米国の週刊誌タイム(6月19日号)の２１世紀テクノロジー特集

米国の週刊誌タイム(6月19日号)に２１世紀テクノロジー特集があり、その１つにナノテクノロジーがありました。ナノテクでnanobotと称するロボットが主役の啓蒙記事です。ナノボトが小さな腕で小さな電子脳により、原子をピックアップして操作し、ナノボトには万能操作型(general assemblers)と自己複製型(self-replicators)がある。とのこと。分かりやすい漫画が書いてあり、分子メデシンでは、ビリオンのナノボトが動脈硬化をなおしたり、バクテリアは駆除したり血栓を除去することが可能になったりとか、楽しい夢が語られています。かなりSFの世界に近い話しですが、21世紀全体を考えれば、大きな夢をかたることになると思われます。

米国の週刊誌タイム(6月19日号)の２１世紀テクノロジー特集
Time Vol. 155, No.24, June 19, 2000
Visions of the 21 st Century; Visions 21; our technology,
Will tiny robots build diamonds one atom at a time?

BY MICMAEL D. LEMONICK

That's just for starters. Nanobots will also make ships, shoes, steaks-and more nanobots. The trick is getting them to stop.
On its face, the notion seems utterly preposterous: A singe 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, may be 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 bulliant 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 wans 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 its possible, using tools like the scanning tunneling electron microsoope, 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. Theyve 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 akeady been constructed with conventional chip-etching technique. Those devices are gargantuan compared with what wiu be built in the future.)

Within 25 years, nanotechnologists expect to move beyond these scientific parlor tricks and create real, working nanomachines, complete with tiny "fingers" that can manipulate molecules and with minuscule electronic brains that tell them how to do it as well as how to search out the necessary raw materials. The fingers may well be made from carbon nanotubes-hairlike carbon molecules, discovered in 1991, that are 100 times as strong as steel and 50,000 times as thin as a human hair.

Their electronic brains could themselves be made from nano-tubes, which can serve both as transistors and as the wires that connect them. Or they may be made out of DNA which can be altered to carry instructions that nature never intended. Armed with the proper software and sufficient dexterity, nanorobot or nanobot, could construct anything at all.

Including copies of itself. To accomplish any sort of useful work, you'd have to unleash huge numbers of nanomachines to do every task-billions in every bloodstream, trillions at every toxic-waste site, quadrillions to put a car together. No assembly line could crank out nanobots in such numbers.

But nanomachines could do it. Nanotechnologists want to design nanobots that can do two things: carry out their primary tasks, and build perfect replicas of themselves. If the frst nanobot makes two copies of itself, and those two make two copies each, you've got a trillion nanobots in no time, each one operating independently to carry out a trillionth of the job.

But as any child who's seen Mickey Mouse wrestle with those multiplying broomsticks in "The Sorcerer's  Apprentice" can tell you, there's a dystopian shadow that hangs over this rosy picture: Wbat if the nanobots forget to stop replicating?

Without some sort of bult-in stop signal, the potential for disaster would be incalculable. A fast-replicating nanobot circulating inside the human body could spread faster than a cancer, crowding out normal tissues; an out-of-control paper-recycling nanobot could convert the world's libraries to corrugated cardboard; a rogue food-fabricating nanobot could turn the planet's entire biosphere into one huge slab of Gorgonzola cheese.

Nanotechnologists don't dismiss the danger, but they believe they can handle it. One idea is to program a nanobot's sofiware to self-destruct after a set number of generations. Another is to design nanobots that can operate only under certain conditions-in the presence of a high ooncentration of toxic chemicals, for example, or within a very narrow range of temperature and humidity. You might even program nanobots to stop reproducing when too many of their fellows are nearby. It's a strategy nature uses to keep bacteria in check.

None of that will help if someone decides to unleash a nanotech weapon of some sort-a prospect that would make computer viruses seem utterly benign by comparison. Indeed, some critics contend that the potential dangers of nanotechnolgy outweigh any potential benefits. Yet those benefits are so potentially enormous that nanotech, even more than computers or genetic medicine, could be the defining technology of the coming century. It may be that the world will end up needing a nanotech immune system, with police nanobots constantly at microscopic war with de-structive bots.

One way or another, nanotechnology is coming.

Vision 21; our technology
What is nanotechnology?
Nanotechnology is the science of creating molecular-size machines that manipulate matter one atom at a time. The name comes from nanometer - one one-billionth of a meter, which is roughly the size of these tiny devices.

What are nanobots?

Nanobots are workhorses of the nano-manufacturing world. They are, as the name implies, nanometer-scale robots that use tiny arms to pick up and move atoms and tiny electronic brains to direct the process. There are two basic types of nanobots: general assemblers and a special class of assemblers known as self-replicators.

Assemblers;

These cell-size robots may be equipped with fingers for manipulating matter, probes for distinguishing one atom or molecule from another and programs to tell the robots what to do.

Self-Replicators;

To build anything of any size, you need a lot of assemblers, and constructing them one by one is expensive and laborious. So most assemblers will need the additional ability to make copies of themselves. To make a skyscraper, for example, a handful of assemblers would first clone themselves into an army of trillions of tiny robots, then start building(see Nightmare Scenario).

The two sides of manufacturing;

The conventional approach is top-dowm: starting with large clumps of steel, wood, plastic, masonry and shaping them into the form you want. Nanotechnology is, by contrast, bottom-up: stacking individual atoms into useful shapes. We know that the bottom-up approach is possible because that's what biology does, assembling proteins from individual atoms and molecules, putting them together to form cells and layering cells upon cells to form large, complex objects such as sperm whales and giant Sequoia trees.

The Allications

Everthing in the physical world is made of atoms. Nanobots manipulate atoms. Thus nanobots could in principle make anthing from apples to airplanes. Nanobots will probably be made from carbon nanotubes, a new form of carbon that is astonishingly versatile.

Nanotubes;

Carbon molecules form a hezagonal mesh that curls into a cylinder like a tube of chicken wire. About 100 times as strong as steel and 50,000 times as thin as a human hair, they can serve as the structure of a nanobot. Acting as semiconductors, nanotubes are also ideal for building a nanobot's tiny microprocessor brain.

Molecular Medicine;

Streaming through the body by the billions, nanobots could chip plaque from arteries, gang up on bacteria and viruses, scour toxins from the bloodstream, repair broken blood vessels - and dozens of jobs doctors haven't dreamed of yet.

Environmental Cleanup;

Specialized nanobots dumped into an oil spill, a toxic-waste site or even a polluted stream could seek out and find dangerous molecules, remove them or change their their chemical structure one by one to render them harmless - or even beneficial.

Electronics;

The advantages of smaller computers - more speed, more money -are well known. But building matchbox-size supercomputers is too delicate a job for conventional mass manufacturing. Nanobots could do it easily, laying down circuits(made of nanotubes) molecule by molecule bwithout a single mistake.

Futuristic Materials;

A diamond's extraordinary clarity and strength make it an ideal building material, but also terribly hard to work with. Nanobots, however, could make diamonds in any shape at all - a sheet a few millimeters thick, say, to make a scratchproof window. And because the basic feedstock is ordinary carbon, these diamonds are as cheap as glass.

Nightmare Scenario;

Self-replication is the best way to build a few trillion nanobots in a hurry: each one makes two more, and each of those makes two and so on. But if they don't stop, the entire planet could rapidly be reduced to a teeming mass of robots. Nanotechnologists plan to program their tiny creations to stop reproducing after a certain point. But it takes only one rogue self-replicator to cause a disaster. If you thought computer viruses were a problem...