Faster Than Light

In Star Wars, as the Millennium Falcon blasts off the desert planet Tatooine, carrying out heroes Luke Skywalker and Han Solo, the ship encounters a squadron of menacing Imperial Battleships orbiting the planet. The Empire's battleships fire a punishing barrage of laser blasts at our heroes' ship that steadily break through its force fields. The Millennium Falcon is outgunned. Buckling under this withering laser fire, Han solo yells that their only hope is to make the jump into "hyperspace" In the nick of time, the hyperdrive engines spring to life. All the stars around them suddenly implode toward the center of their view screen in converging, blinding streaks of light. A hole opens up, which the millennium Falcon blasts through, reaching hyperspace and freedom.

Science fiction? Undoubtedly. But would is be based on scientific fact? Perhaps. Faster than light travel has always been a staple of science fiction, but recently physicists have given serious thought to this possibility.

According to Einstein, the speed of light is the ultimate speed limit in the universe. Even our most power atom smashers, which can only create energies found only at the center of exploding stars or the big bang itself, cannot hurl subatomic particles at a rate faster than the speed of light. Apparently, the speed of light is the ultimate traffic cop in the universe. if so, any hope of our reaching the distant galaxies seems to be dashed. Or maybe not....

In the general theory of relativity, space-time is a fabric that can stretch and shrink. Under certain circumstances the fabric may stretch faster than the speed of light. Think of the big bang, for example, when the universe was born in a cosmic explosion 13.7 billion years ago. One can calculate that the universe originally expanded faster than the speed of light. (This action does not violate special relativity, since it was empty space-the space between stars-that was expanding, not the stars themselves. Expanding space does not carry any information.)

The important point is that special relativity applies only locally, that is, in your nearby vicinity. In your local neighborhood (e.g. the solar system). special relativity holds, as we confirm with our space probes. But globally (e,g,m on cosmological scales involving the universe) we must use general relativity instead. In general relativity, space-time becomes a fabric, and this fabric can stretch faster than light. It can also allow for "holes in space" in which one can take shortcuts through space and time.

Given these caveats, perhaps one way to travel faster than light is to invoke general relativity. There are two ways in which this might be done.

1. Stretching space. If you were to stretch the space behind y0u and contract the space in front of you, then you would have the illusion of having moved faster than light. In fact, you would not have moved at all. But since space has been deformed. It means you can reach the distant stars in a twinkling of an eye.

2. Ripping space. In 1935, Einstein introduced the concept of wormhole. Imagine the Looking Glass of Alice, a magical device that connects the countryside of Oxford to Wonderland. The wormhole is a device that can connect two universes, When we were in primary school, we learned that the shortest distance between two points is a straight line. But this is not necessarily true, because if we curled a sheet of paper until two points touched, then we would see that the shortest distance between two points is actually a wormhole.

The best example of stretching space is the Alcubierre drive, proposed by physicist Miguel Alcubierre in 1994 using Einstein's theory of gravity. It is quite similar to the propulsion system used in Star Trek. The pilot of such a starship would be seated inside a bubble (called a "warp bubble") in which everything seems to appear normal, even as the spacecraft broke the light barrier. In fact, the pilot would think that he was at rest. Yet outside the warp bubble, extreme distortions of space0time would occur as the space in front of the warp bubble was compressed. There would be no time dilation, so time would pass normally inside the warp bubble.

Alcubierre speculates that a journey in his proposed starship would resemble a journey taken on the millennium Falcon in Star Wars. The key to Alcubierre drive is the energy necessary to propel the spacecraft forward at faster-than-light velocities. Normally physicists begin with a positive amount of energy in order to propel a starship, which always travels slower than the speed of light. To move beyond this strategy, so as to be able to travel faster than the speed of light, one would need to change the fuel. A straightforward calculation shows that you would need "negative mass" or "negative energy" perhaps the most exotic entities in the universe, If they exist.

Wormholes and stretched space may give us the most realistic way of breaking the light barrier. But it is not known if these technologies are stable; if they are, it would still take fabulous amount of energy, positive of negative, to make them work. Perhaps an advanced Type III civilization, millions of years more advanced than us, might already have this technology. It might be a millennia before we can even think about harnessing power on this scale. Because there is still controversy over the fundamental laws of governing the fabric of space-time at the quantum level, it would classify as a Class II impossibility.

Starship - Part 2

Alright, continuing from part 1 last week, i was talking about ion engine, solar sails and ramjet engines.

This week i'll cover the remaining alternatives of propulsion system.

The fourth alternative is nuclear electric rocket. In 1956, the U.S. Atomic Energy Commission (AEC) began to look at nuclear rockets seriously under Project Rover. In theory, a nuclear fission reactor would be used to heat up gases like hydrogen to extreme temperatures, and then these gases would be ejected out one end of the rocket, creating thrust.

Continuing from the nuclear propulsion, the fifth is nuclear pulsed rockets. This is a possibility that use a series of mini-nuclear bombs to propel a starship. In project Orion, mini-atomic bombs were to be ejected out the back of the rocket in sequence, so that the space craft would "ride" on the shock waves created by these mini-hydrogen bombs. On paper, such a design could take a spacecraft close to the speed of light. Originally conceived in 1947 by Stanislaw Ulam, who helped designed the first hydrogen bombs, the idea was further developed by Ted Taylor (one of the chief designers of nuclear warheads for the U.S. military) and physicist Freeman Dyson of the Institute for Advanced Study of Princeton.

In the late 1950ss and 1960s elaborate calculations were made for this interstellar rocket. It was estimated that such a starship could make to pluto and back within a year, with a top cruising velocity of 10 percent the speed of light. But even at that speed, it would take about forty-four years to reach the nearest star. Scientist have speculated that a space ark powered by such a rocket would have to cruise for centuries, with a multigenerational crew whose offspring would be born and spend all their lives on the space, in order that their descendants could reach nearby stars.

Another novel means of hurling an object near the speed of light is to use the "slingshot" effect. When sending space probes to the outer planets, NASA sometimes whips them around a neighboring planet, so they use a slingshot effect to boost their velocity. NASA saves on valuable rocket fuel in this way. That's how the Voyager spacecraft was able to reach Neptune, which lies near the very edge of the solar system.

Princeton physicist Freeman Dyson proposed that in the far future, we might find two neutron stars that are revolving around each other at great speed. By traveling extremely close to one of these neutron stars, we could whip around it and then be hurled into space at speeds approaching a third the speed of light. In effect, we would be using gravity to give us an additional boost to nearly the speed of light. On paper this just might work.

Others have proposed taht we whip around out own sun in order to accelerate to near the speed of light. This method, in fact, was used in Star Trek IV: The Voyage Home, when the crew of the Enterprise hijacked a Klingon Ship and then sped close to the sun in order to break the light barrier and go back in time. In the movie When Worlds Collide, when Earth is threatened by a collision with an asteroid, scientists flee the Earth by creating a gigantic roller coaster. A rocket ship descends the roller coaster, gaining velocity, and then whips around the bottom of the roller coaster to blast off into space.

Yet another ingenious method for flinging objects into space at fantastic velocities is the rail gun, which Athur C. Clarke and others have featured in their science fiction tales, and which is also being seriously examined as part of the Star Wars missile shield.

Instead of using rocket fuel or gunpowder to boost a projectile to high velocity, a rail gun uses the power of electromagnetism.

In its simplest form, a rail gun consist of two parallel wires or rails, with a projectile that straddles both wires, form a U-shaped configuration. Even Michael Faraday knew that a current of electricity will experience a force when placed in a magnetic field. (This , in fact, is the basis of all electrical motors.) By sending missions of amperes of electrical power down these wires and through and through the projectile, a huge magnetic field is created around the rails. This magnetic field then propels the projectile down the fails at enormous velocities.

Rail funs have successfully fired metal objects at enormous velocities over extremely short distances. Remarkably, in theory, a simple rail gun should be able to fire a metal projectile at 18,000 miles per hour, so that it would go into orbit around the earth. In principle, NASA's entire rocket fleet could be replaced by rail guns that could blast payloads into orbit from Earth.

Given the slow but steady advances in spaceship design, it is reasonable to assume that the first unmanned probe of some sort might be sent to nearby stars perhaps later in this century or early in the next century, making it a Class I impossibility.

But perhaps the most powerful design for a starship involved the use of antimatter. Although it sounds like scnience fiction, antimatter has already been created on Earth, and may one day provide the most promising design yet for a workable manned starship.

Starships - Part 1

One day in the distant future, we will have our last nice day on Earth. Eventually, billions of years from now, the sky will be on fire. The sun will swell into a raging inferno that will fill up the entire sky, dwarfing everything in the heavens. As temperatures on Earth soar, the oceans will boil and evaporate, leaving a scorched, parched landscape. The mountains will eventually melt and turn liquid, creating lava flows where vibrant citics once stood.

According to the laws of physics, this grim scenario is inevitable. The Earth will eventually die in flames as it is consumed by the sun. This is a law of physics.

This calamity will take place within the next five billion years. On such a cosmic time scale, the rise and fall of human civilizations are but tiny ripples. One day we must leave the Earth or die. So how will humanity, our descendants, cope when conditions on Earth become intolerable?

Mathematician and philosopher Bertrand Russell once lamented "that no fire, no heroism, no intensity of thought or feeling, can preserve a life beyond the grave; that all the labors of the ages, all the devotion, all the inspiration, all the noonday brightness of human genius, are destined to extinction in the vast death of the solar system; and the whole temple of Man's achievement must inevitably be buried beneath the debris of a universe in ruins..."

Given that humanity must one day flee the solar system in the nearby stars to survive, or perish, the question is: how will we get there? The nearest star system, Alpha Centauri, is over 4 light-years away.Conventional chemical propulsion rockets, the workhorses of the current space program, barely reach 40,000 miles per hour. At that speed, it would take 70,000 years just to visit the nearest star.

Alternatives to chemical rockets? Ion engines. Unlike chemical rockets, ion engines do not produce the sudden, dramatic blast of superhot gases that propel conventional rockets. In fact, their thrust is often measured in ounces. Placed on a tabletop on Earth. they are too feeble to move. But what they lack in thrust, they more than make up for in duration, because they can operate for years in the vacuum of outer space.

A typical ion engine looks like the inside of a TV tube. A hot filament is heated by an electric current, which creates a beam of ionized atoms, such as xenon, that is shot out the end of the rocket. Instead of riding on a blast of hot, explosive gas, ion engines ride on a thin but steady flow of ions.

Another alternative is Solar Sails. Solar sails exploits the fact sunlight exerts a very small but steady pressure that is sufficient to propel a huge sail sail through space. The idea for a solar sail is an old one, dating back to the great astronomer Johannes Kepler in his 1611 treatise Somnium.

Although the physics behind a solar sail is simple enough, progress has been spotty in actually creating a solar sail that can be sent into space. proponents of the solar sail have a idea that might take them to the stars: building a huge battery of lasers on the moon that can fire intense beams of laser light at a solar sail, enabling it to coast in the nearest star. The physics of such an interplanetary solar sail are truly daunting. The sail itself would have to be hundreds of miles across and constructed entirely in outer space. One would have to build thousands of powerful laser beams on the moon, each capable of firing continuously for years to decades. (In one estimate, it would be necessary to fire lasers that have one thousand times the current total power output of the planet Earth).

The third alternative is Ramjet Fusion. My favorite candidate for getting us to the stars. There is an abundance of hydrogen in the universe, so a ramjet engine c0uld scoop hydrogen as it traveled in outer space, essentially giving it an inexhaustible source of rocket fuel. Once the hydrogen was collected, it would be heated to millions of degrees, hot enough so that the hydrogen would fuse, releasing the energy of a thermonuclear reaction.

The ram jet fusion engine was proposed by physicist Robert W. Bussard in 1960 and later popularized by Carl Sagan. Burssard calculated that a ramjet engine weighing about 1,000 tons might theoretically be able to main a steady thrust of 1g of force, that is, comparable to standing on the surface of the Earth. If the ramjet engine could maintain a 1g acceleration for one year, it would reach 77 percent of the velocity of light, sufficient to make interstellar travel a serious possibility

In principle, the ramjet engine could propel itself indefinitely, ultimately reaching distant star systems in the galaxy. Since time slows down inside the rocket, according to Einstein, it might be possible to reach astronomical distances without resorting to putting the crew into suspended animation. After accelerating at 1g for eleven years, according to clocks inside the starship, the spacecraft would reach the pleiades star cluster, which is 400 light-years away. In twenty-three years, it would reach the andromeda galaxy, which is 2 million light-years from Earth. In theory, the spacecraft might be able to reach the limit of the visible universe within the lifetime of a crew member (although billions of years might have passed on the Earth).


This is the first part of Starships, Stay tune next week for part two of Starships. See ya

Telepathy

A. E. van Vogt's novel Slan captures the vast potential and our darkest fears associated with the power of telepathy.

Jommy Cross, the protagonist in the novel, is a "slan", a dying race of superintelligent telepaths.
His parents were brutally murdered by enraged mobs of humans, who fear and despise all telepaths, because of the enormous power wielded by those who can intrude on their private, most intimate thoughs. Humans mercilessly hunt down the slan like animals. With their characteristic tendrils growing out of their heads, slans are easy to spot.In the course of the book, Jommy tries to make contact with other slans who have fled into outer space to escape the witch hunts of humans determined to exterminate them.

Historically, mind reading has been seen as so important that it has often been associated with the gods. One of the most fundamental powers of any god is the ability to read our minds and hence answer our deepest prayers. A true telepath could read minds at will could easily become the wealthiest, most powerful person on Earth, able to enter the minds of Wall Street Bankers or to blackmail and coerce his rivals. he would pose a threat in the security of governments. He could effortlessly steal a nation's most sensitive secrets. Like the slans, he would be feared and perhaps hunted down.

One of the most famous cases of telepathy did not involved a shill but an animal, Clever Hans, a wonder horse that astonished European audiences in the 1890s. Clever hans, to the amazement of the audiences, could perform complex mathematical feats of calculation. If, for example, you asked celever hands to devided 48 by 6, the horse would beat his hoof 8 times. Clever hans, in fact could divide, multiply, add fractions, spell and even identify musical tones. Clever Hans' fans declared that he was either more intelligent than many humans, or he could telepathically pick people's brains.

But Clever Hans was no the product of some clever trickery. the marvelous ability of Clever Hans to perform arithmetic even fooled his trainer. In 1904 prominent psychologist Professor C. Strumpf was brought in to analyze the horse and could find no obvious evidence of trickery or covert signaling to the horse, only adding to the public's fascination with Clever Hans' secret. All he really did was observe the subtle facial expressions of his trainer. The horse would continue to beat his hoofs until his trainer's facial expression changed slightly, at which point he would stop beating. Clever hans could not read people's minds of perform arithmetic; he was simply a shrewd observer of people's faces.

Is telepathy really possible? we have to look inside the brain and see the physics behind the workings of the brain. In the nineteenth century, scientists suspected that electrical signals were being transmitted inside the brain. In 1875 Richard Caton discovered that by placing electrodes on the surface of the head, it was possible to detect the tiny electrical signals emitted by the brain. This eventually led to the invention of the electroencephalograph (EEG).

In principle, the brain is a transmitter over which our thoughts are broadcast in the form of tiny electrical signals and electromagnetic waves. But there are problems with using these signals to read someone's thoughs. First, the signals are extremely weak, in the milliwatt range. Second, the signals are gibberish, largely indistinguishable from random noise. Only crude information about our thoughs can be gleaned from this garble. Third, our brain is not capable of receiving similar messages from other brains via these signals; that is, we lack an antenna. And, finally, even if we could receive these faint signals, we would not unscramble them. Using ordinary Newtonian and Maxwellian physics, telepathy via radio does not seem to be possible.

Some believe that perhaps telepathy is mediated by a fifth force, called the "psi" force. But even advocates of parapsychology admit that they have no concrete, reproducible evidence of this psi force.

But this leaves open the question: What about telepathy using the quantum theory?

in the last decade, new quantum instruments have been introduced that for the first time in history enable us to look into the thinking brain. Leading this quantum revolution are the PET (positron-emission tomography) and MRI (magnetic resonance imaging) brain scans. A PET scan is created by injecting radioactive sugar into the blood. This sugar concentrates in parts of the brain that are activated by the thinking process, which requires energy. The radioactive sugar amits positrons (antielectrons) that are easily detected by instruments.

The MRI machine operates in the same way, except it is more precise. A patient's head is placed inside a huge donut-shaped magnetic field. The magnetic field makes the nuclei of the atoms in the brain align parallel to the field lines. A radio pulse is sent into the patient, making these nuclei wobble. When the nuclei flip orientation, they emit a tiny radio "echo" that can be detected, thereby signaling the presence of a particular substance.

If one day we might be able to read the broad outlines of another's thoughts, then would it be possible to perform the opposite, to project your thoughts into another person's head? The answer seems to be a qualified yes. Radio waves can be beamed directly into the human brain to excite areas of the brain known to control certain functions.

In the future, it may be possible to beam electromagnetic signals at precise parts of the brain that are known to control specific functions. By firing such signals into the amygdala, one might be able to elicit certain emotions. By stimulating other areas of the brain, one might be able to evoke visual images and thoughts.

But because the brain is not a computer but a neural network, in which thoughts are spread out throughout the brain, ultimately we hit a stumbling block: the brain itself. So although science will probe deeper and deeper into the thinking brain, making it possible to decipher some of out thinking processes, it will not be possible to "read your thoughts" with the pinpoint accuracy promised by science fiction. Given this, it would term the ability to read general feelings and thought patterns as a Class I impossibility. the ability to read more precisely the inner workings of the mind would have to be categorized as a Class II impossibility.

Teleportation

Teleportation, or the the ability to transport a person or object instantly from one place to another, is a technology that could change the source of civilization and alter the destiny of nations. It could irrevocably alter the rules of warfare: armies could teleport troops behind enemy lines or simply teleport the enemy's leadership and capture them.

Today's transportation system-from cars to ships to airplanes and railroads, and all the many industries that service these systems would become obsolete; we could simply teleport ourselves to work and goods to market. Vacations would become effortless, as we teleport ourselves to our destination. Teleportation would change everything.

According to Newtonian theory, teleporation is clearly impossible. Newton's laws are based on the idea that matter is made of tiny, hard billiard balls. Objects do not move until they are pushed: objects do not suddenly disappear and reappear somewhere else.

But in the quantum theory, that's precisely what particles can do. Newton's laws, which hed sway for 250years, were overthrown in 1925 when Werner Heisenberg, Erwin Schrodinger, and their colleagues developed the quantum theory. When analyzing the bizarre properties of atoms, physicists discovered that electrons acted like waves and could make quantum leaps in their seemingly chaotic motions within the atom.

In 1905 Einstein had shown that waves of light can have particle-like properties; that is, they can be described as packets of energy called photons. But by the 1920s it was becoming apparent to Schrodinger that the opposite was true: that particles like electrons could exhibit wavelike behavior. this idea was first pointed out by the French physicist Louis de Broglie, who won the Nobel Prize for this conjecture.

But there was still a nagging question that haunts physics even today. If the electron is described by a wave, then what is waving? This has been answered by physicist Max Born, who said that these waves are actually waves of probability. These waves tell you only the chance of finding a particlar electron at any place and any time. In other words, the electron is a particle, but the probability of finding that particle is given the Schrodinger's wave. The larger the wave, the greater the chance of finding the particle at that point.

In reality the quantum "jumps" so common inside the atom cannot be easily generalized to large objects such as people, which contain trillions upon trillions of atoms. Even if the election in out body are dancing and jumping in their fantastic journey around the nucleus, there are so many of them that their motions average out.

One can use the laws of quantum theory to create a machine to teleport something on demand, as in science fiction stories? Surprisingly, the answer is a qualified yes.

Then comes Quantum teleportation. Everything changed in 1993, when scientists at IBM, led by Charles Bennett, showed that it was physically possible to teleport objects, as least at the atomic level. Physicists have been able to teleport photons and even entire caesium atoms. Within a few decades scientists may be able to eleport the first DNA molecule and virus.

Quantum teleportation exploits some the more bizarre properties of the EPR experiment. In these teleportation experiments physicists star with two atoms, A and C. Let's say we wish to teleport information from atom A to atom C. We begin by introducing a their atom, B, which starts out being entangled with C, so B and C are coherent. Now atom A comes in contact with atom B. A scans B, so that the information content of atom A is transferred to atom B. A and B become entangled in the process. But since B and C were orignally entangled, information within A has now been transfferred to atom C. In conclusion atom A has now been teleported into atom C, that is the information content of A is now identical to that of C.

Teleportation without entanglement? Progress in teleportation is rapidly accelerating. In 2007 yet another breakthrough was made. Physicists proposed a teleportation method that does not require entanglement.

"We're talking about a beam of 5,000 particles disappearing from one place and appearing somewhere else,," says physicist Aston Bradley of the Austrailian Research Council Center of Excellence for Quantum Atom Optics in Brisbane, Australia.

He and his colleagues take a beam of rubidium atoms, convert all its information into a beam of light, send this beam of light across a fiber-optic cable, and then reconstruct the original beam of atoms in a distant location.

here's how Bradley and company's teleporation device works. First they start with a collection of supercold rubidium atoms in a BEC state ("Bose Einstein condensate" which is a millionth to a billionth of a degree above absolute zero). these atoms in the beam also want to tumble down to the lowest energy state, so they shed their excess energy in the form of a pulse of light. This light beam is then send down a fiber-optic cable. Remarkably the light beam contains all the quantum information necessary to describe the original matter beam (e.g., the location and velocity of all its atoms). Then the light beam hits another BEC, which then converts the light beam into the original matter beam.

So teleportation exists at the atomic level, and we may eventually teleport complex and even organic molecules within a few decades. But the teleporation of a macroscopic object will have to wait for several decades to centuries beyond that, or longer, if indeed it is even possible. Therefore teleporting complex molecules, perhaps even a virus or living cell, qualifies as a Class I impossibility, one that should be possible within this century. But teleporting a human being, although it is allowed by the laws of physics, may take many centuries beyond that, assuming it is possible at all. Hence it would qualify as a Class II impossibility.

Invisibility

In Star Trek IV: The Voyager Home, a Klingon battle cruisier is hijacked by the crew of the Enterprise. Unlike the starships in the Federation Star Fleet, The starships of the Klingon Empire have a secret "cloaking device" that renders them invisible to light or radar, so that the Klingon ships can sneak up behind the Federation starships and ambush them. This cloaking device has given the Klingon Empire a strategic advantage over the Federation of Planets.

Is such a device possible? Invisibility has long been one the marvels of science fiction and fantasy, from the pages of The Invisible Man, to the magic invisibility cloak of Harry Potter, or the one ring in The Lord of the Rings. For at least a century, physicist have dismissed the possibility of invisibility cloaks, stating flatly that they are impossible: They violate the laws of optics and do not conform to any of the known properties of matter.

But today, the impossible may become possible. New advances in "metamaterials" are forcing the major revision of optics textbooks. Working prototypes of such materials have actually been built in the laboratory, sparkling intense interest by the media, industry, and the military in making the visible become invisible.

Invisibility is perhaps one the oldest concepts in ancient mythology. Since the advent of recorded history, people who have been alone on a creepy night have been frightened by the invisible spirits of the dead, the souls of the long-departed lurking in the dark. The Greek hero perseus was able to slay the evil medusa armed with the helmet of invisibility. Military generals have dreamed of an invisibility cloaking device. being invisible, one could easily penetrate enemy lines and capture the enemy by surprise. Criminals could use invisibility to pull off spectacular robberies.

Discoveries behind "metamaterials"? Creation of metamaterials was once thought to be impossible because they violate the laws of optics. But in 2006 researchers at Duke university in Durham, North Carolina, and Imperial College in Longon successfully defied conventional wisdom and used metamaterials to make an object invisible to microwave radiation. For the first time in history, we now have a blue print to render ordinary objects invisible.

Metamaterials are substances that have optical properties not found in nature. Metamaterials are create by embedding tiny implants within a substance that force electromagnetic waves to bend un unorthodox ways. The result was a sophisticated mixture of ceramic, Teflon, fiber composites, and metal compounds. These tiny implants in the copper make it possible to bend and channel the path of microwave radiation in a specific way. Think about the way a river flows around a boulder. If the metamaterial can eliminate all the reflection and shadows, then it can render an object totally invisible to that form of radiation.

Metamaterials for light? One proposal is to use the off-the-shelf technology, that is, to borrow known techniques from the semiconductor industry to create new metamaterials. A technique called "photolithography" lies at the heart of the computer miniaturization and hence drives the computer revolution. Photolithography enables engineers to place hundreds of millions of tiny transistors onto a silicon no bigger than your thumb.

A milestone in the quest for invisibility came when this silicon wafer etching technology was used by a group of scientist to create the first metamaterial that operates in the visible range of red light.

The scientists first started with a glass sheet, and then deposited a thin layer of silver, magnesium fluoride and another layer of silver that is only 100nm thick. Then, using standard etching techniques, they create a grid pattern resembling a fishnet. The next step would be use this technology to create a metamaterial that would bend red light entirely around an object, rendering it invisible to that light.

The key to invisibility may be nanotechnology, that is, the ability to manipulate atomic-sized structures about a billionth of a meter across.

Given the enormous progress made so far in achieving invisibility, it clearly qualifies as a Class I impossibility. Within the next few decades to at least within this century, a form of invisibility may be become commonplace.

Force Fields

"Shields up!"

A famous phrase in the Star trek series that is the first order that captain Kirk says to the crew, raising force fields to protect the starship Enterprise against enemy fire.

Force fields are vital that the tide of the battle can be measured by how the force fields is holding up. Whenever power is drained from the force fields, the Enterprise suffers more and more damage to the hull.

What is force field? In science fiction, it's simple: a thin and invisible yet impenetrable barrier able to deflect lasers and rockets. It could have profound effects on every aspect of our lives. The military could use force fields to become invulnerable, creating an impenetrable shield against enemy missiles and bullets. Bridges, superhighways and roads could be built by a simply pressing a button. Entire cities could appear instantly in the desert, with skyscrapers made entirely out of force field. Force fields appearing over cities could enable the inhabitants to modify the effects of the weather-high winds, blizzards, tornadoes-at will. Cities could be built under the oceans within the safe canopy of a force field. Glass and steel could be entirely replaced.

However, a force field is perhaps one the most difficult devices to create in the laboratory. In fact, some physicists believe it might actually be impossible.

The concept of force fields originates from the work of the great nineteenth-century british scientist Michael Faraday.

The young faraday was fascinated by the breakthroughs in uncovering the mysterious properties of two new forces: electricity and magnetism. Faraday was hired as Professor Davy's secretary, he slowly began to win the confidence of the scientists at the royal institution and was allowed to to conduct important experiments of his own.

In 1829, Faraday was free to make a series of stunning breakthroughs that led to the creation of the generators that would energize entire cities and change the course of the world civilization.

The key to Faraday's greatest discoveries was his "force fields". If one places iron filings over a magnet, one finds that the iron filings create a spiderweb-like pattern that fills up the space. These are Faraday's lines of force.

The theories behind force fields?

A plasma window. If a gas is heated to a high enough temperature, thus creating a plasma, it can be molded and shaped by magnetic and electrical fields. It can be shaped in the form of a sheet or window. In addition, the "plasma window" can be used to separate a vacuum from ordinary air. In another words, one might be able to prevent air within the spaceship from leaking out into space, thereby creating a convenient, transparent interface between outer space and the spaceship.

But the plasma window needs a combination of several other technologies stacked in layers to vaporize incoming projectiles.

The outer layer could be a super charged plasma window, heated to temperatures high enough to vaporize metals in an instant.
A second layer could a curtain of thousands of crisscrossing high-energy laser beams that would heat up objects that passed through it, effectively vaporizing them.
The third layer would be a lattice made of "carbon nanotubes", tiny tubes made of individual carbon atoms that are one atom thick and stronger than steel by a hundred times by comparison.

However, these several layers would not fulfill the science fiction force field because it would be transparent and therefore incapable of stopping a laser beam.

To stop a laser beam, the shield would also need to possess and advanced form of "photochromatics". This is the process used in sunglasses that darken by themselves upon exposure to UV radiation. Photochromatics are based on molecules that can exist in at least two states. In one state, the molecule is transparent. But when it is exposed to UV radiation, it instantly changes to the second state, which is opaque.

One day, we might be able to use nanotechnology to produce a substance as tough as carbon nanotubes that can change it properties when exposed to laser light.

It might be able to simulated many of the properties of force fields by using a multilayered shield, consisting of plasma windows, laser curtain, carbon nanotubes and photochromatics. But developing such a shield could be many decades or even a century away.

Give these consideration, force shields would be classified as Class I impossibility-something that is impossible by today's technology, but possible within a century or so.