Why Do Mirrors Reflect?

A typical mirror consists of a sheet of glass with a thin coating of metal (usually aluminium or silver) on the back. When light hits the smooth metal surface, the free electrons in the metal absorb the incoming photons and re-emit them almost immediately at the same angle (the law of reflection: angle of incidence equals angle of reflection). Because the surface is extremely smooth — smooth at the scale of visible light wavelengths (400-700 nm) — the reflected light maintains its coherent pattern rather than scattering randomly. This specular (mirror-like) reflection preserves the spatial arrangement of the light, creating a faithful image.