But how can anyone predict where science and technology will take us? Although many scientists and technologists have tried to do this, isn't it curious that the most successful attempts were those of science fiction writers like Jules Verne and H. G. Wells, Frederik Pohl, Robert Heinlein, Isaac Asimov, and Arthur C. Clarke? Granted, some of those writers knew a great deal about the science of their times. But perhaps the strongest source of their success was that they were equally concerned with the pressures and choices they imagined emerging from their societies. For, as Clarke himself has emphasized, it is virtually impossible to predict the details of future technologies for more than perhaps half a century ahead. For one thing, it is virtually impossible to predict in detail which alternatives will become technically feasible over any longer interval of time. Why? Simply because if one could see ahead that clearly, one could probably accomplish those things in much less time - given the will to do so. A second problem is that it is equally hard to guess the character of the social changes likely to intervene. Given such uncertainty, looking ahead is like building a very tall and slender tower of reasoning. And we all know that such constructions are untrustworthy.

How could one build a sounder case? First, the foundations must be very firm - and Drexler has built on the soundest areas of present-day technical knowledge. Next, one must support each important conclusion step in several different ways, before one starts the next. This is because no single reason can be robust enough to stand before so many unknowns. Accordingly, Drexler gives us multiple supports for each important argument. Finally, it is never entirely safe to trust one's own judgments in such matters, since all of us have wishes and fears which bias how we think - without our knowing it. But, unlike most iconoclasts, Drexler has for many years courageously and openly exposed these ideas to both the most conservative skeptics and the most wishful-thinking dreamers among serious scientific communities like the one around MIT. He has always listened carefully to what the others said, and sometimes changed his views accordingly.

Engines of Creation begins with the insight that what we can do depends on what we can build. This leads to a careful analysis of possible ways to stack atoms. Then Drexler asks, "What could we build with those atom-stacking mechanisms?" For one thing, we could manufacture assembly machines much smaller even than living cells, and make materials stronger and lighter than any available today Hence, better spacecraft. Hence, tiny devices that can travel along capillaries to enter and repair living cells. Hence, the ability to heal disease, reverse the ravages of age, or make our bodies speedier or stronger than before. And we could make machines down to the size of viruses, machines that would work at speeds which none of us can yet appreciate. And then, once we learned how to do it, we would have the option of assembling these myriads of tiny parts into intelligent machines, perhaps based on the use of trillions of nanoscopic parallel-processing devices which make descriptions, compare them to recorded patterns, and then exploit the memories of all their previous experiments. Thus those new technologies could change not merely the materials and means we use to shape our physical environment, but also the activities we would then be able to pursue inside whichever kind of world we make.

Now, if we return to Arthur C. Clarke's problem of predicting more than fifty years ahead, we see that the topics Drexler treats make this seem almost moot. For once that atom-stacking process starts, then "only fifty years" could bring more change than all that had come about since near-medieval times. For, it seems to me, in spite of all we hear about modern technological revolutions, they really haven t made such large differences in our lives over the past half century. Did television really change our world? Surely less than radio did, and even less than the telephone did. What about airplanes? They merely reduced travel times from days to hours - whereas the railroad and automobile had already made a larger change by shortening those travel times from weeks to days! But Engines of Creation sets us on the threshold of genuinely significant changes; nanotechnology could have more effect on our material existence than those last two great inventions in that domain - the replacement of sticks and stones by metals and cements and the harnessing of electricity. Similarly, we can compare the possible effects of artificial intelligence on how we think - and on how we might come to think about ourselves - with only two earlier inventions: those of language and of writing.

We'll soon have to face some of these prospects and options. How should we proceed to deal with them? Engines of Creation explains how these new alternatives could be directed toward many of our most vital human concerns: toward wealth or poverty, health or sickness, peace or war. And Drexler offers no mere neutral catalog of possibilities, but a multitude of ideas and proposals for how one might start to evaluate them. Engines of Creation is the best attempt so far to prepare us to think of what we might become, should we persist in making new technologies.

MARVIN MINSKY
Donner Professor of Science
Massachusetts Institute of Technology