Downloading e-books makes Kindle heavier?

  • Thread starter Kkamann
  • Start date
  • #1

Main Question or Discussion Point

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," [Broken]. The main point of his explanation is below:

Prof John Kubiatowicz a computer scientist at the University of California, Berkeley, explained in the New York Times last week that storing new data involves holding electrons in a fixed place in the device's memory.

Although the electrons were already present, keeping them still rather than allowing them to float around takes up extra energy – about a billionth of a microjoule per bit of data.

Using Einstein's E=mc² formula, which states that energy and mass are directly related, Prof Kubiatowicz calculated that filling a 4GB Kindle to its storage limit would increase its weight by a billionth of a billionth of a gram, or 0.000000000000000001g.
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.
Last edited by a moderator:

Answers and Replies

  • #3
Staff Emeritus
Science Advisor
Insights Author

I think it would be more educational if the detailed calculations and assumptions were posted (I found a few article, none of them were very techinically oriented.)

But given that the basic premise is that the Kindle uses flash memory, and that the floating gates in the flash memory act like capacitors and store charge when books are downloaded, the rest seems to follow.

I'm not terribly familiar with the Kindle, so my biggest concern would be some crucial detail in their operation that's not accounted for that might affect the results, since they are already unmeasurably small.

One of the biggest issues might be including and accounting for how much the battery discharges when you download the data. But i think the intent of the exercise is to weight the kindle without its battery, attach the battery, download the data, detach the battery, then weight the kindle again.

Do you have any problem with the basic idea that a capacitor weighs more when it's charged than when it's discharged, or that a battery weights more when it's charged? Those are rather more common examples, and there isn't as much of a chance of some small critical detail being overlooked.
Last edited:

Related Threads on Downloading e-books makes Kindle heavier?