Wave-particle duality is one of the most fascinating concepts in quantum mechanics. It tells us that quantum entities like photons and electrons can behave as both waves and particles, depending on how we observe them. This dual nature challenges our classical understanding of physics.
Light demonstrates clear wave properties through interference and diffraction. When two light waves meet, they can interfere constructively or destructively, creating patterns that are characteristic of wave behavior. This wave nature was well established in classical physics through experiments like Young's double-slit experiment.
However, light also shows particle-like behavior, most famously in the photoelectric effect. When light hits a metal surface, it can eject electrons, but only if the light frequency is above a certain threshold. This suggests that light comes in discrete packets of energy called photons, each with energy equal to Planck's constant times frequency.
The double-slit experiment perfectly demonstrates wave-particle duality. When we send individual photons through two slits, they create an interference pattern on the screen, suggesting wave behavior. But when we try to detect which slit the photon goes through, the interference pattern disappears, and the photon behaves like a particle. This shows that the act of observation fundamentally changes quantum behavior.