  According to the standard model of cosmology, LambdaCDM, the mass-energy
budget of the current stage of the universe is not dominated by the luminous
matter that we are familiar with, but instead by some form of dark matter (and
dark energy). It is thus tempting to adopt scientific realism about dark
matter. However, there are barely any constraints on the myriad of possible
properties of this entity -- it is not even certain that it is a form of
matter. In light of this underdetermination I advocate caution: we should not
(yet) be dark matter realists. The "not(-yet)-realism" that I have in mind is
different from Hacking's (1989) anti-realism, in that it is semantic rather
than epistemological. It also differs from the semantic anti-realism of logical
empiricism, in that it is naturalistic, such that it may only be temporary and
does not automatically apply to all other unobservables (or even just to all
other astronomical unobservables, as with Hacking's anti-realism). The argument
is illustrated with the analogy of the much longer history of the concept of a
gene, as the current state of the concept of dark matter resembles in some
relevant ways that of the early concept of genes.
