in·var·i·ant  (ĭn-vâr'ē-ənt)  adj.
in·var'i·ance n. |
invariance
in physics, the concept that the properties of particles such as atoms and molecules remain unchanged after being subjected to a variety of symmetry transformations or "operations." Since the earliest days of natural philosophy (Pythagoras in the 6th century BC), symmetry has furnished insight into the laws of physics and the nature of the cosmos. The two outstanding theoretical achievements of the 20th century, relativity and quantum mechanics, involve notions of symmetry in a fundamental way
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