**Physics Notes - Herong's Tutorial Notes** - v3.22, by Dr. Herong Yang

Constancy of Speed of Light in Minkowski Diagram

This section provides a demonstration of constancy of speed of light using a Minkowski diagram.

The main assumption of the special theory of relativity is that the speed of light has the same value c measured in all inertial frames.

This assumption can be easily demonstrated by the Minkowski diagram. Let's follow a simple thought experiment described below:

- A light pulse travels from Bob's location for 6 seconds.
- The trajactory of the light pulse can be represented by a diagonal line between event O and event E, (X,cT)=(6,6), in Bob's stationary frame.
- So according to Bob's stationary frame, the speed of the light pulse is X/cT = 6/6 = 1 (c).

Now let's assume that Amy's frame is moving at a speed of v=0.6*c:

- The event E would be observed at (X',cT')=(3,3) in Amy's moving frame based on the Minkowski diagram given below.
- So according to Amy's moving frame, the speed of the light pulse is X'/cT' = 3/3 = 1 (c).

So the speed of light is 1 (c) in both Bob's frame and Amy's frame.

Table of Contents

Introducion of Frame of Reference

Introduction of Special Relativity

Time Dilation in Special Relativity

Length Contraction in Special Relativity

The Relativity of Simultaneity

►Minkowski Spacetime and Diagrams

What Is Lorentz Transformation?

►Constancy of Speed of Light in Minkowski Diagram

Time Dilation in Minkowski Diagram

Length Contraction in Minkowski Diagram

Relativity of Simultaneity in Minkowski Diagram

Invariant Spacetime Interval in Minkowski Diagram