# Does the Cosmic microwave background also lies in radio frequency spectrum?

I heard the CMB is the electromagnetic radiation from the big bang. It is 13.7 b years old but isnt it only in the microwave range of the spectrum (300MHz - 300GHz) . Can a FM radio receiver (87-108MHz)pickup the noise from the CMB ?

I don't think it has neat boundaries...

## 3 Answers

So Cosmic Microwave Background radiation corresponds very neatly to a blackbody spectrum of temperature 2.7K. This is an image which shows data collected by satellites:

The key thing to understand is that it is a spectrum, not a set of discrete frequencies that are present. So to answer your question, theoretically yes a FM radio receiver (87-108MHz) could pickup the noise from the CMB, but since CMBR has a very low intensity in the first place, as well as radio waves making up only a tiny part of CMBR's spectrum, in practise it's unlikely.

The CMB has a blackbody spectrum at T = 2.7 K, which peaks in the microwave range ($\lambda \approx 2\,{\rm mm}$). The intensity of the blackbody spectrum is given by Planck's Law: $$B(\nu,T) \propto \frac{\nu^3}{e^{h\nu/kT} -1},$$ which decays but is nonzero at lower frequencies.

yes, it does. if you have an old analog television receiver, you can tune it to an unused channel in the UHF band and look at the random static on the screen. about 10% of that static comes from the CMB.

• I heard it was 1% – ObsessionWithElectricity Sep 5 '18 at 18:31
• could be. I can't remember the original reference. – niels nielsen Sep 5 '18 at 22:33