  The present paradigm in cosmology is the usual Big-Bang Cosmology in which
two stages of accelerated expansion are incorporated: the inflationary phase in
the very early universe which produces the classical inhomogeneities observed
in the universe, and a second stage of acceleration at the present time as the
latest Supernovae observations seem to imply. Both stages could be produced by
a scalar field and observations will strongly constrain the microscopic
lagrangian of any proposed model.
