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Author Topic: where was CMBR emmited from?  (Read 2161 times)

Offline lostinspace

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where was CMBR emmited from?
« on: 17/01/2013 18:22:28 »
There seem to be a lot of references to the CMBR we now see coming from 'matter' which is 46billion light years away now. Where was this 'matter' when the light was first emmited (ie 350000 years after the big bang)?
I'm guessing (never good) it must be less than 13.5billion light years because the distance to travel will have continually expanded. This means the initial expansion rate must have been very much higher than present. Is this the 'inflation' period which gets quoted in the first 10exp-34 second after big bang?


 

Offline Supercryptid

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Re: where was CMBR emmited from?
« Reply #1 on: 17/01/2013 22:55:08 »
I believe it was created in the first moments of the Big Bang, and therefore originated fairly evenly from all points in the Universe at once. So to ask where it came from is like asking where the Big Bang occurred; it happened "everywhere".
 

Offline Phractality

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Re: where was CMBR emmited from?
« Reply #2 on: 18/01/2013 00:19:51 »
I believe it was created in the first moments of the Big Bang, and therefore originated fairly evenly from all points in the Universe at once. So to ask where it came from is like asking where the Big Bang occurred; it happened "everywhere".
The theory is that the CMBR we see today was emitted when the hot plasma first cooled enough to become transparent. That is believed to be about 300,000 years after the big bang. At that time, the light had a color temperature of several thousand degrees, but the expansion of space has stretched and redshifted it to its present temperature of 2.7K. Before the plasma became transparent, light was emitted, but immediately reabsorbed without getting very far. But you're right; it happened everywhere.
 

Offline lostinspace

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Re: where was CMBR emmited from?
« Reply #3 on: 18/01/2013 11:24:33 »
I suppose what I'm really trying to establish is the location of the source of the photons we receive now in the COBE or WMAP telescopes. They would have been sufficiently distance to allow a travel time of 13.5 billion years but as the space between us and the source has been expanding I am assuming that they will have travelled from a distance which was much less than 13.5 billion light years at that time in history, just post big bang (after 350000 years, its all relative!).
Thanks to Phracticality and Supercryptid for the previous replies, they reinforce my understanding of events whereby CMBR was emmited from everywhere once light could travel through space once there were individual particles. Also presumably photons were emmited from our current location at this time which will now be up to 45 billion light years away.
 

Offline Phractality

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Re: where was CMBR emmited from?
« Reply #4 on: 19/01/2013 07:27:35 »
I suppose what I'm really trying to establish is the location of the source of the photons we receive now in the COBE or WMAP telescopes. They would have been sufficiently distance to allow a travel time of 13.5 billion years but as the space between us and the source has been expanding I am assuming that they will have travelled from a distance which was much less than 13.5 billion light years at that time in history, just post big bang (after 350000 years, its all relative!).
Angular diameter distance is how far away the light source was when the light was emitted. You seem to be asking about the luminosity distance to objects whose light-travel distance is estimated at 13.5 Gly. See Wikipedia: Distance measures (cosmology).

Luminosity distance can only be estimated by making assumptions about changes in the expansion rate over the last 13.5 billion years. I've heard estimates as high as 56 Gly. Here are some graphs of various theories of how the expansion has evolved. Pick a theory and calculate an answer to your question.

For a grade-school simple calculation, you could assume that the Hubble parameter (expansion rate) has been the same as it is now, for the last 13.5 billion years. At the present rate of about 2.5 x 10-18/s, distances doubles about every 9 billion years. I worked that out with logarithms on Wolframalpha.com a couple of years ago. Just to double check, here's the problem in reverse:
9 Gy = 2.838 x 1017 s
(1+H0)^2.838 x 1017 = 2.033.

13.5 / 9 = 1.5; so the distance would have increased by a factor of 21.5 = 2.828. 13.5 x 2.828 = 38.18. Estimates higher than that, evidently, are assuming the the expansion, now, is slower than the average over that time period.
 

Offline lostinspace

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Re: where was CMBR emmited from?
« Reply #5 on: 20/01/2013 19:23:22 »
I would have thought from these figures the distance at source would be around 7billion lightyears (very rough estimate), after 1 billion years the light would travel 1billion lightyears but the distance would increase by 10% roughly so leaving 6.6billion lightyears to go. Each time the light gets nearer expansion means the remaining distance increases. Finally after 13.5 billion years it finally reaches us. I realise to get a precise value it is necessary to integrate the increase over all time rather than taking chunks and a precise epansion rate is required, does this make sense?
 

Offline distimpson

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Re: where was CMBR emmited from?
« Reply #6 on: 24/01/2013 16:43:33 »
Somewhat related to this discussion, didn't want to start a new thread:



I just saw this report http://www.laboratoryequipment.com/news/2013/01/universes-temperature-confirms-big-bang%E2%80%99s-prediction?et_cid=3056990&et_rid=54652410&linkid=http%3a%2f%2fwww.laboratoryequipment.com%2fnews%2f2013%2f01%2funiverses-temperature-confirms-big-bang%25E2%2580%2599s-prediction

Is this cooling curve predicted by adiabatic expansion at a constant rate? If so, how well does it agree with other measurements of the Hubble constant?
 

Offline lostinspace

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Re: where was CMBR emmited from?
« Reply #7 on: 29/01/2013 12:08:16 »
Firstly, as I understand it the cooling of the CMBR is due to the emmited photons having a gradually increasing wavelength over time as the universe expands. As the energy is inversely proportional to wavelength this gives a fall in energy. I'm not sure where this energy goes (maybe dark energy?)
Secondly, it seems the hubble constant is now the hubble parameter and this gives a variable expansion rate which started very high and is gradually slowing down (although not to the point of contraction). I'm still trying to figure out how you extrapolate this back to a singular point which is the age of the universe is caculated.
This may help:

newbielink:http://www.mysearch.org.uk/website1/html/511.Interpretation.html [nonactive]

« Last Edit: 29/01/2013 12:10:30 by lostinspace »
 

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Re: where was CMBR emmited from?
« Reply #7 on: 29/01/2013 12:08:16 »

 

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