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carlos.ramos
2009-May-16, 01:48 PM
Hello this is Carlos Ramos from Portugal.

My question is this.
In one of your podcasts, Pamela mentioned that the cosmic microwave background started itīs life in the ultra voilet spectrum and above, but that due to red shift, it existes now in the microwave wave lenght.
If this is correct and since the cosmic microwave background field is all around us. Was there a point in time when the radiation emited from this field was in the spectrum of visible light, creating a universe iluminated from all directions in the process?
If this is so, how long ago would this have been.

Really do love the podcast.

winensky
2009-May-25, 02:44 PM
Hello and welcome.

I believe the answer to your question involves three factors. The human perception of colour at a given temperature Kelvin, the interacton of photons, electrons and baryons in the early universe, and the effect of expansion on the density of scattering and emitting matter in in the early universe.

The CIE1960 is a standardized measure of colour interperetation as a function of frequency and emission energy expressed in degrees K. this relationship is refered to as the Plank locus. At about 1000 degrees K, this locus approaches its limit for human perception. Below this temperature, there is insufficient energy for photons to ellicit a retinal response. This then sets our minimum temperature to produce a perceptible glow.

In order to consider the effect of baryon, electron and photon interaction we need to step back to a temperature of about 3000 K. This cooresponds to a time of about 380,000 years after the big bang. The existing plasma state begins to "decouple" at this point freeing photons and alowing protons and electrons to form Hydrogen. Immediately prior to this, The plasma at a temperature of 3000K would have a yellow whitish glow based on the CIE1960.
Newly formed hydrogen would begin to re-emit in the H alpha and beta frequencies producing a characteristic deep red glow. The resultant orange red glow would continue but decrease in intensity and become deeper red as the universe continued to expand untill aproximately 2.2million years following the Big Bang. At this point the background temperature, having cooled to about 1000 K., would no longer have sufficient energy to register on the retina and so the background glow would fade out.

This interperetation doesn't take into account scattering by hydrogen or emissions from the early stages of star formation but it is a stab at describing how the early background glow might appear. The time and temperature relationships were derived using the WolframAlpha redshift calculator. The Plank locus derived colour interperetations are from Wikipedia.

I would love to see anyone elses ideas on this.