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What is meant by the temperature of the CMB?

This is what I commonly read:

The CMB came to existence when atoms where formed and photons weren't constantly absorbed anymore. In other words, the universe became "transparent". Because of the expansion of the universe that radiation experienced red-shift so that now its temperature is slightly below 3 Kelvin.

So far, so good. But what is the temperature ofdoes it mean for the CMB to have a temperature? Temperature usually means the jiggling about of atoms, but the CMB is radiation. So what is meant when it is said that the temperature of the CMB is about 3 K today?

What is the temperature of the CMB?

This is what I commonly read:

The CMB came to existence when atoms where formed and photons weren't constantly absorbed anymore. In other words, the universe became "transparent". Because of the expansion of the universe that radiation experienced red-shift so that now its temperature is slightly below 3 Kelvin.

So far, so good. But what is the temperature of the CMB? Temperature usually means the jiggling about of atoms, but the CMB is radiation. So what is meant when it is said that the temperature of the CMB is about 3 K today?

What is meant by the temperature of the CMB?

This is what I commonly read:

The CMB came to existence when atoms where formed and photons weren't constantly absorbed anymore. In other words, the universe became "transparent". Because of the expansion of the universe that radiation experienced red-shift so that now its temperature is slightly below 3 Kelvin.

So far, so good. But what does it mean for the CMB to have a temperature? Temperature usually means the jiggling about of atoms, but the CMB is radiation. So what is meant when it is said that the temperature of the CMB is about 3 K today?

1
source | link

What is the temperature of the CMB?

This is what I commonly read:

The CMB came to existence when atoms where formed and photons weren't constantly absorbed anymore. In other words, the universe became "transparent". Because of the expansion of the universe that radiation experienced red-shift so that now its temperature is slightly below 3 Kelvin.

So far, so good. But what is the temperature of the CMB? Temperature usually means the jiggling about of atoms, but the CMB is radiation. So what is meant when it is said that the temperature of the CMB is about 3 K today?