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Wave–Particle Duality
Light and matter can act wave-like or particle-like depending on how the experiment is arranged.
Updated: 2026
Key ideas
One object, different behaviors
Electrons can make interference patterns yet arrive as discrete detection events.
The setup decides what appears
A detector that asks “which path?” removes interference and reveals particle-like outcomes.
Quantum theory unifies both
Wave functions evolve continuously; measurements produce discrete events.
Mental model
- Send particles one by one through two slits.
- Without path detection, an interference pattern appears over time.
- With path detection, the pattern disappears and behaves classically.
FAQ
Are particles secretly tiny billiard balls?
Not in quantum mechanics; classical pictures fail at small scales.
Are waves physically spread like water?
Not exactly. The quantum wave encodes probabilities and phase relations.
Why teach this early?
It builds intuition for uncertainty, measurement, and modern devices.