The double-slit experiment reveals one of quantum mechanics' most striking phenomena. When unobserved, electrons behave as waves — passing through both slits simultaneously and creating an interference pattern.

Detector off: The electron passes through both slits at once and interferes with itself. Multiple bright and dark fringes appear on the screen — proof that the electron exists as a wave function.

The more precisely we measure a particle's position, the less we know about its momentum. When the detector is turned on, the wave function collapses and the electron behaves like a classical particle.