Downloading e-books makes Kindle heavier?? I decided to post this in the Special & General Relativity forum because the professor in the article uses E=mc^2 as the basis for his calculations. For those who haven't heard about the recent article, http://www.telegraph.co.uk/science/science-news/8858355/E-readers-get-heavier-with-each-book.html" [Broken]. The main point of his explanation is below: Is his logic sound? My non-scientific mind says no, because I don't see how mass is created simply by changing the state of an electron on Flash memory. I realize GR/SR states that energy and mass (matter?) are interchangeable, and that one can probably calculate the mass of some energy, IF said energy was converted into mass (I think this is what the professor tried to do). But I don't think any mass/energy converting is actually happening inside a Kindle. So no, there is no weight gain because there is no energy/mass conversion. That's my simplistic view on all this. But I am just a mere accountant with an inquiring mind. I would love to hear from you folks who actually know about all this stuff and what your take is.