The big bang theory is the origin of the universe. Competitor of the Big Bang Theory. What happened a trillion years ago. Chronology of events in the Big Bang theory

After the mysterious cosmological singularity, the no less mysterious Planck era (0 -10 -43 s) follows. It is difficult to say what processes took place in this brief moment of the newborn Universe. But it is known for sure that by the end of the Planck moment, the gravitational influence has separated from the three fundamental forces, united into a single group of the Great Unification.

In order to describe the earlier moment, a new theory is needed, part of which can be the loop quantum gravity model and string theory. It turns out that the Planck era, like the cosmological singularity, is an ultra-small in duration, but significant in terms of scientific weight, a gap in the available knowledge of the early Universe. Also within the Planck time there were peculiar fluctuations of space and time. To describe this quantum chaos, one can use the image of foaming quantum cells of space-time.

Compared with the Planck era, further events appear before us in a bright and understandable light. In the period from 10 -43 s to 10 -35 s, the forces of gravity and the Great Unification were already acting in the young Universe. During this period, strong, weak and electromagnetic influences were a single whole and constituted the force field of the Great Unification.

When 10 -35 s had passed since the Big Bang, the Universe reached a temperature of 10 29 K. At that moment, the strong force separated from the electroweak one. This led to symmetry breaking, which happened differently in different parts of the universe. There is a possibility that the Universe was divided into parts that were fenced off from each other by defects in space-time. Other defects could also exist there - cosmic strings or magnetic monopoles. However, today we cannot see this because of another division of the power of the Grand Unification - cosmological inflation.

At that time, the Universe was filled with gas from gravitons - hypothetical quanta of the gravitational field and bosons of the Grand Unification force. At the same time, there was almost no difference between leptons and quarks.

When a separation of forces occurred in some parts of the universe, a false vacuum arose. The energy is stuck at a high level, causing space to double in size every 10 -34 seconds. Thus, the Universe has moved from quantum scales (one billionth trillion trillionth of a centimeter) to the size of a ball with a diameter of about 10 cm. As a result of the Great Unification era, a phase transition of primary matter occurred, which was accompanied by a violation of the uniformity of its density. The epoch of the Great Unification ended approximately 10 −34 seconds after the Big Bang, when the density of matter was 10 74 g/cm³ and the temperature was 10 27 K. conditions. This separation led to the next phase transition and a large-scale expansion of the Universe, which led to a change in the density of matter and its distribution throughout the Universe.

One of the reasons why we know so little about the state of the universe before inflation is that subsequent events have changed it very much, scattering particles before inflationary age to the farthest corners of the universe. Therefore, even if these particles are preserved, it is quite difficult to detect them in modern matter.

With the rapid development of the Universe, great changes occur, and after the period of the Great Unification comes the era of inflation (10 -35 - 10 -32). This epoch is characterized by the ultra-fast expansion of the young Universe, that is, inflation. In this brief moment, the Universe was an ocean of false vacuum with a high energy density, thanks to which expansion became possible. At the same time, the vacuum parameters were constantly changing due to quantum bursts - fluctuations (space-time foaming).

Inflation explains the nature of the explosion at the Big Bang, that is, why the rapid expansion of the Universe occurred. Einstein's general theory of relativity and quantum field theory served as the basis for describing this phenomenon. In order to describe this phenomenon, physicists built a hypothetical inflator field that filled the entire space. Due to random fluctuations, it took on different values ​​in arbitrary spatial regions and at different points in time. Then, a uniform configuration of critical size formed in the inflator field, after which the spatial region occupied by the fluctuation began to rapidly increase in size. Due to the desire of the inflator field to take a position in which its energy is minimal, the expansion process acquired an increasing character, as a result of which the Universe began to increase in size. At the moment of expansion (10 -34), the false vacuum began to disintegrate, as a result of which particles and antiparticles of high energies begin to form.

In the history of the Universe, the hadron era begins, an important feature of which is the existence of particles and antiparticles. According to modern concepts, in the first microseconds after the Big Bang, the Universe was in a state of quark-gluon plasma. Quarks are the constituents of all hadrons (protons and neutrons), and neutral particles are gluons, carriers of the strong interaction, which ensure the adhesion of quarks into hadrons. In the first moments of the Universe, these particles were only formed and were in a free, gaseous state.

The chromoplasm of quarks and gluons is usually compared to the liquid state of interacting matter. In such a phase, quarks and gluons are released from hadronic matter and can freely move throughout the plasma space, resulting in the formation of color conductivity.

Despite the extremely high temperatures, the quarks were sufficiently bound together, and their movement resembled the movement of atoms in a liquid rather than in a gas. Also, under such conditions, another phase transition occurs, in which the light quarks that make up matter become massless.

CMB observations showed that the initial abundance of particles compared to the number of antiparticles was a negligible fraction of the total. And it was these excess protons that were enough to create the substance of the Universe.

Some scientists believe that in the hadron era there was also a concealment of matter. The carrier of the hidden mass is unknown, but such elementary particles as axions are considered the most probable.

During the development of the explosion, the temperature dropped and after one tenth of a second it reached 3 * 10 10 degrees Celsius. In one second, ten thousand million degrees, and in thirteen seconds, three thousand million. This was already enough for the electrons and positrons to begin to anagylate faster. The energy released during annagilation gradually slowed down the rate of cooling of the universe, but the temperature continued to fall.

The period from 10-4 - 10 s is commonly called the era of leptons. When the energy of particles and photons decreased by a hundred times, the matter was filled with leptons-electrons and positrons. The lepton era begins with the decay of the last hadrons into muons and muon neutrinos, and ends after a few seconds, when the photon energy has sharply decreased and the generation of electron-positron pairs has ceased.

About one hundredth of a second after the Big Bang, the temperature of the universe was 10 11 degrees Celsius. This is much hotter than the center of any star known to us. This temperature is so high that none of the components of ordinary matter, atoms and molecules, could exist. Instead, the young universe consisted of elementary particles. One of these particles were electrons, the negatively charged particles that form the outer parts of all atoms. The other particles were positrons, positively charged particles with a mass exactly equal to that of an electron. In addition, there were neutrinos of various types - ghostly particles that had neither mass nor electric charge. But neutrinos and antineutrinos did not annihilate each other, because these particles interact very weakly with each other and with other particles. Therefore, they should still be found around us, and they could be a good way to test the hot early universe model. However, the energies of these particles are now too low to observe them.

During the lepton era, there were particles like protons and neutrons. And finally, there was light in the Universe, which, according to quantum theory, consists of photons. Proportionately, there were a thousand million electrons for one neutron and one proton. All these particles were continuously born from pure energy, and then annihilated, forming other types of particles. The density in the early universe at these high temperatures was four thousand million times that of water.

As mentioned earlier, it is during this period that an intense birth in nuclear reactions of various types of ghost neutrino, which is called relic, takes place.

The radiation era begins, at the beginning of which the Universe enters the era of radiation. At the beginning of the era (10 s), radiation intensively interacted with charged particles of protons and electrons. Due to the drop in temperature, the photons cooled, and as a result of numerous scatterings on the receding particles, part of their energy was carried away.

About a hundred seconds after the Big Bang, the temperature drops to a thousand million degrees, which is the temperature of the hottest stars. Under such conditions, the energy of protons and neutrons is no longer enough to resist the strong nuclear attraction, and they begin to combine with each other, forming deuterium-heavy hydrogen nuclei. Then the deuterium nuclei attach other neutrons and protons and turn into helium nuclei. After that, heavier elements are formed - lithium and beryllium. The primary formation of atomic nuclei of the emerging substance did not last long. After three minutes, the particles had scattered so far apart that collisions were rare. According to the hot model of the Big Bang, about a quarter of the protons and neutrons should have turned into atoms of helium, hydrogen and other elements. The remaining elementary particles decayed into protons, representing the nuclei of ordinary hydrogen.

A few hours after the Big Bang, the production of helium and other elements ceased. For a million years, the universe just kept expanding and almost nothing else happened. The matter that existed at that time began to expand and cool. Much later, after hundreds of thousands of years, the temperature dropped to several thousand degrees, and the energy of electrons and nuclei was not enough to overcome the electromagnetic attraction between them. They began to collide with each other, forming the first atoms of hydrogen and helium (Fig. 2).

The Big Bang theory has become almost as widely accepted a cosmological model as the rotation of the Earth around the Sun. According to the theory, about 14 billion years ago, spontaneous fluctuations in the absolute void led to the emergence of the universe. Something comparable in size to a subatomic particle expanded to an unimaginable size in a fraction of a second. But in this theory there are many problems over which physicists are struggling, putting forward more and more new hypotheses.

What's Wrong with the Big Bang Theory

It follows from the theory that all the planets and stars were formed from the dust scattered through space as a result of the explosion. But what preceded it is unclear: here our mathematical model of space-time stops working. The universe arose from an initial singular state, to which modern physics cannot be applied. The theory also does not consider the causes of the occurrence of the singularity or the matter and energy for its occurrence. It is believed that the answer to the question of the existence and origin of the initial singularity will be given by the theory of quantum gravity.

Most cosmological models predict that the full universe is much larger than the observable part - a spherical region with a diameter of about 90 billion light years. We see only that part of the Universe, the light from which managed to reach the Earth in 13.8 billion years. But telescopes are getting better, we are discovering more and more distant objects, and so far there is no reason to believe that this process will stop.

Since the Big Bang, the universe has been expanding at an accelerating rate. The most difficult riddle of modern physics is the question of what causes acceleration. According to the working hypothesis, the Universe contains an invisible component called "dark energy". The Big Bang theory does not explain whether the Universe will expand indefinitely, and if so, what this will lead to - to its disappearance or something else.

Although Newtonian mechanics was supplanted by relativistic physics, it cannot be called wrong. However, the perception of the world and the models for describing the universe have completely changed. The Big Bang Theory predicted a number of things that were not known before. Thus, if another theory takes its place, then it should be similar and expand the understanding of the world.

We will focus on the most interesting theories describing alternative Big Bang models.

The universe is like a mirage of a black hole

The universe arose due to the collapse of a star in a four-dimensional universe, scientists from the Perimeter Institute for Theoretical Physics believe. The results of their research were published in Scientific American. Niayesh Afshordi, Robert Mann and Razi Pourhasan say that our three-dimensional universe became like a "holographic mirage" when a four-dimensional star collapsed. Unlike the Big Bang theory, according to which the Universe arose from extremely hot and dense space-time, where the standard laws of physics do not apply, the new hypothesis of a four-dimensional universe explains both the reasons for the birth and its rapid expansion.

According to the scenario formulated by Afshordi and his colleagues, our three-dimensional universe is a kind of membrane that floats through an even larger universe that already exists in four dimensions. If this four-dimensional space had its own four-dimensional stars, they would also explode, just like the three-dimensional ones in our Universe. The inner layer would become a black hole, and the outer layer would be ejected into space.

In our universe, black holes are surrounded by a sphere called the event horizon. And if in three-dimensional space this boundary is two-dimensional (like a membrane), then in a four-dimensional universe, the event horizon will be limited to a sphere that exists in three dimensions. Computer simulations of the collapse of a four-dimensional star have shown that its three-dimensional event horizon will gradually expand. This is exactly what we observe, calling the growth of a 3D membrane the expansion of the universe, astrophysicists believe.

Big Freeze

An alternative to the Big Bang could be the Big Freeze. A team of physicists from the University of Melbourne, led by James Kvatch, presented a model for the birth of the universe, which is more like a gradual process of freezing amorphous energy than its splash and expansion in three directions of space.

The formless energy, according to scientists, cooled like water to crystallization, creating the usual three spatial and one temporal dimensions.

The Big Freeze theory casts doubt on Albert Einstein's currently accepted assertion of the continuity and fluidity of space and time. It is possible that space has constituent parts - indivisible building blocks, like tiny atoms or pixels in computer graphics. These blocks are so small that they cannot be observed, however, following the new theory, it is possible to detect defects that should refract the flows of other particles. Scientists have calculated such effects using the mathematical apparatus, and now they will try to detect them experimentally.

Universe without beginning or end

Ahmed Farag Ali of Benh University in Egypt and Sauria Das of the University of Lethbridge in Canada have come up with a new solution to the singularity problem by ditching the Big Bang. They brought ideas from the famous physicist David Bohm to the Friedmann equation describing the expansion of the Universe and the Big Bang. “It's amazing that small adjustments can potentially solve so many issues,” says Das.

The resulting model combined the general theory of relativity and quantum theory. It not only denies the singularity that preceded the Big Bang, but also prevents the universe from shrinking back to its original state over time. According to the data obtained, the Universe has a finite size and an infinite lifetime. In physical terms, the model describes the Universe filled with a hypothetical quantum fluid, which consists of gravitons - particles that provide gravitational interaction.

The scientists also claim that their findings are consistent with recent measurements of the density of the universe.

Endless chaotic inflation

The term "inflation" refers to the rapid expansion of the universe, which occurred exponentially in the first moments after the Big Bang. By itself, the theory of inflation does not refute the Big Bang theory, but only interprets it differently. This theory solves several fundamental problems of physics.

According to the inflationary model, shortly after its birth, the universe expanded exponentially for a very short time: its size doubled many times over. Scientists believe that in 10 to -36 seconds, the universe increased in size by at least 10 to 30-50 times, and possibly more. At the end of the inflationary phase, the Universe was filled with a superhot plasma of free quarks, gluons, leptons, and high-energy quanta.

The concept implies that exists in the world many isolated universes with different device

Physicists have come to the conclusion that the logic of the inflationary model does not contradict the idea of ​​a constant multiple birth of new universes. Quantum fluctuations - the same as those that created our world - can occur in any quantity, if there are suitable conditions for this. It is quite possible that our universe has emerged from the fluctuation zone formed in the predecessor world. It can also be assumed that sometime and somewhere in our Universe a fluctuation will form, which will “blow out” the young Universe of a completely different kind. According to this model, child universes can bud continuously. At the same time, it is not at all necessary that the same physical laws are established in the new worlds. The concept implies that in the world there are many universes isolated from each other with different structures.

Cyclic theory

Paul Steinhardt, one of the physicists who laid the foundations of inflationary cosmology, decided to develop this theory further. The scientist who heads the Center for Theoretical Physics at Princeton, along with Neil Turok from the Perimeter Institute for Theoretical Physics, outlined an alternative theory in the book Endless Universe: Beyond the Big Bang ("Infinite Universe: Beyond the Big Bang"). Their model is based on a generalization of quantum superstring theory known as M-theory. According to her, the physical world has 11 dimensions - ten spatial and one temporal. Spaces of smaller dimensions “float” in it, the so-called branes (short for "membrane"). Our universe is just one of those branes.

The Steinhardt and Turok model states that the Big Bang occurred as a result of the collision of our brane with another brane - a universe unknown to us. In this scenario, collisions occur indefinitely. According to the hypothesis of Steinhardt and Turok, another three-dimensional brane “floats” next to our brane, separated by a tiny distance. It also expands, flattens, and empties, but in a trillion years, the branes will begin to converge and eventually collide. In this case, a huge amount of energy, particles and radiation will be released. This cataclysm will launch another cycle of expansion and cooling of the universe. From the model of Steinhardt and Turok, it follows that these cycles have been in the past and will certainly repeat in the future. How these cycles began, the theory is silent.

Universe
like a computer

Another hypothesis about the structure of the universe says that our entire world is nothing more than a matrix or a computer program. The idea that the universe is a digital computer was first proposed by the German engineer and computer pioneer Konrad Zuse in his book Calculating Space ("computing space"). Among those who also viewed the universe as a giant computer are physicists Stephen Wolfram and Gerard "t Hooft.

Digital physics theorists suggest that the universe is essentially information and therefore computable. From these assumptions it follows that the Universe can be considered as the result of a computer program or a digital computing device. This computer could be, for example, a giant cellular automaton or a universal Turing machine.

indirect evidence virtual nature of the universe called the uncertainty principle in quantum mechanics

According to the theory, every object and event of the physical world comes from asking questions and registering “yes” or “no” answers. That is, behind everything that surrounds us, there is a certain code, similar to the binary code of a computer program. And we are a kind of interface through which access to the data of the “universal Internet” appears. An indirect proof of the virtual nature of the Universe is called the uncertainty principle in quantum mechanics: particles of matter can exist in an unstable form, and are “fixed” in a specific state only when they are observed.

A follower of digital physics, John Archibald Wheeler, wrote: “It would not be unreasonable to imagine that information is in the core of physics in the same way as in the core of a computer. Everything from the beat. In other words, everything that exists - every particle, every force field, even the space-time continuum itself - receives its function, its meaning, and, ultimately, its very existence.

The answer to the question "What is the Big Bang?" can be obtained in the course of a long discussion, since it takes a lot of time. I will try to explain this theory briefly and to the point. So, the "Big Bang" theory postulates that our universe suddenly appeared approximately 13.7 billion years ago (everything appeared from nothing). And what happened then still affects how and in what way everything in the universe interacts with each other. Consider the key points of the theory.

What happened before the Big Bang?

The Big Bang theory includes a very interesting concept - the singularity. I bet it makes you wonder: what is a singularity? Astronomers, physicists and other scientists are also asking this question. Singularities are believed to exist in the cores of black holes. A black hole is an area of ​​intense gravitational pressure. This pressure, according to the theory, is so intense that matter is compressed until it has an infinite density. This infinite density is called singularity. Our Universe is supposed to have started as one of these infinitely small, infinitely hot and infinitely dense singularities. However, we have not yet come to the Big Bang itself. The Big Bang is the moment at which this singularity suddenly "exploded" and began to expand and created our Universe.

The Big Bang theory would seem to imply that time and space existed before our universe arose. However, Stephen Hawking, George Ellis and Roger Penrose (et al.) developed a theory in the late 1960s that tried to explain that time and space did not exist before the expansion of the singularity. In other words, neither time nor space existed until the universe existed.

What happened after the Big Bang?

The moment of the Big Bang is the moment of the beginning of time. After the Big Bang, but long before the first second (10 -43 seconds), the cosmos experiences an ultra-rapid inflationary expansion, expanding 1050 times in a fraction of a second.

Then the expansion slows down, but the first second has not yet arrived (only 10 -32 seconds more). At this moment, the Universe is a boiling "broth" (with a temperature of 10 27 °C) of electrons, quarks and other elementary particles.

The rapid cooling of space (up to 10 13 ° C) allows quarks to combine into protons and neutrons. However, the first second has not yet arrived (only 10 -6 seconds more).

At 3 minutes, too hot to combine into atoms, the charged electrons and protons prevent light from being emitted. The Universe is a superhot fog (10 8 °C).

After 300,000 years, the universe cools down to 10,000 °C, electrons with protons and neutrons form atoms, mainly hydrogen and helium.

1 billion years after the Big Bang, when the temperature of the universe reached -200 ° C, hydrogen and helium form giant "clouds" that will later become galaxies. The first stars appear.

Big Bang. This is the name of the theory, or rather one of the theories, of the origin or, if you like, the creation of the Universe. The name, perhaps, is too frivolous for such a frightening and awe-inspiring event. Especially intimidating if you have ever asked yourself very difficult questions about the universe.

For example, if the universe is all that is, how did it begin? And what happened before that? If space is not infinite, then what is beyond it? And what exactly should this something be placed in? How can you understand the word "infinite"?

These things are difficult to understand. Moreover, when you start to think about it, you get an eerie feeling of something majestic - terrible. But questions about the universe are one of the most important questions that mankind has asked itself throughout its history.

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Stars and constellations

What was the beginning of the existence of the universe?

Most scientists are convinced that the beginning of the existence of the universe was laid by a grandiose big explosion of matter that occurred about 15 billion years ago. For many years, most scientists shared the hypothesis that the beginning of the universe was marked by a huge explosion, which scientists jokingly dubbed the "Big Bang". In their opinion, all matter and all space, which is now represented by billions and millions of galaxies and stars, 15 billion years ago fit in a tiny space no larger than a few words in this sentence.

How was the universe formed?

Scientists believe that 15 billion years ago, this small volume exploded into tiny particles smaller than atoms, giving rise to the existence of the universe. Initially, it was a nebula of small particles. Later, when these particles were combined, atoms were formed. Star galaxies were formed from atoms. Since that Big Bang, the universe has continued to expand like an inflating balloon.

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Doubts about the Big Bang Theory

But over the past few years, scientists studying the structure of the universe have made some unexpected discoveries. Some of them question the Big Bang theory. What can you do, our world does not always correspond to our comfortable ideas about it.

Distribution of matter during an explosion

One problem is the way in which matter is distributed throughout the universe. When an object explodes, its contents scatter evenly in all directions. In other words, if matter was initially compressed in a small volume and then exploded, then the matter should have been evenly distributed over the space of the Universe.

The reality, however, is very different from the expected representations. We live in a very unevenly filled universe. When looking into space, separate clumps of matter appear far from each other. Enormous galaxies are scattered here and there in outer space. Between

The Big Bang theory in the current decade has a strong competitor - the cyclic theory.

The Big Bang theory is trusted by the vast majority of scientists who study the early history of our universe. It really explains a lot and in no way contradicts the experimental data. However, recently it has a competitor in the form of a new, cyclical theory, the foundations of which were developed by two extra-class physicists - the director of the Institute for Theoretical Science at Princeton University, Paul Steinhardt, and the winner of the Maxwell Medal and the prestigious international TED award, Neil Turok, director of the Canadian Institute for Advanced Study in Theoretical Science. physics (Perimeter Institute for Theoretical Physics). With the help of Professor Steinhardt, Popular Mechanics attempted to explain the cyclic theory and its causes.

Alexey Levin

The title of this article may not seem like a very smart joke. According to the generally accepted cosmological concept, the Big Bang theory, our Universe arose from an extreme state of the physical vacuum generated by a quantum fluctuation. In this state, neither time nor space existed (or they were entangled in space-time foam), and all fundamental physical interactions were merged into one. Later they separated and acquired an independent existence - first gravity, then strong interaction, and only then - weak and electromagnetic.

The moment preceding these changes is commonly referred to as zero time, t=0, but this is pure convention, a tribute to mathematical formalism. According to the standard theory, the uninterrupted flow of time began only after the force of gravity gained independence. This moment is usually attributed to the value t = 10 -43 s (more precisely, 5.4x10 -44 s), which is called the Planck time. Modern physical theories are simply not able to meaningfully work with shorter time intervals (it is believed that this requires a quantum theory of gravity, which has not yet been created). In the context of traditional cosmology, it makes no sense to talk about what happened before the initial moment of time, since time, in our understanding, simply did not exist then.

The Big Bang theory is trusted by the vast majority of scientists who study the early history of our universe. It really explains a lot and in no way contradicts the experimental data. However, it has recently faced a competitor in the face of a new, cyclic theory, the foundations of which were developed by two extra-class physicists - the director of the Institute for Theoretical Science at Princeton University, Paul Steinhardt, and the winner of the Maxwell Medal and the prestigious international TED award, Neil Turok, director of the Canadian Institute for Advanced Study in Theoretical Science. physics (Perimeter Institute for Theoretical Physics). With the help of Professor Steinhardt, Popular Mechanics attempted to explain the cyclic theory and its causes.

Inflationary cosmology

An indispensable part of standard cosmological theory is the concept of inflation (see sidebar). After inflation ended, gravity took over, and the universe continued to expand, but at a decreasing rate. This evolution lasted for 9 billion years, after which another anti-gravitational field of still unknown nature, which is called dark energy, came into play. It again brought the Universe into a mode of exponential expansion, which, it seems, should be preserved in future times. It should be noted that these conclusions are based on astrophysical discoveries made at the end of the last century, almost 20 years after the advent of inflationary cosmology.

The inflationary interpretation of the Big Bang was first proposed about 30 years ago and has been polished many times since then. This theory made it possible to solve several fundamental problems that previous cosmology had failed to solve. For example, she explained why we live in a universe with a flat Euclidean geometry - in accordance with the classical Friedmann equations, this is exactly what it should become with exponential expansion. The inflationary theory explained why cosmic matter has graininess on a scale not exceeding hundreds of millions of light years, and is evenly distributed over long distances. She also explained the failure of any attempt to detect magnetic monopoles, very massive particles with a single magnetic pole, which are believed to be abundant before the onset of inflation (inflation stretched space so that the initially high monopole density was reduced to almost zero, and therefore our instruments cannot detect them).

Soon after the appearance of the inflationary model, several theorists realized that its internal logic did not contradict the idea of ​​a permanent multiple birth of more and more new universes. Indeed, quantum fluctuations, like those to which we owe the existence of our world, can occur in any quantity, if there are suitable conditions for this. It is possible that our universe has left the fluctuation zone formed in the predecessor world. In the same way, it can be assumed that sometime and somewhere in our own universe, a fluctuation will form that will “blow out” a young universe of a completely different kind, also capable of cosmological “childbirth”. There are models in which such child universes arise continuously, sprout from their parents and find their own place. At the same time, it is not at all necessary that the same physical laws are established in such worlds. All these worlds are "embedded" in a single space-time continuum, but they are separated in it so much that they do not feel each other's presence in any way. In general, the concept of inflation allows - moreover, forces! - to consider that in a gigantic megacosmos there are many universes isolated from each other with different arrangements.

Alternative

Theoretical physicists love to come up with alternatives to even the most accepted theories. Competitors have also appeared for the inflationary model of the Big Bang. They did not receive wide support, but they had and still have their followers. The theory of Steinhardt and Turok is not the first among them, and certainly not the last. However, to date it has been developed in more detail than the others and better explains the observed properties of our world. It has several versions, some of which are based on the theory of quantum strings and high-dimensional spaces, while others rely on traditional quantum field theory. The first approach gives more visual pictures of cosmological processes, so we will stop on it.

The most advanced version of string theory is known as M-theory. She claims that the physical world has 11 dimensions - ten spatial and one temporal. It floats spaces of smaller dimensions, the so-called branes. Our universe is just one of those branes, with three spatial dimensions. It is filled with various quantum particles (electrons, quarks, photons, etc.), which are actually open vibrating strings with the only spatial dimension - length. The ends of each string are tightly fixed inside the three-dimensional brane, and the string cannot leave the brane. But there are also closed strings that can migrate beyond the boundaries of branes - these are gravitons, quanta of the gravitational field.

How does the cyclic theory explain the past and future of the universe? Let's start with the current era. The first place now belongs to dark energy, which causes our Universe to expand exponentially, periodically doubling its size. As a result, the density of matter and radiation is constantly falling, the gravitational curvature of space is weakening, and its geometry is becoming more and more flat. Over the next trillion years, the size of the universe will double in size by about a hundred times and it will turn into an almost empty world, completely devoid of material structures. Next to us is another three-dimensional brane, separated from us by a tiny distance in the fourth dimension, and it is also undergoing a similar exponential stretching and flattening. All this time, the distance between the branes remains virtually unchanged.

And then these parallel branes start moving closer together. They are pushed towards each other by a force field whose energy depends on the distance between the branes. Now the energy density of such a field is positive, so the space of both branes expands exponentially - therefore, it is this field that provides the effect that is explained by the presence of dark energy! However, this parameter is gradually decreasing and will drop to zero in a trillion years. Both branes will continue to expand anyway, but not exponentially, but at a very slow pace. Consequently, in our world, the density of particles and radiation will remain almost zero, and the geometry will remain flat.

New cycle

But the end of the old story is only a prelude to the next cycle. The branes move towards each other and eventually collide. At this stage, the energy density of the interbrane field drops below zero, and it begins to act like gravity (recall that gravity has a negative potential energy!). When the branes are very close, the interbrane field begins to amplify quantum fluctuations at every point in our world and converts them into macroscopic deformations of spatial geometry (for example, a millionth of a second before a collision, the calculated size of such deformations reaches several meters). After a collision, it is in these zones that the lion's share of the kinetic energy released upon impact is released. As a result, it is there that the most hot plasma arises with a temperature of about 1023 degrees. It is these areas that become local gravity nodes and turn into the embryos of future galaxies.

Such a collision replaces the Big Bang inflationary cosmology. It is very important that all newly formed matter with positive energy appears due to the accumulated negative energy of the interbrane field, so the law of conservation of energy is not violated.

The inflationary theory allows for the formation of multiple child universes that continuously sprout from existing ones.

And how does such a field behave at this decisive moment? Before the collision, its energy density reaches a minimum (and negative), then it starts to increase, and after a collision it becomes zero. The branes then repel each other and begin to move apart. The interbrane energy density goes through a reverse evolution - again becomes negative, zero, positive. Enriched with matter and radiation, the brane first expands at a decreasing rate under the decelerating effect of its own gravity, and then again switches to exponential expansion. The new cycle ends like the previous one - and so on ad infinitum. The cycles that preceded ours also happened in the past - in this model, time is continuous, so the past exists beyond the 13.7 billion years that have passed since the last enrichment of our brane with matter and radiation! Whether they had any beginning at all, the theory is silent.

The cyclic theory explains the properties of our world in a new way. It has a flat geometry, because at the end of each cycle it stretches beyond measure and only slightly deforms before the start of a new cycle. Quantum fluctuations, which become the precursors of galaxies, arise chaotically, but uniformly on average - therefore, outer space is filled with clumps of matter, but at very large distances it is quite uniform. We cannot detect magnetic monopoles simply because the maximum temperature of the newborn plasma did not exceed 10 23 K, and for the appearance of such particles much higher energies are required - on the order of 10 27 K.

The moment of the Big Bang is the collision of branes. Enormous amounts of energy are released, branes fly apart, slow expansion occurs, matter and radiation cool, and galaxies form. The expansion accelerates again due to the positive interbrane energy density, and then slows down, the geometry becomes flat. Branes are attracted to each other, before the collision, quantum fluctuations are amplified and transformed into deformations of spatial geometry, which in the future will become the embryos of galaxies. A collision occurs and the cycle starts over.

A world without beginning or end

The cyclical theory exists in several versions, as does the theory of inflation. However, according to Paul Steinhardt, the differences between them are purely technical and are of interest only to specialists, while the general concept remains unchanged: “Firstly, in our theory there is no moment of the beginning of the world, no singularity. There are periodic phases of intense production of matter and radiation, each of which, if desired, can be called the Big Bang. But any of these phases does not mark the emergence of a new universe, but only the transition from one cycle to another. Both space and time exist both before and after any of these cataclysms. Therefore, it is quite natural to ask what was the state of affairs 10 billion years before the last Big Bang, from which the history of the universe is counted.

The second key difference is the nature and role of dark energy. Inflationary cosmology did not predict the transition of the decelerating expansion of the Universe into an accelerated one. And when astrophysicists discovered this phenomenon by observing the explosions of distant supernovae, standard cosmology did not even know what to do with it. The dark energy hypothesis was put forward simply to somehow tie the paradoxical results of these observations to the theory. And our approach is much better reinforced by internal logic, since we have dark energy from the very beginning and it is this energy that ensures the alternation of cosmological cycles.” However, as Paul Steinhardt notes, the cyclic theory also has weaknesses: “We have not yet been able to convincingly describe the process of collision and bounce of parallel branes that occurs at the beginning of each cycle. Other aspects of the cyclic theory have been developed much better, and here there are still many ambiguities to be eliminated.

Verification by practice

But even the most beautiful theoretical models need experimental verification. Is it possible to confirm or disprove cyclic cosmology with the help of observations? “Both the inflationary and the cyclical theories predict the existence of relic gravitational waves,” explains Paul Steinhardt. - In the first case, they arise from primary quantum fluctuations, which, during inflation, are spread over space and give rise to periodic fluctuations in its geometry - and this, according to the general theory of relativity, is gravity waves. In our scenario, these waves are also driven by quantum fluctuations, the same ones that get amplified when branes collide. Calculations have shown that each mechanism generates waves with a specific spectrum and a specific polarization. These waves must have left imprints on cosmic microwave radiation, which is an invaluable source of information about early space. So far, no such traces have been found, but, most likely, this will be done within the next decade. In addition, physicists are already thinking about the direct registration of relic gravitational waves using spacecraft, which will appear in two or three decades.”

Radical Alternative

In the 1980s, Professor Steinhardt made a significant contribution to the development of the standard theory of the Big Bang. However, this did not stop him in the least from looking for a radical alternative to the theory in which so much work has been invested. As Paul Steinhardt himself told Popular Mechanics, the inflation hypothesis does reveal many cosmological mysteries, but this does not mean that there is no point in looking for other explanations: “At first it was just interesting for me to try to figure out the basic properties of our world without resorting to inflation. Later, when I delved into this problem, I became convinced that the inflationary theory is not at all as perfect as its supporters claim. When inflationary cosmology was first created, we hoped that it would explain the transition from the original chaotic state of matter to the current orderly universe. She did just that, but she went much further. The internal logic of the theory demanded to recognize that inflation constantly creates an infinite number of worlds. There would be nothing wrong with this if their physical device copied our own, but this just doesn’t work. For example, with the help of the inflationary hypothesis, it was possible to explain why we live in a flat Euclidean world, but most other universes will certainly not have the same geometry. In short, we were building a theory to explain our own world, and it got out of hand and gave rise to an endless variety of exotic worlds. This state of affairs no longer suits me. In addition, the standard theory is unable to explain the nature of the earlier state that preceded the exponential expansion. In this sense, it is as incomplete as pre-inflationary cosmology. Finally, she is unable to say anything about the nature of dark energy, which has been driving the expansion of our Universe for 5 billion years.”

Another difference, according to Professor Steinhardt, is the temperature distribution of the background microwave radiation: “This radiation coming from different parts of the sky is not quite uniform in temperature, it has more and less heated zones. At the level of measurement accuracy provided by modern equipment, the number of hot and cold zones is approximately the same, which coincides with the conclusions of both theories, inflationary and cyclical. However, these theories predict more subtle differences between zones. In principle, the European space observatory "Planck" launched last year and other latest spacecraft will be able to detect them. I hope that the results of these experiments will help to make a choice between inflationary and cyclical theories. But it may also happen that the situation remains uncertain and none of the theories receives unambiguous experimental support. Well, then we'll have to come up with something new."