# Symmetry

## Symmetry Topics

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### Symmetry operation

Symmetry operations include the improper rotation, inversion operation, mirror plane, and rotation. Together, these operations create 32 crystal classes corresponding to the 32 point groups.The inversion operation takesand is denoted . When used in conjunction with a rotation, it becomes an improper rotation. An improper rotation by is denoted (or ). For periodic crystals, the crystallography restriction allows only the improper rotations , , , , and .The mirror plane symmetry operation takesetc., which is equivalent to . Invariance under reflection can be denoted or . The rotation symmetry operation for is denoted (or ). For periodic crystals, crystallography restriction allows only 1, 2, 3, 4, and 6.Symmetry operations can be indicated with symbols such as , , , , , and . 1. indicates rotation about an -fold symmetry axis. 2. indicates improper rotation about an -fold symmetry axis. 3. (or ) indicates invariance under translation. 4...

### Symmetry

An intrinsic property of a mathematical object which causes it to remain invariant under certain classes of transformations (such as rotation, reflection, inversion, or more abstract operations). The mathematical study of symmetry is systematized and formalized in the extremely powerful and beautiful area of mathematics called group theory.Symmetry can be present in the form of coefficients of equations as well as in the physical arrangement of objects. By classifying the symmetry of polynomial equations using the machinery of group theory, for example, it is possible to prove the unsolvability of the general quintic equation.In physics, the extremely powerful Noether's symmetry theorem states that each symmetry of a system leads to a physically conserved quantity. Symmetry under translation corresponds to momentum conservation, symmetry under rotation to angular momentum conservation, symmetry in time to energy conservation,..