Four fundamental interactions. Basic forces of the universe 4 forces in physics

Formation of protogalactic clouds less than about 1 billion years after the Big Bang
Image: Adolf Schaller, Hubble Gallery (NASA)

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 fall apart into individual atoms and can plug laptops into the outlet. Physicist koptchick talks about two more forces that make the universe exactly the way it is.

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

But is this the whole set 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 mentioned two of them above, and it would seem that everything is simple with them, because their manifestations constantly surround us in everyday life: this is gravitational and electromagnetic interaction.

So, due to the action of the first, we firmly stand on the ground and do not fly away into outer space. The second, for example, ensures the attraction of an electron to a proton in atoms, of which we all consist, 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 cut off the head of an annoying neighbor, and for this purpose we have to resort to the help of an ax of various improvised means.

But there is also the so-called strong interaction. What is it responsible for? Were you surprised in school by the fact that, despite the assertion of Coulomb's law that two positive charges must repel each other (only opposite charges attract), the nuclei of many atoms quietly exist for themselves. But they consist, as you remember, of protons and neutrons. Neutrons are neutrons because they are neutral and have no electric charge, but protons are positively charged. And what kind of forces, one wonders, can hold together (at a distance of one trillionth of a micron - which is a thousand times less than the atom itself!) Several protons, which, according to Coulomb's law, must repel each other with terrible energy?

Strong interaction - provides attraction between particles in the nucleus; electrostatic - repulsion
This truly titanic task of overcoming the Coulomb forces is taken over by the strong interaction. So, neither more nor less, due to it, protons (as, indeed, neutrons) in the nucleus are still attracted to each other. By the way, 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, which also works at cosmic distances of many billions of kilometers, the strong interaction is, as they say, short-range. This means that the "strong attraction" field surrounding one proton works only on tiny scales, comparable, in fact, with the size of the nucleus.

Therefore, for example, a proton sitting in the nucleus of one of the atoms cannot, having given a damn about the Coulomb repulsion, take and “strongly” attract a proton from a neighboring atom to itself. 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, occurs in the thickness of neutron stars, into one of which, as you can expect, one day (in about five billion years) our Sun will shrink.

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 named: not only does it work even at distances even shorter than the strong interaction, but also its power is very small. So, unlike its strong "brother", the Coulomb repulsion, it will not overtighten 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 (and therefore are not susceptible to electromagnetic interactions), have an insignificant mass even by the standards of the microworld and, therefore, are practically insensitive to gravity, in fact, are capable of only weak interactions.

What? Neutrinos pass through me?!
At the same time, neutrinos are generated in the Universe in truly colossal quantities, and a huge stream of these particles constantly penetrates the thickness of the Earth. For example, in the volume of a matchbox, on average, there are 20 neutrinos at each moment of time. Thus, one can imagine a huge barrel of water-detector, and the incredible amount of neutrinos that flies through it at any given time. So, scientists working on this detector usually have to wait for months for such a happy occasion, so that at least one neutrino “feels” their barrel and interacts 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 precisely it that turns out to be responsible for one of the types of radioactivity - namely, beta decay, which is second (after gamma radioactivity) in terms of the degree of danger of its effect on living organisms. And, no less important, without weak interaction, it would be impossible for thermonuclear reactions to take place in the interiors of many stars and are responsible for the release of energy from the star.

This is the four horsemen of the Apocalypse of fundamental interactions that rule the Universe: strong, electromagnetic, weak and gravitational.

Modern achievements of high-energy physics are increasingly strengthening the idea that the diversity of the properties of Nature is due to interacting elementary particles. It is apparently impossible to give an informal definition of an elementary particle, since we are talking about the most primary elements of matter. At a qualitative level, we can say that physical objects that do not have constituent parts are called true elementary particles.
Obviously, the question of the elementarity of physical objects is primarily an experimental question. For example, it has been experimentally established that molecules, atoms, atomic nuclei have an internal structure indicating the presence of constituent parts. Therefore, they cannot be considered elementary particles. More recently, it has been discovered that particles such as mesons and baryons also have an internal structure and are therefore not elementary. At the same time, the internal structure of an electron has never been observed, and, therefore, it can be attributed to elementary particles. Another example of an elementary particle is a quantum of light - a photon.
Modern experimental data indicate that there are only four qualitatively different types of interactions in which elementary particles participate. These interactions are called fundamental, that is, the most basic, initial, primary. If we take into account all the diversity of the properties of the World around us, then it seems completely surprising that in Nature there are only four fundamental interactions responsible for all the phenomena of Nature.
In addition to qualitative differences, fundamental interactions differ quantitatively in terms of the strength of the impact, which is characterized by the term intensity. As the intensity increases, the fundamental interactions are arranged in the following order: gravitational, weak, electromagnetic, and strong. Each of these interactions is characterized by a corresponding parameter, called the coupling constant, whose numerical value determines the intensity of the interaction.
How do physical objects carry out fundamental interactions with each other? Qualitatively, the answer to this question is as follows. Fundamental interactions are carried by quanta. At the same time, in the quantum field, fundamental interactions correspond to the corresponding elementary particles, called elementary particles - carriers of interactions. In the process of interaction, a physical object emits particles - interaction carriers, which are absorbed by another physical object. This leads to the fact that objects seem to feel each other, their energy, nature of movement, state change, that is, they experience mutual influence.
In modern high-energy physics, the idea of unification of fundamental interactions is becoming increasingly important. According to the ideas of unification, in Nature there is only one single fundamental interaction, which manifests itself in specific situations as gravitational, or as weak, or as electromagnetic, or as strong, or as some combination of them. The successful implementation of the unification ideas was the creation of the already standard unified theory of electromagnetic and weak interactions. Work is underway to develop a unified theory of electromagnetic, weak and strong interactions, called the grand unification theory. Attempts are being made to find the principle of unification of all four fundamental interactions. We will sequentially consider the main manifestations of fundamental interactions.

Gravitational interaction

This interaction is universal in nature, all types of matter, all objects of nature, all elementary particles participate in it! The generally accepted classical (not quantum) theory of gravitational interaction is Einstein's general theory of relativity. Gravity determines the motion of planets in stellar systems, plays an important role in the processes occurring in stars, controls the evolution of the Universe, and under terrestrial conditions manifests itself as a force of mutual attraction. Of course, we have listed only a small number of examples from the huge list of gravity effects.
According to the general theory of relativity, gravity is related to the curvature of space-time and is described in terms of the so-called Riemannian geometry. At present, all experimental and observational data on gravity fit within the framework of the general theory of relativity. However, data on strong gravitational fields are essentially absent, so the experimental aspects of this theory raise many questions. This situation gives rise to the emergence of various alternative theories of gravity, the predictions of which are practically indistinguishable from the predictions of general relativity for physical effects in the solar system, but lead to different consequences in strong gravitational fields.
If we neglect all relativistic effects and confine ourselves to weak stationary gravitational fields, then the general theory of relativity is reduced to the Newtonian theory of universal gravitation. In this case, as is known, the potential energy of interaction of two point particles with masses m 1 and m 2 is given by the relation

where r is the distance between particles, G is the Newtonian gravitational constant, which plays the role of the gravitational interaction constant. This relationship shows that the potential interaction energy V(r) is nonzero for any finite r and falls to zero very slowly. For this reason, the gravitational interaction is said to be long-range.
Of the many physical predictions of the general theory of relativity, we note three. It is theoretically established that gravitational perturbations can propagate in space in the form of waves called gravitational. Propagating weak gravitational perturbations are in many ways similar to electromagnetic waves. Their speed is equal to the speed of light, they have two states of polarization, they are characterized by the phenomena of interference and diffraction. However, due to the extremely weak interaction of gravitational waves with matter, their direct experimental observation has not yet been possible. Nevertheless, the data of some astronomical observations on the loss of energy in binary star systems indicate the possible existence of gravitational waves in nature.
A theoretical study of the equilibrium conditions for stars within the framework of the general theory of relativity shows that, under certain conditions, sufficiently massive stars can begin to shrink catastrophically. This turns out to be possible at rather late stages of the star's evolution, when the internal pressure caused by the processes responsible for the star's luminosity is not able to balance the pressure of the gravitational forces tending to compress the star. As a result, the compression process can no longer be stopped by anything. The described physical phenomenon, predicted theoretically in the framework of the general theory of relativity, was called gravitational collapse. Studies have shown that if the radius of a star becomes smaller than the so-called gravitational radius

Rg \u003d 2GM / c 2,

where M is the mass of the star, and c is the speed of light, then for an external observer the star goes out. No information about the processes taking place in this star can reach an external observer. In this case, the bodies falling on the star freely cross the gravitational radius. If an observer is meant as such a body, then he will not notice anything but an increase in gravity. Thus, there is a region of space that can be entered, but from which nothing can exit, including a light beam. This region of space is called a black hole. The existence of black holes is one of the theoretical predictions of the general theory of relativity, some alternative theories of gravity are constructed in such a way that they prohibit this type of phenomenon. In this regard, the question of the reality of black holes is of exceptional importance. At present, there are observational data indicating the presence of black holes in the Universe.
Within the framework of the general theory of relativity, for the first time, it was possible to formulate the problem of the evolution of the Universe. Thus, the Universe as a whole becomes not a subject of speculative reasoning, but an object of physical science. The branch of physics that deals with the universe as a whole is called cosmology. It is now considered firmly established that we live in an expanding universe.
The modern picture of the evolution of the universe is based on the idea that the universe, including its attributes such as space and time, arose as a result of a special physical phenomenon called the Big Bang, and has been expanding ever since. According to the theory of the evolution of the universe, the distances between distant galaxies should increase with time, and the entire universe should be filled with thermal radiation with a temperature of the order of 3 K. These predictions of the theory are in excellent agreement with the data of astronomical observations. At the same time, estimates show that the age of the Universe, that is, the time elapsed since the Big Bang, is about 10 billion years. As for the details of the Big Bang, this phenomenon is poorly understood and one can speak of the mystery of the Big Bang as a challenge to physical science as a whole. It is possible that the explanation of the mechanism of the Big Bang is connected with new, as yet unknown, laws of Nature. The generally accepted modern view of a possible solution to the Big Bang problem is based on the idea of combining the theory of gravity and quantum mechanics.

The concept of quantum gravity

Is it even possible to talk about quantum manifestations of gravitational interaction? As is commonly believed, the principles of quantum mechanics are universal and applicable to any physical object. In this sense, the gravitational field is no exception. Theoretical studies show that at the quantum level, the gravitational interaction is carried by an elementary particle called a graviton. It can be noted that the graviton is a massless boson with spin 2. The gravitational interaction between particles, due to the exchange of the graviton, is conventionally depicted as follows:

The particle emits a graviton, due to which the state of its motion changes. Another particle absorbs the graviton and also changes the state of its motion. As a result, particles interact with each other.
As we have already noted, the coupling constant characterizing the gravitational interaction is the Newtonian constant G. It is well known that G is a dimensional quantity. Obviously, to estimate the intensity of interaction it is convenient to have a dimensionless coupling constant. To obtain such a constant, one can use the fundamental constants: (Planck's constant) and c (the speed of light) - and introduce some reference mass, for example, the proton mass m p . Then the dimensionless coupling constant of the gravitational interaction will be

Gm p 2 /(c) ~ 6 10 -39 ,

which, of course, is a very small quantity.
It is interesting to note that from the fundamental constants G, , c it is possible to construct quantities having the dimensions of length, time, density, mass, energy. These quantities are called Planck. In particular, the Planck length l Pl and the Planck time t Pl are as follows:

Each fundamental physical constant characterizes a certain range of physical phenomena: G - gravitational phenomena, - quantum, c - relativistic. Therefore, if some ratio includes G, , c at the same time, then this means that this ratio describes a phenomenon that is simultaneously gravitational, quantum and relativistic. Thus, the existence of Planck values indicates the possible existence of the corresponding phenomena in Nature.
Of course, the numerical values of l Pl and t Pl are very small compared to the characteristic values of quantities in the macrocosm. But this only means that quantum gravitational effects are weakly manifested. They could be significant only when the characteristic parameters would become comparable with the Planck values.
A distinctive feature of the phenomena of the microworld is the fact that physical quantities are subject to the so-called quantum fluctuations. This means that with multiple measurements of a physical quantity in a certain state, in principle, different numerical values should be obtained due to the uncontrolled interaction of the device with the observed object. Recall that gravity is associated with the manifestation of the curvature of space-time, that is, with the geometry of space-time. Therefore, it should be expected that at times of the order of t Pl and distances of the order of l Pl, the space-time geometry should become a quantum object, the geometric characteristics should experience quantum fluctuations. In other words, there is no fixed space-time geometry on the Planck scale, figuratively speaking, space-time is a bubbling foam.
A consistent quantum theory of gravity has not been built. Due to the extremely small values of l Pl , t Pl, it should be expected that in any foreseeable future it will not be possible to carry out experiments in which quantum gravitational effects would manifest themselves. Therefore, the theoretical study of questions of quantum gravity remains the only way forward. Are there, however, phenomena where quantum gravity could be significant? Yes, there are, and we have already talked about them. This is gravitational collapse and the Big Bang. According to the classical theory of gravity, an object subject to gravitational collapse must be compressed to an arbitrarily small size. This means that its dimensions can become comparable to l Pl , where the classical theory is no longer applicable. Similarly, during the Big Bang, the age of the Universe was comparable to t Pl and it had dimensions of the order of l Pl . This means that understanding the physics of the Big Bang is impossible within the framework of classical theory. Thus, the description of the final stage of the gravitational collapse and the initial stage of the evolution of the Universe can only be carried out with the involvement of the quantum theory of gravity.

Weak interaction

This interaction is the weakest of the fundamental interactions experimentally observed in the decays of elementary particles, where quantum effects are fundamentally significant. Recall that quantum manifestations of gravitational interaction have never been observed. Weak interaction is singled out using the following rule: if an elementary particle called a neutrino (or antineutrino) participates in the interaction process, then this interaction is weak.

A typical example of a weak interaction is the neutron beta decay

N p + e - + e,

where n is a neutron, p is a proton, e is an electron, e is an electron antineutrino. However, it should be borne in mind that the above rule does not mean at all that any act of weak interaction must be accompanied by a neutrino or antineutrino. It is known that a large number of neutrinoless decays take place. As an example, we can note the process of decay of a lambda hyperon into a proton p and a negatively charged pion π − . According to modern concepts, the neutron and proton are not truly elementary particles, but consist of elementary particles called quarks.
The intensity of the weak interaction is characterized by the Fermi coupling constant G F . The constant G F is dimensional. To form a dimensionless quantity, it is necessary to use some standard mass, for example, the proton mass m p . Then the dimensionless coupling constant will be

G F m p 2 ~ 10 -5 .

It can be seen that the weak interaction is much more intense than the gravitational one.
The weak interaction, in contrast to the gravitational one, is short-range. This means that the weak interaction between particles only comes into play if the particles are close enough to each other. If the distance between the particles exceeds a certain value, called the characteristic radius of interaction, the weak interaction does not manifest itself. It has been experimentally established that the characteristic radius of the weak interaction of the order of 10 -15 cm, that is, the weak interaction, is concentrated at distances smaller than the size of the atomic nucleus.
Why can we talk about the weak interaction as an independent form of fundamental interactions? The answer is simple. It has been established that there are processes of transformations of elementary particles that cannot be reduced to gravitational, electromagnetic and strong interactions. A good example showing that there are three qualitatively different interactions in nuclear phenomena is related to radioactivity. Experiments indicate the presence of three different types of radioactivity: -, - and -radioactive decays. In this case, -decay is due to strong interaction, -decay - electromagnetic. The remaining -decay cannot be explained by the electromagnetic and strong interactions, and we are forced to accept that there is another fundamental interaction called the weak one. In the general case, the need to introduce a weak interaction is due to the fact that processes occur in nature in which electromagnetic and strong decays are prohibited by conservation laws.
Although the weak interaction is essentially concentrated inside the nucleus, it has certain macroscopic manifestations. As we have already noted, it is associated with the process of β-radioactivity. In addition, the weak interaction plays an important role in the so-called thermonuclear reactions responsible for the mechanism of energy release in stars.
The most amazing property of the weak interaction is the existence of processes in which mirror asymmetry is manifested. At first glance, it seems obvious that the difference between the concepts of left and right is arbitrary. Indeed, the processes of gravitational, electromagnetic, and strong interactions are invariant with respect to spatial inversion, which implements mirror reflection. It is said that in such processes the spatial parity P is conserved. However, it has been experimentally established that weak processes can proceed with nonconservation of spatial parity and, therefore, seem to feel the difference between left and right. At present, there is solid experimental evidence that parity nonconservation in weak interactions is of a universal nature; it manifests itself not only in the decays of elementary particles, but also in nuclear and even atomic phenomena. It should be recognized that mirror asymmetry is a property of Nature at the most fundamental level.
Parity nonconservation in weak interactions seemed to be such an unusual property that almost immediately after its discovery, theorists attempted to show that in fact there is a complete symmetry between left and right, only it has a deeper meaning than previously thought. Mirror reflection must be accompanied by the replacement of particles by antiparticles (charge conjugation C), and then all fundamental interactions must be invariant. However, later it was found that this invariance is not universal. There are weak decays of the so-called long-lived neutral kaons into pions π + , π − , which are forbidden if the indicated invariance actually takes place. Thus, the distinguishing property of the weak interaction is its CP non-invariance. It is possible that this property is responsible for the fact that the matter in the Universe significantly prevails over antimatter, built from antiparticles. The world and the anti-world are not symmetrical.
The question of which particles are carriers of the weak interaction was unclear for a long time. Understanding was achieved relatively recently within the framework of the unified theory of electroweak interactions - the theory of Weinberg-Salam-Glashow. It is now generally accepted that the carriers of the weak interaction are the so-called W ± - and Z 0 -bosons. These are charged W ± and neutral Z 0 elementary particles with spin 1 and masses equal in order of magnitude to 100 m p .

Electromagnetic interaction

All charged bodies, all charged elementary particles participate in electromagnetic interaction. In this sense, it is quite universal. The classical theory of electromagnetic interaction is Maxwellian electrodynamics. The electron charge e is taken as the coupling constant.
If we consider two resting point charges q 1 and q 2, then their electromagnetic interaction will be reduced to a known electrostatic force. This means that the interaction is long-range and slowly decreases with increasing distance between charges.
The classical manifestations of electromagnetic interaction are well known, and we will not dwell on them. From the point of view of quantum theory, the carrier of electromagnetic interaction is the elementary particle photon - a massless boson with spin 1. Quantum electromagnetic interaction between charges is conventionally depicted as follows:

A charged particle emits a photon, whereby the state of its motion changes. Another particle absorbs this photon and also changes the state of its motion. As a result, the particles seem to feel the presence of each other. It is well known that electric charge is a dimensional quantity. It is convenient to introduce the dimensionless coupling constant of the electromagnetic interaction. To do this, we need to use the fundamental constants and c. As a result, we arrive at the following dimensionless coupling constant, which in atomic physics is called the fine structure constant α = e 2 /c ≈1/137.

It is easy to see that this constant significantly exceeds the constants of the gravitational and weak interactions.
From a modern point of view, the electromagnetic and weak interactions are different aspects of the single electroweak interaction. A unified theory of the electroweak interaction has been created - the Weinberg-Salam-Glashow theory, which explains from a unified position all aspects of electromagnetic and weak interactions. Is it possible to understand at a qualitative level how the unified interaction is divided into separate, as it were, independent interactions?
As long as the characteristic energies are small enough, the electromagnetic and weak interactions are separated and do not affect each other. As the energy increases, their mutual influence begins, and at sufficiently high energies these interactions merge into a single electroweak interaction. The characteristic unification energy is estimated in order of magnitude as 10 2 GeV (GeV is short for gigaelectronvolt, 1 GeV = 10 9 eV, 1 eV = 1.6·10 -12 erg = 1.6·10 19 J). For comparison, we note that the characteristic energy of an electron in the ground state of a hydrogen atom is about 10 -8 GeV, the characteristic binding energy of an atomic nucleus is about 10 -2 GeV, the characteristic binding energy of a solid is about 10 -10 GeV. Thus, the characteristic energy of the unification of electromagnetic and weak interactions is enormous compared to the characteristic energies in atomic and nuclear physics. For this reason, electromagnetic and weak interactions do not manifest their common essence in ordinary physical phenomena.

Strong interaction

The strong force is responsible for the stability of atomic nuclei. Since the atomic nuclei of most chemical elements are stable, it is clear that the interaction that keeps them from decay must be strong enough. It is well known that nuclei are made up of protons and neutrons. In order for positively charged protons not to scatter in different directions, it is necessary to have attractive forces between them that exceed the forces of electrostatic repulsion. It is the strong interaction that is responsible for these attractive forces.
A characteristic feature of the strong interaction is its charge independence. The nuclear forces of attraction between protons, between neutrons, and between a proton and a neutron are essentially the same. From this it follows that from the point of view of strong interactions, the proton and neutron are indistinguishable and a single term is used for them nucleon, that is, a particle of the nucleus.

The characteristic scale of the strong interaction can be illustrated by considering two nucleons at rest. The theory leads to the potential energy of their interaction in the form of the Yukawa potential

where the value r 0 ≈10 -13 cm and coincides in order of magnitude with the characteristic size of the nucleus, g is the coupling constant of the strong interaction. This relation shows that the strong interaction is short-range and essentially completely concentrated at distances not exceeding the characteristic size of the nucleus. For r > r 0, it practically disappears. A well-known macroscopic manifestation of the strong interaction is the -radioactivity effect. However, it should be kept in mind that the Yukawa potential is not a universal property of the strong interaction and is not related to its fundamental aspects.
At present, there is a quantum theory of the strong interaction, called quantum chromodynamics. According to this theory, the carriers of the strong interaction are elementary particles - gluons. According to modern concepts, the particles involved in the strong interaction and called hadrons consist of elementary particles - quarks.
Quarks are fermions with spin 1/2 and non-zero mass. The most amazing property of quarks is their fractional electric charge. Quarks form into three pairs (three generations of doublets), denoted as follows:

u	c
d	s	b

Each type of quark is called a flavor, so there are six quark flavors. In this case, u-, c-, t-quarks have an electric charge of 2/3|e| , and d-, s-, b-quarks - electric charge -1/3|e|, where e - electron charge. In addition, there are three quarks of this flavor. They differ in a quantum number called color and taking on three values: yellow, blue, red. Each quark corresponds to an antiquark, which has an opposite electric charge in relation to this quark and the so-called anticolor: antiyellow, antiblue, antired. Taking into account the number of flavors and colors, we see that there are 36 quarks and antiquarks in total.
Quarks interact with each other through the exchange of eight gluons, which are massless bosons with spin 1. During the interaction, the colors of the quarks can change. In this case, the strong interaction is conventionally depicted as follows:

The quark, which is part of the hadron, emits a gluon, due to which the state of motion of the hadron changes. This gluon is absorbed by a quark that is part of another hadron and changes the state of its motion. As a result, hadrons interact with each other.
Nature is arranged in such a way that the interaction of quarks always leads to the formation of colorless bound states, which are just hadrons. For example, a proton and a neutron are made up of three quarks: p = uud, n = udd. The pion π − is composed of a quark u and an antiquark: π − = u. A distinctive feature of the quark-quark interaction through gluons is that as the distance between quarks decreases, their interaction weakens. This phenomenon is called asymptotic freedom and leads to the fact that quarks inside hadrons can be considered as free particles. Asymptotic freedom follows naturally from quantum chromodynamics. There are experimental and theoretical indications that as the distance increases, the interaction between quarks should increase, due to which it is energetically favorable for quarks to be inside the hadron. This means that we can only observe colorless objects - hadrons. Single quarks and gluons with color cannot exist in a free state. The phenomenon of confinement of elementary particles with color inside hadrons is called confinement. Various models have been proposed to explain confinement, but a consistent description following from the first principles of the theory has not yet been constructed. From a qualitative point of view, the difficulties are related to the fact that, having color, gluons interact with all colored objects, including with each other. For this reason, quantum chromodynamics is an essentially non-linear theory, and the approximate methods of investigation adopted in quantum electrodynamics and electroweak theory turn out to be not quite adequate in the theory of strong interactions.

Interaction Combination Trends

We see that at the quantum level, all fundamental interactions manifest themselves in the same way. An elementary particle of a substance emits an elementary particle - an interaction carrier, which is absorbed by another elementary particle of a substance. This leads to mutual influence of particles of matter on each other.
The dimensionless coupling constant of the strong interaction can be constructed by analogy with the fine structure constant in the form g2/(c)10. If we compare the dimensionless coupling constants, then it is easy to see that the gravitational interaction is the weakest, and then the weak, electromagnetic and strong ones are located.
If we take into account the already developed unified theory of electroweak interactions, now called the standard one, and follow the trend of unification, then the problem of constructing a unified theory of electroweak and strong interactions arises. At present, models of such a unified theory have been created, called the grand unification model. All these models have many points in common, in particular, the characteristic unification energy turns out to be of the order of 10 15 GeV, which greatly exceeds the characteristic unification energy of electromagnetic and weak interactions. It follows from this that a direct experimental study of the grand unification looks problematic even in a fairly distant future. For comparison, we note that the highest energy attainable with modern accelerators does not exceed 10 3 GeV. Therefore, if any experimental data regarding the grand unification are obtained, they can only be indirect. In particular, grand unified models predict the decay of the proton and the existence of a magnetic monopole of large mass. Experimental confirmation of these predictions would be a grand triumph for unification tendencies.
The general picture of the division of a single great interaction into separate strong, weak and electromagnetic interactions is as follows. At energies of the order of 10 15 GeV and above, there is a single interaction. When the energy goes below 10 15 GeV, the strong and electroweak interactions separate from each other and appear as different fundamental interactions. As the energy decreases further below 10 2 GeV, the weak and electromagnetic interactions are separated. As a result, on the energy scale characteristic of the physics of macroscopic phenomena, the three interactions under consideration look like they do not have a single nature.
Note now that the energy of 10 15 GeV is not so far from the Planck energy

at which quantum gravitational effects become significant. Therefore, the grand unification theory necessarily leads to the problem of quantum gravity. If we continue to follow the trend of unification, we must accept the idea of the existence of one all-encompassing fundamental interaction, which is divided into separate gravitational, strong, weak and electromagnetic successively as the energy decreases from the Planck value to energies less than 10 2 GeV.
The construction of such a grandiose unifying theory seems to be unfeasible within the framework of the system of ideas that led to the standard theory of electroweak interactions and grand unification models. It is required to attract new, perhaps seemingly crazy, ideas, ideas, methods. Despite very interesting approaches developed recently, such as supergravity and string theory, the problem of unifying all fundamental interactions remains open.

Conclusion

So, we have made a review of the basic information concerning the four fundamental interactions of Nature. The microscopic and macroscopic manifestations of these interactions and the picture of physical phenomena in which they play an important role are briefly described.
Wherever possible, we tried to trace the unification trend, note the common features of fundamental interactions, and provide data on the characteristic scales of phenomena. Of course, the material presented here does not claim to be complete and does not contain many important details necessary for a systematic presentation. A detailed description of the issues raised by us requires the use of the entire arsenal of methods of modern theoretical high-energy physics and is beyond the scope of this article, popular science literature. Our goal was to present the general picture of the achievements of modern theoretical high-energy physics, the trends in its development. We sought to arouse the reader's interest in an independent, more detailed study of the material. Of course, with this approach, certain coarsenings are inevitable.
The proposed list of references allows a more prepared reader to deepen his understanding of the issues discussed in the article.

Okun L.B. a, b, g, Z. M.: Nauka, 1985.
Okun L.B. Physics of elementary particles. Moscow: Nauka, 1984.
Novikov I.D. How the universe exploded. Moscow: Nauka, 1988.
Friedman D., van. Nieuwenhuizen P. // Uspekhi nat. Sciences. 1979. Vol. 128. No. 135.
Hawking S. From the Big Bang to Black Holes: A Brief History of Time. M.: Mir, 1990.
Davis P. Superpower: The Search for a Unified Theory of Nature. M.: Mir, 1989.
Zeldovich Ya.B., Khlopov M.Yu. The drama of ideas in the knowledge of nature. Moscow: Nauka, 1987.
Gottfried K., Weisskopf W. Concepts of elementary particle physics. M.: Mir, 1988.
Coughlan G.D., Dodd J.E. The Ideas of Particle Physics. Cambridge: Cambridge Univ. Press, 1993.

The most common is the division of universal energy into four forces. Many are familiar with the classical elements of earth, water, air and fire. These names are most often used in the Western tradition. All mystics pay tribute to the powers by honoring the four sacred directions, although in various traditions, from witchcraft and alchemy to natural shamanism and medicine, different elements may correspond to different directions.

Everything is made up of these four elements, four forces in their various combinations. It is important to understand that the physical elements are only symbols of energy. There is no direct connection between them, and therefore, using the words sulfur, mercury and salt in relation to different types of energy, we do not mean chemical elements in the literal sense. The element of fire is not the fire of a burning torch at all, but an energy similar in nature to a burning torch, therefore a burning torch symbolizes it and even really embodies it in rituals. In some texts, the elements are called elements of wisdom, thus the element of fire is the wisdom of fire, not the fire of a burning torch. The earth element is the wisdom of the earth, not garden soil or stones. Misunderstanding and underestimation of symbolism has forced modern science to abandon the knowledge of magic and alchemy. Modern psychology, especially those based on the alchemical work of Carl Jung, brought these esoteric symbols back to life in the New Age.

Each element is not just the energy of everything that exists, but also the level of consciousness, dimension or plane of existence on which the elements of the universe are embodied. Each element has its own energy vibration and different characteristics. Any person can be attributed to one of the elements due to his natural inclination to certain qualities and possible problems in interaction with other elements that do not have such qualities. Working with the elements means learning to work with the sources of harmony.

Earth.

Earth is the element we know best. The energy of the earth element is represented by physical forms and the physical world. Everything that can be seen and measured with the senses is made up of the earth element. Our bodies, dwellings, plants, trees, stones and everything man-made - cars, toys and jewelry - is earthly energy. Our body, bones and all the minerals and metals of which they are composed are carriers of the earth element.

This energy governs all physical aspects of being and thus affects our physical health and financial well-being. In Tarot, cards used in divination and meditation, this energy is represented in the form of disks, sometimes called coins or pentacles. The five-pointed star can mean protection at the physical level. People with developed earth energy have power in the physical world, while people who are just looking for contact with this type of energy experience problems in the physical and financial spheres. The highest form of the earth element is independence, which refers to the right to control one's own body, home and destiny. You are the master of your house and the master of your body. From an astrological point of view, the earth signs are Taurus, Virgo, and Capricorn, although in some ways each sign interacts with the physical world. Normally, the terrestrial direction is considered north, at least in the Northern Hemisphere, due to the strong, continuous geomagnetic energy of the North Pole.

The earth element, the mystical earth, is usually distinguished from the planet Earth. Mystics, speaking of the latter, usually have in mind the consciousness, the soul of the planet, personified in the female image of the mother. She changed many names. The Greek name Gaia has become the most popular, because in the recent past, scientist James Lovelock put forward the theory of Gaia, according to which the planet's biosphere is a single intelligent organism, and we are like small particles in this organism. We are like cells in the body of the planet, what affects us affects the whole body.

Water.

Water is the energy of the astral plane, the level of symbolic reality, where shapes and forms are fluid and changeable. Water is the element of dreams. In our body, water is symbolized by the fluids that make up the blood and cells, but in fact, the main energy of water is our astral body, which travels when we sleep and dream. The astral body is our own image, which is influenced by emotions. Like water, this energy is fluid and easily changes shape. The astral body is like a container that holds our emotions, just as a glass holds water. When emotions are calm, the liquid is transparent, when they are overshadowed by something, it is cloudy. The watery level of the universe is known as the astral or emotional level.

The analogy with a glass symbolically embodies another aspect of water energy - the presence of boundaries. The task of water is to define the boundaries of relationships. Emotions are the building blocks of any kind of relationship - family, friendship, love or marriage. Establishment of the emotional spiritual questions that water poses to us.

In addition, water is related to psychic abilities and immersion in the mystical depths of consciousness. Western European traditions usually associate water with the west. Firstly, in the west there was a huge ocean - the Atlantic, and secondly, the place where the sun set over the horizon was always considered the place of death, the focus of everything unknown and mysterious. In the minds of many people, the kingdom of the dead and water are connected by strong ties. Both of these concepts are associated with the West.

The highest, purest form of the water element is unaccountable love, a source of miraculous healing, purification and compassion. In the Tarot system, water is symbolized by bowls, and in a mystical sense, the Grail, a magical bowl or cauldron, endowed with both Christian and pagan associations. The water signs of the zodiac are Cancer, Scorpio and Pisces, each of which is associated with emotional relationships in a certain way.

Air.

Air is an element of the mental plane. This is the realm of ideas, concepts and thoughts. Like the sky, our minds can be clear and peaceful. At other times, they are outraged by the movement of thoughts or covered in a water mist of clouds - our emotions. The relationship between our emotional and mental bodies is like the relationship between the sky and the sea. Before anything takes shape on the astral level, a mental image, a thought, must breathe life into it.

Air is an element of communication. We use the power of our breath to speak words. The air between us carries sound waves so that the words we speak can be heard.

Unfortunately, many who study the air element believe that air is only speaking, yet it is also the power to listen. Air is logic and memorization, but also poetry and sincerity. In the Tarot system, swords are the symbol of air. When characterizing a person with a strong air element, we resort to the metaphor "He has a sharp mind." Having two edges, the swords symbolize the bidirectionality of communication, which involves both listening and speaking. In addition, they symbolize the dual nature of words: the ability to unite people, to serve as a means of communication, and at the same time the ability to hurt. Finally, we use the metaphor "sword" for betrayal, for example: "He stabbed me in the back."

The ultimate realization of the sword symbol can be found in the Arthurian myth. Excalibur is the sword of truth. The main force of air is truth, but the form of its expression depends on the owner of the sword. In most Western traditions, air is associated with the east, but sometimes it is associated with the south direction to contrast the earth-air pair with the north-south pair. Zodiac air signs include Gemini, Libra and Aquarius, as they all function in the field of communication and connection.

Fire.

The most elusive element is fire. The land can be taken over. Water can be drunk. Air can be breathed, but fire cannot be contained. In our body, fire symbolizes metabolism. We know it's there, but we can't feel it like the other three elements. Mystics describe fire in a special way. This is the energy component. Fire is an energetic reality. A spark of fire ignites an idea on the mental level, it takes shape on the emotional and structure on the earth.

For some, the fire finds expression in a career, for others in sex, for others in creative aspirations. Fire is the force that drives us in search of our own individuality through personal aspirations. Fire in its highest form is our will. The will is realized in different ways. The most simple will can be defined as what we want, passionately desire. This is called the will of the ego, or the will of the personality. To rise above the "will of the ego" means to reach the highest will, which is the highest, divine individuality. It is sometimes referred to as the higher self. Fire is the soul, the divine spark of individuality in each of us. By uniting personal will with our divine will, we acquire a true spiritual identity, and all doors are open to us.

In Tarot cards, fire appears as a magic wand, spear or torch, helping us pave the way to individuality. A magic wand is an attribute of a sorcerer or witch who uses them as a means of concentrating magical power.

Mythologically, the spear is the spear of fate that pierced Christ, or the spear of Luh, the supreme god of Irish mythology. The embodiment of the highest will is human destiny: we must make a choice: to refuse our destiny or to accept it. Most often, fire is associated with a southerly direction, because in the Northern Hemisphere, the noonday sun is associated with the south and this is the hottest point of the day. Also, the further south you go, the closer you get to the equator and the hotter it gets. For some, fire as a symbol of the rising sun is associated with the east. Obviously, some of the spatial associations will be different in the Southern Hemisphere. Astrological fire signs - Aries, Leo and Sagittarius. Each of the three signs seeks to express its individuality, ego and will in its own way. In some traditions, the symbols of fire and air change: fire is associated with a blade that is forged on fire. It is the warrior's weapon of fiery discipline, while the twigs symbolize the air, because the branches for them are taken from the top of the tree, which is in the wind. It's just a different system of symbols, no worse and no better than the first.

Fire and air are considered male elements, their peaks are directed upwards. Earth and water are feminine elements with downward points.

A cross consisting of equal segments, inscribed in a circle, is a symbol of the four elements and four cardinal points in the sacred circle. It is also the astrological symbol of the planet Earth.

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 fall apart into individual atoms and can plug laptops into the outlet. The physicist talks about two more forces that make the Universe exactly the way it is.

But is this the whole set of forces and interactions that determine the appearance of the Universe we observe?

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

This truly titanic task of overcoming the Coulomb forces is taken over by the strong interaction. So, neither more nor less, due to it, protons (as, indeed, neutrons) in the nucleus are still 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, which also works at cosmic distances of many billions of kilometers, the strong interaction is, as they say, short-range. This means that the "strong attraction" field surrounding one proton works only on tiny scales, comparable, in fact, with the size of the nucleus.

What? Neutrinos pass through me?!

At the same time, neutrinos are generated in the Universe in truly colossal quantities, and a huge stream of these particles constantly penetrates the thickness of the Earth. For example, in the volume of a matchbox, on average, there are 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 any given time. So, scientists working on this detector usually have to wait for months for such a happy occasion, so that at least one neutrino “feels” their barrel and interacts 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 precisely this that is 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 effect on living organisms. And, no less important, without weak interaction, it would be impossible for thermonuclear reactions to take place in the interiors of many stars and are responsible for the release of energy from the star.

This is the four horsemen of the Apocalypse of fundamental interactions that rule the Universe: strong, electromagnetic, weak and gravitational.

Interaction is the main reason for the movement of matter, therefore interaction is inherent in all material objects, regardless of their natural origin and systemic organization. Features of various interactions determine the conditions of existence and the specifics of the properties of material objects. In total, four types of interaction are known: gravitational, electromagnetic, strong and weak.

gravitational interaction was the first of the known fundamental interactions to become the subject of research by scientists. It manifests itself in the mutual attraction of any material objects that have mass, is transmitted through the gravitational field and is determined by the law of universal gravitation, which was formulated by I. Newton

The law of universal gravitation describes the fall of material bodies in the field of the Earth, the movement of the planets of the solar system, stars, etc. As the mass of matter increases, gravitational interactions increase. Gravitational interaction is the weakest of all interactions known to modern science. Nevertheless, gravitational interactions determine the structure of the entire Universe: the formation of all cosmic systems; existence of planets, stars and galaxies. The important role of gravitational interaction is determined by its universality: all bodies, particles and fields participate in it.

The carriers of gravitational interaction are gravitons - quanta of the gravitational field.

electromagnetic the interaction is also universal and exists between any bodies in the micro-, macro- and mega world. Electromagnetic interaction is due to electric charges and is transmitted using electric and magnetic fields. An electric field arises in the presence of electric charges, and a magnetic field arises in the movement of electric charges. Electromagnetic interaction is described by: Coulomb's law, Ampère's law, etc., and in a generalized form - by Maxwell's electromagnetic theory, which relates electric and magnetic fields. Due to the electromagnetic interaction, atoms, molecules arise and chemical reactions occur. Chemical reactions are a manifestation of electromagnetic interactions and are the results of the redistribution of bonds between atoms in molecules, as well as the number and composition of atoms in the molecules of different substances. Various aggregate states of matter, elastic forces, friction, etc. are determined by electromagnetic interaction. The carriers of the electromagnetic interaction are photons - quanta of the electromagnetic field with zero rest mass.

Inside the atomic nucleus, strong and weak interactions are manifested. Strong interaction ensures the connection of nucleons in the nucleus. This interaction is determined by nuclear forces, which have charge independence, short range, saturation, and other properties. The strong force keeps nucleons (protons and neutrons) in the nucleus and quarks inside nucleons and is responsible for the stability of atomic nuclei. Using the strong force, scientists have explained why the protons of the nucleus of an atom do not fly apart under the influence of electromagnetic repulsive forces. The strong force is transmitted by gluons, particles that “stick together” quarks, which are part of protons, neutrons, and other particles.

Weak interaction also operates only in the microcosm. All elementary particles, except for the photon, participate in this interaction. It causes most of the decays of elementary particles, so its discovery occurred after the discovery of radioactivity. The first theory of the weak interaction was created in 1934 by E. Fermi and developed in the 1950s. M. Gell-Man, R. Feynman and other scientists. The carriers of the weak interaction are considered to be particles with a mass 100 times greater than the mass of protons - intermediate vector bosons.

Characteristics of fundamental interactions are presented in Table. 2.1.

Table 2.1

Characteristics of fundamental interactions

The table shows that the gravitational interaction is much weaker than other interactions. Its range is unlimited. It does not play a significant role in microprocesses and at the same time is the main one for objects with large masses. The electromagnetic interaction is stronger than the gravitational one, although the radius of its action is also unlimited. The strong and weak interactions have a very limited range.

One of the most important tasks of modern natural science is the creation of a unified theory of fundamental interactions that unites various types of interaction. The creation of such a theory would also mean the construction of a unified theory of elementary particles.