The most common
relative directions are , , , , , and . 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 directions, each pair
orthogonal to both of the others. Relative directions are also known as
egocentric coordinates.