Validity of the `Conservation Law' in the Evolution of Cosmological Perturbations

It is shown that the conservation law' for metric fluctuations with long wavelengths is indeed applicable for growing modes of perturbations, which are of interest in cosmology, in spite of a recent criticism [L. P. Grishchuk, Preprint gr-qc/9511074, now published in N. Sanchez, A. Zichichi (eds.), String Gravity and Physics at the Planck Scale’, Kluwer, Dordrecht, p. 369 (1996)]. This is demonstrated both by general arguments, and also by presenting an explicitly solvable toy model for the evolution of metric perturbations during inflation.