  It is a well-known truism, inspired on the general theory of relativity, that
gravity gravitates. Here we suggest the possibility that dark matter may be
caused by the gravitation of the metric. At first sight this seems impossible
since the gravitational fields in galaxies and cumuli are so weak that it would
seem that second order terms are negligible. Nevertheless, the general theory
of relativity tells us that the gravitation due the metric is given by (grad
g_{00})^2. Thus, a metric field g_{00} varying fast in the space directions
could make a sizeable contribution to the gravitational field despite being a
weak field. As a plausible source of such a field consider that during
reheating the inflaton field disintegrates into radiation. Those quantum decays
that involve higher energies and momenta will produce pockets of metric fields
with rapid change in time and space. The expansion of the universe and
dissipative processes (including the emission of gravitational waves)
eventually result in basically stationary pockets of classical g_{00} field
varying rapidly in space that have collapsed along with matter into structures
like galaxies and cumuli. These pockets should gravitate precisely by the term
mentioned above. They are classical fields and are reminiscent of the cosmic
fields that are scattered in our universe.
