Mirror, Mirror on the Wall,…
Symmetry: a feature of beauty.
Baroness Anne Louise Germaine de Staël-Holstein (1766–1817)
In everyday life, what we typically mean by «symmetry» is bilateral symmetry – the preservation of shape after a right-left exchange, as we see it when we look into a plane mirror. Up and down are determined by gravity, and front and back by locomotion. Bilateral symmetry is what humans and animals largely possess.
The Greek word symmetros means matching, well-proportioned, regular. In the extensive meaning of the word, symmetry means measurement relations that fit each other. What all symmetries have in common is that a certain shape or property stays the same despite changes. Symmetry is a feature of beauty, since things that are regular, in proper dimensions, repeating convey orientation. Who does not love the regularity of a heartbeat? Maybe you will only become aware when your pulse leaves its rhythm in the hall of mirrors.