This is the third fundamental interaction, existing only in the microcosm. It is responsible for the transformation of some fermion particles into others, while the color of weakly interacting peptons and quarks does not change. A typical example of weak interaction is the process of beta decay, during which a free neutron decays into a proton, an electron and an electron antineutrino in an average of 15 minutes. The decay is caused by the transformation of a quark of flavor d into a quark of flavor u inside the neutron. The emitted electron ensures the conservation of the total electrical charge, and the antineutrino allows the total mechanical momentum of the system to be preserved.
Strong interaction
Main function strong interaction- combine quarks and antiquarks into hadrons. The theory of strong interactions is in the process of being created. It is a typical field theory and is called quantum chromodynamics. Its starting point is the postulate of the existence of three types of color charges (red, blue, green), expressing the inherent ability of matter to unite quarks in strong interaction. Each of the quarks contains some combination of such charges, but their complete mutual compensation does not occur, and the quark has a resulting color, that is, it retains the ability to interact strongly with other quarks. But when three quarks, or a quark and an antiquark, combine to form a hadron, the net combination of color charges in it is such that the hadron as a whole is color neutral. Color charges create fields with their inherent quanta - bosons. The exchange of virtual color bosons between quarks and/or antiquarks serves as the material basis for the strong interaction. Before the discovery of quarks and color interactions, the nuclear force that unites protons and neutrons in the nuclei of atoms was considered fundamental. With the discovery of the quark level of matter, the strong interaction began to be understood as color interactions between quarks combining into hadrons. Nuclear forces are no longer considered fundamental; they must somehow be expressed through colored forces. But this is not easy to do, because the baryons (protons and neutrons) that make up the nucleus are generally color neutral. By analogy, we can recall that atoms as a whole are electrically neutral, but at the molecular level chemical forces appear, considered as echoes of electric atomic forces.
The four types of fundamental interactions considered underlie all other known forms of matter motion, including those that arose on higher levels development. Any complex shapes movements, when decomposed into structural components, are revealed as complex modifications of these fundamental interactions.
2. Development of scientific views on the interaction of particles before the evolutionary creation of the theory of the “Grand Unification”
The "Grand Unification" theory is a theory that unifies electromagnetic, strong and weak interactions. Mentioning the theory of the “Great Unification”, we are talking about the fact that all the forces that exist in nature are a manifestation of one universal fundamental force. There are a number of considerations that give reason to believe that at the moment of the Big Bang, which gave birth to our universe, only this force existed. However, over time, the universe expanded, which means it cooled, and the single force split into several different ones, which we now observe. The "Grand Unification" theory would describe the electromagnetic, strong, weak and gravitational forces as manifestations of one universal force. There has already been some progress: scientists have managed to construct a theory that combines electromagnetic and weak interactions. However, the main work on the theory of the “Great Unification” is still ahead.
Modern particle physics is forced to discuss questions that, in fact, worried ancient thinkers. What is the origin of particles and chemical atoms built from these particles? And how can the Cosmos, the Universe visible to us, be built from particles, no matter what we call them? And also – was the Universe created, or has it existed from eternity? If one can ask this, what are the pathways of thought that can lead to convincing answers? All these questions are similar to the search for the true principles of existence, questions about the nature of these principles.
Whatever we say about Space, one thing is clear that everything in natural world one way or another consists of particles. But how to understand this composition? It is known that particles interact - they attract or repel each other. Particle physics studies a variety of interactions. [Popper K. On the sources of knowledge and ignorance // Vopr. history of natural science and technology, 1992, No. 3, p. 32.]
Electromagnetic interaction attracted particular attention in the 18th–19th centuries. Similarities and differences between electromagnetic and gravitational interactions were discovered. Like gravity, electromagnetic forces are inversely proportional to the square of the distance. But, unlike gravity, electromagnetic “gravity” not only attracts particles (different charge signs), but also repels them from each other (equally charged particles). And not all particles are carriers of electric charge. For example, the photon and neutron are neutral in this regard. In the 50s years XIX V. electromagnetic theory of D. C. Maxwell (1831–1879) unified electrical and magnetic phenomena and thereby clarified the action of electromagnetic forces. [Grünbaum A. Origin versus creation in physical cosmology (theological distortions of modern physical cosmology). – Question. Philosophy, 1995, No. 2, p. 19.]
The study of radioactivity phenomena led to the discovery special kind interaction between particles, which is called the weak interaction. Since this discovery is related to the study of beta radioactivity, one could call this interaction beta decay. However, in the physical literature it is customary to talk about weak interaction - it is weaker than electromagnetic interaction, although much stronger than gravitational interaction. The discovery was facilitated by the research of W. Pauli (1900–1958), who predicted that during beta decay a neutral particle is released, compensating for the apparent violation of the law of conservation of energy, called a neutrino. And in addition, the discovery of weak interactions was facilitated by the research of E. Fermi (1901–1954), who, along with other physicists, suggested that electrons and neutrinos, before their departure from the radioactive nucleus, do not exist in the nucleus, so to speak, in a ready-made form, but are formed during the radiation process. [Grünbaum A. Origin versus creation in physical cosmology (theological distortions of modern physical cosmology). – Question. Philosophy, 1995, No. 2, p. 21.]
Finally, the fourth interaction turned out to be associated with intranuclear processes. Called the strong interaction, it manifests itself as the attraction of intranuclear particles - protons and neutrons. Due to its large size, it turns out to be a source of enormous energy.
The study of the four types of interactions followed the path of searching for their deep connection. On this unclear, largely dark path, only the principle of symmetry guided the research and led to the identification of the supposed connection various types interactions.
To identify such connections, it was necessary to turn to a search for a special type of symmetries. A simple example This type of symmetry can be represented by the dependence of the work performed when lifting a load on the height of the lift. The energy expended depends on the difference in height, but does not depend on the nature of the ascent path. Only the difference in height is significant and it does not matter at all from what level we start the measurement. We can say that we are dealing here with symmetry with respect to the choice of origin.
In a similar way, you can calculate the energy of motion of an electric charge in an electric field. The analogue of height here will be field voltage or, in other words, electric potential. The energy expended during charge movement will depend only on the potential difference between the final and initial points in the field space. We are dealing here with the so-called gauge or, in other words, scale symmetry. Gauge symmetry referred to electric field, is closely related to the law of conservation of electric charge.
Gauge symmetry turned out to be the most important tool, giving rise to the possibility of resolving many difficulties in the theory of elementary particles and in numerous attempts to unify various types of interactions. IN quantum electrodynamics, for example, various divergences arise. It is possible to eliminate these divergences due to the fact that the so-called renormalization procedure, which eliminates the difficulties of the theory, is closely related to gauge symmetry. The idea appears that the difficulties in constructing a theory of not only electromagnetic, but also other interactions can be overcome if other, hidden symmetries can be found.
Gauge symmetry can take on a generalized character and can be attributed to any force field. At the end of the 1960s. S. Weinberg (b. 1933) from Harvard University and A. Salam (b. 1926) from Imperial College in London, relying on the work of S. Glashow (b. 1932), undertook a theoretical unification of electromagnetic and weak interactions. They used the idea of gauge symmetry and the concept of a gauge field associated with this idea. [Yakushev A. S. Basic concepts of modern natural science. – M., Fakt-M, 2001, p. 29.]
Applicable for electromagnetic interaction simplest form gauge symmetry. It turned out that the symmetry of the weak interaction is more complex than that of the electromagnetic interaction. This complexity is due to the complexity of the process itself, so to speak, the mechanism of weak interaction.
In the process of weak interaction, for example, the decay of a neutron occurs. Particles such as neutron, proton, electron and neutrino can participate in this process. Moreover, due to weak interaction, mutual transformation of particles occurs.
Conceptual provisions of the theory of “Grand Unification”
In modern theoretical physics The tone is set by two new conceptual schemes: the so-called “Grand Unification” theory and supersymmetry.
These scientific trends together lead to a very attractive idea, according to which all of nature is ultimately subject to the action of some superpower, manifesting itself in various “guises.” This force is powerful enough to create our Universe and endow it with light, energy, matter and give it structure. But superpower is more than just a creative force. In it, matter, space-time and interaction are fused into an indivisible harmonious whole, generating such a unity of the Universe that no one had previously imagined. The purpose of science is essentially the search for such unity. [Ovchinnikov N.F. Structure and symmetry // System Research, M., 1969, p. 137.]
Based on this, there is a certain confidence in the unification of all phenomena of living and inanimate nature within the framework of a single descriptive scheme. Today, four fundamental interactions or four forces in nature are known, responsible for all known interactions of elementary particles - strong, weak, electromagnetic and gravitational interactions. Strong interactions bind quarks together. Weak interactions are responsible for some types of nuclear decay. Electromagnetic forces act between electric charges, and gravitational forces act between masses. The presence of these interactions is a sufficient and necessary condition for building the world around us. For example, without gravity, not only would there be no galaxies, stars and planets, but the Universe could not have arisen - after all, the very concepts of the expanding Universe and the Big Bang, from which space-time originates, are based on gravity. Without electromagnetic interactions there would be no atoms, no chemistry or biology, and no solar heat or light. Without strong nuclear interactions, nuclei would not exist, and therefore atoms and molecules, chemistry and biology would not exist, and stars and the Sun would not be able to generate heat and light using nuclear energy.
Even weak nuclear interactions play a role in the formation of the Universe. Without them, nuclear reactions in the Sun and stars would be impossible; apparently, supernova explosions would not occur and the heavy elements necessary for life could not spread throughout the Universe. Life might well not have arisen. If we agree with the opinion that all these four are completely various interactions, each of which is necessary in its own way for the emergence complex structures and determining the evolution of the entire Universe are generated by a single simple superpower, then the presence of a single fundamental law operating both in living and in inanimate nature, there is no doubt. Modern research shows that these four forces may once have been combined into one.
This was possible at the enormous energies characteristic of the era of the early Universe shortly after big bang. Indeed, the theory of unification of electromagnetic and weak interactions has already been confirmed experimentally. The “Grand Unification” theories should combine these interactions with the strong ones, and the “All That Is” theories should unify all four fundamental interactions as manifestations of one interaction. Thermal history of the Universe, starting from 10–43 sec. after the Big Bang to the present day, shows that most of helium-4, helium-3, deuterons (nuclei of deuterium - a heavy isotope of hydrogen) and lithium-7 were formed in the Universe approximately 1 minute after the Big Bang.
Heavier elements appeared inside stars tens of millions or billions of years later, and the emergence of life corresponds to the final stage of the evolving Universe. Based on the theoretical analysis and the results of computer modeling of dissipative systems operating far from equilibrium, under the action of a code-frequency low-energy flow, we concluded that there are two parallel processes in the Universe - entropy and information. Moreover, the entropic process of converting matter into radiation is not dominant. [Soldatov V.K. Theory of the “Great Unification”. – M., Postscript, 2000, p. 38.]
Under these conditions, a new type of evolutionary self-organization of matter arises, connecting the coherent spatiotemporal behavior of the system with dynamic processes within the system itself. Then, on the scale of the Universe, this law will be formulated as follows: “If the Big Bang led to the formation of 4 fundamental interactions, then the further evolution of the space-time organization of the Universe is associated with their unification.” Thus, in our view, the law of increasing entropy must be applied not to individual parts of the Universe, but to the entire process of its evolution. At the moment of its formation, the Universe turned out to be quantized in space-time hierarchy levels, each of which corresponds to one of the fundamental interactions. The resulting fluctuation, perceived as an expanding picture of the Universe, at a certain moment begins to restore its equilibrium. The process of further evolution occurs in a mirror image.
In other words, two processes are happening simultaneously in the observable Universe. One process - anti-entropy - is associated with the restoration of disturbed equilibrium, through the self-organization of matter and radiation into macroquantum states (as physical example we can cite such well-known states of matter as superfluidity, superconductivity and the quantum Hall effect). This process, apparently, determines the consistent evolution of processes thermonuclear fusion in stars, the formation of planetary systems, minerals, flora, unicellular and multicellular organisms. This automatically follows the self-organizing orientation of the third principle of the progressive evolution of living organisms.
The other process is purely entropic in nature and describes the processes of cyclic evolutionary transition of self-organizing matter (decay - self-organization). It is possible that these principles can serve as the basis for creating a mathematical apparatus that allows us to combine all four interactions into one superforce. As already noted, this is the problem that most theoretical physicists are currently occupied with. Further argumentation of this principle goes far beyond the scope of this article and is connected with the construction of the theory of Evolutionary Self-Organization of the Universe. Therefore, let us draw the main conclusion and see how applicable it is to biological systems, the principles of their control, and most importantly, to new technologies for the treatment and prevention of pathological conditions of the body. First of all, we will be interested in the principles and mechanisms of maintaining self-organization and evolution of living organisms, as well as the causes of their violations, manifested in the form of all kinds of pathologies.
The first of them is the principle of code-frequency control, the main purpose of which is to maintain, synchronize and control energy flows within any open self-organizing dissipative system. The implementation of this principle for living organisms requires the presence at each structural hierarchical level of a biological object (molecular, subcellular, cellular, tissue, organoid, organismal, population, biocenotic, biotic, landscape, biosphere, cosmic) presence of a biorhythmological process associated with the consumption and consumption of the transformed energy, which determines the activity and sequence of processes within the system. This mechanism occupies a central place in the early stages of the emergence of life in the processes of formation of DNA structure and the principle of reduplication of discrete codes of hereditary information, as well as in processes such as cell division and subsequent differentiation. As you know, the process of cell division always occurs in a strict sequence: prophase, metaphase, telophase, and then anaphase. You can violate the conditions of division, interfere with it, even remove the nucleus, but the sequence will always be preserved. Without a doubt, our body is equipped with the most perfect synchronizers: a nervous system that is sensitive to the slightest changes in external and internal environment, slower humoral system. At the same time, the slipper ciliate, in the complete absence of the nervous and humoral systems, lives, feeds, excretes, reproduces, and all these complex processes do not occur chaotically, but in strict sequence: any reaction predetermines the next one, and that in turn releases products , which are necessary to start the next reaction. [Soldatov V.K. Theory of the “Great Unification”. – M., Postscript, 2000, p. 59.]
It should be noted that Einstein’s theory marked such important progress in understanding nature that a revision of views on other forces of nature soon became inevitable. At this time, the only "other" force whose existence was firmly established was electromagnetic interaction. However, outwardly it did not resemble gravity at all. Moreover, several decades before the creation of Einstein’s theory of gravity, electromagnetism was successfully described by Maxwell’s theory, and there was no reason to doubt the validity of this theory.
Throughout his life, Einstein dreamed of creating unified theory a field in which all the forces of nature would merge together on the basis of pure geometry. Einstein devoted most of his life to the search for such a scheme after creating the general theory of relativity. However, ironically, the person who came closest to realizing Einstein’s dream was the little-known Polish physicist Theodor Kaluza, who back in 1921 laid the foundations for a new and unexpected approach to the unification of physics, which still amazes the imagination with its audacity.
With the discovery of weak and strong interactions in the 30s of the 20th century, the ideas of unifying gravity and electromagnetism largely lost their attractiveness. A consistent unified field theory should have included not two, but four forces. Obviously, this could not be done without achieving a deep understanding of weak and strong interactions. In the late 1970s, thanks to the fresh wind brought by Grand Unified Theories (GUT) and supergravity, the old Kaluza-Klein theory was remembered. They “blowed off the dust, dressed it up in fashion” and included in it all the interactions known to date.
In GUT, theorists managed to bring together three very different types of interactions within one concept; this is due to the fact that all three interactions can be described using gauge fields. The main property of gauge fields is the existence of abstract symmetries, thanks to which this approach gains elegance and opens up wide possibilities. The presence of force field symmetries quite clearly indicates the manifestation of some hidden geometry. In the Kaluza-Klein theory brought back to life, the symmetries of gauge fields become concrete - these are geometric symmetries associated with additional dimensions of space.
As in original version, interactions are introduced into theories by adding additional spatial dimensions to space-time. However, since we now need to accommodate interactions of three types, we have to introduce several additional dimensions. Simply counting the number of symmetry operations included in the GUT leads to a theory with seven additional spatial dimensions (so their total number reaches ten); if we take into account time, then space-time has eleven dimensions in total. [Soldatov V.K. Theory of the “Great Unification”. – M., Postscript, 2000, p. 69.]
Basic provisions of the theory of "Grand Unification" from the point of view of quantum physics
In quantum physics, each length scale is associated with an energy scale (or equivalent masses). The smaller the length scale being studied, the higher the energy required for this. Studying the quark structure of a proton requires energies equivalent to at least ten times the proton's mass. Significantly higher on the energy scale is the mass corresponding to the Great Unification. If we ever manage to achieve such a huge mass (energy), which we are very far from today, then it will be possible to study the world of X particles, in which the differences between quarks and leptons are erased.
What kind of energy is needed to penetrate “inside” the 7-sphere and explore additional dimensions of space? According to the Kaluza-Klein theory, it is required to exceed the Grand Unification scale and achieve energies equivalent to 10 19 proton masses. Only with such unimaginably enormous energies would it be possible to directly observe the manifestations of additional dimensions of space.
This huge value - 10 19 masses of a proton - is called the Planck mass, since it was first introduced by Max Planck, the creator of quantum theory. At an energy corresponding to the Planck mass, all four interactions in nature would merge into a single superforce, and ten spatial dimensions would be completely equal. If it were possible to concentrate a sufficient amount of energy, “ensuring the achievement of the Planck mass, then the full dimension of space would appear in all its splendor [Yakushev A. S. Basic concepts of modern natural science. – M., Fakt-M, 2001, p. 122. ]
By giving free rein to the imagination, one can imagine that one day humanity will gain superpowers. If this happened, then we would gain power over nature, since superpower ultimately gives rise to all interactions and all physical objects; in this sense, it is the fundamental principle of all things. Having mastered superpower, we could change the structure of space and time, bend the void in our own way and put matter in order. By controlling superpowers, we could create or transform particles at will, generating exotic new forms of matter. We could even manipulate the dimension of space itself, creating bizarre artificial worlds with unimaginable properties. We would truly become masters of the Universe!
But how to achieve this? First of all, it is necessary to obtain a sufficient amount of energy. To get an idea of what we're talking about, remember that the 3 km long linear accelerator at Stanford accelerates electrons to energies equivalent to 20 proton masses. To achieve the Planck energy, the accelerator would need to be lengthened by 10 18 times, making it the size of the Milky Way (about one hundred thousand light years). Such a project is not one that can be implemented in the foreseeable future. [Wheeler J. A. Quantum and the Universe // Astrophysics, quanta and the theory of relativity, M., 1982, p. 276.]
Grand Unified Theory clearly distinguishes three thresholds, or scales, of energy. First of all, this is the Weinberg–Salam threshold, equivalent to almost 90 proton masses, above which electromagnetic and weak interactions merge into a single electroweak interaction. The second scale, corresponding to 10 14 proton masses, is characteristic of the Grand Unification and the new physics based on it. Finally, the ultimate scale - the Planck mass - equivalent to 10 19 proton masses, corresponds to the complete unification of all interactions, as a result of which the world is amazingly simplified. One of the biggest unresolved problems is to explain the existence of these three scales, as well as the reason for such a strong difference between the first and second of them. [Soldatov V.K. Theory of the “Great Unification”. – M., Postscript, 2000, p. 76.]
Modern technology is capable of achieving only the first scale. Proton decay could give us an indirect means of studying physical world on the grand unified scale, although at present there appears to be no hope of directly reaching this limit, let alone on the scale of the Planck mass.
Does this mean that we will never be able to observe manifestations of the original superpower and the invisible seven dimensions of space. Using technical means such as a superconducting supercollider, we are rapidly moving up the scale of energies achievable under terrestrial conditions. However, the technology created by people does not exhaust all possibilities - nature itself also exists. The Universe is a gigantic natural laboratory in which the greatest experiment in the field of elementary particle physics was “conducted” 18 billion years ago. We call this experiment the Big Bang. As will be discussed later, this initial event was enough to release - albeit for a very short moment - superpower. However, this, apparently, was enough for the ghostly existence of superpower to leave its mark forever. [Yakushev A. S. Basic concepts of modern natural science. – M., Fakt-M, 2001, p. 165.]
Time is like a river carrying passing events, and its current is strong; As soon as something appears before your eyes, it has already been carried away, and you can see something else that will also soon be carried away.
Marcus Aurelius
Each of us strives to create complete picture world, including the picture of the Universe, from the smallest subatomic particles to the greatest extent. But the laws of physics are sometimes so strange and counterintuitive that this task can become overwhelming for those who have not become professional theoretical physicists.
A reader asks:
Although this is not astronomy, maybe you can give me a hint. The strong force is carried by gluons and binds quarks and gluons together. Electromagnetic is carried by photons and binds electrically charged particles. Gravity is supposedly carried by gravitons and binds all particles to mass. The weak is carried by W and Z particles, and... is associated with decay? Why is the weak force described this way? Is the weak force responsible for the attraction and/or repulsion of any particles? And which ones? And if not, why then is it one of the fundamental interactions if it is not associated with any forces? Thank you.
Let's get the basics out of the way. There are four fundamental forces in the universe - gravity, electromagnetism, the strong nuclear force and the weak nuclear force.
And all this is interaction, force. For particles whose state can be measured, the application of a force changes its moment - in ordinary life, in such cases we talk about acceleration. And for three of these forces this is true.
In case of gravity, total amount energy (mostly mass, but this includes all energy) bends spacetime, and the motion of all other particles changes in the presence of anything that has energy. This is how it works in the classical (non-quantum) theory of gravity. Maybe there are more general theory, quantum gravity, where gravitons are exchanged, leading to what we observe as gravitational interaction.
Before you continue, please understand:
- Particles have a property, or something inherent to them, that allows them to feel (or not feel) a certain type of force
- Other particles carrying interactions interact with the first ones
- As a result of interactions, particles change their moment, or accelerate
In electromagnetism, the main property is electric charge. Unlike gravity, it can be positive or negative. A photon, a particle that carries the force associated with a charge, results in identical charges repel, and those that differ are attracted.
It is worth noting that moving charges, or electric currents, experience another manifestation of electromagnetism - magnetism. The same thing happens with gravity, and it is called gravitomagnetism (or gravitoelectromagnetism). We won’t go deeper - the point is that there is not only a charge and a force carrier, but also currents.
There is also a strong nuclear interaction, which has three types of charges. Although all particles have energy and are all subject to gravity, and although quarks, half the leptons and a pair of bosons contain electrical charges - only quarks and gluons have a colored charge and can experience the strong nuclear force.
There are a lot of masses everywhere, so gravity is easy to observe. And since the strong force and electromagnetism are quite strong, they are also easy to observe.
But what about the latter? Weak interaction?
We usually talk about it in the context of radioactive decay. A heavy quark or lepton decays into lighter and more stable ones. Yes, weak interaction has something to do with this. But in in this example it is somehow different from other forces.
It turns out that weak interaction is also a force, it’s just not often talked about. She's weak! 10,000,000 times weaker than electromagnetism over a distance the diameter of a proton.
A charged particle always has a charge, regardless of whether it is moving or not. But electricity, created by it, depends on its movement relative to other particles. Current determines magnetism, which is as important as the electrical part of electromagnetism. Compound particles like the proton and neutron have significant magnetic moments, just like the electron.
Quarks and leptons come in six flavors. Quarks - top, bottom, strange, charmed, charming, true (according to their letter designations in Latin u, d, s, c, t, b - up, down, strange, charm, top, bottom). Leptons - electron, electron-neutrino, muon, muon-neutrino, tau, tau-neutrino. Each of them has an electrical charge, but also a scent. If we combine electromagnetism and the weak force to get the electroweak force, then each of the particles will have some weak charge, or electroweak current, and a weak force constant. All this is described in the Standard Model, but it was quite difficult to test it because electromagnetism is so strong.
In a new experiment, the results of which were recently published, the contribution of the weak interaction was measured for the first time. The experiment made it possible to determine the weak interaction of up and down quarks
And the weak charges of the proton and neutron. The Standard Model's predictions for weak charges were:
Q W (p) = 0.0710 ± 0.0007,
Q W (n) = -0.9890 ± 0.0007.
And based on the scattering results, the experiment produced the following values:
Q W (p) = 0.063 ± 0.012,
Q W (n) = -0.975 ± 0.010.
Which coincides very well with the theory, taking into account the error. The experimenters say that by processing more data, they will further reduce the error. And if there are any surprises or discrepancies with Standard model, it'll be cool! But nothing indicates this:
Therefore, particles have a weak charge, but we do not talk about it, since it is unrealistically difficult to measure. But we did it anyway, and it appears that we have reconfirmed the Standard Model.
The reader is familiar with forces of different nature that manifest themselves in interactions between bodies. But fundamentally different types interaction very little. Apart from gravity, which plays a significant role only in the presence of huge masses, then only three types of interactions are known: strong, electromagnetic and weak.
Electromagnetic interaction everyone knows. Thanks to them, a non-uniformly moving electric charge (say, an electron in an atom) emits electromagnetic waves(For example, visible light). All interactions are associated with this class of interactions. chemical processes, as well as all molecular phenomena - surface tension, capillarity, adsorption, fluidity. Electromagnetic interaction, the theory of which is brilliantly confirmed by experience, are deeply connected with electric charge elementary particles.
Strong interaction became known only after disclosure internal structure atomic nucleus. In 1932 it was discovered that it consists of nucleons, neutrons and protons. And exactly strong interaction connect nucleons in the nucleus - are responsible for nuclear forces, which, unlike electromagnetic ones, are characterized by a very short range of action (about 10-13, i.e. one ten-trillionth of a centimeter) and high intensity. Besides, strong interaction appear during collisions particles high energies involving pions and so-called "strange" particles.
It is convenient to estimate the intensity of interactions using the so-called mean free path particles in some substance, i.e. By average the way that particle can pass through this substance until a destructive or strongly deflecting collision occurs. It is clear that the longer the mean free path, the less intense the interaction.
If we consider particles Very high energy, then collisions caused by strong interactions, are characterized by the free path particles, corresponding in order of magnitude to tens of centimeters in copper or iron.
The situation is different with weak interactions. As we have already said, the mean free path of a neutrino in dense matter is measured in astronomical units. This indicates a surprisingly low intensity of weak interactions.
Any process interaction elementary particles characterized by some time that determines it average duration. Processes caused by weak interactions, are often called “slow” because the time for them is relatively long.
The reader may be surprised, however, that a phenomenon occurring in, say, 10-6 (one millionth of a) second is classified as slow. This lifetime is typical, for example, for the decay of a muon caused by weak interactions. But everything is learned by comparison. In the world elementary particles such a period of time is indeed quite long. Natural unit length in the microcosm is 10-13 centimeters - range of action nuclear forces. And since elementary particles high energy have a speed close to the speed of light (about 1010 centimeters per second), then the “normal” time scale for them will be 10-23 seconds.
This means that the time of 10-6 seconds for the “citizens” of the microworld is much longer than for you and me the entire period of existence of life on Earth
electroweak theory
Lesson-lecture explaining new material, 2 hours, 11th grade
You already know that all forces in nature come down to the description of gravitational, electromagnetic and strong interactionsth or their combinations. Gravitational interaction is inherent in all material objects. Not only the interaction between charged bodies and particles, but also elastic, viscous, molecular, chemical and other interactions are reduced to electromagnetic. The strong interaction holds nucleons in atomic nuclei and determines the various transformations of particles into each other.Today we will consider another, 4th, type of fundamental interactions, which cannot be reduced to any of the above - weak interaction. Let's find out amazing fact that at short distances the weak interaction becomes indistinguishable from the electromagnetic one.
Weak interaction. It is no coincidence that this interaction is called weak. Firstly, its manifestations are rare in our Everyday life, while we have long been accustomed to various manifestations of gravitational and electromagnetic interactions (for example, the fall of all bodies to the Earth, friction, lightning, etc.), to the results of the action of nuclear forces that ensure the stability of the matter around us. Secondly, this interaction is indeed weak, because its intensity at low energies not exceeding 1 GeV—the rest energy of the proton—is billions of times less than the intensity of the strong and electromagnetic interactions.
In addition, experience shows that strong and electromagnetic interactions can ensure both various transformations of particles and the integrity of some material object (for example, strong interaction ensures the integrity of the nucleus, electromagnetic interaction ensures the integrity of the crystal lattice). The weak interaction force is not enough to keep particles near each other (i.e., to form bound states). It can only manifest itself during the disintegration and mutual transformations of particles.
Despite all the “weaknesses” of weak interaction, it is very important. It is this interaction at the micro level that is responsible for the release of energy in stars, including the Sun. We can say that we are in literally We can’t live without this interaction! In addition, the decay of radioactive nuclei, as you know, also occurs due to weak interaction.
So, what are the main properties of the weak interaction?
– Weak interaction at low energies much weaker than the strong and electromagnetic interactions;
– weak interaction is short-range: its radius of action is about 10–18 m;
– weak interaction is universal: almost all particles participate in it, except photons. In addition, there are particles that participate only in weak interactions, for example, neutrinos and antineutrinos;
– with weak interaction, some seemingly universal conservation laws are not satisfied (this issue is discussed in the material for self-study, see below).
As is known, each of the interactions is carried out through special elementary particles - carriers of one or another interaction. For example, photons are carriers of electromagnetic interaction, gluons are carriers of strong interaction. Scientists are currently trying to discover carriers gravitational interaction– gravitons.
The carriers of the weak interaction are intermediate vector bosons. There are 3 types of them known: W – , W + , Z 0 . These particles have very large masses: mW 85m p, m Z 96m p, Where m p– proton mass.
Let us describe in more detail the role of intermediate bosons in weak interaction processes. For example, during -decay of a quark d emits a neutron W- boson and turns into a quark u, so the neutron turns into a proton: du + W- , - and then W– - boson decays into an electron and an antineutrino: [However, it should be emphasized that due to the very large mass W-boson effectively -decay occurs in such a way that the entire internal “structure” of weak interactions does not appear and is reflected only in a small interaction constant. But if we study weak interaction processes at energies comparable to mass W(i.e., about 100 GeV), then here the contribution W-boson is clearly visible. – Ed.]
2. Unified electroweak interaction. Further theoretical research led to the fact that the picture of fundamental interactions began to be simplified. It turned out that electromagnetic and weak interactions are manifestations of the same interaction, which is called electroweak interaction. This idea was first expressed (independently) in 1967. S. Weinberg And A.Salam, putting forward the following hypothesis: the nature of weak and electromagnetic interactions is the same, because at short distances, weak interactions are comparable in strength to electromagnetic ones, and the difference between intermediate vector bosons and photons is erased. In other words, at energies exceeding several hundred gigaelectronvolts, electromagnetic and weak interactions become indistinguishable in intensity; they seem to merge into one electroweak interaction.
Note that Weinberg and Salam relied on the earlier assumption that the carriers of the weak interaction are intermediate vector bosons. These particles were discovered experimentally much later (in 1983).
3. Justification of the Weinberg–Salam hypothesis. Weinberg and Salam came to the conclusion about the existence of a single electroweak force based on new fundamental physical ideas:
1) local gauge invariance;
2) spontaneous breaking of symmetry.
It follows from the hypothesis that at small distances intermediate vector bosons do not differ in their properties from photons, which means that intermediate vector bosons and photons are, in fact, two manifestations of the same particle - the carrier of the electroweak interaction (otherwise the interaction force cannot be the same). This is only possible when done principle of local gauge invariance (symmetry),(see diagram).
It turned out that when the scale changes, i.e. as the distance decreases, the carriers of the electroweak interaction move from one of their manifestations - photons - to their other manifestation - intermediate vector bosons - but their exchange is carried out just as easily.
But here a new question arose: how can intermediate vector bosons and photons be manifestations of the same particles, if photons have zero mass, and intermediate vector bosons have very large masses? Since these are the same particles, their masses must match. It seemed that a hopeless situation had arisen.
It turned out that intermediate vector bosons are capable of acquiring their mass as a result of a certain mechanism called spontaneous breaking of symmetry. This mechanism is very complex, but let’s try to look at its essence using a few simple examples.
The laws of motion of individual atoms satisfy the principle of spatial symmetry, i.e. do not change when the atom moves along various directions. But when a crystal is formed, this symmetry is broken by itself, and the properties of the crystal in different directions will no longer be the same. Thus, the crystal, compared to free atoms, has many specific properties, for example, the ability to be magnetized.
The ball located in the center of the raised bottom of the bottle will be in equilibrium. The system has axial symmetry. However, this equilibrium position is unstable. Left to its own devices, the ball, under the influence of an arbitrarily small disturbance, will roll down to the concave bottom. This position of the ball is stable, because it corresponds to a minimum potential energy in the Earth's gravity field. Initial axial symmetry state will be spontaneously disrupted.
Similarly, in the most general terms, the mechanism of spontaneous violation of local gauge symmetry, which ensures the “masslessness” of intermediate vector bosons and their identity with photons, leads to the appearance of mass in intermediate vector bosons and thereby to differences in the external manifestation of weak and electromagnetic interactions.
The above provisions constitute unified theory of electroweak interaction. It was from this that the existence followed three types intermediate vector bosons W – , W + , Z 0 , and the values of their masses were also predicted.
The experimental discovery of intermediate vector bosons in 1983 confirmed the validity of the unified theory of electroweak interaction. You are also invited to familiarize yourself with these experiments (the question is presented in the material for self-study).
Thus, instead of four fundamental interactions, we can only talk about three: gravitational, strong and electroweak.
Self-study material
1. Failure to comply with conservation laws under weak interaction. It was discovered that with weak interaction some seemingly universal conservation laws are not fulfilled, which are fulfilled with the other three fundamental interactions (see diagram).
Let us consider the laws that do not hold in weak interactions.
Law of conservation of spatial parity ( P-parity). They say that law of conservation of spatial parity in any process is executed if the process is mirror symmetric, i.e. proceeds in exactly the same way both to the right and to the left relative to some chosen center. In other words, the process itself and its mirror reflection proceed in exactly the same way.
In 1957, Ts. Wu found that the parity conservation law does not hold true in weak interactions. A certain substance containing the β-active isotope of cobalt was placed inside a coil with current, creating a magnetic field (the field is necessary to order the orientation of spins and the intrinsic magnetic moments of nuclei). It turned out that about 40% more electrons were emitted on one side (for example, up) than on the other.
Experience on a real installation (above) and its reflection in the mirror (below)
When the whole picture is mirrored, for example, relative to a mirror located below, we will see a completely different phenomenon (most electrons fly down, although the field IN circular current is still directed upward). In order for the phenomenon of -decay in the mirror to proceed in exactly the same way, the direction of the “predominant” emission of electrons (upward) must change. There is a violation of the law of conservation of spatial parity, which would not exist if electrons were emitted with equal probability both upward and downward.
The phenomenon of non-conservation of spatial parity in weak interactions can be illustrated this way. Particles born during weak interaction (electrons, muons, taons) are longitudinally polarized. This means that they have own moment momentum - spin j , which for a given particle is always either codirectional with the momentum of the particle p , or directed in the opposite direction. In specular reflection, these particles specified vectors change direction in different ways. The spin does not change direction, but the momentum does. However, particles with the resulting arrangement p And j simply does not exist, so in the mirror the process proceeds differently.
Particle with longitudinal polarization: A) a fall; b) reflection
2. Discovery of intermediate vector bosons. In 1983, the existence of intermediate vector bosons was experimentally confirmed. It is known that the main research method in elementary particle physics is the scattering method, i.e. the collision of different particles with each other, as a result of which new particles are born. Recently, colliders have been widely used - accelerators in which two beams of particles with zero total momentum collide (particles from different beams have impulses equal in magnitude but oppositely directed). They say that the process is considered in the system of the center of inertia of colliding particles. New particles born in the collider are recorded by various detectors.
So, let's collide proton and antiproton beams, in each of which the particle energy is equal to E. Then the total collision energy of two particles is 2 E. Subject to 2 E > Ms 2 in this collision a particle with mass M. Let's look at the process: 
, Where X is a set of all possible states, for example,
We illustrate the birth of intermediate vector bosons with a diagram.
Quark u from a proton and an antiquark from an antiproton can merge into W+ (this is shown in the diagram). Similarly, couples can give when merging Z 9 -boson, pair – W– - boson. But, once born, these particles quickly disintegrate. For example, etc.
A positron or positively charged muon with high efficiency can be registered by detectors, and this will serve as a sign of the birth of an intermediate vector boson. At the same time, neutrinos fly away, carrying away a significant part of the energy.
The experimental discovery of vector intermediate bosons confirmed the validity of the unified theory of electroweak interaction.
Questions for self-control
1. List and explain the conservation laws that apply to weak interaction.
2. What is the essence of the law of conservation of spatial parity?
3. Explain how the non-fulfillment of the law of conservation of spatial parity in weak interaction was proven. When and by whom was this experiment carried out?
4. How else can you illustrate the phenomenon of non-conservation of spatial parity in weak interaction?
5. How does the law of conservation of spatial parity differ from the law of conservation of combined parity? Why can't we talk about its feasibility for weak interaction?
6. Why were weirdness and charm introduced? What values can they take? What can be said about the conservation of these quantities under weak interaction?
7. How does an isotopic spin differ from an isotopic multiplet? Give an example of an isotopic multiplet. Is the law of conservation of isospin always violated in weak interactions?
8. Why do you think, before the construction of colliders, it was not possible to experimentally prove the existence of intermediate vector bosons?
9. Explain the process of creation of intermediate vector bosons in the collider.
10. How are intermediate vector bosons produced in the collider detected?
Literature
Myakishev G.Ya. Elementary particles. – M.: Nauka, 1979.
Guidelines for the course “Physics of the atomic nucleus and elementary particles”: Comp. Vasilevsky A.S. Parts 1, 2. – Kirov: GPI, 1990.
Mukhin K.N. Entertaining nuclear physics. – M.: Energoatomizdat, 1985.
Naumov A.I. Physics of the atomic nucleus and elementary particles. – M.: Education, 1984.
Perch L.B. Physics of elementary particles. – M.: Nauka, 1988.
Orir J. Popular physics. – M.: Mir, 1964.
Physics of elementary particles. Astrophysics: Encyclopedia "Modern Natural Science". T. 4. – M.: Publishing House Magistr-Press, 2000.
Graduate of the Kirov State Pedagogical University in 1996, physics teacher of the highest qualification category, teaching experience 9 years, methodologist, Ph.D. Married, has two children.
5th year student of the Faculty of Physics of Vyat GSU.
This interaction is the weakest of the fundamental interactions experimentally observed in the decays of elementary particles, where the following are fundamentally significant: quantum effects. Let us recall that quantum manifestations of gravitational interaction have never been observed. Weak interactions are highlighted using next rule: if an elementary particle called a neutrino (or antineutrino) is involved in the interaction process, then this interaction is weak.
A typical example of the weak interaction is the beta decay of a neutron, where n– neutron, p– proton, e– – electron, e+ – electron antineutrino. It should, however, 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 to occur big number neutrinoless decays. As an example, we can note the decay process of lambda hyperon D into a proton p+ and negatively charged pion p– . By modern ideas The neutron and proton are not true elementary particles, but are composed of elementary particles called quarks.
The intensity of the weak interaction is characterized by the Fermi coupling constant G F. Constant G F dimensional. To form a dimensionless quantity, it is necessary to use some reference mass, for example the mass of a proton m p. Then the dimensionless coupling constant will be. It can be seen that the weak interaction is much more intense than the gravitational interaction.
The weak interaction, unlike the gravitational interaction, is short-range. This means that the weak force between particles only comes into play if the particles are close enough to each other. If the distance between 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 weak interaction is about 10–15 cm, that is, weak interaction is concentrated at distances smaller sizes atomic nucleus.
Why can we talk about weak interaction as an independent type of fundamental interaction? The answer is simple. It has been established that there are processes of transformation of elementary particles that are not reduced to gravitational, electromagnetic and strong interactions. Good example, showing that there are three qualitatively different interactions in nuclear phenomena, associated with radioactivity. Experiments indicate the presence of three various types radioactivity: α-, β- and γ-radioactive decays. In this case, α-decay is due to strong interaction, γ-decay is due to electromagnetic interaction. The remaining β 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. IN general case the need to introduce weak interaction is due to the fact that processes occur in nature in which electromagnetic and strong decays prohibited by conservation laws.
Although the weak interaction is significantly concentrated within 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 important role in the so-called thermonuclear reactions, responsible for the mechanism of energy release in stars.
The most amazing property 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 left and right is arbitrary. Indeed, the processes of gravitational, electromagnetic and strong interaction are invariant with respect to spatial inversion, which carries out 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 occur with non-conservation of spatial parity and, therefore, seem to feel the difference between left and right. Currently, there is solid experimental evidence that parity nonconservation in weak interactions is universal in 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 non-conservation in weak interactions looked like this unusual property, that almost immediately after its discovery, theorists made attempts to show that in fact there is complete symmetry between left and right, only it has more deep meaning than previously thought. Mirror reflection must be accompanied by the replacement of particles with antiparticles (charge conjugation C), and then everything fundamental interactions must be invariant. However, it was later established that this invariance is not universal. There are weak decays of the so-called long-lived neutral kaons into pions p + , p – , which are forbidden if the indicated invariance actually took place. Thus, distinctive feature weak interaction is its CP non-invariance. It is possible that this property is responsible for the fact that matter in the Universe significantly prevails over antimatter, built from antiparticles. The world and the antiworld are asymmetrical.
The question of which particles are carriers of the weak interaction for a long time was unclear. Understanding was achieved relatively recently within the framework of the unified theory of electroweak interactions - the Weinberg-Salam-Glashow theory. 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.