It is commonly thought that light travels in a straight line. In fact, light is a wave, and, like all waves, it can be made to bend around corners and obstacles. This bending of light is called diffraction. Diffraction is a phenomenon found in all waveforms. It is what causes sound to be heard around corners and waves to fill an enclosed harbor. As a wave encounters an obstacle, a corner, a sharp edge, or a narrow aperture, a new wave begins from that point and radiates out in a circular pattern.

The first person to recognize diffraction was the seventeenth century Italian scientist Francesco Grimaldi. He noticed that shadows do not have sharp edges; rather, they possess bright lines just within the shadow's edges. As he looked more closely he found a series of fainter lines that became dimmer as their distance from...