Re: [Phys-l] Cosmic background radiation

[Calvin Kalman <Calvin.Kalman@concordia.ca>]

> Hi folks!
>
> 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.
>
> Thanks!  (I have great lab activities showing red shift, etc.)
>
> Leanna B. Aker


I just taught that section in my gen-ed course "From particles to Galaxies"

As early as 1912 V. M. Slipher, working at the 
Lowell Observatory had noted that many of the 
spiral nebulae were redshifted. However, until 
Hubble established that nebulae were at large 
distances from Earth, there was no obvious 
interpretation.

In studying the galaxies, Hubble made his second 
remarkable                    discovery--namely, 
that these galaxies are apparently receding from 
the Milky Way and that the further away they are, 
the faster they are receding (1927).

Nonetheless, there arose two rival theories of 
the universe- what would now be called the 
"big-bang theory" and the "steady state theory" 
of Fred Hoyle, Britain's astronomer Royal and 
others. (Although generally not accepted today, 
Hoyle at the end of his life - he died recently- 
still claimed that the steady state theory of the 
universe as infinite and eternal was correct)

In searching for evidence of the big-bang theory 
George Gamow suggested a crude analogy- How would 
you know that a field now fallow once long ago 
was used to graze cows? Gamow's answer - look for 
"pre historic" cow pats.

He suggested that when the universe ceased to be 
a plasma, radiation disconnected from the 
universe and  that primitive radiation "the cow 
pats" must still be around. (In  his usual impish 
way, he approached Hans Bethe to be a co-author 
so that his paper on the subject with Herman 
Alpher could be called the Alpher Bethe Gamow 
paper!)

The high temperature associated with the early 
universe would give rise to a thermal radiation 
field. As the universe expanded, the 
temperature would have dropped. By the present 
epoch the radiation temperature would have 
dropped to very low values, about 5° above 
absolute zero (0 K, or -273° C) according to the 
estimates of Alpher and Herman.

In experiments conducted in connection with the 
first Telstar communication satellite, two 
scientists, Arno Penzias and Robert Wilson, 
measured excess radio noise that seemed to come 
from the sky in a completely isotropic fashion. 
Penzias and Wilson & Robert H. Dicke andP.J.E. 
Peebles, published simultaneously in 1965 papers 
detailing the prediction and discovery of a 
universal thermal radiation field with a 
temperature of about 3 K.

Precise measurements made by the Cosmic 
Background Explorer (COBE) satellite launched in 
late 1989 determined the spectrum to be exactly 
characteristic of a blackbody at 2.735 K.

Observation of this Cosmic Microwave Background 
Radiation convinced just about everyone that the 
"Big Bang Theory" was correct.

--

Best wishes

                     Calvin


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_/   Calvin S. Kalman, P. Phys.         Phone:    (514) 848-2424 xt 3284
_/  Professor,Department of Physics    Fax:      (514) 848-2828
_/  Fellow, Science College
_/  Member, Centre for the Study of Learning and Performance
_/  Concordia University
_/  Montreal, QC  H4B 1R6          Calvin.Kalman@Concordia.ca
_/
_/ Also Adjunct Professor Department of Educational
_/ and Counseling Psychology, McGill University, Montreal, Quebec
_/
_/
_/ homepage- http://physics.concordia.ca/faculty/kalman.html
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