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Stupid Cbr Question


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#1 Flummoxed

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Posted 10 January 2019 - 12:28 PM

I might be having a mental block or missing something.

 

The age of the universe is 13.7 billion years since the inflationary stage in our part of the universe began. Looking at the outer edges of the known universe is like gazing back in time, ie the light takes 46.3 billion light years to reach us. 

 

Why is the observed CBR over the entire observable universe approx 2.7 kelvin and not showing elevated temperatures towards the outer edges of the visible universe where we might expect it to be hotter if we are gazing back in time a billion or so years ?????

 



#2 exchemist

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Posted 10 January 2019 - 02:43 PM

I might be having a mental block or missing something.

 

The age of the universe is 13.7 billion years since the inflationary stage in our part of the universe began. Looking at the outer edges of the known universe is like gazing back in time, ie the light takes 46.3 billion light years to reach us. 

 

Why is the observed CBR over the entire observable universe approx 2.7 kelvin and not showing elevated temperatures towards the outer edges of the visible universe where we might expect it to be hotter if we are gazing back in time a billion or so years ?????

Would it not be because, during the voyage of these photons from long ago to reach our eyes, they traverse space that is expanding - as they come "forward" in time - to the point that their wavelengths have stretched to 2.7K equivalent by the time they get here? 

 

If you see what I mean.....



#3 Dubbelosix

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Posted 10 January 2019 - 02:44 PM

I think we do measure the difference, in fact, you can only look so far back in time because eventually the radiation phase blurs out any ability to measure an extremely distant past, lower than 400,000 years. Not only do temperatures get larger, but galaxies also exhibit evidence of being much denser and smaller.



#4 Flummoxed

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Posted 10 January 2019 - 02:55 PM

The outer galaxies are red shifted, if they are getting further away, or in a few rare cases blue shifted if they are coming this way. If space is expanding, I get it that CBR might be red shifted, but I have not seen anything written or calculations supporting either of your views above. 

 

Do either of you have any kind of citation, or something in detail I can read. My understanding is that CBR is constant everywhere, something does not stack up in my head. 

 

Edit: hold that request first google red shift and CBR https://en.wikipedia...ave_background 

 

This is a really dated link, it references the big bang as being the best model, which is completely wrong, the inflationary theory blows big bang out the water and explains the temperature fluctuations in the CBR. This theory is also being improved. 


Edited by Flummoxed, 10 January 2019 - 03:14 PM.


#5 exchemist

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Posted 10 January 2019 - 03:13 PM

The outer galaxies are red shifted, if they are getting further away, or in a few rare cases blue shifted if they are coming this way. If space is expanding, I get it that CBR might be red shifted, but I have not seen anything written or calculations supporting either of your views above. 

 

Do either of you have any kind of citation, or something in detail I can read. My understanding is that CBR is constant everywhere, something does not stack up in my head. 

 

Edit: hold that request first google red shift and CBR https://en.wikipedia...ave_background 

That's what I was getting at:  the cosmological red shift is, as I understand it, not a Doppler shift due to galaxies receding from one another in space, but by the expansion of the intervening space itself, stretching out the wavelengths. And the CMBR is red-shifted by the same mechanism from this plasma condensation event 380,000yrs after the start. 


Edited by exchemist, 10 January 2019 - 03:15 PM.

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#6 exchemist

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Posted 10 January 2019 - 03:28 PM

I found this undergraduate arxiv pdf on inflationary theory. http://cds.cern.ch/r...es/0005003.pdf 

 

93 pages, not for the faint hearted 

Blimey, I'm not even going to try to read that. But isn't that a bit OTT for your query? 



#7 exchemist

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Posted 10 January 2019 - 03:52 PM

It is now in my reading list, sad but true. :)

Well, when you've read it you can summarise it here, in 3 paragraphs, for lazy gits like me. :)



#8 Dubbelosix

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Posted 10 January 2019 - 04:14 PM

''And though we may spy flickers of the first stars, you don't have to go much deeper into cosmic history to encounter the ultimate limit to how far back we can ever see. As it turns out, we have already "seen" it. This cosmic dead end occurs at about 380,000 years post-big bang and is known as the epoch of recombination. Before this time, the universe was still too hot for electrons and protons to pair up and form the most basic atom, hydrogen. And unbound electrons scatter light. So, until those first hydrogen atoms came onto the scene, scientists think, the cosmos was an opaque soup of energy. Only afterward did the universe became transparent to light—light that was free to stream into our telescopes.''

 

https://www.popularm...e-see-16105099/



#9 OceanBreeze

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Posted 10 January 2019 - 04:46 PM

I might be having a mental block or missing something.

 

The age of the universe is 13.7 billion years since the inflationary stage in our part of the universe began. Looking at the outer edges of the known universe is like gazing back in time, ie the light takes 46.3 billion light years to reach us. 

 

Why is the observed CBR over the entire observable universe approx 2.7 kelvin and not showing elevated temperatures towards the outer edges of the visible universe where we might expect it to be hotter if we are gazing back in time a billion or so years ?????

 

When we look at the CMBR, we are looking at photons that were emitted from the surface of last scattering, approximately 13.7 billion years ago. By the time these photons reach us, they are extremely redshifted into the microwave range. The Temperature of 2.7K they are at today corresponds to a T of about 3000 K when the surface of last scattering formed.


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#10 exchemist

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Posted 11 January 2019 - 10:09 AM

When we look at the CMBR, we are looking at photons that were emitted from the surface of last scattering, approximately 13.7 billion years ago. By the time these photons reach us, they are extremely redshifted into the microwave range. The Temperature of 2.7K they are at today corresponds to a T of about 3000 K when the surface of last scattering formed.

Yes I think that was more or less what I was trying to say too, though less elegantly. 



#11 exchemist

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Posted 11 January 2019 - 10:11 AM

I'll give it a go :) you will have to wait for a couple of weeks for me to suck out the juicy bits. In the meantime wiki have some good links to inflation theory which is absolutely not big bang theory. It appears however that the term big bang is used in pop science articles when referring to both inflation theory and the original big bang.  

OK. Have at it. Distinction between big bang and inflation theory noted, though I am not sure where one draws the line between the two.