1. Forces in nature:

a) elasticity;

b) friction;

c) gravity;

2. Law of universal gravitation;

3. Weightlessness

1. In the world around us, there are countless bodies that interact with each other. But, despite the variety of forces, it is customary to distinguish several of their types.

The force of elasticity called the force that occurs in the body when its shape or size changes. This happens if the body is compressed, stretched, bent or twisted. For example, the elastic force generated in a spring acts on a brick. It arose as a result of compression of the spring.

Elastic force always directed opposite to the force that caused the change in the shape or size of the body. In our example, the fallen brick compressed the spring, that is, it acted on it with a downward force. As a result, an elastic force appeared in the spring, directed in the opposite direction, that is, upwards.

gravity called the force with which all bodies in the world are attracted to each other. A variation of the gravitational force is the force of gravity - the force with which a body located near a planet is attracted to it. For example, a rocket standing on Mars is attracted to it - gravity acts on the rocket.

Gravity always directed towards the center of the planet. For example, the Earth attracts a boy and a ball with forces directed downward, that is, towards the center of the planet.

By the force of friction called the force that prevents one body from slipping on the surface of another. The sharp braking of the car is accompanied by a "squeal of the brakes." It occurs due to tire slippage on the asphalt surface. In this case, a friction force acts between the wheel and the road, preventing such slippage.

The friction force is always directed opposite to the direction of sliding of the considered body over the surface of another. For example, when a car brakes, its wheels slip forward, which means that the friction force acting on them on the road is directed in the opposite direction, that is, backwards.

Buoyant force (or Archimedes force) called the force with which a liquid or gas acts on a body immersed in them. Water in the pond acts on air bubbles - pushes them to the surface. Water also acts on fish and rocks - it pushes them up, reducing their weight (the force with which the rocks press on the bottom of the pond). The Archimedean force is usually directed upwards, opposite to the force of gravity.

2. Newton's law of universal gravitation for a force acting between two bodies with masses m 1 And m2, is written as follows:

F=G ,

Where r is the distance between the bodies, G = 6.67 N is the gravitational constant (1 N = 1 newton is the force with which the Earth attracts a body with a mass of 0.1 kg located on its surface).

The force of gravitational attraction between bodies whose dimensions are much smaller than the distance between them is directly proportional to their masses, inversely proportional to the square of the distance between them and is directed along the straight line connecting them.

The gravitational constant is a world constant, its determination is possible when conducting direct laboratory experiments to measure the force of gravitational attraction of two known masses. For the first time, an experiment to determine G was made by G. Cavendish in 1797. Knowing the value of G, one can determine the mass of the Earth, the masses of other planets in the solar system, and the mass of the Sun. To determine the mass of the Sun, you need to know the distance from the Earth to the Sun and the time it takes the Earth to complete one revolution around the Sun.

The law of universal gravitation allowed Newton to give a quantitative explanation of the motion of the planets around the Sun and the Moon around the Earth, to understand the nature of sea tides.

Even before Newton postulated the law of universal gravitation, I. Kepler, analyzing the movements of the planets of the solar system, proposed three simple laws that very accurately describe these movements not only for all planets, but also for their satellites.

Lecture #4

Subject: 1.1.3. Pulse. Law of conservation of momentum and

Jet propulsion

Plan:

1. General concept. body momentum;

2. Law of conservation of momentum;

3. Jet propulsion.

1. Definition: the momentum (quantity of motion) of a body p is the product of mass and its speed.

We know that the cause of a change in the speed of a body is the actions of other bodies. Let us find out what force is required in order to t increase body speed from 0 to some value υ . According to Newton's second law F=ma , and according to the formula a=υ/t

Thus,

F = mv/t

The right side of the resulting expression includes the product of the body's mass and its speed. Let's call this work p:

The physical quantity equal to the product of the body's mass and its speed is called the momentum of the body:

p is the momentum of the body.

If the body is at rest, then its momentum is zero. As the speed increases, the momentum increases.

The momentum is a vector quantity.

The SI unit of momentum is kilogram-meter per second (1 kg m/s)

The concept of momentum was introduced into physics by René Descartes (1596-1650). Descartes himself called this quantity not an impulse, but a momentum.

2. For momentum, a fundamental law of nature is valid, called the law of conservation of momentum (or momentum). Descartes, who discovered this law, wrote in one of his letters: “I accept that in the Universe, in all created matter, there is a certain amount of motion that never increases, does not decrease, and, thus, if one body sets another in motion, then loses as much of its movement as it communicates"

In the simplest case law of conservation of momentum can be formulated as follows.

It is necessary to know the point of application and the direction of each force. It is important to be able to determine exactly what 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 acting in nature. It is impossible to invent non-existent forces 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 the 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 pointing vertically down.

Friction force

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

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

Support reaction force

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 support reaction. The name of the force "speaks" react support. This force arises whenever there is an impact on the support. The nature of its occurrence at the molecular level. The object, as it were, deformed the usual position and connections of the molecules (inside the table), they, in turn, tend 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 support reaction occurs.

There is no special formula for finding this force. They designate it with the letter, but this force is just a separate type of elastic 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, the force can be depicted from the center

Elastic force

This force arises as a result of deformation (changes in the initial state of matter). For example, when we stretch a spring, we increase the distance between the molecules of the spring material. When we compress the 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, the force can be depicted from the center

When connected in series, for example, springs, the stiffness is calculated by 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, its physical state. Characterizes the ability of a material to resist tensile or compressive deformation. The value of Young's modulus is tabular.

Learn more about the properties of solids.

Body weight

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

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

The support reaction force or elastic force arises in response to the impact of an object on a suspension or support, therefore the body weight 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 a support, not on a body. The force of gravity acts on the body.

Body weight may not be equal to gravity. It can be either more or less, or it can be such that the weight is zero. This state 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

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

Overload- the ratio of weight to gravity

Strength of Archimedes

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 upwards (pushes). Determined by the formula:

In the air, we neglect the force 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. Occur in the presence of an electric charge. These forces, such as the Coulomb force, Ampère force, Lorentz force, are discussed in detail in the Electricity section.

Schematic designation of the forces acting on the body

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

In order to correctly designate the 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, correctly indicate the direction. Attention! The number of forces will coincide with the number of bodies with which the interaction takes place.

The main thing to remember

Friction forces

Distinguish between external (dry) and internal (viscous) friction. External friction occurs between solid surfaces in contact, 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 arises 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, the resistance 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 free fall

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 value of free fall acceleration 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 free fall 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 free fall on the latitude of the area is the fact that the Earth rotates around its axis.

When moving away from the surface of the Earth, the force of gravity and the acceleration of free fall change inversely with the square of the distance to the center of the Earth.

What are the fundamental forces of nature? On what principle are fundamental interactions built? Is the existence of a new fundamental interaction possible? Doctor of Physical and Mathematical Sciences Dmitry Kazakov answers these and other questions.

From school physics, we are faced with the concept of "force". Forces are different: there is an attractive force, a friction force, a rolling force, an elastic force. There are many different powers. Not all of these forces are fundamental - very often the force is a secondary phenomenon. For example, the force of friction is a secondary phenomenon - in fact, it is the interaction of molecules. And even the interaction of molecules can be secondary. For example, in molecular physics there are van der Waals forces. These forces are a secondary consequence of electromagnetic interactions.

I would like to get to the bottom of the most fundamental force: what are the fundamental forces in nature, which determine everything, from which all secondary forces are built? Electromagnetic forces, or electrical forces, are the fundamental forces as we understand them today. Coulomb's law, known since school physics, is a fundamental law, but it has its own generalization, it follows from Maxwell's equations. Maxwell's equations describe in general all electric and magnetic forces in nature, therefore electromagnetic interactions are the fundamental forces of nature.

Another example of the fundamental forces of nature is gravity. From school, Newton's law of universal gravitation is known, which has now been generalized in Einstein's equations - now we have Einstein's theory of gravitation. The force of gravity is also a fundamental interaction in nature. And it once seemed that only these two fundamental forces existed. But later they realized that this was not the case. In particular, when the atomic nucleus was discovered and the problem arose to understand why the particles are kept inside the nucleus and do not fly apart, the concept of nuclear forces was introduced. These nuclear forces have been measured, understood, described. But later it turned out that they are also non-fundamental - nuclear forces in a sense resemble Van der Waals forces.

The truly fundamental forces that ensure the strong interaction are the forces between quarks. interact with each other, and as a secondary effect, the protons and neutrons in the nucleus interact with each other. The fundamental interaction is the interaction of quarks through the exchange of gluons - this is the third fundamental force in nature.

But the story doesn't end there either. It turns out that the decays of elementary particles - and all heavy particles decay into lighter ones - are described by a new interaction, which is called the weak interaction. Weak - because the strength of this interaction is noticeably weaker than electromagnetic forces. But it turned out that the theory of weak interaction, which originally existed and described all decays very well, did not work well with increasing energy, and it was replaced by a new theory of weak interaction, which turned out to be completely universal and built on the same principle on which all the others are built. interactions.

There are four fundamental interactions in the modern world, and I will also talk about the fifth one.

Four fundamental interactions - electromagnetic, strong, weak and gravitational - are built on the same principle.

This principle is that the force between particles arises due to the exchange of some mediator, the carrier of interaction.

Electromagnetic interaction is based on the exchange of a quantum of light or a quantum of electromagnetic waves - this is a photon. A photon is a massless particle, charged particles exchange it, and due to this exchange, interactions between particles arise, a force between particles, Coulomb's law is also described in this way.

The other interaction is strong. There is also an intermediary, a particle exchanged between quarks. These particles are called gluons, there are eight of them, these are also massless particles.

The third particle, the third interaction, is the weak interaction, and here, too, particles, which are called intermediate vector bosons, act as an intermediary. These particles - their pieces - are massive, that is, quite heavy. This mass, the gravity of these particles, explains why the weak interaction is so weak.

The fourth interaction is gravitational, and it is carried out by exchanging a quantum of the gravitational field, it is called. The graviton has not yet been experimentally discovered, we still do not quite feel and do not quite know how to describe.

All interactions are an act of exchanging some particles. Here we return to . Any interaction is associated with symmetry. Symmetry tells how many such particles and what their mass is. If the symmetry is exact, the mass is zero. A photon has a mass of 0, a gluon has a mass of 0. If the symmetry is broken, the mass is non-zero. Intermediate vector bosons have a non-zero mass, the symmetry is broken there. The gravitational symmetry is not broken - the graviton also has a mass of 0.

These four fundamental interactions explain everything we see. All other forces are a secondary effect of these interactions. But in 2012, a new particle was discovered that became very famous - this is the so-called . The Higgs boson is also the carrier of interaction between quarks and between leptons. Therefore, now it is appropriate to say that a fifth force has appeared, the carrier of which is the Higgs boson. Here, too, the symmetry is broken - the Higgs boson is a massive particle. Thus, the number of fundamental interactions - in particle physics the word is usually used not "force", but "interaction" - has reached five.

Are there new interactions? We don't really know. In elementary particle physics there are no other interactions, there are only five. But it is possible that the model that we are now considering and perfectly describes all the experimental data and all the phenomena that we observe in the world may still be incomplete, and then, perhaps, some new forces and new interactions will appear. For example, if there are so-called , that is, if there is a new symmetry in nature, then this new symmetry will entail the emergence of new particles that are mediators between other particles, thereby creating a new fundamental force. Therefore, this possibility still remains.

Interestingly, any new interaction always leads to some new phenomenon. Say, if there were no weak interaction, there would be no decay. If there were no decay, we would not observe nuclear reactions. If there were no nuclear reactions, the Sun would not shine. If the Sun did not shine, life could not exist on Earth. So having that interaction turned out to be vital for us.

If there were no strong interaction, there would be no stable atomic nuclei. If there were no nuclei, there would be no atoms. If there were no atoms, there would be no us. That is, it turned out that all the forces seem to be necessary. Here is the electromagnetic interaction: we receive energy from the Sun - these are the rays of light that come to us from the Sun. Without him, the Earth would be cold. It turns out that all those interactions that we know are needed for something. Higgs interaction with the Higgs boson. Fundamental particles gain mass by interacting with the Higgs field - one cannot live without this either. I'm not talking about gravitational interaction - we would fly away from the surface of the planet.

All the interactions that are in nature that are now open are vital for everything that we understand and know to exist.

And what would happen if there were some new interaction that has not yet been discovered? Here is another example: the proton in the nucleus is stable, and it is very important that it is stable, otherwise, again, there would be no life. But experimentally, the proton lifetime is now limited - 1034 years. This means that there is no prohibition for the proton to decay, but this requires a new force and a new interaction. There are theories that predict the decay of the proton - they have a higher symmetry group, and they have new interactions that we do not know. Whether so it is a question to experiment.

All fundamental interactions are now built on a single principle, and in this sense there is a unity of nature. Sometimes the question arises: is it possible to explain in some way how many interactions there are in nature, that is, to understand the reason why there are four of them or why there are five of them, and maybe there are still more? There are different versions of how one could explain the presence of a certain number of fundamental interactions. Such theories are often referred to as Grand Unification theories. These theories combine various types of interactions into one. It is like a growing tree: there is a single trunk, then it branches, and various branches are obtained.

The idea is about the same: there is a single root of all interactions, a single trunk, and then, as a result of symmetry breaking, this trunk begins to branch, and several fundamental interactions are formed, which we experimentally observe. Testing this hypothesis requires physics at very high energies, which are inaccessible to modern experiment and probably never will be. But you can get around this problem. In the end, we have a natural accelerator - this is the Universe. Some processes going on in the Universe allow us to test bold hypotheses that there is a single root of all interactions.

Another very interesting challenge in understanding the interactions in nature is to understand how gravity relates to all other interactions. Gravity stands somewhat apart, although the principle of constructing the theory is very similar. At one time, Einstein tried to build a unified theory of gravity and electromagnetism. Then it seemed very real, but the theory never happened. Now we know a little more. We know that there is still a strong interaction, a weak interaction, therefore, if we are now building a unified theory, it would seem that we need to include all these interactions together, but nevertheless, such a unified theory has not yet been created, and so far we have not been able to unify gravity with the rest of the interactions. All interactions, except for gravity, obey the laws of quantum physics - this is quantum theory. All particles are quanta of a certain field. Quantum gravity does not yet exist until it can be created. What is the reason for what we do wrong, what we do not understand - all this remains a mystery. But the number of fundamental interactions that have already been discovered suggests that some kind of unified scheme probably exists.

1) The 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) Acceleration of free fall is the acceleration that all bodies acquire in free fall near the surface of the Earth, regardless of their mass. Denoted by the letter g.

The free fall acceleration 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 pulls a body towards itself.

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

Overload is the ratio of weight to gravity.

The state of weightlessness, if P=0.

5) The force of elasticity is the 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 are either elastic or inelastic.

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 deformations:

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

10) Sigma Mechanical stress is the force acting per unit area of ​​the cross section of the body.

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

12. The force of friction is the force that occurs at the boundary of contact between bodies in the absence of relative motion of the bodies.

13. Force of static friction:

Let the body rest on a horizontal surface and an external force acts on it.

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

If the external force changes, then the static friction force also changes.

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

15) Sliding friction force:

If the external forces are greater than the support reaction 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 the normal movement of the body to the surface.

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

17) Force of resistance of the environment:

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

The S.S. force 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 make the body move.

18) Forces of inertia are the 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, the windows of space and time, the great war, and extremely large numbers.

The first of January 7,000,000,000 A.D. e., Ann Arbor.

New Year's Eve is not too big a reason to celebrate. There is no one who can even celebrate his arrival. The surface of the Earth has turned into an unrecognizable wasteland, scorched to the ground by the Sun. The sun swelled without limit: it became so huge that its red-hot disk covers the daytime sky almost entirely. Mercury and Venus have already died, and now the rarefied outer regions of the solar atmosphere threaten to capture the 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. Only a barren rocky surface remained. You can still see faint traces of ancient coastlines, ocean basins and eroded remnants of continents. By noon, the temperature reaches almost three thousand degrees Fahrenheit, and the rocky surface begins to melt. The equator is already partly girded by a wide belt of boiling lava, which, as it cools, forms a thin gray crust, while the bloated Sun rests nightly behind the horizon.

The part of the surface that was once home to the forested moraines of southeast Michigan has changed quite a lot over the past billions of years. The former North American mainland was long ago divided by a geological fault that stretched from the former state of Ontario to Louisiana; it split the old stable platform of the mainland 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 hardened 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. The stone block splits, causing a landslide and exposing a perfectly preserved oak leaf imprint. This trace of the once green world, now so far away, is slowly fading away, melting in an unrelenting fire. Very soon the whole Earth will be engulfed in an ominous red flame.

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

Now our Universe, which is estimated at ten to fifteen billion years old, is still going through its youth. So many astronomical possibilities that are of greater interest have simply 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. In this book, the biography of the universe is told 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 a galaxy. This is a scientific view of 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 of them provides a different type of window to observe 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 finale, similar to death. Death can be swift and violent; for example, a massive star completes its evolution with a spectacular supernova explosion. Another alternative is the agonizingly slow death of dim red dwarfs, which gradually fade away, turning into white dwarfs - the cooling embers of once powerful and active stars.

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

The key question is whether the universe will continue to expand forever, or at some point in the future, the expansion will stop and re-shrink will occur. The current results of astronomical observations strongly suggest that our universe is destined to continuously expand, so most 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 contraction.

Below the vast expanses of cosmology, on a smaller level, follow galaxies, such as our Milky Way. Galaxies are large and rather rarefied collections of stars, gas, and other varieties of matter. Galaxies are not randomly scattered throughout the universe; rather, they are woven into the overall tapestry of space by gravity. Some groups of galaxies are so heavy that they stay 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 arbitrarily combine to form even larger structures that resemble threads, sheets, and walls. The set of patterns formed; galaxies at this level is called the large-scale structure of the universe.

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

It is extremely difficult to comprehend the boundless emptiness of our Universe. A typical galaxy fills only about one millionth of the total volume of outer space in which it is contained, and the galaxies themselves are extremely rarefied. If you were going to take a spaceship to some random point in the universe, the chance of your ship landing within a galaxy is currently about one in a million. This is not too much anymore, and in the future this value will become even less, because the Universe is expanding, but the galaxies are not. Separated from the general expansion of the universe, galaxies exist in relative isolation. They are home to most of the stars in the universe, and hence 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 precisely in galaxies.

Not densely inhabiting space, 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 take 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 trillion (one chance in 10 22). Such emptiness of galaxies speaks rather eloquently about how they evolved and what awaits them in the future. Direct collisions of stars in the galaxy are extremely rare. Therefore, it will take a very long time - much more than it has passed from the birth of our universe to the present moment - before the collisions of stars and the meetings of other astrophysical objects in any way affect the structure of the galaxy. As you will see, these collisions become more and more important as the universe ages.

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

The next, even smaller, level of importance is formed by the stars themselves. At present, the cornerstone of astrophysics are ordinary stars - objects like our Sun, which 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 "forged" almost all the heavy elements that animate the cosmos, including the carbon and oxygen necessary for life. It is 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 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 the relatively short time span of a few million years: their lives are a thousand times shorter than the present age of our universe. At the opposite end of the range are stars whose masses are much less than the mass of our Sun. Such stars can live for trillions of years - about a thousand times the current age of our universe.

At the end of that part of the life of a star, when it exists due to thermonuclear reactions, the star does not disappear without a trace. Stars leave behind exotic clumps called stellar remnants. This caste of degenerate objects is formed by brown dwarfs, white dwarfs, neutron stars and black holes. As we shall see, as the universe ages and ordinary stars disappear from the scene, these strange remnants will play an increasingly important and eventually 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, an extraordinary upheaval has taken place in our understanding of the planets. For the first time in history, planets were definitely detected orbiting other stars. Now we know for sure that the planets are not the result of some rare or special event that occurred in our solar system, but are quite common in the galaxy. The planets do not play a major role in the evolution and dynamics of the universe as a whole. They are important because they are the most likely environment for the emergence and development of life. Thus, the long-term fate of the planets determines the long-term fate of life, at least of the forms we are familiar with.

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. The moons orbiting the planets provide another possible environment for the emergence and development of life. Comets and asteroids are known to regularly collide with planets. These collisions, capable of causing global climate change and the extinction of entire species of living beings, 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; they 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 rule it from now on.

The first of these forces, gravitational force, is closest to our everyday life, and it is the weakest of the four. However, due to its vast 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 an orbit in which it revolves around the Sun. Gravity maintains the existence of stars and controls the process of energy generation in them, as well as their evolution. Finally, it is gravity that is responsible for the formation of most of the 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. Even though the electromagnetic force is intrinsically much stronger than the gravitational force, it has much less effect over long distances. 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 long distances, where there are many charges, the electromagnetic force will self-destruct. At small distances, in particular in atoms, the electromagnetic force plays an important role. It is she who, ultimately, is responsible for the structure of atoms and molecules, and therefore, is the driving force in chemical reactions. At a fundamental level, chemistry and the electromagnetic force rule life.

The electromagnetic force is as much as 10 40 times stronger than the gravitational one. To comprehend this incredible weakness of gravity, one can, for example, imagine an alternative universe in which there are no charges, and therefore no electromagnetic forces. In such a universe, perfectly ordinary atoms would have extraordinary properties. If only gravity connected the electron and the 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 keeps protons and neutrons in the nucleus. B. In the absence of a strong interaction, the nuclei of atoms would explode in response to the repulsive forces acting between positively charged protons. Although this interaction is the strongest of the four, it operates at extremely short distances. It is no coincidence that the range 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 force governs the process of nuclear fusion, which generates most of the energy in stars, and hence in the universe, in the current epoch. It is because of the large, in comparison with the electromagnetic force, the magnitude of the strong interaction that nuclear reactions are much stronger than chemical ones, namely: a million times in terms of a pair of particles.

The fourth force, the weak nuclear force, is probably the furthest removed from public consciousness. This rather mysterious weak force is involved 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. A weak interaction has an even shorter range than a strong one. However, despite its weakness and short range, the weak force plays a surprisingly important role in astrophysics. A significant proportion of the total mass of the universe is likely to consist 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 role gradually increases in importance as the universe moves slowly 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 its fraction entropy. In the most general sense, gravity tends to keep all the components of any system within the limits of this very system, and this is what streamlines the physical structures. Entropy production works in the opposite direction, i.e., it tries to make physical systems more disorganized and "smeared". The interaction of these two competing tendencies is the main drama of astrophysics.

A direct example of this continuous struggle is our Sun. It exists in a delicate balance between the action of gravity and entropy. The gravitational force maintains the integrity of the Sun and pulls all of its matter towards the center. In the absence of 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 a direction from the center to the surface, balancing the gravitational forces and thereby preserving the Sun. The pressure that prevents the collapse of the Sun arises, ultimately, due to the energy of nuclear reactions that occur in its depths. In the course of these reactions, energy and entropy are formed, causing chaotic motions 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 and it would rapidly expand. This expansion would continue until the solar matter spread out in such a thin layer that its density would be equal to the least dense regions of interstellar space. Then the rarified phantom of the Sun would be a hundred million times its current size, stretching in diameter for several light years.

Thanks to the rivalry of two equal competitors, gravity and entropy, our Sun exists in its current state. If this equilibrium is disturbed, whether gravity takes precedence 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 a fierce rivalry between two opposing tendencies.

This same struggle underlies the formation of all kinds of astronomical structures, including planets, stars, galaxies, and the large-scale structure of the universe. The existence of these astrophysical systems is ultimately determined by gravity, which tends to bind matter. Yet in each case, the trend towards gravitational collapse is opposed by forces of expansion. At all levels, the ongoing competition between gravity and entropy ensures that any victory is temporary and never absolute. For example, the formation of astrophysical structures is never 100% efficient. Successful cases of the formation of such objects are just a local victory for gravity, while unsuccessful 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, a 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 dissipation. A further battle can have many different outcomes, which depend on the mass of the star and its other properties (for example, the speed of rotation of the star). As we shall see, this drama will play itself out over and over as stellar objects populate the universe.

A very spectacular example of the ongoing struggle between the force of gravity and entropy is the evolution of the universe itself. As time passes, the universe expands and becomes more diffuse. This direction of evolution is opposed by gravity, which tends to gather the sprawling matter of the Universe together. If gravity is the winner in this battle, the expansion of the universe will eventually stop, and at some point in the future it will begin to re-compress. 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.

The limits of physics

The laws of physics describe how the universe behaves at a wide variety of distances, from monstrously large to negligibly small. The highest achievement of mankind is the ability to explain and predict how nature behaves in conditions that are extremely far from our everyday everyday experience. Such a significant expansion of our horizons has occurred mainly during the last century. The sphere of our knowledge stretches from the large-scale structures of the Universe to subatomic particles. And although such a field of understanding may seem large, we must not forget that the discussion of physical law cannot be extended arbitrarily far in any of these directions. The largest and smallest scales remain beyond the reach of our modern scientific understanding.

Our physical representation of the largest scale of the universe is limited by causality. Information that is outside 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 take into account that while the Universe lived for only about ten billion years, no information signal simply had time to cover a distance exceeding ten billion light years. It is at this distance that the boundary of the universe that we can explore with the help of physics lies; this causality boundary is often referred to as 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 science. Just as a football match must take place within well-defined boundaries, so the physical processes in the universe are limited to the limits of this horizon at any given time. In fact, the existence of a causal horizon leads to some ambiguity as to what the term "universe" actually means. Sometimes this term refers only to the substance that is within the horizon at a given time. However, in the future, the horizon will grow, which means that it will eventually include the substance that is currently outside it. Is this "new" matter part of our universe now? The answer can be yes or no, depending on the definition of the term "universe". Likewise, there may be other regions of space-time that will never fall within our cosmological horizon. For the sake of definiteness, we will consider that such regions of space-time belong to "other universes".

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

Cosmological decades

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

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

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 great it is. Attempts to visualize the number 10100, 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 incomprehensibly large number. However, rough estimates indicate that the total number of all grains of sand is approximately equal to 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 a hundred billion - again a relatively small number. The number of stars in all the galaxies in our visible universe is about 10 22 - also too small. In fact, the total number of protons, the fundamental building blocks that make up matter, in the entire visible universe is only 1078: even this number is ten billion trillion times less than required! The number of years separating the present moment from eternity is truly immeasurable.

In order to describe the time scales associated with the future evolution of the Universe, and not to get completely confused, we will use a new unit of time called the cosmological decade. If we denote time in years as τ, then in the 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, now the Universe is only about ten billion years old, which corresponds to 10 10 years, or η = 10 cosmological decades. In the future, when the Universe is one hundred billion years old, it will be 10 11 years, or η = 11 cosmological decades. The significance of this scheme is that each subsequent cosmological decade represents a tenfold increase in the total age of the universe. Thus, the concept of a cosmological decade allows us to think about infinitely long spans of time. Thus, the defiantly large number in our example, 10 100 , corresponds to the much more understandable 100th cosmological decade, or η = 100.

Cosmological decades can also be used to discuss 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. Due to this expansion, one year after the Big Bang corresponds to 10 0 years, or the zeroth cosmological decade. Then one tenth, or 10 -1 , is a cosmological decade -1, one hundredth, or 10 -2 years, is a cosmological decade -2, etc. The beginning of time, when the Big Bang itself occurred, corresponds to τ = 0; in terms of cosmological decades, the Big Bang occurred on a 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 epochs. As the universe passes from one era to another, its contents and character change very significantly, and in some respects almost entirely. These epochs, analogous 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 govern 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 epoch of radiation. No astrophysical objects like stars and galaxies have had time to form yet.

During this short early epoch, many important events took place that determined the future course of the universe. Light elements such as helium and lithium formed in the first few minutes of this primary 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 hands of the clock are set to an even earlier time, our understanding becomes much less solid. In an extremely early period, when the universe was incredibly hot, what seems to have happened is that very high-energy quantum fields caused fantastically fast expansion and created very small density perturbations in a homogeneous and unremarkable universe. These tiny irregularities persisted and grew into the galaxies, clusters, and large-scale structures that populate the modern universe.

Toward the end of the primary epoch, the energy density of radiation became less than the energy density associated with matter. This transition took place when the universe was about ten thousand years old. Shortly thereafter, another watershed event occurred: the temperature of the universe became cold 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 lumps, not subject to the action of the ubiquitous radiation sea. For the first time, familiar astrophysical objects like galaxies and stars began to form.

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

In the earliest period of the stellar era, 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 emerging galaxies are experiencing turbulent high-energy phases due to the all-devouring black holes located at their centers. When black holes tear apart stars and surround themselves with vortex-like disks of hot gas, huge amounts of energy are released. Over time, these quasars And active galactic nuclei are slowly dying.

In the future, towards the end of the era of stars, the most ordinary stars of the Universe will play a key role - stars with low mass, which are called red dwarfs. Red dwarfs are stars whose mass does not exceed half the mass of the Sun, but there are so many of them that their combined mass undoubtedly exceeds the mass of all larger stars in the Universe. These red dwarfs are true misers when it comes to fusing hydrogen into helium. They accumulate their energy and will exist even in ten trillion years, while more massive stars by that time will have long exhausted their nuclear fuel and evolve into white dwarfs or turn into supernovae. The era of stars will end when hydrogen gas runs out in galaxies, the birth of stars stops, and the long-lived stars (having the smallest mass), red dwarfs, slowly go out. When the stars finally stop shining, the universe will be about a 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 continually 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 outside the galaxy, while others fall towards its center. Occasionally, a beacon can also flare up when, as a result of the collision of two brown dwarfs, a new low-mass star appears, which subsequently lives for trillions of years. On average, at any given time, a galaxy the size of our own Milky Way will have several of these stars shining. From time to time, as a result of the collision of two white dwarfs, the galaxy is shaken by a supernova explosion.

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

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

The era of black holes. 40 < η < 100. По завершении эпохи распада протонов из всех подобных звездам астрофизических объектов остаются только черные дыры. Эти фантастические объекты обладают столь сильным 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. Ultimately, they must evaporate in a very slow quantum mechanical process called Hawking radiation. Despite their name, black holes are not completely black. In fact, they glow, albeit extremely faintly, emitting a thermal spectrum of light and other decay products. After the disappearance of protons, the evaporation of black holes becomes the main source of the already almost invisible energy of the Universe. A black hole having 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 perish. The era of black holes ends after the evaporation of the largest black holes.

The era of eternal darkness.η > 101. After one hundred cosmological decades, protons have long 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 primordial era, when the universe was less than a million years old. In each of these eras, very, very distant in time, there are no star-like objects that could generate energy.

In this cold, distant future, activity in the universe has almost come to an end. The energy has dropped to extremely low levels and the time gaps are staggering. Drifting in outer space, electrons and positrons meet each other and from time to time form positronium atoms. However, these structures that form so late are unstable, and their constituent particles, sooner or later, annihilate. Other low-level annihilation events can occur, albeit very slowly.

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

Life saving

Our society, with no small amount of anxiety, has realized that the extinction of mankind is not such a far-fetched problem. Nuclear confrontation, environmental catastrophes and spreading viruses are far from all the doomsday prospects that cautious, paranoid and profit-seeking people are paying everyone's attention to. But what if we take a slightly outdated but far more romantic perspective on rockets, space colonies and galactic conquest? In such a future, humanity could easily delay the rapidly approaching destruction of the Earth by simply moving to other solar systems. But can we extend the life of the stars themselves? Can 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 all-encompassing devastation of the era of eternal darkness?

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

Although we do not have a solid theoretical paradigm describing the origin of life, we need at least some working model that would allow us to systematize our assessment of the prospects for the preservation and spread of life. To capture at least part of the full range of possibilities, we base our thinking on two very different models of life. In the first and most obvious case, we are considering life, which is based on biochemistry, approximately similar to Earth. Life of this kind could arise on planets like Earth, or on large moons in other solar systems. In keeping with a time-honored tradition among exobiologists, suppose that as long as there is liquid water on a planet, carbon-based life can originate and develop on that planet. The requirement that water must be in a liquid state imposes a fairly strict temperature limit on any potential habitat. For example, for atmospheric pressure, the temperature 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 of the 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, the influential physicist who put forward the scaling hypothesis for abstract life forms. The basic idea is that at any temperature, one can imagine some abstract form of life that thrives just fine at that temperature, at least in principle. Moreover, the rate at which this abstract creature expends energy is directly proportional to its temperature. For example, if we imagine some Dyson organism living at some given temperature, then, according to the law of scale correspondence, all the vital functions of another qualitatively similar life form, content with half the lower temperature, must be slowed down by the same two times. In particular, if the Dyson organisms under consideration have a mind 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 in Dyson organisms living at low temperatures is slower than that of an (otherwise) similar life form living at higher temperatures.

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

"Temporal principle of Copernicus"

As our story continues, and the great epochs 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 we live in today. Since the present universe is sufficiently livable 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 age in some sense as having a special position. In contrast to this opinion, we accept the idea of "temporal principle of Copernicus", which states quite simply that the modern cosmological epoch does not occupy a special place in time. In other words, in the process of evolution and change of the Universe, interesting events will not stop in it. Although the actual levels of energy production and entropy are getting lower and lower, this is offset by the lengthening timelines that will become available in the future. To paraphrase this thought once more, we are arguing that the laws of physics do not predict that the universe will one day reach a state of complete rest, but rather that interesting physical processes will not stop in as far a future as we dare to look.

The idea of ​​the Copernican temporal 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 quite rightly understood that the Earth is just one of the many planets that orbit around the Sun. This obvious belittling of the status of the Earth, and consequently, of humanity at that time caused a strong resonance. As is commonly said, the heretical consequences of such a shift in thought forced Copernicus to delay the publication of his greatest work. De Revolutionibus Orbium Coelestium until 1543 - the year of his death. He hesitated to the very end and came close to hiding his work. In the introduction to his book, Copernicus writes: “I almost put my completed work in a box, because of the contempt that I 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 fell on Copernicus's deathbed. The earth was no longer considered the center of the universe. A global upheaval has begun.

After the Copernican revolution, the decline in our status not only continued, but also accelerated. Very soon, astronomers established that other stars are, in fact, objects like our Sun, and they can, 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 that these planets are inhabited! Subsequently, in 1601, the inquisitors of the Roman Catholic Church burned him at the stake, although allegedly not because of his statements regarding astronomical matters. Since then, the idea that other solar systems might also have planets 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, since 1995, have astronomers established for sure that planets orbiting other stars do exist. With new observational capabilities and tremendous work done, 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, once Copernicus declared that our planet does not have a special place within our solar system, but now modern cosmology has proved that our Galaxy does not occupy a special position in the Universe. In fact, the universe seems to obey cosmological principle(see next chapter), which says 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). The cosmos has neither privileged places nor preferred directions. The universe exhibits amazing regularity and simplicity.

Each successive downgrading of the Earth's central status leads to the irrevocable conclusion that our planet's location in the universe is unremarkable. The Earth is an ordinary planet that orbits a moderately bright star in an ordinary Galaxy located in a randomly selected place in the Universe. The Copernican temporal principle extends this general idea from the realm of space to the realm of time. Just as our planet, and therefore humanity, has no particular location in the universe, so our current cosmological epoch does not occupy a particular place in the vast expanses of time. This principle only continues the destruction of that small fraction of anthropocentric thinking that still survives.

We are writing this book at the very end of the twentieth century - a good time to reflect on our place in the universe. Because of the vastness of understanding gained in this age, we can take a close look at our position in time and space as never before. In accordance with the Copernican temporal principle and the widest range of astrophysical events yet to occur in the vast future, we argue that the end of the universe is not very close at the end of this millennium. 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 embark on our journey through the five great epochs of time.

Notes:

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