The double-slit experiment is a famous physics experiment that demonstrates both the particle-like and wave-like nature of light and matter. It was originally conducted by Thomas Young in 1801 to demonstrate the wave nature of light, but later versions of the experiment have revealed key insights into quantum mechanics. Original Version: Demonstrating Wave Nature of Light In the classic version of the experiment: 1. Setup: A beam of light is directed at a barrier with two narrow, parallel slits.