What is "world line"

n. (context physics English) A path in spacetime, especially that traversed by an elementary particle from its creation to its destruction

The world line (or worldline) of an object is the path of that object in 4- dimensional spacetime, tracing the history of its location in space at each instant in time. It is an important concept in modern physics, and particularly theoretical physics.

The concept of a "world line" is distinguished from concepts such as an " orbit" or a " trajectory" (e.g., a planet's orbit in space or the trajectory of a car on a road) by the time dimension, and typically encompasses a large area of spacetime wherein perceptually straight paths are recalculated to show their ( relatively) more absolute position states — to reveal the nature of special relativity or gravitational interactions.

The idea of world lines originates in physics and was pioneered by Hermann Minkowski. The term is now most often used in relativity theories (i.e., special relativity and general relativity).