You know things, you child of the 21st century. You may not stop to think about it, but you know stuff to get along in the year 2000 that your hallowed progenitors could never have dreamed of. You know how to delete. You can pull down a menu. You know how to change the channel on your TV without getting out of your overstuffed chair, a luxury your grandparents did not enjoy. You know — or should know — how to keep your kid from downloading porn on the Internet. You even know the word download. You know other words too. Scary words. Ebola, mad cow, West Nile virus. At the very mention of these words, your mind knows to give you the creeps.

As always, knowledge is power. What you know gets you through your day. Protects your family. Keeps them safe. And what you need to know has changed — a lot. Twenty years ago, you took notes with a pen, not a pointer pushed across the face of a personal digital assistant. Twenty years ago you still thought a mouse was just a rodent. Had some prescient soul sidled up to you on the street in 1980 and said, "Listen, buddy, soon you're going to need to know how to operate a big glowing box on your desk by sliding a plastic thing around," you would have seen him as a madman, not a prophet.

By the year 2020, you will need to know stuff you can hardly guess today.

You've heard all this before. You're hip to this technology thing. You know the drill: Gadgets change; you adapt to the gadgets. You learn new buzzwords, talk the talk, and keep on going as humans have for millennia. But in doing so, you reduce technology to a heap of glorified hand tools, the equivalent of sticks chimps use to extract ants from a hole.

In 20 years it should be painfully clear that technology never just hands us tools; it grants us a passport to a world where choices multiply, desires are ignited, and new moral decisions confront us. Like an odyssey-starved traveler, you'll wander through a kind of exotic street fair, senses assaulted by too much information. You'll find yourself frazzled just trying to draw a bead on all the options, while a numbing calliope tune insists it's all great fun. A lot of what you'll encounter will just be cool, requiring nothing more than nimble minds and fingers.

By the year 2020, for example, you will need to know how to talk to your house.

Today your home contains dozens of appliances, each working independently. But someday you'll cross the threshold and everything will know you're home. The lights will flicker on, the air conditioner will have kicked in, the refrigerator will clamor to enumerate all the meals you can assemble with the groceries cached inside. In exchange for this convenience, you'll share your abode with a horde of circuit-heavy infants that constantly burble to each other and cry out for your care. If you're the one with mechanical flair at your house, when you come through the door at night, your spouse will be pulling you aside to whisper, "Honey, I need you to talk to the robot."

By the year 2020, you will have to learn to drive a more automated car.

You'll get behind the wheel of a smart car that avoids fender benders by braking before you even see danger looming. At a much later date, you will slip into a bucket seat as if at the movies — snacks, reading material, and sodas at the ready — sit back, relax, program the car, and over the freeways to grandmother's house you'll go. Like the toaster and coffeemaker back home, the car's sensors will monitor the activity and destinations of other cars on the road. "Going my way?" your vehicle will bleep in autospeak. "Indeed," responds the living room on wheels in the left lane. And the two will hitch up and rocket toward their common goal together. This technology will conserve fuel and may save lives, but the pleasure of driving as you know it will be gone. That's something you should know.

But perhaps by now you've realized that for every convenience technology bestows upon us, it chips away at something else. All of us, great souls as well as lost ones, must in time wrestle with this notion. If you are the poet Blake, in metered rhyme you decry the Satanic mills; if you are Kaczynski, you take to the hills and spit death by snail mail. Most of us simply acknowledge the trade-offs and move on.

Each time we do this, though, we march farther away from a world we can touch and comprehend in our bones toward one that we pray will work better.

Consider: In the year 2020, you'll identify yourself, gain access to homes and businesses, and board aircraft after a laser has measured the shape of your irises.

But the price will be loss of privacy. A record of your transactions, your daily comings and goings, will be just a keyboard tap away from others. Booting up your home PC has already become a public act. Meander the Web today, and almost every move you make is cataloged in service to the gods of commerce. They know what you're buying. What you listen to. Where you chat.

By 2020 you'll need to know how to clean up that electronic trail day in and day out.

"Say you were searching for information on hats," theorizes Jaron Lanier, computer scientist, musical composer, and virtual reality pioneer, "and you saw a link about hats, but when you got to it, it was actually a weird pornography site about hat fetishes. Then it turns out there's a record that you visited this site, and now you're getting bombarded with offers from people with hat fetishes. Furthermore, your friends are being contacted in case they have hat fetishes. All of a sudden you're the hat fetish person in your social circle, and you have to go in and undo it."

To throw the hounds off your scent, Lanier says, you could spend the afternoon downloading the Great Books or posing as a do-gooder in search of charities deserving of your drachmas.In time, you'll be wielding electronica for the same reasons medieval crusaders took up sword and lance: to ward off intruders. Rooting out destructive viruses and spam in your equipment will become old hat, as will the regular checks you'll be performing on your groceries and yourself. Tomorrow's Kaczynskis will be able to concoct harmful viruses and insinuate them into the food supply, or perhaps release pathogens in public places. You'll need to be ready for them. Daily computer checkups of your blood, saliva, or bodily waste will be effortless, the medical equivalent of checking your stock portfolio. "Real-time monitoring," says James Weiland, assistant professor of ophthalmology at Johns Hopkins, "will tell you in the morning what vitamin your body is low on and what to have for breakfast."

With all this new information, you'll stand a better chance of living well beyond your biblical allotment of threescore and ten. More than 200,000 centenarians will inhabit the United States in 2020 — why shouldn't you be one of them?

To reach that age you'll need to know enough to make more complicated medical choices: Do I want to jettison a limb and wait five years to regrow another?

Shall I allow a phalanx of nanobots to scrape the plaque out of my arteries or opt to replace the vessels altogether? "Amateurs may be fooling around with black-market genetic manipulation," says Marvin Minsky, one of the founders of the Artificial Intelligence Lab at MIT, "maybe extending their lives by lengthening their own telomeres, the ends of chromosomes believed to control life span. Or they might, in fact, be growing new features in their brain."

By the year 2020, science will understand the Creator's software well enough to tell you a great deal about the genetic hand dealt you and those you love. Science may even help you decide if you should quit loving them. These days it's not unheard of for one partner to investigate the other's background or assets before marrying.

In the future you'll need to access your betrothed's genetic map, see what diseases he or she is likely to contract, assess the appearance and health of your children, and perhaps even size up your love's mental health.

Of course, this swings both ways. In this world, you will be forced to ask: Do I want to know if I'm earmarked for heart disease or breast cancer? Do I want my potential spouse to know? If I know this, and my doctor knows, does it mean that my insurance carrier must know? If this last one scares you, it should. It could mean the end of health care as you know it.

This is just the beginning. Once we know the future, we're going to be tempted to rewrite the software. Clearly, it would be an act of kindness to reach into that fragile, permeable, four- or eight-cell being and rid it of the disease that cut short the life of its great-grandfather. But why wait for conception? Why not design your kid, toes up, out of whole cloth: the blue-eye gene, the blond-hair gene, the excel-at-lacrosse gene. Ban such tinkering, and citizens will merely scurry underground in order to conceive the perfect child.

If we can tear ourselves away from such selfish goals long enough to look around, we will have to face the fact that technology favors some and eclipses others.

Bill Robinson, who spent 30 years as an electrical engineer with Canada's Nortel Networks, has been thinking about this issue recently. "We spend our time and effort creating exciting new communications technologies," he writes, "yet half the world does not have access to a telephone. We use the Internet to order the latest novel, yet many people in the world don't have access to books. We are now discussing embedded processors to connect our refrigerators to bathroom scales and the grocery store, yet many children in the world go to bed hungry at night."

This grisly reality will be harder to hide from when our planet swells to 8 billion people in 2020. For Lanier, the most heartbreaking scenario is festering in the third world, where, he believes, the current generation of children — lacking food, lacking skills, lacking aid, lacking education — will be lost in the next techno-revolution. "What is going to happen to all these people as they start to age, say, 20 years from now?" he wonders.

"You're going to have to somehow live while you watch a billion people starve, which is going to be a new human experience. How will we do that?"

Good question. And just one of many difficult questions waiting. How can I choose between two genetic scripts for a child I have yet to know? How much of myself should I reveal on the Web? How will I cope with all these machines when they break down, including the self-replicating nanopests that may be residing in my flesh? In our zeal to be happy little technologists, we'll turn, much as we do today, to the Web for answers. And we'll perfect the art of being disappointed.

If any medium ever resembled the human unconscious, the Web is it: a place of hidden wonders, stray inane thoughts, peaks of brilliance, valleys of perversity. And no apparent governor. Type your query, hit return, and voilà! — 10,000 hits. Good luck shaking them down.

Even in 2020 you will always need to know if the facts you've dredged up are accurate and truthful.

With so many sources doling out information, you will need to know: What is he selling, and why is he selling it? Most unsettling is the fact that these precious touchstones are not permanent. They never will find their way to the library stacks. Instead we are moving closer to Orwell's nightmare: the truth ceaselessly modified, altered, edited, or altogether obliterated. Here today, gone tomorrow, with nothing but a bewildering ERROR 404 FILE NOT FOUND left in its place.

By then, you will no longer be a child of the 21st century. If anything, you'll be an elder, your mind and body augmented, your chromosomes refreshed, flexible computers woven into the four corners of your garments. On the one hand, your workload will multiply as you bat away each glitch resulting from the increased number of gadgets in your life.

On the other, you will be forced to take on moral questions no human has ever faced.

When will you find time to do that? How will you contemplate when everything is speeding up and time for reflection is practically nonexistent?

That's you in 20 years. Like the machine that inspired your age, you will be constantly scanning, processing, sifting, searching for a code to guide you through. And yet the key, the compass, the answer, was once offered in a temple at Delphi. What will you need to know in 2020? Yourself.

Reporting by Glenn Garelik. For more information about key people and topics discussed in the article, see Jaron Lanier's Web site at www.well.com/ user/jaron, the National Human Genome Research Institute at www.nhgri. nih.gov, and the Whitehead Institute for Genomic Research at www-genome.wi. mit.edu.