Invisibility
|
An example of how an object could appear to be invisible through the use of mirrors |
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 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.
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 )
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.
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.
* 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,
2006 theoretical work predicts that the imperfections need not be serious, and
metamaterials may make real-life "cloaking devices" practical.
The technique is suspected to be applied to
radio waves within five years, and eventually visible light is a possibility.
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 mystical
creatures can make themselves invisible at will, such as
Chinese dragons in some tales, which can shrink so small that humans cannot see.
* 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.
Where
magical invisibility is concerned, the issue may arise of whether or not 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.
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.
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 any 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 appears to be an inevitable drawback which would always offset the advantage of invisibility, even if a practical method of becoming invisible were discovered (unless one's intent was simply to hide and be still, letting the danger pass).
Nevertheless, 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.)
People have attributed invisibility to things that do not exist in order to explain why they're 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.
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.
* 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. Such a suit may actually be possible (see External links below).
** 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
magicianss like
Doctor Strange who have invisibility spells in their possession.
** In the film
Mystery Men (
1999), the "Invisible Boy" is invisible when nobody is looking at him.
** In one episode of
Invader Zim, Zim got an invisibility robot that had the ability to render itself invisible. There were two problems to this however. 1) The robot had to be kept on a constant power cord, restricting the distance it can travel while invisible and 2), only the
robot was able to become invisible, not Zim, therefore the robot is useless.
** 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 also causes serious side effects.
** 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
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.
** Cloaking technology is also employed by large
battleships in the game
Colony Wars.
** In
Metal Gear Solid,
Otacon wore an optic camouflage prototype while sneaking around the facility. The exoskeleton of the
Cyborg Ninja had a similar feature.
The Fear also used it in
Metal Gear Solid 3: Snake Eater. Additionally, it is an unlockable item that the player can use to thwart his enemies.
**
Blizzard Entertainment's
strategy games have always had invisibility as a gameplay device. For example, in
StarCraft, many units employ
cloaking devices, while in
Warcraft III, units employ a range of invisibility spells and camouflage at night time and in
World of Warcraft some of the characters and classes have abilities which render them essentially invisible.
** In
The Incredibles, one of the family members,
Violet Parr (nicknamed Vi) has the ability to render herself invisible. The ability is for her body only. A suit is made for her that can also become invisible when she does.
** The short story "They Go Bump" by
David Barr Kirtley is about a group of soldiers who wear invisibility suits. The main character has trouble walking (not being able to see his feet) and starts to wonder if his invisible companions are really who they say they are.
** The videogame,
Psychonauts features invisibility as one of many psychic powers unlocked and made available to the player throughout the game. The power can be used to escape enemies, and it particularly useful during boss encounters.
** The computer game
Zork Grand Inquisitor includes a very useful spell called
Igram which turns
purple things invisible. The game also features a character called the "six-armed invisible bridge guard" who apparently had Igram cast on him at one point â€" if the player tries to cast this spell on him, he replies, "How do you think I got like this in the first place?"
** In the 1980's animated series Thundercats, the Thundercat Tygra can turn himself invisible sometimes with the aid of his weapon, a 'Bolowhip', which he generally whipped around himself to turn invisible.
** In the book series
Artemis Fowl, fairies can vibrate at a very high frequency, making them invisible to all creatures except rats and two species of monkey.
** In the
Harry Potter book series by
J.K. Rowling, Harry has a
cloak that renders the wearer invisible.
**The popular japanese sci-fi animation film
Ghost in the Shell(1995)as well as it's TV series Ghost in the Shell:
Stand Alone Complex(2002)deals with invisibility of cyborg bodies using thermoptics.This is 1 of many cases of invisibility found in animes.
** In the Sci Fi Channel Series The Invisible Man, Darien Fawkes can turn invisible with the help of a gland in his brain that secreets a liquid called Quicksilver that can bend light around an object/person making the user invisible to the naked eye.
** In the
Space Patrol episode "Husky becomes invisible" - Professor Zellor discovers that his new star-measuring apparatus can make objects disappear.
** Certain characters in
LEGO's
Bionicle line can become invisible.
** Stealth technology is used in
Command & Conquer game series.
NOD in
Tiberian Sun and in
Renegade uses stealth generator and stealth tanks, but stealth generator was not used in Renegade.
*
Qualitative invisibility*
Concealment*
Cloaking device* [https://webspace.utexas.edu/cokerwr/www/index.html/science11.html Invisibility in the real world] Interesting picture of a test tube's bottom half invisible in cooking oil.
*
Info on "stealth suit"*
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
Ã…ngstrom-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
