  It is showed by a conformal rescaling that the inflationary background can be
dual to a slowly expanding background, which is almost Minkowski and described
by a conformal field theory conformally coupled to gravity. It is proved that
the primordial curvature perturbation and tensor perturbation generated during
these two conformally equivalent backgrounds are completely equal, and the
scale invariance of perturbations is determined by the conformal invariance of
field theory in slowly expanding background. In dual slowly expanding scenario,
the primordial universe is asymptotical to a static state in infinite past. We
discuss the implication of the results obtained.
