The Five Greatest Cosmic Inflation Predictions. Inflationary stage of the expansion of the universe

Inflationary model of the Universe(lat. inflatio "swelling") - a hypothesis about the physical state and law of the expansion of the Universe at the early stage of the Big Bang (at temperatures above 10 28 ), suggesting a period of accelerated expansion compared to the standard model of the hot Universe.

The first version of the theory was proposed in 1981 by Alan Gut, however, Soviet and ex-Soviet astrophysicists Aleksey Starobinsky, Andrey Linde, Vyacheslav Mukhanov and a number of others made a key contribution to its creation.

Disadvantages of the Hot Universe Model

where ρ (\displaystyle \rho ) is the average density of the universe.

The disadvantage of this model is the extremely high requirements for the homogeneity and isotropy of the initial state, the deviation from which leads to a number of problems.

The problem of large-scale homogeneity and isotropy of the Universe

The size of the observable region of the universe l 0 (\displaystyle l_(0)) coincides in order of magnitude with the Hubble distance r H = c / H 0 ≈ 10 28 (\displaystyle r_(H)=c/H_(0)\approx 10^(28)) see (where H- Hubble constant), that is, due to the finiteness of the speed of light and the finiteness of the age of the Universe, it is possible to observe only regions (and the objects and particles located in them) that are now at a distance from each other l ≤ l 0 (\displaystyle l\leq l_(0)). However, during the Planck era of the Big Bang, the distance between these particles was:

and the size of the causally connected area (horizon) was determined by the distance:

(Planck time ( t P l a n c k ≈ 10 − 43 (\displaystyle t_(\mathrm (Planck) )\approx 10^(-43)) sec), that is, in the volume l′ (\displaystyle l") contained ~10 90 such Planck regions, the causal relationship (interaction) between which was absent. The identity of the initial conditions in so many causally unrelated regions seems extremely unlikely. In addition, even in the later epochs of the Big Bang, the problem of the identity of the initial conditions in causally unrelated regions is not removed: for example, in the epoch of recombination, the now observed CMB photons coming to us from close directions (differing by arcseconds) should have interacted with regions of primary plasma, between which, according to the standard model of the hot Universe, a causal relationship did not have time to be established during the entire time of their existence from t P l a n c k . (\displaystyle t_(\mathrm (Planck) ).) Thus, one could expect a significant anisotropy of the cosmic microwave background radiation, but observations show that it is highly isotropic (deviations do not exceed ~10 −4).

The Flat Universe Problem

According to observational data, the average density of the universe ρ (\displaystyle \rho ) close to the so-called. critical density, at which the curvature of the space of the Universe is equal to zero. However, according to the calculated data, the density deviation ρ (\displaystyle \rho ) from critical density ρ c r i t (\displaystyle \rho _(\mathrm (crit) )) should increase with time, and in order to explain the observed spatial curvature of the Universe in the framework of the standard model of the hot Universe, one has to postulate the density deviation in the Planck epoch ρ P l a n c k (\displaystyle \rho _(\mathrm (Planck) )) from ρ c r i t (\displaystyle \rho _(\mathrm (crit) )) no more than 10 −60 .

The Problem of the Large-Scale Structure of the Universe

The inflationary model assumes the replacement of the power law of expansion R (t) ∼ t 1 / 2 (\displaystyle R(t)\sim t^(1/2)) to the exponential law:

where H (t) = (1 / R) d R / d t (\displaystyle H(t)=(1/R)dR/dt) is the Hubble constant of the inflationary stage, which generally depends on time.

The value of the Hubble constant at the stage of inflation is 10 42 s −1 > H> 10 36 sec −1 , that is, it is gigantically superior to it contemporary meaning. Such an expansion law can be provided by the states of physical fields (“inflaton field”) corresponding to the equation of state p = − ε (\displaystyle p=-\varepsilon ), i.e. negative pressure; This stage is called the inflationary stage.

What would happen if, in the distant past, the space of the universe was in a state of false vacuum? If the density of matter in that era was less than required to balance the universe, then repulsive gravity would have dominated. This would cause the universe to expand, even if it did not initially expand.

To make our ideas more definite, we will assume that the Universe is closed. Then she puffs up like hot air balloon. As the volume of the Universe grows, matter becomes rarefied and its density decreases. However, the false vacuum mass density is a fixed constant; it always stays the same. So very quickly the density of matter becomes negligible, we are left with a uniform expanding sea of ​​false vacuum.

The expansion is caused by the tension of the false vacuum, which is greater than the attraction associated with its mass density. Since none of these quantities change with time, the rate of expansion remains high precision permanent. This rate is characterized by the proportion in which the universe expands per unit of time (say, one second). In meaning, this value is very similar to the rate of inflation in the economy - the percentage increase in prices per year. In 1980, when Guth was teaching a seminar at Harvard, the US inflation rate was 14%. If this value remained unchanged, prices would double every 5.3 years. Similarly, a constant rate of expansion of the universe implies that there is a fixed interval of time during which the size of the universe doubles.
Growth that is characterized by a constant doubling time is called exponential growth. It is known to lead to gigantic numbers very quickly. If today a slice of pizza costs $1, then after 10 doubling cycles (53 years in our example) its price will be $10^(24)$ dollars, and after 330 cycles it will reach $10^(100)$ dollars. This colossal number, one followed by 100 zeros, has a special name - googol. Guth suggested using the term inflation in cosmology to describe the exponential expansion of the universe.

The doubling time for a universe filled with a false vacuum is incredibly short. And the higher the vacuum energy, the shorter it is. In the case of an electroweak vacuum, the universe will expand by a factor of a googol in one-thirtieth of a microsecond, and in the presence of a Grand Unification vacuum, this will happen $10^(26)$ times faster. In such a short fraction of a second, a region the size of an atom will inflate to a size far larger than the entire observable universe today.

Because the false vacuum is unstable, it eventually disintegrates and its energy ignites a fireball of particles. This event marks the end of inflation and the beginning of normal cosmological evolution. Thus, from a tiny initial embryo we get a huge hot expanding Universe. And as an added bonus, this scenario miraculously eliminates the horizon and flat geometry problems that are characteristic of Big Bang cosmology.

The essence of the horizon problem is that the distances between some parts of the observable universe are such that they seem to have always been greater than the distance traveled by light since the Big Bang. This suggests that they never interacted with each other, and then it is difficult to explain how they achieved almost exact equality of temperatures and densities. In the standard Big Bang theory, the path traveled by light grows in proportion to the age of the universe, while the distance between regions increases more slowly as cosmic expansion is slowed down by gravity. Areas that cannot interact today will be able to influence each other in the future, when the light finally covers the distance separating them. But in the past, the distance traveled by light becomes even shorter than it should be, so if the regions cannot interact today, they certainly were not able to do so before. The root of the problem, therefore, is related to the attractive nature of gravity, due to which the expansion gradually slows down.

However, in a false vacuum universe, gravity is repulsive, and instead of slowing down expansion, it speeds it up. In this case, the situation is reversed: areas that can exchange light signals will lose this opportunity in the future. And, more importantly, those areas that are inaccessible to each other today must have interacted in the past. The horizon problem is gone!
The problem of flat space is solved just as easily. It turns out that the Universe moves away from the critical density only if its expansion slows down. In the case of an accelerated inflationary expansion, the opposite is true: the Universe is approaching a critical density, which means it is becoming flatter. Because inflation enlarges the universe by a colossal factor, we only see a tiny fraction of it. This observable region appears flat, similar to our Earth, which also appears flat when viewed close to the surface.

So, a short period of inflation makes the universe large, hot, uniform, and flat, creating just the kind of initial conditions required for standard big bang cosmology.
The theory of inflation began to conquer the world. As for Gut himself, his postdoc status is over. He accepted an offer from his alma mater, the Massachusetts Institute of Technology, where he continues to work today.

Excerpt from A. Vilenkin's book "Many Worlds in One: The Search for Other Universes"

The generally accepted theory of the Big Bang has many problems in describing the early universe. Even leaving aside the weirdness singular state defying any physical explanation, the gaps are not getting smaller. And this has to be taken into account. Sometimes small inconsistencies lead to the rejection of the whole theory. Therefore, complementary and auxiliary theories usually appear, designed to clarify bottlenecks and resolve the tension of the situation. AT this case inflation theory plays this role. So let's see what the problem is.

Matter and antimatter have equal rights to exist. Then how to explain that the Universe is almost entirely composed of matter?

Based on the background radiation, it has been established that the temperature in the Universe is approximately the same. But its individual parts could not be in contact during expansion. Then how was the thermal equilibrium established?

Why is the mass of the universe just such that it can slow down and stop the Hubble expansion?

In 1981, American physicist and cosmologist, Ph.D. Alan Harvey Guth, associate professor at the University of Massachusetts, dealing elementary particles, suggested that ten to the minus thirty-fifth degree of a second after the Big Bang, superdense and hot matter, consisting mainly of quarks and leptons, underwent a quantum transition similar to crystallization. This happened when strong interactions were separated from the unified field. Alan Guth was able to show that when the strong and weak interactions were separated, there was an abrupt expansion, as in freezing water. This expansion, many times faster than the Hubble one, was called inflationary.

In about ten to a minus thirty-second degree of a second, the Universe expanded by 50 orders of magnitude - it was smaller than a proton, it became the size of a grapefruit. By the way, water expands by only 10%. This rapid inflationary expansion solves two of the three problems identified. The expansion levels out the curvature of space, which depends on the amount of matter and energy in it. And it does not violate the thermal equilibrium, which had time to develop by the beginning of inflation. The problem of antimatter is explained by the fact that initial stage formation arose a few ordinary particles more. After annihilation, a piece of ordinary matter was formed from which the substance of the Universe was formed.

Inflationary model of the formation of the Universe.

The protouniverse was filled with a scalar field. At first it was homogeneous, but quantum fluctuations arose and inhomogeneities arose in it. With the accumulation of these inhomogeneities, a rarefaction occurs with the creation of a vacuum. The scalar field maintains tension and the resulting bubble grows larger and larger, expanding in all directions. The process goes exponentially, in a very short time. Here, the initial characteristics of the field play a decisive role. If the force is constant in time, then for a period of ten to the minus thirty-sixth degree of a second, the initial bubble of Vacuum can expand ten to the twenty-sixth degree of time. And this is consistent with the theory of relativity, we are talking about the movement of space itself in different sides.

As a result, it turns out that there was no explosion, there was a very fast inflation and expansion of the bubble of our Universe. The term inflation comes from the English inflate - to pump up, inflate. But the vacuum was expanding, where did the energy and matter that formed the stars, galaxies come from? And why is it believed that the universe was hot? Can emptiness be high-temperature?

When stretching the bubble of the universe, it begins to accumulate energy. Due to the phase transition, the temperature rises sharply. At the end of the period of inflation, the Universe turns out to be very hot, believed to be due to the singularity. The vacuum was given energy by the curvature of space. According to Einstein, gravity is not the force of attraction between two masses, but the curvature of space. If space is curved, it already has energy, even if it doesn't have mass. Any energy bends space. What pushes the galaxies in different directions and what we call dark energy is part of the scalar field. And the desired Higgs field is generated by this scalar field.

Among the critics of the theory of inflation is Sir Roger Pentrose, an English mathematician, specialist in the field of general relativity and quantum theory, head of the Department of Mathematics at the University of Oxford. He believed that all arguments about inflation are far-fetched and not subject to proof. That is, there is a problem of initial values. How to prove that in the early Universe the inhomogeneities were such that they could give rise to the homogeneous world that is observed now? And if initially there was a large curvature, then its residual phenomena should be observed at the present time.

However, studies carried out within the framework of the Supernova Cosmology Project have shown that inflation is currently observed at a late stage in the evolution of the Universe. The factor causing this phenomenon is called dark energy. Currently, Linde's additions have been made to the theory of inflation in the form of chaotic inflation. One should not rush to discount it, the theory of the inflationary Universe will still serve cosmology.

Information:

Okun L.B. "Leptons and quarks", M., Nauka, 1981

www.cosmos-journal.ru

In addition to the question of the origin of the universe, modern cosmologists face a number of other problems. In order for the standard to be able to predict the distribution of matter that we observe, its initial state must be characterized by a very high degree of organization. The question immediately arises: how could such a structure be formed?

Physicist Alan Guth of the Massachusetts Institute of Technology proposed his version, which explains the spontaneous emergence of this organization, eliminating the need to artificially introduce exact parameters into the equations describing the initial state of the universe. His model has been called the "inflationary universe". Its essence is that inside the rapidly expanding, superheated Universe small plot space cools and begins to expand more strongly, just as supercooled water rapidly freezes, expanding at the same time. This phase of rapid expansion eliminates some of the problems inherent in standard big bang theories.

However, Guth's model is also not without flaws. In order for Guth's equations to correctly describe the inflationary Universe, he had to set the initial parameters for his equations very precisely. Thus, he faced the same problem as the creators of other theories. He hoped to get rid of the need to specify the exact parameters of the conditions of the big bang, but for this he had to introduce his own parameterization, which remained unexplained. Guth and his co-author P. Steingart admit that in their model “calculations lead to acceptable predictions only if the given initial parameters of the equations vary in a very narrow range. Most theorists (including ourselves) consider such initial conditions unlikely.” The authors go on to talk about their hopes that someday new mathematical theories, which will allow them to make their model more believable.

This dependence on as yet undiscovered theories is another shortcoming of Guth's model. The unified field theory, on which the inflationary universe model is based, is completely hypothetical and "poorly lends itself to experimental verification, since most of its predictions cannot be quantitatively tested in the laboratory." (The unified field theory is a rather dubious attempt by scientists to tie together some of the fundamental forces of the universe.)

Another shortcoming of Guth's theory is that it says nothing about the origin of superheated and expanding matter. Guth tested the compatibility of his inflationary theory with three hypotheses for the origin of the universe. He first considered the standard big bang theory. In this case, according to Gut, the inflationary episode should have occurred at one of the early stages of the evolution of the Universe. However, this model poses an unsolvable singularity problem. The second hypothesis postulates that the universe emerged from chaos. Some parts of it were hot, others cold, some expanding and others contracting. In this case, inflation should have started in an overheated and expanding region of the universe. True, Guth admits that this model cannot explain the origin of primary chaos.

The third possibility, favored by Guth, is that a superheated, expanding clump of matter emerges quantum-mechanically from the void. In an article that appeared in Scientific American in 1984, Guth and Steingart argued: “The inflationary model of the universe gives us an idea of ​​the possible mechanism by which the observable universe could emerge from an infinitesimal patch of space. Knowing this, it's hard to resist the temptation to take it one step further and conclude that the universe literally came into existence out of nothing."

However attractive this idea may be for scientists who are ready to take up arms against any mention of the possibility of the existence of a higher consciousness that created the Universe, on closer examination it does not hold water. The "nothing" that Guth is talking about is a hypothetical quantum mechanical vacuum, described by the as yet undeveloped unified field theory, which should unify the equations quantum mechanics and the general theory of relativity. In other words, in this moment this vacuum cannot be described even theoretically.

It should be noted that physicists have described a simpler type of quantum mechanical vacuum, which is a sea of ​​so-called "virtual particles", fragments of atoms that "almost exist". From time to time, some of these subatomic particles pass from the vacuum into the world of material reality. This phenomenon is called vacuum fluctuations. Vacuum fluctuations cannot be directly observed, but theories postulating their existence have been experimentally confirmed. According to these theories, particles and antiparticles arise from a vacuum for no reason and disappear almost immediately, annihilating each other. Guth and his colleagues assumed that at some point, instead of a tiny particle, an entire universe appeared from the vacuum, and instead of immediately disappearing, this universe somehow survived for billions of years. The authors of this model solved the singularity problem by postulating that the state in which the Universe emerges from vacuum is somewhat different from the singularity state.

However, this scenario has two major drawbacks. First, one can only marvel at the boldness of the imagination of scientists who have extended their rather limited experience with subatomic particles to the entire Universe. S. Hawking and G. Ellis wisely warn their overly enthusiastic colleagues: “The assumption that the laws of physics, discovered and studied in the laboratory, will be valid at other points in the space-time continuum is, of course, a very bold extrapolation.” Secondly, strictly speaking, the quantum mechanical vacuum cannot be called "nothing". Description of the quantum mechanical vacuum, even in the simplest of existing theories occupies many pages of highly abstract mathematical calculations. Such a system is undoubtedly “something”, and the same stubborn question immediately arises: “How did such a complexly organized “vacuum” arise?”

Let's go back to the original problem that Guth created the inflationary model to solve: the problem of accurately parameterizing the initial state of the universe. Without such a parametrization, it is impossible to obtain the observed distribution of matter in the Universe. As we have seen, Gut failed to solve this problem. Moreover, the very possibility that any version of the big bang theory, including Guth's version, can predict the observed distribution of matter in the universe is doubtful.

The highly organized initial state in Guth's model, in his own words, eventually turns into a "Universe" with a diameter of 10 centimeters, filled with a homogeneous, super-dense, superheated gas. It will expand and cool, but there is no reason to believe that it will ever turn into anything more than a homogeneous cloud of gas. In fact, all big bang theories lead to this result. If Guth had to resort to many tricks and dubious assumptions in order to finally get the Universe in the form of a cloud of homogeneous gas, then one can imagine what the mathematical apparatus of the theory should be, leading to the Universe as we know it!

A good scientific theory makes it possible to predict many complex natural phenomena based on a simple theoretical framework. But in Guth's theory (and any other version), the opposite is true: as a result of complex mathematical calculations, we get an expanding bubble of a homogeneous gas. Despite this, scientific journals print enthusiastic articles about inflationary theory, accompanied by numerous colorful illustrations, which should give the reader the impression that Guth has finally achieved his cherished goal - he found an explanation for the origin of the universe. It would be more honest to simply open a permanent column in scientific journals to publish in it the theory of the origin of the universe, which is fashionable this month.

It is even difficult to imagine the complexity of the initial state and the conditions necessary for the emergence of our Universe with all the diversity of its structures and organisms. In the case of our universe, the degree of this complexity is such that it can hardly be explained by physical laws alone.

Why thirty-three well-known scientists of various specializations, led by Stephen Hawking, took up arms against three astrophysicists, according to what scenarios our Universe was formed and is it true inflation theory its extensions, the site was sorted out together with specialists.

The Standard Big Bang Theory and its Problems

The hot Big Bang theory was established in the middle of the 20th century, and became generally accepted a couple of decades after the discovery of the CMB. It explains many properties of the Universe around us and assumes that the Universe arose from some initial singular state (formally infinitely dense) and has been continuously expanding and cooling since then.

The relic radiation itself - a light "echo" born just 380,000 years after - turned out to be an incredibly valuable source of information. The lion's share of modern observational cosmology is associated with the analysis of various parameters of the background radiation. It is fairly homogeneous average temperature varies in different directions on a scale of only 10–5, and these inhomogeneities are evenly distributed over the sky. In physics, this property is called statistical isotropy. This means that locally such a value changes, but globally everything looks the same.

Diagram of the expansion of the universe

NASA/WMAP Science Team/Wikimedia Commons

By studying the perturbations of the CMB, astronomers calculate with high accuracy many quantities that characterize the Universe as a whole: the ratio of ordinary matter, dark matter and dark energy, the age of the Universe, the global geometry of the Universe, the contribution of neutrinos to the evolution of a large-scale structure, and others.

Despite the "generally accepted" theory of the Big Bang, it also had drawbacks: it did not answer some questions about the origin of the universe. The main ones are called the "horizon problem" and the "flatness problem".

The first is related to the fact that the speed of light is finite, and the relict radiation is statistically isotropic. The fact is that at the time of the birth of the relict radiation, even light did not have time to travel the distance between those far-distant points in the sky, from where we catch it today. So it's not clear why different areas are so identical, because they have not had time to exchange signals since the birth of the Universe, their causal horizons do not intersect.

The second problem, the problem of flatness, is related to the indistinguishable from zero (at the accuracy level modern experiments) by the global curvature of space. Simply put, at large scales, the space of the universe is flat, and it does not follow from the theory of the hot Big Bang that flat space is more preferable than other curvature options. Therefore, the proximity of this value to zero is at least not obvious.

thirty three against three

To solve these problems, astronomers have created the next generation of cosmological theories, the most successful of which is the theory of the inflationary expansion of the Universe (more simply called the theory of inflation). Raising the price of goods has nothing to do with it, although both terms come from the same Latin word - inflation- "bloating".

The inflationary model of the Universe suggests that before the hot stage (what is considered the beginning of time in the usual Big Bang theory) there was another era with very different properties. At that time, space was expanding exponentially due to the specific field that filled it. In a tiny fraction of a second, space stretched an incredible number of times. This solved both of the problems mentioned above: the universe turned out to be generally homogeneous, since it originated from an extremely small volume that existed at the previous stage. In addition, if there were any geometric inhomogeneities in it, they smoothed out during inflationary expansion.

Many scientists took part in the formation of the theory of inflation. The first models were independently proposed by the physicist, Ph.D. of Cornell University Alan Gut in the USA and theoretical physicist, specialist in the field of gravity and cosmology Alexei Starobinsky in the USSR around 1980. They differed in mechanisms (Guth considered a false vacuum, and Starobinsky - a modified general theory of relativity), but led to similar conclusions. Some problems of the original models were solved by a Soviet physicist, Doctor of Physical and Mathematical Sciences, an employee of the P.N. Lebedev Andrey Linde, who introduced the concept of a slowly changing potential (slow-roll inflation) and explained with its help the completion of the stage of exponential expansion. Next important step there was an understanding that inflation does not generate a perfectly symmetrical Universe, since it is necessary to take into account quantum fluctuations. This was done by Soviet physicists, MIPT graduates Vyacheslav Mukhanov and Gennady Chibisov.

King Harald of Norway awards Alan Gut, Andrei Linde and Alexei Starobinsky (from left to right) with the Kavli Prize in Physics. Oslo, September 2014.

Norsk Telegrambyra AS/Reuters

Within the framework of the theory of inflationary expansion, scientists make testable predictions, some of which have already been confirmed, but one of the main ones is the existence of relict gravitational waves- has not yet been confirmed. The first attempts to fix them are already being made, but at this stage it remains beyond the technological capabilities of mankind.

Nevertheless, the inflationary model of the universe has opponents who believe that it is formulated too generally, to the point that it can be used to get any result. For some time this controversy has been going on in the scientific literature, but recently a group of three IS&L astrophysicists (an abbreviation formed from the first letters of the names of scientists - Ijjas, Steinhardt and Loeb - Anna Iyas, Paul Steinhardt and Abraham Loeb) published a popular science statement of their claims to inflationary cosmology in Scientific American. In particular, IS&L, referring to the map of temperatures of the cosmic microwave background obtained using the Planck satellite, believe that the theory of inflation cannot be estimated scientific methods. Instead of the theory of inflation, astrophysicists offer their own version of the development of events: supposedly the Universe began not with the Big Bang, but with the Big Rebound - the rapid contraction of some "previous" Universe.

In response to this article, 33 scientists, including the founders of the theory of inflation (Alan Gut, Alexey Starobinsky, Andrey Linde) and other well-known scientists, such as Stephen Hawking, published a response letter in the same journal in which they categorically disagree with the claims of IS&L .

the site asked cosmologists and astrophysicists to comment on the validity of these claims, the difficulties in interpreting the predictions of inflationary theories, and the need to revise the approach to the theory of the early Universe.

One of the founders of the theory of inflationary expansion, professor of physics at Stanford University Andrei Linde, considers the claims far-fetched, and the critics' approach is unscrupulous: “If you answer in detail, you will get a big scientific article, but in short it will look like agitation. This is what people use. In short, the leader of the critics is Steinhardt, who for 16 years has been trying to create an alternative [theory] of inflation, and in his articles - a mistake on a mistake. Well, when it doesn’t work out on its own, then there is a desire to scold more popular theories, using methods well known from history textbooks. Most theorists have stopped reading them, but journalists are very fond of them. Physics has almost nothing to do with it.”

Candidate of Physical and Mathematical Sciences, an employee of the Institute for Nuclear Research of the Russian Academy of Sciences Sergey Mironov recalls that scientific truth cannot be born in polemics at a non-professional level. A critical article, in his opinion, is written scientifically and with arguments, it is brought together various problems inflation theory. Such reviews are necessary, they help to prevent the ossification of science.

However, the situation changes when such a discussion goes to the pages of a popular publication, because whether it is right to promote one's scientific idea in this way is a moot point. In this regard, Mironov notes that the response to criticism looks ugly, since some of its authors are not experts in the field at all, while the other writes popular texts about the inflation model. Mironov points out that the response article is written as if the authors had not even read the work of IS&L, and they did not provide any counterarguments to it. Statements about the provocative manner in which the note with criticism is written mean that "the authors of the answer simply fell for trolling."

"Share of Truth"

Nevertheless, scientists, including supporters of the inflationary model, recognize its shortcomings. Physicist Alexander Vilenkin, professor and director of the Institute of Cosmology at Tufts University in Medford (USA), who made an important contribution to the formation modern theory inflation, notes: “There is some truth in the statements of Steinhardt and colleagues, but I think that their claims are extremely exaggerated. Inflation predicts the existence of many regions like ours, with initial conditions determined by quantum fluctuations. Theoretically, any initial conditions are possible with some probability. The problem is that we don't know how to calculate these probabilities. The number of areas of each type is infinite, so you have to compare infinite numbers - this situation is called the measure problem. Of course, the absence of a single measure derivable from a fundamental theory is a worrying sign.”

Sergei Mironov considers the above-mentioned set of models to be shortcomings of the theory, since this makes it possible to fit it to any experimental observations. And this means that the theory does not satisfy the Popper criterion (according to this criterion, a theory is considered scientific if it can be refuted with the help of an experiment - site note), at least for the foreseeable future. Mironov also refers to the problems of the theory that, within the framework of inflation, the initial conditions require fine tuning of the parameters, which makes it, in a sense, not natural. Early Universe Specialist, Candidate of Physical and Mathematical Sciences, Researcher scientific institute Gran Sasso National Institute of Nuclear Physics (Italy) Sabir Ramazanov also acknowledges the reality of these problems, but notes that their existence does not necessarily mean that the inflationary theory is wrong, but some of its aspects do deserve deeper thought.

The creator of one of the first inflationary models, Academician of the Russian Academy of Sciences, Chief Researcher of the Institute of Theoretical Physics of the Russian Academy of Sciences Alexei Starobinsky explains that one of the simplest models proposed by Andrey Linde in 1983 was indeed refuted. She was predicting too many gravitational waves, which is why Linde recently pointed out that inflationary models need to be revisited.

Critical experiment

Astronomers are turning Special attention that an important prediction made possible by the theory of inflation was the prediction of relic gravitational waves. Specialist in the analysis of relic radiation and observational cosmology, Doctor of Physical and Mathematical Sciences, leading researcher at the Special Astrophysical Observatory of the Russian Academy of Sciences Oleg Verkhodanov considers this forecast a significant observational test for the simplest variants of inflationary expansion, while for the theory of the "Big Rebound" advocated by critics, such a decisive no experiment.

Illustration of the Big Rebound Theory

Wikimedia Commons

Therefore, it will be possible to talk about another theory only if serious restrictions are imposed on relic waves. Sergei Mironov also calls the potential discovery of such waves a serious argument in favor of inflation, but notes that so far their amplitude is only limited, which has already allowed us to reject some options, which are replaced by others that do not predict too strong primary gravitational disturbances. Sabir Ramazanov agrees with the importance of this test and, moreover, believes that the inflation theory cannot be considered proven until this phenomenon is discovered in observations. Therefore, while the key prediction of the inflationary model about the existence of primary gravitational waves with a flat spectrum has not been confirmed, it is too early to talk about inflation as a physical reality.

“The correct answer, from which they diligently try to lead the reader away”

Aleksey Starobinsky analyzed the claims of IS&L in detail. He singled out three main statements.

Statement 1. Inflation predicts anything. Or nothing.

"The correct answer, which the IS&L reader is diligently trying to steer away from, is that words like 'inflation'," quantum theory fields", "model of elementary particles", are very general: they combine many different models that differ in the degree of complexity (for example, the number of neutrino varieties),” Starobinsky explains.

After scientists fix the free parameters included in each specific model from experiments or observations, the model's predictions are considered unambiguous. The modern Standard Model of elementary particles contains about 20 such parameters (these are mainly quark masses, neutrino masses and their mixing angle). The simplest viable inflationary model contains only one such parameter, the value of which is fixed by the measured amplitude of the initial spectrum of matter inhomogeneities. After that, all other predictions are unambiguous.

The academician clarifies: “Of course, it can be complicated by adding new members of various physical nature, each of which will come with a new free numeric parameter. But, firstly, in this case, the predictions will not be "anything", but definite. And secondly, and most importantly, today's observations show that these terms are not needed, at the current level of accuracy of about 10% they are not!”

Statement 2. It is unlikely that in the models under consideration there will be an inflationary stage at all, since the potential energy of the inflaton has a long flat “plateau” in them.

“The statement is false,” Starobinsky is categorical. “In my work in 1983 and 1987, it was proved that the inflationary regime in models of this type is general, that is, it occurs in a set of initial conditions with a non-zero measure.” Subsequently, this was also proven by more rigorous mathematical criteria, with numerical simulations, etc.

The results of the Planck experiment, according to Starobinsky, called into question the point of view that Andrei Linde had repeatedly expressed. According to it, inflation must necessarily begin at the Planck density of matter, and, already starting from this limit for classical description space-time parameter, matter was distributed uniformly. However, in the proofs discussed above, this was not assumed. That is, in models of this type, before the stage of inflationary expansion, there is an anisotropic and inhomogeneous stage of the evolution of the Universe with a greater curvature of space-time than during inflation.

“To make it clearer, let's use the following analogy,” explains the cosmologist. - In the general theory of relativity, one of the common solutions is rotating black holes, described by the Kerr metric. What black holes are general solutions does not mean that they are everywhere. For example, they are not in solar system and in its vicinity (fortunately for us). This means that if we search, we will definitely find them. That's how it happened." In the case of inflation, the same thing happens - this intermediate stage is not in all solutions, but in a fairly wide class of them, so that it may well arise in a single implementation, that is, for our Universe, which exists in one copy. How likely this is a one-time event, however, is entirely determined by our hypotheses about what preceded inflation.

Statement 3. The quantum phenomenon of "eternal inflation", which takes place in almost all inflationary models and entails the emergence of a multiverse, leads to the complete uncertainty of inflationary scenario predictions: "Everything that can happen, happens."

“The statement is partly false, partly irrelevant to the observed effects in our Universe,” the academician is adamant. - Although the words in quotation marks are borrowed by IS&L from the reviews by Vilenkin and Gut, their meaning is distorted. There they stood in a different context and meant no more than a banal remark even for a schoolboy that the equations of physics (for example, mechanics) can be solved for any initial conditions: somewhere and someday these conditions are realized.

Why "eternal inflation" and the formation of the "multiverse" do not affect all processes in our Universe after the end of the inflationary stage? The fact is that they occur outside of our light cone of the past (by the way, and of the future too), ”explains Starobinsky. Therefore, it is impossible to say unequivocally whether they occur in our past, present or future. “Strictly speaking, this is true up to exponentially small quantum gravitational effects, but in all existing consistent calculations, such effects have always been neglected,” emphasizes the academician.

“I do not want to say that it is not interesting to explore what lies outside our light cone of the past,” Starobinsky continues, “but this is not yet directly connected with observational data. However, here too IS&L confuse the reader: if the description of "eternal inflation" is correct, then under given conditions at the beginning of the inflationary stage, there is no arbitrariness in predictions (although not all of my colleagues agree with this). Moreover, many predictions, in particular the spectrum of inhomogeneities of matter and gravitational waves that arise at the end of inflation, do not depend on these initial conditions at all,” the cosmologist adds.

“There is no urgent need to revise the foundations of the physics of the early Universe”

Oleg Verkhodanov notes that so far there is no reason to abandon the current paradigm: “Of course, inflation has room for interpretation - a family of models. But even among them, one can choose the most appropriate to the distribution of spots on the CMB map. So far, most of the results of the Planck mission are in favor of inflation.” Aleksey Starobinsky notes that the very first model with the de Sitter stage preceding the hot Big Bang, which he proposed back in 1980, is in good agreement with the data of the Planck experiment, to which IS&L is appealing. (during the de-Sitter stage, which lasted about 10-35 seconds, the Universe expanded rapidly, the vacuum filling it seemed to stretch without changing its properties - approx. site).

On the whole, Sabir Ramazanov also agrees with him: “A number of predictions - the Gaussian nature of the spectrum of primary disturbances, the absence of constant curvature modes, the slope of the spectrum - were confirmed in the WMAP and Planck data. Inflation deservedly plays a dominant role as a theory of the early universe. At the moment, there is no urgent need to revise the foundations of the physics of the early Universe.” Cosmologist Sergei Mironov also acknowledges the positive qualities of this theory: "The very idea of ​​inflation is extremely elegant, it allows one to solve all the fundamental problems of the Hot Big Bang theory in one fell swoop."

“In general, the result for the IS&L item is idle chatter from beginning to end, - sums up Starobinsky. "It has nothing to do with the real problems that cosmologists are currently working on." And at the same time, the academician adds: “Another thing is that any model is like Einstein’s general theory of relativity, like modern model elementary particles, and the model of inflation - is not the last word of science. It is always only approximate, and at some level of accuracy, small corrections to it will certainly appear, from which we will learn a lot, since new physics will stand behind them. It is precisely such small corrections that astronomers are now looking for.”