What is symmetry?

Informally, an object or structure is symmetrical (or equivalently, it has a symmetry) if it looks the same after a specific type of change is applied to it. The object or structure can be material, such as a person, crystal, quilt, floor tiles, or molecule, or it can be an abstract structure such as a mathematical equation or a series of tones (music). The nature of the change can be similarly diverse, ranging from such simple and intuitive operations as moving across a regularly patterned tile floor or rotating an eight-sided vase, to complex transformations of equations or in the way music is played.

圖片參考：http://upload.wikimedia.org/wikipedia/en/thumb/3/3a/Sphere_symmetry_group_o.svg/200px-Sphere_symmetry_group_o.svg.png

This article looks at symmetry from three perspectives. The first is that of mathematics, in which symmetries are defined and categorized precisely. The second perspective the application of symmetry concepts to science and technology. For example, symmetries turn out to underlie some of the most profound results of modern physics, including aspects of space and time. Finally, a third perspective looks at the rich and varied use of symmetry in history, architecture, art, and religion.

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Symmetry is about two(or more than)lines that they parallel to the other lines.
The type of lines must be staight,horizontal or diagonal.
Symmetry can't formed by curve.

2007-02-24 21:48:57 補充：
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