The Afshar experiment is an optics experiment, devised and carried out by Shahriar Afshar at Harvard University in 2004, which is a variation of the double slit experiment in quantum mechanics. The experiment gives information about which of two paths a photon takes through the apparatus while simultaneously allowing interference between the two paths to be observed, by showing that a grid of wires, placed at the nodes of the interference pattern, does not alter the beams.[1] Afshar claimed that the experiment violates the principle of complementarity of quantum mechanics,[2] which states roughly that the particle and wave aspects of quantum objects cannot be observed at the same time, and specifically the Englert–Greenberger duality relation.[3] The experiment has been repeated by a number of investigators and its results have been confirmed, but its interpretation is controversial, and some disagree that it violates complementarity, while also disagreeing amongst themselves as to why.[4][5][6][7][8]