What is the nature of dark matter?
Date: Around 1999
What is the (theorized) nature of dark matter? How can we
tell that it exists? Where in the universe is it thought to exist,
in our galaxy, or our solar system?
Matter that emits light or radio waves or other EM radiation is
called non-dark matter. When we estimate the amount of mass
represented by the non-dark matter, there does not seem to be
enough matter to "close" the universe, that is, to have the
expansion of the universe sometime slow down and have the
universe start to collapse. Most scientists would expect that
the universe is closed or slightly open, but not as open as the
estimate of the mass from visible matter. Thus, dark matter
was invented to be the unseen mass that would close the universe.
Some theories had it be neutrinos with mass (experiments seems to
show that the neutrino mass is too small). Some theories have suggested
that it is made up of neutron stars and the most recent measurements
of gamma ray bursters suggests that the dark matter might be white
dwarfs that are all around. This is an exciting area and no one knows
the answer. I don't know if you can understand all of my answer. If
not, please ask again.
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Update: June 2012