Vacuum value. What is a physical vacuum? Theoretical justification of the concept of ether

Very often people come to us who want to buy a vacuum pump, but have little idea what a vacuum is.
Let's try to figure out what it is.

By definition, a vacuum is a space free of matter (from the Latin word “vacuus” - empty).
There are several definitions of vacuum: technical vacuum, physical vacuum, cosmic vacuum, etc.
We will consider technical vacuum, which is defined as a highly rarefied gas.

Let's look at an example of what vacuum is and how it is measured.
On our planet there is an atmospheric pressure taken as one (one atmosphere). It changes depending on the weather, altitude and sea level, but we will not take this into account, since this will not in any way affect the understanding of the concept of vacuum.
So, we have pressure on the surface of the earth equal to 1 atmosphere. Everything below 1 atmosphere (in a closed vessel) is called technical vacuum.

Let's take a vessel and close it with an airtight lid. The pressure in the vessel will be 1 atmosphere. If we begin to pump air out of a vessel, a vacuum will arise in it, which is called a vacuum.
Let's look at an example: there are 10 circles in the left vessel. Let it be 1 atmosphere.
“pump out” half - we get 0.5 atm, leave one - we get 0.1 atm.

Since there is only one atmosphere in the vessel, then the maximum possible vacuum we can get (theoretically) is zero atmospheres.
"Theoretically" - because It is almost impossible to catch all the air molecules from the vessel.
Therefore, in any vessel from which air (gas) has been pumped out, some minimum amount of it always remains. This is called “residual pressure,” that is, the pressure that remains in the vessel after pumping gases out of it.
There are special pumps that can reach a deep vacuum of up to 0.00001 Pa, but still not to zero.
In ordinary life, a vacuum deeper than 0.5 - 10 Pa (0.00005-0.0001 atm) is rarely required.

There are several options for measuring vacuum, depending on the choice of reference point:
1. The unit is taken to be atmospheric pressure. Everything below one is a vacuum.
That is, the vacuum gauge scale is from 1 to 0 atm (1…0.9…0.8…0.7…..0.2…0.1….0).
2. Atmospheric pressure is taken as zero. That is, a vacuum - all negative numbers are less than 0 and up to -1.
That is, the vacuum gauge scale is from 0 to -1 (0, -0.1...-0.2....,-0.9,...-1).
Also, scales can be in kPa, mBar, but this is all similar to scales in atmospheres.

The picture shows vacuum gauges with different scales that show the same vacuum:

From all that has been said above, it is clear that the magnitude of the vacuum cannot be greater than atmospheric pressure.

People contact us almost every day who want to get a vacuum of -2, -3 atm, etc.
And they are very surprised when they find out that this is impossible (by the way, every second of them says that “you yourself don’t know anything,” “but it’s like that with your neighbor,” etc., etc.)

In fact, all these people want to mold parts under vacuum, but so that the pressure on the part is more than 1 kg/cm2 (1 atmosphere).
This can be achieved by covering the product with a film, pumping out the air from under it (in this case, depending on the vacuum created, the maximum pressure will be 1 kg/cm2 (1 atm=1 kg/cm2)), and then placing it all in an autoclave in which excess pressure will be created. That is, to create a pressure of 2 kg/cm2, it is enough to create an excess pressure of 1 atm in the autoclave.

Now a few words about how many clients measure vacuum at the Ampika Pumps LLC exhibition in our office:
turn on the pump, place your finger (palm) on the suction hole of the vacuum pump and immediately draw a conclusion about the magnitude of the vacuum.

Usually, everyone loves to compare the Soviet vacuum pump 2NVR-5DM and its analogue VE-2100, which we offer.
After such a check, they always say the same thing - the vacuum of the 2NVR-5DM is higher (although in fact both pumps produce the same vacuum parameters).

What is the reason for this reaction? And as always - in the lack of knowledge of the laws of physics and what pressure is in general.

A little educational background: pressure “P” is a force that acts on a certain surface area, directed perpendicular to this surface (the ratio of the force “F” to the surface area “S”), that is, P = F/S.
In simple terms, it is a force distributed over a surface area.
From this formula it can be seen that the larger the surface area, the lower the pressure will be. And also the force that is required to lift a hand or finger from the pump inlet is directly proportional to the surface area (F=P*S).
The diameter of the suction hole of the 2NVR-5DM vacuum pump is 25 mm (surface area 78.5 mm2).
The diameter of the suction opening of the VE-2100 vacuum pump is 6 mm (surface area 18.8 mm2).
That is, to lift a hand from a hole with a diameter of 25 mm, a force 4.2 times greater is required than for a hole with a diameter of 6 mm (at the same pressure).
This is why, when vacuum is measured with fingers, such a paradox results.
Pressure "P", in this case, is calculated as the difference between atmospheric pressure and the residual pressure in the vessel (that is, the vacuum in the pump).

How to calculate the force of pressing a part against a surface?
Very simple. You can use the formula given above, but let's try to explain it more simply.
For example, let’s say you need to find out with what force a part measuring 10x10 cm can be pressed when a vacuum is created under it with a VVN 1-0.75 pump.

We take the residual pressure that this vacuum pump of the BBH series creates.
Specifically, for this water ring pump VVN 1-0.75 it is 0.4 atm.
1 atmosphere is equal to 1 kg/cm2.
The surface area of ​​the part is 100 cm2 (10 cm x 10 cm).
That is, if you create a maximum vacuum (that is, the pressure on the part will be 1 atm), then the part will be pressed with a force of 100 kg.
Since we have a vacuum of 0.4 atm, the pressure will be 0.4x100 = 40 kg.
But this is in theory, under ideal conditions, if there is no air leakage, etc.
In reality, you need to take this into account and the pressure will be 20...40% less depending on the type of surface, pumping speed, etc.

Now a few words about mechanical vacuum gauges.
These devices indicate residual pressure in the range of 0.05...1 atm.
That is, it will not show a deeper vacuum (it will always show “0”). For example, in any rotary vane vacuum pump, once its maximum vacuum is reached, the mechanical vacuum gauge will always read “0”. If a visual display of residual pressure values ​​is required, then you need to install an electronic vacuum gauge, for example VG-64.

Often clients come to us who mold parts under vacuum (for example, parts made of composite materials: carbon fiber, fiberglass, etc.), this is necessary so that during molding gas escapes from the binder (resin) and thereby improves properties of the finished product, as well as the part was pressed to the mold with a film, from under which air was pumped out.
The question arises: which vacuum pump to use - single-stage or two-stage?
They usually think that since the vacuum of a two-stage is higher, the parts will be better.

The vacuum for a single-stage pump is 20 Pa, for a two-stage pump it is 2 Pa. It seems that since the difference in pressure is 10 times, the part will be pressed much stronger.
But is this really so?

1 atm = 100000 Pa = 1 kg/cm2.
This means that the difference in film pressure at a vacuum of 20 Pa and 2 Pa will be 0.00018 kg/cm2 (if you’re not too lazy, you can do the calculations yourself).

That is, practically, there will be no difference, because... a gain of 0.18 g in clamping force will not change the weather.

How to calculate how long it will take for a vacuum pump to pump out a vacuum chamber?
Unlike liquids, gases occupy the entire available volume, and if a vacuum pump has pumped out half of the air in the vacuum chamber, the remaining air will expand again and occupy the entire volume.
Below is the formula to calculate this parameter.

t = (V/S)*ln(p1/p2)*F, Where

t is the time (in hours) required to pump out the vacuum volume from pressure p1 to pressure p2
V - volume of pumped tank, m3
S - operating speed of the vacuum pump, m3/hour
p1 - ​​initial pressure in the pumped out container, mbar
p2 - final pressure in the pumped-out container, mbar
ln - natural logarithm

F - correction factor, depends on the final pressure in the tank p2:
- p2 from 1000 to 250 mbar F=1
- p2 from 250 to 100 mbar F=1.5
- p2 from 100 to 50 mbar F=1.75
- p2 from 50 to 20 mbar F=2
- p2 from 20 to 5 mbar F=2.5
- p2 from 5 to 1 mbar F=3

In a nutshell, that's it.
We hope that this information will help someone make the right choice of vacuum equipment and show off their knowledge over a glass of beer...

In volume, an ideal vacuum is unattainable in practice, since at a finite temperature all materials have a non-zero saturated vapor density. In addition, many materials (in particular thick metal, glass and other vessel walls) allow gases to pass through. IN microscopic volumes, however, achieving an ideal vacuum is in principle possible.

High vacuum in the microscopic pores of some crystals and in ultrathin capillaries is achieved already at atmospheric pressure, since the diameter of the pore/capillary becomes smaller than the free path of the molecule, which is equal to ~60 nanometers in air under normal conditions.

It is worth noting that even in a perfect vacuum at a finite temperature there is always some thermal radiation (gas of photons). Thus, a body placed in an ideal vacuum will sooner or later come into thermal equilibrium with the walls of the vacuum chamber due to the exchange of thermal photons.

Vacuum is a good thermal insulator; The transfer of thermal energy in it occurs only due to thermal radiation, convection and thermal conductivity are excluded. This property is used for thermal insulation in thermoses (Dewar flasks), consisting of a container with double walls, the space between which is evacuated.

Vacuum is widely used in electric vacuum devices - radio tubes (for example, magnetrons of microwave ovens), cathode ray tubes, etc.

Physical vacuum

In quantum physics, the physical vacuum is understood as the lowest (ground) energy state of a quantized field, which has zero momentum, angular momentum and other quantum numbers. Moreover, such a state does not necessarily correspond to emptiness: the field in the lowest state can be, for example, the field of quasiparticles in a solid or even in the nucleus of an atom, where the density is extremely high. A physical vacuum is also called a space completely devoid of matter, filled with a field in this state. This state is not absolute emptiness. Quantum field theory states that, in accordance with the uncertainty principle, virtual particles are constantly born and disappear in the physical vacuum: so-called zero-point field oscillations occur. In some specific field theories, the vacuum may have non-trivial topological properties. In theory, several different vacua may exist, differing in energy density or other physical parameters (depending on the hypotheses and theories used). The degeneracy of the vacuum during spontaneous symmetry breaking leads to the existence of a continuous spectrum of vacuum states, differing from each other in the number of Goldstone bosons. Local energy minima at different values ​​of any field, differing in energy from the global minimum, are called false vacua; such states are metastable and tend to decay with the release of energy, passing into a true vacuum or into one of the underlying false vacua.

Some of these field theory predictions have already been successfully confirmed by experiment. Thus, the Casimir effect and the Lamb shift of atomic levels are explained by zero-point oscillations of the electromagnetic field in the physical vacuum. Modern physical theories are based on some other ideas about vacuum. For example, the existence of multiple vacuum states (the false vacua mentioned above) is one of the main foundations of the Big Bang inflationary theory.

False vacuum

False vacuum- a state in quantum field theory, which is not a state with a globally minimal energy, but corresponds to its local minimum. This state is stable for a certain time (metastable), but can “tunnel” into a state of true vacuum.

Einstein's vacuum

Einstein's vacuum- a sometimes used name for solutions of Einstein's equations in general relativity for empty, matter-free spacetime. Synonym - Einstein space.

Einstein's equations relate the space-time metric (metric tensor gμν ) with the energy-momentum tensor. In general they are written as

where is the Einstein tensor Gμν is a definite function of the metric tensor and its partial derivatives, R- scalar curvature, Λ - cosmological constant, Tμν - energy-momentum tensor of matter, π - number pi, c- speed of light in vacuum, G- Newton's gravitational constant.

Vacuum solutions of these equations are obtained in the absence of matter, that is, when the energy-momentum tensor in the considered region of space-time is identically equal to zero: Tμν = 0 . Often the lambda term is also taken to be zero, especially when studying local (non-cosmological) solutions. However, when considering vacuum solutions with a nonzero lambda term ( lambda vacuum) such important cosmological models arise as the De Sitter model (Λ > 0) and the anti-De Sitter model (Λ< 0 ).

The trivial vacuum solution to Einstein's equations is flat Minkowski space, that is, the metric considered in special relativity.

Other vacuum solutions of Einstein's equations include, but are not limited to, the following cases:

• Milne cosmological model (a special case of the Friedmann metric with zero energy density)
• Schwarzschild metric, describing the geometry around a spherically symmetric mass
• Kerr metric, describing the geometry around a rotating mass
• Plane gravitational wave (and other wave solutions)

Space

Outer space has very low density and pressure and is the best approximation of a physical vacuum. But the vacuum of space is not truly perfect; even in interstellar space there are a few hydrogen atoms per cubic centimeter.

Stars, planets and satellites hold their atmospheres together by gravity, and as such the atmosphere has no clearly defined boundary: the density of atmospheric gas simply decreases with distance from the object. The Earth's atmospheric pressure drops to about 3.2×10−2 Pa per 100 km altitude—at the so-called Kármán line, which is the general definition of the boundary with outer space. Beyond this line, the isotropic pressure of the gas quickly becomes negligible compared to the radiation pressure from the Sun and the dynamic pressure of the solar wind, so the pressure determination becomes difficult to interpret. The thermosphere in this range has large gradients of pressure, temperature and composition, and is highly variable due to space weather.

The atmospheric density during the first few hundred kilometers above the Karman line is still sufficient to provide significant resistance to the movement of artificial Earth satellites. Most satellites operate in this region, called low-Earth orbit, and must fire their engines every few days to maintain a stable orbit.

Outer space is filled with a large number of photons, the so-called cosmic microwave background radiation, as well as a large number of relic neutrinos, which are not yet detectable. The current temperature of these radiations is about 3 K, or −270 °C.

History of vacuum research

The idea of ​​vacuum (emptiness) has been the subject of debate since the times of ancient Greek and Roman philosophers. Atomists - Leucippus (c. 500 BC), Democritus (c. 460-370 BC), Epicurus (341-270 BC), Lucretius (c. 99 -55 BC) and their followers assumed that everything that exists is atoms and the void between them, and without vacuum there would be no movement, atoms could not move if there was no empty space between them. Strato (c. 270 BC) and many philosophers in later times believed that the void could be "solid" ( vacuum coacervatum) and “scattered” (in the spaces between particles of matter, vacuum disseminatum).

Guericke's vacuum pump was significantly improved by Robert Boyle, which allowed him to carry out a number of experiments to elucidate the properties of vacuum and its effect on various objects. Boyle discovered that in a vacuum small animals die, fires go out, and smoke sinks down (and is therefore just as affected by gravity as other bodies). Boyle also found out that the rise of liquid in capillaries also occurs in a vacuum, and thereby refuted the then prevailing opinion that air pressure was involved in this phenomenon. On the contrary, the flow of liquid through the siphon in a vacuum stopped, which proved that this phenomenon was caused by atmospheric pressure. He showed that during chemical reactions (such as slaking lime), as well as during mutual friction of bodies, heat is released in a vacuum.

Effect on people and animals

People and animals exposed to vacuum lose consciousness within seconds and die from hypoxia within minutes, but these symptoms are generally not similar to those shown in popular culture and media. The decrease in pressure lowers the boiling point at which blood and other body fluids must boil, but the elastic pressure of the blood vessels prevents the blood from reaching the boiling point of 37 ° C. Although the blood does not boil, the effect of gas bubbles forming in it and other body fluids at low pressures, known as ebullism (aerial emphysema), is a serious problem. The gas can inflate the body to twice its normal size, but the tissues are elastic enough to prevent tearing. Edema and ebullism can be prevented by wearing a special flight suit. Shuttle astronauts wore special elastic clothing called Crew Altitude Protection Suit(CAPS), which prevents ebullism at pressures greater than 2 kPa (15 mmHg). The rapid evaporation of water cools the skin and mucous membranes to 0 °C, especially in the mouth, but this does not pose a great danger.

Animal experiments show that after 90 seconds of the body being in a vacuum, a rapid and complete recovery of the body usually occurs, but a longer stay in a vacuum is fatal and resuscitation is futile. There is only limited data on the effects of vacuum on humans (usually it has occurred in accidents), but it is consistent with data obtained from animal experiments. Limbs can remain in a vacuum much longer if breathing is not impaired. Robert Boyle was the first to show that vacuum was lethal to small animals in 1660.

Measurement

The degree of vacuum is determined by the amount of substance remaining in the system. Vacuum is primarily determined by absolute pressure, and full characterization requires additional parameters such as temperature and chemical composition. One of the most important parameters is the mean free path (MFP) of the residual gases, which indicates the average distance a particle travels during its free path from one collision to the next. If the gas density decreases, the MFP increases. The MFP in air at atmospheric pressure is very short, about 70 nm, and at 100 mPa (~1×10−3 Torr) the MFP of air is about 100 mm. The properties of a rarefied gas change greatly when the mean free path becomes comparable to the size of the vessel in which the gas is located.

Vacuum is divided into ranges according to the technology required to achieve or measure it. These ranges do not have universally accepted definitions, but a typical distribution looks like this:

Application

Vacuum is useful for many processes and is used in a variety of devices. For the first time for mass-used goods, it was used in incandescent lamps to protect the filament from chemical decomposition. The chemical inertness of materials provided by vacuum is also beneficial for electron beam welding, cold welding, vacuum packaging, and vacuum frying. Ultra-high vacuum is used when studying atomically pure substrates, since only a very high vacuum keeps surfaces clean at the atomic level for quite a long time (from minutes to days). High and ultra-high vacuums eliminate air resistance, allowing particle beams to deposit or remove materials without contamination. This principle underlies chemical vapor deposition, vacuum deposition, and dry etching, which are used in semiconductor and optical coatings manufacturing and in surface chemistry. Reduced convection provides thermal insulation in thermoses. High vacuum lowers the boiling point of a liquid and promotes low-temperature degassing, which is used in freeze drying, glue preparation, distillation, metallurgy, and vacuum cleaning. The electrical properties of vacuum make electron microscopes and vacuum tubes possible, including cathode ray tubes. Vacuum circuit breakers are used in electrical switchgear. Vacuum breakdown is of industrial importance for the production of certain grades of steel or high purity materials. Eliminating air friction is useful for flywheel and ultracentrifuge energy storage.

Vacuum driven machines

Vacuum is commonly used to produce suction, which has an even wider range of applications. Newcomen's steam engine used vacuum instead of pressure to drive the piston. In the 19th century, vacuum was used for traction on Isambard Brunel's experimental pneumatic railway. Vacuum brakes were once widely used on trains in the UK, but except on heritage railways, they have been replaced by air brakes.

This shallow well pump reduces the atmospheric pressure inside its own chamber. The atmospheric vacuum expands down into the well and forces water to flow up the pipe into the pump to equalize the reduced pressure. Pumps with a ground chamber are effective only to a depth of about 9 meters, due to the weight of the water column equalizing atmospheric pressure.

Intake manifold vacuum can be used to control auxiliary equipment on vehicles. The best known application is as a vacuum booster to increase brake power. Vacuum was previously used in Autovac windshield wiper vacuum drives and fuel pumps. Some aircraft instruments (the attitude indicator and heading indicator) are usually operated by vacuum, as insurance against failure of all (electrical) instruments, since early aircraft often did not have electrical systems, and since there are two readily accessible sources of vacuum on a moving aircraft, the engine and the venturi. Vacuum induction melting uses electromagnetic induction in a vacuum.

Maintaining a vacuum in the condenser is important for the efficient operation of steam turbines. For this purpose, a steam injector or a liquid ring pump is used. The normal vacuum maintained in the vapor volume of the condenser at the turbine exhaust (also called turbine condenser pressure) is in the range of 5 to 15 kPa, depending on the type of condenser and environmental conditions.

Degassing

Evaporation and sublimation in a vacuum is called degassing. All materials, solid or liquid, vaporize slightly (gassing occurs), and their degassing is necessary when the vacuum pressure drops below their vapor pressure. Floating materials in a vacuum has the same effect as leakage and can limit the achievable vacuum. Evaporation products can condense on nearby cooler surfaces, which can cause problems if they coat optical instruments or react with other materials. This poses a major challenge when flying in space, where a darkened telescope or solar cell could derail a high-cost operation.

The most common waste product in vacuum systems is water absorbed by the chamber materials. Its amount can be reduced by drying or heating the chamber and removing absorbent materials. Evaporating water can condense in the oil of rotary vane pumps and dramatically reduce their operating speed if a gas ballast device is not used. High vacuum systems must be kept clean and free of organic matter to minimize outgassing.

Ultra-high vacuum systems are typically annealed, preferably under vacuum, to temporarily increase the evaporation of all materials and evaporate them. Once most of the vaporized materials have been evaporated and removed, the system can be cooled to reduce vaporization of materials and minimize residual gas emissions during operational operation. Some systems are cooled significantly below room temperature using liquid nitrogen to completely stop residual gas evolution and at the same time create the effect of cryogenic pumping of the system.

Pumping and atmospheric pressure

Gases cannot be pushed out at all, so a vacuum cannot be created by suction. Suction can spread and dilute the vacuum, allowing high pressure to introduce gases into it, but the vacuum must be created before suction can occur. The easiest way to create an artificial vacuum is to expand the volume of the chamber. For example, the diaphragm muscle expands the chest cavity, which leads to an increase in lung capacity. This expansion reduces the pressure and creates a low vacuum, which is soon filled with air forced by atmospheric pressure.

To continue emptying the chamber indefinitely, without constantly using its expansion, its vacuum compartment can be closed, purged, expanded again, and so on many times. This is the operating principle of positive displacement (gas transfer) pumps, such as a manual water pump. Inside the pump, a mechanism expands a small sealed cavity to create a vacuum. Due to the pressure difference, some of the liquid from the chamber (or well, in our example) is pushed into the small cavity of the pump. The pump cavity is then sealed against the chamber, opened to the atmosphere and compressed to its minimum size, expelling the liquid.

The above explanation is a simple introduction to evacuation and is not representative of the range of pumps used. Many variations of positive displacement pumps have been developed, and many pump designs are based on radically different principles. Pulse transfer pumps, which have some similarities to dynamic pumps used at higher pressures, can provide much higher quality vacuum than positive displacement pumps. Gas bonding pumps, capable of capturing gases in a solid or absorbed state, often operate without moving parts, without seals and without vibration. None of these pumps are universal; each type has serious application limitations. Everyone has difficulty pumping out low-mass gases, especially hydrogen, helium and neon.

Vacuum(English) vacuum, German Vacuum, from lat. vacuus- empty) is a polysemantic physical term that, depending on the context, can mean:

• Rare state of gas. Such a vacuum is called partial. There are high, medium and low vacuums. High is called a vacuum in which the free path of gas molecules exceeds the linear dimensions of the vessel containing the gas; if the free path of gas molecules and the linear dimensions of the vessel are commensurate values, then a vacuum is called average, and if the free path of gas molecules is less than the linear dimensions of the vessel - low.

• An idealized abstraction, a space in which there is no substance at all. Such a vacuum is called ideal.
• A physical system without particles and field quanta. This is the lowest state of a quantum system, in which its energy is minimal, called the vacuum state. According to the uncertainty principle, for such a vacuum a certain part of physical quantities cannot be precisely determined.

Partial vacuum became widely used in industry with the invention of incandescent and vacuum lamps at the beginning of the 20th century. A significant number of physical experiments are carried out in a vacuum: the absence of air or an atmosphere of a different composition makes it possible to reduce unwanted extraneous influences on the object of study. Interest in the study of vacuum increased after man entered space. Near-Earth and interplanetary space is a very rarefied gas, which can be characterized as a vacuum.

Vacuum research began with the creation of the “Torricelli void” (ru) by the Italian physicist Evangelista Torricelli in the mid-17th century.

Technical vacuum

Technical called a partial vacuum formed under terrestrial conditions. The set of tools used in this case is called vacuum technology. The main place among the tools of vacuum technology is occupied by pumps of various designs and operating principles.

The main tool for creating low vacuum is a positive displacement pump. The principle of its operation is to cyclically increase and decrease the volume of gas in the vessel. During the expansion phase, suction, the gas in the vessel expands to fill additional volume, which is then cut off and expelled.

Creation high And ultra high vacuum is a complex technical problem. When there are few gas molecules in a vacuum chamber, problems arise related to contamination of the chamber with oil molecules, insufficient gasket density, degassing of the vessel walls, etc.

To obtain high vacuum, diffusion pumps are used. The operating principle of this type of pump is based on the fact that gas molecules do not diffuse against the flow. Therefore, diffusion pumps use a jet to draw gas molecules from a vacuum chamber.

Trap pumps allow you to achieve even higher vacuums. Their action can be based on various physical and chemical principles: cryogenic pumps use low temperature to condense gas in a vessel, in chemical pumps gas molecules are bound by chemicals or adsorbed on a surface, in ionization pumps the gas in a vacuum chamber is ionized and extracted using strong electrical fields.

Real vacuum installations consist of a combination of pumps of various types, each of which performs its own task and operates at different degrees of gas rarefaction in the vacuum chamber. Vacuum technology tools also include various measuring instruments used to determine the quality of the created vacuum.

Physical vacuum

Physical vacuum called an idealized concept of space in which there are no particles. It is impossible to achieve such a state experimentally; individual atoms and ions exist even in extremely rarefied intergalactic space. The abstract concept of physical vacuum is used, for example, to define the speed of light, as the speed of propagation of electromagnetic interaction in emptiness without particles.

Although it may seem that empty space is the simplest physical system, in reality it is not. The development of quantum mechanics has shown that vacuum is a complex physical object, the properties of which are not yet entirely understood.

Firstly, a vacuum, perhaps filled with zero-point oscillations of the electromagnetic field. The quanta of the electromagnetic field are photons, particles belonging to bosons. The wave functions of bosons in the low state are not zero. When quantizing the boson field, they are treated as harmonic oscillators. In the ground state, bosons not only have a nonzero wave function, but also nonzero energy. Thus, the vacuum is filled with zero-point oscillations of various modes of electromagnetic and other bosonic fields with all possible wave vectors, directions of propagation and polarizations. Each of these modes has an energy where is the summary Planck constant, eh? - cyclic frequency. This gives rise to the problem of vacuum energy, since there are infinitely many such modes, and the total vacuum energy must be infinite. However, physical experiments, in particular the Lamb shift and the Casimir effect, indicate that zero-point oscillations of the electromagnetic field are a reality, and that they can interact with other physical objects.

Another idea that further complicates the understanding of the vacuum is related to the Dirac equation, which describes a relativistic quantum particle, in particular the electron. The Dirac equation for a free electron has four solutions, two of them with negative energy. Paul Dirac showed that, using the operation of charge conjugation, these decouplings can be interpreted as decouplings with positive energy, but for a particle with an opposite, positive charge, i.e. electron antiparticles. Such an antiparticle was discovered experimentally and was called a positron.

Dirac's interpretation is similar to the theria of semiconductors. Particles, electrons, are similar to conduction electrons, while antiparticles, positrons, are similar to holes. In the ground state, corresponding to the vacuum, all energy states with negative energy are filled, and the positron corresponds to the unfilled state.

When considering interactions between particles in quantum electrodynamics, it is often necessary to take into account the possibility of the formation of virtual electron-positron pairs from the vacuum.

Vacuum, an area of ​​extremely low pressure. Interstellar space is a high vacuum, with an average density of less than 1 molecule per cubic centimeter. The rarest vacuum created by man is less than 100,000 molecules per cubic centimeter. It is believed that the first vacuum was created in the mercury BAROMETER by Evangelista Toricelli. In 1650, the German physicist Otto von Guericke (1602-86) invented the first vacuum pump. Vacuum is widely used in scientific research and industry. An example of such an application is vacuum packaging of food products. 22

In classical physics, the concept of empty space is used, that is, of a certain spatial region in which there are no particles and field. Such empty space can be considered synonymous with the vacuum of classical physics. A vacuum in quantum theory is defined as the lowest energy state in which all real particles are absent. It turns out that this state is not a state without a field. Non-existence as the absence of both particles and fields is impossible. In a vacuum, physical processes take place with the participation of not real, but short-lived (virtual) field quanta. In a vacuum, only the average values ​​of physical quantities are zero: field strengths, number of electrons, etc. These values ​​themselves continuously fluctuate (oscillate) around these average values. The reason for the fluctuations is the quantum-mechanical uncertainty relation, according to which the uncertainty in the energy value is greater, the shorter the time of its measurement. 23

Physical vacuum

Currently, a fundamentally new direction of scientific research is being formed in physics, related to the study of the properties and capabilities of the physical vacuum. This scientific direction is becoming dominant, and in applied aspects can lead to breakthrough technologies in the field of energy, electronics, and ecology. 24

To understand the role and place of vacuum in the current picture of the world, we will try to assess how vacuum matter and matter correlate in our world.

In this regard, the reasoning of Ya.B. is interesting. Zeldovich. 25

“The universe is huge. The distance from the Earth to the Sun is 150 million kilometers. The distance from the solar system to the center of the Galaxy is 2 billion times greater than the distance from the Earth to the Sun. In turn, the size of the observable Universe is a million times greater than the distance from the Sun to the center of our Galaxy. And all this huge space is filled with an unimaginably large amount of matter. 26

The mass of the Earth is more than 5.97·10 27 g. This is such a large value that it is difficult to even comprehend. The mass of the Sun is 333 thousand times greater. Only in the observable region of the Universe the total mass is about ten to the 22nd power of the mass of the Sun. The whole boundless vastness of space and the fabulous amount of matter in it amazes the imagination.” 27

On the other hand, an atom that is part of a solid body is many times smaller than any object known to us, but many times larger than the nucleus located at the center of the atom. Almost all the matter of an atom is concentrated in the nucleus. If you enlarge the atom so that the nucleus has the size of a poppy seed, then the size of the atom will increase to several tens of meters. At a distance of tens of meters from the nucleus there will be many times enlarged electrons, which are still difficult to see with the eye due to their small size. And between the electrons and the nucleus there will remain a huge space not filled with matter. But this is not empty space, but a special type of matter, which physicists called physical vacuum. 28

The very concept of “physical vacuum” appeared in science as a consequence of the realization that vacuum is not emptiness, is not “nothing.” It represents an extremely significant “something” that gives birth to everything in the world, and sets the properties of the substance from which the surrounding world is built. It turns out that even inside a solid and massive object, vacuum occupies immeasurably more space than matter. Thus, we come to the conclusion that matter is the rarest exception in the vast space filled with the substance of vacuum. In a gaseous environment, such asymmetry is even more pronounced, not to mention in space, where the presence of matter is more the exception than the rule. One can see how staggeringly huge the amount of vacuum matter in the Universe is in comparison with even the fabulously large amount of matter in it. Currently, scientists already know that matter owes its origin to the material substance of vacuum and all the properties of matter are determined by the properties of physical vacuum. 29

Science is penetrating deeper into the essence of vacuum. The fundamental role of vacuum in the formation of the laws of the material world is revealed. It is no longer surprising that some scientists claim that “everything is from a vacuum and everything around us is a vacuum.” Physics, having made a breakthrough in describing the essence of vacuum, has laid down the conditions for its practical use in solving many problems, including energy and environmental problems. thirty

According to the calculations of Nobel laureate R. Feynman and J. Wheeler, the energy potential of vacuum is so enormous that “in the vacuum contained in the volume of an ordinary light bulb, there is such a large amount of energy that it would be enough to boil all the oceans on Earth.” However, until now the traditional scheme for obtaining energy from matter remains not only dominant, but is even considered the only possible one. The environment still stubbornly continues to be understood as matter, of which there is so little, forgetting about the vacuum, of which there is so much. It is precisely this old “material” approach that has led to the fact that humanity, literally swimming in energy, experiences energy hunger. 31

The new “vacuum” approach proceeds from the fact that the surrounding space, a physical vacuum, is an integral part of the energy conversion system. At the same time, the possibility of obtaining vacuum energy finds a natural explanation without deviating from physical laws. The way is opening up to create energy plants with an excess energy balance, in which the energy received exceeds the energy expended by the primary power source. Energy installations with an excess energy balance will be able to open access to the enormous vacuum energy stored by Nature itself. 32

What's happened vacuum? This question is usually answered: “a space with rarefied air” or “a space inside a vessel from which air has been pumped out.” But is every degree of rarefaction a vacuum and is vacuum in any connection with?

Some prerequisites for the empirical study of vacuum existed in antiquity. Ancient Greek mechanics created various technical devices based on air rarefaction. For example, water pumps, operating by creating a vacuum under a piston, were known back in the time of Aristotle. The empirical study of vacuum began only in the 17th century, with the end of the Renaissance and the beginning of the scientific revolution of modern times. By this time, it had long been known that suction pumps could lift water to a height of no more than 10 meters.

In practice, highly rarefied gas is called technical vacuum. In macroscopic volumes, an ideal vacuum is unattainable in practice, since at a finite temperature all materials have a non-zero saturated vapor density. In addition, many materials (including thick metal, glass and other vessel walls) allow gases to pass through. In microscopic volumes, however, achieving an ideal vacuum is in principle possible.

Strictly speaking, technical vacuum is a gas in a vessel or pipeline with a pressure lower than in the surrounding atmosphere. Usually, between the atmospheric air and the high-vacuum pump there is a so-called fore-vacuum pump, creating a preliminary vacuum, therefore a low vacuum is often called a fore-vacuum. With a further decrease in pressure in the chamber, the mean free path of gas molecules increases. In this case, gas molecules collide with walls much more often than with each other. In this case they talk about high vacuum. High vacuum in the microscopic pores of some crystals is achieved already at atmospheric pressure, since the diameter of the pore is much smaller than the free path of the molecule.

Outer space has very low density and pressure, and is the closest approximation of a physical vacuum. But the vacuum of space is not truly perfect; even in interstellar space there are a few hydrogen atoms per cubic centimeter.

Indeed, let us assume that the air in the cylinder is rarefied 10,000 times compared to its density at normal atmospheric pressure, i.e. the pressure inside the cylinder is 0.076 mm. Hg Art.

Will there be a vacuum in the cylinder? And can we continue to assume that there is a vacuum in the cylinder if this cylinder is raised to a height of 100 km above the surface of the earth, where the air pressure is only 0.007 mm. Hg Art. Indeed, in this case, the air density inside the cylinder will become 10 times greater than outside! Then, where will the vacuum be - inside the cylinder or outside?

Modern physics associates vacuum not with the amount of pressure outside or inside the vessel, but with the free path of gas molecules inside it. Gas molecules are in continuous chaotic thermal motion; at room temperature, the speed of thermal movement of air molecules is approximately 450 m/s, i.e., it approaches the speed. Moving in all directions, molecules constantly collide with each other. The denser the air, the more molecules there are in a unit volume and the more often the molecules collide.

If the air is thinner, the molecules will collide less frequently. On average, they will have to travel a longer distance between two collisions, which is called the mean free path.

From a physical point of view, a vacuum is a rarefaction at which the mean free path is on average greater than the size of the vessel. When collisions of molecules in a vacuum vessel are rare, most of the molecules in their movement from one wall of the vessel to the other will not meet other molecules.

Vacuum is a good thermal insulator; The transfer of thermal energy in it occurs only due to thermal radiation, convection and thermal conductivity are excluded. This property is used for thermal insulation in thermoses, consisting of a container with double walls, the space between which is evacuated.