" Digital information is all ones and zeroes, which means memory cells are either charged or not charged. And charge is energy, so if one believes Einstein’s e=mc2, where e is energy, and m is mass, and c is the speed of light, then one must also believe that m equals e divided by c2, which is the same equation expressed differently, and which would imply that charge has detectable mass. The more songs and the more photos you put on your phone, the heavier it gets. Only by a trillion-billionth of the tiniest fraction of an ounce, but still. "

― Lee Child , Make Me (Jack Reacher, #20)