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Re: [Phys-l] Cosmic background radiation



The CBR is mostly microwaves and far-infrared radiation, which could be emitted by any material with a temperature of 3 degrees above absolute zero. So the obvious alternative explanation would be that the space around us is filled with material at 3 K, "glowing" and emitting this radiation toward us from all directions. According to the steady-state believers, the best candidate for this material would be tiny solid grains, possibly metallic. The problem with this explanation is that any such material would also make the space around us opaque at these wavelengths, yet we easily observe local sources of far-IR and microwave radiation. The steady-staters tried to get around this around 1990 by postulating that the grains of material are spread over cosmological distances, but in that case, if the material is all at the same temperature but moving along with the Hubble flow, we would see a nonthermal (broadened) spectrum composed of a superposition of thermal spectra redshifted by different amounts--in contradiction to the results from COBE which show a perfect thermal spectrum at 2.73 K. So the only alternative seems to be that the radiation comes from even greater distances, from which it has been redshifted by a large, uniform amount. In other words, the radiation is left over from a time when the entire universe was much hotter than 3 K. Thus, the CBR provides evidence that there was a hot early universe. Call it a Big Bang if you like. :-)

Dan


On Nov 6, 2006, at 10:00 AM, phys-l- request@carnot.physics.buffalo.edu wrote:

I teach 9th grade physical science. We are getting ready to discuss the
Big Bang Theory and I was wondering if someone could explain to me just
how the cosmic background radiation is supporting evidence? I know that
the fact it is constant throughout the universe is the key, but I'm
foggy on just how this provides supporting evidence for the Big Bang.