Did you ever have a beautiful dream, then try to describe it to a friend? It's not easy -- dreams often have more intensity of color and detail than we can put into words. Throughout history we've tried to record our dreams -- cavemen picked up bits of charcoal and drew images on the walls of their caves. Artists of the Renaissance drew beautiful, realistic portraits, and more recent artists have painted imaginary scenes of great beauty and meaning. Writers create fantasy worlds that help us understand our own. Composers write music that represents their dreams -- dreams we all can share.

All these ways of expressing ideas can be called "alternate realities." In modern times we have adjusted to things that are make-believe -- motion pictures, cartoons, television. And all these alternate realities have something in common -- we can't change the story. We have had to accept the artist's vision as our own -- until now.

Things are about to change. In computer laboratories all over the world, researchers are experimenting with a new medium of expression called "virtual reality." In virtual reality, powerful computers produce realistic images and sounds and, more important, respond to a person's voice and movements. It isn't television -- you get to decide what happens.

In the near future, you may sit down in a chair and put on a helmet that covers your face and blocks your view of the real world -- the world that young researchers have begun to call "vanilla reality." The helmet contains twin display screens, one for each eye, and stereo headphones. You will don special gloves that sense the movements of your hands and fingers, and special boots.

Then the computer will be turned on. Maybe you would like to travel to Mars and hike to the top of Olympus Mons, a great volcanic mountain higher than Mount Everest. Or perhaps you want to fly a powerful jet fighter at three times the speed of sound -- through the Grand Canyon.

Perhaps you are a chemist who wants to produce a new substance. Instead of trying to imagine how molecules fit together, you simply use your special gloves to pick up the molecules and join them -- if you try to make a bond that isn't possible, the molecule (and your hand) is pushed away.

Perhaps you are an architect who wants to walk through a building before it is built. Do the skylights pleasantly illuminate the garden in the central courtyard, as you planned? If they don't, you may reach up and move them, or change their size. You may move the doors and windows to a better position. Is a hallway too narrow? You just push against the sides with your gloves.

Or perhaps you are just a dreamer -- you want to create flowers and birds never seen, or travel across the clouds. You want to swim through the ocean with whales and dolphins. Maybe you want to build a dream world and share it with others.

Does this sound like science fiction? Some of what I describe lies in the future, but the stories about the chemist and the architect have already happened.

Virtual reality has been possible for about a decade, but only at very high cost. Some applications have been designed anyway, simply because they are less expensive than the alternatives. For example, airline pilots train on "flight simulators," virtual reality environments so realistic and trusted that the first time a pilot actually flies an airliner, there are passengers on board. Astronauts train to fly the NASA Space Shuttle on simulators also, even though the Shuttle is very heavy and difficult to fly and land. As with airline pilots, the first time an astronaut flies the Shuttle, it is during a mission, and (because the Shuttle glides to a landing with no fuel available) he has one chance to get it right.

We should remember the main reason we are able to read -- Gutenberg's invention of the printing press made books inexpensive. And once again, it is an economic change that will bring virtual reality into our lives -- computers are quickly becoming less expensive. We will be able to use virtual reality to solve many kinds of problems, or just to entertain ourselves, at no great cost.

Some may object that virtual reality will be like television, only worse. I agree the possibility exists, but I hope virtual reality is granted the legal protection that writing and speaking have now. I think the power of virtual reality to solve scientific problems, to provide a medium for artistic expression, greatly exceeds its negative aspects. Here are some ways virtual reality might be used and misused:

On the positive side:

Mathematical education: The most important obstacle to widespread understanding of higher mathematics is visualization. Once a person learns to "see" a mathematical truth, it becomes intuitive and lasts a lifetime, but that first vision is very hard to acquire. Many mathematicians found calculus to be the first interesting subject they were taught -- a beautiful description of motion and change. But most of us, unable to picture the equations, stop just short of calculus. Virtual reality can provide those first pictures and give us the necessary intuition, so we might become as comfortable with mathematical ideas as we are with words.

Scientific and technical endeavors: Using virtual reality, chemists are already exploring new molecular structures, saving much time and money, and return to a traditional laboratory to produce only those substances that look promising. In the future, biologists will be able to test vaccines and medicines without risk, using a sophisticated computer model of human cells. Architects and engineers will test earthquake-resistant designs by shaking them with computer earthquakes.

Artistic expression: Virtual reality will create an entirely new relationship between the artist and the observer. In the first phase, the artist will be able to produce works of great power simply because they will be three-dimensional moving images that surround the observer. In the second phase, the traditional barriers between artist and observer will come down, and both will contribute to the work. Finally, groups of people will be able to interact in a kind of "conversation" of  images and sounds.

Human communication: When physicists talk about Einstein's Theory of Relativity, they often have terrible problems communicating with words because the subject lies completely outside normal human experience -- force fields in space, time running at different rates in different places, and so forth. Virtual reality might provide a way to convey some of these complex ideas. Physicists would see gravitational and other fields, and feel the resulting forces through their gloves. Ordinary people might also want to use virtual reality to communicate everyday ideas with much greater effectiveness -- imagine a "birthday card" that literally touches its recipient.

And on the negative side,

Psychological effects: As virtual reality equipment becomes less expensive, people may become addicted to it and begin to prefer it to the normal world. They may lose the ability to distinguish between the virtual and real worlds, and place themselves or others in danger. They may become accustomed to their power to change anything in the virtual reality environment, and develop unrealistic expectations about the real world. Present-day television has a similar, but opposite effect -- people become accustomed to having no effect whatever on the outcome of TV stories, and they become similarly passive toward the real world.

Persuasion effects: Virtual reality may be used by corporations to shape public attitudes in a way that present-day advertisers cannot imagine. The very power of virtual reality to create a believable world could be misused to overwhelm an observer's emotional resistance. In the present day, we are trained to be intellectually skeptical of ideas expressed in words, but we will need something completely new -- call it "emotional skepticism" -- to resist the appeal of an environment of sound, motion and color.

Political effects: Persons convicted of crimes might be required to experience a virtual reality environment designed to modify their behavior. This possibility has some positive, but also very negative, aspects. Prisoners might be returned to society more quickly, unable to commit any further crimes -- but they might also be unable to disagree with government policies ever again.

In spite of these risks, I think virtual reality will come to be treated as a fundamental right. As it becomes less expensive, we will find more applications for it in our lives, just as we have with books. Perhaps we will educate ourselves to avoid its abuses, as we now educate ourselves about alcohol.

At this time, researchers are creating the bits and pieces of virtual reality -- new ways of communicating with a computer, and new ways for the computer to interact with us. At the Massachusetts Institute of Technology,  Margaret Minsky is designing a "texture simulator" that allows you to feel different computer-generated textures -- sandpaper, granite -- by touching a control handle and "dragging" it across the surface being imitated by the computer. This is the first step toward a tactile environment in which you will not only see objects in virtual space, but grasp and feel them as well.

In another demonstration project, an observer dons a helmet and pedals a bicycle through countryside scenes -- scenes produced by a computer. If you pedal the bicycle fast enough, you leave the ground and fly through the air as in the movie "E.T." I hope this idea is used often in the future, because it will keep people physically fit while they experience a make-believe world.

At present, these demonstrations require the use of very powerful and expensive computers -- personal computers are still too slow to provide a believable world with all the subtlety of a real-world scene, and the necessary motions and changes we expect to see in real life.

The simplest computer graphic programs show objects in two dimensions (width and height but no depth) and are reasonably quick to replace one image with another.  The next step in complexity is to add the third dimension of depth, then sources of light that cast shadows. Present-day small computers can create these more realistic images, but with limited detail. For example, you can buy programs today that give you a sense of flying an airplane through a sort of cardboard-cutout world.

To provide another jump in realism, the computer takes optical effects into account -- if you look through a goldfish bowl, the light rays from the room beyond are bent, just as in real life. Glass and mirror surfaces reflect other parts of the scene. Metal is shiny, and clay is not. This level of quality is called "photo-realism," and at first glance it is hard to say whether such an image is real or computer-genessrated. Figure 1 shows my photo-realistic image of a glass of coke. When I first generated this image, I wanted to find out whether my equations correctly imitated the real world -- would the straw look bent inside the liquid? So I filled a glass, put in a straw, and sure enough, I saw the same effect.

Figure 2 shows a pair of glasses resting on a printedss page. For photo-realism, the lenses in the glasses had to bend light rays and the shadows had to fall just as they do in real life. This image was successful, but required ten hours of personal computer time to generate.

Present-day computers are about as fast as they can be -- the messages inside the computer are already traveling at almost the speed of light, and cannot travel faster. So how can computers be made faster? Future computers will use many processors at once to solve a problem -- the computer will work like a symphony orchestra, each processor providing a small part of the result. This idea, now in development, is called "parallel processing," and scientists believe this is why we humans can still outperform computers -- we have many, many individual processes taking place at once.

We've been through many technological revolutions, and each time we measured an invention's success by how well it responded to our control and met our requirements. I believe we will deal with virtual reality in the same way -- for a while it will seem as alien as the first airplane in a sky filled with birds, but finally we will see its value and learn to fly it ourselves.

Virtual reality will allow us to explore make-believe worlds, worlds of pure mathematics, pure music, pure sensation. And, if we use this new resource wisely, we will acquire a greater understanding and appreciation for the real world.
