Double slit experiment. Two illustrations comparing possible results of the double slit experiment. In both illustrations, laser beams (green) are shone at a plate containing two slits, with the result observed on a screen behind the plate. At left is the actual result (an interference pattern), demonstrating that light has the characteristics of both a wave and a particle (wave-particle duality). Each photon of light travels through one of the slits, as would be expected of a particle, but light from the two slits interfere, as would be expected of a wave. At right is the image of two slits that would be observed if light was treated classically as particles and not a wave.