What is a vacuum?
Vacuum is a concept widely used in physics andtechnique. This word comes from the Latin vacuus, which in translation means "empty." This meaning of the word "vacuum" is preserved, in general, vacuum means a space free of substances. In physics and engineering science, a vacuum in which gas is contained at a pressure below atmospheric is considered as a vacuum. Let us consider in more detail what vacuum in physics, technical vacuum and vacuum in space are.
Vacuum in quantum physics
The physical vacuum is the lowerthe energy state of a quantum field that has a momentum moment, a zero momentum, and also other quantum parameters. Vacuum in physics is not always equivalent to emptiness. Thus, it can be a field of quasiparticles in the dense nucleus of an atom or in a solid.
In addition, the physical vacuum is a space,absolutely devoid of substance, but filled with a field, but this can not be considered a full vacuum. The reason is that in a physical vacuum particles all the time appear and disappear, there are insignificant fluctuations in the field.
The technical vacuum in practice is strongrarefied gas. It can be obtained in small quantities. It is impossible to achieve an ideal technical vacuum in large volumes in practice, because at the final temperature the materials will have a nonzero density of saturated vapor. Also, many materials that are used in practice, pass the gases.
Vacuum in space
Outer space itself has a lowdensity and pressure, and therefore is the most approximate to the physical vacuum. But even the cosmic vacuum can not be considered an ideal vacuum medium, since in outer space one can find hydrogen atoms per cubic centimeter.
Vacuum can be divided into several degrees independing on the amount of substance that remains in it. Thus, the following degrees of vacuum are distinguished (the range is represented from the lower to the higher degree):
- Atmospheric pressure is 760 mm. gt; Art.
- Low vacuum - from 760 to 25 Hg. Art.
- Average vacuum - from 25 to 1 × 10-3mm. gt; Art.
- High vacuum - from 1 × 10-3up to 1 × 10-9mm. gt; Art.
- Ultra-high vacuum - from 1 × 10-9up to 1 × 10-12mm. gt; Art.
- Extreme vacuum - <1 × 10-12mm. gt; Art.
- Outer space - from 1 × 10-6up to <3 × 10-17mm. gt; Art.
- Absolute vacuum - 0 mm. gt; Art.
You can find out the meaning of other physical terms in the articles in the section Physical concepts.