# Einstein: speed or velocity?

1. Mar 16, 2005

### philosophking

This is an interesting point that I just thought of while listening to one of Einstein's own lectures on his theory of relativity. In it he said that energy is equal to mass times the velocity of light squared.

But doesn't velocity have direction? And wouldn't this imply energy has direction? Obviously it doesn't. Speed, on the other had, is a scalar, so I would think it would be mass times the speed of light squared.

$$\vec{v}^2 = \vec{v} \cdot \vec{v}$$