Relative direction

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The most common relative directions are left, right, forward(s), backward(s), up, and down. No absolute direction corresponds to any of the relative directions. This is a consequence of the translational invariance of the laws of physics: nature, loosely speaking, behaves the same no matter what direction one moves. As demonstrated by the Michelson-Morley null result, there is no absolute inertial frame of reference. There are definite relationships between the relative directions, however. Left and right, forward and backward, and up and down are three pairs of complementary directions, each pair orthogonal to both of the others. Relative directions are also known as egocentric coordinates.[1]


Cultures not using relative directions

Use of relative directions for reference is almost universal among human cultures. However, exceptions do exist. The Australian Aboriginal people the Guugu Yimithirr for instance, in their language have no words denoting the egocentric directions, but instead exclusively refer to cardinal directions, even when describing small-scale spaces. For instance, if they want someone to move over on the car seat to make room, they would say "move a bit to the east." To tell someone where exactly they left something in their house, they would say, "I left it on the southern edge of the western table." Or they would warn a person to "look out for that big ant just north of your foot." Other peoples from Polynesia to Mexico and from Namibia to Bali similarly have predominantly "geographic languages".[1]

Geometry of natural environment

If someone climbs a rope one meter up, they will have moved negative one meter down. Furthermore, they will not have moved left or right at all, nor forward or backward. One must mind the geometry of the environment when using relative direction to express motion, however. For example, if someone continues walking forward until they have almost circumnavigated the Earth, they will expend much effort only to move backward slightly. This is because Earth is (near-)spherical.

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