back to article Official: Kindles get heavier as you add e-books

Download an e-book and your reader gets (microscopically) heavier. So says University of California at Berkeley boffin John Kubiatowicz in the pages of the New York Times. His argument: that energy is bound in the process of storing the book's bits in the reader's Flash memory and, according to Einstein's most famous equation …


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  1. Camilla Smythe


    If you download something then it takes power to do so so the battery will lose more mass than anything added by a book. In fact, thinking harder, it will be the battery supplying the mass for the book so ideally there would be no net change.

    Plus. Time Slows so 'longer to read' and Length Contracts so 'thicker'.

    1. Tony Smith, Editor, Reg Hardware (Written by Reg staff)

      Re: Eh?

      I think you're taking this story far too seriously.

      1. Northern Fop

        I am not a physicist

        But SURELY, as you're in the same reference frame as your ebook, then it only seems thicker and heavier to the chap watching you from the platform.

        Taking this too seriously, you say? This is not the Daily Mail, Tony, this is the Register - a veritable hive of pedants, scientists and SF afficianados. You asked for it, my dear chap....

        1. Tony Smith, Editor, Reg Hardware (Written by Reg staff)

          Re: I am not a physicist

          We like to chuck the odd metaphorical hand grenade into the commentard pit now and then.

          1. Anonymous Coward
            Anonymous Coward

            Wrong analogy

            Hand grenade? No, I think what you've done is more akin to swatting a beehive with a stick.

      2. zanto
        Paris Hilton

        Re: Re: Eh?

        I think you're taking that comment far too seriously.

      3. Camilla Smythe

        I think you're taking this story far too seriously.

        Oh.. Sorry.

        Still slightly bothered that the 'proponent' of the 'heavy book' theorem might have a swipecard to the large hadron collider and a set of pipe benders.

  2. Lon Bailey

    and what about Heisenberg's uncertainty principle ?

    Of course, as Kubiatowicz points out, the Kindle must get heavier.....but what about the uncertainty principle ? can you be sure the new book is actually on your Kindle !!

    1. Anonymous Coward
      Anonymous Coward


      Heisenberg does not apply to books loaded via USB, only those that go via Kindle email. Clearly an example of Something.

    2. hplasm

      I'm fairly sure the book is elsewhere-

      until I look to see if it's on the Kindle...

      1. Stuart Castle Silver badge

        A sort of "Schrödinger's ebook" then?

      2. John Bailey

        Only if it's a book about cats.. Written by a Mr Schrodinger.

    3. Dave Oldham

      And how does Heisenberg's uncertainty principle work?

      It works very well, apparently!

    4. Naughtyhorse


      clearly not until you've read it

  3. scrubber

    Velocity, not speed

    If the train is travelling west then it is going against the spin of the earth and so travelling slower than it would be 'at rest' (on the surface) and is therefore lighter.

    1. TheRealRoland

      But what about the shoe size

      of the driver?

  4. G0HJQ

    Font Size

    Ah yes, but if the book was used a smaller font size, would it be lighter?

    1. BristolBachelor Gold badge

      So this explains "Helvetica Heavy" ?

    2. Anonymous John

      No, but you can store more books in the Kindle.

  5. Will Gilpin

    Bad Physics?

    Does this article hold water?

    It's beren a long time since my degree, but it seems to me that the kindle maintains the memory state irrespective of whether there are books stored within it. Although one could imagine a computer memory using a scheme such as run-length encoding, or at least switching off entire chips when they are all zero, this is not how it works. The entropy of empty memory is the same as that of full memory under most designs.

    Furthermore, flash does not use energy to maintain state, so there is no energy difference between a zero and and one. Is there?

  6. John Burton


    I thought flash memory was erased by setting it all to '1' bits, and you could store stuff on it by selectively setting bits to zero. So adding books should, if anything, reduce the weight of all those '1's.

    1. NightFox

      Err, He110...

      But surely the 0's are heavier than the 1's? A 1 is more or less just a single straight line whereas a 0 is a full circle consisting of a single, much longer line.

      1. John Bailey


        If it works like my watch, then no.

        A "1" is lighter than a "0" obviously, but my watch has the LEDS light up for a 1, and stay off for a zero. So the light would be heavier... right?

        1. Paul_Murphy


          Why is it called light then? 'cos it's light! otherwise it would be called 'heavy' or 'massive.'

          What I want to know is where the numbers go when they're not being used - I reckon it must be magic, or pygmies or something.



  7. Amonynous

    Based on flawed assumptions?

    This might be correct if the device works in the simplistic manner which he assumes, i.e. "Assuming that all these bits in an empty four-gigabyte Kindle are in a lower energy state and that half have a higher energy in a full Kindle". Is that probable? I don't think so.

    The device must have been tested or formatted before it left the factory. If it was tested with repeated cycles of "10101010" then "01010101" to find any bad 'bits' abd this, which pattern was left in the memory (just marking the space as 'empty' in the file system), then 50% of the bits would be full when it left the factory.

    Depending on your language and choice of reading matter, adding e-books might actually reduce the number of bits that contain the higher energy electrons, thus reducing the mass of the device.

    Must try harder, see me after class.

  8. Mike Bell

    Don't Panic

    If that kind of thing worries you, for God's sake don't take it outdoors: the radiation pressure from the sun will make it weight about 30 nanograms more. That's the equivalent weight of about 30 billion e-books.

  9. Jerry of Oz

    Ones or Zeros?

    As the memory is in flash, the actual data will be an exces or deficit of electrons.

    Guessing that the flash starts off as zeros and has the ones programmed in by adding electrons, then any content will weigh more than no content.

    Alternatively, if the flash starts off as ones and has zeros set by the programming then the book will get lighter with new content

    Obviously YMMV

    1. BristolBachelor Gold badge

      I'm not a physisist either

      So where do all these extra electrons come from / go to?

      Do you get lightning around the Kindle when you upload books to it (I don't have one so I don't know). In a tight corner, could you use one as a tazer?

      1. Charles Manning

        They get wifi'ed back for recycling

        Amazon is an environmentally friendly company.

      2. Robert E A Harvey

        "Yeth Marthter"

        "Igor! the Kindles!"

      3. sisk

        "Stand back, I've got a Kindle"

        "Am I supposed to be scZZZPPHHHHTTT"

    2. Charles Manning

      It actually gets lighter

      Theis is NAND flash. The flash starts as ones, but gets programmed to zero. Programming cells is done by injecting positive charge into a floating gate (ie. electrons are removed).

      Each bit takes somewhere around 100 electrons to program. Assuming 50% of bits are programmed, that's an average of 50 electrons or 400 per byte.

      An electron has a mass of approx 10^-30kg. That makes each byte 4x10^-28kg, each GByte around 4x10^-19kg

      So the moral of the story is to download more and make it easier to move around.

  10. Mike007

    It gets worse

    If you read your kindle outside of a clean room then it will gain even more weight from dust landing on it. Actually thinking about it there are quite a lot of things that can make a kindle gain weight - I advise against taking your kindle anywhere that you don't have ready access to heavy lifting equipment just in case it gets too heavy for you to carry yourself.

    This would never happen with an iProduct, anyone claiming differently is probably holding it wrong.

  11. Peter Simpson 1

    Will we see

    Excess weight charges from the airlines?

    "Excuse me sir, how many books do you have stored on that thing?"

    //paperback in the pocket

  12. Michael H.F. Wilkinson

    What? No reference to L-space theory?

    Mine is the one with "Small Gods" in the pocket.

  13. Anonymous Coward
    Anonymous Coward

    "you have to wonder what the fuss is about"

    No fuss, it's simply for this chap to see his name splashed across the tech daily's!

    Please Reg, stop humouring these morons who only live for getting themselves some attention, you're better than that.

  14. vincent himpe

    physics ...

    'Empty' flash memory is sert to all '1'.

    Erasing a flash cell sets it to logic high...

    So writing means only zeroes get written....

    Thus : storing more books creates additional zeroes : tablet becomes lighter ...

    a factory fresh device will be heavier than a used one.

    Food for thought : deleting something only erases the index pointer... the data is still there until overwritten.

  15. Mike Moyle

    Okay -- I was only an art major...

    "The best thing to do, then, is not read your Kindle on the train, as the conveyance's velocity will only make it even heavier. And thicker."

    ...but wouldn't the Lorentz contraction make your Kindle appear THINNER on the train...? (Assuming, of course, that the Kindle is held vertically with the height and width perpendicular to the direction of motion.)

    The only way that it would appear THICKER would be if it was held with one of the LONGER axes pointing in the direction of travel, and even then the thickness would only APPEAR greater in proportion to the contraction of the affected axis, it wouldn't actually GET thicker.

    That's the way that I remember it, at least.

  16. Anonymous Coward
    Anonymous Coward

    E=MC² ?!

    You mean E=mc²


  17. Anonymous Coward
    Anonymous Coward

    I've also heard

    that if you shake your Kindle vigorously for a few minutes all the data compresses down to the bottom and you can fit even more books on it.

  18. Anonymous Coward
    Paris Hilton


    Do '0's weigh more than '1's because they are fatter?

  19. SPiT

    Oh, come on now

    This article really hasn't considered all the implications of E=mc².

    The dominant effects will be those representing the largest energy changes in the Kindle and from an electrical point of view this is clearly going to be the issue of battery charge so as you read the Kindle gets lighter.

    The next largest effect is likely to be the Kindle cooling off once taken out of your pocket. As it cools it loses energy and hence mass. Mind you this raises the question of what is meant by "heavier" as the reduced bouyancy due to the thermal contraction may actually be more significant. Once you start down the cheesepairing route there are an awful lot of remarkably small numbers to take into account.

    There are a lot more things like this that need to be considered before the internal energy state of the flash memory becomes a significant factor.

    And ... if you thought measuring the speed of neutrinos is difficult ...

  20. JeffyPooh

    Add a 'not' gate and the Universe may implode...

    If information has mass, and it's attributable to the electrons vice holes, then one well-placed 'not' gate would cause the entire Universe to explode in a flaming heap of illogic.

  21. TheRealRoland

    I feel a new Register constant coming up...

    The weight of a unladen Kindle...

    Come to think of it, is the air speed velocity of a unladen swallow part of it too?

  22. Cunningly Linguistic

    I've sussed it...'s all this physics shite, it's very heavy reading. That's why Kubiatowicz's Kindle got weightier.

  23. Pisnaz

    The next question is how does compression affect the weight of said ebooks, and what about different formats?

  24. Robert E A Harvey

    Hard Disks

    This idea surfaced (!) a couple of years ago for hard disks. There, IMHO, the refutation is easier: a magnetic domain weighs the same no matter what way up it is.

    Now I know less about the structure of eeprom cells, and it is not impossible that there are more minority carriers trapped in a '1' than a '0'. Are they symmetrical, these days, or a single junction? That might represent a difference in mass: but as others have said the battery would have to be topped back up before making any measurements.

  25. meteort


    Trying desperately to fill the monthly article quota?

    Sheesh! At least add some decent equations, or a tad bit more science.

  26. Skizz


    That equation does not mean that mass increases when there's more energy! It means that the energy in a thing is equal to its mass times c squared. It's one or the other, not both. Energising a flash ram does not increase the mass. The electrons don't get more mass, they just get more energetic (more speed, higher orbit, etc). When I climb some stairs my mass doesn't go up, even though I've gained a whole lot of energy. What do they teach the kids these days!

    1. philbo


      Thank you for posting that - if said "boffin" did actually use the E=mc^2 to suggest an increase in weight for all those higher-energy electrons and wasn't just taking the piss himself, el Reg (and the many other news outlets who presumably don't have anyone at all with a teensy bit of science to point out the fail) should simply have pointed and laughed.

  27. Simbu

    Sounds like troll physics...

    Surely every time you perform a data-altering on the flash drive (write / delete) you are using energy to change the data! So, over time and use the device will continue to absorb energy and mass.

    I predict in 100 years these devices will have absorbed so much energy the world will be covered in tiny black holes originating from many flash devices!

  28. Andy Farley
    Thumb Up

    Shit at maths?

    Don't worry, so was Einstein.

  29. GettinSadda


    A Kindle with no books loaded contains an equal number of electrons as it does protons (excluding any static charge), and a kindle stuffed with books contains the same balance. Is this boffin seriously suggesting that new atoms are added to the flash memory by writing data? Or that the existing atoms gain protons (and so change to become different elements)? Surely the electrons simply move from one part of the flash cell memory to another when a value is written.

  30. ElNumbre

    Amazon Fire v2

    The Fire v2 will come with a new feature where its memory is entirely filled with 1's. When you buy a book, it will 'unset' the bits it needs to, making it lighter over time. Or something.

  31. Wombling_Free

    No. um, maybe. er, um... whoa.....

    So does a stretched rubber band weigh more than an unstretched one?

    Potential energy /= mass, I thought. A bucket of water at the top of a mountain is the same mass as at the bottom, but has potential energy, right?

    BUT a stretched rubber band is storing energy in Van Der Waals forces & latent heat, so E=mc^2 yes, that increases the mass, right? just by not a measurable amount.

    So... a battery - they are like a rubber band, potential energy using a chemical-electric energy gradient. Electrons really want to get from - to +, but the overall number of electrons doesn't change. ie. the Battery (or cell) DOESN'T have an overall 'charge' in the classical physics sense. Am I right?

    Ok, um, I choose NO - the Kindle does not weigh more, as that would imply direct mass -> energy -> mass conversion, and stuff like that ALWAYS kicks out a few alphas, betas, gammas and probably a plethora of neutrinos.

  32. Zog The Undeniable

    Also, a wound spring

    is heavier than an unwound one, a charged battery is heavier than a discharged one etc. It's all unmeasurably small.

    The premise of the original article does seem wrong though (I know about entropy, but does it really store more energy having Flash bits ordered in the form of "Ulysses" than in a random pattern of ones and zeroes, which would look much the same to an alien lifeform?). And it's all outweighed by the material you just rubbed off the page-turning keys by using the Kindle. Look how polished the space bar is on a well-used keyboard.

  33. TheRealRoland

    So, aside from the fully-laden swallow

    We now have to deal with the weight of a fully-laden Kindle?

    And would Kindle be a 'brand' or more of a 'generic' term? Just like a Thermos Flask, or a thermos flask...

    So much to think about, so little time...

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