Imagine a massive object emitting photons of various frequencies. Because the object is massive, it will exert gravitational acceleration on those photons. Because the energy of a photon is proportional to its frequency, it seems that higher-frequency photons will experience a higher magnitude of gravitational acceleration. Some questions: Is it true that higher-frequency photons experience greater gravitational acceleration? ...and does this mean that there is a "gravitational dispersion" effect even in vacuum? From a classical viewpoint, such acceleration could potentially cause photons to move slower than c. How do relativistic accounts reconcile acceleration of light with the constancy of the speed of light?