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Professor of Journalism, New York University; formerly journalist, Science Magazine; Author, Proofiness: The Dark Arts of Mathematical Deception

For the first time, humans are within reach of a form of immortality. Just a few years ago, we had to be content with archiving a mere handful of events in our lives—storing what we could in a few faded photographs of a day at the zoo, a handful of manuscript pages, a jittery video of an anniversary, or a family legend that gets passed down for three or four generations. All else, all of our memory and knowledge, melts away when we die.

That era is over. It's now within your means to record, in real time, audio and video of your entire existence. A tiny camera and microphone could wirelessly transmit and store everything that you hear and see for the rest of your life. It would take only a few thousand terabytes of hard-drive space to archive a human's entire audiovisual experience from cradle to grave.

Cheap digital memory has already begun to alter our society, at least on a small scale. CDs have become just as quaint as LPs; now, you can carry your entire music collection on a device the size of a credit card. Photographers no longer have to carry bandoliers full of film rolls. Vast databases, once confined to rooms full of spinning magnetic tapes, now wander freely about the world every time a careless government employee misplaces his laptop. Google is busy trying to snaffle up all the world's literature and convert it into a digital format: a task that, astonishingly, now has more legal hurdles than technical ones.

Much more important, though, is that vast amounts of digital memory will change the relationship that humans have with information. For most of our existence, our ability to store and relay knowledge has been very limited. Every time we figured out a better way to preserve and transmit data to our peers and to our descendents—as we moved from oral history to written language to the printing press to the computer age—our civilization took a great leap. Now we are reaching the point where we have the ability to archive every message, every telephone conversation, every communication between human beings anywhere on the planet. For the first time, we as a species have the ability to remember everything that ever happens to us. For millennia, we were starving for information to act as raw material for ideas. Now, we are about to have a surfeit.

Alas, there will be famine in the midst of all that plenty. There are some hundred million blogs, and the number is roughly doubling every year. The vast majority are unreadable. Several hundred billion e-mail messages are sent every day; most of it—current estimates run around 70%—is spam. There seems to be a Malthusian principle at work: information grows exponentially, but useful information grows only linearly. Noise will drown out signal. The moment that we, as a species, finally have the memory to store our every thought, etch our every experience into a digital medium, it will be hard to avoid slipping into a Borgesian nightmare where we are engulfed by our own mental refuse.

We are at the brink of a colossal change: our knowledge is now being limited not only by our ability to gather information and to remember it, but also by our wisdom about when to ignore information—and when to forget.