  An alternative to a cosmological constant is quintessence, defined as a
slowly-varying scalar field potential V(\phi). If quintessence is
observationally significant, an epoch of inflation is beginning at the present
epoch, with \phi the slowly-rolling inflaton field. In contrast with ordinary
inflation, quintessence seems to require extreme fine tuning of the potential
V(\phi). The degree of fine-tuning is quantified in various cases.
