Diffraction

Diffraction is bending of waves around sharp edges, into the region that would otherwise be a geometrical shadow -- a general property shared by every type of wave, sound, water and light alike. This appears to violate the rectilinear (straight-line) propagation of light assumed throughout ray optics, but diffraction is only prominent when the size of the diffracting obstacle or aperture is comparable to the wavelength of the wave. This is why sound waves, whose wavelengths are large and comparable to everyday obstacles like doorways and buildings, diffract very noticeably around them, while light -- whose wavelength is far smaller -- s …