World line

World line is a concept of relativity and describes the trajectory of an object in space-time.

The world lines of freely falling objects, ie objects that are subject only to gravity, are in accordance with the general theory of relativity geodesics in the curved space-time. This is also true for objects whose spatial paths are closed. Thus, in the relatively stationary with respect to the sun system, the global line of the ground, a screw whose axis is the time axis.

In connection with the special theory of relativity, the concept of world-line of Hermann Minkowski (1908 ) has been introduced. World lines are time-like for massless light-like particles and for mass -prone objects.

The concept can be generalized to higher-dimensional objects. Thus, the motion of a one-dimensional strings is given by the space-time surface a world, a two-dimensional object can be assigned to a world volume, etc.