# What's the bandwidth of the Cosmic Microwave Background radiation?

1. Apr 10, 2013

### SpaceBear

What's the bandwidth of CMB and what was the bandwidth of CMB when it was emitted (at the moment when the Universe was 379,000 years old)?

2. Apr 10, 2013

### marcus

Do you know the black body curve? It describes the wavelength mix of the thermal glow from a generic object at a given temperature. It does not have sharp crisp upper and lower limits.

The position and shape of the curve depends only on temperature. It is actually the same curve just scaled differently depending on temperature. Sometimes they plot it on a frequency scale, sometimes on a wavelength scale. It looks like a lopsided mound.

You could look it up in Wikia, CMB is essentially perfect black body. So when they tell you the temperature they have told you the wavelength mix. Initially it was around 3000 kelvin thermal glow.

3. Apr 11, 2013

### SpaceBear

Wikipedia says:
On definition (a), the peak spectral density occurs at a frequency of 160.2 GHz, corresponding to a 1.873 mm wavelength. Using definition (b), the peak is at a wavelength of 1.06 mm, corresponding to a frequency of 283 GHz.

Does that mean that we can say the emission is at maximum between 160.2 GHz and 283 GHz?

If the CMB doesn't have a sharp upper and lower limit, then what's the upper and lower frequency where the output is at say 1/10 of the peak frequency range?
That will give an idea of the bandwidth of the most relevant part of the CMB radiation.

4. Apr 12, 2013

### Naty1

5. Apr 12, 2013

### Mordred

Marcus I'm not sure I would call the CMB a perfect blackbody. A perfect blackbody had total absorbsion of all wavelengths from zero to infinity

6. Apr 12, 2013

### cepheid

Staff Emeritus
The CMB spectrum is the most perfect example of a blackbody spectrum that has ever been measured.

At the OP, look up the Planck function. Then you can compute your 1/10 power points yourself, given this and the knowledge that the CMB radiation temperature is 2.723 K

7. Apr 12, 2013

### Mordred

Perhaps I am misunderstanding in how one defines a blackbody as opposed to a transparent, grey, colored etc body.
This is a subject covered in an article that I have been recently studying

I linked the section of the textbook at the descripive.
I would be interested in what is the mainstay definition of what defines a perfect blackbody in regards or opposition of the related link.

8. Apr 12, 2013

### negativzero

Could you make a lens with a diffraction grating and focus the microwave energy?
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9. Apr 12, 2013

### cepheid

Staff Emeritus
Its spectrum is pretty much exactly the Planck function with T = 2.73 K. So it (the primordial plasma) emits in the way an ideal blackbody radiator would emit. This is because at and before the epoch of recombination, the entire universe was in thermal equilibrium (including the matter with the radiation) at the same temperature.

You can make lenses that focus microwave radiation, and they can just be simple conics. I don't see why it would have to be a diffraction grating. Also, focus the microwave energy for what purpose?

10. Apr 13, 2013

### Naty1

You mean collect and amplifying the CMBR?? Isn't that what Wilson and Arno Penzias at Bell Telephone Labs got the Nobel prize for doing:

http://en.wikipedia.org/wiki/Penzias

11. Apr 13, 2013

### negativzero

Cephied wrote: "...focus the microwave energy for what purpose?"
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i can't be the first naive individual to observe that the background is a continuous source of [a little bit] of energy. With a nice lens to focus it, perhaps i could power the hibachi in my space ship. Is there a practical way to soak up energy from the background? A microwave panel perhaps?
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Last edited: Apr 13, 2013
12. Apr 13, 2013

### negativzero

Naty1 in part: "...Isn't that what Wilson and Arno Penzias at Bell Telephone Labs got the Nobel prize for doing:..."
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Yeah, i thought about them too, but the mere fact that they had to amplify the signal means that you will need a really big antena to power a very small hibachi.---unless maybe you want to accelerate, in which case the spot in the CMB you are approaching will blue shift. If you go fast enough you might want to hide in the shadow of the lens, and use any energy captured to run the air conditioners.
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13. Apr 14, 2013

### Naty1

not yet. I'm pretty sure that's been discussed in these forums....

14. Apr 14, 2013

### Mordred

There is better sources of free energy to soak up such as solar power. As well as reactive elements such hydrogen.

15. Apr 20, 2013

### negativzero

http://science.nasa.gov/science-news/science-at-nasa/2013/21mar_cmb/
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There it is! You build a big flat black balloon and absorb energy on the side side exposed to the "hot end" of the universe. Your balloon has gas in it so it swells up (not much i'll grant). But here is the trick: you have another flat balloon running parallel and when the first balloon heats up, you flip them like two chickens on a bar-b-cue spit. Now the cold balloon is exposed to the hot side of the universe. The deflation and expansion of the two balloons might generate enough power to rotate the mess.
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Call it, "the rotisserie cycle."
Please don't trample me in the rush to the Patent Office.
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Last edited: Apr 20, 2013