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Critique of Nanotechnology: A Debate In Four Parts
by Eric K. Drexler and Simson Garfinkel
THE WORD "nanotechnology" means very different things to different people.
While most would agree that Nanotechnology is technology performed on the
scale of nanometers - one nanometer being about the size of four zinc atoms
laid side-by-side - that is where the agreement often ends. To Howard
Craighead, director of the National Nanofabrication Facility at Cornell
University, Nanotechnology is a science that uses the chip-making techniques
of the microelectronics revolution to produce devices of increasingly
smaller dimensions. To Rick L. Danheiser, a professor of chemistry at the
Massachusetts Institute of Technology, Nanotechnology is a word that
describes synthetic organic chemistry - a science which seeks to place atoms
in precise and complex arrangements in order to accomplish exacting goals.
To K. Eric Drexler, an author and visiting scholar in the Computer Science
department at Stanford University, Nanotechnology describes a technology of
the future - a technology based upon self replicating microscopic robots
controlled by tiny mechanical computers, capable of manipulating matter atom
by atom. Who is right?
Everybody and nobody, really, because
"nanotechnology" isn't a scientific term. Nanotechnology is a mind set, an
ideology, a way of solving big problems by thinking small - thinking very
small. My first exposure to Nanotechnology was several years ago when I was
a student at MIT. A new student activity was forming called the
Nanotechnology Study Group, a band of individuals committed to exploring the
technology and implications of Nanotechnology" The Study Group's handouts
were drawings of atoms arranged into nanometer-sized gears and bearings, as
well as arrangements of atoms that were supposed to be memory circuits and
logic building blocks for nanometer-scale computers. But the people in the
Study Group weren't chemists and physicists: they were computer scientists.
The questions that the Study Group was interested in exploring were not will
these particular drawings of nanodevices work? " - it was taken for granted
that if these didn't, others would - but rather, what would be the uses and
implications of such robots to medicine, science, industry and warfare; what
would happen if an army of nanorobots got out of control; and what would be
their long-term impact on society. The people of the Nanotechnology Study
Group were the forerunners to today's cult of Nanotechnology.
The basic tool
of the Nanotechnologist is the "assembler," according to Engines of
Creation, the book by K. Eric Drexler that reads like the Nanotechnologist
Manifesto. No larger than a few hundred atoms across, assemblers would be
constructed from gears that use single atoms for teeth and turn on
frictionless pivots made from single chemical bonds. These nanomachines
would come equipped with a computer and a robotic arm, and have the
remarkable ability to construct ("assemble") materials or molecule-sized
devices a single atom at a time. Assemblers would rebuild' produce by
building exact copies of themselves - thus it would only be necessary to
build a single assembler, and this first assembler would build the rest.
Although it would be slow for a single assembler to construct anything
larger than a fly speck, billions of assemblers working together could do
almost anything. You could set a fleet of them about the task of covering
your car's paint job with a micron-thin coating of diamond, constructed an
atom at a time by assemblers using carbon from carbon dioxide plucked from
the surrounding air: forget about rust and car washes. Assemblers could
restore the ecological balance of the planet by making more ozone in the
upper atmosphere. They could clean up oil spills by eating up the oil, or
alternatively th could make oil from air and seawater. In wartime,
assemblers would be the ultimate weapon, programmed to be ... omnivores" and
rip apart attacking armies atom by atom. There is certainly evidence that
such manipulations at the atomic level are possible. Every cell of every
living thing is constantly manufacturing, using and destroying tremendous
numbers of relatively simple nanomachines called proteins. Some of them are
structural, some of them perform chemical reactions, and some of them
transmit messages. But proteins are almost always single-purpose devices
which require nearly all of the machinery of the cell to produce and
regulate them. No protein does all of the things that an assembler would
supposedly be able to do. One of the most intriguing of the proposed
nanomachines is the nanosub, a device a little smaller than a red blood cell
which could swim through a person's circulatory system in search of plaque
or fatty deposits. Whenever the sub bumped into something that doesn't
belong, it would switch on a powerful set of drills and shred the offending
blockage. With a few robot arms, the sub could even repair damage. Sort of a
nano-Fantastic Voyage, the concept of this sub has appeared in prestigious
newspapers like The New York Times and The Wall Street Journal, as well as
magazines such as Scientific American. The sub represents the best of what
Nanotechnology has to offer: the ability to make our lives better. The Cult
of Nanotechnology paints a future in which technology has grown unimaginably
more powerful than it is today. As a much bigger lever than any technology
before it, they argue, it would do us well to think about the potential of
the technology before the revolution happens: this is what they are doing.
The problem with these people's ideas is that they envision working with
atoms the same way a modelmaker might work with wooden sticks and styrofoam
balls - breaking a bond here, moving an atom to the other side, and forming
a new bond. It is that conceptual model which is at the heart of all the
Nanotechnologists' drawings of gears, motors and nanocomputer parts, as well
as the very idea of the assembler's robot arm and the nanosub's drill. But
atoms don't work that way. " [Drexlerl discusses these molecular systems as
mechanical systems," says Robert J. Silby, a professor of chemistry at MIT.
"He bangs them and they go." The problem is, Dr. Silby explains, "molecules
are not rigid - they vibrate, they have bending motions." Even cross-linked
or interlocked networks of carbon atoms exhibit these characteristics, Silby
explains. "Therefore these will not act, mechanically, in the way he has
written down. There is more to it than he has said." Take the example of the
assembler's ... robot arm." Such an arm could probably pick up a single
atom, since lone atoms are very reactive and likely to stick to anything
that they come into contact with. Getting the atom off the arm, on the other
hand, would require a lot of energy - quite possibly more energy than the
nanomachine would have available. The robot arm might have a little more
luck working with groups of atoms, called molecular fragments. The energy
required to work with molecular fragments is much lower than the energy
needed to work with single atoms - this is the reason that proteins almost
always work with molecular fragments. The only ways that a robot arm could
hold a molecular fragment in place would be by making a chemical bond to it
or by clamping the fragment in place with some sort of molecular cage. There
are plenty of proteins that move molecular fragments around by using
chemical bonds. But it is always the case that the proteins can form these
bonds only with one or two specific fragments. It is doubtful that an arm
could be designed to bond with any arbitrary piece of an arbitrary molecule.
Molecular cages do occur in nature, but they tend to be bulky and unwieldy.
While there are some proteins which hold molecules in their active sites
with flaps constructed from chains of amino acids, such active sites are
always at the heart of the protein not on flexible arms which can easily be
maneuvered around. And, as with molecular bonds, the cages and the molecular
fragments they hold always come in matched sets.
Presuming an "arm" could be constructed, it would need some sort of "eye" to
locate molecular fragments that it would reach out and grab. What sort of
sensors would the nanocomputer at the heart of the assembler use to locate
the fragments in the first place? What would such a sensor be based on?
Visible light has a wavelength fifty to a hundred times the size of a
molecule. Light does not "bounce off " a molecule but more often goes
straight through, only causing slight disturbances in the very outermost
electrons of the molecule's atoms. Light that has atomic-sized wavelengths
is known as X-rays. However, even if the nanomachines could not generate
enough energy to emit an X-ray without breaking apart, there is no way that
they could detect the reflected rays or collimate them into recognizable
images. Perhaps the nanomachine will use electrons or some other sub-atomic
particle as a kind of atomic .radar," but there seems no way that a
nanomachine could generate a predictable stream of such particles or
interpret their reflections. Nature gets around the imaging problem by
relying on molecular diffusion and randomness to bring molecules to the
places where chemical reactions can take place. As a protein comes into
contact with a target molecule, thermal noise and motion cause molecules to
explore trillions of positions and orientations every second. But Drexler
and other Nanotechnologists maintain that nanomachines will not rely on
diffusion because it is not precise enough for their purposes.
Unfortunately, it is all that you have at the atomic level: even the
biological process of active transport which moves molecules across
membranes relies upon diffusion and random motion to get the molecules into
the molecular pumps. The idea of a universal assembler is somehow a very
comforting one: a programmable machine, capable of manipulating atoms and
carrying out reactions the way that a blacksmith might repair a horseshoe
with anvil and fire, is an easier image than proteins or inorganic catalysts
carrying out complicated chemical reactions by transferring electrons from
atom to atom. And indeed, in the beginning of his book, Drexler describes an
assembler grasping "a large molecule (the work piece) while bringing a small
molecule up against it in just the right place. Like an enzyme, it will then
bond the molecules together." The idea of using a few well-crafted machines
to make billions, and then using a billion machines to solve the world's
problems is really an appealing one. It is especially appealing to a
generation of computer scientists that has been raised on ideas such as
recursion (a way of solving a problem with a function that refers to itself)
and massive parallelism (an approach that uses thousands or millions of
simple computers, all working together in unison to solve different chunks
of complicated problems in seconds, instead of the days that a conventional
computer might take.) Nanotechnology is the physical embodiment of these
mathematical ideas. It is no accident that Nanotechnology's loudest
spokesmen have been computer scientists, rather than chemists and biologists
and materials scientists - people who have experience at moving atoms around
on the nanoscale. An assembler would necessarily be far more complicated
than anything that has been built by nature on the atomic scale. This isn't
an argument that such constructions aren't possible: a lap-top computer is
another good example of something more complicated than nature can build.
But natural or not, assemblers would have to exist in the same environment
as the biological molecules that they would be designed to operate on. At
MIT, professor of chemistry Rick L. Danheiser says that just because some
advocates of Nanotechnology haven't had a training in chemistry doesn't mean
that their ideas shouldn't be taken seriously. "I see some anti-aromatic
structures that can't possibly exist," Danheiser says, referring to the
designs that Drexler has proposed for the "rod-based logic" of a
nanocomputer.."It's unfortunate that he draws something that doesn't look so
good, because a lot of people see it and discredit the whole thing."
Nevertheless, Danheiser says, "I think that they are doing a great service.
Students in high school are reading Omni, thinking 'that's really neat.' "
Indeed, what the advocates of Nanotechnology are doing, Danheiser says, is
"putting a lot of glamor into chemistry. Chemistry suffers compared to
physics and biology... That's why I hesitate to do anything to puncture
their balloon." What upsets Danheiser is some of the descriptions of
chemistry that are used by advocates of Nanotechnology - a description, he
says, that seems based on a freshman chemistry course's understanding of the
field. One common analogy used by Drexler, for example, is that chemists
throw bolts and nuts into a bag, shake it, and hope for a machine to come
together. "That's not an accurate picture of what one does in organic
synthesis," says Danheiser. "We take nuts and bolts that are cleverly
machined so that they self assemble in a specific manner." james S. Nowick,
who is completing a doctorate in organic chemistry at MIT and plans to work
in the field of molecular devices, puts it this way: "My main criticism of
Nanotechnology, or more in particular, of Drexler, is that he's coming forth
as being sort of a visionary without actually doing anything. . . . Whatever
he is putting forth as science has to be tempered by the fact that we are
dealing with somebody who is basically making predictions.... In my field,
for instance, if you have a prediction of how something will work you can't
just go publish that. You really have to have scientific results. I 11 think
that there are some problems and unreasonable aspects of some of the
structures that Drexler has drawn. However," Nowick says, "I see them
essentially as a sketch that one might give an architect." The most
important developments in modern chemistry, Danheiser says, is by very,
very serious chemists who are actually involved in molecules that have
complex function. This is rudimentary nanotechnology, although I don't think
that they would call it that." For example, the 1987 Nobel Prize in
chemistry was awarded to three scientists who had done pioneering work in
the field of molecular recognition - which in a way can be thought of as
'robot arms" that are pre-programmed to "pick up" specific molecules.
Danheiser is also enchanted by the idea of a nanosubmarine that swims around
a person's circulatory system, looking for cancerous cells to destroy. But
Danheiser describes the sub as a large molecule with an artificial antibody
on the front, grafted to a molecule of snake venom - a molecule which nature
has given the capacity to cut up and destroy cells. Such a machine,
Danheiser stresses, wouldn't have to self-reproduce or even self-repair to
be a medical success. The machine could be made synthetically, in a
laboratory, and it could be "reprogrammed" by chemically removing one
antibody and replacing it with another one. "Chemists are getting the short
end of the stick," says Nowick. "The best thing that chemists can do is get
one or more spokespeople who are willing to beat the dram for the public,
saying that 'this is chemistry, this is exciting technology, you should be
interested in it, young people should pursue careers in it, and congressmen
should provide more funding.' " ri e -
2. Under special conditions, chemistry can build stable nanostructures.
BY K. ERIC DREXLER
I have been asked to reply to the preceding critique and have done so in
a hypertext style [to refer to Simson Garfinkel's comments]; Whole Earth
Review plans to give Mr. Garfinkel another ability that hypertext will
provide more widely - the ability to respond to a response.
1. What is nanotechnology?
Simson Garfinkel says that Howard Craighead defines nanotechnology as
advanced microtechnology, while Rick L. Danheiser defines it as
synthetic organic chemistry.
As this shows, these fields already have names. So far as I can
tell, it was I who introduced the term "nanotechnology" into general
use, and as Mr. Garfinkel's paragraph on my usage suggests, there is no
commonly accepted alternative name for the capabilities that
"nanotechnology" is generally taken to describe. If this technology is
important, then it needs to be discussed and it needs a brief,
unambiguous name. Sticking with the original meaning of nanotechnology"
would be useful for this reason. (There is no perfectly clear line
between synthetic organic chemistry and nanotechnology, but neither is
there a perfectly clear line between night and day; they are distinct,
though one leads to the next.)
2 Why are computer scientists prevalent among those interested in
nanotechnology?
Chemists and physicists are best placed to critique proposals in
nanotechnology, but their orientation is that of scientists, not of
engineers. The tend to focus on what can be studied today, not on what
can be built tomorrow. Computer scientists (despite their name) are, in
this sense, engineers. Further, they recognize the value of tiny, fast,
controllable things, and they are habituated to technological
revolution.
3. What are we to make of the excitement caused by the concept of
nanotechnology?
I believe Marx once said, "I am not a Marxist." I may be forced to
echo this remark. The basic concepts of nanotechnology are technical and
open to technical criticism. If they are true, then they have enormous
consequences, and it is natural for people to become excited and for
some to become starry-eyed. It would be an ad hominem fallacy, however,
to judge the validity of technical concepts by emotional characteristics
of the response they raise. Still, it is a good rule of thumb to be
especially skeptical of ideas that people seem to want to believe;
accordingly, in my technical talks I urge my audiences "to be harshly
critical of any ideas they hear labeled nanotechnology, starting with my
own."
4. Can gears turn on frictionless pivots made from single chemical bonds?
All pivots (or bearings) have some sliding friction, or drag, though
they can be made to have a negligible amount of static friction, or
stickiness. Single chemical bonds are too weak and elastic to use as
bearings for the gears mentioned here, but there are other, more
adequate approaches based on sliding surfaces. Like many of the points
that follow, this was discussed in my course at Stanford,
"Nanotechnology and Exploratory Engineering."
5. Will assemblers build devices a single atom at a time?
In general, probably not, though I have sometimes used language that may
suggest literal atom-by-atom construction. A more accurate statement
would be something like Assemblers will maneuver reactive chemical
moeties to tenth-nanometer precision, effecting a series of elementary
chemical reactions, each of which adds one or several atoms to a
workpiece, giving precise control of the resulting molecular structure."
And even this is a simplification, since a typical operation will often
do something a bit more complex, such as adding three atoms while
removing one. The shorter description gives a clear picture of the net
effect.
6. Will assemblers do all these things?
Not directly. Assemblers will be general-purpose manufacturing machines,
able to make almost anything so long as they are given the right raw
materials, fuels, operating conditions, and instructions. They will be
used to make many special-purpose machines, and the latter will do most
of the work. To make a particular product in quantity, it will make no
sense to use general-purpose assemblers; these will instead be used to
build a special-purpose production line, like an engine fabrication line
in Detroit. These production lines will then be used to turn out devices
like Simson Garfinkel's hypothetical diamond-coating appliers (perhaps
formulated into a rub-on paste?), or the more desperately needed devices
able to clean up the mess made by 20th-century industrial technology.
Weapons are among the potential products we need to worry about, but
ripping attacking armies apart atom by atom is rather too crude and too
dramatic; one suspects that the military mind will find other
applications for a manufacturing technology characterized by the
construction of precise and sophisticated devices. In general, having an
image of assemblers doing everything in the future would be a bit like
having an image of lathes and milling machines doing everything today.
7. What does nanotechnology assume about how atoms and molecules work?
Gears, motors, mechanical nanocomputer parts, and Simson Garfinkel's
proposed drill would work in an essentially mechanical fashion, as would
the positioning operations of assembler arms (resembling those of
industrial robot arms). The actual chemical transformations effected by
assemblers, however, have little resemblance to familiar mechanical
operations. Note that describing molecular motions in mechanical terms
(e.g., in the field of molecular mechanical is a standard part of
chemistry.
8. What about elasticity and vibrations?
Every physical object is a collection of atoms; nanomachines will
simply be very small physical objects. Everything vibrates, everything
bends, and machines work regardless; the differences here are more
quantitative than qualitative. On a very small scale, the vibrations
associated with heat itself become of tremendous importance, and are a
crucial issue in nanomachine design and operation. I mention this issue
in Engines of Creation, and have done quantitative analyses of thermal
vibrations in both logic systems for mechanical nanocomputers and in
assembler arms. There is a lag in publication and distribution of
information in new, interdisciplinary fields, though, so it would be
surprising if these results were universally known in the MIT chemistry
department.
9. What about problems with picking up and placing lone atoms?
See (5).
10. Need an arm bond with any arbitrary piece of an arbitrary molecule?
Assembler arms will wield a variety of tools, each with a standard
"handle" fitting a standard "hand"; the tools themselves will be
specialized. Further, only a limited range of tools would be needed to
build a wide variety of products, since even a complex product can be
built through a complex series of simple operations. All this is
familiar from macroscopic manufacturing technology.
11. Will nanomachines use x-ray or electron-beam radar" to spot
molecules?
Surely not, for reasons well-stated here (I have not seen
this proposed elsewherel. Further, freely moving molecules would elude
grabbing even if they could be seen; assembler arms would simply be too
slow. Industrial robots typically pick pre-positioned, preoriented parts
off something like a conveyor belt, rather than rummaging around in a
bin - and this despite the greater ease of vision on a macroscopic
scale. I expect that assemblers will work in a similar fashion.
12. Will nanomachines rely on diffusion?
There is a distinction to be drawn between relying on diffusion
somewhere, and relying on it everywhere. Assemblers will enable precise
construction of large, complex molecular systems because they (i.e.,
their positioning arms) will be able to direct chemical reactions with a
specificity and reliability that cannot be achieved when molecules are
free to bump together in all possible positions and orientations. Thus,
they avoid diffusion when moving molecules to the site of reaction.
General-purpose assemblers are expected to pluck tools incorporating
reactive molecules off conveyor belts which have been loaded with
activated tools by special-purpose systems of somewhat enzyme-like
machinery, which in turn have gotten their raw materials from the
surrounding solution. This earliest step will involve the transfer of
molecules by diffusion - from that solution to selective binding sites
like those familiar in proteins and supramolelar chemistry.
13. How complicated are assemblers?
Assemblers and nanocomputers will be roughly as complex as industrial
robots and microcomputers, because they will contain similar numbers of
parts performing similar functions. All these devices, however, will be
far less complex (and adaptable) than living organisms; they will have
broader capabilities in some respects, but not in all.
14. Can these anti-aromatic structures exist?
For quantum-mechanical reasons, some molecules that can be drawn as
rings with alternating double and single bonds are especially stable
like the sixmembered benzene ring) and others are especially unstable
(like the four-membered cyclobutadiene ring). One of my nanomechanical
designs contains a ring resembling the latter; it has the advantage of
having a useful shape for the purpose. Is its "instability" a problem?
Chemists regard chemicals as unstable when for example) they
spontaneously dissociate, or rearrange, or react with themselves at a
high rate, or when they readily react with a variety of other molecules.
This final process is not intrinsic to the molecule, but results from
the presence of other reactive molecules. In a different environment,
the molecule will be stable. Chemists ordinarily work with molecules in
solution, and in vast numbers; these molecules are free to encounter
others of the same kind, so any reactions that occur will be
unavoidable. This is a stronger kind of instability, typically dealt
with by studying molecules under low-density, near-vacuum conditions, or
in solid matrices of noble gases at temperatures near absolute zero.
Under the latter conditions, cyclobutadiene exists, but it begins
reacting with itself on even slight warming (to 25 degrees Kelvin). In a
nanomachine, of course, molecules do not wander freely; they encounter
only certain other structures in certain orientations. Under these
conditions, the cyclobutadiene ring can indeed be stable (as it is at
room temperature when surrounded by bulky, branched side-chains). A call
to Rick L. Danheiser confirmed that he shares this view of stability and
its application to the case at hand; I had run these structures by
another organic chemist for criticism before publishing them. Only
instability in the sense of a molecule falling apart or rearranging
spontaneously can be used to criticize a structure out of context (and
even then a suitable molecular environment can create exceptions, left
as an exercise for the nanotechnologically inclined chemist).
15. What about these freshman-chemistry-course analogies?
They are intended to inform readers with diverse backgrounds,
sometimes lacking even freshman chemistry itself. They are useful in the
same way that Danheiser's reference to "machined" molecules is useful -
as metaphors to convey a qualitative understanding of some aspect of the
subject matter, such as the ability of synthetic organic chemists to
make a wide range of moderately complex structures with precision. (For
perspective: in chemical synthesis, a hundred-atom structure is
considered large and complex but an assembler arm will likely have on
the order of a million).
16. Should one talk about what has not been demonstrated?
james S. Nowick is correct that predictions are not publishable in
many fields of science. However, nanotechnology is not a branch of
science (as I have taken pains to point out in Engines of Creation]; it
is an engineering discipline based on established science. Engineering
projects are often discussed and written about before they are
undertaken. Indeed, in the 1930s members of the British Interplanetary
Society performed feasibility studies which argued that one could fly to
the Moon with rockets. With care, feasibility studies can be done today
in the field of nanotechnology The required intellectual discipline
includes strict avoidance of areas of scientific uncertainty for pursuit
of designs which are robust despite a given range of uncertainty); it is
thus closer to engineering than it is to science. To scientists, engaged
in learning new facts about nature, talk of future knowledge is
speculative and often pointless. To engineers, engaged in building new
devices, talk of future possibilities grounded in established science
need not be speculative and is often essential. The above is a
fragmentary sketch of some issues in the methodology of exploratory
engineering. A chapter-length exposition is available (see the closing
note for further information). If one can indeed understand something
about future technologies, should we ask that everyone refrain from
doing so (or at least from publishing the results) before these
technologies are demonstrated? To do so would be to request that society
turn a blind eye to a significant scrap of knowledge regarding our
future. I believe that exploratory engineering deserves a genuinely tiny
fraction of society's technical effort, and that its products, when they
seem interesting, deserve rigorous criticism - or partial, carefully
hedged approval, when merited - from those with competence in a relevant
field.
17. Are we doing nanotechnology today?
The developments and goals cited here are relevant, and show how
short-term objectives are leading toward steadily more sophisticated
molecular devices. In my work I have focused on long-term developments,
and have described devices that no one would consider trying to build
today (because we lack the tools) and that no one is likely to build
tomorrow because we will then have better designs). Still, even the
crude nanotechnology I am able to describe and defend would have
capabilities far beyond what has been achieved today. We are speaking of
the difference between a mousetrap on the floor and a gripper on an
industrial robot arm backed up by a computer. In closing . . . I thank
Simson Garfinkel for a stimulating critique of my work; it has provided
an occasion to explain several points previously made only in teaching
or in conference proceedings. A general observation seems in order,
however, given a natural and widespread misunderstanding of my view and
the it-would-be-nice-if tone of his essay: I have not advocated
nanotechnology, I have advocated understanding it. Reporters, hearing me
describe a technology that can accomplish many long-sought goals, often
assume I must think that it is an unalloyed blessing, or at least a good
thing - even when I emphasize its great potential for abuse (Engines of
Creation has a chapter titled "Engines of Destruction"). My position
seems just a shade too subtle to fit a simple, stereotyped story: I
believe that in our diverse, competitive world, basic human motivations
make nanotechnology effectively inevitable, and that, in light of this,
we need to understand its great potential for good and ill so that we
can formulate and act in accord with effective policies. Nanotechnoloy
will, I believe, be the dominant manufacturing technology of the coming
century, making possible a host of amazing products. What we build with
it will make a vast difference to human life, the biosphere, and the
future of the world. Ideas regarding nanotechnology need to be taken
seriously, which means evaluating them with proper care and skepticism.
El
3.
Molecules are too unstable to be controlled the way Nanotechnology needs.
by Garfinkel A BIT OF BACKGROUND ... In january, I found myself in a
lecture room in California, talking with Stewart Brand about the
possibility of machines no larger than a wavelength of light. "I don't
believe in Nanotechnology," I finally said, referring to the lectures
and writings of K. Eric Drexler. It wasn't that I didn't believe that
atoms couldn't be placed into precise arrangements, I explained. I
simply didn't believe that the laws of physics and chemistry would ever
allow the creation of machines as small, yet as complex, as Drexler's
would necessarily have to be. Brand invited me to write an article
explaining my objections, so when I returned to Cambridge I started
showing Drexler's papers to chemists and physicists whose opinions I
respected. Many of them laughed, saying that Drexler's predictions were
... impossible." Others refused to comment, hoping to stay away from
what they saw as science fiction masquerading as scientific controversy
Making predictions is a tricky art, and Mr. Drexler, whose training is
in computer science, not chemistry, is bound to misplace a bond here or
there. But in formulating my disagreements with Drexler, I came to
realize that many of his writings contain the seeds of possibility, if
some of his words were translated and not taken at face value, and so my
first article was born. The heart of my continued disagreement with Mr.
Drexler is summed up by the matter of capitalization: Drexler believes
that the word Nanotechnology" should not be capitalized, just as the
words "biotechnology" and ... microtechnology" are not capitalized. But
Nanotechnology is not like biotechnology or microtechnology: Both
biotechnology and microtechnology exist: there are laboratories where
work is done, journals where results are published, and physical devices
which put these technologies to work. Nanotechnology has none of these
physical trappings; it is not yet an "engineering discipline," as
Drexler maintains [16], because there is nothing that is being
engineered in any conventional sense. This is why many scientists think
Nanotechnology is science fiction. It isn't that there is a lag in
publication and distribution of information in new, interdisciplinary
fields," as Drexler contends 18]. Indeed, an astounding number of people
are familiar with his work. Perhaps the word "nanotechnology" (the
uncapitalized version) wasn't in wide use when Drexler started out, but
it is now, and it is generally regarded by those in the microelectronic
and microfabrication communities to mean lithography at the nanometer
scale. "Nanotechnology" and ... nanotechnology" therefore mean different
things to different people, and this is my reason for insisting on the
capital-N. Names are important, because they are the place-markers that
we use for ideas. Science fiction - or, more appropriately, speculative
fiction - serves many useful purposes. Drexler's predictions force one
to think about the problems caused by chemistry, biotechnology and
physics, and how to solve them. But to talk about Nanotechnology in such
certain terms as Drexler does, always writing about what it ... will
do," leaves a bad taste in the mouths of many scientists. It isn't that
chemists and physicists "tend to focus on what can be studied today, not
on what can be built tomorrow," [21 as Drexler asserts. Scientists
simply tend to focus on what they think is allowed under the laws of
chemistry and physics. Whether Drexler's Nanomachines follows these laws
remains to be seen. In Drexler's world of Nanotechnology, atoms do
exactly what he wants them to do. Drexler's atomic bonds, for example,
are extremely rigid - they have to be, so that his atom-sized gears will
turn instead of simply having their teeth bent. Likewise, physical
effects like diffusion seem to turn on or off as needs are dictated by
Drexler's designs. Small reactive molecules, for example, never, ever
slip into the Nanomachines and gum up the works. "In a nanomachine, of
course, molecules do not wander freely; they encounter only certain
other structures in certain orienations," Drexler writes [14]. How does
a Nanomachine protect itself? How does it repair itself when it breaks?
It all goes back to the very mechanistic view of atoms and bonds which
most of Drexler's work is based on. While "describing molecular motions
in mechanical terms is a standard part of chemistry," [7] chemists do
not think about chemical reactions in such terms. The most important
thing in chemistry is the movement of electronic charge, not the
movement of atoms. Once electrons move, atoms rearrange themselves
automatically, because at the atomic level electrostatic force is
thousands of times stronger than mechanical force. Nevertheless, Drexler
continues to write about atoms if they were so many wooden balls, pegs
and springs. To say, as Drexler does, that the arms of Assembler need
not be able to bind to arbitrary molecules - instead, they wield tools
that have this ability 110], is to restate the question, not answer it.
How will a "limited range of tools" be used to "build a wide variety of
products?" "Macroscopic manufacturing technology," it turns out, is a
very bad model for how to build things at the molecular level. I can
lift a quarter from a table top with a tweezer, a pair of pliers, or
even with two chopsticks. But biology teaches us that nearly every
molecular fragment must be manipulated by a unique tool, a
special-purpose protein designed specifically for the task. Other
proteins simply don't work: they either can't pick up the particular
molecular fragments (because the fragments don't fit properly and slip
out due to vibrations), or they can't let go (because the fragments
irreversibly bind to the tools.) Likewise, if Assemblers do not need
radar or vision because they pick "pre-positioned, pre-oriented parts
off something like a conveyor belt," [111 the next logical questions to
ask is "how do the parts get on the conveyor belt in the first place?"
and "what prepositioned and pre-oriented them?" I was quite surprised
that Drexler defended his published structures as stable. Although it is
impossible to know with certainty whether or not a proposed molecule is
stable without actually making it, there are many guidelines that
chemists follow to assess stability. In general, four-member rings, such
as: are intrinsically unstable because they place carbon bonds at
90-degree angles, instead of the preferred tetrahedral angle of 109.5
degrees. Yet it is these instable structures that appear in Drexler's
proposed "Probe knob structure" and "Gate knob structure," which are the
basis of his mechanical Nanocomputer. If these structures begin to
disintegrate at 25 degrees Kelvin [141, how will they last inside a
Nanocomputer? Even if the computer were supercooled, the smallest amount
of mechanical energy perhaps a result of the computer's operation?]
would be enough to set them off. In my original article, I tried to stay
clear from arguments about whether this or that arrangement of atoms
would be stable or not, because such arguments cannot be productive. It
is impossible to prove that something cannot exist. If by some chance I
should convince Drexler that he made a mistake, all he would have to do
is come up with some alternative arrangement of atoms and say, "Well,
how about this one?" I agree with Drexler that he has "described devices
that no one would consider trying to build today (because we lack the
tools) and that no one is likely to build tomorrow (because we will then
have better designs)." [171 1 think that he should include this
statement as a footnote to every molecular structure he publishes.
Certainly we should talk and think about things that have not been
demonstrated; such discourse is at the heart of all future discoveries.
But if we claim that such discussions are scientific, then it is
important to stay within the laws of established science. I have read
philosophy and scholarly discussion about the possibility and
implications of time travel, but I do not consider it a serious
possibility, nor would I write an article on all the things that we
could do "when time travel is a reality." I wouldn't say that "since
time travel is an interdisciplinary study, it is understandable that
many people are not familiar with the means by which it will be
achieved." Drexler has made many such statements about Nanotechnology,
angering and alienating many scientists. In closing, as a science writer
whose first scientific training was in chemistry, I can only hope that
Drexler's graphic descriptions of his world of Nanotechnology stimulate
more popular interest in the chemical and biological sciences. I simply
fear that he has been too cavalier in many of his descriptions, and that
scientific possibility has often been pushed aside for sensationalism.
To say flat out that "I don't believe in Nanotechnology is probably a
misnomer. I certainly believe that our ability to control the placement
and arrangement of atoms will only get better as time goes on. A century
from now, a student of history may discover Drexler's articles and, with
some amusement, note the similarities between what Drexler predicted and
what came to pass, just as I might read Charles Babbage's plans for a
computer based upon a steam engine. But I think that the technology that
future manufacturers use to arrange the placement of atoms will look a
lot more like conventional chemistry and biology. And while this might
be a "Nanotechnology" of a sort, it is a far cry from self-reproducing,
self-repairing Nanomachines driven by tiny mechanical computers. F]
4.
Natural materials prove that nanostructures can be built.
by Drexler I AM SOMEWHAT disappointed by the tone of Mr. Garfinkel's
response to my response; much of it shifts away from his original,
valuable focus on technical criticism to a focus on style, words, and
feelings. These are important in their place, but are scarcely
scientific or professional in the context of a technical debate. Some of
his criticisms amount to a request that I repeat certain elementary
points throughout my writings. This might inhibit misunderstandings, but
it would also inhibit communication of anything new. If the term
"nanotechnology" were widely used in the U.S. in the manner that Mr.
Garfinkel suggests, I would expect a reasonable fraction of technical
papers and news articles to use it that way; they don't. His strongest
criticism, if true, would be my proposing unstable four-membered rings
and thus revealing a dramatic ignorance of chemistry. But these rings do
not "disintegrate" at 25 degrees Kelvin, they dimezize, and this
requires that two molecules encounter one another in an orientation
which would be prevented by mechanical constraints in the nanocomputer.
Again, and more clearly: I have discussed this matter with Prof.
Danheiser, whom Mr. Garfinkel quotes against me, and he agrees with my
view of the matter. Indeed, he stated that he had never heard me say
anything that was inconsistent with today's chemical knowledge, though
he noted that he had heard some serious distortions at second hand. Mr.
Garfinkel speaks of "many scientists," "an astounding number of people,"
etc.) as being critical of my work, but who are they, and what are their
substantive criticisms? In the case of Prof. Danheiser we were given a
name and a direct, substantive quote; after a few minutes of discussion
with him, the difficulty evaporated. I have yet to encounter a major
technical criticism of the core concepts of nanotechnology that does not
evaporate once it is examined. There seems to be a lot of smoke in the
air, but no fire - perhaps the haze is fog? A few notes: My training is
not in computer science, as Mr. Garfinkel states, but in
interdisciplinary science and engineering. Molecular diffusion is indeed
controllable, being rapid in gases and liquids and effectively blocked
by suitable solid walls. I trust this explains why I assume that it
occurs in some places and not in others. Molecular mechanics is indeed
not the whole story of chemistry - it gives a decent description of
molecular vibrations and rotations, but not of chemical reactions.
Single-atom gear teeth will indeed bend under load (why would anyone
assume that I think otherwise?), but they will also turn the gear, given
any sort of reasonable bearing. How will a limited range of tools build
a wide variety of products? In much the same way that they do in
synthetic organic chemistry, in living organisms, in home Workshops, and
in flexible manufacturing plants; ask J. Baldwin. Time travel is a straw
man, and no friend of mine. Regarding Mr. Garfinkel's last two
sentences, amen! But I have been at some pains to distinguish my designs
from "predictions"; they are intended only to show that devices having
certain capabilities are physically possible, so that we can try to
prepare for their emergence in the real world. I am glad that this
intertwined collection of arguments and design concepts has persuaded
Mr. Garfinkel that these prospects are real.
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