  We have determined the lattice dynamics of MgSiO$_3$ perovskite (bridgmanite)
by a combination of single-crystal inelastic x-ray scattering and ab initio
calculations. We observe a remarkable agreement between experiment and theory,
and provide accurate results for phonon dispersion relations, phonon density of
states and the full elasticity tensor. The present work constitutes an
important milestone to extend this kind of combined studies to extreme
conditions of pressure and temperature, directly relevant for the physics and
the chemistry of Earth's lower mantle.
