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Invisibility

From Wikipedia, the free encyclopedia
"Invisible" redirects here. For other uses, seeInvisible (disambiguation).
By using two parabolic cylindric mirrors and one plane mirror, the image of the background is directed around an object, making the object itself invisible - at least from two sides.

Invisibilityis the state of an object that cannot beseen.An object in this state is said to beinvisible(literally, "not visible" ). The phenomenon is studied byphysicsandperceptual psychology.

Since objects can be seen bylightfrom a source reflecting off their surfaces and hitting the viewer'seyes,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 sensorialperceptionit has been shown that invisibility is perceived in cycles.[2]

Invisibility is often considered to be the supreme form ofcamouflage,as it does not reveal to the viewer any kind ofvital signs,visualeffects, or any frequencies of theelectromagnetic spectrumdetectable to thehuman eye,instead making use ofradio,infraredorultravioletwavelengths.

Inillusion optics,invisibility is a special case of illusion effects: the illusion of free space.

The term is often used infantasyandscience fiction,where objects cannot be seen by means ofmagicorhypothetical technology.

Practical efforts

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Main article:Cloak of invisibility

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 asactive camouflage.Thoughstealth technologyis declared to be invisible toradar,all officially disclosed applications of the technology can onlyreducethe size and/or clarity of the signature detected by radar.

In 2003 the Chilean scientistGunther Uhlmannpostulates the first mathematical equations to create invisible materials.[3][better source needed] In 2006, a team effort of researchers from Britain and the US announced the development of a realcloak of invisibility,an artificially mademeta materialthat is invisible to the microwave spectrum, though it is only in its first stages.[4]

Infilmmaking,people, objects, or backgrounds can be made to look invisible on camera through a process known aschroma keying.

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 oftransformation optics,which have given rise to severaltheories of cloaking.

Currently, a practical cloaking device does not exist.[5][6]A 2006 theoretical work predicts that the imperfections are minor, andmetamaterialsmay make real-life "cloaking devices" practical.[7][8]The technique is predicted to be applied toradio waveswithin 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 ofThe Invisible Man.

Two teams of scientists worked separately to create two "Invisibility Cloaks" from 'metamaterials' engineered at thenanoscalelevel. 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 theUniversity of California,Berkeleysaid: "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 Berkeleyresearcher 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. 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.

TheImperial College Londonresearch team achieved results withmicrowaves.An invisibility cloak layout of a copper cylinder was produced in May, 2008, by physicist Professor SirJohn Pendry.Scientists working with him atDuke Universityin 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 inNew Journal of Physicsthat 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 Biotechnologyhas 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. This is despite its actual application requiring artificial backgrounds made up of horizontal lines.[13]

Psychological

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Main article:Social invisibility

A person can be described as invisible if others refuse to see them or routinely overlook them. The term was used in this manner in the title of the bookInvisible Man,byRalph Ellison,in reference to the protagonist, likely modeled after the author, being overlooked on account of his status as anAfrican American.This is supported by the quote taken from the Prologue, "I am invisible, understand, simply because people refuse to see me." (Prologue.1)[14]

Fictional use

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Main article:Invisibility in fiction
Alberichputs on theTarnhelmand vanishes; illustration byArthur RackhamtoRichard Wagner'sDas Rheingold

In fiction, people or objects can be rendered completely invisible by several means:

  • Magical objects such asrings,cloaksandamuletscan be worn to grant the wearer permanent invisibility (or temporary invisibility until the object is taken off).
  • Magicalpotionscan be consumed to grant temporary or permanent invisibility.
  • Magic spells can be cast on people or objects, usually giving temporary invisibility.
  • Some mythicalcreaturescan make themselves invisible at will, such as in some tales in whichleprechaunsorChinese dragonscan shrink so much that humans cannot see them.
  • In science fiction, the idea of a "cloaking device".

In some works, the power of magic creates an effective means of invisibility by distracting anyone who might notice the character. But since the character is not truly invisible, the effect could be betrayed by mirrors or other reflective surfaces.

Wheremagicalinvisibility is concerned, the issue may arise of whether theclothingworn by and any items carried by the invisible being are also rendered invisible. In general they are also regarded as being invisible, but in some instances clothing remains visible and must be removed for the full invisibility effect.

See also

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References

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  1. ^Moreno, Ivan; Jauregui-Sánchez, Y.; Avendaño-Alejo, Maximino (2014)."Invisibility assessment: a visual perception approach"(PDF).Journal of the Optical Society of America A.31(10): 2244–2248.Bibcode:2014JOSAA..31.2244M.doi:10.1364/josaa.31.002244.PMID25401251.Archived fromthe original(PDF)on 2017-08-08.Retrieved2016-01-24.
  2. ^Craig, Eugene A.; Lichtenstein, M. (1953). "Visibility-Invisibility Cycles as a Function of Stimulus-Orientation".The American Journal of Psychology.66(4): 554–563.doi:10.2307/1418951.JSTOR1418951.PMID13124563.
  3. ^Alonso, N. (March 21, 2013)."Un genio invisible"[An invisible genius].Qué Pasa(in Spanish).
  4. ^"Cloak of invisibility: Fact or fiction?".NBC News.
  5. ^Nachman, Adrian I.(November 1988). "Reconstructions From Boundary Measurements".Annals of Mathematics.128(3): 531–576.doi:10.2307/1971435.JSTOR1971435.
  6. ^Wolf, Emil; Tarek Habashy (May 1993). "Invisible Bodies and Uniqueness of the Inverse Scattering Problem".Journal of Modern Optics.40(5): 785–792.Bibcode:1993JMOp...40..785W.doi:10.1080/09500349314550821.
  7. ^Pendry, J. B.; D. Schurig; D. R. Smith (June 2006)."Controlling Electromagnetic Fields".Science.312(5781): 1780–1782.Bibcode:2006Sci...312.1780P.doi:10.1126/science.1125907.PMID16728597.S2CID7967675.
  8. ^Leonhardt, Ulf (June 2006)."Optical Conformal Mapping".Science.312(5781): 1777–1780.Bibcode:2006Sci...312.1777L.doi:10.1126/science.1126493.PMID16728596.S2CID8334444.
  9. ^Cho, Adrian (2006-05-26)."High-Tech Materials Could Render Objects Invisible".Science.p. 1120.Retrieved2006-08-01.
  10. ^"Scientists Turn Fiction Into Reality, Closer to Make Objects" Invisible "".themoneytimes.com.Archived fromthe originalon 2008-08-16.
  11. ^"Secrets of invisibility discovered".mirror.co.uk.10 August 2008.
  12. ^John Pendry (18 October 2011)."video: The birth and promise of metamaterials".SPIE.doi:10.1117/2.3201110.02.
  13. ^"Hyperstealth Biotechnology's" invisibility cloak "can conceal people and buildings".Dezeen.2019-11-07.Retrieved2019-11-16.
  14. ^Ellison, Ralph (1947).Invisible man.New York: Modern Library/Random House.ISBN9780679601395.
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