Invisibility
From Wikipedia, the free encyclopedia
Jump to navigationJump to search
"Invisible" redirects here. For other uses, see Invisible (disambiguation).
This article possibly contains original
research. Please improve it by verifying the claims
made and adding inline citations. Statements consisting
only of original research should be removed. (September
2011) (Learn how and when to remove this template message)
Invisibility is the state of an object that cannot be seen. An object in this state
is said to be invisible (literally, "not visible").
The term is often used in fantasy/science fiction, where objects cannot be
seen by magical or technological means; however, its effects can also be
demonstrated in the real world, particularly in physics and perceptual
psychology classes.
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 that neither reflects nor
absorbs light (that is, it allows light to pass through it). This is known
as transparency, and is seen in many naturally occurring materials (although
no naturally occurring material is 100% transparent).
Invisibility perception depends on several optical and visual factors. [1] For
example, invisibility 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. In research on sensorial perception it has been shown
that invisibility is perceived in cycles.[2]
Invisibility is often considered to be the supreme form of camouflage, as it
does not reveal to the viewer any kind of vital signs, visual effects, or any
frequencies of the electromagnetic spectrum detectable to the human eye,
instead making use of radio, infrared or ultraviolet wavelengths.
In illusion optics, invisibility is a special case of illusion effects: the illusion of
free space.
Contents
1Practical efforts
2Psychological
3Fictional use
4See also
5References
6External links
Practical efforts[edit]
This article is in list format, but may read better
as prose. You can help by converting this article, if
appropriate. Editing help is available. (June 2016)
Technology can be used theoretically or practically to render real-world
objects invisible:
Making use of a real-time image displayed on a wearable display, it is possible to
create a see-through effect. This is known as active camouflage.
Though stealth technology is declared to be invisible to radar, all officially disclosed
applications of the technology can only reduce the size and/or clarity of the signature
detected by radar.
In 2003 the Chilean scientist Gunther Uhlmann postulates the first mathematical
equations to create invisible materials.[3][better source needed]
2006: A team effort of researchers from Britain and the US announced the
development of a real cloak of invisibility, though it is only in its first stages.[4]
In filmmaking, people, objects, or backgrounds can be made to look invisible on
camera through a process known as chroma keying.
An artificially made meta material that is invisible to the microwave spectrum.
Engineers and scientists have performed various kinds of research to
investigate the possibility of finding ways to create real optical invisibility
(cloaks) for objects. Methods are typically based on implementing the
theoretical techniques of transformation optics, which have given rise to
several theories of cloaking.
Currently, a practical cloaking device does not exist. [5][6] A 2006 theoretical
work predicts that the imperfections are minor, and metamaterials may make
real-life "cloaking devices" practical. [7][8] The technique is predicted to be
applied to radio waves within five years, and the distortion of visible light is an
eventual possibility. The theory that light waves can be acted upon the same
way as radio waves is now a popular idea among scientists. The agent can be
compared to a stone in a river, around which water passes, but slightly down-
stream leaves no trace of the stone. Comparing light waves to the water, and
whatever object that is being "cloaked" to the stone, the goal is to have light
waves pass around that object, leaving no visible aspects of it, possibly not
even a shadow.[9] This is the technique depicted in the 2000 television
portrayal of The Invisible Man.
Two teams of scientists worked separately to create two "Invisibility Cloaks"
from 'metamaterials' engineered at the nanoscale level. They demonstrated
for the first time the possibility of cloaking three-dimensional (3-D) objects with
artificially engineered materials that redirect radar, light or other waves around
an object. While one uses a type of fishnet of metal layers to reverse the
direction of light, the other uses tiny silver wires. Xiang Zhang, of
the University of California, Berkeley said: "In the case of invisibility cloaks or
shields, the material would need to curve light waves completely around the
object like a river flowing around a rock. An observer looking at the cloaked
object would then see light from behind it, making it seem to disappear."
UC Berkeley researcher Jason Valentine's team made a material that affects
light near the visible spectrum, in a region used in fibre optics: 'Instead of the
fish appearing to be slightly ahead of where it is in the water, it would actually
appear to be above the water's surface. It's kind of weird. For a metamaterial
to produce negative refraction, it must have a structural array smaller than the
wavelength of the electromagnetic radiation being used." Valentine's team
created their 'fishnet' material by stacking silver and metal dielectric layers on
top of each other and then punching holes through them. The other team
used an oxide template and grew silver nanowires inside porous aluminum
oxide at tiny distances apart, smaller than the wavelength of visible light. This
material refracts visible light.
The Imperial College London research team achieved results
with microwaves. An invisibility cloak layout of a copper cylinder was
produced in May, 2008, by physicist Professor Sir John Pendry. Scientists
working with him at Duke University in the US put the idea into practice.[10][11]
Pendry, who theorized the invisibility cloak "as a joke" to illustrate the potential
of metamaterials, said in an interview in August 2011 that grand, theatrical
manifestations of his idea are probably overblown: "I think it’s pretty sure that
any cloak that Harry Potter would recognize is not on the table. You could
dream up some theory, but the very practicality of making it would be so
impossible. But can you hide things from light? Yes. Can you hide things
which are a few centimeters across? Yes. Is the cloak really flexible and
flappy? No. Will it ever be? No. So you can do quite a lot of things, but there
are limitations. There are going to be some disappointed kids around, but
there might be a few people in industry who are very grateful for it." [12]
In Turkey in 2009, Bilkent University Search Center Of Nanotechnology
researches explained and published in New Journal of Physics that they
achieved to make invisibility real in practice using nanotechnology making an
object invisible with no shadows etc. next to perfect transparent scene by
producing nanotechnologic material that can also be produced like a suit
anyone can wear.
In 2019, Hyperstealth Biotechnology has patented the technology behind a
material that bends light to make people and objects near invisible to the
naked eye. The material, called Quantum Stealth, is currently still in the
prototyping stage, but was developed by the company's CEO Guy Cramer
primarily for military purposes, to conceal agents and equipment such as
tanks and jets in the field. Unlike traditional camouflage materials, which are
limited to specific conditions such as forests or deserts, according to Cramer
this "invisibility cloak" works in any environment or season, at any time of day.
[13]
In 2020, a physical phenomenon (related to the electronic resonance of laser
processed materials) that allows the direct fabrication of invisible structures
was discovered.[14] Using the new technology, researchers from Laval
University, Canada, have fabricated invisible photonic circuits. They
discovered that the structure of a material can be modified to be usable for
frequencies operating photonic devices and sensors, for example, while the
structural modification becomes invisible for frequencies detectable by the
eye. More precisely, they found that the positive refractive index (RI) change
induced by the electronic resonance variation can exactly compensate the
negative RI change induced by a structural expansion (both caused by the
laser-induced modification), resulting in a zero RI change for certain colors,
enabling invisibility.[15]
