On Thu, 5 Dec 2002, Ryan B****t wrote:
> Why is it that the 1 percent or so of matter we see radiates energy as it
> heats up but dark matter doesn't? Is it possible that it radiates outside the known electromagnetic spectrum?

This is actually an illustrative question.
I'll give you a long answer since it will go 
on the website!

Here is the difference.  "Ordinary" matter,
which is the stuff of which you, planets and
stars are made, is all made of the same
building blocks: atoms consisting of protons
and neutrons in the dense inner nucleus and
electrons in orbitals around this nucleus.
Now, dark matter, if it be real, is almost
definitely not made of atoms.  The zoo of
fundamental particles, some of which constitute
the pieces of atoms, is called the "Standard Model"
and it used to be the comprehensive list of all
matter. Dark matter changed that.  Some physicists
now suggest that each of the members of the Standard
Model family have some heretofore unknown "cousins"
in another entire family of particles.  That is
what we believe dark matter is made of.  These cousin
particles resemble their Standard Model kin, but each
may be different in some important ways.  As far
as we can quess, this would prevent them from forming
atoms like the Standard Model particles do.

So, after all that, we can see why dark matter particles don't
radiate.  Electromagnetic radiation is the result
of charged particles getting accelerated.  What does
that have to do with an atom?  Atoms radiate because
the particles from which they are made will get
"excited" in some way and will jiggle out of place, but then
get accelerated back into their natural states releasing
radiation.  The lights in our homes and offices and the
flames of a fire are generated this way: the electrons
in the atoms of a material get excited (with heat or
electricity) and wiggle back into place, releasing light.
Dark matter may be made of a bunch of lone, weakly
interacting neutral particles.  There is no way for them
to "get excited" and release light by "wiggling back into place"
since they may be these heavy, un-charged, ghostly particles which
don't form atomic structures, so there is no jiggling back
into place.

Regards,
Scott Funkhouser