However, inroads have been made that might facilitate this futuristic possibility. Biologists were amazed to find that the genes that describe the layout of the body (from head to toe) were mirrored in the order in which they appear in the chromosomes. These are called the HOX genes, and they describe how the body is constructed. Nature, apparently, has taken a shortcut, mirroring the order of the organs of the body with the sequence found in the chromosomes themselves. This, in turn, has greatly accelerated the process by which the evolutionary history of these genes can be deciphered.

Furthermore, there are master genes that apparently govern the properties of many other genes. By manipulating a handful of these master genes, you can manipulate the properties of dozens of other genes.

In retrospect, we see that Mother Nature has decided to create the layout of the body in much the way an architect might create blueprints. The geometric layout of the blueprint is in the same order as the actual physical layout of the building. Also, the blueprints are modular, so that blocks of sub-blueprints are contained in a single master blueprint.

In addition to creating entirely new hybrid animals by exploiting the modularity of the genome, there is also the possibility of applying genetics to humans, using biotechnology to bring back historical figures. Lanza believes that as long as an intact cell can be extracted from a long-dead person, it will be possible to bring this person back to life. In Westminster Abbey, we have the carefully preserved bodies of long-dead kings and queens, as well as poets, religious figures, politicians, and even scientists like Isaac Newton. One day, Lanza confided to me, it may be possible to find intact DNA within their bodies and bring them back to life.

In the movie The Boys from Brazil, The Boys from Brazil, the plot revolves around bringing back Hitler. One should not believe, however, that one will be able to bring back the genius or notoriety of any of these historic figures. As one biologist noted, if you bring back Hitler, maybe all you get is a second-rate artist (which is what Hitler was before he led the n.a.z.i movement). the plot revolves around bringing back Hitler. One should not believe, however, that one will be able to bring back the genius or notoriety of any of these historic figures. As one biologist noted, if you bring back Hitler, maybe all you get is a second-rate artist (which is what Hitler was before he led the n.a.z.i movement).

BAN ALL DISEASES?.

The prophetic movie Things to Come Things to Come was based on a novel by H. G. Wells and predicted the future of civilization, where World War II unleashed a cycle of endless suffering and misery. Eventually, all the achievements of the human race are reduced to rubble, with gangs of warlords ruling over crushed, impoverished people. But at the end of the movie, a group of farsighted scientists, armed with powerful superweapons, begin to restore order. Civilization finally rises again from the ashes. In one scene, a child is taught the brutal history of the twentieth century and learns about something called colds. What is a cold, she asks? She is told that colds were something that were cured a long time ago. was based on a novel by H. G. Wells and predicted the future of civilization, where World War II unleashed a cycle of endless suffering and misery. Eventually, all the achievements of the human race are reduced to rubble, with gangs of warlords ruling over crushed, impoverished people. But at the end of the movie, a group of farsighted scientists, armed with powerful superweapons, begin to restore order. Civilization finally rises again from the ashes. In one scene, a child is taught the brutal history of the twentieth century and learns about something called colds. What is a cold, she asks? She is told that colds were something that were cured a long time ago.

Maybe not.

Curing all diseases has been one of our most ancient goals. But even by 2100, scientists will not be able to cure all diseases, since diseases mutate faster than we can cure them, and there are too many of them. We sometimes forget that we live in an ocean of bacteria and viruses, which existed billions of years before humans walked the surface of the earth, and will exist billions of years after h.o.m.o sapiens h.o.m.o sapiens is gone. is gone.

Many diseases originally came from animals. This is one of the prices we paid for the domestication of animals, which began roughly 10,000 years ago. So there is a vast reservoir of diseases lurking in animals that will probably outlast the human race. Normally, these diseases infect only a handful of individuals. But with the rise of large cities, these communicable diseases could spread rapidly among the human population, reaching critical ma.s.s and creating pandemics.

For example, when scientists a.n.a.lyzed the genetic sequence of the flu virus, they were surprised to find its origin: birds. Many birds can carry variations of the flu virus without any effects. But then pigs sometimes act as genetic mixing bowls, after eating bird droppings. And then farmers often live near both. Some speculate that this is the reason the flu virus often comes from Asia, because farmers there engage in polyfarming, i.e., living in close proximiy to both ducks and pigs.

The recent H1N1 flu epidemic is only the most recent wave of bird flu and pig flu mutations.

One problem is that humans are continually expanding into new environments, cutting down forests, building suburbs and factories, and in the process encountering ancient diseases lurking among the animals. Because the human population is continuing to expand, this means that we expect to find more surprises coming out of the forest.

For example, there is considerable genetic evidence that HIV began as simian immunodeficiency virus (SIV), which originally infected monkeys but then jumped to humans. Similarly, the hantavirus affected people in the Southwest as they encroached on the territory of prairie rodents. Lyme disease, which is spread largely by ticks, has invaded the suburbs of the Northeast because people now build houses close to the forests where the ticks live. The Ebola virus probably affected tribes of humans back in antiquity, but it was only with the coming of jet travel that it spread to a larger population and made the headlines. Even Legionnaires" disease is probably an ancient one that sp.a.w.ned in stagnant water, but it was the proliferation of air-conditioning units that spread this disease to the elderly on cruise ships.

This means that there will be plenty of surprises to come, with new waves of exotic diseases dominating the headlines of the future.

Unfortunately, cures for these diseases may be late in coming.

For example, even the common cold currently has no cure. The plethora of products found in any drugstore for it treats only the symptoms, rather than killing the virus itself. The problem is that there are probably more than 300 variations of the rhinovirus that causes the common cold, and it is simply too expensive to create a vaccine for all 300.

The situation for HIV is much worse, since there may be thousands of different strains. In fact, HIV mutates so rapidly that, even if you can develop a vaccine for one variety, the virus will soon mutate. Devising a vaccine for HIV is like trying to hit a moving target.

So while we will cure many diseases in the future, probably we will always have some disease that can evade our most advanced science.

BRAVE NEW WORLD.

By 2100, when we will have control over our genetic destiny, we have to compare our fate with the dystopia laid out by Aldous Huxley in his prophetic novel Brave New World, Brave New World, which is set in the year 2540. The book caused universal shock and dismay when it was first published in 1932. which is set in the year 2540. The book caused universal shock and dismay when it was first published in 1932.

Yet more than seventy-five years later, many of his predictions have already come to pa.s.s. He scandalized British society when he wrote about test tube babies, when recreation and procreation would be separated, and when drugs became commonplace, yet today we live in a world where in vitro fertilization and birth control pills are taken for granted. (The only major prediction he made that has not come to pa.s.s is human cloning.) He envisioned a hierarchical world where doctors deliberately clone brain-damaged human embryos, which grow up to become servants of the ruling elite. Depending on the level of mental damage, they could be ranked into the Alphas, who are perfect and destined to rule, down to the Epsilons, who are little more than mentally r.e.t.a.r.ded slaves. So technology, instead of liberating humanity from poverty, ignorance, and disease, has become a nightmare, enforcing an artificial and corrupt stability at the expense of enslaving an entire population.

Although the novel was accurate in many ways, Huxley did not antic.i.p.ate genetic engineering. If he had known about this technology, then he might have worried about another problem: Will the human species split into fragments, with fickle parents and devious governments meddling with the genes of our children? Parents already dress their kids in outlandish outfits and make them compete in silly contests, so why not change the genes to fit the parents" whims? Indeed, parents are probably hardwired by evolution to give every benefit to their progeny, so why not tamper with their genes as well?

As an elementary example of what might go wrong, consider the lowly sonogram. Although doctors innocently introduced the sonogram to help with pregnancies, this has led to a ma.s.sive epidemic of abortions of female fetuses, especially in the countrysides of China and India. One study in Bombay found that 7,997 out of 8,000 aborted fetuses were female. In South Korea 65 percent of all third-born children are male. The generation of children whose parents chose this gender-based abortion will soon be of marriageable age, and millions will find that there are no females to be found. This in turn could cause enormous social dislocation. Peasants who wanted only boys to carry on their name will find that they have no grandchildren.

And in the United States, there is rampant misuse of human growth hormone (HGH), which is often touted as a cure for aging. Originally, HGH was intended to correct hormone deficiencies in children who were too short. Instead, HGH has grown into a huge underground industry based on questionable data concerning aging. In effect, the Internet has created a huge population of human guinea pigs for specious therapies.

So, given the chance, people will often misuse technology and create an enormous amount of mischief. What happens if they get hold of genetic engineering?

In a worst-case scenario, we might have the nightmare imagined by H.G. Wells in his cla.s.sic science fiction novella The Time Machine, The Time Machine, when the human race, in the year 802,701 AD, splits into two distinct races. He wrote, "Gradually, the truth dawned on me: that Man had not remained one species, but had differentiated into two distinct animals: that my graceful children of the Upper World were not the sole descendants of our generation, but that this bleached, obscene, nocturnal Thing, which had flashed before me, was also heir to all the ages." when the human race, in the year 802,701 AD, splits into two distinct races. He wrote, "Gradually, the truth dawned on me: that Man had not remained one species, but had differentiated into two distinct animals: that my graceful children of the Upper World were not the sole descendants of our generation, but that this bleached, obscene, nocturnal Thing, which had flashed before me, was also heir to all the ages."

To see what variations of the human race are possible, simply look at the household dog. Although there are thousands of breeds of dogs, all originally descended from Canis lupus, the gray wolf, which was domesticated roughly 10,000 years ago at the end of the last Ice Age. Because of selective breeding by their human masters, dogs today come in a bewildering variety of sizes and shapes. Body shape, temperament, color, and abilities have all been radically altered by selective breeding. the gray wolf, which was domesticated roughly 10,000 years ago at the end of the last Ice Age. Because of selective breeding by their human masters, dogs today come in a bewildering variety of sizes and shapes. Body shape, temperament, color, and abilities have all been radically altered by selective breeding.

Since dogs age roughly seven times faster than humans, we can estimate that about 1,000 generations of dogs have existed since they separated from wolves. If we apply this to humans, then systematic breeding of humans might split the human race into thousands of breeds in only 70,000 years, although they would be of the same species. With genetic engineering, this process could conceivably be vastly accelerated, to a single generation.

Fortunately, there are reasons to believe the speciation of the human race will not happen, at least not in the coming century. In evolution, a single species usually splits apart if it separates geographically into two separate breeding populations. This happened, for example, in Australia, where the physical separation of many animal species has led to the evolution of animals found nowhere else on earth, such as marsupials like the kangaroo. Human populations, by contrast, are highly mobile, without evolutionary bottlenecks, and are highly intermingled.

As Gregory Stock of UCLA has said, "Traditional Darwinian evolution now produces almost no change in humans and has little prospect of doing so in the foreseeable future. The human population is too large and entangled, and selective pressures are too localized and transitory."

There are also constraints coming from the Cave Man Principle.

As we mentioned earlier, people often reject the advances of technology (for example, the paperless office) when it contradicts human nature, which has remained relatively constant over the past 100,000 years. People may not want to create designer children who deviate from the norm and are considered freaks by their peers. This decreases their chances of success in society. Dressing one"s children in silly clothing is one thing, but permanently changing their heredity is an entirely different thing. (In a free market, there probably will be a place for weird genes, but it will be small, since the market will be driven by consumer demand.) More than likely, by the end of the century, a couple will be given a library of genes to choose from, mostly those for eliminating genetic diseases but also some for genetic enhancement. However, there will be little market pressure to finance the study of bizarre genes because the demand for them will be so small.

The real danger will come not so much from consumer demand but from dictatorial governments that may want to use genetic engineering for their own purposes, such as breeding stronger but more obedient soldiers.

Another problem arises in the distant future, when we have s.p.a.ce colonies on other planets whose gravity and climactic conditions are much different from the earth. At that point, perhaps in the next century, it becomes realistic to think of engineering a new breed of humans who can adjust to different gravity fields and atmospheric conditions. For example, a new breed of humans may be able to consume different amounts of oxygen, adjust to a different length of day, and have a different body weight and metabolism. But s.p.a.ce travel will be expensive for a long time. By the end of the century, we may have a small outpost on Mars, but an overwhelming fraction of the human race will still be on the earth. For decades to centuries to come, s.p.a.ce travel will be for astronauts, the wealthy, and maybe a handful of hardy s.p.a.ce colonists.

So the splitting of the human race into different s.p.a.cefaring species around the solar system and beyond will not happen in this century, or perhaps even the next. For the foreseeable future, unless there are dramatic breakthroughs in s.p.a.ce technology, we are largely stuck on the earth.

Lastly, there is yet another threat that faces us before we reach 2100: that this technology may be deliberately turned against us, in the form of designer germ warfare.

GERM WARFARE.

Germ warfare is as old as the Bible. Ancient warriors used to hurl diseased bodies over the walls of enemy cities or poison their wells with the bodies of diseased animals. Deliberately giving smallpox-infected clothing to an adversary is another way to destroy them. But with modern technology, germs can be genetically bred to wipe out millions of people.

In 1972, the United States and the former Soviet Union signed an historic treaty banning the use of germ warfare for offensive purposes. However, the technology of bioengineering is so advanced today that the treaty is meaningless.

First, there is no such thing as offensive and defensive technology when it comes to DNA research. The manipulation of genes can be used for either purpose.

Second, with genetic engineering, it is possible to create weaponized germs, those that have been deliberately modified to increase their lethality or their ability to spread into the environment. It was once believed that only the United States and Russia possessed the last vials containing smallpox, the greatest killer in the history of the human race. In 1992, a Soviet defector claimed that the Russians had weaponized smallpox and actually produced up to twenty tons of it. With the breakup of the Soviet Union, there is the nagging fear that one day a terrorist group may pay to gain access to weaponized smallpox.

In 2005, biologists successfully resurrected the Spanish flu virus of 1918, which killed more people than World War I. Remarkably, they were able to resurrect the virus by a.n.a.lyzing a woman who had died and was buried in the permafrost of Alaska, as well as samples taken from U.S. soldiers during the epidemic.

The scientists then proceeded to publish the entire genome of the virus on the Web, making it known to the entire world. Many scientists felt uneasy about this, since one day even a college student with access to a university laboratory might be able to resurrect one of the greatest killers in the history of the human race.

In the short term, the publication of the genome of the Spanish flu virus was a bonanza for scientists, who then could examine the genes to solve a long-standing puzzle: How did a tiny mutation cause such widespread damage to the human population? The answer was soon found. The Spanish flu virus, unlike other varieties, causes the body"s immune system to overreact, releasing large amounts of fluid that eventually kills the patient. The person literally drowns in his own fluids. Once this was understood, the genes that cause this deadly effect could be compared to the genes of the H1N1 flu and other viruses. Fortunately, none of them possessed this lethal gene. Moreover, one could actually calculate how close a virus was to attaining this alarming capability, and the H1N1 flu was still far from achieving this ability.

But in the long term, there is a price to pay. Every year, it becomes easier and easier to manipulate the genes of living organisms. Costs keep plummeting, and the information is widely available on the Internet.

Within a few decades, some scientists believe that it will be possible to create a machine that will allow you to create any gene simply by typing the desired components. By typing in the A-T-C-G symbols making up a gene, the machine will then automatically splice and dice DNA to create that gene. If so, then it means that perhaps even high school students may one day do advanced manipulations of life-forms.

One nightmare scenario is airborne AIDS. Cold viruses, for example, possess a few genes that allow them to survive in droplets of aerosols, so that sneezing can infect others. At present, the AIDS virus is quite vulnerable when it is exposed to the environment. But if the cold virus genes are implanted into the AIDS virus, then it is conceivable that they might make it able to survive outside the human body. This could then cause the AIDS virus to spread like the common cold, thereby infecting a large portion of the human race. It is also known that viruses and bacteria do exchange genes, so there is also the possibility that the AIDS and common cold viruses can exchange genes naturally, although this is less likely.

In the future, a terrorist group or nation-state may be able to weaponize AIDS. The only thing preventing them from unleashing it would be the fact that they, too, would also perish if the virus were to be dispersed into the environment.

This threat became real right after the tragedy of 9/11. An unknown person mailed packets of a white powder containing anthrax spores to well-known politicians around the country. A careful, microscopic a.n.a.lysis of the white powder showed that the anthrax spores had been weaponized for maximum death and destruction. Suddenly, the entire country was gripped with fear that a terrorist group had access to advanced biological weapons. Although anthrax is found in the soil and throughout our environment, only a person with advanced training and maniacal intentions could have purified and weaponized the anthrax and pulled off this feat.

Even after one of the largest manhunts in U.S. history, the culprit was never found, even to this day (although a leading suspect recently committed suicide). The point here is that even a single individual with some advanced biological training can terrorize an entire nation.

One restraining factor that has kept germ warfare in check is simple self-interest. During World War I, the efficacy of poison gas on the battlefield was mixed. The wind conditions were often unpredictable, so the gas could blow back onto your own troops. Its military value was largely in terrorizing the enemy, rather than defeating him. Not a single decisive battle was won using poison gas. And even at the height of the Cold War, both sides knew that poison gas and biological weapons could have unpredictable effects on the battlefield, and could easily escalate to a nuclear confrontation.

All the arguments mentioned in this chapter, as we have seen, involved the manipulation of genes, proteins, and molecules. Then the next question naturally arises: How far can we manipulate individual atoms?

The principles of physics, as far as I can see, do not speak against the possibility of maneuvering things atom by atom.

-RICHARD FEYNMAN, n.o.bEL LAUREATE Nanotechnology has given us the tools to play with the ultimate toy box of nature-atoms and molecules. Everything is made from these, and the possibilities to create new things appear limitless.

-HORST STORMER, n.o.bEL LAUREATE The role of the infinitely small is infinitely large.

-LOUIS PASTEUR

The mastery of tools is a crowning achievement that distinguishes humanity from the animals. According to Greek and Roman mythology, this process began when Prometheus, taking pity on the plight of humans, stole the precious gift of fire from Vulcan"s furnace. But this act of thievery enraged the G.o.ds. To punish humanity, Zeus devised a clever trick. He asked Vulcan to forge a box and a beautiful woman out of metal. Vulcan created this statue, called Pandora, and then magically brought her to life, and told her never to open the box. Out of curiosity, one day she did, and unleashed all the winds of chaos, misery, and suffering in the world, leaving only hope in the box.

So from Vulcan"s divine furnace emerged both the dreams and the suffering of the human race. Today, we are designing revolutionary new machines that are the ultimate tools, forged from individual atoms. But will they unleash the fire of enlightenment and knowledge or the winds of chaos?

Throughout human history, the mastery of tools has determined our fate. When the bow and arrow were perfected thousands of years ago, it meant that we could fire projectiles much farther than our hands could throw them, increasing the efficiency of our hunting and increasing our food supply. When metallurgy was invented around 7,000 years ago, it meant that we could replace huts of mud and straw and eventually create great buildings that soared above the earth. Soon, empires began to rise from the forest and the desert, built by the tools forged from metals.

And now we are on the brink of mastering yet another type of tool, much more powerful than anything we have seen before. This time, we will be able to master the atoms themselves out of which everything is created. Within this century, we may possess the most important tool ever imagined-nanotechnology that will allow us to manipulate individual atoms. This could begin a second industrial revolution, as molecular manufacturing creates new materials we can only dream about today, which are superstrong, superlight, with amazing electrical and magnetic properties.

n.o.bel laureate Richard Smalley has said, "The grandest dream of nanotechnology is to be able to construct with the atom as the building block." Philip Kuekes of Hewlett-Packard said, "Eventually, the goal is not just to make computers the size of dust particles. The idea would be to make simple computers the size of bacteria. Then you could get something as powerful as what"s now on your desktop into a dust particle."

This is not just the hope of starry-eyed visionaries. The U.S. government takes it seriously. In 2009, because of nanotechnology"s immense potential for medical, industrial, aeronautical, and commercial applications, the National Nanotechnology Initiative allocated $1.5 billion for research. The government"s National Science Foundation Nanotechnology Report states, "Nanotechnology has the potential to enhance human performance, to bring sustainable development for materials, water, energy, and foods, to protect against unknown bacteria and viruses...."

Ultimately, the world economy and fate of nations may depend on this. Around 2020 or soon afterward, Moore"s law will begin to falter and perhaps eventually collapse. The world economy could be thrown into disarray unless physicists can find a suitable replacement for silicon transistors to power our computers. The solution to the problem may come from nanotechnology.

Nanotechnology might also, perhaps by the end of this century, create a machine that only the G.o.ds can wield, a machine that can create anything out of almost nothing.

THE QUANTUM WORLD.

The first to call attention to this new realm of physics was n.o.bel laureate Richard Feynman, who asked a deceptively simple question: How small can you make a machine? This was not an academic question. Computers were gradually becoming smaller, changing the face of industry, so it was becoming apparent that the answer to this question could have an enormous impact on society and the economy.

In his prophetic talk given in 1959 to the American Physical Society t.i.tled "There"s Plenty of Room at the Bottom," Feynman said, "It is interesting that it would be, in principle, possible (I think) for a physicist to synthesize any chemical substance that the chemist writes down. Give the orders and the physicist synthesizes it. How? Put the atoms down where the chemist says, and so you make the substance." Feynman concluded that machines made out of individual atoms were possible, but that new laws of physics would make them difficult, but not impossible, to create.

So ultimately, the world economy and the fate of nations may depend on the bizarre and counterintuitive principles of the quantum theory. Normally, we think that the laws of physics remain the same if you go down to smaller scales. But this is not true. In movies like Disney"s Honey, I Shrunk the Kids Honey, I Shrunk the Kids and and The Incredible Shrinking Man, The Incredible Shrinking Man, we get the mistaken impression that miniature people would experience the laws of physics the same way we do. For example, in one scene in the Disney movie, our shrunken heroes ride on an ant during a rainstorm. Raindrops fall onto the ground and make tiny puddles, just as in our world. But in reality, raindrops can be larger than ants. So when an ant encounters a raindrop, it would see a huge hemisphere of water. The hemisphere of water does not collapse because surface tension acts like a net that holds the droplet together. In our world, surface tension of water is quite small, so we don"t notice it. But on the scale of an ant, surface tension is proportionately huge, so rain beads up into droplets. we get the mistaken impression that miniature people would experience the laws of physics the same way we do. For example, in one scene in the Disney movie, our shrunken heroes ride on an ant during a rainstorm. Raindrops fall onto the ground and make tiny puddles, just as in our world. But in reality, raindrops can be larger than ants. So when an ant encounters a raindrop, it would see a huge hemisphere of water. The hemisphere of water does not collapse because surface tension acts like a net that holds the droplet together. In our world, surface tension of water is quite small, so we don"t notice it. But on the scale of an ant, surface tension is proportionately huge, so rain beads up into droplets.

(Furthermore, if you tried to scale up the ant so that it was the size of a house, you have another problem: its legs would break. As you increase the size of the ant, its weight grows much faster than the strength of its legs. If you increase the size of an ant by a factor of 10, its volume and hence its weight is 10 10 10 = 1,000 times heavier. But its strength is related to the thickness of its muscles, which is only 10 10 = 100 times stronger. Hence, the giant ant is 10 times weaker, relatively speaking, than an ordinary ant. This also means that King Kong, instead of terrorizing New York City, would crumble if he tried to climb the Empire State Building.) Feynman noted that other forces also dominate at the atomic scale, such as hydrogen bonding and the van der Waals force, caused by tiny electrical forces that exist between atoms and molecules. Many of the physical properties of substances are determined by these forces.

(To visualize this, consider the simple problem of why the Northeast has so many potholes in its highways. Every winter, water seeps into tiny cracks in the asphalt; the water expands as it freezes, causing the asphalt to crumble and gouging out a pothole. But it violates common sense to think that water expands when it freezes. Water does expand because of hydrogen bonding. The water molecule is shaped like a V, with the oxygen atom at the base. The water molecule has a slight negative charge at the bottom and a positive charge at the top. Hence, when you freeze water and stack water molecules, they expand, forming a regular lattice of ice with plenty of s.p.a.ces between the molecules. The water molecules are arranged like hexagons. So water expands as it freezes since there is more s.p.a.ce between the atoms in a hexagon. This is also the reason snowflakes have six sides, and explains why ice floats on water, when by rights it should sink.) WALKING THROUGH WALLS.

In addition to surface tension, hydrogen bonding, and van der Waals forces, there are also bizarre quantum effects at the atomic scale. Normally, we don"t see quantum forces at work in everyday life. But quantum forces are everywhere. For example, by rights, since atoms are largely empty, we should be able to walk through walls. Between the nucleus at the center of the atom and the electron sh.e.l.ls, there is only a vacuum. If the atom were the size of a football stadium, then the stadium would be empty, since the nucleus would be roughly the size of a grain of sand.

(We sometimes amaze our students with a simple demonstration. We take a Geiger counter, place it in front of a student, and put a harmless radioactive pellet in back. The student is startled that some particles pa.s.s right through his body and trigger the Geiger counter, as if he is largely empty, which he is.) But if we are largely empty, then why can"t we walk through walls? In the movie Ghost, Ghost, Patrick Swayze"s character is killed by a rival and turns into a ghost. He is frustrated every time he tries to touch his former fiancee, played by Demi Moore. His hands pa.s.s through ordinary matter; he finds that he has no material substance and simply floats through solid objects. In one scene, he sticks his head into a moving subway car. The train races by with his head sticking inside, yet he doesn"t feel a thing. (The movie does not explain why gravity does not pull him through the floor so he falls to the center of the earth. Ghosts, apparently, can pa.s.s through anything except floors.) Patrick Swayze"s character is killed by a rival and turns into a ghost. He is frustrated every time he tries to touch his former fiancee, played by Demi Moore. His hands pa.s.s through ordinary matter; he finds that he has no material substance and simply floats through solid objects. In one scene, he sticks his head into a moving subway car. The train races by with his head sticking inside, yet he doesn"t feel a thing. (The movie does not explain why gravity does not pull him through the floor so he falls to the center of the earth. Ghosts, apparently, can pa.s.s through anything except floors.) So why can"t we pa.s.s through solid objects like ghosts? The answer resides in a curious quantum phenomenon. The Pauli exclusion principle states that no two electrons can exist in the same quantum state. Hence when two nearly identical electrons get too close, they repel each other. This is the reason objects appear to be solid, which is an illusion. The reality is that matter is basically empty.

When we sit in a chair, we think we are touching it. Actually, we are hovering above the chair, floating less than a nanometer above it, repelled by the chair"s electrical and quantum forces. This means that whenever we "touch" something, we are not making direct contact at all but are separated by these tiny atomic forces. (This also means that if we could somehow neutralize the exclusion principle, then we might be able to pa.s.s through walls. However, no one knows how to do this.) Not only does the quantum theory keep atoms from crashing through one another, it also binds them together into molecules. Imagine for the moment that an atom is like a tiny solar system, with planets revolving around a sun. Now, if two such solar systems collided, then the planets would either crash into one another or fly out in all directions, causing the solar system to collapse. Solar systems are never stable when they collide with another solar system, so by rights, atoms should collapse when they b.u.mp into one another.

In reality, when two atoms get very close, they either bounce off each other or they combine to form a stable molecule. The reason atoms can form stable molecules is because electrons can be shared between two atoms. Normally, the idea of an electron being shared between two atoms is preposterous. It is impossible if the electron obeyed the commonsense laws of Newton. But because of the Heisenberg uncertainty principle, you don"t know precisely where the electron is. Instead, it"s smeared out between two atoms, which holds them together.

In other words, if you turn off the quantum theory, then your molecules fall apart when they b.u.mp into one another and you would dissolve into a gas of particles. So the quantum theory explains why atoms can bind to form solid matter, rather than disintegrate.

(This is also the reason you cannot have worlds within worlds. Some people imagine that our solar system or galaxy might be an atom in someone else"s gigantic universe. This was, in fact, the final scene in the movie Men in Black, Men in Black, where the entire known universe was in fact just an atom in some alien"s ball game. But according to physics, this is impossible, since the laws of physics change as we go from scale to scale. The rules governing atoms are quite different from the rules governing galaxies.) where the entire known universe was in fact just an atom in some alien"s ball game. But according to physics, this is impossible, since the laws of physics change as we go from scale to scale. The rules governing atoms are quite different from the rules governing galaxies.) Some of the mind-bending principles of the quantum theory are: *you cannot know the exact velocity and location of any particle-there is always uncertainty *particles can in some sense be in two places at the same time *all particles exist as mixtures of different states simultaneously; for example, spinning particles can be mixtures of particles whose axes spin both up and down simultaneously *you can disappear and reappear somewhere else

All these statements sound ridiculous. In fact, Einstein once said, "the more successful the quantum theory is, the sillier it looks." No one knows where these bizarre laws come from. They are simply postulates, with no explanation. The quantum theory has only one thing going for it: it is correct. Its accuracy has been measured to one part in ten billion, making it the most successful physical theory of all time.

The reason we don"t see these incredible phenomena in daily life is because we are composed of trillions upon trillions of atoms, and these effects, in some sense, average out.

MOVING INDIVIDUAL ATOMS.

Richard Feynman dreamed of the day when a physicist could manufacture any molecule, atom for atom. That seemed impossible back in 1959, but part of that dream is now a reality.

I had a chance to witness this up close, when I visited the IBM Almaden Research Center in San Jose, California. I came to observe a remarkable instrument, the scanning tunneling microscope, which allows scientists to view and manipulate individual atoms. This device was invented by Gerd Binnig and Heinrich Rohrer of IBM, for which they won the n.o.bel Prize in 1986. (I remember, as a child, my teacher telling us that we would never be able to see atoms. They are just too small, he said. By then, I had already decided to become an atomic scientist. I realized that I would spend the rest of my life studying something I would never be able to observe directly. But today, not only can we see atoms, but we can play with them, with atomic tweezers.) The scanning tunneling microscope is actually not a microscope at all. It resembles an old phonograph. A fine needle (with a tip that is only a single atom across) pa.s.ses slowly over the material being a.n.a.lyzed. A small electrical current travels from the needle, through the material, to the base of the instrument. As the needle pa.s.ses over the object, the electrical current changes slightly every time it pa.s.ses over an atom. After multiple pa.s.ses, the machine prints out the stunning outline of the atom itself. Using an identical needle, the microscope is then capable not just of recording these atoms but also of moving them around. In this way, one can spell out the letters, such as the initials IBM, and in fact even design primitive machines built out of atoms.

(Another recent invention is the atomic force microscope, which can give us stunning 3-D pictures of arrays of atoms. The atomic force microscope also uses the needle with a very small point, but it shines a laser onto it. As the needle pa.s.ses over the material being studied, the needle jiggles, and this motion is recorded by the laser beam image.) I found that moving individual atoms around was quite simple. I sat in front of a computer screen, looking at a series of white spheres, each resembling a Ping-Pong ball about an inch across. Actually, each ball was an individual atom. I placed the cursor over an atom and then moved the cursor to another position. I pushed a b.u.t.ton that then activated the needle to move the atom. The microscope rescanned the substance. The screen changed, showing that the ball had moved to precisely where I wanted it.