How can interfering light waves transport particle characteristics? Up to now it was supposed that wave-particle duality was a quantum mechanical phenomenon which was not accessible to any classical explanation. The present article is disproving this assumption, by showing o n e single case which is entirely subject to a classical explanation: Photons in vacuum. The suggested classical explanation of wave-particle duality is simple, and it is deriving directly from special relativity: The particle characteristics are transported directly from A to B, without any intermediate of spacetime, because the interval is zero. The observed wave is a sort of placeholder in our spacetime.