What does Young's double-slit experiment demonstrate?

Young's double-slit experiment is a foundational demonstration in physics that illustrates the wave nature of light through the observation of interference patterns. In this experiment, coherent light is directed at two closely spaced slits. When the light passes through the slits, it behaves as a wave, creating overlapping wavefronts that can constructively and destructively interfere with each other. This results in a characteristic pattern of bright and dark fringes on a screen, known as an interference pattern.

The appearance of these patterns is evidence that light behaves as a wave, rather than strictly as a collection of particles. If light were solely a particle, one would expect to see two distinct light bands aligned with the slits, rather than an alternating pattern of light and dark. This profound result helped to establish the principle that light exhibits both wave-like and particle-like properties, a concept known as wave-particle duality.

Understanding this experiment is crucial in the study of optics, as it lays the groundwork for further explorations into the nature of light and other quantum phenomena.