Question

T3B10) Does it make sense to talk about the temperature of a vacuum? If so, how could you measure or calculate it? If not, why not?

Answer 1

We can take it as electronic radiation

Electromagnetic radiation can travel through a vacuum, so objects in space of any temperature above the near absolute zero (0 Kelvin = about -273 deg C.) temperature of cosmic background radiation (which is about 3 Kelvin) will radiate energy into space.

One doesn't determine the temperature of a vacuum. Just as 'nothingness' has no color, taste, smell, etc. it also has no temperature. As there are no particles whose kinetic energy can be measured or averaged.

Only objects within a vacuum can have a temperature, and that temperature will depend on the balance of incoming and outgoing radiation. Electromagnetic radiation can travel through a vacuum, so objects in space of any temperature above the near absolute zero (0 Kelvin = about -273 deg C.) temperature of cosmic background radiation (which is about 3 Kelvin) will radiate energy into space. Without another source of energy replacing that loss (a nearby Sun, for example) the object's temperature will decrease. That is why you read about 'the coldness of outer space'.