Why is light both a wave and a particle?
Quick Answer
Light behaves like a wave in interference and diffraction, but like particles called photons when it exchanges energy. This wave-particle duality is a central result of quantum physics.
The Full Story
Experiments show that light can spread, interfere, and diffract like a wave, yet it also arrives in discrete packets of energy called photons. The photoelectric effect, explained by Albert Einstein in 1905, showed that light ejects electrons only when individual photons carry enough energy. Quantum theory reconciles these observations by treating light as a quantum object that does not fit classical categories perfectly. In modern physics, the behavior you observe depends on how the light is measured. This duality is not a contradiction; it is a feature of nature at small scales.
Key Facts
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