The Net Advance of Physics: The Nature of Dark Matter, by Kim Griest -- Section 2.
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Evidence for dark matter (DM) exists on many scales, and it is
important to remember that the dark matter on different scales
may be different - the dark matter in dwarf spirals may not be the
dark matter which contributes
may not exist. This consideration is especially important when
discussing dark matter detection, since detection is done in the
Milky Way and its environs, and evidence for dark matter outside
the Milky Way may not be relevant. So, let me start with an
inventory of dark matter in the Universe.
The cosmological density of dark matter on different scales is
quoted using
averaged over the Universe,
and
determinations of Omega are made by measuring the
mass-to-light ratio
the average luminosity density of the Universe:
our uncertainty of the Hubble constant. There are methods, such as
from bulk flows, which do not depend
upon
involve taking an inventory of material depend upon it. For
example, the mass-to-light ratio in the solar neighborhood
is
neighborhood is typical, the amount of material in stars, dust and
gas is far below the critical value.
Physical Evidence for Dark Matter
;
in fact,
the dark matter
,
where 
is the density of some material
is the critical density. Most
of some system
and then multiplying this by
[67].
Here h = 0.4 - 1 parameterizes
from big bang nucleosynthesis,
and potential reconstruction
, but methods which
, giving 
. If the solar
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