B Early Predictions of Hot Big Bang CMB: Gamov & Alpher

[windy miller]

As I understand it the fact the COBE measured the CMB to be a perfect black body implies strong evidence for the hot big bang. However, I am wondering what was the earliest prediction that this must be so from big bang cosmology? Does it go all the way back to Gamov and Alpher? is it older ? more recent?

 

[mfb]

Not a perfect black body, the deviations are small but interesting because they tell us more about the early universe.
Gamov and Alpher were calculating nuclear processes, but the same Alpher predicted a cosmic microwave background radiation. Wikipedia has a list of papers.

 

[windy miller]

Ok sorry I should have said near perfect black body . But anyway the question remains , when was the black body properties of the CMB first worked out? If anyone knows Id very grateful for the reference.

 

[mfb]

Did you check the publications Wikipedia references?

 

[Klystron]

Ok sorry I should have said near perfect black body . But anyway the question remains , when was the black body properties of the CMB first worked out? If anyone knows Id very grateful for the reference.

Attribution can be difficult to assign when several academic groups cooperate on shared data and ideas. From the papers cited by @mfb I suggest studying Robert Dicke's physics papers on radar designs circa 1950-1960's specifically antenna temperature and receivers.

To elaborate, RF antennae such as developed by Bell Labs at Homdel were designed to both transmit and receive leaving an expectation that operators can fine tune reception based on data from transmission phase. Dicke and others proved that data inherent in a (passive) received signal can be isolated, amplified, compared to a stable source and fed back to "fix" the receiver. Penzias and Wilson modified a "Dicke fix" type RF receiver coupled with a stabilized cold stack to collect data that indicated the black body properties of the CMB for the first time.

 

[windy miller]

Did you check the publications Wikipedia references?

Yes I did, I did not find what I was looking. What was the earliest paper to predict the CMB should be a near perfect black body.

 

[Vanadium 50]

Yes I did, I did not find what I was looking.

Really? It's Ref. [23] on the very first line of the link that mfb posted.

 

[windy miller]

Really? It's Ref. [23] on the very first line of the link that mfb posted.

I read the whole of that article and did a search for the term " black body" just in case I missed it. The search time didn't pop and I couldn't find anything the said the CMB should be a near perfect black body. I did a see prediction for the temperature of the CMB of 5k but that is not what I am asking about. So any further help is much appreciated.

 

[mfb]

To define a temperature of a radiation spectrum it needs to be a blackbody spectrum.

 

[windy miller]

Sorry I did put this discussion to be at the beginner level and I am not sure i follow how the paper contents leads to a clear prediction of black body spectrum. Can anyone explain it? Or is there another paper with something more clearly stated?

 

[Klystron]

Really? It's Ref. [23] on the very first line of the link that mfb posted.

Concur. Alpher has precedence on publication. Took that as given and interpreted "work out" as "detecting and measuring the background radiation". CMB detection did not involve a typical radio frequency (RF) signal but manifested as an anomaly in antenna temperature.

[Edit: Just read your last post. Most of us now equate microwaves with heating objects. Alpher and others suggested that experimenters look for microwaves that correspond to a very low temperature, below 10 degrees Kelvin IIRC. Penzias and Wilson, after eliminating other sources of microwave noise in their antenna, first measured the CMBR by comparing the remaining antenna temperature to the temperature of a regulated super-cold device. Essentially both the CMB measurement and the cold pack reference temperature correspond to black body spectrums.]

 

[Vanadium 50]

Im not sure i follow how the paper contents leads to a clear prediction of black body spectrum. Can anyone explain it?

They used the word "temperature" which is a synonym for "black body". They didn't use the words you would have liked them to use.

 

[windy miller]

They used the word "temperature" which is a synonym for "black body". They didn't use the words you would have liked them to use.

 

[windy miller]

Im not trying to criticize them or you , I am just trying to understand and I am afraid i don't. Are you saying that anything that has a temperature is a black body?

 

[PeterDonis]

Are you saying that anything that has a temperature is a black body?

Read what @mfb said in post #9:

To define a temperature of a radiation spectrum it needs to be a blackbody spectrum.

The CMB is a radiation spectrum, so in order to define a temperature for it it must be a blackbody spectrum. That means the reference in question was predicting a black body CMB. It just didn't bother explicitly using the term "black body" because that part would have been obvious to the intended readers of the reference.

 

[windy miller]

They used the word "temperature" which is a synonym for "black body". They didn't use the words you would have liked them to use.

Read what @mfb said in post #9:
The CMB is a radiation spectrum, so in order to define a temperature for it it must be a blackbody spectrum. That means the reference in question was predicting a black body CMB. It just didn't bother explicitly using the term "black body" because that part would have been obvious to the intended readers of the reference.

thank you