World-line

1. In the General Theory of Relativity, the four-dimensional world point or event trajectory of a particle represented graphically. In the presence of a gravitational field the world-lines of a freely moving particle and of light are curved.

2. In the Special Theory of Relativity of particle moving uniformly and progressing in a linear motion has a straight world-line but angularly inclined to the time coordinate axis. An angle of 45 degrees represents the world-line of light.

3. In Kabbalistic cosmology the green line which circles the world.