Wave-particle duality describes how quantum objects such as photons and electrons can produce wave-like interference in some experiments while being detected as discrete particles in others.
Why “wave” and “particle” both appear
Light produces interference and diffraction, behaviors associated with waves, yet light is also exchanged in discrete packets called photons. Electrons and other matter particles can likewise form interference patterns even though detectors register localized events.
Quantum mechanics does not say that an electron is secretly switching between a tiny ball and a classical wave. Instead, the quantum state evolves according to wave-like mathematics while measurements produce particular outcomes.
The double-slit experiment
If individual quantum particles pass through an apparatus with two available paths and the experiment does not reveal which path each particle took, many detections can build an interference pattern. The probability distribution contains contributions from both alternatives.
If the apparatus records reliable which-path information, the interference changes or disappears. The result illustrates that the experimental arrangement determines which aspects of the quantum state can be observed together.
De Broglie matter waves
Louis de Broglie proposed that matter has a wavelength related to momentum. Electron diffraction later confirmed that particles of matter display wave-like behavior. The effect is most obvious for microscopic objects because their wavelengths are large enough relative to experimental scales.
For everyday objects the associated wavelength is extraordinarily small and interactions with the environment rapidly destroy observable quantum coherence, so classical behavior dominates.
What duality teaches us
Wave-particle duality is a reminder that classical categories are approximations. Quantum mechanics provides a single framework that predicts both interference and discrete detection events without requiring a quantum object to fit one classical picture at all times.
The same framework underlies modern technologies including semiconductors, lasers and quantum information systems.
