Wave-particle duality
Every particle, including electrons, has an associated wavelength, and every wave, including light, can transfer energy and momentum in discrete particle-like packets.
Practise this conceptLight behaves like a wave in some experiments — producing interference patterns — and like a stream of particles in others, like the photoelectric effect. Neither description alone is the full story; light is simply both, depending on what you ask it to do.
The surprise runs the other way too: matter, not just light, has wave properties. Louis de Broglie proposed that every particle, including electrons, has an associated wavelength, related to its momentum — a relationship strange enough that it was decades before diffraction experiments confirmed electrons really do produce interference patterns, just like light does.
This duality doesn't mean a particle is literally split into a wave half and a particle half at the same time — it's a description that has both behaviours available, showing whichever one an experiment is set up to reveal. It's a genuinely strange feature of nature at small scales, not a compromise or a contradiction to be smoothed away.
Key ideas
Requires: Photons and quanta, Interference and diffraction
Common misconceptions
- Only light shows both wave and particle behavior; matter particles like electrons behave purely as particles.
- A particle's de Broglie wavelength depends only on its mass, not its speed.
- Wave-particle duality means a particle is literally split into a wave part and a particle part at the same time.