In 1959 physicist Richard Feynman gave an after-dinner talk exploring the limits of miniaturization. He set out from known technology (at a time when an adding machine could barely fit in your pocket), surveyed the limits set by physical law and ended by arguing the possibility-even inevitability-of "atom by atom" construction.

What at the time seemed absurdly ambitious, even bizarre, has recently become a widely shared goal. Decades of technological progress have shrunk microelectronics to the threshold of the molecular scale, while scientific progress at the molecular level-especially on the molecular machinery of living systems-has now made clear to many what was envisioned by a sole genius so long ago.

Inspired by molecular biology, studies of advanced nanotechnologies have focused on bottom-up construction, in which molecular machines assemble molecular building blocks to form products, including new molecular machines. Biology shows us that molecular machine systems and their products can be made cheaply and in vast quantities.

Photo: PETER MENZEL NANOSCRIBE K. Eric Drexler conceived the concept of molecular machine systems (a component of one is shown in the background).

Stepping beyond the biological analogy, it would be a natural goal to be able to put every atom in a selected place (where it would serve as part of some active or structural component) with no extra molecules on the loose to jam the works. Such a system would not be a liquid or gas, as no molecules would move randomly, nor would it be a solid, in which molecules are fixed in place. Instead this new machine-phase matter would exhibit the molecular movement seen today only in liquids and gases as well as the mechanical strength typically associated with solids. Its volume would be filled with active machinery.

The ability to construct objects with molecular precision will revolutionize manufacturing, permitting materials properties and device performance to be greatly improved. In addition, when a production process maintains control of each atom, there is no reason to dump toxic leftovers into the air or water. Improved manufacturing would also drive down the cost of solar cells and energy storage systems, cutting demand for coal and petroleum, further reducing pollution. Such advances raise hope that those in the developing world will be able to reach First World living standards without causing environmental disaster.

Low-cost, lightweight, extremely strong materials would make transportation far more energy efficient and-finally-make space transportation economical. The old dreams of expanding the biosphere beyond our one vulnerable planet suddenly look feasible once more.

Perhaps the most exciting goal is the molecular repair of the human body. Medical nanorobots are envisioned that could destroy viruses and cancer cells, repair damaged structures, remove accumulated wastes from the brain and bring the body back to a state of youthful health.

Another surprising medical application would be the eventual ability to repair and revive those few pioneers now in suspended animation (currently regarded as legally deceased), even those who have been preserved using the crude cryogenic storage technology available since the 1960s. Today's vitrification techniques-which prevent the formation of damaging ice crystals-should make repair easier, but even the original process appears to preserve brain structure well enough to enable restoration.

Those researchers most familiar with the field of molecular nanotechnology see the technology base underpinning such capabilities as perhaps one to three decades off. At the moment, work focuses on the earliest stages: finding out how to build larger structures with atomic precision, learning to design molecular machines and identifying intermediate goals with high payoff.

To understand the potential of molecular manufacturing technology, it helps to look at the macroscale machine systems used now in industry. Picture a robotic arm that reaches over to a conveyor belt, picks up a loaded tool, applies the tool to a workpiece under construction, replaces the empty tool on the belt, picks up the next loaded tool, and so on-as in today's automated factories.

In principle, Drexler says, a molecular construction system called an assembler could build almost anything, including copies of itself.

Now mentally shrink this entire mechanism, including the conveyor belt, to the molecular level to form an image of a nanoscale construction system. Given a sufficient variety of tools, this system would be a general-purpose building device, nicknamed an assembler. In principle, it could build almost anything, including copies of itself.

Molecular nanotechnology as a field does not depend on the feasibility of this particular proposal-a collection of less general building devices could carry out the functions mentioned above. But because the assembler concept is still controversial, it's worth mentioning the objections being raised.

One prominent chemist speaking at a recent event sponsored by the American Association for the Advancement of Science asked how one could power and direct an assembler and whether it could really break and re-form strong molecular bonds. These are reasonable questions that can be answered only by describing designs and calculations too bulky to fit in this essay. Fortunately, technical literature providing seemingly adequate answers has been available since at least 1992, when my book Nanosystems was published.

Another well-known chemist objects that an assembler would need 10 robotic "fingers" to carry out its operations and that there isn't room for them all. The need for such a large number of manipulators, however, has never been established or even seriously argued. In contrast, the designs that have received (and survived) the most peer review use one tool at a time and grip their tools without using any fingers at all.

These examples point to the difficulty of finding appropriate critiques of nanotechnology designs. Many researchers whose work seems relevant are actually the wrong experts-they are excellent in their discipline but have little expertise in systems engineering. The shortage of molecular systems engineers will probably be a limiting factor in the speed with which nanotechnology can be developed.

It is important that critiques of nanotechnology are well executed, because vital societal decisions depend on them. If molecular nanotechnology as described here is correct, policy issues can look quite different from what is generally expected. Today most people believe that global warming will be hard to correct-with nanotechnology, excess greenhouse gases could be inexpensively removed from the atmosphere. Current Social Security projections assume increasing numbers of aged citizens in poor health. With advanced medical nanotechnology, tomorrow's seniors could be more active and healthy than they are now, bringing new meaning to the "golden years."

Likewise, we need to focus now on avoiding accidents and preventing abuse of this powerful technology. Solid work has been done on the problem of heading off major nanotechnology accidents. The Foresight Guidelines, available on the World Wide Web, sketch out proposed safety rules [see below].

But the challenge of preventing abuse-the exploitation of this technology by aggressive governments, terrorist groups or even individuals for their own purposes-still looms large. The closest analogy to this problem these days is the difficulty of controlling the proliferation of chemical and biological weapons. The advance toward molecular nanotechnology highlights the urgency in finding effective ways to manage emerging technologies that are powerful, valuable and open to misuse.

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Further Information:

Engines of Creation: The Coming Era of Nanotechnology. K. E. Drexler. Fourth Estate, 1990.

Nanosystems: Molecular Machinery, Manufacturing, and Computation. K. E. Drexler. John Wiley & Sons, 1992.