Physics of the Future: How Science Will Shape Human Destiny and Our Daily Lives by the Year 2100 (36 page)

One problem with the replicator is the sheer number of atoms that must be rearranged in order to copy an object. The human body, for example, has over 50 trillion cells and in excess of 10
²⁶
atoms. That is a staggering number, requiring a colossal amount of memory space just to store the locations of all these atoms.

But one way to overcome this problem is to create a nanobot, a still-hypothetical molecular robot. These nanobots have several key properties. First, they can reproduce themselves. If they can reproduce once, then they can, in principle, create an unlimited number of copies of themselves. So the trick is to create just the first nanobot. Second, they are capable of identifying molecules and cutting them up at precise points. Third, by following a master code, they are capable of reassembling these atoms into different arrangements. So the task of rearranging 10
²⁶
atoms is reduced to making a similar number of nanobots, each one designed to manipulate individual atoms. In this way, the sheer number of atoms of the body is no longer such a daunting obstacle. The real problem is creating just the first one of these mythical nanobots and letting it reproduce by itself.

However, the scientific community is split on the question of whether the full-blown dream of a nanofabricator is physically possible. A few, like Eric Drexler, a pioneer in nanotechnology and author of
The Engines of Creation,
envision a future where all products are manufactured at the molecular level, creating a cornucopia of goods that we can only dream of today. Every aspect of society would be turned upside down by the creation of a machine that can create anything you want. Other scientists, however, are skeptical.

The late Nobel laureate Richard Smalley, for example, raised the problem of “sticky fingers” and “fat fingers” in an article in
Scientific American
in 2001. The key question is: Can a molecular nanobot be built that is nimble enough to rearrange molecules at will? He said the answer was no.

This debate spilled open when Smalley squared off with Drexler in a series of letters, reprinted in the pages of
Chemical and Engineering News
in 2003 to 2004. The repercussions of that debate are being felt even today. Smalley’s position was that the “fingers” of a molecular machine would not be able to perform this delicate task for two reasons.

First, the “fingers” would face tiny attractive forces that would make them stick to other molecules. Atoms stick to each other, in part, because of tiny electrical forces, like the van der Waals force, that exist between their electrons. Think of trying to repair a watch when your tweezers are covered with honey. Assembling anything as delicate as watch components would be impossible. Now imagine assembling something even more complicated than a watch, like a molecule, that constantly sticks to your fingers.

Second, these fingers might be too “fat” to manipulate atoms. Think of trying to repair that watch wearing thick cotton gloves. Since the “fingers” are made of individual atoms, as are the objects being manipulated, the fingers may simply be too thick to perform the delicate operations needed.

Smalley concluded, “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 …. Chemistry, like love, is more subtle than that.”

This debate goes to the very heart of whether a replicator will one day revolutionize society or be treated as a curiosity and relegated to the trash bin of technology. As we have seen, the laws of physics in our world do not easily translate to the physics of the nanoworld. Effects that we can ignore, such as van der Waals forces, surface tension, the uncertainty principle, the Pauli exclusion principle, etc., become dominant in the nanoworld.

To appreciate this problem, imagine that the atom is the size of a marble and that you have a swimming pool full of these atoms. If you fell into the swimming pool, it would be quite different from falling into a swimming pool of water. These “marbles” would be constantly vibrating and hitting you from all directions, because of Brownian motion. Trying to swim in this pool would be almost impossible, since it would be like trying to swim in molasses. Every time you tried to grab one of the marbles, it would either move away from you or stick to your fingers, due to a complex combination of forces.

In the end, both scientists agreed to disagree. Although Smalley was unable to throw a knockout punch against the molecular replicator, several things became clear after the dust settled. First, both agreed that the naive idea of a nanobot armed with molecular tweezers cutting and pasting molecules had to be modified. New quantum forces become dominant at the atomic scale.

Second, although this replicator, or universal fabricator, is science fiction today, a version of it already exists. Mother Nature, for example, can take hamburgers and vegetables and turn them into a baby in just nine months. This process is carried out by DNA molecules (which encode the blueprint for the baby) that guide the actions of ribosomes (which cut and splice the molecules into correct order) using the proteins and amino acids present in your food.

And third, a molecular assembler might work, but in a more sophisticated version. For example, as Smalley pointed out, bringing two atoms together does not guarantee a reaction. Mother Nature often gets around this problem by employing a third party, an enzyme in a water solution, to facilitate a chemical reaction. Smalley pointed out that many chemicals found in computers and the electronics industry cannot be dissolved in water. But Drexler countered by saying that not all chemical reactions involve water or enzymes.

One possibility, for example, is called self-assembly, or the bottom-up approach. Since antiquity, humans have used the top-down approach to building. With tools like a hammer and saw, one begins to cut wood and then piece together boards to create larger structures like a house according to a plan. You have to carefully guide this process from above at every step of the way.

In the bottom-up approach, things assemble by themselves. In nature, for example, beautiful snowflakes crystallize all by themselves in a thunderstorm. Trillions upon trillions of atoms rearrange to create novel forms. No one has to design each snowflake. This often occurs in biological systems as well. Bacterial ribosomes, which are complex molecular systems containing at least fifty-five different protein molecules and several RNA molecules, can spontaneously self-assemble in a test tube.

Self-assembly is also used in the semiconductor industry. Components used in transistors sometimes assemble by themselves. By applying various complex techniques and processes in a precise sequence (such as quenching, crystallization, polymerization, vapor deposition, solidification, etc.) one can produce a variety of commercially valuable computer components. As we saw earlier, a certain type of nanoparticle used against cancer cells can be produced using this method.

However, most things do not create themselves. In general, only a tiny fraction of nanomaterials have been shown to self-assemble properly. You cannot order a nanomachine using self-assembly like you can order from a menu. So progress in creating nanomachines this way will be steady but slow.

In sum, molecular assemblers apparently violate no law of physics, but they will be exceedingly difficult to build. Nanobots do not exist now, and will not in the near future, but once (and if) the first nanobot is successfully produced, it might alter society as we know it.

What might a replicator look like? No one knows exactly, since we are decades to a century away from actually building one, but I got a taste of how a replicator might appear when I had my head examined (literally). For a Science Channel special, they created a realistic 3-D copy of my face out of plastic by scanning a laser beam horizontally across my face. As the beam bounced off my skin, the reflection was recorded by a sensor that fed the image into a computer. Then the beam made the next pass across my face, but slightly lower. Eventually, it scanned my entire face, dividing it up into many horizontal slices. By looking at a computer screen, you could see a 3-D image of the surface of my face emerge, to an accuracy of perhaps a tenth of a millimeter, consisting of these horizontal slices.

Then this information was fed into a large device, about the size of a refrigerator, that can create a plastic 3-D image of almost anything. The device has a tiny nozzle that moves horizontally, making many passes. On each pass, it sprays out a tiny amount of molten plastic, duplicating the original laser image of my face. After about ten minutes and numerous passes, the mold emerged from this machine, bearing an eerie resemblance to my face.

The commercial applications of this technology are enormous, since you can create a realistic copy of any 3-D object, such as complicated machine parts, within a matter of a few minutes. However, one can imagine a device that, decades to centuries from now, may be able to create a 3-D copy of a real object, down to the cellular and atomic level.

At the next level, it is possible to use this 3-D scanner to create living organs of the human body. At Wake Forest University, scientists have pioneered a novel way to create living heart tissue, with an ink-jet printer. First, they have to carefully write a software program that successively sprays out living heart cells as the nozzle makes each pass. For this, they use an ordinary ink-jet printer but one whose ink cartridge is filled with a mixture of fluids containing living heart cells. In this way, they have control over the precise 3-D placement of every cell. After multiple passes, they can actually create the layers of heart tissue.

There is another instrument that might one day record the location of every atom of our body: the MRI. As we observed earlier, the accuracy of the MRI scan is about a tenth of a millimeter. This means that every pixel of a sensitive MRI scan may contain thousands of cells. But if you examine the physics behind the MRI, you find that the accuracy of the image is related to the uniformity of the magnetic field within the machine. Thus, by making the magnetic field increasingly uniform, one can even go below a tenth of a millimeter.

Already, scientists are envisioning an MRI-type machine with a resolution down to the size of a cell, and even smaller, one that can scan down to the individual molecules and atoms.

In summary, a replicator does not violate the laws of physics, but it would be difficult to create using self-assembly. By late in this century, when the techniques of self-assembly are finally mastered, we can think about commercial applications of replicators.

GRAY GOO?

Some people, including Bill Joy, a founder of Sun Microsystems, have expressed reservations about nanotechnology, writing that it’s only a matter of time before the technology runs wild, devours all the minerals of the earth, and spits out useless “gray goo” instead. Even Prince Charles of England has spoken out against nanotechnology and the gray-goo scenario.

The danger lies in the key property of these nanobots: they can reproduce themselves. Like a virus, they cannot be recalled once they are let loose into the environment. Eventually, they could proliferate wildly, taking over the environment and destroying the earth.

My own belief is that there are many decades to centuries before this technology is mature enough to create a replicator, so concerns about the gray goo are premature. As the decades pass, there will be plenty of time to design safeguards against nanobots that run amok. For example, one can design a fail-safe system so that, by pressing a panic button, all the nanobots are rendered useless. Or one could design “killer bots,” specifically designed to seek out and destroy nanobots that have run out of control.

Another way to deal with this is to study Mother Nature, who has had billions of years of experience with this problem. Our world is full of self-replicating molecular life-forms, called viruses and bacteria, that can proliferate out of control and mutate as well. However, our body has also created “nanobots” of its own, antibodies and white blood cells in our immune system that seek out and destroy alien life-forms. The system is certainly not perfect, but it provides a model for dealing with this out-of-control-nanobot problem.

For a BBC/Discovery Channel special I once hosted, Joel Garreau, author of
Radical Evolution,
said, “If a self-assembler ever does become possible, that’s going to be one of history’s great ‘holy s—!’ moments. Then you are really talking about changing the world into something we’ve never recognized before.”

There is an old saying, Be careful what you wish for, because it may come true. The holy grail of nanotechnology is to create the molecular assembler, or replicator, but once it is invented, it could alter the very foundation of society itself. All philosophies and social systems are ultimately based on scarcity and poverty. Throughout human history, this has been the dominant theme running through society, shaping our culture, philosophy, and religion. In some religions, prosperity is viewed as a divine reward and poverty as just punishment. Buddhism, by contrast, is based on the universal nature of suffering and how we cope with it. In Christianity, the New Testament reads: “It is easier for a camel to go through the eye of a needle than for a rich man to enter into the kingdom of God.”

The distribution of wealth also defines the society itself. Feudalism is based on preserving the wealth of a handful of aristocrats against the poverty of the peasants. Capitalism is based on the idea that energetic, productive people are rewarded for their labors by starting companies and getting rich. But if lazy, nonproductive individuals can get as much as they want almost for free by pushing a button, then capitalism no longer works. A replicator upsets the entire apple cart, turning human relations upside down. The distinctions between the haves and have-nots may disappear, and along with it the notion of status and political power.