What is a vacuum?
Vacuum is a concept widely used in physics and technology. This word comes from the Latin vacuus, which means "empty." The meaning of the word "vacuum" is preserved, in a general sense, vacuum means the space free from substances. In physics and engineering science, a vacuum is considered to be an environment that contains gas at a pressure below atmospheric. Let us take a closer look at what vacuum is in physics, technical vacuum and vacuum in space.
Vacuum in quantum physics
The physical vacuum is the lowest energy state of a quantum field, which has an angular momentum, zero momentum, as well as other quantum indices. The vacuum in physics is not always equivalent to emptiness. Thus, it can be a field of quasiparticles in a dense nucleus of an atom or in a solid.
In addition, the physical vacuum is a space that is completely devoid of substance, but filled with a field, however, this cannot be considered a full-fledged vacuum. The reason is that in the physical vacuum all the time particles appear and disappear, there are minor oscillations in the field.
The technical vacuum in practice is a highly rarefied gas. It can be obtained in small quantities. To achieve the ideal technical vacuum in a large volume is impossible in practice, because at the final temperature the materials will have a non-zero density of saturated vapors. Also, many materials that are used in practice, pass gases.
Vacuum in space
Outer space itself has a low density and pressure, and therefore is closest to the physical vacuum. But even the cosmic vacuum cannot be considered an ideal vacuum medium, since in outer space one can detect hydrogen atoms per cubic centimeter.
Vacuum can be divided into several degrees depending on the amount of substance that remains in it. So, there are the following degrees of vacuum (the range is presented from a lesser degree to a greater one):
- Atmospheric pressure - 760 mm. Hg st.
- Low vacuum - from 760 to 25 Hg. st.
- Medium vacuum - from 25 to 1 × 10−3mm Hg st.
- High vacuum - from 1 × 10−3up to 1 × 10−9mm Hg st.
- Ultra high vacuum - from 1 × 10−9up to 1 × 10−12mm Hg st.
- Extreme Vacuum - <1 × 10−12mm Hg st.
- Outer space - from 1 × 10−6up to <3 × 10−17mmHg st.
- Absolute vacuum - 0 mm. Hg st.