The meaning of a vacuum is the state of the gas below a single atmospheric pressure in a given space and is a physical phenomenon. In Void, sound can not be delivered because there is no medium, but the transmission of electromagnetic waves is not affected by the vacuum. In fact, in vacuum technology, for the atmosphere, the vacuum system is designed to discharge some of the material inside a given space to a pressure less than one standard atmosphere, which is what we call the vacuum or vacuum. Vacuum commonly used Pascal (Pascal) or Torr (Torr) as a unit of pressure. In the natural environment, only outer space can be called the space closest to the vacuum.
In 1641 the Italian mathematician Torricelli filled a long tube with mercury and then slowly turned the nozzle in a mercury-filled bowl with the end of the mercury column about 76 cm tall. At this moment, the top of the glass tube is in a vacuum state without mercury. This experiment is "Torricelli experiment", completed the experiment of the glass tube "Tori tube".
Einstein used the theory of field to study gravitation. He realized that there was a problem with the empty concept of vacuum, and he had put forward the idea that vacuum is a special state of gravitational field. First give the vacuum new physical content is P.A.M. Dirac. Dirac in 1930 in order to get rid of Dirac equation negative energy predicament, proposed vacuum is full of negative energy electronic sea.