Quantum fluctuations as the source of classical gravitational perturbations in inflationary universe models

The vacuum state wave functional of a free scalar field in the de Sitter phase of an inflationary universe is used to calculate the classical matter perturbations which couple to gravity. The transition to classical matter observables is made by defining a classical scalar field which contains the information about both the spread of the wave functional in time and spatial correlations. The result predicts a scale-invariant Zeldovich spectrum. (orig.)