CMBR Frequency range

[petrushka.googol]

Why is CMBR in the microwave range? (Eg. not in the radio freq range).?

 

Or is this restricted only to the known Universe?

 

 

[imatfaal]

Why is CMBR in the microwave range? (Eg. not in the radio freq range).?

 

Or is this restricted only to the known Universe?

 

 

Take UV light produced from the recombination of Hydrogen (at about 3000K) red-shift it by the amount that the universe has expanded and you get microwave at about 2.725K. As the universe continues to expand the CBR will be further red-shifted into the radio spectrum

[Enthalpy]

I expect telecom people to include microwaves in radiofrequencies. Just a matter of wording that evolves as RF technology gets faster.

 

The spectrum is of a blackbody, hence broad. It does contain power at lower frequencies. Its first observation was at a few GHz.

 

Though, the power density from a 3K body is faint, it decreases outside the optimum frequency (which must be around 1mm or 300GHz) AND other background noise gets worse at low frequencies, making the cosmologic background harder to observe or measure.

[swansont]

Take UV light produced from the recombination of Hydrogen (at about 3000K) red-shift it by the amount that the universe has expanded and you get microwave at about 2.725K. As the universe continues to expand the CBR will be further red-shifted into the radio spectrum

 

 

IIRC it's actually the thermal radiation that was already present at this point, redshifted by the expansion.

[imatfaal]

 

 

IIRC it's actually the thermal radiation that was already present at this point, redshifted by the expansion.

 

Not sure about it now to be honest.

 

Wikipedia on Recombination(Cosmology) says the following and I think lead to my thoughts

 

Shortly after, photons decoupled from matter in the universe, which leads to recombination sometimes being called photon decoupling, although recombination and photon decoupling are distinct events. Once photons decoupled from matter, they traveled freely through the universe without interacting with matter, and constitute what we observe today as cosmic microwave background radiation. Recombination occurred when the universe was roughly 378,000 years old, or at a redshift of z = 1,100.

 

 

But the more I think back about it the more I think you are correct. There were far more photons than baryons (confirmed on same wikipage) and it is those thermal radiation that makes the bulk of what we see now. Is there a one part in a billion which are slightly hotter and are the remnants of actual recombination?