On its face, the notion seems utterly preposterous: a single technology so incredibly versatile that it can fight disease, stave off aging, clean up toxic waste, boost the world's food supply and build roads, automobiles and skyscrapers--and that's only to start with. Yet that's just what the proponents of nanotechnology claim is going to be possible, maybe even before the century is half over.

Crazy though it sounds, the idea of nanotechnology is very much in the scientific mainstream, with research labs all over the world trying to make it work. Last January President Clinton even declared a National Nanotechnology Initiative, promising $500 million for the effort.

In fact, nanotechnology has an impeccable and longstanding scientific pedigree. It was back in 1959 that Richard Feynman, arguably the most brilliant theoretical physicist since Einstein, gave a talk titled "There's Plenty of Room at the Bottom," in which he suggested that it would one day be possible to build machines so tiny they would consist of just a few thousand atoms. (The term nanotechnology comes from nanometer, or a billionth of a meter; a typical virus is about 100 nanometers across.)

What would such a machine be good for? Construction projects, on the tiniest scale, using molecules and even individual atoms as building blocks. And that in turn means you can make literally anything at all, from scratch--for the altering and rearrangement of molecules is ultimately what chemistry and biology come down to, and manufacturing is simply the process of taking huge collections of molecules and forming them into useful objects.

Indeed, every cell is a living example of nanotechnology: not only does it convert fuel into energy, but it also fabricates and pumps out proteins and enzymes according to the software encoded in its DNA. By recombining DNA from different species, genetic engineers have already learned to build new nanodevices--bacterial cells, for example, that pump out medically useful human hormones.

But biotechnology is limited by the tasks cells already know how to carry out. Nanotech visionaries have much more ambitious notions. Imagine a nanomachine that could take raw carbon and arrange it, atom by atom, into a perfect diamond. Imagine a machine that dismembers dioxin molecules, one by one, into their component parts. Or a device that cruises the human bloodstream, seeks out cholesterol deposits on vessel walls and disassembles them. Or one that takes grass clippings and remanufactures them into bread. Literally every physical object in the world, from computers to cheese, is made of molecules, and in principle a nanomachine could construct all of them.

Going from the principle to the practical will be a tall order, of course, but nanomechanics have already shown that it's possible, using tools like the scanning tunneling electron microscope, to move individual atoms into arrangements they'd never assume in nature: the IBM logo, for example, or a map of the world at one ten-billionth scale, or even a functioning submicroscopic guitar whose strings are a mere 50 nanometers across. They've also designed, though not yet built, minuscule gears and motors made of a few score molecules. (These should not be confused with the "tiny" gears and motors, built with millions of molecules, that have already been constructed with conventional chip-etching technique. Those devices are gargantuan compared with what will be built in the future.)

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