Was The CMB Ever Visible?

[Keydar]

I understand that the expansion of the universe has caused CMB radiation to redshift into the microwave range. What I am wondering is how long ago was the background radiation in the visible light range, before it redshifted into the infrared? Also, when it was in the visible range, did it have enough intensity to be visible with the naked eye? Was the universe habitable at this time?

 

What I am getting at, in general, is was there a time in the universe, when life forms similar to humans could have observed background radiation with the naked eye?

[mathematic]

The CMB started out as blackbody radiation of 3000 deg K. This is somewhat cooler than the surface of the sun. I don't know exactly how it would look, but I suspect it would be red.

[J.C.MacSwell]

I understand that the expansion of the universe has caused CMB radiation to redshift into the microwave range. What I am wondering is how long ago was the background radiation in the visible light range, before it redshifted into the infrared? Also, when it was in the visible range, did it have enough intensity to be visible with the naked eye? Was the universe habitable at this time?

 

What I am getting at, in general, is was there a time in the universe, when life forms similar to humans could have observed background radiation with the naked eye?

 

Why would they evolve an eye that would observe the background? Not detecting would work just as well.

[Keydar]

The CMB started out as blackbody radiation of 3000 deg K. This is somewhat cooler than the surface of the sun. I don't know exactly how it would look, but I suspect it would be red.

 

Ah, okay. So I take that to mean that when the CMB was visible the universe was not exactly habitable?

 

Why would they evolve an eye that would observe the background? Not detecting would work just as well.

 

I'm not certain you understood my question. I'm talking about whether or not the universe was habitable when the background radiation was in the visible spectrum. Whether or not an eye would evolve to perceive the background is not specifically relevant to my question. We didn't evolve eyes to observe stars, but nonetheless we can do so as a byproduct of our eyes capabilities to detect light.

 

Basically, I'm wondering if the night sky over some planet long ago (maybe even an early Earth) was not exactly black as it appears today, but slightly reddish?

[mathematic]

Highly unlikely. In order for life (as we know it) to exist, the background has to be cool enough, which would imply a temperature cooler than infra-red.

[swansont]

Highly unlikely. In order for life (as we know it) to exist, the background has to be cool enough, which would imply a temperature cooler than infra-red.

 

I agree. The background temperature would be a lower limit of any planet's temperature.

 

Looking at this form another perspective, the temperature has to drop as the universe expands, so one could work backwards and see when the background was at, say 273K. Could life (as we know it) have arisen much earlier than that?

[Airbrush]

I understand that the expansion of the universe has caused CMB radiation to redshift into the microwave range. What I am wondering is how long ago was the background radiation in the visible light range, before it redshifted into the infrared? Also, when it was in the visible range, did it have enough intensity to be visible with the naked eye? Was the universe habitable at this time?

 

What I am getting at, in general, is was there a time in the universe, when life forms similar to humans could have observed background radiation with the naked eye?

 

The CMB did not redshift into the microwave range. The CMB IS visible light that is now redshifted into the microwave range because of the vast distance. A redshift implies great distance from us, the more redshift the greater the distance.

 

The background radiation burst into the visible light range about 380,000 years after the Big Bang, when the universe became transparent, and became visible to the naked eye at that time, but there were no stars around yet, so no life could have evolved. After that was the "dark ages" when hydrogen slowly clumped together into stars and galaxies. The dark ages lasted until about 800 Million years after the Big Bang, when the first stars ignited. They were the first light after the dark ages. Life as we know it needs heavy elements which were not created until the first generation of stars began to supernova. The first stars, "Population III stars", are thought to have been very massive, maybe 100 solar masses and larger with short live spans, maybe tens or hundreds of millions of years. So life could not start evolving until about a Billion years after the Big Bang.

 

"...Before decoupling occurs most of the photons in the universe are interacting with electrons and protons in the photon–baryon fluid. The universe is opaque or "foggy" as a result. There is light but not light we could observe through telescopes. The baryonic matter in the universe consisted of ionized plasma, and it only became neutral when it gained free electrons during "recombination," thereby releasing the photons creating the CMB. When the photons were released (or decoupled) the universe became transparent. At this point the only radiation emitted is the 21 cm spin line of neutral hydrogen. There is currently an observational effort underway to detect this faint radiation, as it is in principle an even more powerful tool than the cosmic microwave background for studying the early universe. The Dark Ages are currently thought to have lasted between 150 million to 800 million years after the Big Bang. The recent (October 2010) discovery of UDFy-38135539, the first observed galaxy to have existed during the following reionization epoch, gives us a window into these times. There was a report in January 2011 of yet another more than 13 billion years old that existed a mere 480 million years after the Big Bang...."

 

http://en.wikipedia.org/wiki/Timeline_of_the_Big_Bang#Dark_ages

Edited August 25, 2011 by Airbrush

[MigL]

The CMB is not visible light. It was 300000 yrs after the Big Bang, but it has since lost most of its energy because its wavelength has increased to the microwave range.

 

Prior to 300000 yrsABB the universe was filled with a plasma, much like the Sun, where the temperature or particle energy is high enoigh ( approx 4000 deg ) that electrons cannot stick to Hydrogen and Helium nuclei ( as soon as they do, they are bounced free by energetic photons ). This plasma is by definition , opaque, ie the whole universe would have been filled with glowing plasma like the surface of the sun.

 

After 300000 yrs ABB, the temperature dropped enough that electrons were no longer kicked free ( ionized ) by the radiation ( photons )and could form stable atoms of Hydrogen and Helium ( and miniscule quantities of deuterium and lithiun. nothing else I think, but not sure ). It was at this point that the universe became transparent, and is the earliest point we will be able to see.

 

I hope this explanation is a little simpler to follow.

Edited August 25, 2011 by MigL