Imagine a technology so powerful that it will allow such feats as desktop manufacturing, cellular repair, artificial intelligence, inexpensive space travel, clean and abundant energy, and environmental restoration; a technology so portable that everyone can reap its benefits; a technology so fundamental that it will radically change our economic and political systems; a technology so imminent that most of us will see its impact within our lifetimes. Such is the promise of Nanotechnology.

by Kai Wu

    Nanotechnology, or more accurately, molecular manufacturing, is based on the idea that any chemically specified structure consistent with the known laws of physics can be built. As "bottom-up" manufacturing, nanotech will represent a radical departure from all previous technologies: any object or structure desired will be created atom by atom, instead of the crude bulk-matter shaping technologies now existent. The ability to assemble structures at the atomic scale will require the development of molecular assemblers: tiny, programmable robots able to provide precise positional chemical bonding. With the power of self-replication, assemblers can take advantage of exponential efficiency in creating desired products, and thus keep manufacturing costs to little more than the necessary energy and raw material. Atomically precise, fast and inexpensive manufacturing capabilities will have an enormous impact on society and open up undreamt of possibilities. And, perhaps, new nightmares as well.

"I, an atom in the universe, a universe of atoms..."
The late Nobel laureate Richard Feynman once said that if some cataclysm were to occur where all scientific knowledge were lost except one sentence, that one sentence should be: "All things are made of atoms - little particles that move around in perpetual motion, attracting each other when they are a little distance apart, but repelling upon being squeezed into one another." Combined with some insight and imagination, this summary of atomic theory provides a tremendous amount of information about our world. Atomic theory is so crucial and basic an idea in the scientific canon that it's taken for granted, yet for most of human history it was ignored or even ridiculed by such thinkers as Aristotle. Even today, despite being surrounded by technology based on the understanding and use of atoms, some people stubbornly believe that atoms are merely a theory and an article of faith.

    Atoms are not a modern idea. Over twenty-five centuries ago, the Greek thinker Leucippus is credited as first proposing that all things were made of atoms, "atom" meaning indivisible in Greek. What little is known of him survived through the writings of Democritus, who claimed, "Nothing exists but atoms and the void." He based his early atomic theory on observations, reasoning, and thought experiments. He argued, for example, that a knife could cut objects only if there were gaps in the material that made up the objects. Since we don't see such gaps, it follows that the object has to be composed of tiny, invisible atoms, and empty space between the atoms where the blade could cut. Sadly, after the "Greek explosion" in philosophy and science, Democritus' work and that of other atomists were forgotten by an apathetic Roman Empire, and later a superstitious Dark Ages. Atomic theory, along with other ideas such as a heliocentric universe and circulation of the blood, were to be revived only during the Renaissance.

    The success stories of modern science and engineering are tied closely with an ever increasing understanding of the universe at smaller and smaller scales. Electronics, computers, biotechnology, drug-design, and an enormous number of less dramatic inventions all rely on knowledge of quantum mechanics, and of the electric forces between atoms and molecules. Yet the atomic world remains mysterious simply because it is six or seven orders of magnitude beyond human perception. Our eyes can resolve details down to the millimeter range (10-3m), but molecules lie in the nanometer range (10-9m) and individual atoms are another order of magnitude smaller, in the angstrom range (10-10m). It is in the middle ground of nanometers (10-9m) that matter is defined.

The definition of matter is often of great interest, although we seldom think of it that way. Consider, then, that carbon atoms arranged one way makes cheap, common graphite, but arranged differently it comprises precious diamond. Arsenic by itself makes deadly poison, but incorporated into the crystal structure of gallium it makes for very valuable semiconductors. PCBs and other toxic wastes could be made harmless and even recycled into useful materials if their molecular structure could be decomposed. A few missing atoms in an enzyme, or a few misspelled bases in the genetic code, can wreak havoc with your health. Thus the arrangement and variety of atoms is a critical, pervasive aspect of human life. In this light, one can appreciate the potential of nanotechnology, as it gives us ultimate control over matter.

Flipping the technological pyramid
    Presently, nearly all of our technology is of a "top-down" or bulk-shaping variety: raw materials are extracted at great cost from mines, forests or fields, shipped to smelters, refineries or other processing centers, then shipped again to factories to be assembled into desired goods before being distributed. At each stage matter is cleaned, cut, melted, refined, and generally more and more finely processed. Each stage usually costs more than the last. Each stage brings environmental destruction as the usual by-product, in the form of pollution and the destruction of land and ecologies.

    Nanotechnology, on the other hand, represents "bottom-up" technology. Any desired product will be built directly, atom by atom or molecule by molecule. Raw materials and energy need not be gathered from distant sources. Instead, any materials nearby, such as dirt, garbage, and even air can be broken down into their constituent atoms and then reassembled into useful products with the molecular assemblers of nanotechnology. The sun or even the biological energy source of an ATP molecule can be harnessed for energy, avoiding dirty and dangerous oil or uranium.

Nanotechnology as a term is often confused with the current technology of lithography, and occasionally with biotechnology. Lithography, although responsible for the stunning miniaturizations of integrated circuits, is a far cry from nanotechnology's expected capability. Although it can regularly create micron (10-6m) level structures used in our computers, it's still a "top-down" approach involving the imprecise processing of trillions of atoms at a time. Current micromachines and other products of lithography are a full 3 orders of magnitude away from the domain of nanotech (9 orders, if one considers 3-D volume, as lithography is mainly a 2-D technology). Biotechnology could be considered a very crude form of nanotech, in its use of enzymes and other natural molecular "machines", but molecular assemblers will be quite different in form and function.

 A robot by any other name...
What, then, is nanotechnology? We've described several key features:
Nanotech will be atomically precise, i.e. anything made by nanotechnology must have nearly every atom in the right place. Nanotech will be able to make any structure consistent with the laws of physics that we can specify in atomic detail.

 The products of nanotechnology will be inexpensive, with total costs about equal to the amount of raw material and energy used.

To meet the three criteria above, we need atomically precise positional control, and self-replication. Universal molecular assemblers, first proposed by Dr. Eric Drexler (the leading exponent of nanotech), will provide both. At the most basic level, an assembler will be comprised of a molecular manipulator arm and a nanocomputer. The programmable nanocomputer will be able to read in instructions and direct the manipulator arm to place the correct atom (or molecule) in the desired position and orientation, thus giving precise control over the locations of chemical reactions. In bonding atoms or molecules to one another, the assembler can provide any needed energy (if the reaction happens not to be energetically favored) through physical force, thus performing mechanosynthesis (as opposed to the traditional means of chemical synthesis in solution). In fact, a molecular assembler can be seen as the ultimate chemical catalyst, able to effect any physically allowable chemical reaction. This ability, combined with a chemically acceptable blueprint, will allow large, atomically precise structures to be built, atom by atom and molecule by molecule. Equally important will be the ability of assemblers to build copies of themselves, which will dramatically reduce the time and costs of manufacturing.

    What would an assembler look like? How big would it be? What parts would comprise it? Although we don't yet have the technological means of building assemblers, we can have a fairly good idea of how the final product might look and work. This is because the design and eventual implementation of assemblers and other products of nanotechnology do not involve any new fundamental physical laws, only new techniques and technology to work at smaller and smaller scales (which still entails much hard work in the near future). Thus it is possible to accurately model molecular scale structures on computers using the known laws of chemistry and physics. A great deal of theoretical nanoengineering has already been done: Drexler and others have contributed extensive molecular designs for assembler components, such as molecular sorters, gears, joints, bearings, drives, mechanical logic gates, tape storage, etc. {see graphics} using computer models.

Right: A molecular model of a nanogear. Produced by CrystalClear Software

    Most of these designs use carbon, oxygen, hydrogen and nitrogen atoms as the building blocks, and diamond as the preferred base structure. Carbon is a particular favorite because of its abundance and versatility: from it, one can make anything from light, stiff diamond to long, flexible molecular chains and countless variations of shapes in between. As the atom of choice for the most complex molecular machine of nature, life, it's no surprise that it's also the choice of molecular engineers in their designs. Many of these designs will seem strangely familiar, like molecular scale cousins of common macroscopic mechanical parts. This is no coincidence, as many of the traits relevant to macromachines such as strength, deformation, power, stiffness, etc. scale down well in the nanoworld, allowing well-understood design principles to be applied.

    Based upon these models and designs, some initial estimates of size and mass for molecular assemblers have been made. The smallest assembler design has been estimated to mass in the tens of millions of amu (atomic mass units); this includes the mass of the arm and its controlling nanocomputer. A typical design would weigh more. A basic cylindrical nanoarm design with length of 100nm, a 30nm diameter, and multiple rotary joints should weigh around 10 million amu or less (an arm of solid diamond with the above dimensions would weigh about 16 million amu). A basic nanocomputer based on mechanical logic rod operations, wherein several logic rods make up a mechanical switch (a functional equivalent of a transistor) and wherein each switch occupies about 20 cubic nanometers, may have a total volume of about 200000 cubic nanometers. That's enough space for about 10000 switches, at the level of a simple 8-bit general computer. Tossing in the necessary fast (logic-rod based) and slow (atomic tape) memory systems, of perhaps 1KB and 100KB respectively, gives us a total mass for the nanocomputer in the hundreds of millions of amu. Thus the complete assembler, with arm and multiple tips (for holding different atoms and molecules), computer, power source, sorting system and chassis should weigh in the range of billions of amu. This is midway between the mass of a ribosome and a bacterium, which weigh about a million and a trillion amu respectively. We can expect that an assembler would be midway in size as well. Because of their small size, assemblers will work very quickly, on the order of a million operations per second.

Left: Another model of a nanogear with C, O, and N atoms courtesy of CrystalClear

    How would assemblers work, alone and together? Again, the idea of scale is crucial, and the easiest way to picture assemblers at work is to imagine them as tiny factories. Assemblers, perhaps immersed in some presorted bath of "feedstock" parts or molecules, will gather the provided "stock" molecules, sort them, then transport them internally along molecular conveyance systems to the nanomanipulator arm, which can then position and bond the atom or molecule onto the structure being built, analogous with a robotic welder in a modern factory. Assemblers could also be arranged in another familiar way, assembly-line style, with thousands or more arrayed in parallel, adding atoms or whole molecules at each step, and able to churn out countless numbers of complex molecular parts such as logic rods (mechanical logic gates) or complete molecular gear casings in mere seconds. There are other ideas of how to organize assemblers as well. Drexler suggests, for example, that a small initial group of assemblers could arrange themselves into the skeleton of a structure, which other assemblers could build upon, "fleshing out" the final product molecule by molecule.

Defining the possible
    Many skeptical questions arise when one first encounters the ideas of nanotechnology and molecular assemblers. In thinking about their feasibility, it helps to remember that biology has existed for billions of years with naturally evolved molecular manufacturing. Nanotechnology will be a refinement and expansion upon how nature works at the molecular scale. Nature's examples (such as ourselves) serve to answer the very basic skeptical questions, such as: Can macroscopic objects be built from molecular scale processes? Yes, thanks to exponential growth. Are molecular objects stable? Thankfully for us, yes. What about quantum effects? Clearly, they don't rule out molecular structures; in fact, they might help us make extremely fast electrical nanocomputers, instead of the simpler mechanical nanocomputers now envisioned, once we are well into a nanotech era.

    The first critical breakthrough needed is the development of the universal assembler described above. One likely scenario will have us building simple molecular parts, then combining them into an increasingly complex whole until we have an assembler. Such basic components as molecular rods, gears, bearings, and joints might first be made through chemistry and protein engineering, then precisely combined through proximal probe technology. Some combination of these three enabling technologies (supramolecular chemistry, protein engineering and proximal probes), combined with developments still unknown, may likely be the path to a universal assembler (see articles elsewhere in this issue). It may seem odd that a goal, an assembler, can be so well specified while the path remains vague, but nanotechnology is in a position where no new fundamental principles need be found, only new techniques and refinements of existing ones.

    Nanotechnology will be the culmination of a persistent goal in technology: increasing control over matter with better tools, from chipping stone to x-ray lithography. Examining the drive of technology, it seems inevitable, as Feynman expressed in his prophetic 1959 speech "There's Plenty of Room at the Bottom". Physical laws, he said, "...do not speak against the possibility of maneuvering things atom by atom." He felt the ability to do so would be "...a development which I think cannot be avoided."

Right: Molecular ring/gear, made of C, O, and assorted atoms. courtesy of CrystalClear

Matter matters
    To begin to appreciate the power of nanotechnology, look carefully all around you, taking your time. Unless you happen to be an astronaut, everywhere there is matter, visible or invisible, heavy or light, the product of nature or of tools, from chaotic jumbles to the most highly refined products. All of technology is the manipulation of matter and of atoms; even the use of energy requires refinement of matter. From this perspective, the potential of nanotechnology is clear: unequaled, unprecedented, thorough control of matter. We can only guess at the ultimate possibilities. In the realm of present needs and uses, nanotechnology will revolutionize manufacturing, computers, medicine, education, transportation, communications, and entertainment; virtually any area we use machines in (see The Promise of Nanotechnology next in this issue).

    Our economic systems will be revolutionized as well. Nanotechnology can break the chains of waste and exploitation. There will be no need for raw materials or cheap labor from other nations. Almost anything that one wants built can be built of abundantly available carbon. Any existing object can be broken down into its component atoms and reassembled into another object, i.e. 100% recycling. Most forms of scarcity will have little meaning in a nanotechnology society, particularly if colonies in space relieve population pressures. With self-replicating assemblers doing construction, costs are minimal (just think of the costs of present products of natural nanotech: potatoes, wood) and human labor is unnecessary. Software and design work will likely constitute the majority of costs in a nanotech world. Economic decentralization will be another major consequence, as assemblers can easily make manufacturing a portable affair. By disconnecting our material needs from distant places and relocating ultraclean manufacturing locally, the highly undemocratic trend of the past few centuries, of concentration of technology and wealth in the hands of the few, can be quickly reversed. With economic decentralization may come political and geographical decentralization, opening up new opportunities for meaningful democracy.

    Of course, such huge changes will have unpredictable effects on society. While nanotech may solve traditional problems of poverty and hunger, will it create new ones of boredom and avarice? Perhaps, given freedom from material want, people will wisely channel their efforts into understanding each other, and themselves.

About the Author...
Kai Wu is a junior studying physics and materials science. He continues his in-situ, real-time, first-person, triple-blind studies of delta brain waves in the classroom.
{For more information on Nanotechnology, see resource guide on page 5.}
{Molecular gear assemblies in background generated by MASS software.}

Further reading:
The nanotechnology page at Xerox PARC... (courtesy of Ralph C. Merkle)