The assumption underlying many of our efforts at space exploration is that to explore fully, humans must physically travel to the place being explored. This assumption engenders the view that it's OK to send machines to do the preliminary observations, but that the manifest destiny of space exploration is for humans to travel there, that our future is to travel to other planets, perhaps colonize some of them, and maybe even travel to other stars.

More than a century of science fiction and other popular lore have ingrained that view in our collective consciousness, fixing it as firmly in our minds as the concept of Manifest Destiny was to early American settlers. But romantic as it sounds, there are some very real problems with the viewpoint that the goal of space exploration is to send humans to other celestial bodies.

The key to the first part of the problem is the phrase "far, far away." Never mind galaxies -- even the nearest stars are so distant as to defy human comprehension. To put it in a scale we can more readily understand, consider the following:

Let's say that the entire universe was shrunk to about one five-billionth of its true size, a scale that conveniently makes the sun about the size of a basketball. You might think this scale would make the entire solar system only a few yards across, but that is because few of us really grasp the scale of things in the cosmos.

On that scale Mercury, the nearest planet to the sun, would be a tiny dot about 1 millimeter across at a distance of 36 feet (11 meters) from the "sun." The next planet -- Venus -- would be a dot 2.5 millimeters across and 67 feet (20 meters) away. Our huge beautiful Earth would become a tiny dot the same size as Venus, but 93 feet (28 meters) from the basketball-sized sun.

But those are only the inner reaches of our solar system. From there outward, the distances really start to grow. Mars would be another pinhead 142 feet (43 meters) away. Jupiter, a ball 1-inch (2.5 centimeters) in size, would sit 480 feet (147 meters) away, while Saturn, a slightly smaller ball, would be placed almost 900 feet (270 meters) from the "sun" -- and so on out to distant Pluto, another tiny pinhead, circling the "sun" at an average distance of well over half a mile (over 1kilometer).

Not quite what most of us imagine -- is it -- that if the sun were the size of a basketball, the solar system would still be more than a mile across?

What about the nearest star? That's where the distances become truly insurmountable. On that scale the nearest star would be almost 5,000 miles (8,000 kilometers) away. If our basketball-sized sun were in downtown Los Angeles, distant Pluto would be a few blocks away, but the nearest star would be another basketball somewhere in the North Atlantic, near Greenland.

It is those enormous distances that make travel to the stars something that humans will probably never accomplish or even attempt. The fastest speed any vehicle carrying people has ever reached is 25,000 miles (40,000 kilometers) per hour, at which speed a voyage to the nearest star would require over 100,000 years. Even assuming a tenfold increase in speed, a one-way trip would still require over 10,000 years, a period of time longer than the history of civilization.

Some proponents of future space travel pin their hopes on methods of travel that "cheat" physical distances, such as space warps, faster-than-light travel, etc. These sorts of devices are staples of science fiction, but in the real world there is absolutely no evidence that any such thing can be built. (There are conjectures about such things, but conjecture is not evidence.) At present there is more reason to believe in Merlin the Magician than in the possibility of humans traveling faster than light.

Traveling to other stars may be impossible, but what about colonizing other planets? Given enough money and effort it's certainly possible for humans to reach nearby planets, but could we truly colonize them?

Probably not, because there are no planets or moons with climates in any way close to that of Earth. Mars comes the closest, but as far as humans are concerned it's not very close at all. Consider that even with all our technology and modern means of travel we still find it difficult to sustain more than token colonies on Antarctica. Yet, compared with Mars, Antarctica is a human-friendly paradise -- and it is certainly much closer.

Some of the hopes of colonizing Mars or other bodies rely on the concept of "terraforming," the idea that we could seed the planet with special microorganisms that over time would completely transform the planet into something easier for humans to colonize. As with warp drives, this concept is also very unproven, but even if it could be made to work, a much larger question looms: What right do we have to destroy another planet and try to re-make it into something more to our liking? We are only now starting to realize the folly (and to a great degree, the arrogance) of trying to do such things on a much smaller scale here on Earth -- that should give us great pause before considering such wholesale destruction of what presently exists on a neighboring planet.

It's for those reasons that interstellar travel and remote colonies will likely always remain science fantasy. But to accomplish real exploration - the things we really can do -- requires that we abandon the assumption that a place is not truly explored until a human foot has trod on it. That, in my view, represents very outmoded thinking about what it means to be human and what it means to "be there." Consider, for instance, the transformation that has taken place in the meaning of human communication:

In the year 1850, conversing meant being at the same place at the same time. There was no concept of conversing at a distance.

By the year 1900 the telephone had been invented, but it was used chiefly for message passing. It was still ingrained in human thought that true intimate conversation required physical presence.

By 1950 it had become accepted that warm, intimate conversation was possible at a distance, as witnessed by the telephone conversations in romantic comedies of the day.

Now as the year 2000 approaches it is becoming accepted that not only do both parties not have to be in the same place, they don't even have to be there at the same time. E-mail has taken the art of letter writing and made it rapid and interactive, a medium by which many people share intimate thoughts and carry on close relationships, yet without real-time contact.

E-mail communication is a distillation of communication to its purest essence: Nothing physical is transmitted, not even sound, but only pure thought. By means of wire, radio and electrons the human mind is in effect freed from the body, able to travel at the speed of light to any point electrical signals can reach. Thought and knowledge can now propagate at speeds our bodies could never attain and go places our bodies never could -- all at a cost that is near nothing. It is this great release of mind and knowledge from material constraints that is powering the transition of our culture from one of physical interaction to one of mind-to-mind communication across space and time.

What is being demonstrated by the explosive growth of e-mail communication and the internet in general is what we have always known, but not always applied: That what is essential about humans is not their bodies, but their minds, that our minds can experience things for which our bodies were not present.

The extension of this concept to space exploration is the realization that for us to explore and experience another world need not require us to send humans there, but only our senses and intelligence. Rather than invest mind-boggling sums in sending a few humans to extremely hostile and distant environments, send machines to be our eyes and ears and let us experience the place at a distance. By this I do not mean conventional space probes sending back drips of data that only a Ph.D. can interpret. I mean very intelligent probes with the sensing and communication capability to send back a complete sense of their environment, enough data that at this end we can assemble it into a virtual world -- something that could then be experienced interactively by anyone.

This is a concept I'll call "tele-presence" -- the ability to experience another world or another locale via remote sensors. It's similar in concept to remote-controlled probes used for deep-sea exploration, except that to overcome the lags in communication with other worlds the probe would have to be sufficiently intelligent to gather an ongoing stream of environmental data and to make a few basic choices for itself (such as not propelling itself over a cliff).

We have already had some sample of this with the recent Mars Pathfinder probe. Because the probe was equipped with stereo vision, it was possible to get a 360-degree, three-dimensional view of Mars. By completely mapping its surroundings, the probe allowed us to look around Mars and view the landscape in any direction with binocular vision as we have on Earth.

Of course the Pathfinder probe had limitations, such as not being mobile. (Even the rover was very limited in its mobility.) But future probes are already in the works that will be able to move around intelligently and send back more data -- both of which are steps towards providing us with a greater sense of the environment on the distant planet.

This change in mind-set has some very practical and immediate advantages. Today when we talk about plans and budgets for future space exploration, we often do so with the assumption that we will be sending humans wherever we can. That assumption makes for huge budgets, and it is those enormously high costs -- hundreds of billions to send a few people to Mars, for instance -- that chiefly accounts for public and governmental opposition to such ventures.

But if instead we plan to send machines to be our eyes and ears, the costs are much, much lower, and the public and government are much more willing to fund such voyages. Because budgets and resources will always be finite and always in contention, we will achieve far more in space exploration if we find ways to explore the cosmos without breaking the bank.

The concept of tele-presence offers another advantage, too: Sending our minds and senses rather than a few bodies makes for a type of space exploration that can be shared not only by a few astronaut heroes, but by everyone. The tiny Mars rover caught the fancy of people worldwide not only because of what it saw, but because we were all able to share in its experience. The same would be true of any other remote space probe. It becomes the remote eyes and other senses of not just a handpicked few, but of everyone in the world at once.

This ability for everyone to participate in the exploration has advantages not only for gaining popular support, but also in maximizing the scientific discovery by bringing more minds to bear. We've already experienced this with the Pathfinder probe: Because the Pathfinder images were directly available on the internet, a college student in Nevada, Stephen Metzger, was able to apply his own color filtering and image processing methods to Pathfinder images. He discovered the existence of "dust devils" (miniature tornadoes) on the martian surface, something that the Pathfinder science team had been looking for but had been unable to find. Who knows how much more we will discover as a result of millions of co-explorers taking part in the exploration, the experience and the analysis.

This vision of space exploration makes space exploration more a voyage of the mind than the body. It's an enterprise in which not just a few, but all of us can participate -- and that requires some re-thinking. Let's quit focusing on the heroes who might travel to other worlds. Instead let's think of how we - you, me, everyone -- will explore those worlds. If you could immerse yourself in a "virtual" remote world, what would you want to look at? What would you want to see? What could you notice or discover before anyone else?

It's all within our reach if we can adjust our thinking to this new concept of exploration. This change of mind-set, when we achieve it, will greatly accelerate our progress in space exploration, truly launching a new age for humans as creatures at home in the cosmos.