Dirac (2002) for his contribution to the development of the theory of cosmological inflation.

ADDITIONAL LITERATURE

1. The Inflationary Universe. Alan
   Guth. Basic Books, 1998.
2. Quantum Cosmology, Inflation, and the Anthropic Principle. Andrei Lindc in Science and Ultimate Reality: Quantum Theory, Cosmology and Complexity. Edited by John D. Barrow, Paul C.W. Davies and Charles L. Harper, Jr. Cambridge University Press, 2004.
3. Endless Universe: Beyond the Big Bang. Paul J. Steinhardt and Neil Turok. Doubleday, 2007.
4. The Measure Problem in Cosmology. G.W. Gibbons and Neil Tbrok in Physical Review D, Vol. 77, No. 6, Paper No. 063516; March 2008.
5. The Birth of the Universe // VMN, No. 7, 2005.

Epigraph:
And the whole world is not enough!

I bet that among those reading these lines there is not a single person who has never heard of the Big Bang theory in their life. I admit that there are similar characters on Earth - a peasant from an abandoned village in the mountains of Tibet, a native of the Tonga-Tonga tribe, a Mormon from Utah, they probably exist somewhere. However, if you know how to read, have access to the Internet and were able, even by chance, to visit this blog, I can guarantee that you have definitely heard at least something about the Big Bang theory.

In this post I will talk about the current scientific understanding of this theory, the text is rather long, but I promise that today you will learn something new, something that you didn’t know before and didn’t even think about.

First of all, it’s funny, but few people have thought about what, exactly, the Big Bang theory is? Try right now to spin the facts in your head that you know about it, and then I will explain how it sounds In fact.

Have you tried it? Well, another 20 seconds to think...

So. The Big Bang theory states that our Universe used to be small and hot, but since then it has been expanding and cooling. Dot. There is nothing more in this theory, don’t invent too much.

Surprisingly, the classical theory of the Big Bang lacks the most important thing - there is no Big Bang itself. Nowhere is it mentioned what kind of “explosion” it was, what exploded there, where it exploded, how or why.

Following the main thesis that "at first our Universe was small and hot", you can mentally stretch it even further (although I draw your attention to the fact that this is NOT the Big Bang theory anymore, these are precisely attempts to stretch the boundaries of applicability into the realm of guesswork and fantasy) and come to the assumption that even earlier the entire universe was gathered into one point called singularity point, which later exploded for some internal reasons.

Let me note that the Big Bang theory (“the Universe was small and hot before, and then it became big and cold”) is not today theory, as such. We can consider this to be quite scientifically established. fact, confirmed by a huge number of observations, today there is not a single scientist worth his salt who doubts it. But regarding the point of singularity (which, I repeat, lies outside the limits of applicability of the Big Bang theory), scientists not only do not have a common opinion, they have no opinion at all.

Nobody has any the slightest idea what is this "singularity". Singularity is generally a placeholder (a substitute word) for the phrase “I don’t know.” That is, to the question “Are classes P and NP equal?”, or “Is Schrödinger’s cat alive?”, or even “What does the clap of one hand sound like?” You can safely answer “Singularity!”
You can't go wrong.

The Big Bang theory was formulated in the 20s of the last century, and since then, for a whole century, scientists have been doing nothing but trying to understand what the essence of the singularity is, and is it possible to somehow get rid of it?

The main problem of the singularity is that natural division by zero occurs in it, and in the most literal sense. All formulas turn into nonsense, 3 becomes equal to 5, and one infinity begins to creep onto another. And this is the end of physics, the end of science, only dragons-EGGOGs live on, and somewhere from the folds of space the Almighty himself winks sarcastically.

Many different methods, approaches and tricks have been proposed to replace the singularity; the best one so far was done by the American physicist Alan Guth in 1981. As always, let me remind you once again that science is a collective matter. Gut, like all his predecessors, climbed onto the shoulders of giants, but in this short text on your fingers™ I will not list all predecessors, colleagues and opponents, I will mention only one name that deserves it - Alexey Starobinsky, who expressed similar ideas earlier, but the glory of the discoverer was assigned to Alan Gut.

Gut suggested making a clever feint with his ears. Watch your hands and ears carefully, now I will show you a trick. Let's mentally(!) Let’s take the word “singularity” out of all the texts and put the phrase “scalar field” in its place. Please note that at this stage nothing has changed, the term “scalar field” continues to be a complete analogue of () “singularity”, which in turn, as we remember, is only a substitute for the phrase “I don’t know”.

What kind of “scalar field” is this, what are its characteristics, where did it come from, what the hell is going on - there are still no answers. As long as the “scalar field”, or as it is also called in English tradition The “inflaton field” (because “inflation” is the same) is just the result of a thought experiment in attempts to escape from the singularity and come to something else. So far this is nothing more than replacing sewing with soap. But let's be real scientists, let's bring our thought experiment to the end, and see what happens in the end.

So, according to Guth, the original proto-Universe was formless and empty, there was nothing in it and nothing happened, it was infinite, or at least very, very, very large, much larger than the modern one Observable Universe, and all of it was filled with this very thing scalar field, about which we know nothing, except that it is some kind of field, and that, as is clear from the name, it is scalar.

I won’t burden the reader with the definition of “scalar”, it’s not particularly necessary within the framework of this post, it’s quite simple and on your fingers™ we can assume that this field contains some "tension". The field carries a certain energy, just as a thundercloud carries water ready to rain.

How is this situation better than the previous one with a singularity from the point of view of physics? Yes to everyone! Even if we don’t know a single characteristic of this field, even if we have no idea what kind of tension there was and where it came from, but this is not division by zero! Now we have a solvable problem, we can start writing some formulas (you understand, don’t feed a real scientist honey, just let him screw up some three-story formulas), into which it is possible to substitute initial conditions and coefficients, divide and multiply, calculate what result in the end, and then compare with the results of direct observations and experiments.

Yes, it sounds funny and even somehow stupid, a natural “fuck,” but it turned out to be a real breakthrough. This is a step forward from the total "I don't know" written on concrete wall, this is already a serious application for success, for a detour, for a dig, or at least for a ladder.

However, the funny thing is that Alan Guth’s scalar field trick was a success, but the formulas just didn’t work out. Alan brought the idea of ​​a scalar field and its inflation to science (more on the inflation mechanism a little later), but he was unable to correctly describe his thoughts in the dry language of mathematics. The ranks diverged, everything again began to divide by zero, in short, a complete failure.

And only a year later, the dimmed torch of the inflation model was raised high by Andrei Linde, a Soviet scientist temporarily residing in the United States and heading the department of physics at Stanford University.

He corrected the errors of Alan Guth’s theory, made the formulas converge and give predictable and testable results, but along the way he opened a real Pandora’s box, which I will mention at the very end of the post, I’ll leave it for dessert.

The essence of the inflationary model of the Universe (in short, figuratively and vaguely) is as follows:

We remember that the proto-Universe, the predecessor of our Universe, was filled with a certain scalar field, about which we know nothing except the presence of the field itself and its “scalarity”. Scalar, not scalar, but the principles of quantum mechanics have not been canceled! It has been a hundred years since anyone, including Albert Einstein himself, has ever succeeded in mastering the principles of quantum mechanics. Which means that even if this field was initially homogeneous (and it, in principle, does not have to be initially homogeneous), still, over time, under the influence of quantum fluctuations, small inhomogeneities will appear in it, which, according to the instructions of His Majesty the Quantum Case, can overlap each other, forming large heterogeneities.

Well, large by quantum standards. All the same, this is still milli-milli-milli-...(and another 10 times milli-) Joules, meters and kilograms, we are not talking about any of our Universe, with trillions of stars and galaxies.

And here suddenly It turns out that our field is not just any, but a very tricky one! In an ordinary field, in which there is no friction, inhomogeneities simply come sooner or later" close up and shorten"to ourselves. For example, let's take a well-known and understandable electromagnetic field. If a potential difference has arisen somewhere, which continues to increase, then sooner or later, it will definitely short-circuit. A discharge will run, a mini-spark will appear (or mega-lightning, if the potential difference was as big as a thunderstorm) and the heterogeneity is leveled out.

By the way, first of all, attentive reader with asterisk(*), here I must state that the electromagnetic field is not a scalar field, but just the opposite - a vector field, and a very confusing one at that. But in this specific example This doesn't matter at all. In both fields the shortening is almost the same, according to the same scenario. Well, and secondly, it cannot be said that it will definitely shorten immediately; charges can accumulate over years and even millions of years. It all depends on a thousand different conditions, but if you wait long enough (for example, forever), then short circuit inhomogeneities will definitely happen. Naturally, this is all nothing more than an analogy, and at this point it’s not very direct, I’m just trying on fingers™ explain the behavior of an incomprehensible scalar field using the example of an understandable electromagnetic field.

So, in the electromagnetic field virtually no friction, so to speak. Electrons have a finite speed of movement and they experience direct resistance from the medium, which we call electric current resistance, but field changes are transmitted at the speed of the electromagnetic field itself, i.e. at the speed of light. If we stray too far from the topic, then reader with two stars (**) should know that even complete and absolute vacuum has some analogue of “resistance” to electromagnetic waves, but this is already a very deep jungle of the Casimir force and other effects of vacuum fluctuations, we should not go deeper there yet, even though such posts are from the series on fingers™ are planned for the unknown but foreseeable future.

In short, we can say that the electromagnetic field has no internal friction, or it is negligible. Well, it was short and short in the blink of an eye. If we apply analogy to analogy, we can say that the closure of the electromagnetic field is like a mountain located in an area of ​​​​high potential on which the ball lies, and an area of ​​low potential is a hole under the mountain where this ball will eventually fall. Since there is almost no friction, the ball rushes down at full speed, practically at the speed of light. Bam, and fell.

When falling, some energy will certainly be released, which will be used to heat the surrounding space, the ground and the ball. In the case of an electromagnetic field, a natural discharge of the field occurs, i.e. lightning. If this happened under water (and electrical discharges can short-circuit even under water), then a tiny air bubble will form in this place when the water breaks down into its constituent oxygen and hydrogen. The discharge is literally lightning fast, the potential difference drops quickly, the air bubble is very small.

Now let's return to our hypothetical scalar field. Since it is still hypothetical, you can fantasize about it and its properties as you like. Let us assume that there is internal friction in this field and it is very large. Very, very big. Shifting to the analogy with a ball, it will fall from a mountain not in a vacuum or air, but in a very viscous and viscous liquid, for example in sunflower oil or honey.

Therefore, the force of gravity pulls the ball down, and the force of friction prevents it from falling quickly and pulls it back up. And instead of rapidly rushing to the bottom (and we remember that this is only an analogy of how quickly uneven field strength discharges), the ball smoothly, at almost constant speed, i.e. goes down almost evenly. The rarefaction of the scalar field is responsible for the creation of a vacuum, i.e. of our native space-time, the drop in its potential seems to inflate balloon, only instead of air there is a vacuum, and instead of a ball there is our Universe. If everything happened without friction, the intensity of the scalar field would drop very quickly and we would end up with a small bubble of vacuum in the huge boundless ocean of the proto-Universe. But friction (and in fact the scalar field itself) does not allow the tension to fall quickly, it interferes with pulls itself back. Because of this, while the tension slowly decreases, the “inflating force”, i.e., actually stands still. the force that expands the resulting vacuum in all directions remains constant and continues to pump with the same effort, despite the fact that the size of the newborn Universe is increasing and increasing.

Scientists know, and you can take my word for it, or you can check and google it, that in this case we get an equation whose solution is an exponential. Those. it turns out natural exponential expansion of the universe. Billions of billions of billions of times. In a not very long, very short period of time. It all depends on what coefficients are included in the exponential, i.e. what was the initial intensity of the scalar field, what was the friction force, etc.

Calculations show that if the “expansion force” does not fall with time, in some 10–36 fractions of a second the new Universe in the heat of the day (i.e., this initial vacuum bubble) can expand 10 26 times. Yes, this exceeds the speed of light by many orders of magnitude, but there is no paradox here. The theory of relativity prohibits any matter from moving in space faster than the speed of light, but does not at all prohibit space itself (i.e., emptiness) from expanding laterally at any speed.

It turns out that there was no Big Bang as an “explosion” at all. There was a fast, very fast, explosive or exponentially fast “inflation and expansion” of the bubble of our Universe, exactly that inflation, from English word inflate- “pump up”, “inflate”.

But here is a tricky moment! The vacuum expands, i.e. absolute emptiness, where did all the energy and matter that now makes up all our stars, galaxies and other content of modern space come from? And why was the Universe hot before, why should there be a hot, empty vacuum or something?

Here again there is a complex piece of crap with tooth-crushing formulas, I’ll try to explain it using what do you think? Analogies on your fingers™, Well, of course!

You know that if something expands very quickly in our country, then this something also rapidly loses energy, in the sense that it spreads it just as quickly throughout the entire expanding volume, and at each individual point or cubic meter of space the energy becomes less and less less. This is not a lot of bullshit, this is, by the way, the first law of thermodynamics!

With us it turns out the other way around. If you stretch a bubble of the Universe very quickly, it will begin instantly accumulate energy. After all, gravitational energy always comes with a minus sign. If you separate two bodies in space, or, say, lift a heavy load above the surface of the Earth, the potential, and therefore the total energy of the system will increase! And since everything happens quickly (let me remind you, very, very, very... and 26 more times very quickly), then in the case of some gas, for example air, it cools sharply, forms fog and water vapor in it precipitates to form natural snow or ice. Everyone has seen that if you open the valve of a liquefied gas cylinder, the cylinder immediately becomes covered with frost.

But in the case of the Universe, on the contrary, the temperature rises sharply, a phase transition occurs and the released energy “precipitates” in the form of energy itself (photons) and matter (electrons, protons and other elementary particles). This is why, at the end of inflation, which started out not so hot, the Universe quickly warms up to limitless energies and temperatures that were previously thought to burst out directly from the singularity point. And then when the ball reached the bottom of the hole and the period of exponential expansion is over, everything continues according to the old scenario of the classical Big Bang, the Universe is expanding, but no longer exponentially, but slowly, by inertia. But now all this comes out without the Big Bang itself and its singularity.

It sounds unusual, it sounds like some kind of deception, but if you think about it, everything is logical - the increased potential energy, the gravitational energy with a minus sign, is exactly compensated by the kinetic energy, the energy of motion (temperature) and the rest energy (mass) of the “precipitated” particles of matter. The total energy of the Universe remains equal to zero, minus one hundred and plus one hundred results in zero. Like minus a billion and plus a billion.

To be completely precise, the result there is not exactly exactly zero, because the intensity of the original scalar field, from which it all began, did drop to almost zero in this place. But the absolute value of this fall, some fractions of Joule ( or how do we measure the field strength of inflatons?), still remains within the limits of albeit large, but still quantum effects. This cannot be compared with trillions to billions (more precisely, 10 50 and so on) kilograms of newly formed matter and the same orders of magnitude of stored gravitational energy. The mouse gave birth to a mountain, in the truest sense of the word. More precisely, a mountain and a hole nearby for balance.

Once again, for clarity, I will repeat the previous paragraph in slightly different words. When, as a result of a drop in the intensity of the scalar field, a small bubble of our space-time appeared in it, i.e. ordinary vacuum, this space-time turns out to be “a little bent.” Why? Because this is how any energy affects space. Newton thought there was gravity force attraction of two masses. And Einstein said that gravity is only bendability space. If the space is “bent”, some kind of gravitational energy is already stored in it, even if this space is absolutely empty and there is no mass in it. Why is space oppressing us? It is oppressed by energy (more correctly, the energy-momentum tensor). Mass is also energy, a lot of energy, but you can do without mass at all; in general, any energy bends space. When, under the influence of a drop in the energy of the scalar field, a “small vacuum bubble is inflated,” it already contains the energy of the scalar field, the vacuum in it is already “bent.” If this bubble is quickly stretched to the sides, the gravitational energy will increase sharply, which will cause “precipitation” of mass, which, on the one hand, adds energy to the Universe (since E = mc 2) with a plus sign, and on the other hand, adds energy to the Universe the gravity of this mass has a minus sign, which means that the race-competition between the mountain and the mouse will continue.

Yes, I remind you, in case anyone has forgotten, that all this is happening as part of a thought experiment to get rid of the singularity! This is just mental gymnastics for now; there is not much of a smell of science here yet, although the thought experiment itself is a mandatory attribute scientific method. To rise in rank to even a hypothesis, let alone a theory, you need to go through a lot and explain a lot.

I repeat, we are still in the process of exchanging sewing for soap. We have not moved away from the incomprehensible initial singularity, we just called it a little differently and, as a result, stood upside down. However, specific details of the theory of inflationary expansion of the Universe, in contrast to the classical theory of the Big Bang, make it possible to find explanations for many observed phenomena (the problem of initial conditions, the problem of homogeneity and isotropy of the observable Universe, the problem of the plane of the observable Universe, the problem with magnetic monopoles and much more), before which the Big Bang singularity passed on. This makes the inflation model very attractive, but does not prove it at all and does not declare it correct. In the state of a “young and promising”, but “unproven and slightly fantastic” theory, the inflation model was in the 80s of the last century of the last millennium (I said that “30 years ago” in an intricate way), until in 2014 the first, all still timid, unconfirmed and very indirect evidence, in the sense experimental results confirming it. And here it’s no longer just an application, here it’s a real success!

What kind of experiments are these, what are their results, what are “gravitational waves”, how are they related to inflation and why is their discovery so important? Nobel Prize, which, I think, Alan Gut and Andrei Linda will be given in the end, as well as all other technical details are collected together and will be described separately, in the second part of this story, they deserve a full-fledged separate post. Here I have only outlined the essence of the inflation theory, stopping it at the stage of 2013 - interesting, tempting, but not confirmed by anything.

And now the promised sweets.

Yes, it is too early to say with firm certainty. Yes, all this is still very much written with a pitchfork, and does not necessarily have to be. Yes, there is still a long, long road of calculations, mistakes and experiments ahead, but...

The best part is that the inflation theory of Alan Guth, or rather the mathematical calculations of Andrei Linde, imply an absolutely wonderful and mind-blowing thing.

Linde's additions are officially called the "chaotic theory of inflation". Its central part, the very essence of the theory, says that these “discharges of the scalar field” are simply obliged chaotically, i.e. randomly, to happen anywhere and everywhere in the original proto-Universe. This means that our specific Big Bang (which, as we already know from the current post, was not an explosion at all), which led to the formation of our specific Universe, is only one discharge, a separate specific bubble of the resulting space, which we call our cosmos. And it’s not just “maybe”, but according to the formulas it’s downright “definitely” that there must be billions and billions of other bubbles, other universes floating around. In each of these universes (with a small letter), the scalar field fell/discharged a little differently, and therefore the laws of physics in these universes may differ significantly from ours. Stars and galaxies might not have formed there at all, or, on the contrary, things might have formed there that we had never even dreamed of in our wildest fantasies.

This entire conglomerate of inflating bubbles-universes is usually called multiverse, although Linde himself prefers to say “The Many-Faced Universe” in Russian. It turns out that the modern scientific understanding of the origin and structure of our world is now as follows:

There is an infinite or at least a very large multiverse filled with some kind of scalar field. How long it has existed, where it came from, what the conditions are in this multiverse - we have no idea. Even half a bump. But scientists are quite confident that in some places in this multiverse the scalar field begins to fall, inflating the bubbles of ordinary universes and forming the space-time familiar to us in them. Our particular bubble began to inflate about 13.8 billion years ago, and the scalar field in our Universe, by the way, has not gone anywhere, now it is almost at a minimum, but not equal to zero! What pushes the galaxies of our Universe to the sides, and what we call Dark Energy, is that very “scalar field”, more precisely, only a part of it. Here, by the way, there should be several paragraphs explaining that the long-searched Higgs field, formed by the seemingly recently discovered Higgs boson, is also a product of the scalar field, namely its grandson, because between the scalar and the Higgs there is, it should be more accurate, another super-Higgs field into which the scalar field degenerates and which in turn degenerates into the Higgs field. But this is not entirely proven, and is completely aside from our current conversation, so perhaps that’s enough about this.

Around The bubble of our Universe contains bubbles of other universes, which are formed from the fall of the scalar field in those specific places. Somewhere their own small town big Bang(also with a small letter) is just beginning, but somewhere everything has already ended a long time ago, and “between” these universes there is simply a scalar field in its high energy state. The multiverse becomes like Swiss cheese, where the cheese itself is a scalar field, and the holes in it are myriads and myriads of universes, one of which is ours.

Is it possible to drill tunnels through this scalar field to reach other "parallel" universes? Unknown.
How far is it from our bubble to the neighboring one, and is it possible to get there through higher dimensions? Unknown.
Do these other universes around ours really exist at all, or are they all just fantasies? It is unknown, but now there is very strong confidence in science.

Isn't it wonderful?

UPD: Read the continuation of the post in the article.