According to the definition in physics, the concept of "vacuum" implies the absence of any substance and elements of matter in a certain space, in this case one speaks of an absolute vacuum. A partial vacuum is observed when the density of the substance in a given place in space is low. Let's take a closer look at this issue in the article.
Vacuum and pressure
In the definition of the concept "absolute vacuum" we are talking about the density of matter. From physics it is known that if gaseous matter is considered, then the density of the substance is directly proportional to the pressure. In turn, when one speaks of a partial vacuum, one implies that the density of matter particles in a given space is less than that for air at normal atmospheric pressure. That is why the question of vacuum is a question of pressure in the system in question.
In physics, absolute pressure is a quantity equal to the ratio of the force(measured in newtons (N)), which is perpendicularly applied to some surface, to the area of this surface (measured in square meters), that is, P=F / S, where P is pressure, F is force, S is surface area. The unit of pressure is pascal (Pa), so 1 [Pa]=1 [N]/ 1 [m2].
Partial vacuum
It has been experimentally established that at a temperature of 20 °C on the Earth's surface at sea level, atmospheric pressure is 101,325 Pa. This pressure is called the 1st atmosphere (atm.). Approximately, we can say that the pressure is 1 atm. equals 0.1 MPa. Answering the question of how many atmospheres are in 1 pascal, we make up the corresponding proportion and get that 1 Pa=10-5 atm. Partial vacuum corresponds to any pressure in the considered space, which is less than 1 atm.
If we translate the indicated figures from the language of pressure into the language of the number of particles, then it should be said that at 1 atm. 1 m3 of air contains approximately 1025 molecules. Any decrease in the named concentration of molecules leads to the formation of a partial vacuum.
Vacuum measurement
The most common device for measuring a small vacuum is a conventional barometer, which can only be used when the gas pressure is a few tens of percent of atmospheric.
To measure higher vacuum values, an electrical circuit with a Wheatstone bridge is used. The idea of using is to measurethe resistance of the sensing element, which depends on the surrounding concentration of molecules in the gas. The greater this concentration, the more molecules hit the sensing element, and the more heat it transfers to them, this leads to a decrease in the temperature of the element, which affects its electrical resistance. This device can measure vacuum with pressures of 0.001 atm.
Historical background
It is interesting to note that the concept of "absolute vacuum" was completely rejected by famous ancient Greek philosophers, such as Aristotle. In addition, the existence of atmospheric pressure was not known until the beginning of the 17th century. Only with the advent of the New Age, experiments began to be carried out with tubes filled with water and mercury, which showed that the earth's atmosphere exerts pressure on all surrounding bodies. In particular, in 1648, Blaise Pascal was able to measure pressure using a mercury barometer at an altitude of 1000 meters above sea level. The measured value turned out to be much lower than at sea level, thus the scientist proved the existence of atmospheric pressure.
The first experiment that clearly demonstrated the power of atmospheric pressure and also emphasized the concept of vacuum was carried out in Germany in 1654, now known as the Magdeburg Sphere Experiment. In 1654, the German physicist Otto von Guericke was able to tightly connect two metal hemispheres with a diameter of only 30 cm, and then pumped air out of the resulting structure, thereby creatingpartial vacuum. The story tells that two teams of 8 horses each, which pulled in opposite directions, could not separate these spheres.
Absolute vacuum: does it exist?
In other words, is there a place in space that does not contain any matter. Modern technologies make it possible to create a vacuum of 10-10 Pa and even less, but this absolute pressure does not mean that there are no particles of matter left in the system under consideration.
Let's turn now to the most empty space in the Universe - to open space. What is the pressure in the vacuum of space? The pressure in outer space around the Earth is 10-8 Pa, at this pressure there are about 2 million molecules in a volume of 1 cm3. If we talk about intergalactic space, then according to scientists, even in it there is at least 1 atom in a volume of 1 cm3. Moreover, our Universe is permeated with electromagnetic radiation, the carriers of which are photons. Electromagnetic radiation is energy that can be converted into the corresponding mass according to the famous Einstein formula (E=mc2), that is, energy, along with matter, is a state of matter. This leads to the conclusion that there is no absolute vacuum in the Universe known to us.
