Young's double-slit experiment

An experiment in which light passing through two narrow openings forms alternating bright and dark fringes. Its interference pattern demonstrates light's wave behavior.

Wave interference: The combination of overlapping waves that produces reinforcement or cancellation. Light from the two openings overlaps, creating the experiment's alternating bright and dark bands.
Thomas Young: An English polymath whose work established evidence for the wave theory of light. He presented the interference experiment in support of light's wave behavior.
Single-photon interference: Interference observed when photons are sent through an interferometer one at a time. It shows that the pattern builds up even when photons do not arrive together.
Single-slit diffraction: The spreading and interference of waves passing through one narrow opening. It produces a diffraction envelope, unlike the repeated two-source fringes central to Young's setup.
Huygens–Fresnel principle: A principle describing each point on a wavefront as a source of secondary wavelets. It models the emerging light spreading from each narrow opening.
Wave theory of light: The account of light as a propagating wave, explaining phenomena such as interference and diffraction. Young used the pattern to argue against a purely corpuscular account of light.
Which-way information: Information identifying which alternative path a quantum system followed. Obtaining it can reduce or eliminate the interference pattern.
Mach–Zehnder interferometer: An interferometer that splits and recombines light along two separate paths using beam splitters. It tests path interference with distinct optical routes rather than two openings in a screen.
Path difference: The difference between the distances traveled by two waves to the same point. It determines whether the two contributions arrive in phase or out of phase.
Corpuscular theory of light: A theory that explains light as a stream of particles rather than a wave. The observed fringes challenged the simple particle model dominant in Newton's account.

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