Joe Jacobson, coauthor of this article, believes that paper is a medium for the future. A medium that will build on its current ubiquity, but in an exciting and revolutionary way.

How important are paper and ink in today's world? One in seven US patents makes mention of either paper or ink - more than make mention of any type of electronics! Hard to believe? Look around your office or home and count the number of items that have some form of print on them, then compare that with the number containing chips.

The phenomenal readability and economy of printed ink on paper compels us, even in the digital age, to mark our behavior in this age-old manner. There is no lag when going from page 1 to page 44 of a book and then back to the appendix. So, too, with a newspaper. The presentation is immediate. No start-up, no logon, no button click, just paper where and how you expect it. Ink is great because every page and object gets its own. You don't have to go to a special corner of your desk to see ink. It's everywhere.

Electronic ink
One disadvantage to ink is that it's tough to erase. What we need is electronic ink that can be printed as freely onto as many different surfaces as traditional ink, but that is electronically mutable. It should be able to get up and walk away and change its shape, color, or intensity.

Joe's ink can do all this. His secret takes a page from carbonless paper. The back of carbonless paper has a thin coating composed of tiny capsules filled with clear ink. These capsules, about 1 million per square inch, are then broken with the pressure of your pen. When the clear ink oozes out the back, it chemically changes a colored ink on the page underneath.

Now, put that thin coating on the front of the page, and instead of putting ink in those capsules, imagine stuffing them with ping-pong balls one one-thousandth of their normal size, black on one side and white on the other. Then add some lubricant. Assuming you can control the rotation of the contents of each capsule - independently, electronically, and with the knowledge of where it's facing - you have electronic and reusable paper.

Given that the flat-panel display market is US$30 billion per year and growing, Joe is not alone in his quest. Enormous energy and thought is being given worldwide to making better computer displays. The current standard is the thin-film transistor LCD. It draws 2.6 watts, costs about US$1,000, and is constructed on glass. TFT displays are expensive because their million or more transistors are spread over the large screens. They consume generous amounts of power because the TFT backplane eats about a watt, as does the required backlight (transmissive LCDs let through less than 20 percent of the light). Because of the glass sandwich they are packed in, LCDs are not as rugged and cannot be used as flexibly as they should be. Technical improvements can still be made, and electronics companies around the world are investing billions of dollars in research and manufacturing facilities to do so.

So, how can Joe compete with these deep-pocketed giants? Simple: he looks at the problem differently. It's not a display he is building. It's ink. The advantage of his mind-set is that ink is more general than paper. It can go on almost anything, and it-s cheap. To make a display, just add a grid of addressing lines - which, by the way, is just another type ink (of the conductive variety) - to control the behavior of your e-ink.

Paper comes alive
Once you've got working e-ink, there is nothing to stop you from binding several hundred e-pages to construct an e-book worthy of the name.

Coming from the flat-panel LCD point of view, one would never envision an electronic book containing hundreds of displays. It would be much too heavy, too power hungry, and way too expensive, not to mention fragile. But e-ink gets you there. My grandchildren and Joe's children may carry around a single volume containing a whole library of books whose pages are used over and over again. No other book would be required.

But let's go one step further. When your printer is loaded with conductor e-inks, you need not stop at books. Everyone agrees that shipping newsprint is absurd. Yet few people read their news on a screen (I may be one of the few). In general, the screen is not in the right place - you are forced into a specific position and cannot always take the monitor with you. What screens do allow is easy change, be that video, personalization, or up-to-the-minute news. Not a new concept, by the way.

When Thomas Edison was 14, he set up his famous printing press in the baggage car of Port Huron's Grand Trunk Express. He received the daily news via telegraph, which he would then typeset and distribute as an up-to-the-hour newspaper on the train ride to work. The same thing can be done with e-ink.

Radio paper
It turns out that the conductive inks used to make e-paper can function as radio antennas. Other inks used in e-paper can be turned into radio transistors. This makes "radio paper," which can be as thin as notepad stock and sit on a coffee table or in your pocket, receiving FM news broadcasts. It "typesets" itself - every hour or day - with the latest news. With e-ink, a single piece of paper displays the news for years.

By extension, any surface can now be modified into a display. Wallpaper of the future will be sold by the gallon in one customizable color, billboards will be painted once, wine labels will tell you when to drink the bottle, T-shirts will be watches, and our trees might live a little longer.

This paper was coauthored with Joe Jacobson, assistant professor of µMedia at the MIT Media Lab.