A classical investigation into the wave nature of light, first performed by Thomas Young in 1801. The experiment involved splitting a single beam of light into two beams, then recombining them. The resulting beam of light shows a pattern of dark and light fringes. Young concluded that the pattern was caused by the two light beams being waves out of phase with each other. Physicists did not accept Young's work until François Arago and Augustin-Jean Frésnel confermed it many years later.