The Singularity Is Near: When Humans Transcend Biology (42 page)

An alternate method of designing nanobots is to learn from nature. Nano-technologist Michael Simpson of Oak Ridge National Laboratory describes the possibility of exploiting bacteria “as ready-made machine[s].” Bacteria, which are natural nanobot-size objects, are able to move, swim, and pump liquids.
⁹¹
Linda Turner, a scientist at the Rowland Institute at Harvard, has focused on their thread-size arms, called fimbriae, which are able to perform a wide variety of tasks, including carrying other nanoscale objects and mixing fluids. Another approach is to use only parts of bacteria. A research group headed by Viola Vogel at the University of Washington built a system using just the limbs of
E. coli
bacteria that was able to sort out nanoscale beads of different sizes. Since bacteria are natural nanoscale systems that can perform a wide variety of functions, the ultimate goal of this research will be to reverse engineer the bacteria so that the same design principles can be applied to our own nanobot designs.

Fat and Sticky Fingers

In the wake of the rapidly expanding development of each facet of future nano-technology systems, no serious flaw in Drexler’s nanoassembler concept has been described. A highly publicized objection in 2001 by Nobelist Richard Smalley in
Scientific American
was based on a distorted description of the Drexler proposal;
⁹²
it did not address the extensive body of work that has been carried out in the past decade. As a pioneer of carbon nanotubes Smalley has been enthusiastic about a variety of applications of nanotechnology, 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,” but he remains skeptical about molecular nanotechnology assembly.

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 in which a molecular-assembly nanorobot 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 also points out that an “intricate three-dimensional waltz . . . is carried out” by five to fifteen atoms in a typical chemical reaction.

In fact, 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, uses a single “finger.” Moreover, there have been extensive descriptions 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. In addition to the examples I provided above (for example, the DNA hand), the feasibility of moving hydrogen atoms using Drexler’s “propynyl hydrogen abstraction” tip has been extensively confirmed in the intervening years.
⁹³
The ability of the scanning-probe microscope (SPM), developed at IBM in 1981, and the more sophisticated atomic-force microscope (AFM) to place individual atoms through specific reactions of a tip with a molecular-scale structure provides additional proof of the concept. Recently, scientists at Osaka University used an AFM to move individual nonconductive atoms using a mechanical rather than electrical technique.
⁹⁴
The ability to move both conductive and nonconductive atoms and molecules will be needed for future molecular nanotechnology.
⁹⁵

Indeed, if Smalley’s critique were valid, none of us would be here to discuss it, because life itself would be impossible, given that biology’s assembler does exactly what Smalley says is 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 use trillions of nanobots to accomplish meaningful results—a factor that is also the source of the safety concerns that have received so much attention. Creating this many nanobots at reasonable cost will require self-replication at some level, which while solving the economic issue will introduce potentially grave dangers, a concern I will address in
chapter 8
. Biology uses 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 has shown them to be thousands of times more stable in the presence of thermal effects than are biological systems, so they can operate in a far wider temperature range.
⁹⁶

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 twenty thousand times more massive than an electron. A nanobot will be constructed from millions to billions of carbon and other atoms, making it up to trillions of times more massive than an electron. Plugging this ratio in the fundamental equation for quantum positional uncertainty shows it to be an insignificant factor.
⁹⁷

Power has represented another challenge. Proposals involving glucose-oxygen fuel cells have held up well in feasibility studies by Freitas and others.
⁹⁸
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.
⁹⁹
However, recent progress in implementing MEMS-scale and even nanoscale hydrogen-oxygen fuel cells has provided an alternative approach, which I report on below.

The Debate Heats Up

In April 2003 Drexler challenged Smalley’s
Scientific American
article with an open letter.
¹⁰⁰
Citing twenty years of research by himself and others, the letter responded specifically to Smalley’s fat- and sticky-fingers objections. As I discussed above, molecular assemblers were never described as having fingers at all but rather relying on precise positioning of reactive molecules. Drexler cited biological enzymes and ribosomes as examples of precise molecular assembly in the natural world. Drexler closed by quoting Smalley’s own observation, “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 occurred in 2003. Smalley responded to
Drexler’s open letter by backing off of his fat- and sticky-fingers objections and acknowledging that enzymes and ribosomes do indeed engage in the precise molecular assembly that Smalley had earlier indicated was impossible. Smalley then argued that biological enzymes work only in water and that such water-based chemistry is limited to biological structures such as “wood, flesh and bone.” As Drexler has stated, this, too, is erroneous.
¹⁰¹
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.
¹⁰²

Smalley goes on to state (without any derivation or citations) that enzymatic-like reactions can take place only with biological enzymes and in chemical reactions involving water. This is also mistaken. MIT professor of chemistry and biological engineering Alexander Klibanov demonstrated such nonaqueous (not involving water) enzyme catalysis in 1984. Klibanov writes in 2003, “Clearly [Smalley’s] statements about nonaqueous enzyme catalysis are incorrect. There have been hundreds and perhaps thousands of papers published about nonaqueous enzyme catalysis since our first paper was published 20 years ago.”
¹⁰³

It’s easy to see why biological evolution adopted water-based chemistry. Water is a very abundant substance on our planet, and constitutes 70 to 90 percent of our bodies, our food, and indeed of all organic matter. The three-dimensional electrical properties of water are quite powerful and can break apart the strong chemical bonds of other compounds. Water is considered “the universal solvent,” and because it is involved in most of the biochemical pathways in our bodies 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 thirty thousand 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 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 material has been extensively studied, including the ability to remove a single hydrogen atom from a hydrogenated diamond surface
¹⁰⁴
and the ability to add one or more carbon atoms to a diamond surface.
¹⁰⁵
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 at the University of Kentucky; the U.S. Naval Academy; and the Xerox Palo Alto Research Center.
¹⁰⁶

Smalley also avoids mentioning the well-established SPM mentioned above, which uses precisely controlled molecular reactions. Building on these concepts, Ralph Merkle has described possible tip reactions that could involve up to four reactants.
¹⁰⁷
There is an extensive literature on site-specific reactions that have the potential to be precisely guided and thus could be feasible for the tip chemistry in a molecular assembler.
¹⁰⁸
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 to his initial letter by alluding once again to the extensive body of literature that Smalley fails to address.
¹⁰⁹
He cited the analogy to a modern factory, only at a nano-scale. He cited analyses of transition-state theory indicating that positional control would be feasible at megahertz frequencies for appropriately selected reactants.

Smalley again responded with a letter that is short on specific citations and current research and long on imprecise metaphors.
¹¹⁰
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. . . . [It] cannot be done simply by mushing two molecular objects together.” He again acknowledges that enzymes do in fact accomplish this but refuses to accept that such reactions could take place outside of a biology-like system: “This is why I led you . . . to talk about real chemistry with real enzymes. . . . [A]ny 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.”

Smalley’s argument is of the form “We don’t have X today, therefore X is impossible.” We 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. For example, such critics disregard the extensive list of contemporary examples of AI (see the section “A Narrow AI Sampler” on
p. 279
) that represent commercially available working systems 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. A small body of thought at the beginning of the twentieth century insisted 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?

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.