Physics of the Future_ How Science Will Shape Human Destiny... Part 11

The whole process took only a minute to move each atom to any position I wanted. In fact, in about thirty minutes, I found that I could actually spell out some letters on the screen, made of individual atoms. In an hour, I could make rather complex patterns involving ten or so atoms.

I had to recover from the shock that I had actually moved individual atoms, something that was once thought to be impossible.

MEMS AND NANOPARTICLES.

Although nanotechnology is still in its infancy, it has already generated a booming commercial industry in chemical coatings. By spraying thin layers of chemicals only a few molecules thick onto a commercial product, one can make it more resistant to rust or change its optical properties. Other commercial applications today are stain-resistant clothing, enhanced computer screens, stronger metal-cutting tools, and scratch-resistant coatings. In the coming years, more and more novel commercial products will be marketed that have microcoatings to improve their performance.

For the most part, nanotechnology is still a very young science. But one aspect of nanotechnology is now beginning to affect the lives of everyone and has already blossomed into a lucrative $40 billion worldwide industry-microelectromechanical systems (MEMS)-that includes everything from ink-jet cartridges, air bag sensors, and displays to gyroscopes for cars and airplanes. MEMS are tiny machines so small they can easily fit on the tip of a needle. They are created using the same etching technology used in the computer business. Instead of etching transistors, engineers etch tiny mechanical components, creating machine parts so small you need a microscope to see them.

Scientists have made an atomic version of the abacus, the venerable Asian calculating device, that consists of several vertical columns of wires containing wooden beads. In 2000, scientists at the IBM Zurich Research Laboratory made an atomic version of the abacus by manipulating individual atoms with a scanning microscope. Instead of wooden beads that move up and down the vertical wires, the atomic abacus used buckyb.a.l.l.s, which are carbon atoms arranged to form a molecule shaped like a soccer ball, 5,000 times smaller than the width of a human hair.

At Cornell, scientists have even created an atomic guitar. It has six strings, each string just 100 atoms wide. Laid end to end, twenty of these guitars would fit inside a human hair. The guitar is real, with real strings that can be plucked (although the frequency of this atomic guitar is much too high to be heard by the human ear).

But the most widespread practical application of this technology is in air bags, which contain tiny MEM accelerometers that can detect the sudden braking of your car. The MEM accelerometer consists of a microscopic ball attached to a spring or lever. When you slam on the brakes, the sudden deceleration jolts the ball, whose movement creates a tiny electrical charge. This charge then triggers a chemical explosion that releases large amounts of nitrogen gas within 1/25 of a second. Already, this technology has saved thousands of lives.

NANOMACHINES IN OUR BODIES.

In the near future, we should expect a new variety of nanodevices that may revolutionize medicine, such as nanomachines coursing throughout the bloodstream. In the movie Fantastic Voyage, Fantastic Voyage, a crew of scientists and their s.h.i.+p are miniaturized to the size of a red blood cell. They then embark on a voyage through the bloodstream and brain of a patient, encountering a series of harrowing dangers within the body. One goal of nanotechnology is to create molecular hunters that will zoom in on cancer cells and destroy them cleanly, leaving normal cells intact. Science fiction writers have long dreamed about molecular search-and-destroy craft floating in the blood, constantly on the lookout for cancer cells. But critics once considered this to be impossible, an idle dream of fiction writers. a crew of scientists and their s.h.i.+p are miniaturized to the size of a red blood cell. They then embark on a voyage through the bloodstream and brain of a patient, encountering a series of harrowing dangers within the body. One goal of nanotechnology is to create molecular hunters that will zoom in on cancer cells and destroy them cleanly, leaving normal cells intact. Science fiction writers have long dreamed about molecular search-and-destroy craft floating in the blood, constantly on the lookout for cancer cells. But critics once considered this to be impossible, an idle dream of fiction writers.

Part of this dream is being realized today. In 1992, Jerome Schentag of the University at Buffalo invented the smart pill, which we mentioned earlier, a tiny instrument the size of a pill that you swallow and that can be tracked electronically. It can then be instructed to deliver medicines to the proper location. Smart pills have been built that contain TV cameras to photograph your insides as they go down your stomach and intestines. Magnets can be used to guide them. In this way, the device can search for tumors and polyps. In the future, it may be possible to perform minor surgery via these smart pills, removing any abnormalities and doing biopsies from the inside, without cutting the skin.

A much smaller device is the nanoparticle, a molecule that can deliver cancer-fighting drugs to a specific target, which might revolutionize the treatment of cancer. These nanoparticles can be compared to a molecular smart bomb, designed to hit a specific target with a chemical payload, vastly reducing collateral damage in the process. While a dumb bomb hits everything, including healthy cells, smart bombs are selective and home in on just the cancer cells.

Anyone who has experienced the horrific side effects of chemotherapy will understand the vast potential of these nanoparticles to reduce human suffering. Chemotherapy works by bathing the entire body with deadly toxins, killing cancer cells slightly more efficiently than ordinary cells. The collateral damage from chemotherapy is widespread. The side effects-including nausea, loss of hair, loss of strength, etc.-are so severe that some cancer patients would rather die of cancer than subject themselves to this torture.

Nanoparticles may change all this. Medicines, such as chemotherapy drugs, will be placed inside a molecule shaped like a capsule. The nanoparticle is then allowed to circulate in the bloodstream, until it finds a particular destination, where it releases its medicine.

The key to these nanoparticles is their size: between 10 to 100 nanometers, too big to penetrate a blood cell. So nanoparticles harmlessly bounce off normal blood cells. But cancer cells are different; their cell walls are riddled with large, irregular pores. The nanoparticles can enter freely into the cancer cells and deliver their medicine but leave healthy tissue untouched. So doctors do not need complicated guidance systems to steer these nanoparticles to their target. They will naturally acc.u.mulate in certain types of cancerous tumors.

The beauty of this is that it does not require complicated and dangerous methods, which might have serious side effects. These nanoparticles are simply the right size: too big to attack normal cells but just right to penetrate a cancer cell.

Another example is the nanoparticles created by the scientists at BIND Biosciences in Cambridge, Ma.s.sachusetts. Its nanoparticles are made of polylactic acid and copolylactic acid/glycolic acid, which can hold drugs inside a molecular mesh. This creates the payload of the nanoparticle. The guidance system of the nanoparticle is the peptides that coat the particle and specifically bind to the target cell.

What is especially appealing about this work is that these nanoparticles form by themselves, without complicated factories and chemical plants. The various chemicals are mixed together slowly, in proper sequence, under very controlled conditions, and the nanoparticles self-a.s.semble.

"Because the self-a.s.sembly doesn't require multiple complicated chemical steps, the particles are very easy to manufacture.... And we can make them on a kilogram scale, which no one else has done," says BIND's Omid Farokhzad, a physician at the Harvard Medical School. Already, these nanoparticles have proven their worth against prostate, breast, and lung cancer tumors in rats. By using colored dyes, one can show that these nanoparticles are acc.u.mulating in the organ in question, releasing their payload in the desired way. Clinical trials on human patients start in a few years.

ZAPPING CANCER CELLS.

Not only can these nanoparticles seek out cancer cells and deliver chemicals to kill them, they might actually be able to kill them on the spot. The principle behind this is simple. These nanoparticles can absorb light of a certain frequency. By focusing laser light on them, they heat up, or vibrate, destroying any cancer cells in the vicinity by rupturing their cell walls. The key, therefore, is to get these nanoparticles close enough to cancer cells.

Several groups have already developed prototypes. Scientists at the Argonne National Laboratory and the University of Chicago have created t.i.tanium dioxide nanoparticles (t.i.tanium dioxide is a common chemical found in sunscreen). This group found that they could bind these nanoparticles to an antibody that naturally seeks out certain cancer cells called glioblastoma multiforme (GBM). So these nanoparticles, by hitching a ride on this antibody, are carried to the cancer cells. Then a white light is illuminated for five minutes, heating and eventually killing the cancer cells. Studies have shown that 80 percent of the cancer cells can be destroyed in this way.

These scientists have also devised a second way to kill cancer cells. They created tiny magnetic disks that can vibrate violently. Once these disks are led to the cancer cells, a small external magnetic field can be pa.s.sed over them, causing them to shake and tear apart the cell walls of the cancer. In tests, 90 percent of the cancer cells were killed after just 10 minutes of shaking.

This result is not a fluke. Scientists at the University of California at Santa Cruz have devised a similar system using gold nanoparticles. These particles are only 20 to 70 nanometers across and only a few atoms thick, arranged in the shape of a sphere. Scientists used a certain peptide that is known to be attracted to skin cancer cells. This peptide was made to connect with the gold nanoparticles, which then were carried to the skin cancer cells in mice. By s.h.i.+ning an infrared laser, these gold particles could destroy the tumor cells by heating them up. "It's basically like putting a cancer cell in hot water and boiling it to death. The more heat the metal nanospheres generate, the better," says Jin Zhang, one of the researchers.

So in the future, nanotechnology will detect cancer colonies years to decades before they can form a tumor, and nanoparticles circulating in our blood might be used to destroy these cells. The basic science is being done today.

NANOCARS IN OUR BLOOD.

One step beyond the nanoparticle is the nanocar, a device that can actually be guided in its travels inside the body. While the nanoparticle is allowed to circulate freely in the bloodstream, these nanocars are like remote-controlled drones that can be steered and piloted.

James Tour and his colleagues at Rice University have made such a nanocar. Instead of wheels, it has four buckyb.a.l.l.s. One future goal of this research is to design a molecular car that can push a tiny robot around the bloodstream, zapping cancer cells along the way or delivering lifesaving drugs to precise locations in the body.

But one problem with the molecular car is that it has no engine. Scientists have created more and more sophisticated molecular machines, but creating a molecular power source has been one of the main roadblocks. Mother Nature has solved this problem by using the molecule adenosine triphosphate (ATP) as her energy source. The energy of ATP makes life possible; it energizes every second of our muscles' motions. This energy of ATP is stored within an atomic bond between its atoms. But creating a synthetic alternative has proven difficult.

Thomas Mallouk and Ayusman Sen of Pennsylvania State University have found a potential solution to this problem. They have created a nanocar that can actually move tens of microns per second, which is the speed of most bacteria. (They first created a nanorod, made of gold and platinum, the size of a bacterium. The nanorod was placed into a mixture of water and hydrogen peroxide. This created a chemical reaction at either end of the nanorod that caused protons to move from one end of the rod to the other. Since the protons push against the electrical charges of the water molecule, this propels the nanorod forward. The rod continues to move forward as long as there is hydrogen peroxide in the water.) Steering these nanorods is also possible using magnetism. Scientists have embedded nickel disks inside these nanorods, so they act like compa.s.s needles. By moving an ordinary refrigerator magnet next to these nanorods, you can steer them in any direction you want.

Yet another way to steer a molecular machine is to use a flashlight. Light can break up the molecules into positive and negative ions. These two types of ions diffuse through the medium at different speeds, which sets up an electric field. The molecular machines are then attracted by these electric fields. So by pointing the flashlight one can steer the molecular machines in that direction.

I had a demonstration of this when I visited the laboratory of Sylvain Martel of the Polytechnic Montreal in Canada. His idea was to use the tails of ordinary bacteria to propel a tiny chip forward in the bloodstream. So far, scientists have been unable to manufacture an atomic motor, like the one found in the tails of bacteria. Martel asked himself: If nanotechnology could not make these tiny tails, why not use the tails of living bacteria?

He first created a computer chip smaller than the period at the end of this sentence. Then he grew a batch of bacteria. He was able to place about eighty of these bacteria behind the chip, so that they acted like a propeller that pushed the chip forward. Since these bacteria were slightly magnetic, Martel could use external magnets to steer them anywhere he wanted.

I had a chance to steer these bacteria-driven chips myself. I looked in a microscope, and I could see a tiny computer chip that was being pushed by several bacteria. When I pressed a b.u.t.ton, a magnet turned on, and the chip moved to the right. When I released the b.u.t.ton, the chip stopped and then moved randomly. In this way, I could actually steer the chip. While doing this, I realized that one day, a doctor may be pus.h.i.+ng a similar b.u.t.ton, but this time directing a nanorobot in the veins of a patient.

Molecular robots will be patrolling our bloodstreams, identifying and zapping cancer cells and pathogens. They could revolutionize medicine. (photo credit 4.1)

One can imagine a future where surgery is completely replaced by molecular machines moving through the bloodstream, guided by magnets, homing in on a diseased organ, and then releasing medicines or performing surgery. This could make cutting the skin totally obsolete. Or, magnets could guide these nanomachines to the heart in order to remove a blockage of the arteries.

DNA CHIPS.

As we mentioned in Chapter 3 Chapter 3, in the future we will have tiny sensors in our clothes, body, and bathroom, constantly monitoring our health and detecting diseases like cancer years before they become a danger. The key to this is the DNA chip, which promises a "laboratory on a chip." Like the tricorder of Star Trek, Star Trek, these tiny sensors will give us a medical a.n.a.lysis within minutes. these tiny sensors will give us a medical a.n.a.lysis within minutes.

Today, screening for cancer is a long, costly, and laborious process, often taking weeks. This severely limits the number of cancer a.n.a.lyses that can be performed. However, computer technology is changing all this. Already, scientists are creating devices that can rapidly and cheaply detect cancer, by looking for certain biomarkers produced by cancer cells.

Using the very same etching technology used in computer chips, it is possible to etch a chip on which there are microscopic sites that can detect specific DNA sequences or cancer cells.

Using transistor etching technology, DNA fragments are embedded into the chip. When fluids are pa.s.sed over the chip, these DNA fragments can bind to specific gene sequences. Then, using a laser beam, one can rapidly scan the entire site and identify the genes. In this way, genes do not have to be read one by one as before, but can be scanned by the thousands all at once.

In 1997, the Affymetrix company released the first commercial DNA chip that could rapidly a.n.a.lyze 50,000 DNA sequences. By 2000, 400,000 DNA probes were available for a few thousand dollars. By 2002, prices had dropped to $200 for even more powerful chips. Prices continue to plunge due to Moore's law, down to a few dollars.

Shana Kelley, a professor at the University of Toronto's medical school, said, "Today, it takes a room filled with computers to evaluate a clinically relevant sample of cancer biomarkers and the results aren't quickly available. Our team was able to measure biomolecules on an electronic chip the size of your fingertip." She also envisions the day when all the equipment to a.n.a.lyze this chip will be shrunk to the size of a cell phone. This lab on a chip will mean that we can shrink a chemical laboratory found in a hospital or university down to a single chip that we can use in our own bathrooms.

Doctors at Ma.s.sachusetts General Hospital have created their own custom-made biochip that is 100 times more powerful than anything on the market today. Normally, circulating tumor cells (CTCs) make up fewer than one in a million cells in our blood, but these CTCs eventually kill us if they proliferate. The new biochip is sensitive enough to find one in a billion CTCs circulating in our blood. As a result, this chip has been proven to detect lung, prostate, pancreatic, breast, and colorectal cancer cells by a.n.a.lyzing as little as a teaspoon of blood.

Standard etching technology carves out chips containing 78,000 microscopic pegs (each 100 microns tall). Under an electron microscope, they resemble a forest of round pegs. Each peg is coated with an antibody for the epithelial cell adhesion molecule (EpCAM), which is found in many types of cancer cells but is absent in ordinary cells. EpCAM is vital for cancer cells to communicate with one another as they form a tumor. If blood is pa.s.sed through the chip, the CTC cells stick to the round pegs. In clinical trials, the chip successfully detected cancers in 115 out of 116 patients.

The proliferation of these labs on a chip will also radically affect the cost of diagnosing disease. At present, it may cost several hundred dollars to have a biopsy or chemical a.n.a.lysis, which might take a few weeks. In the future, it may cost a few pennies and take a few minutes. This could revolutionize the speed and accessibility of cancer diagnoses. Every time we brush our teeth, we will have a thorough checkup for a variety of diseases, including cancer.

Leroy Hood and his colleagues at the University of Was.h.i.+ngton created a chip, about 4 centimeters wide, that can test for specific proteins from a single drop of blood. Proteins are the building blocks of life. Our muscles, skin, hair, hormones, and enzymes are all made of proteins. Detecting proteins from diseases like cancer could lead to an early warning system for the body. At present, the chip costs only ten cents and can identify a specific protein within ten minutes, so it is several million times more efficient than the previous system. Hood envisions a day when a chip will be able to rapidly a.n.a.lyze hundreds of thousands of proteins, alerting us to a wide variety of diseases years before they become serious.

CARBON NANOTUBES.

One preview of the power of nanotechnology is carbon nanotubes. In principle, carbon nanotubes are stronger than steel and can also conduct electricity, so carbon-based computers are a possibility. Although they are enormously strong, one problem is that they must be in pure form, and the longest pure carbon fiber is only a few centimeters long. But one day, entire computers may be made of carbon nanotubes and other molecular structures.

Carbon nanotubes are made of individual carbon atoms bonded to form a tube. Imagine chicken wire, where every joint is a carbon atom. Now roll up the chicken wire into a tube, and you have the geometry of a carbon nanotube. Carbon nanotubes are formed every time ordinary soot is created, but scientists never realized that carbon atoms could bond in such a novel way.

The near-miraculous properties of carbon nanotubes owe their power to their atomic structure. Usually, when you a.n.a.lyze a solid piece of matter, like a rock or wood, you are actually a.n.a.lyzing a huge composite of many overlapping structures. It is easy to create tiny fractures within this composite, which cause it to break. So the strength of a material depends on imperfections in its molecular structure. For example, graphite is made of pure carbon, but it is extremely soft because it is made of layers that can slide past each other. Each layer consists of carbon atoms, each of which is bonded with three other carbon atoms.

Diamonds are also made of pure carbon, but they are the strongest naturally occurring mineral. The carbon atoms in diamonds are arranged in a tight, interlocking crystal structure, giving them their phenomenal strength. Similarly, carbon nanotubes owe their amazing properties to their regular atomic structure.

Already, carbon nanotubes are finding their way into industry. Because of their conductivity, they can be used to create cables to carry large amounts of electrical power. Because of their strength, they can be used to create substances tougher than Kevlar.

But perhaps the most important application of carbon will be in the computer business. Carbon is one of several candidates that may eventually succeed silicon as the basis of computer technology. The future of the world economy may eventually depend on this question: What will replace silicon?

POST-SILICON ERA.

As we mentioned earlier, Moore's law, one of the foundations of the information revolution, cannot last forever. The future of the world economy and the destiny of nations may ultimately hinge on which nation develops a suitable replacement for silicon.

The question-When will Moore's law collapse?-sends shudders throughout the world economy. Gordon Moore himself was asked in 2007 if he thought the celebrated law named after him could last forever. Of course not, he said, and predicted that it would end in ten to fifteen years.

This rough a.s.sessment agreed with a previous estimate made by Paolo Gargini, an Intel Fellow, who is responsible for all external research at Intel. Since the Intel Corporation sets the pace for the entire semiconductor industry, his words were carefully a.n.a.lyzed. At the annual Semicon West conference in 2004, he said, "We see that for at least the next fifteen to twenty years, we can continue staying on Moore's law."

The current revolution in silicon-based computers has been driven by one overriding fact: the ability of UV light to etch smaller and smaller transistors onto a wafer of silicon. Today, a Pentium chip may have several hundred million transistors on a wafer the size of your thumbnail. Because the wavelength of UV light can be as small as 10 nanometers, it is possible to use etching techniques to carve out components that are only thirty atoms across. But this process cannot continue forever. Sooner or later, it collapses, for several reasons.

First, the heat generated by powerful chips will eventually melt them. One naive solution is to stack the wafers on top of one another, creating a cubical chip. This would increase the processing power of the chip but at the expense of creating more heat. The heat from these cubical chips is so intense you could fry an egg on top of them. The problem is simple: there is not enough surface area on a cubical chip to cool it down. In general, if you pa.s.s cool water or air across a hot chip, the cooling effect is greater if you have more surface contact with the chip. But if you have a cubical chip, the surface area is not enough. For example, if you could double the size of a cubical chip, the heat it generates goes up by a factor of eight (since the cube contains eight times more electrical components), but its surface area increases only by a factor of four. This means that the heat generated in a cubical chip rises faster than the ability to cool it down. The larger the cubical chip, the more difficult it is to cool it. So cubical chips will provide only a partial, temporary solution to the problem.

Some have suggested that we simply use X-rays instead of UV light to etch the circuits. In principle, this might work, since X-rays can have a wavelength 100 times smaller than UV light. But there is a trade-off. As you move from UV light to X-rays, you also increase the energy of the beam by a factor of 100 or so. This means that etching with X-rays may destroy the wafer you are trying to etch. X-ray lithography can be compared to an artist trying to use a blowtorch to create a delicate sculpture. X-ray lithography has to be very carefully controlled, so X-ray lithography is only a short-term solution.

Second, there is a fundamental problem posed by the quantum theory: the uncertainty principle, which says that you cannot know for certain the location and velocity of any atom or particle. Today's Pentium chip may have a layer about thirty atoms thick. By 2020, that layer could be five atoms across, so that the electron's position is uncertain, and it begins to leak through the layer, causing a short circuit. Thus, there is a quantum limit to how small a silicon transistor can be.

As I mentioned earlier, I once keynoted a major conference of 3,000 of Microsoft's top engineers in their headquarters in Seattle, where I highlighted the problem of the slowing down of Moore's law. These top software engineers confided to me that they are now taking this problem very seriously, and parallel processing is one of their top answers to increase computer processing power. The easiest way to solve this problem is to string a series of chips in parallel, so that a computer problem is broken down into pieces and then rea.s.sembled at the end.

Parallel processing is one of the keys to how our own brain works. If you do an MRI scan of the brain as it thinks, you find that various regions of the brain light up simultaneously, meaning that the brain breaks up a task into small pieces and processes each piece simultaneously. This explains why neurons (which carry electrical messages at the excruciatingly slow pace of 200 miles per hour) can outperform a supercomputer, in which messages travel at nearly the speed of light. What our brain lacks in speed, it more than makes up for by doing billions of small calculations simultaneously and then adding them all up.

The difficulty with parallel processing is that every problem has to be broken into several pieces. Each piece is then processed by different chips, and the problem is rea.s.sembled at the end. The coordination of this breakup can be exceedingly complicated, and it depends specifically on each problem, making a general procedure very difficult to find. The human brain does this effortlessly, but Mother Nature has had millions of years to solve this problem. Software engineers have had only a decade or so.

ATOMIC TRANSISTORS.

One possible replacement for silicon chips is transistors made of individual atoms. If silicon transistors fail because wires and layers in a chip are going down in size to the atomic scale, then why not start all over again and compute on atoms?

One way of realizing this is with molecular transistors. A transistor is a switch that allows you to control the flow of electricity down a wire. It's possible to replace a silicon transistor with a single molecule, made of chemicals like rotaxane and benzenethiol. When you see a molecule of benzenethiol, it looks like a long tube, with a "k.n.o.b," or valve, made of atoms in the middle. Normally, electricity is free to flow down the tube, making it conductive. But it is also possible to twist the "k.n.o.b," which shuts off the flow of electricity. In this way, the entire molecule acts like a switch that can control the flow of electricity. In one position, the k.n.o.b allows electricity to flow, which can represent the number "1." If the k.n.o.b is turned, then the electric flow is stopped, which represents the number "0." Thus, digital messages can be sent by using molecules.

Molecular transistors already exist. Several corporations have announced that they have created transistors made of individual molecules. But before they can be commercially viable, one must be able to wire them up correctly and ma.s.s-produce them.

One promising candidate for the molecular transistor comes from a substance called graphene, which was first isolated from graphite in 2004 by Andre Geim and Kostya Novoselov of the University of Manchester, who won a n.o.bel Prize for their work. It is like a single layer of graphite. Unlike carbon nanotubes, which are sheets of carbon atoms rolled up into long, narrow tubes, graphene is a single sheet of carbon, no more than one atom thick. Like carbon nanotubes, graphene represents a new state of matter, so scientists are teasing apart its remarkable properties, including conducting electricity. "From the point of view of physics, graphene is a goldmine. You can study it for ages," remarks Novoselov. (Graphene is also the strongest material ever tested in science. If you placed an elephant on a pencil, and balanced the pencil on a sheet of graphene, the graphene would not tear.) Novoselov's group has employed standard techniques used in the computer industry to carve out some of the smallest transistors ever made. Narrow beams of electrons can carve out channels in graphene, making the world's smallest transistor: one atom thick and ten atoms across. (At present, the smallest molecular transistors are about 30 nanometers in size. Novoselov's smallest transistors are thirty times smaller than that.) These transistors of graphene are so small, in fact, they may represent the ultimate limit for molecular transistors. Any smaller, and the uncertainty principle takes over and electrons leak out of the transistor, destroying its properties. "It's about the smallest you can get," says Novoselov.

Although there are several promising candidates for molecular transistors, the real problem is more mundane: how to wire them up and a.s.semble them into a commercially viable product. Creating a single molecular transistor is not enough. Molecular transistors are notoriously hard to manipulate, since they can be thousands of times thinner than a human hair. It is a nightmare thinking of ways to ma.s.s-produce them. At present, the technology is not yet in place.

For example, graphene is such a new material that scientists do not know how to produce large quant.i.ties of it. Scientists can produce only about .1 millimeter of pure graphene, much too small for commercial use. One hope is that a process can be found that self-a.s.sembles the molecular transistor. In nature, we sometimes find arrays of molecules that condense into a precise pattern, as if by magic. So far, no one has been able to reliably re-create this magic.

QUANTUM COMPUTERS.

The most ambitious proposal is to use quantum computers, which actually compute on individual atoms themselves. Some claim that quantum computers are the ultimate computer, since the atom is the smallest unit that one can calculate on.

An atom is like a spinning top. Normally, you can store digital information on spinning tops by a.s.signing the number "0" if the top is spinning upward, or "1" if the top is spinning down. If you flip over a spinning top, then you have converted a 0 into a 1 and have done a calculation.

But in the bizarre world of the quantum, an atom is in some sense spinning up and down simultaneously. (In the quantum world, being several places at the same time is commonplace.) An atom can therefore contain much more information than a 0 or a 1. It can describe a mixture of 0 and 1. So quantum computers use "qubits" rather than bits. For example, it can be 25 percent spinning up and 75 percent spinning down. In this way, a spinning atom can store vastly more information than a single bit.

Quantum computers are so powerful that the CIA has looked into their code-breaking potentials. When the CIA tries to break the code of another nation, it searches for the key. Nations have devised ingenious ways of constructing the key that encodes their messages. For example, the key may be based on factorizing a large number. It's easy to factorize the number 21 as the product of 3 and 7. Now let's say that you have an integer of 100 digits, and you ask a digital computer to rewrite it as the product of two other integers. It might take a digital computer a century to be able to factorize this number. A quantum computer, however, is so powerful that in principle it can effortlessly crack any such code. A quantum computer quickly outperforms a standard computer on these huge tasks.

Quantum computers are not science fiction but actually exist today. In fact, I had a chance to see a quantum computer for myself when I visited the MIT laboratory of Seth Lloyd, one of the pioneers in the field. His laboratory is full of computers, vacuum pumps, and sensors, but the heart of his experiment is a machine that resembles a standard MRI machine, except much smaller. Like the MRI machine, his device has two large coils of wire that create a uniform magnetic field in the s.p.a.ce between them. In this uniform magnetic field, he places his sample material. The atoms inside the sample align, like spinning tops. If the atom points up, it corresponds to a 0. If it points down, it corresponds to a 1. Then he sends an electromagnetic pulse into the sample, which changes the alignment of the atoms. Some of the atoms flip over, so a 1 becomes a 0. In this way, the machine has performed a calculation.

So why don't we have quantum computers sitting on our desks, solving the mysteries of the universe? Lloyd admitted to me the real problem that has stymied research in quantum computers is the disturbances from the outside world that destroy the delicate properties of these atoms.