As often occurs, the answer to one question just leads to more questions ;)

in answering the question posed here
http://answers.google.com/answers/threadview?id=452113

juggler-ga quoted:

"As the universe cooled, however, conditions finally began to allow
stable atoms to form, releasing the photons from matter?s grip and
creating the beginnings
of what researchers have termed the Cosmic Microwave Background (CMB)."

my understanding of cooling is that energy (heat) has to go somewhere
in order for an object to be cooled.  if we're talking about the
universe cooling, then where is the heat going?

(you may notice that i posed the same question as a comment to the
original TIME AND SPACE thread)

jadbal-ga

            You are right that total energy in the universe is constant.

 It cannot leave the universe, and yet, universe is cooling down.

 It would be a mystery if universe would have a constant volume.
 But universe is expanding.

  Same amount of energy, spread over a larger volume, means 
  less energy density - and therefore smaller temperature.

  The equation

          Total amount of heat = Temperature * Cv * Volume

 Could be applied, whre Cv is specific heat per unit volume.

  So, as volume is increasing, the temperatire goes down.
  
 

  Good popular book, which goes into more details is

http://www.amazon.com/exec/obidos/ASIN/0465024378/104-1098412-6883962
or

http://www.amazon.com/exec/obidos/ASIN/0939680149/104-1098412-6883962

But book may be too much.
 Here are some graph which summarise the
expansion and cooling of the early universe: 

http://gould.as.arizona.edu/~mmeyer/nats102/lectures/lecture26.html


Hope this helps.

Hedgie

good answer.  thanks!

The same total energy was contained in an increasingly greater space
as the universe expanded, so the temperature dropped.

so as the universe expands, more material is being created?  how?

The steady state theory suggested that new matter was produced
spontaneously as the universe expanded.  This theory has been
discarded in light of compelling evidence from microwave background
radiation data from the COBE satellite (among others).

The most widely accepted theories of cosmology now have a constant
matter/energy content in the universe.