Quantum shadows. (cover story)

The article presents a historical overview of the scientific debate over the question of whether light is composed of waves or particles, focusing on the application of quantum physics theories to the issue. Topics include physicist Albert Einstein's theory that photons are particles, quantum physicist Neils Bohr's complementarity principle about the behavior of photons as waves and particles, and theoretical physicist John Archibald Wheeler's 1978 experiment on the movements of photons measured with an interferometer. Physicists Radu Ionicioiu and Daniel Temo suggested measuring quantum mechanics of photons using a control photon in a quantum superposition of two states and a system photon moving through the interferometer.