The landscapes of the past are strewn with the bodies of what I like to call "false futures." A false future is simply something that was predicted, often with great confidence, but didn't happen.

I divide false futures into three types, which sometimes overlap:

1) It didn't happen yet but someday it may (it seems unwise, when making predictions, to attach specific dates to them). 2) It didn't happen, because it was based on the assumption that the future will be just like the past and present. 3) It didn't happen, because it was based on the assumption that the future will be different from the past and present.

The past century has seen scores of wrong predictions. I will offer just one example of each of the three kinds I listed.

"It didn't happen yet but someday it may." Vannevar Bush was a noted scientist and an adviser to presidents. In the mid-1940s, he predicted that nuclear energy would give us a world where electricity would be too cheap to meter. Others went farther: "With energy as abundant as the air we breathe, there will be no longer any reason to fight for oil or coal. By using atomic energy to mine the ocean for its vast mineral content, every nation will be able to obtain easily all the raw materials that it needs. There will be no such thing as a division of the world, on the basis of mineral resources, into the `have' and the `have-not' nations. Universal and perpetual peace will reign in the Era of Atomic Energy..."

Looking at the world today, this future appears ludicrously false. Yet I am reluctant to say that it will be wrong forever. The old predictions were based on nuclear fission, which is a working technology, although one highly mistrusted by a large fraction of the public. The future promise comes from nuclear fusion, which we do not yet have, but which might one day provide a clean and inexhaustible supply of energy.

"The future will be just like the past and present." From the 1930s through the 1950s, popular magazines were full of drawings of aircars. The commuter of the future would fly to work, rather than drive. Sometimes the predictions said you would not even need a car. A personal jet-pack, strapped to your back, would lift you into the air and carry you to your place of employment.

An aircar is not a dream. Aircars, and even personal jet-packs, have been built. The Naval Museum at Patuxent, Maryland, actually has a little one-man helicopter that I rather coveted when I saw it. The machine looks like a chair built inside a skimpy pyramidal scaffolding, with a rotor on top. My enthusiasm dampened when the display next to the helicopter stated that experiments with the device had ceased, following several "incidents" which included a fatality.

What was missed in the vision of personal aircars is the way in which the telephone, computers, faxes, and e-mail are changing business. Few people (I am tempted to say, no people) enjoy commuting. The very people who are rich enough to afford an aircar are the ones most likely to use the new technologies to avoid commuting to the office.

The commuter aircar also contains an element of another false future, "the future will be different from the past and present." Do you worry today when your teenage child says, "Is it all right if I borrow the car tonight? I promise I'll not drive faster than forty?" How would you feel about, "Is it all right if I borrow the aircar tonight? I promise I'll keep it below two thousand feet?"

I don't like the sound of that, either. Our children won't like it, either, when they themselves become parents. Parents and children and human nature in general are not likely to change in the next half century.

"The future will be different from the past and present." If human nature will not change, neither will the basic laws of economics. One attractive vision from the 1970s ignored this fact. The idea was that we would build self-sufficient colonies out in space, usually called "L-5 colonies" because they would be placed at a particular place, known as the L-5 location, in the Earth-Moon system.

These colonies were largely the brainchild of an inventive and charismatic Princeton physicist, Gerard O'Neill. The colonies that he and his supporters designed were large rotating cylinders, with effective gravity being provided by the centrifugal force of their rotation. Within the cylinder would be a complete and self-contained world, with its own water, air, soil, and plant and animal life. Supplies from Earth or Moon would be needed only rarely, to replace inevitable losses due to small leaks. The colony would pay for itself by collecting solar energy using vast space antennas and beaming it down to users back home. The idea was a huge success, and in 1975 the L-5 Society was formed to promote the further study and eventual building of such a colony.

Could such a colony be built? Almost certainly, yes. Will one be built in the next century or two? Almost certainly, no. The prospects for a large self-sufficient space colony fade as soon as we ask who would pay for it, and why. The cost, like the risk, is enormous, while the benefits are dubious. O'Neill and his supporters did what we all do when we really want something to happen: all their assumptions as to cost and feasibility were optimistic. In performing a more hardheaded analysis of the idea, Freeman Dyson, a forward-looking man who is strongly in favor of space exploration, calculated that an L-5 colony's cost/benefit ratio would be hundreds of times greater than any successful effort of the past. In other words, the idea is doomed by basic economics.

Doomed forever? I don't know. But doomed certainly, unless and until available wealth and technology far exceed what we have now.

Things will be the same - things will be different - things will be as I said but will take a little longer. We have been wrong far more often than right.

So, given our poor track record, will we go on making confident predictions about the future?

I make the confident prediction that we will.

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