# Mechanics problem

## Homework Statement

Assuming we used Hamilton's Principle to obtain the most general form of the Doppler shift for light. We said that it better be that kaua≠0. Show that this is the case.

(Use local Minkowski coordinates)

## Homework Equations

Doppler shift equations

kaua≠0

## The Attempt at a Solution

I am still trying to understand the re-derivation of the Doppler shift for light.