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What are fundamental interactions? Types of fundamental interactions in physics.

What's in various substances ah contains quite a lot of elementary particles, fundamental physical interactions are represented by four types: strong, electromagnetic, weak and gravitational. The latter is considered the most comprehensive.

All macrobodies and microparticles, without exception, are subject to gravity. Absolutely all elementary particles are subject to gravitational influence. It appears in the form universal gravity. This fundamental interaction controls the most global processes occurring in the Universe. Gravity provides structural stability solar system.

According to modern ideas, fundamental interactions arise due to the exchange of particles. Gravity is formed through the exchange of gravitons.

Fundamental interactions - gravitational and electromagnetic - are long-range in nature. The corresponding forces can manifest themselves over considerable distances. These fundamental interactions have their own characteristics.

Described by charges of the same type (electric). In this case, the charges can have both a positive and a negative sign. Electromagnetic forces, unlike (gravity), can act as repulsive and attractive forces. This interaction causes chemical and physical properties various substances, materials, living tissue. Electromagnetic forces drive both electronic and electrical equipment, connecting charged particles with each other.

Fundamental interactions are known beyond a small circle of astronomers and physicists in to varying degrees.

Despite being less famous (compared to other types), weak forces play important role in the life of the Universe. So, if there were no weak interaction, the stars and the Sun would go out. These forces are short-range. The radius is approximately a thousand times smaller than that of nuclear forces.

Nuclear forces are considered the most powerful of all. The strong interaction determines the bonds only between hadrons. Acting between nucleons nuclear forces are its manifestation. approximately one hundred times more powerful than electromagnetic. Differing from gravitational (as, in fact, from electromagnetic), it is short-range at a distance of more than 10-15 m. In addition, it can be described using three charges that form complex combinations.

Range is considered the most important feature of fundamental interaction. The radius of action is the maximum distance that is formed between particles. Outside of this, interaction can be neglected. A small radius characterizes the force as short-range, a large radius as long-range.

As noted above, weak and strong interactions are considered short-range. Their intensity decreases quite quickly as the distance between particles increases. These interactions manifest themselves at small distances inaccessible to perception through the senses. In this regard, these forces were discovered much later than the others (only in the twentieth century). In this case, quite complex experimental setups were used. Gravitational and electromagnetic types fundamental interactions are considered long-range. They are characterized by a slow decrease as the distance between particles increases and are not endowed with a finite range of action.

1.1. Gravity.

1.2. Electromagnetism.

1.3. Weak interaction.

1.4. The problem of the unity of physics.

2. Classification of elementary particles.

2.1. characteristics of subatomic particles.

2.2. leptons.

2.3. Hadrons.

2.4. Particles are carriers of interactions.

3. Theories of elementary particles.

3.1. Quantum electrodynamics.

3.2. Quark theory.

3.3. Theory of electroweak interaction.

3.4. Quantum chromodynamics.

3.5. On the way to great unification.

References.

Introduction.

In the middle and second half of the twentieth century, truly amazing results were obtained in those branches of physics that study the fundamental structure of matter. First of all, this manifested itself in the discovery of a whole host of new subatomic particles. They are usually called elementary particles, but not all of them are truly elementary. Many of them, in turn, consist of even more elementary particles. The world of subatomic particles is truly diverse. These include protons and neutrons that make up atomic nuclei, as well as electrons orbiting the nuclei. But there are also particles that are practically never found in the matter around us. Their life time is extremely short, it is the smallest fractions of a second. After this extremely short time, they disintegrate into ordinary particles. There are an amazing number of such unstable short-lived particles: several hundred of them are already known. In the 1960s and 1970s, physicists were completely baffled by the number, variety, and strangeness of the newly discovered subatomic particles. There seemed to be no end to them. It is completely unclear why there are so many particles. Are these elementary particles chaotic and random fragments of matter? Or perhaps they hold the key to understanding the structure of the Universe? The development of physics in subsequent decades showed that there is no doubt about the existence of such a structure. At the end of the twentieth century. physics is beginning to understand the significance of each of the elementary particles. The world of subatomic particles is characterized by a deep and rational order. This order is based on fundamental physical interactions.

1. Fundamental physical interactions.

In your everyday life a person is faced with many forces acting on their bodies. Here is the force of the wind or the oncoming flow of water, air pressure, a powerful release of explosive chemicals, human muscular strength, the weight of heavy objects, the pressure of light quanta, the attraction and repulsion of electrical charges, seismic waves that sometimes cause catastrophic destruction, and volcanic eruptions that led to the death of civilization, etc. Some forces act directly upon contact with the body, others, for example, gravity, act at a distance, through space. But, as it turned out as a result of the development of theoretical natural science, despite such great diversity, all the forces operating in nature can be reduced to just four fundamental interactions. It is these interactions that are ultimately responsible for all changes in the world; they are the source of all transformations of bodies and processes. The study of the properties of fundamental interactions is main task modern physics.

      Gravity.

In the history of physics, gravity (gravity) became the first of the four fundamental interactions to be the subject of scientific research. After its appearance in the 17th century. Newton's theory of gravity - the law of universal gravitation - managed for the first time to realize the true role of gravity as a force of nature. Gravity has a number of features that distinguish it from other fundamental interactions. The most surprising feature of gravity is its low intensity. The magnitude of gravitational interaction between the components of a hydrogen atom is 10n, where n = - 3 9, from the force of interaction electric charges. (If the dimensions of a hydrogen atom were determined by gravity, and not by the interaction between electric charges, then the lowest (closest to the nucleus) electron orbit would be larger in size than the observable part of the Universe!) (If the dimensions of a hydrogen atom were determined by gravity, and not by the interaction between electrical charges, then the lowest (closest to the nucleus) electron orbit would be larger in size than the observable part of the Universe!). It may seem surprising that we feel gravity at all, since it is so weak. How can she become the dominant force in the Universe? It's all about the second amazing feature of gravity - its universality. Nothing in the Universe is free from gravity. Each particle experiences the action of gravity and is itself a source of gravity. Since every particle of matter exerts a gravitational pull, gravity increases as larger clumps of matter form. We feel gravity in everyday life because all the atoms of the Earth work together to attract us. And although the effect of the gravitational attraction of one atom is negligible, the resulting force of attraction from all atoms can be significant. Gravity is a long-range force of nature. This means that, although the intensity of gravitational interaction decreases with distance, it spreads in space and can affect bodies very distant from the source. On an astronomical scale, gravitational interactions tend to play a major role. Thanks to long-range action, gravity prevents the Universe from falling apart: it holds planets in orbits, stars in galaxies, galaxies in clusters, clusters in the Metagalaxy. The gravitational force acting between particles is always an attractive force: it tends to bring the particles closer together. Gravitational repulsion has never been observed before (Although in the traditions of quasi-scientific mythology there is a whole field called levitation - the search for the “facts” of antigravity). Since the energy stored in any particle is always positive and gives it positive mass, particles under the influence of gravity always tend to get closer. What is gravity, a certain field or a manifestation of the curvature of space-time - there is still no clear answer to this question. As we have already noted, there are different opinions and concepts of physicists on this matter.

      Electromagnetism.

Electrical forces are much larger than gravitational forces. Unlike the weak gravitational interaction, the electrical forces acting between bodies of normal size can be easily observed. Electromagnetism has been known to people since time immemorial (auroras, lightning flashes, etc.). For a long time, electrical and magnetic processes were studied independently of each other. As we already know, the decisive step in the knowledge of electromagnetism was made in the middle of the 19th century. J.C. Maxwell, who combined electricity and magnetism in a unified theory of electromagnetism - the first unified field theory. The existence of the electron was firmly established in the 90s of the last century. It is now known that the electric charge of any particle of matter is always a multiple of the fundamental unit of charge - a kind of “atom” of charge. Why this is so is an extremely interesting question. However, not all material particles are carriers of electric charge. For example, the photon and neutrino are electrically neutral. In this respect, electricity differs from gravity. All material particles create a gravitational field, while only charged particles are associated with an electromagnetic field. Like electric charges, like magnetic poles repel, and opposite ones attract. However, unlike electric charges, magnetic poles do not occur individually, but only in pairs - a north pole and a south pole. Since ancient times, attempts have been known to obtain, by dividing a magnet, only one isolated magnetic pole - a monopole. But they all ended in failure. Perhaps the existence of isolated magnetic poles in nature is excluded? There is no definite answer to this question yet. Some theoretical concepts allow for the possibility of a monopole. Like electrical and gravitational interactions, the interaction of magnetic poles obeys the inverse square law. Consequently, electric and magnetic forces are “long-range”, and their effect is felt at large distances from the source. Thus, the Earth's magnetic field extends far into outer space. The Sun's powerful magnetic field fills the entire Solar System. There are also galactic magnetic fields. Electromagnetic interaction determines the structure of atoms and is responsible for the vast majority of physical and chemical phenomena and processes (except nuclear).

      Weak interaction.

Physics has moved slowly towards identifying the existence of the weak interaction. The weak force is responsible for particle decays; and therefore its manifestation was confronted with the discovery of radioactivity and the study of beta decay. Beta decay was found in highest degree strange feature. Research led to the conclusion that this decay violates one of the fundamental laws of physics - the law of conservation of energy. It seemed that in this decay part of the energy disappeared somewhere. In order to “save” the law of conservation of energy, W. Pauli suggested that, together with the electron, during beta decay, another particle is emitted. It is neutral and has an unusually high penetrating ability, as a result of which it could not be observed. E. Fermi called the invisible particle "neutrino". But the prediction and detection of neutrinos is only the beginning of the problem, its formulation. It was necessary to explain the nature of neutrinos, but there remained a lot of mystery here. The fact is that both electrons and neutrinos were emitted by unstable nuclei. But it was irrefutably proven that there are no such particles inside nuclei. How did they arise? It has been suggested that electrons and neutrinos do not exist in the nucleus in " finished form", but are somehow formed from the energy of a radioactive nucleus. Further research showed that the neutrons included in the nucleus, left to themselves, after a few minutes decay into a proton, electron and neutrino, i.e. instead of one particle, three new ones appear. The analysis led to the conclusion that known forces could not cause such a decay. It was apparently generated by some other, unknown force. Research showed that this force corresponds to some weak interaction It is much weaker than the electromagnetic one, although it is stronger than the gravitational one. at very small distances. The radius of the weak interaction is very small. The weak interaction stops at a distance greater than 10n cm (where n = - 1 6) from the source and therefore cannot affect macroscopic objects, but is limited to individual subatomic particles. unstable elementary particles participate in weak interaction. The theory of weak interaction was created in the late 60s by S. Weinberg and A. Salam. Since Maxwell's theory of the electromagnetic field, the creation of this theory was the largest step towards the unity of physics. 10.

      Strong interaction.

The last in the series of fundamental interactions is the strong interaction, which is a source of enormous energy. The most typical example of energy released by the strong force is our Sun. In the depths of the Sun and stars, starting from a certain time, thermonuclear reactions caused by strong interaction continuously occur. But man has also learned to release strong interactions: a hydrogen bomb has been created, technologies for controlled thermonuclear reactions have been designed and improved. Physics came to the idea of ​​the existence of strong interaction during the study of the structure of the atomic nucleus. Some force must hold the protons in the nucleus, preventing them from scattering under the influence of electrostatic repulsion. Gravity is too weak for this; Obviously, some new interaction is needed, moreover, stronger than electromagnetic. It was subsequently discovered. It turned out that although the strong interaction significantly exceeds all other fundamental interactions in its magnitude, it is not felt outside the nucleus. The radius of action of the new force turned out to be very small. Strong interaction drops sharply at a distance from the proton or neutron greater than about 10n cm (where n = - 13). In addition, it turned out that not all particles experience strong interactions. It is experienced by protons and neutrons, but electrons, neutrinos and photons are not subject to it. Only heavier particles participate in strong interactions. The theoretical explanation of the nature of the strong interaction has been difficult to develop. A breakthrough occurred in the early 60s, when the quark model was proposed. In this theory, neutrons and protons are considered not as elementary particles, but as composite systems built from quarks. Thus, in fundamental physical interactions the difference between long-range and short-range forces is clearly visible. On the one hand, there are interactions of unlimited range (gravity, electromagnetism), and on the other, interactions of short range (strong and weak). The world of physical elements as a whole unfolds in the unity of these two polarities and is the embodiment of the unity of the extremely small and the extremely large - short-range action in the microworld and long-range action throughout the Universe.

      The problem of the unity of physics.

Knowledge is a generalization of reality, and therefore the goal of science is the search for unity in nature, linking disparate fragments of knowledge into a single picture. In order to create unified system, it is necessary to discover a connecting link between various branches of knowledge, some fundamental relationship. The search for such connections and relationships is one of the main tasks of scientific research. Whenever it is possible to establish such new connections, the understanding of the surrounding world deepens significantly, new ways of knowing are formed that point the way to previously unknown phenomena. Establishing deep connections between different areas of nature is both a synthesis of knowledge and a method that guides scientific research along new, untrodden roads. Newton's discovery of the connection between the attraction of bodies under terrestrial conditions and the movement of planets marked the birth of classical mechanics, on the basis of which the technological base was built modern civilization. The establishment of a connection between the thermodynamic properties of gas and the chaotic movement of molecules put the atomic-molecular theory of matter on a solid basis. In the middle of the last century, Maxwell created a unified electromagnetic theory that covered both electrical and magnetic phenomena. Then, in the 20s of our century, Einstein made attempts to combine electromagnetism and gravity in a single theory. But by the middle of the twentieth century. The situation in physics has changed radically: two new fundamental interactions have been discovered - strong and weak, i.e. when creating a unified physics, one has to take into account not two, but four fundamental interactions. This somewhat cooled the ardor of those who hoped for quick solution this problem. But the idea itself was not seriously questioned, and the enthusiasm for the idea of ​​a single description did not go away. There is a point of view that all four (or at least three) interactions represent phenomena of the same nature and their unified theoretical description must be found. The prospect of creating a unified theory of the world of physical elements based on a single fundamental interaction remains very attractive. This is the main dream of 20th century physicists. But for a long time it remained only a dream, and a very vague one. However, in the second half of the twentieth century. there were prerequisites for the realization of this dream and the confidence that this was by no means a matter of the distant future. It looks like it could soon become a reality. The decisive step towards a unified theory was made in the 60-70s. with the creation first of the theory of quarks, and then of the theory of electroweak interaction. There is reason to believe that we are on the threshold of a more powerful and deeper unification than ever before. There is a growing belief among physicists that the contours of a unified theory of all fundamental interactions - the Grand Unification - are beginning to emerge.

2 . Classification of elementary particles.

The most important properties of matter are movement and interaction. In a broad sense, movement is understood as any change that occurs in nature. All forms of movement have something in common. They all come down to the interaction of bodies. For any object to exist means to interact, to somehow manifest itself in relation to other bodies. Over the centuries, two fundamental principles have emerged in science: different ways descriptions of the interaction mechanism – principles of long-range and short-range action.

Historically, it was first formulated by I. Newton long-range principle, according to which interaction between bodies occurs instantly at any distance without any material carriers. In the 19th century was introduced into science by M. Faraday short range principle, later clarified: the interaction is transferred by the field from point to point at a speed not exceeding the speed of light in a vacuum. From the point of view modern physics interaction always obeys the principle of short-range action. But in many problems that describe mechanical processes with slowly moving objects, the approximate principle of short-range action can be used.

The nature of the interactions may vary. Currently, physicists distinguish four types of fundamental interactions: gravitational, electromagnetic, strong and weak.

Gravitational interaction first became the subject of research by scientists. The classical (Newtonian) theory of gravity was created back in the 17th century. after the discovery of the law of universal gravitation. This is the weakest of all known interactions, it is 10 40 times weaker than the force of interaction of electric charges. However, this very weak force determines the structure of the Universe: formation space systems, the existence of planets, stars, galaxies. Gravitational interaction is universal and manifests itself only as an attractive force. It involves not only all bodies with mass, but also fields. The greater the mass of interacting bodies, the greater it is. Therefore, in the microworld, gravitational force does not play a significant role, but in the macroworld and megaworld it dominates. Gravity is a long-range force. Its intensity decreases with distance, but continues to affect very large distances.



Electromagnetic interaction is also universal and acts between any bodies, but unlike gravitational interaction it manifests itself in both the form of attraction and repulsion. Thanks to electromagnetic connections, atoms, molecules and macrobodies arise. All chemical and biological processes– manifestations of electromagnetic interaction. All ordinary forces are reduced to it: elasticity, friction, surface tension, etc. In its magnitude, this interaction is much greater than gravitational interaction, so its action is easy to observe even between bodies of ordinary sizes. It is also long-range, its effect is noticeable even at large distances from the source. It decreases with distance, but does not disappear. Electromagnetic interaction is described in physical theory called quantum electrodynamics.

The study of the structure of the atomic nucleus led to the discovery of a new type of interaction, which was called strong, since on the nuclear scale (~10 -15 m) it is two to three orders of magnitude greater than the electromagnetic one and allows us to explain why equally charged protons in the nucleus do not fly apart. Strong interaction ranks first in strength and is a source of enormous energy. It connects quarks and antiquarks in atomic nucleus. It is short-range and has a limited range of action - up to 10-15 m. Strong interaction is described in the framework of quantum chromodynamics.

Then the fourth type of interaction was discovered - weak interaction, responsible for the transformation of elementary particles into each other and playing an important role not only in the microcosm, but also in many phenomena on a cosmic scale. In terms of intensity, it ranks third (between electromagnetic and gravitational interactions) and is short-range.

The interaction mechanism is usually interpreted as an exchange of intermediary particles carrying elementary portions of energy - quanta. It is believed that each interaction is carried by a certain type of elementary particles - bosons:

· in weak interactions the mediators are mesons;

· in electromagnetic – photons;

· strong interactions are realized gluons(English) glue- glue), which carry so much energy that they tightly hold the quarks inside the particle;

· gravitational interaction is carried by quanta of gravitation – gravitons, which have not yet been discovered experimentally.

The theories built for each of the four types of interactions turned out to be different, and physicists did not like it. I wanted to unite them. A good example served unified theory electromagnetic interactions, built by J. Maxwell in the 19th century. At the turn of the 60-70s. In the twentieth century, through the efforts of three physicists (S. Weinberg, S. Glashow, A. Salam), it was possible to combine the theories of electromagnetic and weak interactions. A quantum carrying the combined electroweak interaction can exist in four states, one of which is photonic, and the other three have large mass. Such a combination requires energies of the order of 10 11 eV, which corresponds to temperatures 4 trillion times higher than room temperature.

Now physicists are busy building a theory of the Grand Unification, which would include strong interactions. The sought-after quantum intermediary must be multidimensional, and the energy required to implement this unification is unattainable in modern installations. The superunification project, which includes gravity, still exists only as a dream.

To understand whether it is worth continuing to write short sketches that literally explain different physical phenomena and processes. The result dispelled my doubts. I'll 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, you 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. Everyone is well known gravitational And electromagnetic. And almost unknown to the general public strong And weak. Let us describe them sequentially.
Gravitational interaction . People have known it since ancient times. Because 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 rotates around the Earth, the Earth and other planets around the Sun, and the latter, together with other stars, around the center of our Galaxy.
The rather slow decrease in the strength of gravitational interaction with distance (inversely proportional to the square of the distance) forces physicists to talk about 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 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 repel, and those with different signs attract. Therefore, electromagnetic interaction, like gravitational interaction, is called by physicists long-range.
At the same time, electromagnetic interaction is more complex than gravitational interaction. From school physics we know that the electric field is created by electric charges, magnetic charges does not exist in nature, but a magnetic field is created electric currents.
In fact, an electric field can also be created by a time-varying magnetic field, and a magnetic field can also be created by a time-varying magnetic field electric field. The latter circumstance makes it possible to exist electromagnetic field without any electrical charges or currents at all. And this possibility is realized in the form of electromagnetic waves. For example, radio waves and light quanta.
Because electrical and gravitational forces are equally dependent on distance, it is natural to try to compare their intensities. Thus, for two protons, the forces of gravitational attraction turn out to be 10 to the 36th power of times (a billion billion billion billion times) weaker than the forces of electrostatic repulsion. Therefore, in the physics of the microworld, gravitational interaction can quite reasonably be neglected.
Strong interaction . This - 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.
This is why equally electrically charged protons in the atomic nucleus are not repelled from each other by electrostatic forces, but are held together by strong interactions. Because the dimensions of a proton and a neutron are about one femtometer.
Weak interaction . It is really very weak. Firstly, it operates at distances a thousand times smaller than one femtometer. And at long distances it is practically not felt. Therefore, like the strong one, it belongs to the class short-range. Secondly, its intensity is approximately one hundred billion times less than the intensity of electromagnetic interaction. The weak force is responsible for some decays of elementary particles. Including free neutrons.
There is only one type of particle that interacts with matter only through weak interaction. This is a neutrino. Through every square centimeter Almost a hundred billion solar neutrinos pass through our skin every second. And we don’t notice them at all. In the sense that during our lifetime, it is unlikely that a few neutrinos will interact with the matter of our body.
We will not talk about theories that describe all these types of interactions. For what is important to us is a high-quality picture of the world, and not the delights of theorists.

Many fundamental concepts modern natural science directly or indirectly related to the description of fundamental interactions. Interaction and movement are the most important attributes of matter, without which its existence is impossible. Interaction determines the unification of various material objects into systems, i.e., the systemic organization of matter. Many properties of material objects are derived from their interaction and are the result of their structural connections with each other and interactions with the external environment.

By now known four types of basic fundamental interactions:

· gravitational;

· electromagnetic;

· strong;

· weak.

Gravitational interaction characteristic of all material objects, regardless of their nature. It consists in the mutual attraction of bodies and is determined by the fundamental law of universal gravitation: between two point bodies there is an attractive force directly proportional to the product of their masses and inversely proportional to the square of the distance between them. Gravitational interaction determines the fall of bodies in the field of Earth's gravitational forces. The law of universal gravitation describes, for example, the movement of the planets of the solar system, as well as other macro-objects. It is assumed that gravitational interaction is caused by certain elementary particles - gravitons, the existence of which has not yet been experimentally confirmed.

Electromagnetic interaction associated with electrical and magnetic fields. Electric field occurs in the presence of electric charges, and a magnetic field occurs when they move. In nature, there are both positive and negative charges, which determines the nature of electromagnetic interaction. For example, electrostatic interaction between charged bodies, depending on the sign of the charge, is reduced to either attraction or repulsion. When charges move, depending on their sign and direction of movement, either attraction or repulsion occurs between them. Various states of aggregation of a substance, the phenomenon of friction, elastic and other properties of a substance are determined primarily by the forces of intermolecular interaction, which is electrostatic in nature. Electromagnetic interaction is described by the fundamental laws of electrostatics and electrodynamics: Coulomb’s law, Ampere’s law, etc. Its most general description gives Maxwell's electromagnetic theory, based on fundamental equations connecting electric and magnetic fields.

Strong interaction ensures the connection of nucleons in the nucleus and determines nuclear forces. It is assumed that nuclear forces arise during the exchange of virtual particles between nucleons - mesons.


Finally, weak interaction describes some types of nuclear processes. It is short-acting and characterizes all types of beta transformations.

Usually for quantitative analysis the listed interactions use two characteristics: the dimensionless interaction constant, which determines the magnitude of the interaction, and the radius of action (Table 3.1).

Table 3.1

According to the table. 3.1 it is clear that the gravitational interaction constant is the smallest. Its range of action, like that of electromagnetic interaction, is unlimited. In the classical view, gravitational interaction does not play a significant role in the processes of the microworld. However, in macro processes it plays a decisive role. For example, the movement of the planets of the solar system occurs in strict accordance with the laws of gravitational interaction.

The strong interaction is responsible for the stability of nuclei and extends only within the size of the nucleus. The stronger the interaction of nucleons in a nucleus, the more stable it is, the greater its binding energy, determined by the work that must be done to separate the nucleons and remove them from each other at such distances at which the interaction becomes zero. As the size of the nucleus increases, the binding energy decreases. Thus, the nuclei of elements at the end of the periodic table are unstable and can decay. This process is often called radioactive decay.

The interaction between atoms and molecules is predominantly electromagnetic in nature. This interaction explains the formation of various aggregate states of matter: solid, liquid and gaseous. For example, between the molecules of a substance in the solid state, the interaction in the form of attraction is much stronger than between the same molecules in the gaseous state.