# Relativistic invariance

1. Apr 18, 2007

### gulsen

In Feynman lectures in physics v2 28-6, Feynman points out that we can add a constant times $\phi$ to D'Alembertian without distrupting the relativistic invariance. How and why?? Can someone work out a mathematical proof?

2. Apr 18, 2007

### lalbatros

The sum of two invariant quantities is an invariant quantity.

3. Apr 19, 2007

### Mentz114

The derivative of a constant wrt any variable is zero.