Why does the cosmic microwave background make a noise

[g.lemaitre]

For about the 7th time I've been told the story of how Penzias and Wilson discovered a noise the source of which they could not detect. It turned out to be the CMB. Well, why should the cmb make a noise? It's just photons in the microwave spectrum.

 

[Nabeshin]

When you turn on an AM/FM radio, what you're picking up is just photons in the radio spectrum. All they did was build a 'radio' for microwave photons.

 

[g.lemaitre]

Thanks, I understand