  Models of inflationary cosmology admit a choice of the metric for which the
geometry of homogeneous isotropic solutions becomes flat Minkowski space in the
infinite past. In this primordial flat frame all mass scales vanish in the
infinite past and quantum scale symmetry is realized. The cosmological
evolution is dominantly described by the slow increase of a scalar field which
sets the scale of all masses. We construct the primordial flat frame for
standard models of inflation as Starobinsky inflation or chaotic inflation. In
particular, we discuss the evolution of inhomogeneous solutions in the
neighborhood of the homogeneous isotropic background solution and their
relation to the observable primordial fluctuation spectrum. If the propagators
for the graviton and scalar field remain regular, our observed inhomogeneous
Universe can be extrapolated back to the infinite past in physical time. In
this case there is no physical big-bang singularity -- the latter reflects only
a singular choice of ``field coordinates". Independently of the issue of
singularity the primordial flat frame offers a new view on the physical
properties of the inflationary universe, which can be characterized as a very
slowly evolving almost empty vacuum state with approximate scale symmetry.
