double-slit experiment

noun1

1. •
   An experiment demonstrating that light and matter can satisfy the seemingly incongruous classical definitions for both waves and particles, regarded as evidence for the fundamentally probabilistic nature of quantum mechanics. A coherent light source, such as a laser beam, illuminates a plate pierced by two parallel slits, and the light passing through the slits is observed on a screen behind the plate, where the wave nature of light causes bright and dark bands due to interference.