# Photon absorption - Newton vs. Einstein

1. Apr 25, 2013

### zincshow

A note from Newton's Principles definition #4 in 1687:

Impressed Force - This force conflicts in the action only; and remains no longer in the body when the action is over.

In Einstein's second paper on relativity in 1905, he explicitly concludes:

"Radiation carries inertia between emitting and absorbing bodies". It is important that not only does something receive a "kick" from the momentum of the energy, but the internal inertia (i.e., the inertial mass) of the body is actually increased. (from mathpages.com)