Vacuum is a concept in physics, which initially reflects the state of nothingness, similar to "nothing". In the 20th century, P.A.M. Dirac proposed the concept of quantum vacuum, that is, the vacuum is not empty, but is always transformed by virtual particles and physical particles, but the whole is a macroscopic whole without obvious physical properties. Vacuum is a sea of energy, a constantly oscillating objective existence full of huge energy; And space is just a mathematical concept, reflecting the properties of motion and the concept of geometric size.


     That is to say, space and vacuum are a mathematical concept and a physical concept, which have no relation to each other. It is true that the properties of vacuum need to be described by space, but that is just a mathematical representation, a parameter introduced for the convenience of research, not that the properties of vacuum depend on space.


    In fact, in vacuum technology, the vacuum system is for the atmosphere, a certain part of the material inside the space is expelled, so that the pressure is less than a standard atmospheric pressure, then we call this space vacuum or vacuum state. Vacuum is often used as a unit of pressure in Pascal or Torr. In the natural environment, only outer space is the closest to vacuum.


     When Einstein studied the phenomenon of gravitation from the viewpoint of field theory, he had already realized that the concept of empty space is problematic. He once proposed that vacuum is a special state of the gravitational field. The first thing that gave the vacuum new physics was P.A.M. Dirac. In 1930, in order to get rid of the predicament of the negative energy solution of the Dirac equation, Dirac proposed that vacuum is a sea of electrons filled with negative energy states.


     As far back as 1643, Italian physicist torricelli discovered that there was an atmosphere and atmospheric pressure in vacuum and natural space. When he filled a long glass tube with mercury, which was closed at one end, and stood upside down in the mercury tank, he found that the mercury level in the tube dropped until it was 76 centimeters away from the mercury level outside. Torricelli believes that the space on the mercury surface of the glass tube is vacuum, and the 76cm high mercury column is due to atmospheric pressure.


  In 1650, galy of Germany restrained himself as a piston vacuum pump.


    In 1654, he conducted his famous experiment on the hemispheres of magdeburg: two combined copper hemispheres 14 inches (35.5 centimeters) in diameter were vacuumed by a vacuum pump, and then eight horses in each group pulled the copper balls in the opposite direction, never separating the two hemispheres. This famous experiment proves once again that there is an atmosphere in space and that the atmosphere is under great pressure. In honor of torricelli's great scientific discoveries and contributions, the vacuum pressure unit used in the past was named after him.


     The success of the British industrial revolution in the mid and late 19th century promoted the development of productivity and scientific experiments, as well as the development of vacuum technology.


    The mercury column vacuum pump and the mercury drop vacuum pump were invented in 1850 and 1865, resulting in incandescent light bulb (1879), cathode ray tube (1879), dewar bottle (1893) and compression vacuum gauge (1874). The application of the compressed vacuum gauge made low pressure measurement possible for the first time


    In the early 20th century, vacuum tube appeared, which promoted the development of vacuum technology to high vacuum.


   Gas ballast vacuum pump, oil diffusion pump and cold cathode ionization gauge were developed from 1935 to 1937. These results and the pilani vacuum gauge made in 1906 are still used in most vacuum systems today.


      After 1940, the application of vacuum technology expanded to nuclear research (cyclotron and isotope separation, etc.), vacuum metallurgy, vacuum coating and freeze-drying, etc. Vacuum technology began to become an independent discipline. During the second world war, the need for atomic physics tests and communication for high-quality electro-vacuum devices further promoted the development of vacuum technology.