How many degrees does a vacuum have?

In a Vodafone advertisement, it seems that Google will surely provide a correct and clear answer to this question. The trouble is that the question is not clear at all. What is meant by those degrees? It could refer to vacuum bands or temperature degrees.

Into which bands is a vacuum divided?

From a technician's point of view, a vacuum is an environment from which air has been evacuated, so the pressure is lower than atmospheric pressure.

According to pressure, we distinguish various vacuum bands, a total of six vacuum degrees:

1. Negative pressure – used, for example, in vacuum packaging and for gripping objects in handling and packaging lines.
2. Rough vacuum (300 to 1 mbar) – a chemically inert environment that prevents the oxidation of hot components, and is therefore used in discharge lamps, light bulbs, vacuum heating, melting, welding, soldering, etc.
3. Fine vacuum (1 to 0.001 mbar) – vacuum and X-ray discharge tubes.
4. High vacuum (10⁻³ to 10⁻⁷ mbar) – vacuum tubes and CRT screens, semiconductor manufacturing.
5. Ultra-high vacuum (10⁻⁷ to 10⁻¹²) – in particle accelerators.
6. Extremely high vacuum (<10⁻¹² mbar) – in particle accelerators or tokamaks.

What temperature does a vacuum have?

Let's simplify the question to the temperature of a perfect vacuum.

Many of us remember from high school physics that the temperature of a vacuum is –273.15 °C, 0 K, i.e., absolute zero.

But let's look at it more closely. Heat is energy, the movement of molecules. The faster the molecules move, the greater the heat. Temperature is a measure of how fast the molecules of a given substance are moving. A vacuum is an empty space. If we imagine perfectly evacuating the air from a container so that no molecules remain, there is no movement, no heat, and no temperature. Therefore, in a vacuum, there is no temperature that can be measured.

It is different with the temperature in space. But even there, a vacuum does not have the value of absolute zero, –273.15 °C (0 K); due to photon radiation, the temperature is just under 3 K, which is approximately –270 °C.

Vacuum temperature and electromagnetic radiation

We've said that in a container with a perfect vacuum, there is no movement of molecules. But something is moving in there after all: electromagnetic waves. In electromagnetic waves, no particles move. Movement, and thus heat, is caused by the expansion and contraction of electrical and magnetic fields. Waves are created, which hit the walls of the container and heat them up (transferring their energy), while at the same time, the walls of the container emit thermal radiation. If the container is isolated from the outside world, the intensity of the incoming and emitted electromagnetic radiation eventually equalizes – the walls of the container and the vacuum are in thermodynamic equilibrium and have the same temperature. Thus, a vacuum has a temperature corresponding to the temperature of the objects with which it is in thermodynamic equilibrium. Here, too, the temperature of a vacuum cannot be measured directly and is calculated from the intensity and spectrum of the radiation.

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