On Wed, 12 Sep 2001, Shayla wrote:
> what is the theory of dark matter??


Hi, Shayla.

So, the universe began with the Big Bang about
13 billion years ago.

Many particles and anti-particles were created in the
Big Bang.  In the first moments, most particles were
annihilated with their anti-particle partner, but a small
fraction remained due to a slight imbalance in the proportions
of particle and anti-particle.  This slight excess is responsible
for the atoms which got propelled through the universe.
They eventually formed galaxies, stars and you and me.

But, the catch is that this known form of mass (which
formed all of the elements of the periodic table) is
probably not the only set of particles which survived
the Big Bang.  We believe that another entire family of
particles was created and survived the Big Bang.  These
are invisible but constitute *most of the mass of the
universe*!  They survived the Big Bang not due to an excess
in their particle/anti-particle ratio but because the
universe expanded too quickly relative to their annihilation
rate and they were dispersed before they got a chance to 
annihilate.

The particles of ordinary (not dark) matter are part
of the "Standard Model" of particles.  The dark matter
particles are conjectured to be members of a new family
of particles called the "Super Symmetric" family.
For each particle in the Standard Model, there would be
a cousin particle in the Super Symmetric family.  They have
different properties and are NOT the same thing as
anti-particles.

So, particle accelerators on Earth are being used also to
try to find these SUSY (short for Super Symmetric)
particles.  If we can find them in the lab, we have better
reason to suspect that they are indeed the culprit in the
missing mass problem.

Hope this helps,
Michael Scott Armel
Berkeley