What Is World Line?

This section provides a quick introduction of world line, which is the path of an object left in a spacetime frame of reference.

What Is World Line? A world line is the path of an object left in a spacetime frame of reference.

For example, if we define a spacetime frame of reference fixed on Sun and uses only 2 dimension x and y on the Ecliptic plane, the world line of Sun will be a straight line along the t-Axis as shown on the right hand side of the picture below.

In the same spacetime frame, the world line of Earth will be a helix line.

As comparison, if we look at a space frame of reference fixed on Sun and uses only 2 dimension x and y on the Ecliptic plane, the trajectory of Sun will be a stationary point and tre trajectory of Earth will be a circle. See the left hand side of the picture.

World Lines of Sun and Earth in Spacetime
World Lines of Sun and Earth in Spacetime

Last update: 2014.

Table of Contents

 About This Book

 Introduction of Space

 Introducion of Frame of Reference

 Introducion of Time

 Introduction of Speed

 Newton's Laws of Motion

 Introduction of Special Relativity

 Time Dilation in Special Relativity

 Length Contraction in Special Relativity

 The Relativity of Simultaneity

Introduction of Spacetime

 What Is Spacetime?

What Is World Line?

 What Is Light Cone?

 Moving Frames and Galilean Transformation

 Galilean Diagram of Moving Frames

 Minkowski Spacetime and Diagrams

 References

 PDF Printing Version