<p>Photons from the CMB outnumber all other photons by more than 200:1.  This is contained in Pela's excellent answer to: <a href="https://physics.stackexchange.com/questions/196366/does-the-number-density-of-photons-n-gamma-approx-108-mathrm-m-3-refer/196373#196373">Does the number density of photons  nγ≈108m−3  refer to CMB photons only?</a>.  Pela uses this graph from <a href="https://arxiv.org/abs/1802.03694" rel="nofollow noreferrer">Hill et al. 2018</a> to derive this ratio.  Note that the CMB forms the largest contribution to the electromagnetic spectrum.
<a href="https://i.sstatic.net/PMNvQ.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/PMNvQ.png" alt="enter image description here" /></a></p>

CC BY-SA 4.0
2020-11-12T19:36:25.693Z
2020-11-12T19:36:25.693Z
Connor Garcia
<p>I would like to know the ratio of cosmic microwave background radiation to normal radiation in the universe.  I am considering cosmic microwave background radiation to include the microwave, and any other radiation that is being emanated from near the "edge of the universe", while normal radiation is radiation emmitted by stars, nebulae, and other sources within the universe (excluding the cosmic microwave background).  Since we are in a galaxy, I know that the normal radiation here far exceeds the cosmic microwave background, but I am interested in the "average" value over the universe.  For example: total cosmic microwave background radation in the universe / total normal radiation in the universe.</p>

CC BY-SA 3.0
2014-07-04T14:44:25.937Z
Measured in what way? In energy density?
adrianmcmenamin
CC BY-SA 3.0
2014-07-04T15:23:30.560Z
Yes, energy density would probably be the best way to measure it.
Jonathan
CC BY-SA 3.0
2014-09-09T01:13:31.893Z
What do you mean by "edge of the universe"?
HDE 226868
CC BY-SA 3.0
2014-09-12T17:30:37.150Z
@HDE 226868 By "edge of the universe", I am referring to the area where it took so long for the light to reach us that the universe was opaque at this location.
Jonathan
CC BY-SA 3.0
2014-10-09T14:40:11.673Z
@Jonathan: The "area" you are describing is called **the surface of last scattering**. See [cosmic microwave background](https://en.wikipedia.org/wiki/Cosmic_microwave_background) on Wikipedia.
pabouk - Ukraine stay strong
<light><cosmic-microwave-background><radiation>
What is the ratio of cosmic microwave background radiation to normal radiation?
Jonathan
# What is the ratio of cosmic microwave background radiation to normal radiation?

(Asked by: username_0 on 2014-07-03)

I would like to know the ratio of cosmic microwave background radiation to normal radiation in the universe. I am considering cosmic microwave background radiation to include the microwave, and any other radiation that is being emanated from near the "edge of the universe", while normal radiation is radiation emmitted by stars, nebulae, and other sources within the universe (excluding the cosmic microwave background). Since we are in a galaxy, I know that the normal radiation here far exceeds the cosmic microwave background, but I am interested in the "average" value over the universe. For example: total cosmic microwave background radation in the universe / total normal radiation in the universe.

**Tags:** light, cosmic-microwave-background, radiation

> **Comments:**
> **username_1**: Measured in what way? In energy density?  
> **username_0**: Yes, energy density would probably be the best way to measure it.  
> **username_2**: What do you mean by "edge of the universe"?  
> **username_0**: @username_2 By "edge of the universe", I am referring to the area where it took so long for the light to reach us that the universe was opaque at this location.  
> **username_3**: @username_0: The "area" you are describing is called **the surface of last scattering**. See [cosmic microwave background](https://en.wikipedia.org/wiki/Cosmic_microwave_background) on Wikipedia.  

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## 1 answers

### Answer by username_4 on 2020-11-12. Score: 4 | Accepted answer

Photons from the CMB outnumber all other photons by more than 200:1. This is contained in Pela's excellent answer to: [Does the number density of photons nγ≈108m−3 refer to CMB photons only?](https://physics.stackexchange.com/questions/196366/does-the-number-density-of-photons-n-gamma-approx-108-mathrm-m-3-refer/196373#196373). Pela uses this graph from [Hill et al. 2018](https://arxiv.org/abs/1802.03694) to derive this ratio. Note that the CMB forms the largest contribution to the electromagnetic spectrum.
[![enter image description here](https://i.sstatic.net/PMNvQ.png)](https://i.sstatic.net/PMNvQ.png)


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