# How can photons impart momentum to objects?

17 July 2012

## Question

How can massless photons impart momentum to objects like asteroids?

Dominic - This is actually a very common misconception because at school, of course, you're taught a lot of Newtonian physics where something without mass can't exert a force. It doesn't have momentum. But, in fact, a photon is a relativistic particle; and in relativity, energy and mass are equivalent to another. So, although the photon doesn't have any mass, it has momentum still, which is associated with its energy and that's significant because the photon is traveling at this relative speed of the speed of light. Einstein's theory of relativity has completely taken over from Newtonian physics. And that explains how the photon can have this momentum which it can impart to an asteroid...