 Reasoning along these lines, Ohanian (2009, 2012) has argued that Einstein should not be credited with proving his famous equation. On the other hand, the physicist N. David Mermin (2011, 2012) claims that Ohanian’s demands for what counts as a “proof” in physics are too stringent. Even though we are considering a very specific interaction \(\boldsymbol{I}\), Mermin might say, we can understand that it is such a generic situation that we can confidently expect the result in all circumstances. Einstein himself believed that if \(\boldsymbol{I}\) involved a physical process in which there was an interaction between an electromagnetic field (say in the form of light) and an ordinary physical object, then \(\boldsymbol{I}\) was too specific to support the general conclusion that in all cases, a change in the rest energy of a body is accompanied by a change to its mass (i.e., rest-mass). 