There are four types of forces in nature: gravitational, electromagnetic, nuclear and weak.

Gravitational forces or gravity, act between all bodies. But these forces are noticeable if at least one of the bodies has dimensions comparable to the size of the planets. The forces of attraction between ordinary bodies are so small that they can be neglected. Therefore, the forces of interaction between planets, as well as between planets and the Sun or other bodies that have a very large mass, can be considered gravitational. These can be stars, satellites of planets, etc.

Electromagnetic forces act between bodies having an electric charge.

Nuclear forces(strong) are the most powerful in nature. They act inside atomic nuclei at distances of 10 -13 cm.

Weak forces, like nuclear ones, act at short distances of the order of 10 -15 cm. As a result of their action, processes occur inside the nucleus.

Mechanics considers gravitational forces, elastic forces and frictional forces.

Gravitational forces

Gravity is described law of universal gravitation. This law was outlined by Newton in the middle XVII V. in the work “Mathematical principles of natural philosophy”.

By gravitycalled the force of gravity with which any material particles attract each other.

The force with which material particles attract each other is directly proportional to the product of their masses and inversely proportional to the square of the distance between them .

G – gravitational constant, numerically equal to the modulus of the gravitational force with which a body having unit mass acts on a body having the same unit mass and located at a unit distance from it.

G = 6.67384(80) 10 −11 m 3 s −2 kg −1, or N m² kg −2.

On the surface of the Earth, the force of gravity (gravitational force) manifests itself as gravity.

We see that any object thrown in a horizontal direction still falls down. Any object thrown up also falls down. This happens under the influence of gravity, which acts on any material body located near the surface of the Earth. The force of gravity acts on bodies and on the surfaces of other astronomical bodies. This force is always directed vertically downwards.

Under the influence of gravity, a body moves towards the surface of the planet with acceleration, which is called acceleration of free fall.

The acceleration of gravity on the Earth's surface is denoted by the letter g .

Ft = mg ,

hence,

g = Ft / m

g = 9.81 m/s 2 at the Earth’s poles, and at the equator g = 9.78 m/s 2 .

When solving simple physical problems, the value g is considered to be equal to 9.8 m/s 2.

The classical theory of gravity is applicable only to bodies whose speed is much lower than the speed of light.

Elastic forces

Elastic forces are called forces that arise in a body as a result of deformation, causing a change in its shape or volume. These forces always strive to return the body to its original position.

During deformation, particles of the body are displaced. The elastic force is directed in the direction opposite to the direction of particle displacement. If the deformation stops, the elastic force disappears.

The English physicist Robert Hooke, a contemporary of Newton, discovered a law establishing a connection between the force of elasticity and the deformation of a body.

When a body is deformed, an elastic force arises that is directly proportional to the elongation of the body and has a direction opposite to the movement of particles during deformation.

F = k ∆ l ,

Where To – body rigidity, or elasticity coefficient;

∆ l – the amount of deformation showing the amount of elongation of the body under the influence of elastic forces.

Hooke's law applies to elastic deformations when the elongation of the body is small, and the body restores its original dimensions after the forces that caused this deformation disappear.

If the deformation is great and the body does not return to its original shape, Hooke's law does not apply. At Very large deformations cause destruction of the body.

Friction forces

Friction occurs when one body moves on the surface of another. It is of electromagnetic nature. This is a consequence of the interaction between atoms and molecules of contacting bodies. The direction of the friction force is opposite to the direction of movement.

Distinguish dry And liquid friction. Friction is called dry if there is no liquid or gaseous layer between the bodies.

A distinctive feature of dry friction is static friction, which occurs when bodies are at relative rest.

Magnitude static friction forces always equal to the magnitude of the external force and directed in the opposite direction. The force of static friction prevents the movement of a body.

In turn, dry friction is divided into friction slip and friction rolling.

If the magnitude of the external force exceeds the magnitude of the friction force, then slippage will occur, and one of the contacting bodies will begin to move forward relative to the other body. And the friction force will be called sliding friction force. Its direction will be opposite to the direction of sliding.

The force of sliding friction depends on the force with which the bodies press on each other, on the state of the rubbing surfaces, on the speed of movement, but does not depend on the area of ​​contact.

The sliding friction force of one body on the surface of another is calculated by the formula:

F tr. = k N ,

Where k – sliding friction coefficient;

N – normal reaction force acting on the body from the surface.

Rolling friction force occurs between a body that rolls over a surface and the surface itself. Such forces appear, for example, when car tires come into contact with the road surface.

The magnitude of the rolling friction force is calculated by the formula

Where Ft – rolling friction force;

f – rolling friction coefficient;

R – radius of the rolling body;

N – pressing force.

1) Law of universal gravitation: Two material points are attracted to each other with forces proportional to the product of the masses of the bodies and inversely proportional to the square of the distance between them.

2) Gravity acceleration is the acceleration that all bodies acquire during free fall near the Earth’s surface, regardless of their mass. Denoted by the letter g.

The acceleration of gravity on Earth is approximately g = 9.81 m/s2.

Free fall is uniformly accelerated motion. Its acceleration is always directed towards the center of the Earth.

3) Gravity is the force with which the Earth attracts a body towards itself.

4) Body weight is the force with which the body acts on a support or suspension.

G-force is the ratio of weight to gravity.

State of weightlessness if P=0.

5) The elastic force is a force that arises as a result of deformation of the body and tends to restore the previous size and shape of the body.

6) Deformation is a change in the shape and size of the body. Deformations can be elastic or non-elastic.

7) If the deformation is elastic, then after removing the external influence, the body restores its original shape and size.

If the deformation is not elastic, then the body does not restore its original shape and size.

8. Absolute and relative deformation:

9) Hooke's Law: During elastic deformations, an elastic force arises, directed against the displacement of particles of the body and directly proportional to the change in the linear dimensions of the body (absolute deformation).

10) Sigma Mechanical stress is the force acting on a unit cross-sectional area of ​​a body.

11) Young's modulus [E] depends only on the material of the body and does not depend on the size of the body.

12.Friction force is a force that arises at the boundary of contact of bodies in the absence of relative motion of the bodies.

13.Frictional force:

Let the body rest on a horizontal surface and be acted upon by an external force.

If the external force lies within the range of zero, then it remains at rest. Because the external force will be balanced by the force of static friction.

If the external force changes, then the static friction force changes at the same time.

14) The coefficient of static friction depends on the materials of the body and surface, as well as the state of the contacting surfaces.

15) Sliding friction force:

If the external forces are greater than the reaction of the support and the coefficient of friction, then the body begins to slide and a sliding friction force arises.

The force of sliding friction does not depend on the area of ​​the contacting surfaces and is directly proportional to the force of normal movement of the body onto the surface.

16) The sliding friction coefficient depends on the materials of the body and surface, as well as on the condition of these surfaces. The presence of lubricant reduces the sliding friction force.

17) Medium resistance force:

If a body moves in a liquid or gas, a drag force arises from the medium.

The force of S.S depends on the speed of the body, the shape of the body and its size.

If the speed of movement is small, then the force is proportional to the speed.

For the force S.S there is no static friction force. Any small force will cause the body to move.

18) Inertial forces are forces that arise in the ISO, due to acceleration, are always equal in magnitude and opposite in direction.

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

First of January 7,000,000,000 A.D. e., Ann Arbor.

The coming New Year is not too big a reason for celebration. There is no one who can even mark his arrival. The surface of the Earth turned into an unrecognizable wasteland, scorched to the ground by the Sun. The sun has swollen limitlessly: it has become so huge that its red-hot disk covers almost the entire daytime sky. Mercury and Venus have already died, and now the thin outer regions of the solar atmosphere threaten to capture Earth's receding orbit.

The oceans that once gave birth to life evaporated long ago, turning first into a heavy, sterilizing cloud of water vapor, and then completely dissolving into outer space. All that remained was a barren, rocky surface. Faint traces of ancient coastlines, ocean basins and eroded remains of continents can still be seen. By midday the temperature reaches nearly three thousand degrees Fahrenheit and the rocky surface begins to melt. The equator is already partially surrounded by a wide belt of boiling lava, which, as it cools, forms a thin gray crust while the swollen Sun rests nightly behind the horizon.

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

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

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

Now our Universe, whose age is estimated at ten to fifteen billion years, is still experiencing the time of its youth. So many astronomical possibilities that are of greater interest simply have not yet had time to manifest themselves. However, as the distant future approaches, the Universe will gradually change, turning into an arena in which a great variety of amazing astrophysical processes will unfold. This book tells the biography of the Universe from beginning to end. This is the story of how the familiar stars of the night sky gradually turn into strange frozen stars, evaporating black holes and atoms the size of the Galaxy. This is a scientific look at the face of eternity.

Four windows to the Universe

The biography of our Universe and the study of astrophysics in general unfolds on four important scales - at the level of planets, stars, galaxies and the Universe as a whole. Each provides a different type of window for observing the properties and evolution of nature. At each of these levels, astrophysical objects go through all life cycles, starting with formation - an event similar to birth, and - often ending with a very specific ending, similar to death. Death can be fast and furious; for example, a massive star ends its evolution with a spectacular supernova explosion. Another alternative is the painfully slow death that awaits faint red dwarfs, which gradually fade into white dwarfs - the cooling embers of once powerful and active stars.

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

The key question is whether the Universe will expand forever or whether at some point in the future the expansion will stop and contract again. Current astronomical observations strongly suggest that our universe is destined to expand continuously, so much of our narrative follows this scenario. Nevertheless, we decided to briefly outline the consequences of the second possible scenario - the terrible death of the Universe in repeated hot compression.

Below the vast expanse of cosmology, on a smaller level, come galaxies such as our Milky Way. Galaxies are large and rather sparse collections of stars, gas and other types of matter. Galaxies are not randomly scattered throughout the Universe; rather, they are woven into the overall tapestry of the cosmos by gravity. Some groups of galaxies are so heavy that they remain together under the influence of gravitational forces, and these clusters of galaxies can be considered independent astrophysical objects. In addition to belonging to clusters, galaxies randomly combine to form even larger structures resembling threads, sheets and walls. The set of patterns formed; galaxies at this level are called the large-scale structure of the Universe.

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

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

Although they do not populate space too densely, the galaxies themselves are also mostly empty. And although they contain billions of stars, only a very small part of their volume is actually filled with stars. If you were going to go on a spaceship to some random point in our Galaxy, the probability of your ship landing on some star is extremely small, on the order of one billion in a trillion (one chance in 10 22). Such emptiness of galaxies is quite eloquent evidence of how they developed and what awaits them in the future. Direct collisions between stars in a galaxy are extremely rare. Consequently, a very long time will pass - much more than has passed from the birth of our Universe to the present moment - before collisions of stars and encounters of other astrophysical objects have any effect on the structure of the galaxy. As you will see, these collisions become more and more important as the Universe ages.

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

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

But these nuclear power plants don't last forever. The nuclear fusion reactions that produce energy in the interior of stars will eventually cease; and this will happen as soon as the supply of nuclear fuel is depleted. Stars much heavier than our Sun burn out in a relatively short period of time of a few million years: their lives are a thousand times shorter than the actual age of our Universe. At the opposite end of the spectrum are stars whose masses are much smaller than the mass of our Sun. Such stars can live for trillions of years - about a thousand times the current age of our Universe.

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

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

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

Four forces of nature

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

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

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

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

The strong nuclear force, our third fundamental force of nature, is responsible for the integrity of the nuclei of atoms. This force holds protons and neutrons in the nucleus. B. in the absence of a strong force, the atomic nuclei would explode in response to the repulsive forces acting between the positively charged protons. Although this force is the strongest of the four, it operates over extremely short distances. It is no coincidence that the range of action of the strong nuclear force is approximately equal to the size of a large atomic nucleus: about ten thousand times smaller than the size of an atom (on the order of ten fermi or 10 -12 cm). The strong interaction drives the process of nuclear fusion, which produces most of the energy in stars, and therefore in the Universe in the current era. It is precisely because of the large, compared to the electromagnetic force, magnitude of the strong interaction that nuclear reactions are much stronger than chemical reactions, namely: a million times per pair of particles.

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

Great War

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

A direct example of this continuous struggle is our Sun. It exists in a state of delicate balance between the effects of gravity and entropy. The gravitational force maintains the integrity of the Sun and attracts all its matter to the center. Without opposing forces, gravity would quickly compress the Sun, turning it into a black hole no more than a few kilometers in diameter. The fatal collapse is prevented by pressure forces that act in the direction from the center to the surface, balancing gravitational forces and thereby preserving the Sun. The pressure that prevents the collapse of the Sun ultimately arises due to the energy of nuclear reactions that occur in its depths. During these reactions, energy and entropy are generated, causing chaotic movements of particles in the center of the Sun and, ultimately, preserving the structure of the entire Sun.

On the other hand, if the gravitational force were somehow turned off, then the Sun would no longer be held back by anything and it would rapidly expand. This expansion would continue until the solar matter spread out into such a thin layer that its density would be equal to the least dense parts of interstellar space. Then the rarefied ghost of the Sun would be a hundred million times larger than its current size, stretching several light years in diameter.

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

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

This great war between gravity and entropy determines the long-term fate and evolution of astrophysical objects such as stars and galaxies. For example, having exhausted all its reserves of nuclear fuel, the star must change its internal structure accordingly. Gravity pulls matter toward the center of the star, while the tendency for entropy to increase favors its dispersion. The subsequent battle can have many different outcomes, which depend on the mass of the star and its other properties (for example, the speed of rotation of the star). As we will see, this drama will play out again and again as long as stellar objects populate the Universe.

A very spectacular example of the ongoing struggle between gravity and entropy is the evolution of the Universe itself. Over time, the Universe expands and becomes more blurry. This direction of evolution is opposed by gravity, which strives to gather the spreading matter of the Universe together. If gravity wins this battle, the expansion of the Universe will eventually stop and at some point in the future it will begin to contract again. On the other hand, if gravity loses this battle, the Universe will expand forever. Which of these fates awaits our Universe in the future depends on the total amount of mass and energy contained in the Universe.

Limits of Physics

The laws of physics describe how the universe behaves at a variety of distances, from the monstrously large to the negligible. The highest achievement of humanity is the ability to explain and predict how nature behaves in conditions that are extremely far from our everyday experience. This significant expansion of our horizons has occurred mainly during the last century. The scope of our knowledge extends from the large-scale structures of the Universe to subatomic particles. And although such a field of understanding may seem large, it must not be forgotten that discussions of physical law cannot be continued arbitrarily far in any of these directions. The largest and smallest scales remain beyond the reach of our modern scientific understanding.

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

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

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

Cosmological decades

In this biography of the Universe, the past ten billion years represent a very insignificant period of time. We must take on the serious challenge of introducing a time scale that describes the universally interesting events that are likely to occur over the next 10,100 years.

10,100 is a big number. If you write it without using scientific notation, it will consist of a one followed by one hundred zeros and will look like:

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

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

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

τ = 10 η years,

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

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

Five great eras

Our current understanding of the past and future of the Universe can be systematized by highlighting certain time periods. As the Universe passes from one era to another, its contents and character change very significantly, and in some respects almost entirely. These epochs, similar to geological epochs, help form a general impression of the life of the Universe. Over time, a series of natural astronomical catastrophes shape the Universe and control its subsequent evolution. The chronicle of this story may look like this.

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

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

If the clocks are moved to an even earlier time, our understanding becomes much less solid. In an extremely early period, when the Universe was incredibly hot, what appears to have happened is that very high-energy quantum fields caused fantastically rapid expansion and created very small density perturbations in a homogeneous and unremarkable Universe. These tiny irregularities survived and grew into the galaxies, clusters and large-scale structures that populate the modern Universe.

Towards the end of the primary epoch, the radiation energy density became less than the energy density associated with matter. This transition occurred when the Universe was about ten thousand years old. Shortly after this, another watershed event occurred: the temperature of the universe became low enough to allow the existence of atoms (more precisely, hydrogen atoms). The first appearance of neutral hydrogen atoms is called recombination. After recombination, perturbations in the density of matter in the Universe allowed it to form clumps that were not affected by the omnipresent sea of ​​radiation. For the first time, familiar astrophysical objects like galaxies and stars began to form.

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

In the earliest period of the age of stars, when the Universe was only a few million years old, the first generation of stars was born. In the first billion years, the first galaxies arose, and their associations into clusters and superclusters began.

Many newly emerged galaxies experience turbulent, high-energy phases due to the all-consuming black holes located at their centers. When black holes tear apart stars and surround themselves with vortex-like disks of hot gas, enormous amounts of energy are released. Over time these quasars And active galactic nuclei slowly dying.

In the future, towards the end of the stellar age, the most ordinary stars in the Universe - low-mass stars called red dwarfs - will play a key role. Red dwarfs are stars whose mass is less than half the mass of the Sun, but there are so many of them that their combined mass undoubtedly exceeds the mass of all the larger stars in the Universe. These red dwarfs are true misers when it comes to converting hydrogen into helium. They accumulate their energy and will exist even in ten trillion years, while more massive stars will have long since exhausted their nuclear fuel reserves and evolved into white dwarfs or turned into supernovae. The era of stars will end when the galaxies run out of hydrogen gas, the birth of stars stops, and the long-lived stars (those with the least mass), red dwarfs, slowly go out. When the stars finally stop shining, the Universe will be about one hundred trillion years old (cosmological decade η = 14).

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

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

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

At the end of the decay epoch, the mass-energy stored in the interiors of white dwarfs and neutron stars is dissipated as radiation as the protons and neutrons that make up those stars decay. The white dwarf, fueled by proton decay, generates about four hundred watts: this amount of energy is enough to run several light bulbs. The total luminosity of an entire galaxy of such old stars is less than that of a single ordinary hydrogen-burning star, like our Sun. With the completion of the proton decay process, the era of decay comes to an end. The universe - even darker, even more rarefied - is changing again.

Age of black holes. 40 < η < 100. По завершении эпохи распада протонов из всех подобных звездам астрофизических объектов остаются только черные дыры. Эти фантастические объекты обладают столь сильным гравитационным полем, что даже свет не может покинуть их поверхности. Распад протонов никак не влияет на черные дыры, так что по окончании эпохи распада они остаются целыми и невредимыми.

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

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

In this cold, distant future, activity in the universe has virtually ceased. The energy has dropped to extremely low levels, and the time gaps are simply stunning. Electrons and positrons drifting in space meet each other and from time to time form positronium atoms. However, these structures that form so late are unstable, and the particles that make them up, sooner or later, annihilate. Other low-level annihilation events may occur, albeit very slowly.

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

Saving life

Our society has realized with no small amount of concern that human extinction is not such a far-fetched problem. Nuclear confrontation, environmental disasters, and spreading viruses are not all the doomsday prospects that the cautious, paranoid, and profit-minded people are paying attention to. But what if we accepted the somewhat outdated, but much more romantic perspective of rockets, colonies in space and conquest of the Galaxy? In such a future, humanity could easily delay the rapidly approaching death of the Earth by simply moving to other solar systems. But can we extend the life of the stars themselves? Will we find a way to bypass proton decay? Will we be able to do without the properties of black holes that provide the Universe with energy? Will any living organisms be able to survive the final comprehensive devastation of the era of eternal darkness?

In this book we consider the prospects and possibilities for preserving life in each era of the future evolution of the Universe. An atmosphere of some uncertainty inevitably accompanies this analysis. The general theoretical understanding of life is conspicuous by its absence. Even in the only habitat where we have direct experience, our native Earth, the origin of life is still not understood. Thus, in our bold discussions of the possibility of the existence of life in the distant future, we are in a qualitatively different position than when we are dealing with purely astrophysical phenomena.

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

The second class of life forms is based on a much more abstract model. In this last case, we draw heavily on the ideas of Freeman Dyson, an influential physicist who hypothesized scale correspondence for abstract life forms. The basic idea is that at any temperature it is possible to imagine some abstract form of life that thrives at that particular temperature, at least in principle. Moreover, the rate at which this abstract creature consumes energy is directly proportional to its temperature. For example, if we imagine some kind of Dyson organism living at a certain given temperature, then, according to the law of correspondence of scales, all vital functions of another qualitatively similar form of life, content with half the lower temperature, should be slowed down by the same two times. In particular, if the Dyson organisms in question have intelligence and some kind of consciousness, then the actual speed of their perception of ongoing events is determined not by real physical time, but by the so-called scale time, proportional to temperature. In other words, the rate of awareness is slower in Dyson organisms living at low temperatures than in an (otherwise) similar life form living at higher temperatures.

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

"Copernican Time Principle"

As our narrative continues, and great ages succeed each other, the character of the physical Universe changes almost completely. A direct consequence of this change is that the Universe of the distant future or distant past is completely different from the Universe in which we live today. Since the present universe is sufficiently conducive to life as we know it—we have stars to supply us with energy and planets to live on—we are all quite naturally inclined to regard the modern era as in some sense occupying a special position. In contrast to this opinion, we accept the idea of "Copernican's temporal principle" which quite simply states that the modern cosmological era does not occupy a special place in time. In other words, during the process of evolution and change in the Universe, interesting events will not stop in it. Although actual levels of energy production and entropy are becoming increasingly lower, this is offset by the lengthening time scales that will become available in the future. To paraphrase this idea again, we argue that the laws of physics do not predict that the universe will one day reach a state of complete rest, but rather that interesting physical processes will continue as far into the future as we dare to look into.

The idea of ​​the Copernican Time Principle serves as a natural extension of our ever-expanding view of the Universe. A global revolution in worldview occurred in the sixteenth century, when Nicolaus Copernicus declared that the Earth is not the center of our solar system, as previously thought. Copernicus understood quite correctly that the Earth is just one of many planets that orbit the Sun. This apparent belittlement of the status of the Earth, and therefore of humanity, caused a strong resonance at the time. As is usually said, because of the heretical consequences of such a shift in thinking, Copernicus was forced to postpone the publication of his greatest work De Revolutionibus Orbium Coelestium until 1543 - the year of his death. He hesitated until the very end and was close to hiding his work. In the introduction to his book, Copernicus writes: “I was about to put my completed work in a drawer, because of the contempt that I foresaw, with good reason, due to the novelty and obvious contradiction of my theory to common sense.” Despite the delay, this work was eventually published, and the first printed copy lay on Copernicus's deathbed. The Earth was no longer considered the center of the Universe. A global revolution has begun.

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

Interestingly, for almost four centuries, the idea of ​​the existence of planets outside our solar system remained a purely theoretical concept, for which there was no evidence to support it. Only in the last few years, starting in 1995, have astronomers established for sure that planets orbiting other stars do indeed exist. With new observational capabilities and extensive work, Jeff Marcy, Michel Mayor and their associates have shown that planetary systems are a relatively common phenomenon. Now our solar system has become just one of perhaps billions of solar systems that exist in the galaxy. A new revolution has begun.

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

Each subsequent downgrade of the Earth's central status leads to the irrevocable conclusion that our planet's location in the Universe is unremarkable. Earth is an ordinary planet that rotates in the orbit of a moderately bright star in an ordinary Galaxy located in a randomly selected place in the Universe. Copernicus' time principle extends this general idea from the realm of space to the realm of time. Just as our planet, and therefore humanity, does not have a special location in the Universe, so our current cosmological era does not occupy a special place in the vast expanses of time. This principle only continues to destroy what little anthropocentric thinking remains.

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

Notes:

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

It is necessary to know the point of application and direction of each force. It is important to be able to determine which forces act on the body and in what direction. Force is denoted as , measured in Newtons. In order to distinguish between forces, they are designated as follows

Below are the main forces operating in nature. It is impossible to invent forces that do not exist when solving problems!

There are many forces in nature. Here we consider the forces that are considered in the school physics course when studying dynamics. Other forces are also mentioned, which will be discussed in other sections.

Gravity

Every body on the planet is affected by Earth's gravity. The force with which the Earth attracts each body is determined by the formula

The point of application is at the center of gravity of the body. Gravity always directed vertically downwards.

Friction force

Let's get acquainted with the force of friction. This force occurs when bodies move and two surfaces come into contact. The force occurs because surfaces, when viewed under a microscope, are not as smooth as they appear. The friction force is determined by the formula:

The force is applied at the point of contact of two surfaces. Directed in the direction opposite to movement.

Ground reaction force

Let's imagine a very heavy object lying on a table. The table bends under the weight of the object. But according to Newton's third law, the table acts on the object with exactly the same force as the object on the table. The force is directed opposite to the force with which the object presses on the table. That is, up. This force is called the ground reaction. The name of the force "speaks" support reacts. This force occurs whenever there is an impact on the support. The nature of its occurrence at the molecular level. The object seemed to deform the usual position and connections of the molecules (inside the table), they, in turn, strive to return to their original state, “resist.”

Absolutely any body, even a very light one (for example, a pencil lying on a table), deforms the support at the micro level. Therefore, a ground reaction occurs.

There is no special formula for finding this force. It is denoted by the letter , but this force is simply a separate type of elasticity force, so it can also be denoted as

The force is applied at the point of contact of the object with the support. Directed perpendicular to the support.

Since the body is represented as a material point, force can be represented from the center

Elastic force

This force arises as a result of deformation (change in the initial state of the substance). For example, when we stretch a spring, we increase the distance between the molecules of the spring material. When we compress a spring, we decrease it. When we twist or shift. In all these examples, a force arises that prevents deformation - the elastic force.

Hooke's law

The elastic force is directed opposite to the deformation.

Since the body is represented as a material point, force can be represented from the center

When connecting springs in series, for example, the stiffness is calculated using the formula

When connected in parallel, the stiffness

Sample stiffness. Young's modulus.

Young's modulus characterizes the elastic properties of a substance. This is a constant value that depends only on the material and its physical state. Characterizes the ability of a material to resist tensile or compressive deformation. The value of Young's modulus is tabular.

Read more about properties of solids.

Body weight

Body weight is the force with which an object acts on a support. You say, this is the force of gravity! The confusion occurs in the following: indeed, often the weight of a body is equal to the force of gravity, but these forces are completely different. Gravity is a force that arises as a result of interaction with the Earth. Weight is the result of interaction with support. The force of gravity is applied at the center of gravity of the object, while weight is the force that is applied to the support (not to the object)!

There is no formula for determining weight. This force is designated by the letter.

The support reaction force or elastic force arises in response to the impact of an object on the suspension or support, therefore the weight of the body is always numerically the same as the elastic force, but has the opposite direction.

The support reaction force and weight are forces of the same nature; according to Newton’s 3rd law, they are equal and oppositely directed. Weight is a force that acts on the support, not on the body. The force of gravity acts on the body.

Body weight may not be equal to gravity. It may be more or less, or it may be that the weight is zero. This condition is called weightlessness. Weightlessness is a state when an object does not interact with a support, for example, the state of flight: there is gravity, but the weight is zero!

It is possible to determine the direction of acceleration if you determine where the resultant force is directed

Please note that weight is force, measured in Newtons. How to correctly answer the question: “How much do you weigh”? We answer 50 kg, not naming our weight, but our mass! In this example, our weight is equal to gravity, that is, approximately 500N!

Overload- ratio of weight to gravity

Archimedes' force

Force arises as a result of the interaction of a body with a liquid (gas), when it is immersed in a liquid (or gas). This force pushes the body out of the water (gas). Therefore, it is directed vertically upward (pushes). Determined by the formula:

In the air we neglect the power of Archimedes.

If the Archimedes force is equal to the force of gravity, the body floats. If the Archimedes force is greater, then it rises to the surface of the liquid, if less, it sinks.

Electrical forces

There are forces of electrical origin. Occurs in the presence of an electrical charge. These forces, such as the Coulomb force, Ampere force, Lorentz force, are discussed in detail in the section Electricity.

Schematic designation of forces acting on a body

Often a body is modeled as a material point. Therefore, in diagrams, various points of application are transferred to one point - to the center, and the body is depicted schematically as a circle or rectangle.

In order to correctly designate forces, it is necessary to list all the bodies with which the body under study interacts. Determine what happens as a result of interaction with each: friction, deformation, attraction, or maybe repulsion. Determine the type of force and correctly indicate the direction. Attention! The amount of forces will coincide with the number of bodies with which the interaction occurs.

The main thing to remember

Friction forces

There are external (dry) and internal (viscous) friction. External friction occurs between contacting solid surfaces, internal friction occurs between layers of liquid or gas during their relative motion. There are three types of external friction: static friction, sliding friction and rolling friction.

Rolling friction is determined by the formula

The resistance force occurs when a body moves in a liquid or gas. The magnitude of the resistance force depends on the size and shape of the body, the speed of its movement and the properties of the liquid or gas. At low speeds of movement, the drag force is proportional to the speed of the body

At high speeds it is proportional to the square of the speed

The relationship between gravity, the law of gravity and the acceleration of gravity

Let's consider the mutual attraction of an object and the Earth. Between them, according to the law of gravity, a force arises Now let's compare the law of gravity and the force of gravity

The magnitude of the acceleration due to gravity depends on the mass of the Earth and its radius! Thus, it is possible to calculate with what acceleration objects on the Moon or on any other planet will fall, using the mass and radius of that planet.

The distance from the center of the Earth to the poles is less than to the equator. Therefore, the acceleration of gravity at the equator is slightly less than at the poles. At the same time, it should be noted that the main reason for the dependence of the acceleration of gravity on the latitude of the area is the fact of the Earth’s rotation around its axis.

As we move away from the Earth's surface, the force of gravity and the acceleration of gravity change in inverse proportion to the square of the distance to the center of the Earth.

Fundamental Interactions

In nature, there is a huge variety of natural systems and structures, the features and development of which are explained by the interaction of material objects, that is, mutual action on each other. Exactly interaction is the main reason for the movement of matter and it is characteristic of all material objects, regardless of their origin and their systemic organization. Interaction is universal, as is movement. Interacting objects exchange energy and momentum (these are the main characteristics of their movement). In classical physics, interaction is determined by the force with which one material object acts on another. For a long time the paradigm was the concept of long-range action - the interaction of material objects located at a great distance from each other and it is transmitted through empty space instantly. Currently, another has been experimentally confirmed - concept of short-range interaction - interaction is transmitted using physical fields with a finite speed not exceeding the speed of light in a vacuum. A physical field is a special type of matter that ensures the interaction of material objects and their systems (the following fields: electromagnetic, gravitational, field of nuclear forces - weak and strong). The source of the physical field is elementary particles (electromagnetic - charged particles), in quantum theory the interaction is due to the exchange of field quanta between particles.

There are four fundamental interactions in nature: strong, electromagnetic, weak and gravitational, which determine the structure of the surrounding world.

Strong interaction(nuclear interaction) is the mutual attraction of the constituent parts of atomic nuclei (protons and neutrons) and acts at a distance of the order of 10 -1 3 cm, transmitted by gluons. From the point of view of electromagnetic interaction, a proton and a neutron are different particles, since a proton is electrically charged, and a neutron is not. But from the point of view of strong interaction, these particles are indistinguishable, since in a stable state the neutron is an unstable particle and decays into a proton, electron and neutrino, but within the nucleus it becomes similar in its properties to a proton, which is why the term “nucleon ( from lat. nucleus- nucleus)” and a proton with a neutron began to be considered as two different states of the nucleon. The stronger the interaction of nucleons in the nucleus, the more stable the nucleus, the greater the specific binding energy.

In a stable substance, the interaction between protons and neutrons at not too high temperatures increases, but if a collision of nuclei or their parts (high-energy nucleons) occurs, then nuclear reactions occur, which are accompanied by the release of enormous energy.

Under certain conditions, strong interaction very firmly binds particles into atomic nuclei - material systems with high binding energy. It is for this reason that the nuclei of atoms are very stable and difficult to destroy.

Without strong interactions, atomic nuclei would not exist, and stars and the Sun would not be able to generate heat and light using nuclear energy.

Electromagnetic interaction transmitted using electric and magnetic fields. An electric field arises in the presence of electric charges, and a magnetic field arises when they move. A changing electric field generates an alternating magnetic field - this is the source of the alternating magnetic field. This type of interaction is characteristic of electrically charged particles. The carrier of electromagnetic interaction is a photon that has no charge - a quantum of the electromagnetic field. In the process of electromagnetic interaction, electrons and atomic nuclei combine into atoms, and atoms into molecules. In a certain sense, this interaction is fundamental in chemistry and biology.

We receive about 90% of information about the world around us through an electromagnetic wave, since various states of matter, friction, elasticity, etc. are determined by the forces of intermolecular interaction, which are electromagnetic in nature. Electromagnetic interactions are described by the laws of Coulomb, Ampere and Maxwell's electromagnetic theory.

Electromagnetic interaction is the basis for the creation of various electrical appliances, radios, televisions, computers, etc. It is about a thousand times weaker than a strong one, but much longer-range.

Without electromagnetic interactions there would be no atoms, molecules, macro-objects, heat and light.

3. Weak interaction perhaps between various particles, except for the photon, it is short-range and manifests itself at distances smaller than the size of the atomic nucleus 10 -15 - 10 -22 cm. Weak interaction is weaker than strong interaction and processes with weak interaction proceed more slowly than with strong interaction. Responsible for the decay of unstable particles (for example, the transformation of a neutron into a proton, electron, antineutrino). It is due to this interaction that most particles are unstable. The weak interaction carriers are ions, particles with a mass 100 times greater than the mass of protons and neutrons. Due to this interaction, the Sun shines (a proton turns into a neutron, positron, neutrino, the emitted neutrino has a huge penetrating ability).

Without weak interactions, nuclear reactions in the depths of the Sun and stars would not be possible, and new stars would not arise.

4. Gravitational interaction the weakest, is not taken into account in the theory of elementary particles, since at characteristic distances (10 -13 cm) the effects are small, and at ultra-small distances (10 -33 cm) and at ultra-high energies, gravity becomes important and the unusual properties of the physical vacuum begin to appear .

Gravity (from the Latin gravitas - “gravity”) - the fundamental interaction is long-range (this means that no matter how massive a body moves, at any point in space the gravitational potential depends only on the position of the body at a given moment in time) and all material bodies are subject to it . Basically, gravity plays a decisive role on a cosmic scale, the Megaworld.

Within the framework of classical mechanics, gravitational interaction is described law of universal gravitation Newton, who states that the force of gravitational attraction between two material points of mass m 1 and m 2 separated by distance R, There is

Where G- gravitational constant.

Without gravitational interactions there were no galaxies, stars, planets, or evolution of the Universe.

The time during which the transformation of elementary particles occurs depends on the strength of interaction (with strong interaction, nuclear reactions occur within 10 -24 - 10 -23 s., with electromagnetic - changes occur within 10 -19 - 10 -21 s., with weak disintegration within 10 -10 s.).

All interactions are necessary and sufficient for the construction of a complex and diverse material world, from which, according to scientists, one can obtain superpower(at very high temperatures or energies all four forces combine to form one).