Expert: Jayendra Upadhye - 1/1/2008

Question
Hi Jayen, I know that cosmic background radiation is supposed to be an "echo" of the big bang, etc, but I don't understand how it is supposed to pervade all of space, or how it hangs around so long after the big bang. Descriptions of it sound more like that of a gas, or intergalactic matter rather than radiation which moves in pretty straight lines from source to observer. After all, we can't see now any light from the big bang, so how has this cosmic radiation persisted?

Answer
Hi Jayen,
Firstly, just go thru this site:- http://en.wikipedia.org/wiki/Black_body

and this one:-
http://en.wikipedia.org/wiki/Cosmic_microwave_background_radiation

Coming to your question,
The universe is considered as a black body on the whole because, Nothing ever can escape it, and also because the characteristic of this radiation resembles that of a black body radiation almost completely.

It is "lingering" or appears to be an echo as, it is the radiation emitted from all reaches of space (sort of an "isothermal wash" rather like a painter "immersing his painting in a "wash of a certain shade for some effect ...amber comes to mind). All over the universe, in its every nook and cranny, is elementary hydrogen that is NOT cooler than 2.75 deg kelvin...The temperature of space even where there is no light, in the centers of the icy balls in the outer reaches of the system..anywhere you might imagine, things are always as cool as 2.75 deg kelvin or hotter, but never cooler.

That is because the whole universe "on the average" has cooled to this temperature since the Bang.

Since interstellar space has this source dispersed in almost every nook and corner of it, no matter where one looks, one sees this "glow" coming to him from that area of space.

It was this that was found by ERNO Panzeas back when he accidentally discovered it using a radio telescope.
It is so all pervading and so much a "property" or a characteristic of the universe (it represents its age), that it is isotropic (same) in all directions.
"The cosmic microwave background is isotropic to roughly one part in 100,000". - ref: wikipedia.

Smaller anisotropies have been thought to be the reason we see the universe as it is as of now.

Yes! It is radiation, and it does "move straight"!
It is the "light from the bang"!

You see, As you look farther into space, you are actually lloking back in time! What appears to you as the Background radiation, is also light that started off as a "terrible flash when the universe had cooled off to about 3000 deg Kelvin (uniformly at each point).
That is when the decoupling of matter and energy occured, allowing stable matter to exist as plasma. The photons (decoupled free energy) scattered all over the universe by the process known as thompson scatter (successive capture and re-radiation...(the process that occurs even in the solar core in the radiative zone at its center).

The photons have been cooling with the adiabatically cooling universe (remember nothing escapes the universe!) So its cooling is perforce adiabatic (without loss of heat).

Naturally it will persist as long as the universe endures.

THAT IS all one can say about it.
regards,
Jayen