Cloak of invisibility

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Cloak of invisibility
Folk lore and fairy tales element
Illustration to Richard Wagner's "Das Rheingold".jpg
Alberich puts on the Tarnkappe and vanishes; illustration by Arthur Rackham to Richard Wagner's Das Rheingold
First appearanceAncient
GenreFolklore and fairy tales
In-universe information
TypeMagical cape
FunctionRenders the wearer invisible

A cloak of invisibility is an item that prevents the wearer from being seen. In folklore, mythology and fairy tales, a cloak of invisibility appears either as a magical item used by duplicitous characters or an item worn by a hero to fulfill a quest. It is a common theme in Welsh and Germanic folklore, and may originate with the cap of invisibility seen in ancient Greek myths. The motif falls under "D1361.12 magic cloak of invisibility" in the Stith Thompson motif index scheme.

Contents

In folklore

Cloaks of invisibility are magical items found in folklore and fairy tales. Such cloaks are common in Welsh mythology; a "Mantle of Invisibility" is described in the tale Culhwch and Olwen (c. 1100) as one of King Arthur's most prized possessions. [1] The mantle is described again, and in more detail, [1] in the Breuddwyd Rhonabwy, and is later listed as one of the Thirteen Treasures of the Island of Britain. A similar mantle appears in the Second Branch of the Mabinogi, in which it is used by Caswallawn to assassinate the seven stewards left behind by Bran the Blessed and usurp the throne. [1] [2]

In the English fairy tale Jack the Giant Killer , the hero is rewarded with several magical gifts by a giant he has spared, among them a coat of invisibility. Iona and Peter Opie observe in The Classic Fairy Tales (1974), that Jack's coat may have been borrowed from the Tale of Tom Thumb or from Norse mythology, but they also draw comparisons with the Celtic stories of the Mabinogion. [3]

The counterpart in Japan is the kakuremino (隠れ蓑), a magical "straw cape" or "raincoat" of invisibility. In the folktale of the "Peach Boy" Momotarō , one of the treasures the hero collects from the ogres is a cape of invisibility, paralleling the story of Jack the giant-slayer. [4]

Tarnkappe

Although occurrences in fairy tales are rare, [5] the cloak of invisibility appears in the German tale The Twelve Dancing Princesses (KHM 133) and in The King of the Golden Mountain (KHM 92) in Grimm's Fairy Tales. [6] The cloak in German fairy tales may be traceable to the tarnkappe ("cloak of concealment"), [5] such as the one that the hero Sîfrit (Siegfried) acquires from the dwarf Alberich in the Middle High German epic Nibelungenlied . [7] The Grimms clarify that Sîfrit's kappe is a cape that covers not just the head but enshrouds the body, though in later times tarnkappe came to be regarded as a cap of invisibility. The tarnkappe (or tarnkeppelin [8] ) is also owned by the dwarf king who is the title character in Laurin . In different passages or variant manuscripts of these works, the tarnkappe is also referred to as the tarnhût (mod. Ger. Haut "skin") [7] [9] or hehlkappe (mod. Ger. hehlen "to hide"). [10] [11]

Modern adaptations

In the original epic Nibelungenlied, the hero's cloak not only grants him invisibility, but also increases his strength, to win over the Icelandic queen Brünhild. In Richard Wagner's opera cycle Der Ring des Nibelungen , the cloak becomes a magic helmet called the Tarnhelm, which also imparts the ability to transform upon its wearer. When Fritz Lang adapted Nibelungenlied for the movie screen in his 1924 film Die Nibelungen , Siegfried uses a veil or net of invisibility gained from the dwarf Alberich.[ citation needed ]

In fiction

Raoul Walsh's film The Thief of Bagdad , was released in the same year as Die Nibelungen and also features a cloak of invisibility playing a pivotal role.[ citation needed ]

Edgar Rice Burroughs uses the idea of an invisibility cloak in his 1931 novel A Fighting Man of Mars . The movie Erik the Viking humorously depicts the title character using a cloak of invisibility, which he does not realize apparently works only on elderly men. In The Lord of the Rings , Frodo, and the other members of the Fellowship of the Ring, were given cloaks by the Elves, and Samwise asked, "Are these magic cloaks?" The cloak given to Frodo camouflaged him so that the enemy could see "nothing more than a boulder where the Hobbits were."[ citation needed ]

Camouflaging cloaks form a central plot element in Samuel R. Delany's 1975 novel Dhalgren .[ citation needed ]

Cloaks of invisibility also exist in the Harry Potter series of novels by J.K. Rowling. [12] Harry Potter uses a Cloak of Invisibility, that was passed down to him by his father, to sneak into forbidden areas of his school and remain unseen. It is later revealed that this specific cloak was once owned by Death himself, making it one of the Deathly Hallows.[ citation needed ]

In The Secret History by Donna Tartt (1992), the character Richard says, "I became expert at making myself invisible"..."Sunday afternoons, my cloak of invisibility around my shoulders, I would sit in the infirmary for sometimes six hours at a time..."[ citation needed ]

In science

On October 19, 2006, a cloak was produced that routed microwaves of a particular frequency around a copper cylinder in a way that made them emerge almost as if there were nothing there. The cloak was made from metamaterials. It cast a small shadow, which the designers hope to fix.

The device obscures a defined two dimensional region and only at a particular microwave frequency. Work on achieving similar results with visible light is in progress. [13] [14] Other types of invisibility cloak are also possible, including ones that cloak events rather than objects.

However, cloaking a human-sized object at visible wavelengths appears to have low probability. [15] Indeed, there appears to be a fundamental problem with these devices as "invisibility cloaks": [16]

It's not yet clear that you're going to get the invisibility that everyone thinks about with Star Trek cloaking device or the Harry Potter's cloak. To make an object literally vanish before a person's eyes, a cloak would have to simultaneously interact with all of the wavelengths, or colors, that make up light.

On the other hand, a group of researchers connected with Berkeley Lab and the University of California, Berkeley believe that cloaking at optical frequencies is indeed possible. Furthermore, it appears within reach. Their solution to the hurdles presented by cloaking issues are dielectrics. These nonconducting materials (dielectrics) are used for a carpet cloak, which serves as an optical cloaking device. [17] [18] According to the lead investigator:

We have come up with a new solution to the problem of invisibility based on the use of dielectric (nonconducting) materials. Our optical cloak not only suggests that true invisibility materials are within reach, it also represents a major step towards transformation optics, opening the door to manipulating light at will for the creation of powerful new microscopes and faster computers.

Furthermore, a new cloaking system was announced in the beginning of 2011 that is effective in visible light and hides macroscopic objects, i.e. objects that can be seen with the human eye. The cloak is constructed from ordinary, and easily obtainable calcite. The crystal consists of two pieces configured according to specific parameters. The calcite is able to refract the light around a solid object positioned between the crystals. The system employs the natural birefringence of the calcite. From outside the system the object is not visible "for at least 3 orders of magnitude larger than the wavelength of light in all three dimensions." The calcite solves for the limitations of attempting to cloak with metallic inclusions - this method does not require a nanofabrication process as has become necessary with the other methods of cloaking. The nanofabrication process is time-consuming and limits the size of the cloaked region to a microscopic area. The system works best under green light. In addition the researchers appear to be optimistic about a practical cloaking device in the future: [19] [20]

In summary, we have demonstrated the first macroscopic cloak operating at visible frequencies, which transforms a deformed mirror into a flat one from all viewing angles. The cloak is capable of hiding three-dimensional objects three to four orders of magnitudes larger than optical wavelengths, and therefore, it satisfies a layman's definition of an invisibility cloak: namely, the cloaking effect can be directly observed without the help of microscopes. Because our work solves several major issues typically associated with cloaking: size, bandwidth, loss, and image distortion, it paves the way for future practical cloaking devices

Another design calls for tiny metal needles to be fitted into a hairbrush-shaped cone at angles and lengths that would force light to pass around the cloak. This would make everything inside the cone appear to vanish because the light would no longer reflect off it. "It looks pretty much like fiction, I do realize, but it's completely in agreement with the laws of physics," said lead researcher Vladimir Shalaev, a professor of electrical and computer engineering at Purdue. "Ideally, if we make it real it would work exactly like Harry Potter's invisibility cloak," he said. "It's not going to be heavy because there's going to be very little metal in it."

Furthermore, on April 30, 2009, two teams of scientists developed a cloak that rendered objects invisible to near-infrared light. Unlike its predecessors, this technology did not utilize metals, which improves cloaking since metals cause some light to be lost. Researchers mentioned that since the approach can be scaled down further in size, it was a major step towards a cloak that would work for visible light. [21]

Problems of refraction and opacity

The headlined claims that laboratory results with metamaterials are demonstrations of prototype invisibility cloaks conflicts with two facts resulting from fundamental characteristics of the underlying metamaterial technology:

Acoustic cloaking

Though perfect cloaking based on invisible paint is impossible if detectors (such as microphones) and sources (such as loudspeakers) are placed round a volume and if a particular formula is used to calculate the signals to be fed to the sources, perfect cloaking is possible. Such perfect cloaking does require that the information can flow through the volume fast enough and the calculations can be performed fast enough so that the necessary information can get to the sources on the far side of the volume fast enough. As a result, perfect cloaking for light is still probably at least very difficult if not impossible. For sound waves, though, such perfect cloaking is possible in principle; an object could therefore be made invisible to sonar, for example.

According to Fermat's Principle, light follows the trajectory of the shortest optical path, that is, the path over which the integral of the refractive index function is minimal. Therefore, the refractive index of an optical medium determines how light propagates within it. Consequently, by a suitable choice of refractive index profile for an optical medium, light rays can be bent around and made to propagate in closed loops.

See also

Related Research Articles

<span class="mw-page-title-main">Cloaking device</span> Theoretical device to render objects invisible

A cloaking device is a hypothetical or fictional stealth technology that can cause objects, such as spaceships or individuals, to be partially or wholly invisible to parts of the electromagnetic (EM) spectrum. Fictional cloaking devices have been used as plot devices in various media for many years.

<span class="mw-page-title-main">Invisibility</span> State of a matter that cannot be seen

Invisibility is the state of an object that cannot be seen. An object in this state is said to be invisible. The phenomenon is studied by physics and perceptual psychology.

<span class="mw-page-title-main">Photonic crystal</span> Periodic optical nanostructure that affects the motion of photons

A photonic crystal is an optical nanostructure in which the refractive index changes periodically. This affects the propagation of light in the same way that the structure of natural crystals gives rise to X-ray diffraction and that the atomic lattices of semiconductors affect their conductivity of electrons. Photonic crystals occur in nature in the form of structural coloration and animal reflectors, and, as artificially produced, promise to be useful in a range of applications.

<span class="mw-page-title-main">Metamaterial</span> Materials engineered to have properties that have not yet been found in nature

A metamaterial is any material engineered to have a property that is rarely observed in naturally occurring materials. They are made from assemblies of multiple elements fashioned from composite materials such as metals and plastics. These materials are usually arranged in repeating patterns, at scales that are smaller than the wavelengths of the phenomena they influence. Metamaterials derive their properties not from the properties of the base materials, but from their newly designed structures. Their precise shape, geometry, size, orientation and arrangement gives them their smart properties capable of manipulating electromagnetic waves: by blocking, absorbing, enhancing, or bending waves, to achieve benefits that go beyond what is possible with conventional materials.

A superlens, or super lens, is a lens which uses metamaterials to go beyond the diffraction limit. The diffraction limit is a feature of conventional lenses and microscopes that limits the fineness of their resolution depending on the illumination wavelength and the numerical aperture (NA) of the objective lens. Many lens designs have been proposed that go beyond the diffraction limit in some way, but constraints and obstacles face each of them.

<span class="mw-page-title-main">John Pendry</span> British physicist

Sir John Brian Pendry, is an English theoretical physicist known for his research into refractive indices and creation of the first practical "Invisibility Cloak". He is a professor of theoretical solid state physics at Imperial College London where he was head of the department of physics (1998–2001) and principal of the faculty of physical sciences (2001–2002). He is an honorary fellow of Downing College, Cambridge, and an IEEE fellow. He received the Kavli Prize in Nanoscience "for transformative contributions to the field of nano-optics that have broken long-held beliefs about the limitations of the resolution limits of optical microscopy and imaging.", together with Stefan Hell, and Thomas Ebbesen, in 2014.

<span class="mw-page-title-main">Negative-index metamaterial</span> Material with a negative refractive index

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<span class="mw-page-title-main">Terahertz metamaterial</span>

A terahertz metamaterial is a class of composite metamaterials designed to interact at terahertz (THz) frequencies. The terahertz frequency range used in materials research is usually defined as 0.1 to 10 THz.

<span class="mw-page-title-main">Acoustic metamaterial</span> Material designed to manipulate sound waves

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<span class="mw-page-title-main">Photonic metamaterial</span> Type of electromagnetic metamaterial

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<span class="mw-page-title-main">Metamaterial cloaking</span> Shielding an object from view using materials made to redirect light

Metamaterial cloaking is the usage of metamaterials in an invisibility cloak. This is accomplished by manipulating the paths traversed by light through a novel optical material. Metamaterials direct and control the propagation and transmission of specified parts of the light spectrum and demonstrate the potential to render an object seemingly invisible. Metamaterial cloaking, based on transformation optics, describes the process of shielding something from view by controlling electromagnetic radiation. Objects in the defined location are still present, but incident waves are guided around them without being affected by the object itself.

A metamaterial absorber is a type of metamaterial intended to efficiently absorb electromagnetic radiation such as light. Furthermore, metamaterials are an advance in materials science. Hence, those metamaterials that are designed to be absorbers offer benefits over conventional absorbers such as further miniaturization, wider adaptability, and increased effectiveness. Intended applications for the metamaterial absorber include emitters, photodetectors, sensors, spatial light modulators, infrared camouflage, wireless communication, and use in solar photovoltaics and thermophotovoltaics.

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<span class="mw-page-title-main">Theories of cloaking</span>

Theories of cloaking discusses various theories based on science and research, for producing an electromagnetic cloaking device. Theories presented employ transformation optics, event cloaking, dipolar scattering cancellation, tunneling light transmittance, sensors and active sources, and acoustic cloaking.

<span class="mw-page-title-main">Transformation optics</span> Branch of optics which studies how EM radiation can be manipulated with metamaterials

Transformation optics is a branch of optics which applies metamaterials to produce spatial variations, derived from coordinate transformations, which can direct chosen bandwidths of electromagnetic radiation. This can allow for the construction of new composite artificial devices, which probably could not exist without metamaterials and coordinate transformation. Computing power that became available in the late 1990s enables prescribed quantitative values for the permittivity and permeability, the constitutive parameters, which produce localized spatial variations. The aggregate value of all the constitutive parameters produces an effective value, which yields the intended or desired results.

A plasmonic metamaterial is a metamaterial that uses surface plasmons to achieve optical properties not seen in nature. Plasmons are produced from the interaction of light with metal-dielectric materials. Under specific conditions, the incident light couples with the surface plasmons to create self-sustaining, propagating electromagnetic waves known as surface plasmon polaritons (SPPs). Once launched, the SPPs ripple along the metal-dielectric interface. Compared with the incident light, the SPPs can be much shorter in wavelength.

Artificial dielectrics are fabricated composite materials, often consisting of arrays of conductive shapes or particles in a nonconductive support matrix, designed to have specific electromagnetic properties similar to dielectrics. As long as the lattice spacing is smaller than a wavelength, these substances can refract and diffract electromagnetic waves, and are used to make lenses, diffraction gratings, mirrors, and polarizers for microwaves. These were first conceptualized, constructed and deployed for interaction in the microwave frequency range in the 1940s and 1950s. The constructed medium, the artificial dielectric, has an effective permittivity and effective permeability, as intended.

Illusion optics is an electromagnetic theory that can change the optical appearance of an object to be exactly like that of another virtual object, i.e. an illusion, such as turning the look of an apple into that of a banana. Invisibility is a special case of illusion optics, which turns objects into illusions of free space. The concept and numerical proof of illusion optics was proposed in 2009 based on transformation optics in the field of metamaterials. It is a scientific disproof of the idiom 'Seeing is Believing'.

References

  1. 1 2 3 Stephens (1998) p. 479
  2. ↑ Gantz, Jeffrey (1987). The Mabinogion. New York: Penguin. p.  80. ISBN   978-0-14-044322-6.
  3. ↑ Opie, Iona; Opie, Peter (1992) [1974]. The Classic Fairy Tales. Oxford University Press. pp.  47–50. ISBN   978-0-19-211559-1.
  4. ↑ Eberts, Ray E.; Eberts, Cindelyn G. (1995). The myths of Japanese quality . Prentice-Hall. p.  135. ISBN   9780131808034.
  5. 1 2 Gregorson Campbell, John (2004) [1900], Tatar, Maria (ed.), The Annotated Brothers Grimm, JW. W. Norton & Company, p. 332, ISBN   978-0-393-05848-2
  6. ↑ Jacob & Wilheim Grimm. "The King of the Gold Mountain". Household Tales.
  7. 1 2 Grimm, Jacob (1883). "XVII. Wights and Elves". Teutonic mythology. Vol. 2. James Steven Stallybrass (tr.). W. Swan Sonnenschein & Allen. p. 462.
  8. ↑ Müllenhoff (1874) ed., Laurin, v. 485
  9. ↑ Ettmüller (1829) ed., Kunech Laurin, v. 39 and note, p. 63
  10. ↑ von der Hagen (1807) ed., Der Nibelungen Lied ms. B 1735, 2614
  11. ↑ Ettmüller (1829) ed.,
  12. ↑ John Schwartz (October 20, 2006). "Scientists Take Step Toward Invisibility". The New York Times .
  13. ↑ Peter N. Spotts (2006-10-20). "Disappear into thin air? Scientists take step toward invisibility". The Christian Science Monitor . Retrieved 2007-05-05.
  14. ↑ Sean Markey (2006-10-19). "First Invisibility Cloak Tested Successfully, Scientists Say". National Geographic News. Archived from the original on October 22, 2006. Retrieved 2007-05-05.
  15. ↑ Robert F. Service & Adrian Cho (17 December 2010). "Strange New Tricks With Light". Science. 330 (6011): 1622. Bibcode:2010Sci...330.1622S. doi:10.1126/science.330.6011.1622. PMID   21163994.
  16. ↑ "Invisibility Cloak Demonstrated!". Computing News. 2006. Retrieved 2007-05-05.
  17. ↑ Yarris, Lynn (May 1, 2009). "Blurring the Line Between Magic and Science: Berkeley Researchers Create an "Invisibility Cloak"". Lawrence Berkeley National Laboratory . Retrieved 2011-03-23.
  18. ↑ Valentine, Jason; Li, Jensen; Zentgraf, Thomas; Bartal, Guy; Zhang, Xiang (2009). "An optical cloak made of dielectrics" (PDF). Nature Materials. 8 (7): 568–71. arXiv: 0904.3602 . Bibcode:2009NatMa...8..568V. doi:10.1038/nmat2461. PMID   19404237. S2CID   118454430. Archived from the original (PDF) on 2011-10-07. Retrieved 2011-03-23.
  19. ↑ Chen, Xianzhong; Luo, Yu; Zhang, Jingjing; Jiang, Kyle; Pendry, John B.; Zhang, Shuang (2011). "Macroscopic invisibility cloaking of visible light". Nature Communications. 2 (2): 176. arXiv: 1012.2783 . Bibcode:2011NatCo...2..176C. doi:10.1038/ncomms1176. PMC   3105339 . PMID   21285954.
  20. ↑ Zhang, Baile; Luo, Yuan; Liu, Xiaogang; Barbastathis, George (2011). "Macroscopic Invisibility Cloak for Visible Light". Physical Review Letters. 106 (3): 033901. arXiv: 1012.2238 . Bibcode:2011PhRvL.106c3901Z. doi:10.1103/PhysRevLett.106.033901. PMID   21405275. S2CID   13851653.
  21. ↑ "Scientists Develop New Invisibility Cloak Technology". redOrbit. April 30, 2009.
  22. ↑ Miller, David A. B. (2006). "On perfect cloaking". Optics Express. 14 (25): 12457–12466. Bibcode:2006OExpr..1412457M. doi: 10.1364/OE.14.012457 . PMID   19529679.

Bibliography

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