Invisibility

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Invisibility is the state of an object which cannot be seen. An object in this state is said to be invisible (literally, "not visible"). The term is usually used as a fantasy/science fiction term, where objects are literally made unseeable by magical or technological means. However, its effects can also be seen in the real world, particularly in physics.

Since objects can be seen by light in the visible spectrum from a source reflecting off their surfaces and hitting the viewer's eye, the most natural form of invisibility (whether real or fictional) is an object which does not reflect nor absorbs light (that is, it allows light to pass through it). In nature, this is known as transparency, and is seen in many naturally-occurring materials (although no naturally-occurring material is 100% transparent).

Visibility also depends on the eyes of the observer and/or the instruments used. Thus an object can be classified as "invisible to" a person, animal, instrument, etc.

Contents 1 Invisibility by environment 2 Invisibility in physics 3 Invisibility by technology 4 Invisibility by magic 5 Simultaneous invisibility and color 6 Sight while invisible 7 Invisibility of controversial things 8 Examples in fiction 9 See also 10 External links 11 References

[edit] Invisibility by environment

An object may be classified as "invisible" if it cannot be seen due to environmental factors other than the fact that it doesn't reflect light. An object that might normally be seeable may be classified as invisible if it is:

• Behind an object.
• The same colour or pattern as the background. (Camouflage)
• Patterned so that its outline is hard to determine.
• In an environment which is too dark or too bright.
• Not in a particular observer's line-of-sight. (Especially when driving)
• Transparent. (air and many other gases)

[edit] Invisibility in physics

Theoretical and practical physics offer several causes of invisibility. An object may be invisible if it is:

• So massive that its escape velocity exceeds the speed of light (e.g. a black hole)
• Emitting or reflecting light outside the wavelength range of visible light. (Radiation is generally invisible by this means.) Unfortunately, this would result in any obscured human being becoming not invisible and transparent, but completely opaque and resembling a human-shaped black hole.
• So tiny that it cannot be detected by an observer.
• A recent breakthrough (2006) at Imperial College London has shown that invisibility is possible by using specifically patterned crystals made up of nanoscale boxes that hold electrons. When light hits these crystals, it becomes entangled within the boxes, causing the object to become transparent.^[1]

[edit] Invisibility by technology

Technology can be used theoretically or practically to render real-world objects invisible:

• Making use of real-time image displayed on a wearable display, scientists are able to create a see-through effect, if not invisibility. This is known as optical camouflage and has been used in many science fiction works.
• Invisibility (lower visibility) for radar is called stealth technology.
• In some science fiction stories, a hypothetical "cloaking device" is used to make objects invisible. On Thursday October 19, 2006 a team effort of researchers from Britain and the U.S announced the development of a real cloak of invisibility, though it is only in its first stages.^[2]
• In filmmaking, people, objects, or backgrounds can be made to look invisible on camera through a process known as chroma keying.
• Theoretically, it is possible to make an object invisible, if the object has the same refractive index as the surrounding medium. (e.g. air)
• Although it has been shown that making opaque objects perfectly invisible ("non-scattering scatterers") is impossible,^[3][4] 2006 theoretical work predicts that the imperfections need not be serious, and metamaterials may make real-life "cloaking devices" practical.^[5][6] The technique is suspected to be applied to radio waves within five years, and eventually visible light is a possibility. The theory that light waves can be acted upon the same way as radio waves is now a popular idea among scientists and can be compared to a stone in a river, in where the water passes around it, but leaving no trace of a stone being in the water slightly down-stream. Comparing light waves to the water and whatever object that is being "cloaked" to the stone, the desire is to have light waves pass around that object, leaving no visible aspects of it, possibly not even a shadow.^[7] This is the technique utilized with the "Quicksilver gland" in the most recent television portrayal of The Invisible Man.

[edit] Invisibility by magic

Invisibility, usually by magic, is a popular theme in fantasy, mythology and Ceremonial magic. It is often used as a gameplay device in role-playing and strategy games. Typically, people or objects can be rendered completely invisible by several means:

• Magical objects such as rings, cloaks and amulets can be worn to grant the wearer permanent invisibility.
• Magical potions can be consumed to grant temporary invisibility.
• Magic spells can be cast on people or objects, usually giving temporary invisibility.
• Some mythical creatures can make themselves invisible at will, such as some versions of Leprechaun, and Chinese dragons in some tales, which can shrink so small that humans cannot see them.
• An invisibility ritual is described in the manuscripts of the Hermetic Order of the Golden Dawn and appears on the Book The Golden Dawn by Israel Regardie.
• In the Artemis Fowl, fairies can become invisible, or shield, by vibrating faster than the eye can see.

In some works, magical invisibility is "psychic" invisibility; while the character could be normally seen by anyone who notices him, the magic distracts anyone who actually could notice him. Such invisibility can be betrayed by mirrors or other reflective surfaces.

Where magical invisibility is concerned, the issue may arise of whether the clothing and items carried by the invisible wearer/carrier are also rendered invisible. In general, they are, but in some instances, clothing remains visible and must be removed for the full invisibility effect -- as for instance, the movie The Incredibles, where Violet Parr can only turn her clothing invisible when it has been specially made to allow it.

[edit] Simultaneous invisibility and color

Since something that is invisible has no color associated with it, it is somewhat paradoxical to imagine an object that is both invisible and coloured. This idea is most famous in the parody goddess, the Invisible Pink Unicorn.

[edit] Sight while invisible

According to the laws of physics as presently understood, an invisible person would necessarily be blind, no matter how their invisibility were achieved. In order to see light, it must be absorbed by the retina, but in order for a person to be invisible, the body must not absorb light. In fact, according to the no cloning theorem of quantum mechanics, they could not even make a copy of the photons so they could see one copy and allow the other copy to pass through or around them.

This physical barrier appears to offset the advantage of any perfect invisibility method, unless one's intent was simply to hide and be still, letting the danger pass. On the other hand, a practical invisibility method need not allow light of all frequencies to pass all the time, so there may be ways around this limitation.

Alternatively, many works of fiction portray invisibility as a magic achievement, and since paranormal magic may be interpreted as breaking the laws of physics, it could theoretically allow sight. Invisibility is often utilized in science fiction and fantasy works which people go into with a healthy suspension of disbelief, anyway.

One of the few fictional examples of a double-blind cloak comes from the Thrawn Trilogy of Star Wars novels. Grand Admiral Thrawn's cloaking devices make the ships wielding them invisible, but also prevent those inside the ship from seeing out. Thus, most of the time, ships using this type of cloak remain stationary, dropping the cloak just before battle. (See the beginning of Specter of the Past for an example of this tactic.)

In the Halo video game series, the "active camouflage" power-up renders the wearer only partially invisible — the visible silhouette of the wearer is likely necessary so that the wearer's retinas can absorb what little light they need to see (though it also exists for game balance issues). In the video game Quake, picking up a magic ring turns the player invisible to monsters for thirty seconds. In multiplayer deathmatch mode, only the player's eyes are visible, giving his opponents only a small clue to his location.

[edit] Invisibility of controversial things

People have attributed invisibility to things that are mythical, things that do not exist or things are of a religious or supernatural nature in order to explain why they are not apparent. In the Middle Ages, fern seeds were thought to be invisible since ferns don't have seeds. They were also said to grant invisibility.[1] In medieval astronomy, the crystal spheres[2] that held up the sun, moon, stars, and planets were invisible. Historically, creatures such as goblins and brownies have also been described as invisible or able to become invisible. Currently, many entities or phenomena whose existence is disputed, such as ghosts, demons, qi, and auras, are also ascribed invisibility. In religion, gods, goddesses, angels and demons are commonly thought to be invisible, at least part of the time. Indeed, the omnipresence attributed to the monotheistic God of Abrahamic religions would seem to require invisibility, since otherwise God would be constantly visible to to all people because of inhabiting all places.

[edit] Examples in fiction

The idea of being unseen and hence undetectable has fascinated mankind for generations. This concept of invisibility has been explored in many myths, novels, movies and video games, some of them comedies.

• Mythology and folklore
  • In many myths and legends, gods, spirits, fairies, angels, and demons are often invisible or can choose to become invisible at will.
  • The ring of Gyges is described in a story in Plato's The Republic. A peasant finds a ring in the tomb of a dead king which allows him to become invisible at will. Plato has him enter the palace, seduce the queen, and plot to kill the king, arguing that power, such as this, corrupts absolutely.
  • The hero Perseus went equipped with a helmet of invisibility to kill Medusa.
  • A magic cloak, made by Alberich the dwarf, granted invisibility to Sigurd.
  • In German fairy tales, magical caps called tarnkappes are worn by dwarfs. The caps can make an entire village of dwarfs invisible.
  • In The Twelve Dancing Princesses, the old soldier is able to follow the princesses by use of an invisibility cloak
  • In The King of the Gold Mountain, the hero can sneak into the home of his treacherous wife by means of a cloak of invisibility
• Modern fiction
  • The Invisible Man (1897) by H. G. Wells is a well-known novel about invisibility, later made into a film and several TV series.
  • One function of the One Ring in J. R. R. Tolkien's The Lord of the Rings series was to render the user invisible. Unfortunately, it had an evil influence with negative effects on the wearer's actions.
  • The Philadelphia Experiment (1984) is a movie about an attempt to make a ship invisible.
  • The film Predator and animated television series like Batman Beyond and Max Steel depict a kind of stealth mode that is a partial invisibility where the subject is largely transparent and/or translucent. While a concentrated look in optimal lighting conditions can spot it, it still makes the wearer extremely hard to see which eases stealth movement.
  • In comic books, there are superheroes such as the Invisible Woman (who can bend light around herself without distortion) that have the power to become invisible at will as well as magicians like Doctor Strange who have invisibility spells in their possession.
  • In the film Hollow Man (2000), an injection is tested on animals (and eventually, humans) which made the organism invisible, organ by organ. Unfortunately, the serum can only be counteracted by electricity, and the long term effects of invisibility proved serious.
  • In The Hitchhiker's Guide to the Galaxy "trilogy" of novels by Douglas Adams, the Somebody Else's Problem field is a humorous concept of a field which makes people believe the object in question is "somebody else's problem" and therefore do not see it. The concept of the "somebody else's problem field", as it is explained in the book, bases off of a statement to the effect that actual, invariable, invisibility is basically impossible and that the field is merely a way to make something close to being invisible by actually making it hard to notice deliberately.
  • In the video game The Legend of Zelda: Majora's Mask, the "stone mask" item works similarly. It causes the wearer to be "as plain and uninteresting as a rock" and thus functionally invisible, causing enemies to ignore their presence. The soldier that gives Link the mask is invisible to the player without the use of the Lens of Truth.
  • In the Star Trek universe, some ships of the Klingon Empire and the Romulan Star Empire, as well as the Federation ship USS Defiant, are equipped with pieces of hardware known as cloaking devices that conceal them from most varieties of scans, including visual.
  • The popular Japanese sci-fi animation film Ghost in the Shell (1995) as well as its TV series Ghost in the Shell:Stand Alone Complex (2002) deals with invisibility of cyborg bodies using thermoptics. This is one of many cases of invisibility found in animes.

[edit] See also

• Qualitative invisibility
• Concealment
• Cloaking device
• Active camouflage
• Invisibility in fiction

[edit] External links

• Invisibility in the real world Interesting picture of a test tube's bottom half invisible in cooking oil.
• Info on "stealth suit"
• Metamaterial Technology for Invisibility
• Radar Invisibility
• Some examples
• CNN article on an "actual" invisibility suit
  • Note: the picture was taken by a special camera that displays images behind the wearer of the suit. The suit itself does not render invisibility. In essence, the suit functions as a bluescreen onto which the image behind the suit can be displayed through camera.
• Plasmonic invisibility effect Plasmons are electron configurations on a metallic surface that resonate with a specific frequency or photon wavelength of light. This effect has so far been observed only in gold foil perforated with holes smaller than the photons. The oversize photons pass through the foil anyway (reportedly with amplification), so a quantum-tunneling phenomenon may be associated with the light wave trapping.
  • A monochromatic LED flashlight shined on a plasmonicly resonant surface would not allow that specific color of light to scatter back toward the light source. Plasmons act analogously to wave trap circuits familiar to builders of amateur radio equipment, except plasmons measure in Ångstrom-unit sizes.
• Theoretical method of scattering light (Nature.com subscription) that could make objects "invisible" to certain light frequencies. This is the source of the Livescience.com story on plasmons (above).
  • Unfortunately, this could not be used to hide anything but a microscopic object from visible light because the object has to be either the same size as the wavelength of light from which it is hidden, or only somewhat larger.
• Brief piece on why visible light is visible
• Says how an invisibility cloak works
• Scientists Aim to Duplicate Harry Potter's Invisibility Cloak
• Invisibility shield
• Reuters about Ulf Leonhart bending light to flow around an object, making it appear invisible

[edit] References