worldline

A worldline (or world line) is the path of an object (actually, a point, e.g., a specific location on an object) through time and space. If one were to ignore the effects of relativity, this would correspond to a function mapping the object's time to its position, but the concept was developed to demonstrate the effects of relativity, in which such a non-relativistic mapping depends upon the frame of reference. Given relativity, worldline is defined within a 4-dimensional spacetime within which the path is unique. The line in terms of some particular frame of reference can be produced through a transformation implied by the relativity theory: there is a transformation associated with special relativity and a more complex one that handles the additional characteristics of general relativity. (In the case of special relativity, the space and time axes directions of an inertial reference frame are simply a rotation of those of another.) Spacetime diagrams demonstrate some of the characteristics of worldlines.