  Although a discovery of wimps either at colliders or in direct experiments
would have enormous implications for our understanding of particle physics, it
would imply less than one would like about our understanding of the dark matter
in the universe or in the galactic halo: it surely is possible that the
discovered particles account for only a little of the total dark matter. To
establish the cosmological significance of a wimp discovery, their density must
be determined. We show that data from neither hadron colliders nor direct
detection experiments alone can be sufficient to determine the local or relic
density of discovered wimps, even allowing all needed assumptions about
cosmology and astrophysics. We provide examples of dark matter models where
nearly identical detector or collider signals correspond to very different
densities. We show, however, that it may be possible to determine the density
of wimps by combining data from both experiments; we present a general method
to do this in the case of supersymmetric dark matter, and describe how similar
studies could be made for other wimp candidates.
