Electromagnetic scattering is the physical effect of an electromagnetic wave, such as light or radio waves, hitting an object. Instead of proceeding in a straight line, as light waves do unimpeded, the light refracts or bounces off of microscopic textures in the object. Electromagnetic scattering is often responsible for the appearance of color, and has several distinct forms.
Given enough knowledge about the scattering particles and waves, prediction of how light will scatter is possible. The process can also work in reverse, as scientific observation of scattering can provide information about the incoming wave and the particles that that are scattering it. The study of scattering has lead to important advances in several areas, including computer-generated imagery, radar, and medical technology.
Why the sky is blue is a popular question that can be explained by electromagnetic scattering. Rayleigh scattering is based on the experiments of an early 20th century English scientist, John Strutt, the third Baron of Rayleigh. His work was conducted on the scattering effects of light waves on particles smaller than the incoming waves. Because blue has a short wave length, it is particularly susceptible to scattering as it bounces off gas particles of the air surrounding Earth. Red, yellow and orange hues are much longer wavelengths, which is why they are only visible in the sky when looking near or at the sun.
Because of the small size of scattering particles in Rayleigh scattering, the shape of the particles is not considered significant. Larger scattering centers are covered by the Mie theory of electromagnetic scattering, named for German physicist Gustav Mie. Mie determined that changes in color and opacity are determinant on the size and shape of the scattering center. His work is considered particularly useful in understanding electromagnetic scattering through hazes or clouds.
Both Rayleigh and Mie’s solutions are considered elastic, meaning that the scattering of waves does not significantly weaken their energy. Several other forms that deal with energy shifts due to electromagnetic scattering also exist, including Brillouin, Raman, and Compton scattering. Compton scattering is considered particularly significant, as it gives evidence that light can have properties of both a wave and a stream of particles. Inelastic electromagnetic scattering is used in several fields, including astrophysics, X-ray technology, and in measuring the elastic response of living tissue.
Electromagnetic scattering is, at its basis, a simple concept, visible in every day situations. The scientific study of scattering is extremely complex, and even the various solutions listed above do not fully explain the effects and results of all scattering situations. What has been discovered has lead to tremendous scientific innovation in imagery techniques, as well as letting us understand at last exactly why the sky is blue.
