<P> Bringing to bear the lessons of the absolutism / relationalism debate with the powerful mathematical tools invented in the 19th and 20th century, Michael Friedman draws a distinction between invariance upon mathematical transformation and covariance upon transformation . </P> <P> Invariance, or symmetry, applies to objects, i.e. the symmetry group of a space - time theory designates what features of objects are invariant, or absolute, and which are dynamical, or variable . </P> <P> Covariance applies to formulations of theories, i.e. the covariance group designates in which range of coordinate systems the laws of physics hold . </P> <P> This distinction can be illustrated by revisiting Leibniz's thought experiment, in which the universe is shifted over five feet . In this example the position of an object is seen not to be a property of that object, i.e. location is not invariant . Similarly, the covariance group for classical mechanics will be any coordinate systems that are obtained from one another by shifts in position as well as other translations allowed by a Galilean transformation . </P>

What do space and time have in common