Formation of protogalactic clouds less than about 1 billion years after the Big Bang

We are well aware of the force of gravity that keeps us on the ground and makes it difficult to fly to the moon. And electromagnetism, thanks to which we do not disintegrate into separate atoms and can plug in laptops. The physicist talks about two more forces that make the universe exactly what it is.

From school, we all know well the law of gravitation and Coulomb's law. The first explains to us how massive objects such as stars and planets interact (attract) with each other. The other shows (recall the experiment with an ebonite stick) what forces of attraction and repulsion arise between electrically charged objects.

But is this exhausted by the whole multitude of forces and interactions that determine the appearance of the universe we observe?

Modern physics says that there are four types of basic (fundamental) interactions between particles in the Universe. I have already said about two of them above, and with them, it would seem, everything is simple, since their manifestations constantly surround us in everyday life: this is the gravitational and electromagnetic interaction.

So, due to the action of the first, we stand firmly on the ground and do not fly into open space... The second, for example, ensures the attraction of an electron to a proton in the atoms of which we are all made up and, ultimately, the attraction of atoms to each other (i.e., it is responsible for the formation of molecules, biological tissues, etc.). So it is precisely because of the forces of electromagnetic interaction, for example, that it turns out that it is not so easy to take off the head of an annoying neighbor, and for this purpose we have to resort to using an ax of various improvised means.

But there is also the so-called strong interaction. What is it responsible for? Didn't it surprise you at school that, despite the Coulomb's law that two positive charge should repel each other (only opposite ones attract), the nuclei of many atoms calmly exist for themselves. But they consist, as you remember, of protons and neutrons. Neutrons - they are neutrons because they are neutral and have no electric charge, but protons are positively charged. And what, one wonders, forces can hold together (at a distance of one trillionth of a micron - which is a thousand times smaller than the atom itself!) Several protons, which, according to Coulomb's law, should repel each other with terrible energy?

Strong interaction - provides attraction between particles in the core; electrostatic - repulsion

This truly titanic task of overcoming the Coulomb forces is undertaken by a strong interaction. So, neither more nor less, due to it, the protons (as well as neutrons) in the nucleus are nevertheless attracted to each other. By the way, the protons and neutrons themselves also consist of even more "elementary" particles - quarks. So quarks also interact and are attracted to each other "strongly". But, fortunately, unlike the same gravitational interaction that works at cosmic distances of many billions of kilometers, the strong interaction is said to be short-range. This means that the field of "strong attraction" surrounding one proton works only on a tiny scale, comparable, in fact, with the size of the nucleus.

Therefore, for example, a proton sitting in the nucleus of one of the atoms cannot, spitting on the Coulomb repulsion, take and “strongly” attract a proton from a neighboring atom. Otherwise, all proton and neutron matter in the Universe could be "attracted" to the common center of mass and form one huge "supernucleus". Something similar, however, happens in the thick neutron stars, in one of which, as can be expected, one day (about five billion years later) our Sun will contract.

So, the fourth and last of the fundamental interactions in nature is the so-called weak interaction. It is not for nothing that it is so called: not only does it work even at distances even shorter than strong interaction, but also its power is very small. So, unlike its strong "brother", the Coulomb repulsion, it will not outweigh it in any way.

A striking example demonstrating the weakness of weak interactions are particles called neutrinos (can be translated as "small neutron", "neutron"). These particles, by their nature, do not participate in strong interactions, do not have an electric charge (therefore, they are not susceptible to electromagnetic interactions), have an insignificant mass even by the standards of the microcosm and, therefore, are practically insensitive to gravity, in fact, are only capable of weak interactions.

Cho? Neutrinos pass through me ?!

At the same time, in the Universe, neutrinos are born in truly colossal quantities, and a huge stream of these particles constantly permeates the thickness of the Earth. For example, in the volume of a matchbox, on average, there are about 20 neutrinos at each moment of time. Thus, one can imagine a huge barrel of water-detector, which I wrote about in my last post, and the incredible amount of neutrinos that flies through it at every moment of time. So, scientists working on this detector usually have to wait for months for such a happy occasion for at least one neutrino to "feel" their barrel and interact in it with its weak forces.

However, even despite its weakness, this interaction plays a lot important role in the universe and in human life. So, it is it that turns out to be responsible for one of the types of radioactivity - namely, beta decay, which is the second (after gamma radioactivity) in terms of the degree of danger of its impact on living organisms. And, no less important, without weak interaction it would be impossible for thermonuclear reactions occurring in the bowels of many stars and responsible for the release of the energy of the star.

Such is the four horsemen of the Apocalypse of fundamental interactions that reign in the Universe: strong, electromagnetic, weak and gravitational.

One of the greatest advances in physics over the past two millennia has been the identification and definition of four types of interactions that rule the universe. All of them can be described in the language of the fields to which we owe Faraday. Unfortunately, however, none of the four species has the full properties of the force fields described in most science fiction books. Let's list these types of interaction. Paylex price.

1. Gravity. The silent power that keeps our feet from leaving the support. It does not allow the Earth and the stars to crumble, helps to maintain integrity Solar system and the Galaxy. Without gravity, the planet's rotation would kick us off Earth and into space at 1,000 miles per hour. The problem is that the properties of gravity are exactly the opposite of the properties of fantastic force fields. Gravity is the force of attraction, not repulsion; it is extremely weak - relatively, of course; it works at enormous, astronomical distances. In other words, it is almost the exact opposite of the flat, thin, impenetrable barrier that can be found in almost any fantasy novel or a movie. For example, an entire planet, the Earth, attracts a feather to the floor, but we can easily overcome the Earth's gravity and lift the feather with one finger. The impact of one of our fingers can overcome the gravity of an entire planet, which weighs more than six trillion kilograms.

2. Electromagnetism (EM). The power that illuminates our cities. Lasers, radio, television, modern electronics, computers, the Internet, electricity, magnetism are all consequences of the manifestation of electromagnetic interaction. Perhaps this is the most useful force that humanity has managed to curb throughout its history. Unlike gravity, it can work both for attraction and repulsion. However, it is not suitable for the role of a force field for several reasons. First, it can be easily neutralized. For example, plastic or any other non-conductive material can easily penetrate a powerful electric or magnetic field. A piece of plastic thrown into a magnetic field will freely fly right through it. Secondly, electromagnetism acts at large distances, it is not easy to concentrate it in a plane. The laws of EM interaction are described by the equations of James Clerk Maxwell, and it seems that force fields are not a solution to these equations.

3 and 4. Strong and weak nuclear interactions. Weak interaction is the force of radioactive decay, the one that heats up the radioactive core of the Earth. This force is behind volcanic eruptions, earthquakes and continental plate drift. Strong interaction does not allow the nuclei of atoms to crumble; it provides energy to the sun and stars and is responsible for lighting the universe. The problem is that nuclear interaction only works at very small distances, mostly within atomic nucleus... It is so strongly associated with the properties of the core itself that it is extremely difficult to control it. Currently, we know of only two ways to influence this interaction: we can break a subatomic particle into pieces in an accelerator or detonate an atomic bomb.

Although science fiction protective fields do not obey the known laws of physics, there are still loopholes that are likely to make the creation of a force field possible in the future. First, there is perhaps a fifth kind of fundamental interaction that no one has yet been able to see in the laboratory. It may turn out, for example, that this interaction only works at distances of a few inches to a foot - and not at astronomical distances. (True, the first attempts to detect the fifth type of interaction yielded negative results.)

Second, we may be able to get the plasma to mimic some of the properties of the force field. Plasma is the "fourth state of matter." The first three, familiar to us, states of matter are solid, liquid and gaseous; nevertheless, the most common form of matter in the universe is plasma: a gas made up of ionized atoms. The atoms in the plasma are not connected with each other and are devoid of electrons, and therefore have an electric charge. They can be easily controlled using electric and magnetic fields.

The visible matter of the universe exists for the most part in the form of various kinds of plasma; the sun, stars and interstellar gas are formed from it. In ordinary life, we almost never encounter plasma, because on Earth this phenomenon is rare; nevertheless, the plasma can be seen. All you need to do is look at lightning, the sun, or a plasma TV screen.

To understand whether it is worth continuing to write short sketches explaining various physical phenomena and processes literally on the fingers. The result dispelled my doubts. I will continue. But in order to approach rather complex phenomena, you will have to make separate sequential series of posts. So, in order to get to the story about the structure and evolution of the Sun and other types of stars, we will have to start with a description of the types of interaction between elementary particles. Let's start with this. No formulas.
In total, four types of interaction are known in physics. All familiar gravitational and electromagnetic... And almost unknown to the general public strong and weak... Let's describe them sequentially.
Gravitational interaction . Man has known him since ancient times. For it is constantly in the gravity field of the Earth. And from school physics we know that the force of gravitational interaction between bodies is proportional to the product of their masses and inversely proportional to the square of the distance between them. Under the influence of gravitational force, the Moon revolves around the Earth, the Earth and other planets around the Sun, and the latter, together with other stars, around the center of our Galaxy.
A rather slow decrease in the force of gravitational interaction with distance (inversely proportional to the square of the distance) forces physicists to speak of this interaction as long-range... In addition, the forces of gravitational interaction acting between bodies are only forces of attraction.
Electromagnetic interaction . In the simplest case of electrostatic interaction, as we know from school physics, the force of attraction or repulsion between electrically charged particles is proportional to the product of their electric charges and is inversely proportional to the square of the distance between them. Which is very similar to the law of gravitational interaction. The only difference is that electric charges with the same signs are repelled, and with different ones - they are attracted. Therefore, the electromagnetic interaction, like gravitational, physicists call long-range.
At the same time, the electromagnetic interaction is more complex than the gravitational one. We know from school physics that an electric field is created by electric charges, magnetic charges does not exist in nature, but the magnetic field is created electric currents.
In fact, the electric field can also be created by changing in time magnetic field, and the magnetic field - changing in time electric field... The latter circumstance makes it possible to exist for an electromagnetic field without any electric charges and currents at all. And this possibility is realized in the form electromagnetic waves... For example, radio waves and light quanta.
Due to the same distance dependence of electric and gravitational forces, it is natural to try to compare their intensities. So, for two protons, the forces of gravitational attraction are 10 to 36 times (billion billion billion billion times) weaker than the forces of electrostatic repulsion. Therefore, in the physics of the microworld, the gravitational interaction can be quite reasonably neglected.
Strong interaction . It - short-range strength. In the sense that they act at distances of only about one femtometer (one trillionth of a millimeter), and at large distances their influence is practically not felt. Moreover, at distances of the order of one femtometer, the strong interaction is about a hundred times more intense than the electromagnetic one.
That is why equally electrically charged protons in an atomic nucleus are not repelled from each other by electrostatic forces, but are held together by strong interaction. Since the dimensions of the proton and neutron are about one femtometer.
Weak interaction . It is really very weak. First, it acts at distances a thousand times less than one femtometer. And at long distances it is practically not felt. Therefore, like the strong, it belongs to the class short-range... Secondly, its intensity is about a hundred billion times less than the intensity of electromagnetic interaction. The weak interaction is responsible for some decays of elementary particles. Including free neutrons.
There is only one type of particles that interact with matter only through weak interaction. These are neutrinos. Almost a hundred billion solar neutrinos pass through every square centimeter of our skin every second. And we do not notice them at all. In the sense that during our lifetime hardly a few pieces of neutrinos will interact with the matter of our body.
We will not talk about the theories describing all these types of interactions. For us, a qualitative picture of the world is important, and not the sophistication of theoreticians.

A guide to the big picture, fundamental law of physics, windows of space and time, the great war, and extremely large numbers.

1st January 7,000,000,000 AD BC, Ann Arbor.

Advancing New Year- not too big a reason to celebrate. There is no one who can even celebrate his arrival. The surface of the Earth has turned into an unrecognizable wasteland, scorched to ashes by the Sun. The sun has inflated infinitely: it has become so huge that its red-hot disk covers the daytime sky almost entirely. Mercury and Venus have already died, and now the tenuous outer regions of the solar atmosphere threaten to capture the receding orbit of the Earth.

The oceans, in which life once originated, evaporated a long time ago, turning first into a heavy sterilizing cloud of water vapor, and then completely dissolving into outer space. Only a barren rocky surface remained. It can still show faint traces of ancient coastlines, ocean basins and eroded remnants of continents. By noon, temperatures reach nearly three thousand degrees Fahrenheit and the rocky surface begins to melt. The equator is already partially encircled by a wide belt of boiling lava, which, as it cools, forms a thin gray crust while the swollen Sun rests behind the horizon every night.

The part of the surface that once served as the cradle for the forested moraines of southeastern Michigan has changed dramatically over the past billions of years. The former North American mainland long ago divided a geologic fault that stretched from the former state of Ontario to Louisiana; he split the old stable platform of the mainland and formed a new seabed. The fossilized and frozen remains of Ann Arbor were covered with lava, which descended along the beds of old rivers from nearby volcanoes. Subsequently, when a group of islands the size of New Zealand collided with the coastline, solidified lava and sedimentary rocks hidden beneath it pressed into the mountain range.

Now the surface of the ancient rock is weakened by the unbearable heat of the Sun. The block of stone splits, causing a landslide and exposing the perfectly preserved imprint of an oak leaf. This trace of a once green world, now so distant, is slowly disappearing, melting into relentless fire. Very soon, the entire Earth will be engulfed in an ominous red flame.

This picture of the death of the Earth is not written off from the first pages of the script of a second-rate science fiction film; this is a more or less realistic description of the fate that awaits our planet, when the Sun ceases to exist in the form of an ordinary star and expands, turning into a red giant. The catastrophic melting of the Earth's surface is just one of a great many events that will strike when the universe and its contents are old.

Now our Universe, which is estimated to be ten to fifteen billion years old, is still in its early years. So many astronomical possibilities of greater interest have simply not yet had time to prove themselves. However, as the distant future approaches, the Universe will gradually change, turning into an arena in which a great variety of amazing astrophysical processes will unfold. In this book, the biography of the universe is told from beginning to end. This is the story of how familiar stars in the night sky gradually turn into strange frozen stars, evaporating black holes and atoms the size of a galaxy. This is a scientific view of the face of eternity.

The biography of our Universe and the study of astrophysics in general unfolds on four important scales - at the level of planets, stars, galaxies and the Universe as a whole. Each of them provides its own type of window for observing the properties and evolution of nature. At each of these levels, astrophysical objects go through all life cycles, starting with education - an event similar to birth, and - often ending with a very specific ending, like death. Death can be quick and violent; for example, a massive star completes its evolution with a spectacular supernova explosion. Another alternative is the excruciatingly slow death prepared for dim red dwarfs, which are gradually fading away, turning into white dwarfs - the cooling embers of once powerful and active stars.

On the largest scale, we can consider the Universe as a single developing organism and study its life cycle. There has been significant scientific progress in this area of ​​cosmology over the past few decades. The universe has been expanding since its inception in the strongest explosion - the very Big Bang. The Big Bang theory describes the subsequent evolution of the universe over the past ten to fifteen billion years, and it has been amazingly successful in explaining the nature of our universe as it expands and cools.

The key question is whether the Universe will expand forever or whether at some point in the future the expansion will stop and re-contraction will occur. The current results of astronomical observations strongly suggest that our universe is written to expand continuously, so most of our narrative follows this scenario. Nevertheless, we decided to briefly outline the consequences of the second possible scenario of the development of events - the terrible death of the Universe in repeated hot compression.

Below the vast expanses of cosmology, at a lesser level, there are galaxies, for example, our Milky Way. Galaxies are large and rather rarefied clusters of stars, gas, and other types of matter. Galaxies are not randomly scattered throughout the universe; rather, they are woven into the common tapestry of the cosmos by gravity. Some groups of galaxies are so heavy that they stay together under the influence of gravitational forces, and these galaxy clusters can be considered independent astrophysical objects. In addition to belonging to clusters, galaxies randomly combine to form even larger structures that resemble filaments, sheets and walls. A collection of patterns formed; galaxies at this level are called the large-scale structure of the universe.

Galaxies contain a large proportion of the ordinary matter of the Universe; these star systems are clearly separated from each other, even within clusters. This division is so pronounced that galaxies were once called "islands of the universe." In addition, galaxies play an extremely important role as markers of space-time positions. Our universe is constantly expanding, and galaxies, like beacons in the void, allow us to observe this expansion.

It is extremely difficult to comprehend the boundless emptiness of our Universe. A typical galaxy fills only about one millionth of the total volume of outer space in which it is contained, and the galaxies themselves are extremely rarefied. If you were going to go to spaceship at some random point in the universe, the probability of your ship landing within a galaxy is currently about one millionth. This is not too much, and in the future this value will become even smaller, because the Universe is expanding, but galaxies are not. Separated from the general expansion of the Universe, galaxies exist in relative isolation. They are inhabited by most of the stars in the Universe, and therefore, most of the planets. As a result, many interesting physical processes taking place in the Universe - from stellar evolution to the development of life - occur in galaxies.

Not too densely populating space, the galaxies themselves are also mostly empty. Although they contain billions of stars, only a very small fraction of their volume is actually filled with stars. If you were going to go on a spaceship to some random point in our Galaxy, the probability of your spacecraft landing on some star is extremely small, on the order of one billion trillionth (one chance in 10 22). Such emptiness of galaxies is eloquent enough evidence of how they evolved and what awaits them in the future. Direct collisions of stars in the galaxy are extremely rare. Consequently, it will take a very long time - much more than has elapsed from the birth of our universe to the present moment - before collisions of stars and the encounter of other astrophysical objects have any effect on the structure of the galaxy. As you will see, these collisions become more and more important as the universe ages.

However, interstellar space is not completely empty. Our Milky Way is saturated with gas different density and temperature. Average density is one particle (one proton) per cubic centimeter; the temperature ranges from ten degrees cool to boiling at a million degrees on the Kelvin scale. At low temperatures, about one percent of the substance remains in a solid state - in the form of tiny stone dust particles. This gas and dust that fills interstellar space is called the interstellar medium.

The next, even smaller, level of importance is formed by the stars themselves. Currently, the cornerstone of astrophysics is ordinary stars - objects like our Sun, existing due to nuclear fusion reactions that occur in their depths. Stars make up galaxies and generate most of the visible light in the universe. Moreover, it is the stars that have formed the modern "register" of our Universe. Massive stars have forged almost all of the heavy elements that animate space, including carbon and oxygen necessary for life. It was the stars that gave birth to most of the elements that make up common matter that we encounter every day: books, cars, groceries.

But these nuclear power plants will not last forever. Nuclear fusion reactions, thanks to which energy is generated in the bowels of stars, will eventually stop; and this will happen as soon as the stock of nuclear fuel is depleted. Stars much heavier than our Sun burn out in a relatively short period of time of several million years: their life is a thousand times shorter than the present age of our Universe. At the opposite end of the range are stars whose masses are much less than the mass of our Sun. Such stars can live for trillions of years - about a thousand times the present age of our universe.

At the end of that part of a star's life when it exists due to thermonuclear reactions, the star does not disappear without a trace. Stars leave behind exotic clumps called stellar remnants. This caste of degenerate objects is formed by brown dwarfs, white dwarfs, neutron stars and black holes. As we will see, as the universe ages and ordinary stars disappear from the scene, these strange remnants will play an increasingly important and ultimately dominant role.

The fourth, the smallest in size, but not in importance, the level of our interest is formed by the planets. There are at least two varieties of them: relatively small rocky bodies like our Earth and large gas giants like Jupiter and Saturn. Over the past few years, there has been an extraordinary upheaval in our understanding of the planets. For the first time in history, planets were most definitely discovered in the orbits of other stars. Now we know for sure that the planets are not the result of some rare or special event that has occurred in our solar system, but are widespread in the galaxy quite ubiquitous. The planets do not play a major role in the evolution and dynamics of the universe as a whole. They are important because they are the most likely environment for the emergence and development of life. Thus, the long-term fate of the planets determines the long-term fate of life - at least those of its forms that are familiar to us.

In addition to planets, solar systems contain many much smaller objects: asteroids, comets, and a huge variety of moons. Like the planets, these bodies do not play a significant role in the course of the evolution of the Universe as a whole, but they have a huge impact on the evolution of life. The moons orbiting planets provide another possible environment for the emergence and development of life. It is known that comets and asteroids regularly collide with planets. It is believed that these collisions, which can cause global climate change and the extinction of entire species of living things, have played an important role in shaping the history of life here on Earth.

Nature can be described in terms of four fundamental forces that ultimately govern the dynamics of the entire universe; these are gravity, electromagnetic force, strong nuclear force and weak nuclear force. All these forces play an important role in the biography of space. They made our Universe as we know it today, and will rule in it from now on.

The first of these forces, gravitational forces, is closest to our daily life, and it is the weakest of the four. However, due to the vastness of the range of its action and the extremely attractive nature, at sufficiently large distances, gravity dominates over other forces. Thanks to gravity, various objects are held on the surface of the Earth, while the Earth itself remains in orbit, in which it revolves around the Sun. Gravity supports the existence of stars and controls the process of energy formation in them, as well as their evolution. Finally, it is gravity that is responsible for the formation of most structures in the universe, including galaxies, stars and planets.

The second force is electromagnetic; it has electrical and magnetic components. At first glance, they may appear to be different, but at a fundamental level, they are just two aspects of a single underlying force. Despite the fact that the internal electromagnetic force is much stronger than the gravitational force, at large distances it has much less effect. Positive and negative charges are the source of the electromagnetic force, and in the Universe, apparently, they are contained in equal quantities. Since the forces created by charges with opposite signs act in opposite directions, at large distances, where there are many charges, the electromagnetic force self-destructs. At small distances, in particular in atoms, the electromagnetic force plays an important role. It is she who, ultimately, is responsible for the structure of atoms and molecules, and therefore is driving force in chemical reactions. At a fundamental level, life is ruled by chemistry and electromagnetic force.

The electromagnetic force is as much as 10 to 40 times stronger than the gravitational force. To comprehend this incredible weakness of gravity, one can, for example, imagine an alternative universe in which there are no charges, and therefore no electromagnetic forces. In such a universe, perfectly ordinary atoms would have extraordinary properties. If the electron and the proton were bound only by gravity, then the hydrogen atom would be larger than the entire visible part of our Universe.

Strong nuclear forces, our third fundamental force in nature, are responsible for the integrity of the nuclei of atoms. This force keeps protons and neutrons in the nucleus. In the absence of strong interaction, atomic nuclei would explode in response to repulsive forces acting between positively charged protons. Despite the fact that this interaction is the strongest of the four, it operates at extremely short distances. It is no coincidence that the range of action of a strong nuclear interaction is approximately equal to the size of a large atomic nucleus: about ten thousand times less than the size of an atom (about ten Fermi or 10 -12 cm). Strong interactions governs the process of nuclear fusion, which generates most of the energy in the stars, and therefore in the universe in the current era. It is because of the large, in comparison with the electromagnetic force, the magnitude of the strong interaction that nuclear reactions are much stronger than chemical ones, namely, a million times per pair of particles.

The fourth force, weak nuclear force, is probably the most distant from public consciousness. This rather mysterious weak interaction takes part in the decay of neutrons into protons and electrons, and also plays a role in the process of nuclear fusion, appears in the phenomenon of radioactivity and the formation chemical elements in the stars. A weak interaction has an even shorter range of action than a strong one. However, despite its weakness and small range of action, the weak interaction plays a surprisingly important role in astrophysics. A significant fraction of the total mass of the universe is likely to be composed of weakly interacting particles, in other words, particles that interact with each other only through weak interaction and gravity. Due to the fact that such particles tend to interact for a very long time, their role gradually increases as the universe slowly moves into the future.

Throughout the life of our Universe, the same question constantly arises in it - a continuous struggle between the force of gravity and the desire of physical systems to evolve towards more disorganized states. The amount of disorder in a physical system is measured by its fraction entropy... In the most general sense, gravity tends to keep all the components of any system within this very system, which orders the physical structures. Entropy production works in the opposite direction, i.e. it tries to make physical systems more disorganized and "smeared". It is the interaction of these two competing trends that consists of main drama astrophysics.

Our Sun is a direct example of this ongoing struggle. It exists in a delicate balance between gravity and entropy. The gravitational force maintains the integrity of the Sun and attracts all of its matter to the center. In the absence of forces opposing it, gravity would quickly squeeze the Sun, turning it into a black hole no more than a few kilometers in diameter. The fatal collapse is prevented by pressure forces that act from the center to the surface, balancing the gravitational forces and thereby preserving the Sun. The pressure that prevents the collapse of the Sun arises, ultimately, due to the energy of nuclear reactions that occur in its depths. In the course of these reactions, energy and entropy are formed, causing chaotic movements of particles in the center of the Sun and, ultimately, preserving the structure of the entire Sun.

On the other hand, if gravitational force somehow turned off, then the Sun would no longer be restrained and it would quickly expand. This expansion would continue until the solar matter would not spread out so thin that its density would be equal to the least dense regions of interstellar space. Then the rarefied ghost of the Sun would be a hundred million times its current size, stretching several light years in diameter.

Thanks to the rivalry of two competitors of equal strength, gravity and entropy, our Sun exists in its present state. In the event of a violation of this equilibrium, whether gravity prevails over entropy or vice versa, the Sun will turn either into a small black hole or into an extremely rarefied gas cloud. The same state of affairs - the balance that exists between gravity and entropy - determines the structure of all the stars in the sky. Stellar evolution is driven by a fierce rivalry between two opposing tendencies.

This same struggle underlies the formation of all kinds of astronomical structures, including planets, stars, galaxies and the large-scale structure of the Universe. The existence of these astrophysical systems is ultimately due to gravity, which tends to bind matter. Yet in each case, the tendencies towards gravitational collapse are opposed by the forces of expansion. At all levels, the incessant competition between gravity and entropy ensures that any victory is a temporary phenomenon and is never absolute. For example, the formation of astrophysical structures is never 100% effective. Successfully completed cases of the formation of such objects are just a local victory of gravity, while failed attempts to create something are a triumph of disorder and entropy.

This Great War between gravity and entropy determines the long-term fate and evolution of astrophysical objects such as stars and galaxies. For example, having depleted all its nuclear fuel reserves, a star must change its internal structure... Gravity pulls matter towards the center of the star, while the tendency to increase entropy favors its dissipation. Further battle can have many different outcomes, which depend on the mass of the star and its other properties (for example, the speed of rotation of the star). As we will see, this drama will play out over and over as stellar objects inhabit the universe.

The evolution of the Universe itself is a very effective example of the ongoing struggle between the force of gravity and entropy. Over time, the universe expands and becomes more blurred. This direction of evolution is opposed by gravity, which seeks to collect the sprawling matter of the Universe together. If gravity is the winner in this battle, the expansion of the universe will eventually stop and at some point in the future it will begin to re-contract. On the other hand, lose this battle to gravity, the universe will expand forever. Which of these destinies awaits our Universe in the future depends on the total amount of mass and energy contained in the Universe.

The laws of physics describe how the universe behaves at the most different distances: from monstrously large to negligible. The highest achievement of mankind is the ability to explain and predict how nature behaves in conditions that are extremely far from our everyday life experience. Such a significant expansion of our horizons has occurred mainly during the past century. The realm of our knowledge stretches from the large-scale structures of the Universe to subatomic particles. And although this area of ​​understanding may seem large, it should not be forgotten that the discussion of physical law cannot be continued as far as desired in any of these directions. The largest and smallest scales remain beyond the reach of our modern scientific understanding.

Our physical representation of the largest scale of the universe is limited by causality. Information that is beyond a certain maximum distance simply did not have time to reach us in that relatively short time during which our Universe exists. According to Einstein's theory of relativity, no signals containing information are able to move. faster speed Sveta. Thus, if we take into account that while the universe has lived only about ten billion years, no information signal simply had time to cover a distance exceeding ten billion light years. It is at this distance that the boundary of the universe that we can explore with the help of physics is located; this causality boundary is often called the size of the cosmological horizon. Because of the existence of this barrier of causality, very little can be learned about the Universe at distances beyond the size of the cosmological horizon. This horizon size depends on cosmological time. In the past, when the universe was much younger, the size of the horizon was correspondingly smaller. As the universe ages, it continues to grow.

The cosmological horizon is an extremely important concept that limits the field of science. Just as a football match must take place within clearly defined boundaries, so physical processes in the Universe are limited by the boundaries of this horizon at any the given time... In fact, the existence of a horizon of causality leads to some ambiguity as to what the term "universe" actually means. Sometimes this term refers only to a substance that is within the horizon at a given time. However, the horizon will grow in the future, which means it will eventually include matter that is currently outside of it. Is this "new" substance part of our universe now? The answer can be yes or no, depending on the definition of the term "universe". Likewise, there may be other regions of spacetime that will never fall within our cosmological horizon. For the sake of definiteness, we will assume that such regions of space-time belong to "other universes."

At the smallest distances, the predictive power of physics is also limited, but for a completely different reason. On a scale of less than 10 -33 centimeters (this value is called the Planck length), space-time has a completely different nature than at large distances. At such tiny distances, our traditional concepts of space and time are no longer applicable due to quantum mechanical fluctuations. At this level, to describe space and time, physics must simultaneously include both quantum theory and general relativity. Quantum theory assumes that nature has a wave character at sufficiently small distances. For example, in ordinary matter, electrons orbiting the nucleus of an atom exhibit many wave properties. Quantum theory explains this “waviness”. General relativity states that the geometry of space itself (along with time: at this fundamental level, space and time are closely related) changes in the presence of large quantities of matter, creating strong gravitational fields. However, at the moment, to our great regret, we do not have a complete theory that would combine quantum mechanics with general relativity. The absence of such a theory of quantum gravity very significantly limits what we can say about distances less than the Planck length. As we will see, this limitation of physics largely hinders our understanding of the earliest moments in the history of the universe.

In this biography of the universe, the past ten billion years represent a very small period of time. We must face a major challenge to introduce a timeline that describes the universe of interesting events that are likely to occur over the next 10,100 years.

10 100 - big number... If written without using exponential notation, it will consist of one followed by one hundred zeros and will look like:

10 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000 000.

This number 10 100 is not only too long to write; it is also extremely difficult to imagine exactly how immensely great it is. Attempts to visually represent the number 10 100 by imagining a collection of familiar objects soon fizzle out. For example, the number of grains of sand on all beaches in the world is often cited as an example of an inconceivably large number. However, rough estimates indicate that the total number of all grains of sand is approximately 10 23 (one followed by twenty-three zeros) - a large number, but still hopelessly inadequate for our task. How about the number of stars in the sky? The number of stars in our galaxy is close to one hundred billion - again a relatively small number. The number of stars in all galaxies in our visible universe is about 10 22 - too few. Actually, the total number of protons, the fundamental building blocks that make up matter, in the entire visible universe is only 10 78: even this value is ten billion trillion times less than required! The number of years separating the present moment from eternity is truly immeasurable.

To describe the time scales associated with the future evolution of the Universe, and not to get completely confused, we will use a new unit of time called the cosmological decade. If we denote by τ the time in years, then in the exponential representation τ can be written in the form

τ = 10 η years,

where η is some number. In accordance with our definition, the exponent η is the number of cosmological decades. For example, now the Universe is only about ten billion years old, which corresponds to 10 10 years, or η = 10 cosmological decades. In the future, when the Universe is one hundred billion years old, it will be 10 11 years, or η = 11 cosmological decades. The significance of this scheme is that each subsequent cosmological decade represents a tenfold increase general age The universe. Thus, the concept of the cosmological decade allows us to think about infinitely long periods of time. Thus, the defiantly large number from our example, the number 10 100, corresponds to the much more understandable hundredth cosmological decade, or η = 100.

Cosmological decades can also be used to discuss very short but eventful periods of time immediately after the Big Bang. In this case, we allow the cosmological decade to be negative. Thanks to this expansion, one year after the Big Bang corresponds to 10 0 years, or zero cosmological decade. Then one tenth, or 10 -1, is a cosmological decade -1, one hundredth, or 10 -2 years, is a cosmological decade -2, etc. The beginning of time, when the Big Bang itself occurred, corresponds to τ = 0; in terms of cosmological decades, the Big Bang occurred in the cosmological decade corresponding to infinity with a minus sign.

Our present understanding of the past and future of the Universe can be systematized by highlighting certain time periods. As the universe moves from one epoch to another, its contents and character change quite significantly, and in some respects, almost entirely. These eras, analogous to geological eras, help form an overall impression of the life of the universe. Over time, a number of natural astronomical catastrophes shape the Universe and govern its subsequent evolution. The chronicle of this story can be as follows.

Primary era. -50 < η < 5. Эта эпоха включает раннюю фазу истории Вселенной. В то время, когда Вселенной не исполнилось и десяти тысяч лет, основная часть плотности энергии Вселенной существовала в виде излучения, поэтому этот ранний период часто называют the era of radiation... No astrophysical objects like stars and galaxies have yet formed.

In this short early era, many important events that determined the future course of the development of the Universe. Light elements such as helium and lithium were formed in the first few minutes of this primordial era. Even earlier, complex physical processes caused a slight predominance of ordinary baryonic matter over antimatter. Antimatter almost completely annihilated with most of the substance, after which a small fraction of the latter remained, of which the modern Universe consists.

If the hands of the clock are moved to even more early time, our understanding becomes much less solid. In an extremely early period, when the universe was incredibly hot, the following seems to have happened: quantum fields with very high energies caused fantastically rapid expansion and created very small density perturbations in a homogeneous and unremarkable universe. These tiny irregularities survived and grew into galaxies, clusters and large-scale structures that inhabit the modern universe.

Toward the end of the primary epoch, the radiation energy density became less than the energy density associated with matter. This transition took place when the universe was about ten thousand years old. Shortly thereafter, another watershed event occurred: the temperature of the universe became low enough to allow the existence of atoms (more precisely, hydrogen atoms). First appearance neutral atoms hydrogen is called recombinations... After recombination, perturbations of the density of matter in the Universe allowed it to form clumps that are not subject to the action of the ubiquitous radiation sea. For the first time, familiar astrophysical objects like galaxies and stars began to form.

Age of Stars. 6 < η < 14. Такое название обусловлено наличием звезд. В эту эпоху большая часть энергии, образующейся во Вселенной, возникает в результате реакций ядерного синтеза, которые происходят в обычных звездах. Мы живем в середине эпохи звезд - в то время, когда звезды активно рождаются, живут и умирают.

In the earliest period of the age of stars, when the universe was only a few million years old, the first generation of stars was born. In the first billion years, the first galaxies emerged and began to merge into clusters and superclusters.

Many newly emerging galaxies are experiencing turbulent high-energy phases from the devouring black holes at their centers. When black holes rip apart stars and surround themselves with vortex-like disks of hot gas, huge quantities energy. Over time, these quasars and active galactic nuclei die slowly.

In the future, towards the end of the stellar era, the most common stars in the Universe - low-mass stars called red dwarfs - will play a key role. Red dwarfs are stars whose mass does not exceed half the mass of the Sun, but there are so many of them that their combined mass, undoubtedly, exceeds the mass of all larger stars in the Universe. These red dwarfs are curmudgeons when it comes to converting hydrogen to helium. They accumulate their energy and will exist even after ten trillion years, while more massive stars by that time will have long depleted their nuclear fuel reserves and will evolve into white dwarfs or turn into supernovae. The era of stars will end when the hydrogen gas in galaxies ends, the birth of stars stops, and the long-lived stars (having the smallest mass), red dwarfs, will slowly go out. When the stars finally stop shining, the universe will be about one hundred trillion years old (cosmological decade η = 14).

The era of decay. 15 < η < 39. По завершении эпохи образования и эволюции обычных звезд большая часть обычного вещества во Вселенной окажется заключенной в вырожденных остатках звезд - единственном, что останется по окончании эволюции звезд. В этом контексте под термином вырожденность подразумевается особое квантово-механическое состояние вещества, а никак не состояние аморальности. В список вырожденных объектов входят коричневые карлики, белые карлики, нейтронные звезды и черные дыры. В эпоху распада Вселенная выглядит совсем не так, как сейчас. Нет видимого излучения обычных звезд, которое могло бы оживить небо, согреть планеты или придать галактикам слабое сияние, присущее им сегодня. Вселенная стала холоднее, темнее, а вещество в ней - еще более рассеянным.

And yet the pitch darkness is continually enlivened by astronomically interesting events. Accidental collisions destroy the orbits of dead stars, and galaxies gradually change their structure. Some stellar remnants are ejected far beyond the galaxy, while others fall towards its center. Occasionally, a beacon can also flare up when, as a result of the collision of two brown dwarfs, a new star with a low mass appears, which subsequently lives for trillions of years. On average, at any given time, there will be several such stars shining in a galaxy the size of our Milky Way. From time to time, as a result of the collision of two white dwarfs, the galaxy is shaken by a supernova explosion.

During the decay epoch, white dwarfs, the most common stellar remnants, contain most of the normal baryonic matter in the universe. They collect particles dark matter that orbit the galaxy, forming a huge, blurry halo. Once inside a white dwarf, these particles will subsequently annihilate, thereby providing the universe with an important source of energy. Indeed, the annihilation of dark matter replaces traditional nuclear combustion reactions in stars as the main mechanism of energy generation. However, by the thirtieth cosmological decade (η = 30) or even earlier, the supply of dark matter particles is depleted, as a result of which this method of energy generation comes to its logical conclusion. Now the material content of the Universe is limited to white dwarfs, brown dwarfs, neutron stars and dead planets scattered over great distances from each other.

At the end of the decay epoch, the mass-energy stored in the depths of white dwarfs and neutron stars is scattered as radiation as the protons and neutrons that make up these stars decay. A white dwarf, supported by proton decay, generates about four hundred watts: enough energy to run several light bulbs. The total luminosity of an entire galaxy of such old stars is less than that of one ordinary star, which exists due to the burning of hydrogen, like our Sun. With the completion of the proton decay process, the decay epoch is coming to an end. The universe - even darker, even more rarefied - is changing again.

The era of black holes. 40 < η < 100. По завершении эпохи распада протонов из всех подобных звездам астрофизических объектов остаются только черные дыры. Эти фантастические объекты обладают столь сильным gravitational field that even light cannot leave their surfaces. The decay of protons does not affect black holes in any way, so at the end of the decay epoch they remain safe and sound.

As white dwarfs evaporate and disappear, black holes absorb matter and grow larger. Yet even black holes cannot live forever. Ultimately, they must evaporate in a very slow quantum mechanical process called Hawking radiation... Despite their name, black holes are not completely black. In fact, they glow, albeit extremely faintly, emitting a thermal spectrum of light and other decay products. After the disappearance of protons, the evaporation of black holes becomes the main source of the almost invisible energy of the Universe. A black hole, which has the mass of the Sun, will live for about sixty-five cosmological decades; a large black hole, which has the mass of a galaxy, will evaporate in ninety-eight or one hundred cosmological decades. Thus, all black holes are destined to perish. The era of black holes ends after the evaporation of the largest black holes.

The era of eternal darkness.η> 101. After a hundred cosmological decades, protons have long decayed, and black holes have evaporated. Only the residual products of these processes remain: photons with huge wavelengths, neutrinos, electrons and positrons. There is a strange parallel between the era of eternal darkness and the primordial era, when the universe was less than a million years old. In each of these epochs, very, very distant in time, there are no star-like objects that could generate energy.

In this cold, distant future, activity in the Universe is almost over. Energy has dropped to extremely low levels, and the time gaps are mind-boggling. Electrons and positrons drifting in space meet each other and from time to time form positronium atoms. However, these structures formed so late are unstable, and their constituent particles, sooner or later, annihilate. Other low-level annihilation events can occur, albeit very slowly.

Compared to its lavish past, the universe is now living a relatively conservative and humble life. Or not? The apparent poverty of this era so far from us, perhaps, is due to the uncertainty of our extrapolation, and not the real transition of the Universe to old age.

Our society has realized with no small measure of concern that the extinction of humanity is not such a far-fetched problem. Nuclear confrontation, environmental disasters and spreading viruses are far from all the prospects for the end of the world, which are drawn to everyone's attention by cautious, paranoid and profit-minded people. But what if we accept the somewhat outdated but far more romantic perspective on rockets, colonies in space, and the conquests of the galaxy? In such a future, humanity could easily postpone the rapidly approaching death of the Earth, simply by moving to other solar systems. But can we extend the life of the stars themselves? Can we find a way to get around the decay of the proton? Can we do without the properties of black holes that provide the Universe with energy? Will any living organisms be able to survive the final all-encompassing devastation of the era of eternal darkness?

In this book, we consider the prospects and possibilities of preserving life in each era of the future evolution of the Universe. This analysis is inevitably accompanied by an atmosphere of some uncertainty. The general theoretical understanding of life is notable for its absence. Even in the only habitat where we have direct experience, on our native Earth, the emergence of life has not yet been understood. Thus, in our audacious discussions of the possibility of the existence of life in the distant future, we are in a qualitatively different position than when we are dealing with purely astrophysical phenomena.

Despite the fact that we do not have a solid theoretical paradigm describing the origin of life, we need at least some working model that would allow us to systematize our assessment of the prospects for the preservation and spread of life. To cover at least part of the full range of possibilities, we base our thinking on two very different models of life. In the first and most obvious case, we consider life, which is based on biochemistry, approximately similar to that of the earth. This kind of life could arise on planets like Earth, or on large moons in other solar systems. Paying tribute to a time-honored tradition among exobiologists, suppose that as long as there is liquid water on a planet, life based on carbon can arise and develop on this planet. The requirement that water must be in a liquid state imposes a fairly strict temperature limit on any potential habitat. For example, for atmospheric pressure, the temperature should be greater than 273 degrees Kelvin, which corresponds to the freezing point of water, and less than 373 degrees Kelvin, which corresponds to the boiling point of water. This temperature range excludes most astrophysical environments.

The second class of life forms is based on a much more abstract model. In this last case, we are in to a large extent we use the ideas of Freeman Dyson, an influential physicist who put forward the hypothesis of the correspondence of scales for abstract life forms. The main idea is that at any temperature one can imagine some abstract form of life that feels great at a given temperature, at least in principle. Moreover, the rate at which this abstract creature expends energy is directly proportional to its temperature. For example, if we imagine some kind of Dyson's organism living at a certain given temperature, then, according to the law of scale correspondence, all vital functions of another qualitatively similar life form, content with half the temperature, should be slowed down by the same two times. In particular, if the Dyson organisms under consideration have intelligence and some kind of consciousness, then the actual speed of their sensation of the events taking place is determined not by real physical time, but by the so-called scale time proportional to temperature. In other words, the rate of awareness in Dyson organisms living at low temperatures is lower than that of (otherwise) a similar life form existing at higher temperatures.

This abstract approach takes the discussion far beyond the usual carbon-based life form that exists on our planet, but it still allows some assumptions about the nature of life in general. First of all, it is necessary to accept that the primary basis of thinking is structure life form, and not in the substance that forms it. For example, in humans, thinking somehow arises in the course of many complex biochemical processes in the brain. The question is whether this organic structure is necessary. If we could somehow create another copy of this entire structure - a human - using a different set of building materials, would this copy be able to think in the same way? Would the copy think she was that very person? If an organic design is necessary for any reason, then a key role is played substance, of which life is composed, and the possibility of the existence of abstract life forms in a vast range of different environments is very limited. If, on the contrary, as we assume here, only structure then many life forms can exist in a wide range of different environments. The Dyson scale correspondence hypothesis gives us a rough idea of ​​the metabolic and thinking rates of these abstract life forms. This frame of reference is highly optimistic, but, as we shall see, it has rich and interesting implications.

As our story continues, and the great eras succeed each other, the nature of the physical universe changes almost completely. A direct consequence of this change is that the universe of the distant future or distant past is completely different from the universe in which we live today. Since the modern Universe is comfortable enough for life in the form in which we know it - we have stars that supply us with energy, and planets on which to live - we are all quite naturally inclined to consider modern era in a sense occupying a special position. In opposition to this opinion, we accept the idea of "Copernicus's time principle" which simply says that the modern cosmological epoch does not occupy a special place in time. In other words, in the process of evolution and changes in the Universe, interesting events will not stop in it. While real levels of energy and entropy production are getting lower, this is offset by lengthening timelines that will become available in the future. To paraphrase this thought once again, we argue that the laws of physics do not predict that the universe will one day reach a state of complete rest, but rather that interesting physical processes will not stop in such a distant future as we dare to look.

Copernicus's idea of ​​the time principle is a natural extension of our ever-expanding view of the universe. A global revolution in worldview took place in the sixteenth century, when Nicolaus Copernicus declared that the Earth was not the center of our solar system, as previously thought. Copernicus understood quite correctly that the Earth is just one of the many planets that orbit around the Sun. This obvious belittling of the status of the Earth, and, consequently, of humanity at that time caused a strong resonance. As is usually said, due to the heretical consequences of such a shift in thinking, Copernicus was forced to postpone the publication of his the greatest work De Revolutionibus Orbium Coelestium until 1543 - the year of his death. He hesitated to the very end and was close to hiding his work. In the introduction to his book, Copernicus writes: “I almost put my completed work in a box, because of the contempt that I had a presentiment for, having reasons for that, due to the novelty and obvious contradiction of my theory common sense". Despite the delay, this work was eventually published, and the first printed copy went to Copernicus's deathbed. The earth was no longer considered the center of the universe. A global revolution has begun.

After the revolution made by Copernicus, the decline in our status not only continued, but also accelerated. Very soon, astronomers established that other stars are, in fact, objects similar to our Sun, and they can, at least in principle, have their own planetary systems... One of the first to this conclusion was Giordano Bruno, who stated that other stars not only have planets, but that these planets are inhabited! Subsequently, in 1601, the inquisitors of the Roman Catholic Church burned him at the stake, although allegedly not because of his statements regarding questions of astronomy. Since then, the idea that planets may also exist in other solar systems has been picked up from time to time by eminent scientists, including Leonard Euler, Immanuel Kant, and Pierre Simon Laplace.

Interestingly, for almost four centuries, the idea of ​​the existence of planets outside our solar system remained pure theoretical concept, in support of which there was no data. Only in the last few years, starting in 1995, astronomers have established for sure that planets orbiting other stars do exist. With new opportunities for observation and great work done, Jeff Marcy, Michelle Major and their associates have shown that planetary systems are relatively common. Now our solar system has become just one of the possibly billions of solar systems that exist in the galaxy. A new coup has begun.

Climbing to the next level, we find that our Galaxy is not the only one in the Universe. As cosmologists first realized in the early twentieth century, the visible universe is full of galaxies, each containing billions of stars that may well have their own planetary systems. Moreover, once Copernicus said that our planet does not have a special place within our solar system, but now modern cosmology has proved that our Galaxy does not occupy a special position in the Universe. In fact, the universe appears to obey cosmological principle(see next chapter), which states that at large distances the universe is the same everywhere in space (the universe is homogeneous) and that the universe looks the same in all directions (the universe is isotropic). The cosmos has neither privileged places nor preferred destinations. The universe exhibits striking regularity and simplicity.

Each subsequent lowering of the central status of the Earth leads to the irrevocable conclusion that the location of our planet in the Universe is unremarkable. The Earth is an ordinary planet orbiting a moderately bright star in an ordinary Galaxy located in a randomly selected place in the Universe. Copernicus's temporal principle extends this general idea from the realm of space to the realm of time. Just as our planet, and hence humanity, does not have a special location in the Universe, so our current cosmological epoch does not occupy a special place in the vast expanses of time. This principle only continues the destruction of that little bit of anthropocentric thinking that still exists.

We are writing this book at the very end of the twentieth century - an opportune time to reflect on our place in the universe. Thanks to the vastness of understanding gained in this century, we can look more closely at our position in time and space than ever before. In accordance with the Copernican time principle and the widest range of astrophysical events that are yet to occur in the immense future, we argue that at the end of this millennium, the end of the universe is not very close. Armed with four forces of nature, four astronomical windows to view the Universe, and a new calendar that measures time in cosmological decades, we set off on our journey through five great eras of time.

Notes:

On the rotations of the celestial spheres (lat.). - Approx. transl.

Formation of protogalactic clouds less than about 1 billion years after the Big Bang

We are well aware of the force of gravity that keeps us on the ground and makes it difficult to fly to the moon. And electromagnetism, thanks to which we do not disintegrate into separate atoms and can plug in laptops. The physicist talks about two more forces that make the universe exactly what it is.

From school, we all know well the law of gravitation and Coulomb's law. The first explains to us how massive objects such as stars and planets interact (attract) with each other. The other shows (recall the experiment with an ebonite stick) what forces of attraction and repulsion arise between electrically charged objects.

But is this exhausted by the whole multitude of forces and interactions that determine the appearance of the universe we observe?

Modern physics says that there are four types of basic (fundamental) interactions between particles in the Universe. I have already said about two of them above, and with them, it would seem, everything is simple, since their manifestations constantly surround us in everyday life: this is the gravitational and electromagnetic interaction.

So, due to the action of the first, we stand firmly on the ground and do not fly into open space. The second, for example, ensures the attraction of an electron to a proton in the atoms of which we are all made up and, ultimately, the attraction of atoms to each other (i.e., it is responsible for the formation of molecules, biological tissues, etc.). So it is precisely because of the forces of electromagnetic interaction, for example, that it turns out that it is not so easy to take off the head of an annoying neighbor, and for this purpose we have to resort to using an ax of various improvised means.

But there is also the so-called strong interaction. What is it responsible for? Didn't you be surprised at school by the fact that, despite the statement of Coulomb's law that two positive charges should repel each other (only opposite ones attract), the nuclei of many atoms quietly exist for themselves. But they consist, as you remember, of protons and neutrons. Neutrons - they are neutrons because they are neutral and have no electric charge, but protons are positively charged. And what, one wonders, forces can hold together (at a distance of one trillionth of a micron - which is a thousand times smaller than the atom itself!) Several protons, which, according to Coulomb's law, should repel each other with terrible energy?

Strong interaction - provides attraction between particles in the core; electrostatic - repulsion

This truly titanic task of overcoming the Coulomb forces is undertaken by a strong interaction. So, neither more nor less, due to it, the protons (as well as neutrons) in the nucleus are nevertheless attracted to each other. By the way, the protons and neutrons themselves also consist of even more "elementary" particles - quarks. So quarks also interact and are attracted to each other "strongly". But, fortunately, unlike the same gravitational interaction that works at cosmic distances of many billions of kilometers, the strong interaction is said to be short-range. This means that the field of "strong attraction" surrounding one proton works only on a tiny scale, comparable, in fact, with the size of the nucleus.

Therefore, for example, a proton sitting in the nucleus of one of the atoms cannot, spitting on the Coulomb repulsion, take and “strongly” attract a proton from a neighboring atom. Otherwise, all proton and neutron matter in the Universe could be "attracted" to the common center of mass and form one huge "supernucleus". Something similar, however, happens in the thickness of neutron stars, into one of which, as can be expected, one day (about five billion years later) our Sun will contract.

So, the fourth and last of the fundamental interactions in nature is the so-called weak interaction. It is not for nothing that it is so called: not only does it work even at distances even shorter than strong interaction, but also its power is very small. So, unlike its strong "brother", the Coulomb repulsion, it will not outweigh it in any way.

A striking example demonstrating the weakness of weak interactions are particles called neutrinos (can be translated as "small neutron", "neutron"). These particles, by their nature, do not participate in strong interactions, do not have an electric charge (therefore, they are not susceptible to electromagnetic interactions), have an insignificant mass even by the standards of the microcosm and, therefore, are practically insensitive to gravity, in fact, are only capable of weak interactions.

Cho? Neutrinos pass through me ?!

At the same time, in the Universe, neutrinos are born in truly colossal quantities, and a huge stream of these particles constantly permeates the thickness of the Earth. For example, in the volume of a matchbox, on average, there are about 20 neutrinos at each moment of time. Thus, one can imagine a huge barrel of water-detector, which I wrote about in my last post, and the incredible amount of neutrinos that flies through it at every moment of time. So, scientists working on this detector usually have to wait for months for such a happy occasion for at least one neutrino to "feel" their barrel and interact in it with its weak forces.

However, even despite its weakness, this interaction plays a very important role in the Universe and in human life. So, it is it that turns out to be responsible for one of the types of radioactivity - namely, beta decay, which is the second (after gamma radioactivity) in terms of the degree of danger of its impact on living organisms. And, no less important, without weak interaction it would be impossible for thermonuclear reactions occurring in the bowels of many stars and responsible for the release of the energy of the star.

Such is the four horsemen of the Apocalypse of fundamental interactions that reign in the Universe: strong, electromagnetic, weak and gravitational.