Vacuum introduction
The meaning and characteristics of vacuum
Historical development of human understanding of vacuum
Characteristics of vacuum
Utilization technology of vacuum and microgravity environment
Physical vacuum
[Edit this paragraph] Introduction to vacuum
Vacuum:
zhēn káng
British vacuum
According to its etymological meaning, it is vanity, that is, empty space; According to the viewpoint of modern physics, vacuum is not empty, it contains extremely rich physical contents. There is a theory that when the pressure in a container is lower than atmospheric pressure, the part below atmospheric pressure is called vacuum and the pressure in the container is called absolute pressure. To put it another way, the space in a container with a pressure below atmospheric pressure is called vacuum. There are some differences in vacuum: when there is no pressure in the container, that is, the absolute pressure is equal to zero, it is called complete vacuum; The rest is called an incomplete vacuum.
[Edit this paragraph] The meaning and characteristics of vacuum
In vacuum science, vacuum means the state of gas below atmospheric pressure in a given space. People usually call this thin gas state a vacuum state. Compared with the existing state of the atmosphere on which human beings depend, this specific vacuum state has the following basic characteristics:
(1) The gas pressure in vacuum is lower than one atmosphere. Therefore, all kinds of vacuum containers on the earth's surface will be subjected to atmospheric pressure, and the pressure difference depends on the pressure difference inside and outside the containers. Because the atmospheric pressure acting on the earth's surface is about 10 1325 N/m 2, when the pressure in the container is very small, the atmospheric pressure borne by the container can reach one atmosphere.
(2) Due to the rareness of gas in vacuum, the number of gas molecules per unit volume, that is, the molecular density of gas, is less than that of gas at atmospheric pressure. Therefore, the number of collisions between molecules, between molecules and other particles (such as electrons and ions) and between molecules and various surfaces (such as walls) is relatively reduced, and the molecular free path of gas is increased.
Physical vacuum
Here refers to the space without any physical particles, but there is no space without anything. Suppose you drive away all the gas in a space, you will find that basic particles appear and disappear from time to time in a vacuum, and they are made out of nothing. Physical vacuum is actually an ocean of fluctuating energy. When the energy reaches the peak, the energy is transformed into a pair of positive and negative elementary particles, and when the energy reaches the trough, the pair of positive and negative elementary particles annihilates each other and is transformed into energy.
Industrial vacuum
Industrial vacuum refers to the gas space with air pressure less than a standard atmospheric pressure, and refers to the state of thin gas, which can be divided into high vacuum, medium vacuum and low vacuum. The vast space between the earth and the stars is a vacuum. Usually, vacuum is obtained by using a special air pump. Its gas thinness is measured by a vacuum gauge, and now a high vacuum of 0.0000000001atmospheric pressure can be obtained by molecular pump and diffusion pump. Vacuum is of great use in science and technology, electric vacuum instruments, electron tubes and other electronic instruments. Vacuum pressure range) Pa (pa)
Low vacuum 760 ~10/01325 ~1333
Medium vacuum10 ~10-31333 ~1.33x10-1.
High vacuum10-3 ~10-81.33x10-10-6
Ultra high vacuum10-8 ~10-1210-6 ~10
Extremely high vacuum <10-12 <10-10.
electron-positron collider
The function of the electron-positron collider is not only as simple as a pair of electrons colliding to produce photons and energy. A pair of photons can also collide to produce a pair of positive and negative protons, and the collided vacuum can be excited to a high energy state, which can produce more and more kinds of elementary particles, serving the study of the origin and composition of the universe.
[Edit this paragraph] The historical development of human understanding of vacuum
Human understanding of vacuum has undergone several fundamental changes and repetitions. Democritus's atomism in ancient Greece believed that everything was made up of atoms, and there was nothing outside the atoms. /kloc-in the 0/7th century, R Descartes put forward the theory of etheric vortex, arguing that space is full of ether and used it to explain the motion of planets. Soon I Newton established Newtonian mechanics based on the three laws of motion and the law of universal gravitation, which successfully solved the problem of planets moving around the sun. Gravitation is regarded as the action at a distance, and it does not need ether as the transmission medium, thus denying the etherism. The fluctuation of light was discovered in the19th century, and it is believed that the wave propagation must depend on the medium, especially the fluctuation of electromagnetic field was discovered later. Etherism rises again, thinking that no matter when and where the universe is, any object is full of ether, and light and electromagnetic waves are interpreted as mechanical vibration of ether. Later, although the concept changed, both light and electromagnetic waves were regarded as vibrations of electromagnetic fields, the ether still retained some absolute properties and could be regarded as an absolutely static reference system to describe the movement of everything. 19 At the end of the 20th century, all kinds of experiments trying to detect the speed of the earth relative to the ether failed. A Einstein established the special theory of relativity and once again denied the existence of this absolutely static ether. Later, when Einstein studied the phenomenon of gravity from the viewpoint of field theory, he realized that the concept of empty vacuum was problematic. He once proposed that vacuum is a special state of gravity field.
It was the first time that P.A.M Dirac gave vacuum a brand-new physical content. 1930, in order to get rid of the dilemma of negative energy solution of Dirac equation, Dirac proposed that vacuum is an electron sea full of negative energy States. When the electrons in the negative energy state absorb enough energy to transition to the positive energy state and become ordinary electrons, they can leave observable holes in the electron sea, that is, positrons. Judging from the energy of the system, this situation is higher than the vacuum state with only electrons in the sea, so vacuum is the state with the lowest energy. From the perspective of modern quantum field theory, each particle corresponds to a quantum field, and the particle is the field quantum corresponding to the field quantization. When there is a particle in space, it means that the quantum field is in an excited state; Conversely, when there are no particles, it means that the field is in the ground state. So vacuum is a state in which no field quantum is excited, or vacuum is the ground state of quantum field system.
Modern understanding of vacuum is no longer philosophical speculation, but can be tested through experiments. Many phenomena need to be explained by modern vacuum concept. For example, the Lamb shift of hydrogen atomic energy level and the abnormal magnetic moment of electrons have been experimentally confirmed with very high accuracy. It is also well proved that high-energy electrons and positrons collide and annihilate into high-energy photons, which can excite a large number of particles in vacuum. The understanding of vacuum is still in the primary exploration stage, and physicists are still exploring the spontaneous breaking of vacuum and vacuum phase transition, which will certainly promote the further development of physics.
[Edit this paragraph] The essence of vacuum
Vacuum has the following characteristics:
1, empty is not nothing. If there are no particles in the vacuum, we will accurately measure the changing curvature of field (0) and field (0). However, Heisenberg's uncertainty principle shows that it is impossible to accurately measure a pair of yokes at the same time, so it can be "empty" but not "nothing". Therefore, in a vacuum, particles are constantly produced from thin air in the form of virtual particles and virtual antiparticle pairs, and they annihilate each other. In this process, the total energy remains the same.
2. Vacuum is polar, so it is asymmetric. But this asymmetry is relatively local and symmetrical as a whole, and this circular nesting constitutes this property of vacuum.
3. Every part of vacuum has all the characteristics of vacuum. Big and small are relative. Time is also relative to space. Without a specific space, time cannot exist alone.
[Edit this paragraph] Vacuum and microgravity environment utilization technology
The vacuum microgravity environment provided by spacecraft orbital flight is a treasure house, which provides people with scientific experiments and production process conditions that are difficult to obtain on the ground, carries out scientific experiments that are difficult to produce on the ground, and produces materials, industrial products and drugs that are difficult to produce on the ground.
When conducting life and biological science experiments in high vacuum and microgravity environment, there will be no organic pollution, mixing or measurement errors, and microorganisms used in experiments such as bacteria will not spread everywhere, which is very safe. Under the condition of zero gravity or microgravity, containerless melting can be carried out without any impurities, and high-quality alloys can be obtained; Metals or nonmetals with different specific gravity can be evenly mixed to obtain new alloy materials; It can overcome the defects of supercooling fluctuation and high density in ground processing, and grow semiconductor materials such as high quality and large diameter single crystal gallium arsenide. It can produce ball industrial products such as ball bearings with 100% roundness, but on the ground, ball bearings are not really spherical due to the influence of gravity.
Space pharmacy is an important aspect of vacuum and microgravity environment utilization. On the ground, due to the gravity of the earth, the culture will precipitate, and the microorganisms in the precipitate will die due to lack of oxygen; If oxygen is delivered and stirred, the formed low-pressure bubbles will destroy the cells again; If defoamer is added, it will reduce the solubility of oxygen, hinder the reproduction of microorganisms and form a vicious circle. In microgravity environment, the culture solution contains a lot of bubbles, which will not precipitate, and microorganisms can get oxygen at any time, and the growth rate is more than twice as fast as that on the ground. Many drugs can be manufactured with high efficiency and high purity, such as epidermal growth factor for treating burns, erythropoietin for treating anemia, immune serum for preventing and treating virus infection, trypsin inhibitor for treating emphysema, urokinase for treating thrombosis, anti-hemolytic factor 8 for treating hemophilia, beta cells for treating diabetes, interferon for treating cancer, and so on. The main pharmaceutical method is electrophoresis, under the action of DC electric field, the mixture of different components is accurately separated into different components. The first generation of its equipment is static electrophoresis instrument, and the second generation is continuous flow electrophoresis instrument.
[Edit this paragraph] Physical vacuum
Physical vacuum refers to the conditions that have no influence on the experimental results, not empty.
For example, if air resistance can be neglected, the motion law of an object in air is the same as that in vacuum.
When the air is too thin to transmit sound, we say that "vacuum" cannot transmit sound, but the sound can be received by improving the listening ability or increasing the sound power. We can only say "this vacuum degree can't be called vacuum for the present sound"!
Similarly, space can transmit light, or it may be the environment in space. For light, it will not become a "vacuum", so light can be transmitted. No one has proved that pure "vacuum" can transmit light, because humans can't do that kind of vacuum. In addition, light particles can propagate in a vacuum, which will also conflict with another law: in a vacuum without external force, objects will move in a straight line at a uniform speed, rather than fluctuate.
The speed of light in glass is only constant relative to the speed of light in glass. No matter how glass moves in other frames of reference, everyone must admit that glass, air, water and so on can only be used as optical media to spread light. In the past, I mistakenly thought that Ethernet medium was not equal to light, so there must be no medium.
Light is not the speed of light for any reference frame, or it cannot exceed the speed of light. Light only travels at the same speed in a "static" frame of reference. Please read Einstein's article on electrodynamics of moving objects carefully. This "static" is a medium frame of reference. So Einstein's argument is valid under this condition. The university textbook General Physics 1 assumes that the speed of light measured in any reference frame in vacuum is constant, so the relativistic conclusion discussed only holds in vacuum. However, which relativistic experiment was completed in a vacuum? Is there no condition for the use of relativity? Therefore, the exposition of university textbooks is not falsifiable and unprovable, and it is not science.
Question:
Sound waves and light waves are not comparable on this issue.
Acoustic wave carriers must have static mass, while optical wave carriers or photons or electromagnetic fields have no static mass.
These are two completely different and incomparable fluctuations.
Physical vacuum does not refer to the conditions that have no influence on the experimental results, but refers to the spatial region where the static mass density drops below a certain condition.
The ultimate physical vacuum is a spatial region where non-zero static mass density cannot be detected by existing physical means.
Note that the physical vacuum itself is a space region with energy state, or an energy field region or a force field region.
Therefore, physical vacuum, purely defined, can be said to be an area that can only transmit force field fluctuations. In other words, it can't transmit mechanical waves and fluctuations of other static mass carriers.
Philosophical "vacuum" is pure enough, but for our physical world, its existence is "zero existence", that is, it does not exist and has no meaning of existence.
Vacuum specialty
Schools: Hefei University of Technology, Northeastern University.
Hefei University of Technology: Vacuum major is one of the four modules of mechanical design, manufacturing and automation (mechanical design, mechanical manufacturing, mechatronics, vacuum). As a highly interdisciplinary subject, vacuum has penetrated into all walks of life, including machinery, electronics, bioengineering, material science, surface science and so on. Especially in recent years, the rapid development of some emerging technologies has provided an increasingly broad application stage for vacuum technology. From the development of various nano-materials with special functions to the manufacture of integrated micro-electromechanical systems, from the operation of large particle accelerators and controlled nuclear fusion to the successful launch of satellites and spaceships, vacuum has been fully recognized by more and more people as an indispensable technology and condition.
Vacuum module, formerly known as vacuum acquisition technology and equipment specialty, was established in 1974, which is one of the only two vacuum specialties in China. Over the past 30 years, more than 1000 undergraduate graduates have been trained. They have made great achievements in the field of vacuum science and technology at home and abroad, including chief engineer, professor, general manager and chairman. Over the years, the vacuum graduates of Hefei University of Technology are not only active in the high-tech research stage at home and abroad, but also occupy half of the domestic vacuum industry.
This major was awarded the master's degree in vacuum engineering on 1993, and was renamed as fluid machinery and engineering on 1997 according to the catalogue of disciplines and specialties adjusted by the State Council Academic Degree Office. The main courses include: mechanics, control engineering, vacuum technology, thin film technology, etc.
The discipline has been engaged in the research of rare gas (vacuum technology) in fluid machinery for a long time, and has created an academic team with reasonable structure, high academic level, strong scientific research and engineering practice ability and rich experience. Since 1990s, it has won the first prize 1 item of national major equipment scientific and technological progress, the third prize 1 item of national invention, 6 second and third prizes of provincial and ministerial scientific and technological progress and 5 invention patents. More than 40 graduate students have been trained. After years of construction and development, this discipline has formed five stable and distinctive academic research directions: modern design theory and method of fluid machinery, fluid measurement and control technology, vacuum application technology, thin film technology and micro-nano processing technology. In recent years, he has presided over 863 exploratory projects such as the National High-tech Plan, the National Natural Fund, the Innovation of the Ministry of Science and Technology, and the Anhui Natural Fund, as well as a number of enterprise cooperation projects.
Vacuum system:
The structural material of the vacuum system is the material that constitutes the main body of the vacuum system, which separates the vacuum system from the atmosphere and bears the atmospheric pressure. This kind of materials are mainly all kinds of metal and nonmetal materials, including sealing gasket materials at detachable joints.
The reflux of vacuum system includes the migration of pump liquid from diffusion pump to vacuum chamber and the migration of organic pollutants in mechanical pump oil to system (especially vacuum chamber). When the oil diffusion pump works, no matter what oil is pumped, even if a cold trap is added at the pump mouth, more or less some oil vapor will always flow back to the high vacuum end. The pressure they build at the port of diffusion pump is sometimes much higher than the vapor pressure of saturated oil at the pump wall temperature. This not only affects the limit pressure of the vacuum system, but also pollutes the pumped container, so the oil return rate is the main evaluation index of the diffusion pump system.
The graduates of this major have solid basic theory, wide professional caliber, strong practical ability, active thinking, pioneering spirit, large social demand and high one-time employment rate. It mainly enters domestic key scientific research institutes, information industry, aerospace, national science projects and large state-owned enterprises, mostly in economically developed areas such as Beijing, Tianjin, Shanghai and Guangdong.
[1] Vacuum packaging Vacuum packaging The food is put into a packaging bag, and the air in the packaging bag is pumped out to reach a predetermined vacuum degree, and then the sealing process is completed. Vacuum inflatable packaging is to put food into a packaging bag, pump the air in the packaging bag to a predetermined vacuum degree, then fill it with nitrogen or other mixed gases, and then complete the sealing process.
The main function of vacuum packaging is to remove oxygen, which is beneficial to prevent food from spoilage. Its principle is relatively simple, because food mildew and corruption are mainly caused by microbial activities, and most microorganisms (such as mold and yeast) need oxygen to survive. Vacuum packaging is the use of this principle, the oxygen in packaging bags and food cells, so that microorganisms lose their living environment.