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In physics, scattering means changing the direction of movement of a particle. The word is commonly used for the scattering of photons and electrons but applies to other particles as well. Photon scattering is considered one of the phenomena in radiative transfer (along with absorption and emission) and is sometimes equivalent to absorption followed by emission due to the energy gained from the absorption. The word scattering might be used if emission is immediately following the previous absorption, and the "scattering" concept might be stretched to include longer time intervals between if doing so does not affect the analysis. Some types of scattering:
Some types/models of photon scattering:
Note that some photon-scattering phenomena follow the pattern of classical (wave) electromagnetic radiation theory, whereas some do not, and are only explained by light's quantum nature.
The more-specific term, elastic scattering is used in particle physics for that in which kinetic energy is preserved (within an inertial reference frame), such that the same amount of energy comprises the kinetic energy of the particles on their new trajectory, none absorbed and converted some other form such as potential energy. Such scattering is analogous to a rubber ball so perfect that it bounces up to the same height it fell from. Thomson scattering is basically elastic, as is the scattering of atoms within monatomic gases. Inelastic scattering naturally means scattering in which some of the kinetic energy is absorbed, i.e., converted to some other form of energy.
Quantum theory includes theories to explain scattering, down at the particle-level.
The term scattering is also used regarding the dynamics of planetary systems, e.g., planets redirected from their orbits. The term may be similarly used for interactions between stars in "crowded" regions such as globular clusters and the centers of galaxies.