In Star Trek IV: The Voyage Home, the Enterprise's crew captures a Klingon battle cruiser. Unlike the ships of the Federation Starfleet, the ships of the Klingon Empire are equipped with a secret "cloaking device" that can make them invisible to the eye and radar. This device allows Klingon ships to go unnoticed at the tail of Federation ships and strike with impunity. Thanks to the cloaking device, the Klingon Empire has a strategic advantage over the Federation of Planets.
Is such a device actually possible? Invisibility has long become one of the usual wonders of sci-fi and fantasy works - from "The Invisible Man" to the magic invisibility cloak of Harry Potter or the ring from "The Lord of the Rings". Nevertheless, for at least a hundred years, physicists have unanimously denied the possibility of creating invisibility cloaks and have unequivocally stated that this is impossible: cloaks, they say, violate the laws of optics and do not agree with any of the known properties of matter.
But today, the impossible can become possible. Advances in the field of "metamaterials" are forcing a significant revision of optics textbooks. Working samples of such materials created in the laboratory are of great interest to the media, industrialists and the military; everyone is interested in how to make the visible invisible.
Invisibility in history
Invisibility is perhaps one of the oldest concepts in ancient mythology. Since the beginning of time, a man, left alone in the frightening silence of the night, felt the presence of invisible beings and was afraid of them. All around him in the darkness lurked the spirits of the dead - the souls of those who had gone before him. The Greek hero Perseus, armed with an invisible helmet, managed to kill the evil gorgon Medusa. Generals of all times dreamed of a cloaking device that would allow them to become invisible to the enemy. Using invisibility, one could easily penetrate the enemy's line of defense and take him by surprise. Criminals could use invisibility to commit daring robberies.
In Plato's theory of ethics and morality, invisibility played a major role. In his philosophical work "The State" Plato told us the myth of the Giga ring. In this myth, the poor but honest shepherd Gigus of Lydia enters a secret cave and finds a tomb there; he sees a gold ring on the corpse's finger. Gig further discovers that the ring has magical powers and can make it invisible. The poor shepherd is literally drunk with the power that the ring has given him. Having made his way into the royal palace, Gigus seduces the queen with a ring, then with her help he kills the king and becomes the next king of Lydia.
The moral that Plato deduced from this story is that no person is able to resist the temptation to take someone else's and kill with impunity. People are weak, and morality is a social phenomenon that must be implanted and supported from the outside. In public, a person can observe moral standards in order to look decent and honest and maintain his own reputation, but once you give him the opportunity to become invisible, he will not be able to resist and will certainly use his new power. (Some believe that this moral parable inspired JRR Tolkien to create The Lord of the Rings trilogy; the ring that makes its owner invisible is also a source of evil.)
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In science fiction, invisibility is one of the most common plot drives. In the 1930s comic series. "Flash Gordon" Flash becomes invisible to hide from the firing squad of the villainous Ming the Ruthless. In the novels and films about Harry Potter, the main character, putting on a magic cloak, can wander around Hogwarts Castle unnoticed.
H. G. Wells, in the classic novel The Invisible Man, has embodied roughly the same ideas in concrete form. In this novel, a medical student accidentally discovers the possibilities of the fourth dimension and becomes invisible. Unfortunately, he uses the obtained fantastic opportunities for personal gain, commits a whole series of petty crimes and eventually dies in a desperate attempt to escape from the police.
Maxwell's equations and the mystery of light
Physicists have gained any clear understanding of the laws of optics relatively recently as a result of the work of the Scotsman James Clerk Maxwell, one of the giants of physics in the 19th century. In a sense, Maxwell was the complete opposite of Faraday. If Faraday had an excellent sense of the experimenter, but did not have any formal education, then his contemporary Maxwell was a master of higher mathematics. He completed his training in mathematical physics with honors at Cambridge, where Isaac Newton worked two centuries before him.
Newton invented differential calculus - it describes in the language of differential equations how objects continuously undergo infinitely small changes in time and space. The movement of ocean waves, liquids, gases, and cannonballs can all be described in terms of differential equations. Maxwell began to work with a clear goal in mind: to express Faraday's revolutionary discoveries and his physical fields using precise differential equations.
Maxwell began with Faraday's assertion that electric fields can turn into magnetic and vice versa. He took pictures of physical fields drawn by Faraday and wrote them down in the exact language of differential equations. As a result, one of the most important systems of equations in modern science was obtained. This is a system of eight differential equations of a rather creepy kind. Every physicist and engineer in the world had to sweat over them at one time, mastering electromagnetism at the institute.
Then Maxwell asked himself a fateful question: if a magnetic field can turn into an electric field and vice versa, then what happens if they constantly change from one to another in an endless series of transformations? Maxwell discovered that such an electromagnetic field would generate an ocean-like wave. He calculated the speed of movement of such waves and, to his own amazement, found that it was equal to the speed of light! In 1864, having discovered this fact, he prophetically wrote: "This speed is so close to the speed of light that we seem to have every reason to conclude that light itself … is an electromagnetic disturbance."
This discovery became, perhaps, one of the greatest in the history of mankind - the secret of light was finally revealed! Maxwell suddenly realized that everything - the glow of the summer sunrise, and the furious rays of the setting sun, and the dazzling colors of the rainbow, and the stars in the night sky - can be described using waves, which he casually depicted on a piece of paper. Today we understand that the entire electromagnetic spectrum: radar signals, microwave radiation and television waves, infrared, visible and ultraviolet light, X-rays and gamma rays are nothing more than Maxwellian water; and these, in turn, represent the vibrations of the Faraday physical fields.
Speaking about the significance of Maxwell's equations, Einstein wrote that this is "the most profound and fruitful thing that physics has experienced since the time of Newton."
(Tragically, Maxwell, one of the greatest physicists of the 19th century, died young enough, at the age of 48, of stomach cancer - probably the same disease that killed his mother at that age. If he lived longer, he may have succeeded would discover that his equations allowed space-time to be distorted, leading directly to Einstein's theory of relativity The idea that if Maxwell had lived longer and the theory of relativity could have emerged during the American Civil War is shocking to the core.)
Maxwell's theory of light and the atomic theory of the structure of matter give optics and invisibility a simple explanation. In a solid, atoms are tightly packed, while in a liquid or gas, the distance between molecules is much greater. Most solids are opaque, since light rays cannot pass through a dense array of atoms, which acts as a brick wall. Many liquids and gases, on the other hand, are transparent, because it is easier for light to pass between rare atoms, the distance between which is greater than the wavelength of visible light. For example, water, alcohol, ammonia, acetone, hydrogen peroxide, gasoline and other liquids are transparent, as are transparent and gases such as oxygen, hydrogen, nitrogen, carbon dioxide, methane, etc.
There are several important exceptions to this rule. Many crystals are both solid and transparent. But the atoms in the crystal are located at the sites of a regular spatial lattice and form regular rows with equal intervals between them. As a result, there are always many paths in the crystal lattice along which a ray of light can pass through it. Therefore, although the atoms in a crystal are packed no less densely than in any other solid, light is still able to penetrate it.
Under certain circumstances, even a solid object with randomly spaced atoms can become transparent. For some materials, this effect can be achieved by heating the object to a high temperature and then rapidly cooling it. For example, glass is a solid that, due to the random arrangement of atoms, has many of the properties of a liquid. Some candies can also be made transparent this way.
Obviously, the invisibility property arises at the atomic level, according to Maxwell's equations, and therefore it is extremely difficult, if not impossible, to reproduce it using conventional methods. To make Harry Potter invisible, he will have to be liquidated, boiled and turned into steam, crystallized, heated and cooled - you must agree, any of these actions would be very difficult even for a wizard.
The military, unable to build invisible aircraft, tried to do a simpler thing: they created the stele technology, which makes aircraft invisible to radars. Stele technology, based on Maxwell's equations, performs a series of tricks. The stele jet fighter is easy to see with the naked eye, but on the enemy's radar screen, its image is roughly the size of a large bird. (In fact, stele technology is a combination of several completely different tricks. Whenever possible, the fighter's construction materials are replaced by radar-transparent ones: instead of steel, various plastics and resins are used; fuselage angles change; engine nozzle design, etc. all these tricks can be made the enemy's radar beam hitting the plane,scatter in all directions and not return to the receiving device. But even with this technology, the fighter does not become completely invisible; it just deflects and scatters the radar beam as much as technically possible.)
Metamaterials and invisibility
Perhaps the most promising of recent advances in invisibility is an exotic new material known as "metamaterial"; it is possible that someday he will make objects actually invisible. It's funny, but once the existence of metamaterials was also considered impossible, since they violate the laws of optics. But in 2006, researchers from Duke University in Durham, North Carolina and Imperial College London successfully refuted this conventional wisdom and made the object invisible to microwave radiation using metamaterials. There are still enough obstacles on this path, but for the first time in history, mankind has a technique that makes it possible to make ordinary objects invisible. (This research was funded by DARPA, the Defense Advanced Research Projects Agency.)
Nathan Myhrvold, former chief technologist at Microsoft, argues that the revolutionary power of metamaterials "will completely change the way we approach optics and almost every aspect of electronics … Some of the metamaterials are capable of feats that would have seemed like miracles decades ago."
What are metamaterials? These are substances with optical properties that do not exist in nature. When metamaterials are created, tiny implants are embedded in matter, forcing electromagnetic waves to take non-standard paths. At Duke University, scientists have inserted many tiny electrical circuits into copper tapes laid in flat concentric circles (all a bit like a hotplate). The result is a complex structure made of ceramics, Teflon, composite fibers and metal components. Tiny implants present in copper make it possible to deflect microwave radiation and direct it along a predetermined path. Imagine a river flowing around a boulder. The water turns around the stone very quicklytherefore, its presence downstream does not affect in any way and it is impossible to reveal it. Likewise, metamaterials are capable of continuously changing the route of microwaves so that they flow around, say, a certain cylinder and thus make everything inside this cylinder invisible to radio waves. If the metamaterial can also eliminate all reflections and shadows, then the object will become completely invisible to this form of radiation.
Scientists have successfully demonstrated this principle with a device composed of ten fiberglass rings covered with copper elements. The copper ring inside the device was almost invisible to microwave radiation; it only cast a faint shadow.
The unusual properties of metamaterials are based on their ability to control a parameter known as the "refractive index". Refraction - the property of light to change the direction of propagation when passing through a transparent material. If you put your hand in water or just look through the lenses of your glasses, you will notice that water and glass deflect and distort the path of ordinary light rays.
The reason for the deflection of a light beam in glass or water is that the light slows down as it enters a dense transparent material. The speed of light in an ideal vacuum is constant, but in glass or water, light "squeezes" through a cluster of trillions of atoms and therefore slows down. (The ratio of the speed of light in a vacuum to the speed of light in a medium is called the refractive index. Since light in any medium slows down, the refractive index is always greater than one.) For example, the refractive index for a vacuum is 1.00; for air -1,0003; for glass-1.5; for a diamond-2.4. As a rule, the denser the medium, the more it deflects the light beam and, accordingly, the higher the refractive index.
Mirages can serve as a very clear demonstration of the phenomena associated with refraction. If you, driving along the highway on a hot day, look straight ahead at the horizon, then the road will seem to you shimmering in places and will create the illusion of a sparkling water surface. In the desert, you can sometimes see the outlines of distant cities and mountains on the horizon. This happens because the air heated above the roadbed or desert sand has a lower density and, accordingly, a lower refractive index than the surrounding normal, cooler air; therefore, light from distant objects can be refracted in a heated layer of air and then enter the eye; this gives you the illusion that you really see distant objects.
As a rule, the refractive index is a constant value. A narrow beam of light, penetrating the glass, changes direction, and then continues to move in a straight line. But suppose for a moment that we are able to control the refractive index so that at each point of the glass it can constantly change in a given way, Light, moving in such a new material, could change direction arbitrarily; the path of the ray in this environment would meander like a snake.
If it was possible to control the refractive index in a metamaterial so that the light bends around a certain object, then this object will become invisible. To obtain such an effect, the refractive index in a metamaterial must be negative, but any textbook on optics says that this is impossible, (Metamaterials were first predicted theoretically in the work of Soviet physicist Viktor Veselago in 1967. It was Veselago who showed that these materials must have such unusual optical properties as negative refractive index and the inverse Doppler effect. Metamaterials seem so strange and even absurd that at first their practical implementation was considered simply impossible. However, in the last few years, metamaterials were still obtained in the laboratory, which forced physicists to start rewriting textbooks on optics.)
Researchers who deal with meta materials are constantly annoyed by journalists with the question: when will invisibility cloaks finally appear on the market? The answer can be formulated very simply: not soon.
David Smith of Duke University says: “Reporters are calling and begging for at least a deadline. In how many months or, say, years it will happen. They press, press and press, and in the end you can't stand it and say that maybe in fifteen years. And right there - a newspaper headline, right? Fifteen years before Harry Potter's cloak. That is why he now refuses to name any dates.
Fans of Harry Potter or Star Trek will likely have to wait. Although the real invisibility cloak no longer contradicts the known laws of nature - and most physicists agree with this at the moment - scientists still have many difficult technical obstacles to overcome before this technology can be extended to work with visible light, and not just with microwave radiation.
In the general case, the dimensions of the internal structures embedded in the metamaterial should be less than the radiation wavelength. For example, microwaves can have a wavelength of the order of 3 cm, so if we want the metamaterial to bend the microwaves path, we must insert implants into it smaller than 3 cm. But to make the object invisible to green light (with a wavelength of 500 nm), the metamaterial should have embedded structures only about 50 nm long. But nanometers are already an atomic scale, and nanotechnology is required to work with such sizes. (A nanometer is one billionth of a meter. One nanometer can hold about five atoms.) Perhaps this is the key problem we will have to face when creating a true invisibility cloak. To bend at will, like a snake, the path of a light beam,we would have to modify individual atoms within the metamaterial.
Metamaterials for visible light
So the race began.
Immediately after the announcement of the receipt of the first metamaterials in the laboratory, feverish activity began in this area. Every few months we hear about revolutionary insights and startling breakthroughs. The goal is clear: to create metamaterials using nanotechnology that can bend not only microwaves, but also visible light. Several approaches have already been proposed, and all of them seem to be quite promising.
One of the proposals is to use ready-made methods, that is, to borrow the used technologies of the microelectronic industry for the production of metamaterials. For example, the miniaturization of computers is based on the technology of "photolithography"; it is also the engine of the computer revolution. This technology allows engineers to place hundreds of millions of tiny transistors on a silicon wafer the size of a thumbnail.
The power of computers doubles every 18 months (this pattern is called Moore's Law). This is due to the fact that scientists with the help of ultraviolet radiation "etch" more and more tiny components on silicon chips. This technology is very similar to the process by which a pattern is stenciled onto a colorful T-shirt. (Computer engineers start with a thin substrate, on which the finest layers of various materials are superimposed on top. Then the substrate is covered with a plastic mask that acts as a template. The complex pattern of conductors, transistors and computer components that form the basis of the circuit diagram is pre-applied to the mask. The workpiece is irradiated with hard UV light, that is, exposed to ultraviolet radiation with a very short wavelength;this radiation, as it were, transfers the pattern of the matrix onto a light-sensitive substrate. Then the workpiece is treated with special gases and acids, and the complex pattern of the matrix is etched onto the substrate in those places where it was exposed to ultraviolet radiation. The result of this process is a plate with hundreds of millions of tiny indentations that form the circuits of the transistors.) Currently, the smallest components that can be created using the described process are about 30 nm (or about 150 atoms). The result of this process is a plate with hundreds of millions of tiny indentations that form the circuits of the transistors.) Currently, the smallest components that can be created using the described process are about 30 nm (or about 150 atoms). The result of this process is a plate with hundreds of millions of tiny indentations that form the circuits of the transistors.) Currently, the smallest components that can be created using the described process are about 30 nm (or about 150 atoms).
A notable milestone on the road to invisibility was a recent experiment by a group of scientists from Germany and the US Department of Energy, in which the process of etching a silicon substrate was used to make the first metamaterial capable of operating in the visible range of light. In early 2007, scientists announced that the metamaterial they created was affecting red light. The "impossible" was implemented in a surprisingly short time.
Physicist Kostas Sukulis of Ames Laboratory and Iowa State University, along with Stephan Linden, Martin Wegener and Gunnar Dolling of the University of Karlsruhe in Germany, managed to create a metamaterial with a refractive index of -0.6 for red light with a wavelength of 780 nm. (Prior to this, the world record for the wavelength of radiation that was "wrapped" with a metamaterial was 1400 nm; this is no longer visible, but infrared light.)
To begin with, the scientists took a sheet of glass and applied a thin layer of silver to it, then a layer of magnesium fluoride, then again a layer of silver; thus, a "sandwich" with fluoride with a thickness of only 100 nm was obtained. The scientists then used standard etching technology to make many tiny square holes in this sandwich (only 100 nm wide, much less than the wavelength of red light); the result is a lattice structure reminiscent of a fishing net. Then they passed a beam of red light through the resulting material and measured the refractive index, which was -0.6.
The authors anticipate that the technology they invented will find widespread use. Metamaterials “may someday lead to a kind of flat superlens that works in the visible spectrum,” says Dr. Sukulis. "This lens will allow you to get higher resolution than traditional technology and distinguish between details that are significantly smaller than the wavelength of light." Obviously, one of the first applications of a "superlens" would be to photograph microscopic objects with unprecedented clarity; we can talk about photographing inside a living human cell or about diagnosing diseases of the fetus in the womb. Ideally, it will be possible to photograph the components of a DNA molecule directly, without the use of crude X-ray crystallography techniques.
So far, scientists have been able to demonstrate a negative refractive index only for red light. But the method needs to be developed, and the next step is to create a metamaterial that could completely circle the red ray around the object, making it invisible to red light.
Further development can also be expected in the field of "photonic crystals". The goal of photonic crystal technology is to create a chip that uses light instead of electricity to process information. The idea is to use nanotechnology to etch tiny components onto the substrate so that the refractive index changes with each component. Transistors in which light works have many advantages over electronic ones. For example, in photonic crystals there is much less heat loss. (Complex silicon chips generate enough heat to fry an egg. These chips need to be continually cooled to keep them from failing, which is very expensive.)
It is not surprising that the technology for producing photonic crystals should be ideal for meta-materials, since both technologies involve manipulating the refractive index of light at the nanoscale.
Invisibility through plasmonics
Not wanting to be outdone by rivals, another group of physicists announced in mid-2007 the creation of a metamaterial capable of rotating visible light, based on a completely different technology called plasmonics. Physicists Henri Lesek, Jennifer Dionne and Harry Atwater of the California Institute of Technology announced the creation of a metamaterial that has a negative refractive index for the more complex blue-green region of the visible spectrum.
The purpose of plasmonics is to "squeeze" light in this way so that objects can be manipulated at the nanoscale, especially on metal surfaces. The reason for the electrical conductivity of metals lies in the fact that electrons in metal atoms are weakly bound to the nucleus and can freely move along the surface of the metal lattice. The electricity running through the wires in your home is a smooth flow of these loosely bound electrons across a metal surface. But under certain conditions, when a beam of light hits a metal surface, electrons can vibrate in unison with the light. In this case, wave-like movements of electrons appear on the surface of the metal (these waves are called plasmons) in time with the oscillations of the electromagnetic field above the metal. More importantly, these plasmons can be "compressed" so that they have the same frequency asas the original light beam (which means they will carry the same information), but a much shorter wavelength. In principle, these compressed waves can then be squeezed into nanowires. As with photonic crystals, the ultimate goal of plasmonics is to create computer chips that run light, not electricity.
A group at California Tech built their metamaterial with two layers of silver and a silicon-nitrogen insulating layer (just 50 nm thick) between them. This layer acts as a "waveguide" capable of directing plasmon waves in the desired direction. A laser beam enters the device through a slit cut in the metamaterial; it passes through the waveguide and then exits through the second slit. If you analyze the angles at which a laser beam is bent when passing through a metamaterial, you can determine that the material has a negative refractive index for light with a given wavelength.
The future of metamaterials
Progress in the study of metamaterials in the future will accelerate for the simple reason that there is already a great deal of interest in creating transistors that work on a light beam instead of electricity. Therefore, it can be assumed that research in the field of invisibility will be able to "drive a ride", ie, take advantage of the results of already ongoing research to create a replacement for a silicon chip using photonic crystals and plasmonics. Already today, hundreds of millions of dollars are being invested in the development of a technology designed to replace silicon chips, and research in the field of metamaterials will also benefit.
Currently, new major discoveries in this area are made every few months, so it is not surprising that some physicists expect the first samples of a real invisibility shield to appear in the laboratory within a few decades. So, scientists are confident that they will be able to create metamaterials in the next few years that can make an object completely invisible, at least in two dimensions, for visible light of any particular frequency. To achieve this effect, it will be necessary to introduce tiny nanoimplants into the metamaterial not in regular rows, but in a complex pattern, so that as a result, the light smoothly bends around the hidden object.
Next, scientists will have to invent and create metamaterials that can bend light in three dimensions, not just on flat two-dimensional surfaces. Photolithography is a proven technology for producing flat silicon circuits; the creation of three-dimensional metamaterials will require at least a complex arrangement of several flat diagrams.
After that, scientists will have to solve the problem of creating metamaterials that bend light not of one frequency, but of several - or, say, a band of frequencies. This is arguably the most difficult task, because all the tiny implants developed so far only deflect light of one precise frequency. Scientists may have to tackle multi-layered metamaterials, where each layer will act at one specific frequency. It is not yet clear what the solution to this problem will be.
But the shield of invisibility, even after being finally created in the laboratory, may not be at all what we want, most likely, it will be a heavy and unwieldy device. Harry Potter's cloak was sewn from a thin, soft fabric and made anyone who wrapped themselves in it invisible. But for such an effect to be possible, the refractive index inside the tissue must constantly change in a complex manner in accordance with the vibrations of the tissue and the movements of the person. This is impractical. Most likely, the invisibility cloak, at least initially, will be a solid cylinder of metamaterial. In this case, the refractive index inside the cylinder can be made constant. (In more advanced models, over time, flexible metamaterials may appear that can bend and at the same time keep the light inside themselves on the right path.who will be inside the "cloak" will get some freedom of movement.)
The invisibility shield has one drawback, which has already been repeatedly pointed out: the one who is inside cannot look out without becoming visible. Imagine Harry Potter with only his eyes visible; while they seem to float through the air at the appropriate height. Any eye holes in the invisibility cloak would be clearly visible from the outside. If you make Harry Potter completely invisible, then he will have to sit blindly and in complete darkness under his cloak. (One possible solution to this problem would be two small glasses in front of the eyes. These glasses would act as "beam splitters"; they would pinch off and direct a small portion of the light falling on them into the eyes. However, most of the light falling on the cloak was would bypass, making the person invisible inside, but some, very small,part of it would separate and enter the eyes.)
Undoubtedly, the obstacles to invisibility are very serious, but scientists and engineers are optimistic and believe that an invisibility shield of one kind or another can be created within the next few decades.
Invisibility and nanotechnology
As I already mentioned, the key to invisibility can be the development of nanotechnology, i.e. the ability to manipulate structures of atomic (about one billionth of a meter across) sizes.
The moment of the birth of nanotechnology is called the famous lecture with the ironic title "The Bottom is Full of Space", which was given by the Nobel laureate Richard Feynman before the American Physical Society in 1959. In this lecture, he discussed how the smallest machines might look like according us by the laws of physics. Feynman realized that the size of machines would get smaller and smaller until they approach the size of an atom, and then the atoms themselves could be used to create new machines. He concluded that the simplest atomic machines like a block, lever or wheel do not contradict the laws of physics, but it will be extremely difficult to manufacture them.
For many years nanotechnology has languished in oblivion - simply because the technology of the time did not allow the manipulation of individual atoms. But in 1981, there was a breakthrough - physicists Gerd Binnig and Heinrich Rohrer of the IBM laboratory in Zurich invented the scanning tunneling microscope, which later won them the Nobel Prize in physics.
Scientists were suddenly able to get amazing "pictures" of individual atoms combined into structures - exactly the same as usually depicted in books on chemistry; at one time, critics of atomic theory considered this impossible. Now it was possible to get magnificent photographs of atoms arranged in rows in the correct structure of a crystal or metal. The chemical formulas with which scientists tried to reflect the complex structure of the molecule could now be seen with the naked eye. Moreover, the scanning tunneling microscope made it possible to manipulate individual atoms. The discoverers laid out the letters IBM from individual atoms, which made a real sensation in the scientific world. Scientists are no longer blind in the world of individual atoms; they were able to see and work with atoms.
The operating principle of a scanning tunneling microscope is deceptively simple. Just as a gramophone scans a disc with a needle, this microscope slowly passes a sharp probe over the substance under study. (The tip of this probe is so sharp that it ends in a single atom.) The probe carries a weak electrical charge; an electric current flows from its end through the material under study to the conductive surface below it. When the probe passes over each individual atom, the current changes slightly; changes in current are carefully recorded. The rises and falls of the current when the needle passes over the atom very accurately and in detail reflect its outline. Having processed and presented in graphic form the data on current fluctuations for a large number of passes, you can get a beautiful picture of individual atoms that form a spatial lattice.
(A scanning tunneling microscope can exist thanks to a strange law of quantum physics. Usually electrons do not have enough energy to travel from the tip of the probe to the substrate through the layer of matter. That is, they penetrate the barrier, although this contradicts Newton's theory. That is why the current passing through the material is so sensitive to the subtle quantum effects in it. Later I will dwell on the consequences of quantum theory in more detail.)
In addition, the probe of the microscope is sensitive enough to move individual atoms and build simple "machines" from them. At the moment, this technology is so advanced that you can see a group of atoms on a computer screen and, by simply moving the cursor, move individual atoms in an arbitrary way. Dozens of atoms can be manipulated as easily as Lego bricks. You can not only lay out letters from atoms, but also create toys, such as, for example, abacus, where knuckles are assembled from single atoms. For this, the atoms are laid out on a surface equipped with vertical grooves. Spherical fullerenes ("soccer balls" composed of individual carbon atoms) are inserted into the grooves. These carbon balls serve as the bones of atomic accounts, moving up and down their grooves.
You can also cut atomic devices with electron beams. For example, scientists from Cornell University carved out of crystalline silicon the world's smallest guitar, the size of which is 20 times smaller than the thickness of a human hair. The guitar has six strings, each one hundred atoms thick, that can be pulled with an atomic force microscope. (The guitar will indeed play music, but the frequencies it produces are far beyond the audibility of the human ear.)
Nowadays, almost all "nanomachines" are just toys. More complex machines with gears and bearings have yet to be created. But many engineers are confident that the time for real atomic machines is on its way. (In nature, such machines exist. Single-celled organisms are able to float freely in water due to the movements of tiny hairs. But if you carefully consider the connection between a hair and a cell, it becomes clear that it is the atomic machine that allows a hair to move arbitrarily in all directions. Therefore, one of the ways of developing nanotechnology is a copying of nature, which mastered the production of atomic machines billions of years ago.)
Holograms and invisibility
Another way to make a person somewhat invisible is to photograph the view behind him and then project that image directly onto the person's clothing or some kind of screen in front of him. If you look from the front, it will seem that the person has become transparent and the light somehow passes through his body.
This process, known as "optical cloaking," has been seriously pursued, in particular, by Naoki Kawakami of the Tachi Laboratory of the University of Tokyo. He says, "This technology could be used to help pilots see the runway through the floor of the cockpit or to help drivers look around when parked." Kawakami's cloak is covered in tiny reflective beads that act like a movie screen. What happens from behind is filmed with a video camera. This image then goes to a video projector, which, in turn, projects it onto the cloak in front. It seems that the light penetrates the person through and through.
Prototypes of raincoats with an optical camouflage system have already been created in the laboratory. If you look directly from the front at a person in such a cloak, it seems that he disappears, because you only see an image of what is happening behind. But if you, and with you your eyes, move a little, and the image on the cloak remains the same, it will become clear that this is just a deception. In a more realistic optical cloaking system, it will be necessary to create the illusion of a three-dimensional image. This will require holograms.
A hologram is a 3D image created by lasers (think of the 3D image of Princess Leia in Star Wars). You can make a person invisible if you take a picture of the background behind him using a special holographic camera and then recreate it on a special holographic screen in front of him. The observer will see a holographic screen in front of him with an image of everything that is actually in front, with the exception of a person. It will look as if the person just disappeared. In its place will be an accurate 3D image of the background. Even after moving, you will not be able to understand that there is a fake in front of you.
The creation of such three-dimensional images is possible due to the "coherence" of the laser light, i.e. the fact that electromagnetic oscillations in it occur strictly in unison. To build a hologram, a coherent laser beam is split into two parts. One half is directed to the photographic film, the other - to the same photographic film, but after reflection from the object. When the two halves of the beam interfere, an interference pattern appears on the film, which contains all the information about the original three-dimensional beam. The film after development does not look very promising - only a web of incomprehensible lines and curls is visible on it. But if you pass a laser beam through this film, an exact three-dimensional copy of the object appears in the air, as if by magic.
Nevertheless, holographic invisibility poses very serious problems for researchers. One of them is the creation of a holographic camera capable of taking at least 30 pictures per second. Another is the storage and processing of all this information. Finally, you will need to project the image onto the screen so that it looks realistic.
Invisibility through the fourth dimension
One more, much more cunning way of becoming invisible should be mentioned, as outlined by H. G. Wells in the novel The Invisible Man. This method involves using the capabilities of the fourth dimension. (Later in this book, I will talk more about the possible existence of higher dimensions.) Can a person leave our three-dimensional universe and hover above it in the fourth dimension, observing what is happening from the side? Like a three-dimensional butterfly fluttering over a two-dimensional sheet of paper, such a person would be invisible to any inhabitant of the universe below. The only problem is that the existence of higher dimensions has not yet been proven. Moreover, a hypothetical journey into one of these dimensions would require much more energy than we currently have at our current state of the art. If we talk about real ways to achieve invisibility, then this method, obviously, lies far beyond our current knowledge and capabilities.
Given the tremendous progress already made on the road to invisibility, I think we can safely classify it as a Class I impossibility. Invisibility of one kind or another may become commonplace in the next few decades, at least by the end of the century.