If space is a vacuum, how is the temperature in space on average °2.7 Kelvin and not °0 Kelvin?

Question

If space is a vacuum, how is the temperature in space on average °2.7 Kelvin and not °0 Kelvin?

In: 4

Answer 1

First, just like absolute zero is impossible to get to, space isn’t a perfect vacuum. That 2.7K number is calculated and has more to do with the flux of light and other particles through the vacuum than how we traditionally think of temperature.