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The Drexler-Smalley Debate on Molecular Assembly
Nanotechnology pioneer Eric Drexler and Rice University Professor and Nobelist Richard Smalley have engaged in a crucial debate on the feasibility of molecular assembly. Smalley's position, which denies both the promise and the peril of molecular assembly, will ultimately backfire and will fail to guide nanotechnology research in the needed constructive direction, says Ray Kurzweil. By the 2020s, molecular assembly will provide tools to effectively combat poverty, clean up our environment, overcome disease, extend human longevity, and many other worthwhile pursuits, he predicts.
Published on Kurzweilai.net Dec. 1, 2003.
Nanotechnology pioneer Eric Drexler and Rice University Professor
and Nobelist Richard Smalley have engaged in a crucial debate on
the feasibility of molecular assembly, which is the key to the most
revolutionary capabilities of nanotechnology. Although Smalley
was originally inspired by Drexler's ground-breaking works and has
himself become a champion of contemporary research initiatives in
nanotechnology, he has also taken on the role of key critic of Drexler's
primary idea of precisely guided molecular manufacturing.
This debate has picked up intensity with today's publication
of several rounds of this dialogue between these two pioneers. First
some background:
Background: The Roots of Nanotechnology
Nanotechnology promises the tools to rebuild the physical world, our
bodies and brains included, molecular fragment by molecular fragment,
potentially atom by atom. We are shrinking the key feature size of
technology, in accordance with what I call the "law of accelerating
returns," at the exponential rate of approximately a factor of 4 per
linear dimension per decade. At this rate, the key feature sizes
for most electronic and many mechanical technologies will be in the
nanotechnology range, generally considered to be under 100 nanometers,
by the 2020s (electronics has already dipped below this threshold,
albeit not yet in three-dimensional structures and not self-assembling).
Meanwhile, there has been rapid progress, particularly in the last
several years, in preparing the conceptual framework and design ideas
for the coming age of nanotechnology.
Most nanotechnology historians date the conceptual birth of nanotechnology
to physicist Richard Feynman's seminal speech in 1959, "There's Plenty
of Room at the Bottom," in which he described the profound implications
and the inevitability of engineering machines at the level of atoms:
"The principles of physics, as far as I can see, do not speak against
the possibility of maneuvering things atom by atom. It would be,
in principle, possible. . . .for a physicist to synthesize any chemical
substance that the chemist writes down. . .How? Put the atoms down
where the chemist says, and so you make the substance. The problems
of chemistry and biology can be greatly helped if our ability to
see what we are doing, and to do things on an atomic level, is ultimately
developed – a development which I think cannot be avoided."
An even earlier conceptual root for nanotechnology was formulated
by the information theorist John Von Neumann in the early 1950s
with his model of a self-replicating system based on a universal
constructor combined with a universal computer. In this proposal,
the computer runs a program that directs the constructor, which
in turn constructs a copy of both the computer (including its self-replication
program) and the constructor. At this level of description, Von
Neumann's proposal is quite abstract -- the computer and constructor
could be made in a great variety of ways, as well as from diverse
materials, and could even be a theoretical mathematical construction.
He took the concept one step further and proposed a "kinematic constructor,"
a robot with at least one manipulator (arm) that would build a replica
of itself from a "sea of parts" in its midst.
It was left to Eric Drexler to found the modern field of nanotechnology,
with a draft of his seminal Ph.D. thesis in the mid 1980s, by essentially
combining these two intriguing suggestions. Drexler described a
Von Neumann Kinematic Constructor, which for its "sea of parts"
used atoms and molecular fragments, as suggested in Feynman's speech.
Drexler's vision cut across many disciplinary boundaries, and was
so far reaching, that no one was daring enough to be his thesis
advisor, except for my own mentor, Marvin Minsky. Drexler's doctoral
thesis (premiered in his book, Engines
of Creation in 1986 and articulated technically in his 1992
book Nanosystems)
laid out the foundation of nanotechnology and provided the road
map still being pursued today.
Von Neumann's Universal Constructor, as applied to atoms and molecular
fragments, was now called a "universal assembler." Drexler's assembler
was universal because it could essentially make almost anything
in the world. A caveat is in order here. The products of a universal
assembler necessarily have to follow the laws of physics and chemistry,
so only atomically stable structures would be viable. Furthermore,
any specific assembler would be restricted to building products
from its sea of parts, although the feasibility of using individual
atoms has been repeatedly demonstrated.
Although Drexler did not provide a detailed design of an assembler,
and such a design has still not been fully specified, his thesis
did provide extensive existence proofs for each of the principal
components of a universal assembler, which include the following
subsystems:
- The computer: to provide the intelligence to control
the assembly process. As with all of the subsystems, the computer
needs to be small and simple. Drexler described an intriguing
mechanical computer with molecular "locks" instead of transistor
gates. Each lock required only 5 cubic nanometers of space and
could switch 20 billion times a second. This proposal remains
more competitive than any known electronic technology, although
electronic computers built from three-dimensional arrays of carbon
nanotubes may be a suitable alternative.
- The instruction architecture: Drexler and his colleague
Ralph Merkle have proposed a "SIMD" (Single Instruction Multiple
Data") architecture in which a single data store would record
the instructions and transmit them to trillions of molecular-sized
assemblers (each with their own simple computer) simultaneously.
Thus each assembler would not have to store the entire program
for creating the desired product. This "broadcast" architecture
also addresses a key safety concern by shutting down the self-replication
process if it got out of control by terminating the centralized
source of the replication instructions. However, as Drexler points
out[1], a nanoscale assembler
does not necessarily have to be self-replicating. Given the inherent
dangers in self-replication, the ethical standards proposed by
the Foresight Institute contain prohibitions against unrestricted
self-replication, especially in a natural environment.
- Instruction transmission: transmission of the instructions
from the centralized data store to each of the many assemblers
would be accomplished electronically if the computer is electronic
or through mechanical vibrations if Drexler's concept of a mechanical
computer were used.
- The construction robot: the constructor would be a simple
molecular robot with a single arm, similar to Von Neumann's kinematic
constructor, but on a tiny scale. The feasibility of building
molecular-based robot arms, gears, rotors, and motors has been
demonstrated in the years since Drexler's thesis, as I discuss
below.
- The robot arm tip: Drexler's follow-up book in 1992,
Nanosystems: molecular machinery, manufacturing, and computation,
provided a number of feasible chemistries for the tip of the robot
arm that would be capable of grasping (using appropriate atomic
force fields) a molecular fragment, or even a single atom, and
then depositing it in a desired location. We know from the chemical
vapor deposition process used to construct artificial diamonds
that it is feasible to remove individual carbon atoms, as well
as molecular fragments that include carbon, and then place them
in another location through precisely controlled chemical reactions
at the tip. The process to build artificial diamond is a chaotic
process involving trillions of atoms, but the underlying process
has been harnessed to design a robot arm tip that can remove hydrogen
atoms from a source material and deposit it at desired location
in a molecular machine being constructed. In this proposal, the
tiny machines are built out of a diamond-like (called "diamondoid")
material. In addition to having great strength, the material
can be doped with impurities in a precise fashion to create electronic
components such as transistors. Simulations have shown that gears,
levers, motors, and other mechanical systems can also be constructed
from these carbon arrays. Additional proposals have been made
in the years since, including several innovative designs by Ralph
Merkle[2]. In recent years, there has been a great deal of attention
on carbon nanotubes, comprised of hexagonal arrays of carbon atoms
assembled in three dimensions, which are also capable of providing
both mechanical and electronic functions at the molecular level.
- The assembler's internal environment needs to prevent
environmental impurities from interfering with the delicate assembly
process. Drexler's proposal is to maintain a near vacuum and
build the assembler walls out of the same diamondoid material
that the assembler itself is capable of making.
- The energy required for the assembly process can be
provided either through electricity or through chemical energy.
Drexler proposed a chemical process with the fuel interlaced with
the raw building material. More recent proposals utilize nanoengineered
fuel cells incorporating hydrogen and oxygen or glucose and oxygen.
Although many configurations have been proposed, the typical assembler
has been described as a tabletop unit that can manufacture any physically
possible product for which we have a software description. Products
can range from computers, clothes, and works of art to cooked meals.
Larger products, such as furniture, cars, or even houses, can be built
in a modular fashion, or using larger assemblers. Of particular importance,
an assembler can create copies of itself. The incremental cost of
creating any physical product, including the assemblers themselves,
would be pennies per pound, basically the cost of the raw materials.
The real cost, of course, would be the value of the information describing
each type of product, that is the software that controls the assembly
process. Thus everything of value in the world, including physical
objects, would be comprised essentially of information. We are not
that far from this situation today, since the "information content"
of products is rapidly asymptoting to 100 percent of their value.
In operation, the centralized data store sends out commands simultaneously
to all of the assembly robots. There would be trillions of robots
in an assembler, each executing the same instruction at the same
time. The assembler creates these molecular robots by starting
with a small number and then using these robots to create additional
ones in an iterative fashion, until the requisite number of robots
has been created.
Each local robot has a local data storage that specifies the type
of mechanism it is building. This local data storage is used to
mask the global instructions being sent from the centralized data
store so that certain instructions are blocked and local parameters
are filled in. In this way, even though all of the assemblers are
receiving the same sequence of instructions, there is a level of
customization to the part being built by each molecular robot.
Each robot extracts the raw materials it needs, which includes individual
carbon atoms and molecular fragments, from the source material.
This source material also includes the requisite chemical fuel.
All of the requisite design requirements, including routing the
instructions and the source material, were described in detail in
Drexler's two classic works.
Nature shows that molecules can serve as machines because living
things work by means of such machinery. Enzymes are molecular machines
that make, break, and rearrange the bonds holding other molecules
together. Muscles are driven by molecular machines that haul fibers
past one another. DNA serves as a data-storage system, transmitting
digital instructions to molecular machines, the ribosomes, that
manufacture protein molecules. And these protein molecules, in
turn, make up most of the molecular machinery.
-- Eric Drexler
The ultimate existence proof of the feasibility of a molecular
assembler is life itself. Indeed, as we deepen out understanding
of the information basis of life processes, we are discovering specific
ideas to address the design requirements of a generalized molecular
assembler. For example, proposals have been made to use a molecular
energy source of glucose and ATP similar to that used by biological
cells.
Consider how biology solves each of the design challenges of a
Drexler assembler. The ribosome represents both the computer and
the construction robot. Life does not use centralized data storage,
but provides the entire code to every cell. The ability to restrict
the local data storage of a nanoengineered robot to only a small
part of the assembly code (using the "broadcast" architecture),
particularly when doing self-replication, is one critical way nanotechnology
can be engineered to be safer than biology.
With the advent of full-scale nanotechnology in the 2020s, we will
have the potential to replace biology's genetic information repository
in the cell nucleus with a nanoengineered system that would maintain
the genetic code and simulate the actions of RNA, the ribosome,
and other elements of the computer in biology's assembler. There
would be significant benefits in doing this. We could eliminate
the accumulation of DNA transcription errors, one major source of
the aging process. We could introduce DNA changes to essentially
reprogram our genes (something we'll be able to do long before this
scenario, using gene-therapy techniques).
With such a nanoengineered system, the recommended broadcast architecture
could enable us to turn off unwanted replication, thereby defeating
cancer, autoimmune reactions, and other disease processes. Although
most of these disease processes will have already been defeated
by genetic engineering, reengineering the computer of life using
nanotechnology could eliminate any remaining obstacles and create
a level of durability and flexibility that goes vastly beyond the
inherent capabilities of biology.
Life's local data storage is, of course, the DNA strands, broken
into specific genes on the chromosomes. The task of instruction-masking
(blocking genes that do not contribute to a particular cell type)
is controlled by the short RNA molecules and peptides that govern
gene expression. The internal environment the ribosome is able
to function in is the particular chemical environment maintained
inside the cell, which includes a particular acid-alkaline equilibrium
(pH between 6.8 and 7.1 in human cells) and other chemical balances
needed for the delicate operations of the ribosome. The cell wall
is responsible for protecting this internal cellular environment
from disturbance by the outside world.
The robot arm tip would use the ribosome's ability to implement
enzymatic reactions to break off each amino acid, each bound to
a specific transfer RNA, and to connect it to its adjoining amino
acid using a peptide bond.
However, the goal of molecular manufacturing is not merely to replicate
the molecular assembly capabilities of biology. Biological systems
are limited to building systems from protein, which has profound
limitations in strength and speed. Nanobots built from diamondoid
gears and rotors can be thousands of times faster and stronger than
biological cells. The comparison is even more dramatic with regard
to computation: the switching speed of nanotube-based computation
would be millions of times faster than the extremely slow transaction
speed of the electrochemical switching used in mammalian interneuronal
connections (typically around 200 transactions per second, although
the nonlinear transactions that take place in the dendrites and
synapses are more complex than single computations).
The concept of a diamondoid assembler described above uses a consistent
input material (for construction and fuel). This is one of several
protections against molecule-scale replication of robots in an uncontrolled
fashion in the outside world. Biology's replication robot, the
ribosome, also requires carefully controlled source and fuel materials,
which are provided by our digestive system. As nano-based replicators
become more sophisticated, more capable of extracting carbon atoms
and carbon-based molecular fragments from less well-controlled source
materials, and able to operate outside of controlled replicator
enclosures such as in the biological world, they will have the potential
to present a grave threat to that world, particularly in view of
the vastly greater strength and speed of nano-based replicators
over any biological system. This is, of course, the source of great
controversy, which is alluded to in the Drexler-Smalley debate article
and letters.
In the decade since publication of Drexler's Nanosystems,
each aspect of Drexler's conceptual designs has been strengthened
through additional design proposals, supercomputer simulations,
and, most importantly, actual construction of molecular machines.
Boston College chemistry professor T. Ross Kelly reported in the
journal Nature that his construction of a chemically-powered
nanomotor was built from 78 atoms.[3]
A biomolecular research group headed by C. D. Montemagno created
an ATP-fueled nanomotor.[4]
Another molecule-sized motor fueled by solar energy was created
by Ben Feringa at the University of Groningen in the Netherlands
out of 58 atoms.[5] Similar
progress has been made on other molecular-scale mechanical components
such as gears, rotors, and levers. Systems demonstrating the use
of chemical energy and acoustic energy (as originally described
by Drexler) have been designed, simulated, and, in many cases, actually
constructed. Substantial progress has been made in developing various
types of electronic components from molecule-scale devices, particularly
in the area of carbon nanotubes, an area that Smalley has pioneered.
Fat and Sticky Fingers
In the wake of rapidly expanding development of each facet of future
nanotechnology systems, no serious flaw to Drexler's universal assembler
concept has been discovered or described. Smalley's highly publicized
objection in Scientific American [6]
was based on a distorted description of the Drexler proposal; it
ignored the extensive body of work in the past decade. As a pioneer
of carbon nanotubes, Smalley has gone back and forth between enthusiasm
and skepticism, having written that "nanotechnology holds the answer,
to the extent there are answers, to most of our pressing material
needs in energy, health, communication, transportation, food, water
…."
Smalley describes Drexler's assembler as consisting of five to
ten "fingers" (manipulator arms) to hold, move, and place each atom
in the machine being constructed. He then goes on to point out
that there isn't room for so many fingers in the cramped space that
a nanobot assembly robot has to work (which he calls the "fat fingers"
problem) and that these fingers would have difficulty letting go
of their atomic cargo because of molecular attraction forces (the
"sticky fingers" problem). Smalley describes the "intricate three-dimensional
waltz that is carried out" by five to fifteen atoms in a typical
chemical reaction. Drexler's proposal doesn't look anything like
the straw man description that Smalley criticizes. Drexler's proposal,
and most of those that have followed, have a single probe, or "finger."
Moreover, there have been extensive description and analyses of
viable tip chemistries that do not involve grasping and placing
atoms as if they were mechanical pieces to be deposited in place.
For example, the feasibility of moving hydrogen atoms using Drexler's
"propynyl hydrogen abstraction" tip[7] has been extensively confirmed in the intervening years.[8] The ability of the scanning probe microscope (SPM), developed
at IBM in 1981, and the more sophisticated atomic force microscope
to place individual atoms through specific reactions of a tip with
a molecular-scale structure provide additional existence proofs.
Indeed, if Smalley's critique were valid, none of us would be here
to discuss it because life itself would be impossible.
Smalley also objects that despite "working furiously . . . generating
even a tiny amount of a product would take [a nanobot] … millions
of years." Smalley is correct, of course, that an assembler with
only one nanobot wouldn't produce any appreciable quantities of
a product. However, the basic concept of nanotechnology is that
we will need trillions of nanobots to accomplish meaningful results.
This is also the source of the safety concerns that have received
ample attention. Creating trillions of nanobots at reasonable cost
will require the nanobots to make themselves. This self-replication
solves the economic issue while introducing grave dangers. Biology
used the same solution to create organisms with trillions of cells,
and indeed we find that virtually all diseases derive from biology's
self-replication process gone awry.
Earlier challenges to the concepts underlying nanotechnology have
also been effectively addressed. Critics pointed out that nanobots
would be subject to bombardment by thermal vibration of nuclei,
atoms, and molecules. This is one reason conceptual designers of
nanotechnology have emphasized building structural components from
diamondoid or carbon nanotubes. Increasing the strength or stiffness
of a system reduces its susceptibility to thermal effects. Analysis
of these designs have shown them to be thousands of times more stable
in the presence of thermal effects than biological systems, so they
can operate in a far wider temperature range[9].
Similar challenges were made regarding positional uncertainty from
quantum effects, based on the extremely small feature size of nanoengineered
devices. Quantum effects are significant for an electron, but
a single carbon atom nucleus is more than 20,000 times more massive
than an electron. A nanobot will be constructed from hundreds of
thousands to millions of carbon and other atoms, so a nanobot will
be billions of times more massive than an electron. Plugging this
ratio in the fundamental equation for quantum positional uncertainty
shows this to be an insignificant factor.
Power has represented another challenge. Drexler's original proposals
involved glucose-oxygen fuel cells, which have held up well in feasibility
studies. An advantage of the glucose-oxygen approach is that nanomedicine
applications can harness the glucose, oxygen, and ATP resources
already provided by the human digestive system. A nanoscale motor
was recently created using propellers made of nickel and powered
by an ATP-based enzyme.[10]
However, recent progress in implementing MEMS-scale and even nanoscale
hydrogen-oxygen fuel cells have provided an alternative approach.
Hydrogen-oxygen fuel cells, with hydrogen provided by safe methanol
fuel, have made substantial progress in recent years. A small company
in Massachusetts, Integrated Fuel Cell Technologies, Inc.[11]
has demonstrated a MEMS-based fuel cell. Each postage-stamp- sized
device contains thousands of microscopic fuel cells and includes
the fuel lines and electronic controls. NEC plans to introduce
fuel cells based on nanotubes in 2004 for notebook computers and
other portable electronics. They claim their small power sources
will power devices for up to 40 hours before the user needs to change
the methanol canister.
The Debate Heats Up
On April 16, 2003, Drexler responded to Smalley's Scientific American
article with an open
letter. He cited 20 years of research by himself and others
and responded specifically to the fat and sticky fingers objection.
As I discussed above, molecular assemblers were never described
as having fingers at all, but rather precise positioning of reactive
molecules. Drexler cited biological enzymes and ribosomes as examples
of precise molecular assembly in the natural world. Drexler closes
by quoting Smalley's own observation that "when a scientist says
something is possible, they're probably underestimating how long
it will take. But if they say it's impossible, they're probably
wrong."
Three
more rounds of this debate were published today. Smalley responds
to Drexler's open letter by backing off of his fat and sticky fingers
objection and acknowledging that enzymes and ribosomes do indeed
engage in the precise molecular assembly that Smalley had earlier
indicated was impossible. Smalley says biological enzymes only work
in water and that such water-based chemistry is limited to biological
structures such as "wood, flesh and bone." As Drexler has stated[12],
this is erroneous. Many enzymes, even those that ordinarily work
in water, can also function in anhydrous organic solvents and some
enzymes can operate on substrates in the vapor phase, with no liquid
at all. [13].
Smalley goes on to state (without any derivation or citations)
that enzymatic-like reactions can only take place with biological
enzymes. This is also erroneous. It is easy to see why biological
evolution adopted water-based chemistry. Water is the most abundant
substance found on our planet. It also comprises 70 to 90 percent
of our bodies, our food, and indeed of all organic matter. Most
people think of water as fairly simple, but it is a far more complex
phenomenon than conventional wisdom suggests.
As every grade school child knows, water is comprised of molecules,
each containing two atoms of hydrogen and one atom of oxygen, the
most commonly known chemical formula, H 2O. However, consider some
of water's complications and their implications. In a liquid state,
the two hydrogen atoms make a 104.5° angle with the oxygen atom,
which increases to 109.5° when water freezes. This is why water
molecules are more spread out in the form of ice, providing it with
a lower density than liquid water. This is why ice floats.
Although the overall water molecule is electrically neutral, the
placement of the electrons creates polarization effects. The side
with the hydrogen atoms is relatively positive in electrical charge,
whereas the oxygen side is slightly negative. So water molecules
do not exist in isolation, rather they combine with one another
in small groups to assume, typically, pentagonal or hexagonal shapes[14]. These multi-molecule structures can change back and
forth between hexagonal and pentagonal configurations 100 billion
times a second. At room temperature, only about 3 percent of the
clusters are hexagonal, but this increases to 100 percent as the
water gets colder. This is why snowflakes are hexagonal.
These three-dimensional electrical properties of water are quite
powerful and can break apart the strong chemical bonds of other
compounds. Consider what happens when you put salt into water.
Salt is quite stable when dry, but is quickly torn apart into its
ionic components when placed in water. The negatively charged oxygen
side of the water molecules attracts positively charged sodium ions
(Na+), while the positively charged hydrogen side of
the water molecules attracts the negatively charged chlorine ions
(Cl-). In the dry form of salt, the sodium and chlorine
atoms are tightly bound together, but these bonds are easily broken
by the electrical charge of the water molecules. Water is considered
"the universal solvent" and is involved in most of the biochemical
pathways in our bodies. So we can regard the chemistry of life
on our planet primarily as water chemistry.
However, the primary thrust of our technology has been to develop
systems that are not limited to the restrictions of biological evolution,
which exclusively adopted water-based chemistry and proteins as
its foundation. Biological systems can fly, but if you want to
fly at 30,000 feet and at hundreds or thousands of miles per hour,
you would use our modern technology, not proteins. Biological systems
such as human brains can remember things and do calculations, but
if you want to do data mining on billions of items of information,
you would want to use our electronic technology, not unassisted
human brains.
Smalley is ignoring the past decade of research on alternative
means of positioning molecular fragments using precisely guided
molecular reactions. Precisely controlled synthesis of diamondoid
(diamond-like material formed into precise patterns) has been extensively
studied, including the ability to remove a single hydrogen atom
from a hydrogenated diamond surface.[15] Related research supporting the feasibility of hydrogen abstraction
and precisely-guided diamondoid synthesis has been conducted at
the Materials and Process Simulation Center at Caltech; the Department
of Materials Science and Engineering at North Carolina State University;
the Institute for Molecular Manufacturing, the University of Kentucky;
the United States Naval Academy, and the Xerox Palo Alto Research
Center.[16]
Smalley is also ignoring the well-established scanning probe microscope
mentioned above, which uses precisely controlled molecular reactions.
Building on these concepts, Ralph Merkle has described tip reactions
that can involve up to four reactants.[17]
There is extensive literature on site-specific reactions that can
be precisely guided and that would be feasible for the tip chemistry
in a molecular assembler.[18]
Smalley ignores this body of literature when he maintains that only
biological enzymes in water can perform this type of reaction.
Recently, many tools that go beyond SPMs are emerging that can reliably
manipulate atoms and molecular fragments.
On September 3, 2003, Drexler responded
to Smalley's
response by alluding once again to the extensive body of literature
that Smalley ignores. He cites the analogy to a modern factory,
only at a nano-scale. He cites analyses of transition state theory
indicating that positional control would be feasible at megahertz
frequencies for appropriately selected reactants.
The latest installment of this debate is a follow-up
letter by Smalley. This letter is short on specifics and
science and long on imprecise metaphors that avoid the key issues.
He writes, for example, that "much like you can't make a boy and
a girl fall in love with each other simply by pushing them together,
you cannot make precise chemistry occur as desired between two molecular
objects with simple mechanical motion…cannot be done simply by mushing
two molecular objects together." He again acknowledges that enzymes
do in fact accomplish this, but refuses to acknowledge that such
reactions could take place outside of a biological-like system:
"this is why I led you…..to talk about real chemistry with real
enzymes….any such system will need a liquid medium. For the enzymes
we know about, that liquid will have to be water, and the types
of things that can be synthesized with water around cannot be much
broader than meat and bone of biology."
I can understand Drexler's frustration in this debate because I
have had many critics that do not bother to read or understand the
data and arguments that I have presented for my own conceptions
of future technologies. Smalley's argument is of the form that
"we don't have 'X' today, therefore 'X' is impossible." I encounter
this class of argument repeatedly in the area of artificial intelligence.
Critics will cite the limitations of today's systems as proof that
such limitations are inherent and can never be overcome. These
critics ignore the extensive list of contemporary examples of AI
(for example, airplanes and weapons that fly and guide themselves,
automated diagnosis of electrocardiograms and blood cell images,
automated detection of credit card fraud, automated investment programs
that routinely outperform human analysts, telephone-based natural
language response systems, and hundreds of others) that represent
working systems that are commercially available today that were
only research programs a decade ago.
Those of us who attempt to project into the future based on well-grounded
methodologies are at a disadvantage. Certain future realities may
be inevitable, but they are not yet manifest, so they are easy to
deny. There was a small body of thought at the beginning of the
20th century that heavier-than-air flight was feasible,
but mainstream skeptics could simply point out that if it was so
feasible, why had it never been demonstrated? In 1990, Kasparov
scoffed at the idea that machine chess players could ever possibly
defeat him. When it happened in 1997, observers were quick to dismiss
the achievement by dismissing the importance of chess.
Smalley reveals at least part of his motives at the end of his
most recent letter when he writes:
"A few weeks ago I gave a talk on nanotechnology and energy titled
'Be a Scientist, Save the World' to about 700 middle and high school
students in the Spring Branch ISD, a large public school system
here in the Houston area. Leading up to my visit the students
were asked to 'write an essay on 'why I am a Nanogeek. Hundreds
responded, and I had the privilege of reading the top 30 essays,
picking my favorite top 5. Of the essays I read, nearly half assumed
that self-replicating nanobots were possible, and most were deeply
worried about what would happen in their future as these nanobots
spread around the world. I did what I could to allay their fears,
but there is no question that many of these youngsters have been
told a bedtime story that is deeply troubling. You and people around
you have scared our children."
I would point out to Smalley that earlier critics also expressed
skepticism that either world-wide communication networks or software
viruses that would spread across them were feasible. Today, we
have both the benefits and the damage from both of these capabilities.
However, along with the danger of software viruses has also emerged
a technological immune system. While it does not completely protect
us, few people would advocate eliminating the Internet in order
to eliminate software viruses. We are obtaining far more benefit
than damage from this latest example of intertwined promise and
peril.
Smalley's approach to reassuring the public about the potential
abuse of this future technology is not the right strategy. Denying
the feasibility of both the promise and the peril of molecular assembly
will ultimately backfire and fail to guide research in the needed
constructive direction. By the 2020s, molecular assembly will provide
tools to effectively combat poverty, clean up our environment, overcome
disease, extend human longevity, and many other worthwhile pursuits.
Like every other technology that humankind has created, it can
also be used to amplify and enable our destructive side. It is
important that we approach this technology in a knowledgeable manner
to gain the profound benefits it promises, while avoiding its dangers.
Drexler and his colleagues at the Foresight Institute have been
in the forefront of developing the ethical guidelines and design
considerations needed to guide the technology in a safe and constructive
direction.
Denying the feasibility of an impending technological transformation
is a short-sighted strategy.
Notes
[1] Chemical
& Engineering News, December 1, 2003
[2] Ralph C. Merkle, "A proposed
'metabolism' for a hydrocarbon assembler," Nanotechnology
8 (1997): 149-162; http://www.zyvex.com/nanotech/hydroCarbonMetabolism.html.
[3] T.R. Kelly, H. De Silva,
R.A. Silva, "Unidirectional rotary motion in a molecular system,"
Nature 401 (September 9, 1999): 150-152.
[4] C.D. Montemagno, G.D.
Bachan, "Constructing nanomechanical devices powered by biomolecular
motors," Nanotechnology 10 (1999): 225-231; G. D.
Bachand, C.D. Montemagno, "Constructing organic / inorganic NEMS
devices powered by biomolecular motors," Biomedical Microdevices
2 (2000): 179-184.
[5] N. Koumura, R.W. Zijlstra,
R.A. van Delden, N. Harada, B.L. Feringa, "Light-driven monodirectional
molecular rotor," Nature 401 (September 9, 1999):
152-155.
[6] Richard E. Smalley, "Of
chemistry, love, and nanobots," Scientific American 285
(September, 2001): 76-77. http://smalley.rice.edu/rick's%20publications/SA285-76.pdf.
[7] Nanosystems: molecular
machinery, manufacturing, and computation, by K. Eric Drexler,
Wiley 1992.
[8] See for example, Theoretical
Studies of a Hydrogen Abstraction Tool for Nanotechnology, by
Charles B. Musgrave, Jason K. Perry, Ralph C. Merkle, and William
A. Goddard III, Nanotechnology 2, 1991 pages 187-195.
[9] See equation and explanation
on page 3 of "That's Impossible!" How good scientists reach bad
conclusions by Ralph C. Merkle, http://www.zyvex.com/nanotech/impossible.html.
[10] Montemagno, C., and
Bachand G. 1999 Nanotechnology 10 225.
[11] By way of disclosure,
the author is an advisor and investor in this company.
[12] Chemical
& Engineering News, December 1, 2003
[13] A. Zaks and A.M. Klibanov
in Science (1984, 224:1249-51)
[14] "The apparent simplicity
of the water molecule belies the enormous complexity of its interactions
with other molecules, including other water molecules" (A. Soper.
2002. "Water and ice." Science 297: 1288-1289). There is
much that is still up for debate, as shown by the numerous articles
still being published about this most basic of molecules, H20. For
example, D. Klug. 2001. "Glassy water." Science 294:2305-2306;
P. Geissler et al., 2001. "Autoionization in liquid water." Science
291(5511):2121-2124; J.K. Gregory et al. 1997. "The water dipole
moment in water clusters." Science 275:814-817; and K. Liu
et al. 1996. "Water clusters." Science 271:929-933;
A water molecule has slightly negative and slightly positive ends,
which means water molecules interact with other water molecules
to form networks. The partially positive hydrogen atom on one molecule
is attracted to the partially negative oxygen on a neighboring molecule
(hydrogen bonding). Three-dimensional hexamers involving 6 molecules
are thought to be particularly stable, though none of these clusters
lasts longer than a few picoseconds.
The polarity of water results in a number of anomalous properties.
One of the best known is that the solid phase (ice) is less dense
than the liquid phase. This is because the volume of water varies
with the temperature, and the volume increases by about 9% on freezing.
Due to hydrogen bonding, water also has a higher-than-expected boiling
point.
[15] http://www.foresight.org/SciAmDebate/SciAmResponse.html,
http://www.imm.org/SciAmDebate2/smalley.html,
http://www.rfreitas.com/Nano/DimerTool.htm.
[16] The analysis of the
hydrogen abstraction tool has involved many people, including: Donald
W. Brenner, Richard J. Colton, K. Eric Drexler, William A. Goddard,
III, J. A. Harrison, Jason K. Perry, Ralph C. Merkle, Charles B.
Musgrave, O. A. Shenderova, Susan B. Sinnott, and Carter T. White.
[17] Ralph C. Merkle, "A
proposed 'metabolism' for a hydrocarbon assembler," Nanotechnology
8(1997):149-162; http://www.zyvex.com/nanotech/hydroCarbonMetabolism.html
[18] Wilson Ho, Hyojune
Lee, "Single bond formation and characterization with a scanning
tunneling microscope," Science 286(26 November
1999):1719-1722; http://www.physics.uci.edu/~wilsonho/stm-iets.html.
K. Eric Drexler, Nanosystems: Molecular Machinery, Manufacturing,
and Computation, John Wiley & Sons, New York, 1992, Chapter
8.
Ralph C. Merkle, "A proposed 'metabolism' for a hydrocarbon
assembler," Nanotechnology 8(1997):149-162; http://www.zyvex.com/nanotech/hydroCarbonMetabolism.html.
Charles B. Musgrave, Jason K. Perry, Ralph C. Merkle, William A.
Goddard III, "Theoretical studies of a hydrogen abstraction
tool for nanotechnology," Nanotechnology 2(1991):187-195;
http://www.zyvex.com/nanotech/Habs/Habs.html.
Michael Page, Donald W. Brenner, "Hydrogen abstraction from
a diamond surface: Ab initio quantum chemical study using
constrained isobutane as a model," J. Am. Chem. Soc.
113(1991):3270-3274.
Susan B. Sinnott, Richard J. Colton, Carter T. White, Donald W.
Brenner, "Surface patterning by atomically-controlled chemical
forces: molecular dynamics simulations," Surf. Sci.
316(1994):L1055-L1060.
D.W. Brenner, S.B. Sinnott, J.A. Harrison, O.A. Shenderova, "Simulated
engineering of nanostructures," Nanotechnology 7(1996):161-167;
http://www.zyvex.com/nanotech/nano4/brennerPaper.pdf
S.P. Walch, W.A. Goddard III, R.C. Merkle, "Theoretical studies
of reactions on diamond surfaces," Fifth Foresight Conference
on Molecular Nanotechnology, 1997; http://www.foresight.org/Conferences/MNT05/Abstracts/Walcabst.html.
Stephen P. Walch, Ralph C. Merkle, "Theoretical studies of
diamond mechanosynthesis reactions," Nanotechnology
9(1998):285-296.
Fedor N. Dzegilenko, Deepak Srivastava, Subhash Saini, "Simulations
of carbon nanotube tip assisted mechano-chemical reactions on a
diamond surface," Nanotechnology 9(December 1998):325-330.
J.W. Lyding, K. Hess, G.C. Abeln, D.S. Thompson, J.S. Moore, M.C.
Hersam, E.T. Foley, J. Lee, Z. Chen, S.T. Hwang, H. Choi, P.H. Avouris,
I.C. Kizilyalli, "UHV-STM nanofabrication and hydrogen/deuterium
desorption from silicon surfaces: implications for CMOS technology,"
Appl. Surf. Sci. 130(1998):221-230.
E.T. Foley, A.F. Kam, J.W. Lyding, P.H. Avouris, P. H. (1998),
"Cryogenic UHV-STM study of hydrogen and deuterium desorption
from Si(100)," Phys. Rev. Lett. 80(1998):1336-1339.
M.C. Hersam, G.C. Abeln, J.W. Lyding, "An approach for efficiently
locating and electrically contacting nanostructures fabricated via
UHV-STM lithography on Si(100)," Microelectronic Engineering
47(1999):235-.
L.J. Lauhon, W. Ho, "Inducing and observing the abstraction
of a single hydrogen atom in bimolecular reaction with a scanning
tunneling microscope," J. Phys. Chem. 105(2000):3987-3992.
Ralph C. Merkle, Robert A. Freitas Jr., “Theoretical analysis
of a carbon-carbon dimer placement tool for diamond mechanosynthesis,”
J. Nanosci. Nanotechnol. 3(August 2003):319-324. http://www.rfreitas.com/Nano/JNNDimerTool.pdf
Jingping Peng, Robert A. Freitas Jr., Ralph C. Merkle, “Theoretical
Analysis of Diamond Mechanosynthesis. Part I. Stability of C2 Mediated
Growth of Nanocrystalline Diamond C(110) Surface,” J. Comp.
Theor. Nanosci. 1(March 2004). In press.
David J. Mann, Jingping Peng, Robert A. Freitas Jr., Ralph C. Merkle,
“Theoretical Analysis of Diamond Mechanosynthesis. Part II.
C2 Mediated Growth of Diamond C(110) Surface via Si/Ge-Triadamantane
Dimer Placement Tools,” J. Comp. Theor. Nanosci. 1(March 2004).
In press.
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