Invisibility

"Invisible" redirects here. For other uses, see Invisible (disambiguation).
An example of how an object could appear to be invisible through the use of mirrors

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.

Practical efforts

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

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.

Psychological

A person can be described as invisible if others refuse to see him or routinely overlook him. The term was used in this manner in the title of the book Invisible Man, by Ralph Ellison, in reference to the protagonist, likely modeled after the author, being overlooked on account of his status as an African American.

Fictional use

Alberich puts on the Tarnhelm and vanishes; illustration by Arthur Rackham to Richard Wagner's Das Rheingold

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

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.

Where magical invisibility is concerned, the issue may arise of whether the clothing worn 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

References

  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. doi:10.1364/josaa.31.002244.
  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. JSTOR 1418951. PMID 13124563.
  3. Cloak of invisibility: Fact or fiction? - Innovation - MSNBC.com
  4. Nachman, Adrian I. (November 1988). "Reconstructions From Boundary Measurements". Annals of Mathematics. Annals of Mathematics. 128 (3): 531–576. doi:10.2307/1971435. JSTOR 1971435.
  5. 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.
  6. 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. PMID 16728597. Retrieved 2006-08-01.
  7. Leonhardt, Ulf (June 2006). "Optical Conformal Mapping". Science. 312 (5781): 1777–1780. Bibcode:2006Sci...312.1777L. doi:10.1126/science.1126493. PMID 16728596. Retrieved 2006-08-01.
  8. Cho, Adrian (2006-05-26). "High-Tech Materials Could Render Objects Invisible". Science. p. 1120. Retrieved 2006-08-01.
  9. "Invisibility cloak a step closer as scientists bend light 'the wrong way'". Daily Mail. London. 2008-08-11.
  10. themoneytimes.com,Scientists Turn Fiction Into Reality, Closer to Make Objects "Invisible"
  11. mirror.co.uk, Secrets of invisibility discovered
  12. John Pendry video: The birth and promise of metamaterials, SPIE Newsroom, 18 October 2011, doi:10.1117/2.3201110.02.

External links

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