Double-slit experiment

An experiment sends waves or particles through two narrow openings and records their distribution. The resulting interference pattern reveals wave behavior and, in quantum physics, superposition.

Young's interference experiment: Thomas Young's early nineteenth-century demonstration that light passing through two slits produces interference fringes. Its light-fringe demonstration established the experiment's classic form.
Wave interference: The reinforcement or cancellation that occurs when waves overlap. The alternating bright and dark regions are the experiment's defining pattern.
Thomas Young: An English physician and physicist who used interference experiments to support the wave theory of light. His two-slit work made the experiment a landmark in the debate over light.
Electron double-slit experiment: A double-slit experiment in which electrons produce an interference distribution at a detector. It tests whether individual material particles build up a wave-like pattern.
Measurement problem: The problem of explaining how definite outcomes arise from quantum states that evolve as superpositions. The experiment leaves open how a spread-out state yields one localized detection.
Quantum superposition: A quantum state can combine multiple possible states until measurement yields an outcome. A particle can have contributions from both slit paths before detection.
Diffraction: The spreading and bending of waves as they pass openings or encounter obstacles. Each narrow slit spreads the incoming wave before the two contributions overlap.
Augustin-Jean Fresnel: A French physicist who developed a mathematical wave theory of light and explained diffraction and interference. His wave optics supplied a fuller account of the fringes Young observed.
Neutron interferometry: A method that splits and recombines neutron waves to measure phase shifts and quantum effects. It extends two-path interference to controlled paths for massive particles.
Copenhagen interpretation: A family of quantum interpretations that treats measurement outcomes as fundamental and limits claims about unobserved properties. It frames the fringes through quantum probabilities rather than definite unobserved paths.

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