Human vestigiality

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https://en.wikipedia.org/wiki/Human_vestigiality 

 

The muscles connected to the ears of a human do not develop enough to have the same mobility allowed to monkeys. Arrows show the vestigial structure called Darwin's tubercle.

In the context of human evolution, human vestigiality involves those traits (such as organs or behaviors) occurring in humans that have lost all or most of their original function through evolution. Although structures called vestigial often appear functionless, a vestigial structure may retain lesser functions or develop minor new ones. In some cases, structures once identified as vestigial simply had an unrecognized function. Vestigial organs are sometimes called rudimentary organs.

The examples of human vestigiality are numerous, including the anatomical (such as the human tailbone, wisdom teeth, and inside corner of the eye), the behavioral (goose bumps and palmar grasp reflex), and molecular (pseudogenes). Many human characteristics are also vestigial in other primates and related animals.

History

Charles Darwin listed a number of putative human vestigial features, which he termed rudimentary, in The Descent of Man (1871). These included the muscles of the ear; wisdom teeth; the appendix; the tail bone; body hair; and the semilunar fold in the corner of the eye. Darwin also commented on the sporadic nature of many vestigial features, particularly musculature. Making reference to the work of the anatomist William Turner, Darwin highlighted a number of sporadic muscles which he identified as vestigial remnants of the panniculus carnosus, particularly the sternalis muscle.

In 1893, Robert Wiedersheim published The Structure of Man, a book on human anatomy and its relevance to man's evolutionary history. This book contained a list of 86 human organs that he considered vestigial, or as Wiedersheim himself explained: "Organs having become wholly or in part functionless, some appearing in the Embryo alone, others present during Life constantly or inconstantly. For the greater part Organs which may be rightly termed Vestigial." His list of supposedly vestigial organs included many of the examples on this page as well as others then mistakenly believed to be purely vestigial, such as the pineal gland, the thymus gland, and the pituitary gland. Some of these organs that had lost their obvious, original functions later turned out to have retained functions that had gone unrecognized before the discovery of hormones or many of the functions and tissues of the immune system. Examples included:

• the role of the pineal in the regulation of the circadian rhythm (neither the function nor even the existence of melatonin was yet known);
• discovery of the role of the thymus in the immune system lay many decades in the future; it remained a mystery organ until after the mid-20th century;
• the pituitary and hypothalamus with their many and varied hormones were far from understood, let alone the complexity of their interrelationships.

Historically, there was a trend not only to dismiss the vermiform appendix as being uselessly vestigial, but an anatomical hazard, a liability to dangerous inflammation. As late as the mid-20th century, many reputable authorities conceded it no beneficial function. This was a view supported, or perhaps inspired, by Darwin himself in the 1874 edition of his book The Descent of Man, and Selection in Relation to Sex. The organ's patent liability to appendicitis and its poorly understood role left the appendix open to blame for a number of possibly unrelated conditions. For example, in 1916, a surgeon claimed that removal of the appendix had cured several cases of trifacial neuralgia and other nerve pain about the head and face, even though he stated that the evidence for appendicitis in those patients was inconclusive. The discovery of hormones and hormonal principles, notably by Bayliss and Starling, argued against these views, but in the early twentieth century, there remained a great deal of fundamental research to be done on the functions of large parts of the digestive tract. In 1916, an author found it necessary to argue against the idea that the colon had no important function and that "the ultimate disappearance of the appendix is a coordinate action and not necessarily associated with such frequent inflammations as we are witnessing in the human".

There had been a long history of doubt about such dismissive views. Around 1920, the prominent surgeon Kenelm Hutchinson Digby documented previous observations, going back more than thirty years, that suggested lymphatic tissues, such as the tonsils and appendix, may have substantial immunological functions.

Anatomical

Appendix

Ileum, caecum and colon of rabbit, showing Appendix vermiformis on fully functional caecum

 

The human vermiform appendix on the vestigial caecum

In modern humans, the appendix is sometimes believed to be a vestige of a redundant organ that in ancestral species had digestive functions, much as it still does in extant species in which intestinal flora hydrolyze cellulose and similar indigestible plant materials. This view has changed over the past decades, with research suggesting that the appendix may serve an important purpose. In particular, it may serve as a reservoir for beneficial gut bacteria.

Some herbivorous animals, such as rabbits, have a terminal vermiform appendix and cecum that apparently bear patches of tissue with immune functions and may also be important in maintaining the composition of intestinal flora. It does not however seem to have much digestive function, if any, and is not present in all herbivores, even those with large caeca. As shown in the accompanying pictures however, the human appendix typically is about comparable to that of the rabbit's in size, though the caecum is reduced to a single bulge where the ileum empties into the colon. Some carnivorous animals may have appendices too, but seldom have more than vestigial caeca. In line with the possibility of vestigial organs developing new functions, some research suggests that the appendix may guard against the loss of symbiotic bacteria that aid in digestion, though that is unlikely to be a novel function, given the presence of vermiform appendices in many herbivores. Intestinal bacterial populations entrenched in the appendix may support quick re-establishment of the flora of the large intestine after an illness, poisoning, or after an antibiotic treatment depletes or otherwise causes harmful changes to the bacterial population of the colon.

A 2013 study, however, refutes the idea of an inverse relationship between cecum size and appendix size and presence. It is widely present in euarchontoglires (a superorder of mammals that includes rodents, lagomorphs and primates) and has also evolved independently in the diprotodont marsupials, monotremes, and is highly diverse in size and shape which could suggest it is not vestigial. Researchers deduce that the appendix has the ability to protect good bacteria in the gut. That way, when the gut is affected by a bout of diarrhea or other illness that cleans out the intestines, the good bacteria in the appendix can repopulate the digestive system and keep the person healthy.

Coccyx

The coccyx, or tailbone, is the remnant of a lost tail. All mammals have a tail at some point in their development; in humans, it is present for a period of 4 weeks, during stages 14 to 22 of human embryogenesis. This tail is most prominent in human embryos 31–35 days old. The tailbone, located at the end of the spine, has lost its original function in assisting balance and mobility, though it still serves some secondary functions, such as being an attachment point for muscles, which explains why it has not degraded further. The coccyx serves as an attachment site for tendons, ligaments, and muscles. It also functions as an insertion point of some of the muscles of the pelvic floor. In rare cases, congenital defect results in a short tail-like structure being present at birth. Twenty-three cases of human babies born with such a structure have been reported in the medical literature since 1884. In rare cases such as these, the spine and skull were determined to be entirely normal. The only abnormality was that of a tail approximately twelve centimeters long. These tails, though of no deleterious effect, were almost always surgically removed.

Wisdom teeth

Wisdom teeth are vestigial third molars that human ancestors used to help in grinding down plant tissue. The common postulation is that the skulls of human ancestors had larger jaws with more teeth, which were possibly used to help chew down foliage to compensate for a lack of ability to efficiently digest the cellulose that makes up a plant cell wall. As human diets changed, smaller jaws were naturally selected, yet the third molars, or "wisdom teeth", still commonly develop in human mouths. In modern human populations, wisdom teeth have become useless and often present harmful complications to the extent that surgical procedures are frequently performed to remove them.

Agenesis (failure to develop) of wisdom teeth in human populations ranges from zero in Tasmanian Aboriginals to nearly 100% in indigenous Mexicans. The difference is related to the PAX9 gene (and perhaps other genes).

Vomeronasal organ

In some animals, the vomeronasal organ (VNO) is part of a second, completely separate sense of smell, known as the accessory olfactory system. Many studies have been performed to find if there is an actual presence of a VNO in adult human beings. Trotier et al. estimated that around 92% of their subjects who had not had septal surgery had at least one intact VNO. Kjaer and Fisher Hansen, on the other hand, stated that the VNO structure disappeared during fetal development as it does for some primates. However, Smith and Bhatnagar (2000) asserted that Kjaer and Fisher Hansen simply missed the structure in older fetuses. Won (2000) found evidence of a VNO in 13 of his 22 cadavers (59.1%) and in 22 of his 78 living patients (28.2%). Given these findings, some scientists have argued that there is a VNO in adult human beings. However, most investigators have sought to identify the opening of the vomeronasal organ in humans, rather than identify the tubular epithelial structure itself. Thus it has been argued that such studies, employing macroscopic observational methods, have sometimes missed or even misidentified the vomeronasal organ.

Among studies that use microanatomical methods, there is no reported evidence that human beings have active sensory neurons like those in working vomeronasal systems of other animals. Furthermore, there is no evidence to date that suggests there are nerve and axon connections between any existing sensory receptor cells that may be in the adult human VNO and the brain. Likewise, there is no evidence for any accessory olfactory bulb in adult human beings, and the key genes involved in VNO function in other mammals have become pseudogenes in human beings. Therefore, while the presence of a structure in adult human beings is debated, a review of the scientific literature by Tristram Wyatt concluded, "most in the field ... are sceptical about the likelihood of a functional VNO in adult human beings on current evidence."

Ear

Top: Muscles of the human ear.
Bottom: The non-vestigial auricular muscle in the donkey can help it to move its ears like antennae.

The ears of a macaque monkey and most other monkeys have far more developed muscles than those of humans, and therefore have the capability to move their ears to better hear potential threats. Humans and other primates such as the orangutan and chimpanzee however have ear muscles that are minimally developed and non-functional, yet still large enough to be identifiable. A muscle attached to the ear that cannot move the ear, for whatever reason, can no longer be said to have any biological function. In humans there is variability in these muscles, such that some people are able to move their ears in various directions, and it can be possible for others to gain such movement by repeated trials. In such primates, the inability to move the ear is compensated mainly by the ability to turn the head on a horizontal plane, an ability which is not common to most monkeys—a function once provided by one structure is now replaced by another.

The outer structure of the ear also shows some vestigial features, such as the node or point on the helix of the ear known as Darwin's tubercle which is found in around 10% of the population.

Eye

The plica semilunaris is a small fold of tissue on the inside corner of the eye. It is the vestigial remnant of the nictitating membrane, i.e., third eyelid, an organ that is fully functional in some other species of mammals. Its associated muscles are also vestigial. Only one species of primate, the Calabar angwantibo, is known to have a functioning nictitating membrane.

The orbitalis muscle is a vestigial or rudimentary nonstriated muscle (smooth muscle) of the eye that crosses from the infraorbital groove and sphenomaxillary fissure and is intimately united with the periosteum of the orbit. It was described by Johannes Peter Müller and is often called Müller's muscle. The muscle forms an important part of the lateral orbital wall in some animals, but in humans it is not known to have any significant function.

Reproductive system

Main article: List of homologues of the human reproductive system

Genitalia

In the internal genitalia of each human sex, there are some residual organs of mesonephric and paramesonephric ducts during embryonic development:

• Gartner's duct
• Epoophoron
• Vesicular appendages of epoophoron
• Paroophoron

Human vestigial structures also include leftover embryological remnants that once served a function during development, such as the belly button, and analogous structures between biological sexes. For example, men are also born with two nipples, which are not known to serve a function compared to women. In regards to genitourinary development, both internal and external genitalia of male and female fetuses have the ability to fully or partially form their analogous phenotype of the opposite biological sex if exposed to a lack/overabundance of androgens or the SRY gene during fetal development. Examples of vestigial remnants of genitourinary development include the hymen, which is a membrane that surrounds or partially covers the external vaginal opening that derives from the sinus tubercle during fetal development and is homologous to the male seminal colliculus. Some researchers have hypothesized that the persistence of the hymen may be to provide temporary protection from infection, as it separates the vaginal lumen from the urogenital sinus cavity during development. Other examples include the glans penis and the clitoris, the labia minora and the ventral penis, and the ovarian follicles and the seminiferous tubules.

In modern times, there is controversy regarding whether the foreskin is a vital or vestigial structure. In 1949, British physician Douglas Gairdner noted that the foreskin plays an important protective role in newborns. He wrote, "It is often stated that the prepuce is a vestigial structure devoid of function ... However, it seems to be no accident that during the years when the child is incontinent the glans is completely clothed by the prepuce, for, deprived of this protection, the glans becomes susceptible to injury from contact with sodden clothes or napkin." During the physical act of sex, the foreskin reduces friction, which can reduce the need for additional sources of lubrication. "Some medical researchers, however, claim circumcised men enjoy sex just fine and that, in view of recent research on HIV transmission, the foreskin causes more trouble than it's worth." The area of the outer foreskin measures between 7 and 100 cm², and the inner foreskin measures between 18 and 68 cm², which is a wide range. Regarding vestigial structures, Charles Darwin wrote, "An organ, when rendered useless, may well be variable, for its variations cannot be checked by natural selection." Charles Darwin speculated that the sensitivity of the foreskin to fine touch might have served as an "early warning system" in our naked ancestors while it protected the glans from the intrusion of biting insects and parasites.

Musculature

A number of muscles in the human body are thought to be vestigial, either by virtue of being greatly reduced in size compared to homologous muscles in other species, by having become principally tendonous, or by being highly variable in their frequency within or between populations.

Head

The occipitalis minor is a muscle in the back of the head which normally joins to the auricular muscles of the ear. This muscle is very sporadic in frequency—always present in Malays, present in 56% of Africans, 50% of Japanese, and 36% of Europeans, and nonexistent in the Khoikhoi people of southwestern Africa and in Melanesians. Other small muscles in the head associated with the occipital region and the post-auricular muscle complex are often variable in their frequency.

The platysma, a quadrangular (four sides) muscle in a sheet-like configuration, is a vestigial remnant of the panniculous carnosus of animals. In horses, it is the muscle that allows it to flick a fly off its back.

Face

In many lower animals, the upper lip and sinus area is associated with whiskers or vibrissae which serve a sensory function. In humans, these whiskers do not exist but there are still sporadic cases where elements of the associated vibrissal capsular muscles or sinus hair muscles can be found. Based on histological studies of the upper lips of 20 cadavers, Tamatsu et al. found that structures resembling such muscles were present in 35% (7/20) of their specimens.

Arm

The palmaris longus muscle is seen as a small tendon between the flexor carpi radialis and the flexor carpi ulnaris, although it is not always present. The muscle is absent in about 14% of the population, however this varies greatly with ethnicity. It is believed that this muscle actively participated in the arboreal locomotion of primates, but currently has no function, because it does not provide more grip strength. One study has shown the prevalence of palmaris longus agenesis in 500 Indian patients to be 17.2% (8% bilateral and 9.2% unilateral). The palmaris is a popular source of tendon material for grafts and this has prompted studies which have shown the absence of the palmaris does not have any appreciable effect on grip strength.

The levator claviculae muscle in the posterior triangle of the neck is a supernumerary muscle present in only 2–3% of all people but nearly always present in most mammalian species, including gibbons and orangutans.

Torso

The pyramidalis muscle of the abdomen is a small and triangular muscle, anterior to the rectus abdominis, and contained in the rectus sheath. It is absent in 20% of humans and when absent, the lower end of the rectus then becomes proportionately increased in size. Anatomical studies suggest that the forces generated by the pyramidalis muscles are relatively small.

The latissimus dorsi muscle of the back has several sporadic variations. One particular variant is the existence of the dorsoepitrochlearis or latissimocondyloideus muscle which is a muscle passing from the tendon of the latissimus dorsi to the long head of the triceps brachii. It is notable due to its well developed character in other apes and monkeys, where it is an important climbing muscle, namely the dorsoepitrochlearis brachii. This muscle is found in ≈5% of humans.

Leg

The plantaris muscle is composed of a thin muscle belly and a long thin tendon. The muscle belly is approximately 5–10 centimetres (2–4 inches) long, and is absent in 7–10% of the human population. It has some weak functionality in moving the knee and ankle but is generally considered redundant and is often used as a source of tendon for grafts. The long, thin tendon of the plantaris is humorously called "the freshman's nerve", as it is often mistaken for a nerve by new medical students.

Tongue

Another example of human vestigiality occurs in the tongue, specifically the chondroglossus muscle. In a morphological study of 100 Japanese cadavers, it was found that 86% of fibers identified were solid and bundled in the appropriate way to facilitate speech and mastication. The other 14% of fibers were short, thin and sparse – nearly useless, and thus concluded to be of vestigial origin.

Breasts

Extra nipples or breasts sometimes appear along the mammary lines of humans, appearing as a remnant of mammalian ancestors who possessed more than two nipples or breasts. One recent report demonstrated that all healthy young men and women who participated in an anatomic study of the front surface of the body exhibited 8 pairs of focal fat mounds running along the embryological mammary ridges from axillae to the upper inner thighs. These were always located in the same relative anatomic sites – analogous to the loci of breasts in other placental mammals – and often had nipple-like moles or extra hairs located atop the mounds. Therefore, focal fatty prominences on the fronts of human torsos likely represent chains of vestigial breasts composed of primordial breast fat.

Behavioral

See also: Vestigial response § In humans

Humans also bear some vestigial behaviors and reflexes.

Goose bumps

Goose bumps are an example of a vestigial human reaction to stress.

The formation of goose bumps in humans under stress is a vestigial reflex; a possible function in the distant evolutionary ancestors of humanity was to raise the body's hair, making the ancestor appear larger and scaring off predators. Raising the hair is also used to trap an extra layer of air, keeping an animal warm. Due to the diminished amount of hair in humans, the reflex formation of goose bumps when cold is also vestigial.

Palmar grasp reflex

The palmar grasp reflex is thought to be a vestigial behavior in human infants. When placing a finger or object to the palm of an infant, it will securely grasp it. This grasp is found to be rather strong. Some infants—37% according to a 1932 study—are able to support their own weight from a rod, although there is no way they can cling to their mother. The grasp is also evident in the feet too. When a baby is sitting down, its prehensile feet assume a curled-in posture, similar to that observed in an adult chimp. An ancestral primate would have had sufficient body hair to which an infant could cling, unlike modern humans, thus allowing its mother to escape from danger, such as climbing up a tree in the presence of a predator without having to occupy her hands holding her baby.

Hiccup

It has been proposed that the hiccup is an evolutionary remnant of earlier amphibian respiration. Amphibians such as tadpoles gulp air and water across their gills via a rather simple motor reflex akin to mammalian hiccuping. The motor pathways that enable hiccuping form early during fetal development, before the motor pathways that enable normal lung ventilation form. Thus, according to recapitulation theory, the hiccup is evolutionarily antecedent to modern lung respiration. Additionally, they point out that hiccups and amphibian gulping are inhibited by elevated CO₂ and may be stopped by GABA_B receptor agonists, illustrating a possible shared physiology and evolutionary heritage. These proposals may explain why premature infants spend 2.5% of their time hiccuping, possibly gulping like amphibians, as their lungs are not yet fully formed. Fetal intrauterine hiccups are of two types. The physiological type occurs before 28 weeks after conception and tend to last five to ten minutes. These hiccups are part of fetal development and are associated with the myelination of the phrenic nerve, which primarily controls the thoracic diaphragm. The phylogeny hypothesis explains how the hiccup reflex might have evolved, and if there is not an explanation, it may explain hiccups as an evolutionary remnant, held-over from our amphibious ancestors. This hypothesis has been questioned because of the existence of the afferent loop of the reflex, the fact that it does not explain the reason for glottic closure, and because the very short contraction of the hiccup is unlikely to have a significant strengthening effect on the slow-twitch muscles of respiration.

Molecular

Further information: Pseudogene

There are also vestigial molecular structures in humans, which are no longer in use but may indicate common ancestry with other species. One example of this is L-gulonolactone oxidase, a gene that is functional in most other mammals and produces an enzyme that synthesizes vitamin C. In humans and other members of the suborder Haplorrhini, a mutation disabled the gene and made it unable to produce the enzyme. However, the remains of the gene are still present in the human genome as a vestigial genetic sequence called a pseudogene.

Tradition

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Tradition 

Olin Levi Warner, Tradition (1895). Bronze tympanum over the main entrance, Library of Congress, Thomas Jefferson Building, Washington, D.C.

A tradition is a belief or behavior (folk custom) passed down within a group or society with symbolic meaning or special significance with origins in the past. A component of cultural expressions and folklore, common examples include holidays or impractical but socially meaningful clothes (like lawyers' wigs or military officers' spurs), but the idea has also been applied to social norms such as greetings. Traditions can persist and evolve for thousands of years—the word tradition itself derives from the Latin tradere literally meaning to transmit, to hand over, to give for safekeeping. While it is commonly assumed that traditions have an ancient history, many traditions have been invented on purpose, whether that be political or cultural, over short periods of time. Various academic disciplines also use the word in a variety of ways.

The phrase "according to tradition", or "by tradition", usually means that whatever information follows is known only by oral tradition, but is not supported (and perhaps may be refuted) by physical documentation, by a physical artifact, or other quality evidence. Tradition is used to indicate the quality of a piece of information being discussed. For example, "According to tradition, Homer was born on Chios, but many other locales have historically claimed him as theirs." This tradition may never be proven or disproven. In another example, "King Arthur, by tradition a true British king, has inspired many well loved stories." Whether they are documented fact or not does not decrease their value as cultural history and literature.

Traditions are a subject of study in several academic fields, especially in social sciences such as folklore studies, anthropology, archaeology, and biology.

The concept of tradition, as the notion of holding on to a previous time, is also found in political and philosophical discourse. For example, it is the basis of the political concept of traditionalism, and also strands of many world religions including traditional Catholicism. In artistic contexts, tradition is used to decide the correct display of an art form. For example, in the performance of traditional genres (such as traditional dance), adherence to guidelines dictating how an art form should be composed are given greater importance than the performer's own preferences. A number of factors can exacerbate the loss of tradition, including industrialization, globalization, and the assimilation or marginalization of specific cultural groups. In response to this, tradition-preservation attempts have now been started in many countries around the world, focusing on aspects such as traditional languages. Tradition is usually contrasted with the goal of modernity and should be differentiated from customs, conventions, laws, norms, routines, rules and similar concepts.

Definition

Textual traditions of bound manuscripts of the Sefer Torah (Torah scroll) are passed down providing additional vowel points, pronunciation marks and stress accents in the authentic Masoretic Text of the Jewish Bible, often the basis for translations of the Christian Old Testament

The English word tradition comes from the Latin traditio via French, the noun from the verb tradere (to transmit, to hand over, to give for safekeeping); it was originally used in Roman law to refer to the concept of legal transfers and inheritance. According to Anthony Giddens and others, the modern meaning of tradition evolved during the Enlightenment period, in opposition to modernity and progress.

As with many other generic terms, there are many definitions of tradition. The concept includes a number of interrelated ideas; the unifying one is that tradition refers to beliefs, objects or customs performed or believed in the past, originating in it, transmitted through time by being taught by one generation to the next, and are performed or believed in the present.

Tradition can also refer to beliefs or customs that are Prehistoric, with lost or arcane origins, existing from time immemorial. Originally, traditions were passed orally, without the need for a writing system. Tools to aid this process include poetic devices such as rhyme and alliteration. The stories thus preserved are also referred to as tradition, or as part of an oral tradition. Even such traditions, however, are presumed to have originated (been "invented" by humans) at some point. Traditions are often presumed to be ancient, unalterable, and deeply important, though they may sometimes be much less "natural" than is presumed. It is presumed that at least two transmissions over three generations are required for a practice, belief or object to be seen as traditional. Some traditions were deliberately invented for one reason or another, often to highlight or enhance the importance of a certain institution. Traditions may also be adapted to suit the needs of the day, and the changes can become accepted as a part of the ancient tradition. Tradition changes slowly, with changes from one generation to the next being seen as significant. Thus, those carrying out the traditions will not be consciously aware of the change, and even if a tradition undergoes major changes over many generations, it will be seen as unchanged.

There are various origins and fields of tradition; they can refer to:

1. the forms of artistic heritage of a particular culture.
2. beliefs or customs instituted and maintained by societies and governments, such as national anthems and national holidays, such as Federal holidays in the United States.
3. beliefs or customs maintained by religious denominations and Church bodies that share history, customs, culture, and, to some extent, body of teachings. For example, one can speak of Islam's tradition or Christianity's tradition.

Many objects, beliefs and customs can be traditional. Rituals of social interaction can be traditional, with phrases and gestures such as saying "thank you", sending birth announcements, greeting cards, etc. Tradition can also refer to larger concepts practiced by groups (family traditions at Christmas), organizations (company's picnic) or societies, such as the practice of national and public holidays. Some of the oldest traditions include monotheism (three millennia) and citizenship (two millennia). It can also include material objects, such as buildings, works of art or tools.

Tradition is often used as an adjective, in contexts such as traditional music, traditional medicine, traditional values and others. In such constructions tradition refers to specific values and materials particular to the discussed context, passed through generations.

Invention of tradition

Main article: Invented tradition

The term "invention of tradition", introduced by E. J. Hobsbawm, refers to situations when a new practice or object is introduced in a manner that implies a connection with the past that is not necessarily present. For example, the Panhellenic Games were a tradition in Ancient Greece where only Greek men from Greece and Greek colonies could compete. A tradition may be deliberately created and promulgated for personal, commercial, political, or national self-interest, as was done in colonial Africa; or it may be adopted rapidly based on a single highly publicized event, rather than developing and spreading organically in a population, as in the case of the white wedding dress, which only became popular after Queen Victoria wore a white gown at her wedding to Albert of Saxe-Coburg.

An example of an invention of tradition is the rebuilding of the Palace of Westminster (location of the British Parliament) in the Gothic style. Similarly, most of the traditions associated with monarchy of the United Kingdom, seen as rooted deep in history, actually date to 19th century. Other examples include the invention of tradition in Africa and other colonial holdings by the occupying forces. Requiring legitimacy, the colonial power would often invent a "tradition" which they could use to legitimize their own position. For example, a certain succession to a chiefdom might be recognized by a colonial power as traditional in order to favour their own candidates for the job. Often these inventions were based in some form of tradition, but were exaggerated, distorted, or biased toward a particular interpretation.

Invented traditions are a central component of modern national cultures, providing a commonality of experience and promoting the unified national identity espoused by nationalism. Common examples include public holidays (particularly those unique to a particular nation), the singing of national anthems, and traditional national cuisine (see national dish). Expatriate and immigrant communities may continue to practice the national traditions of their home nation.

In scholarly discourse

In science, tradition is often used in the literature in order to define the relationship of an author's thoughts to that of his or her field. In 1948, philosopher of science Karl Popper suggested that there should be a "rational theory of tradition" applied to science which was fundamentally sociological. For Popper, each scientist who embarks on a certain research trend inherits the tradition of the scientists before them as he or she inherits their studies and any conclusions that superseded it. Unlike myth, which is a means of explaining the natural world through means other than logical criticism, scientific tradition was inherited from Socrates, who proposed critical discussion, according to Popper. For Thomas Kuhn, who presented his thoughts in a paper presented in 1977, a sense of such a critical inheritance of tradition is, historically, what sets apart the best scientists who change their fields is an embracement of tradition.

Traditions are a subject of study in several academic fields in social sciences—chiefly anthropology, archaeology, and biology—with somewhat different meanings in different fields. It is also used in varying contexts in other fields, such as history, psychology and sociology. Social scientists and others have worked to refine the commonsense concept of tradition to make it into a useful concept for scholarly analysis. In the 1970s and 1980s, Edward Shils explored the concept in detail. Since then, a wide variety of social scientists have criticized traditional ideas about tradition; meanwhile, "tradition" has come into usage in biology as applied to nonhuman animals.

Tradition as a concept variously defined in different disciplines should not be confused with various traditions (perspectives, approaches) in those disciplines.

Anthropology

Tradition is one of the key concepts in anthropology; it can be said that anthropology is the study of "tradition in traditional societies". There is however no "theory of tradition", as for most anthropologists the need to discuss what tradition is seems unnecessary, as defining tradition is both unnecessary (everyone can be expected to know what it is) and unimportant (as small differences in definition would be just technical). There are however dissenting views; scholars such as Pascal Boyer argue that defining tradition and developing theories about it are important to the discipline.

Archaeology

In archaeology, the term tradition is a set of cultures or industries which appear to develop on from one another over a period of time. The term is especially common in the study of American archaeology.

Biology

Biologists, when examining groups of non-humans, have observed repeated behaviors which are taught within communities from one generation to the next. Tradition is defined in biology as "a behavioral practice that is relatively enduring (i.e., is performed repeatedly over a period of time), that is shared among two or more members of a group, that depends in part on socially aided learning for its generation in new practitioners", and has been called a precursor to "culture" in the anthropological sense.

Behavioral traditions have been observed in groups of fish, birds, and mammals. Groups of orangutans and chimpanzees, in particular, may display large numbers of behavioral traditions, and in chimpanzees, transfer of traditional behavior from one group to another (not just within a group) has been observed. Such behavioral traditions may have evolutionary significance, allowing adaptation at a faster rate than genetic change.

Musicology and ethnomusicology

In the field of musicology and ethnomusicology tradition refers to the belief systems, repertoire, techniques, style and culture that is passed down through subsequent generations. Tradition in music suggests a historical context with which one can perceive distinguishable patterns. Along with a sense of history, traditions have a fluidity that cause them to evolve and adapt over time. While both musicology and ethnomusicology are defined by being 'the scholarly study of music' they differ in their methodology and subject of research. 'Tradition, or traditions, can be presented as a context in which to study the work of a specific composer or as a part of a wide-ranging historical perspective.'

Sociology

The concept of tradition, in early sociological research (around the turn of the 19th and 20th century), referred to that of the traditional society, as contrasted by the more modern industrial society. This approach was most notably portrayed in Max Weber's concepts of traditional authority and modern rational-legal authority. In more modern works, One hundred years later, sociology sees tradition as a social construct used to contrast past with the present and as a form of rationality used to justify certain course of action.

Traditional society is characterized by lack of distinction between family and business, division of labor influenced primarily by age, gender, and status, high position of custom in the system of values, self-sufficiency, preference to saving and accumulation of capital instead of productive investment, relative autarky. Early theories positing the simple, unilineal evolution of societies from traditional to industrial model are now seen as too simplistic.

In 1981 Edward Shils in his book Tradition put forward a definition of tradition that became universally accepted. According to Shils, tradition is anything which is transmitted or handed down from the past to the present.

Another important sociological aspect of tradition is the one that relates to rationality. It is also related to the works of Max Weber (see theories of rationality), and were popularized and redefined in 1992 by Raymond Boudon in his book Action. In this context tradition refers to the mode of thinking and action justified as "it has always been that way". This line of reasoning forms the basis of the logical flaw of the appeal to tradition (or argumentum ad antiquitatem), which takes the form "this is right because we've always done it this way." In most cases such an appeal can be refuted on the grounds that the "tradition" being advocated may no longer be desirable, or, indeed, may never have been despite its previous popularity.

Philosophy

Further information: Tradition (perennialism)

The idea of tradition is important in philosophy. Twentieth century philosophy is often divided between an 'analytic' tradition, dominant in Anglophone and Scandinavian countries, and a 'continental' tradition, dominant in German and Romance speaking Europe. Increasingly central to continental philosophy is the project of deconstructing what its proponents, following Martin Heidegger, call 'the tradition', which began with Plato and Aristotle. In contrast, some continental philosophers - most notably, Hans-Georg Gadamer - have attempted to rehabilitate the tradition of Aristotelianism. This move has been replicated within analytic philosophy by Alasdair MacIntyre. However, MacIntyre has himself deconstructed the idea of 'the tradition', instead posing Aristotelianism as one philosophical tradition in rivalry with others.

In political and religious discourse

Main articles: Traditional values and Traditionalist conservatism

The concepts of tradition and traditional values are frequently used in political and religious discourse to establish the legitimacy of a particular set of values. In the United States in the twentieth and twenty-first centuries, the concept of tradition has been used to argue for the centrality and legitimacy of conservative religious values. Similarly, strands of orthodox theological thought from a number of world religions openly identify themselves as wanting a return to tradition. For example, the term "traditionalist Catholic" refers to those, such as Archbishop Lefebvre, who want the worship and practices of the Church to be as they were before the Second Vatican Council of 1962–65. Likewise, Sunni Muslims are referred to as Ahl el-Sunnah wa Al-Jamā‘ah (Arabic: أهل السنة والجماعة), literally "people of the tradition [of Muhammad] and the community", emphasizing their attachment to religious and cultural tradition.

More generally, tradition has been used as a way of determining the political spectrum, with right-wing parties having a stronger affinity to certain ways of the past than left-wing ones. Here, the concept of adherence tradition is embodied by the political philosophy of traditionalist conservatism (or simply traditionalism), which emphasizes the need for the principles of natural law and transcendent moral order, hierarchy and organic unity, agrarianism, classicism and high culture, and the intersecting spheres of loyalty. Traditionalists would therefore reject the notions of individualism, liberalism, modernity, and social progress, but promote cultural and educational renewal, and revive interest in the Church, the family, the State and local community. This view has been criticised for including in its notion of tradition practices which are no longer considered to be desirable, for example, stereotypical views of the place of women in domestic affairs.

In other societies, especially ones experiencing rapid social change, the idea of what is "traditional" may be widely contested, with different groups striving to establish their own values as the legitimate traditional ones. Defining and enacting traditions in some cases can be a means of building unity between subgroups in a diverse society; in other cases, tradition is a means of othering and keeping groups distinct from one another.

In artistic discourse

Holiday celebrations may be passed down as traditions, as is the case with this distinctly Polish Christmas meal, decor with Christmas tree, a tradition since the late eighteenth and early nineteenth century

In artistic contexts, in the performance of traditional genres (such as traditional dance), adherence to traditional guidelines is of greater importance than performer's preferences. It is often the unchanging form of certain arts that leads to their perception as traditional. For artistic endeavors, tradition has been used as a contrast to creativity, with traditional and folk art associated with unoriginal imitation or repetition, in contrast to fine art, which is valued for being original and unique. More recent philosophy of art, however, considers interaction with tradition as integral to the development of new artistic expression.

Relationship to other concepts

In the social sciences, tradition is often contrasted with modernity, particularly in terms of whole societies. This dichotomy is generally associated with a linear model of social change, in which societies progress from being traditional to being modern. Tradition-oriented societies have been characterized as valuing filial piety, harmony and group welfare, stability, and interdependence, while a society exhibiting modernity would value "individualism (with free will and choice), mobility, and progress." Another author discussing tradition in relationship to modernity, Anthony Giddens, sees tradition as something bound to ritual, where ritual guarantees the continuation of tradition. Gusfield and others, though, criticize this dichotomy as oversimplified, arguing that tradition is dynamic, heterogeneous, and coexists successfully with modernity even within individuals.

Tradition should be differentiated from customs, conventions, laws, norms, routines, rules and similar concepts. Whereas tradition is supposed to be invariable, they are seen as more flexible and subject to innovation and change. Whereas justification for tradition is ideological, the justification for other similar concepts is more practical or technical. Over time, customs, routines, conventions, rules and such can evolve into traditions, but that usually requires that they stop having (primarily) a practical purpose. For example, wigs worn by lawyers were at first common and fashionable; spurs worn by military officials were at first practical but now are both impractical and traditional.

Preservation

Woman welcoming the Shabbat, a more than 3300-year-old tradition.

The legal protection of tradition includes a number of international agreements and national laws. In addition to the fundamental protection of cultural property, there is also cooperation between the United Nations, UNESCO and Blue Shield International in the protection or recording of traditions and customs. The protection of culture and traditions is becoming increasingly important nationally and internationally.

In many countries, concerted attempts are being made to preserve traditions that are at risk of being lost. A number of factors can exacerbate the loss of tradition, including industrialization, globalization, and the assimilation or marginalization of specific cultural groups. Customary celebrations and lifestyles are among the traditions that are sought to be preserved. Likewise, the concept of tradition has been used to defend the preservation and reintroduction of minority languages such as Cornish under the auspices of the European Charter for Regional or Minority Languages. Specifically, the charter holds that these languages "contribute to the maintenance and development of Europe's cultural wealth and traditions". The Charter goes on to call for "the use or adoption... of traditional and correct forms of place-names in regional or minority languages". Similarly, UNESCO includes both "oral tradition" and "traditional manifestations" in its definition of a country's cultural properties and heritage. It therefore works to preserve tradition in countries such as Brazil.

In Japan, certain artworks, structures, craft techniques and performing arts are considered by the Japanese government to be a precious legacy of the Japanese people, and are protected under the Japanese Law for the Protection of Cultural Properties. This law also identifies people skilled at traditional arts as "National Living Treasures", and encourages the preservation of their craft.

For native peoples like the Māori in New Zealand, there is conflict between the fluid identity assumed as part of modern society and the traditional identity with the obligations that accompany it; the loss of language heightens the feeling of isolation and damages the ability to perpetuate tradition.

Traditional cultural expressions

The phrase "traditional cultural expressions" is used by the World Intellectual Property Organization to refer to "any form of artistic and literary expression in which traditional culture and knowledge are embodied. They are transmitted from one generation to the next, and include handmade textiles, paintings, stories, legends, ceremonies, music, songs, rhythms and dance."

Soliton

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Soliton 

Solitary wave in a laboratory wave channel

In mathematics and physics, a soliton or solitary wave is a self-reinforcing wave packet that maintains its shape while it propagates at a constant velocity. Solitons are caused by a cancellation of nonlinear and dispersive effects in the medium. (Dispersive effects are a property of certain systems where the speed of a wave depends on its frequency.) Solitons are the solutions of a widespread class of weakly nonlinear dispersive partial differential equations describing physical systems.

The soliton phenomenon was first described in 1834 by John Scott Russell (1808–1882) who observed a solitary wave in the Union Canal in Scotland. He reproduced the phenomenon in a wave tank and named it the "Wave of Translation".

Definition

A single, consensus definition of a soliton is difficult to find. Drazin & Johnson (1989, p. 15) ascribe three properties to solitons:

1. They are of permanent form;
2. They are localized within a region;
3. They can interact with other solitons, and emerge from the collision unchanged, except for a phase shift.

More formal definitions exist, but they require substantial mathematics. Moreover, some scientists use the term soliton for phenomena that do not quite have these three properties (for instance, the 'light bullets' of nonlinear optics are often called solitons despite losing energy during interaction).

Explanation

A hyperbolic secant (sech) envelope soliton for water waves: The blue line is the carrier signal, while the red line is the envelope soliton.

Dispersion and nonlinearity can interact to produce permanent and localized wave forms. Consider a pulse of light traveling in glass. This pulse can be thought of as consisting of light of several different frequencies. Since glass shows dispersion, these different frequencies travel at different speeds and the shape of the pulse therefore changes over time. However, also the nonlinear Kerr effect occurs; the refractive index of a material at a given frequency depends on the light's amplitude or strength. If the pulse has just the right shape, the Kerr effect exactly cancels the dispersion effect and the pulse's shape does not change over time. Thus, the pulse is a soliton. See soliton (optics) for a more detailed description.

Many exactly solvable models have soliton solutions, including the Korteweg–de Vries equation, the nonlinear Schrödinger equation, the coupled nonlinear Schrödinger equation, and the sine-Gordon equation. The soliton solutions are typically obtained by means of the inverse scattering transform, and owe their stability to the integrability of the field equations. The mathematical theory of these equations is a broad and very active field of mathematical research.

Some types of tidal bore, a wave phenomenon of a few rivers including the River Severn, are 'undular': a wavefront followed by a train of solitons. Other solitons occur as the undersea internal waves, initiated by seabed topography, that propagate on the oceanic pycnocline. Atmospheric solitons also exist, such as the morning glory cloud of the Gulf of Carpentaria, where pressure solitons traveling in a temperature inversion layer produce vast linear roll clouds. The recent and not widely accepted soliton model in neuroscience proposes to explain the signal conduction within neurons as pressure solitons.

A topological soliton, also called a topological defect, is any solution of a set of partial differential equations that is stable against decay to the "trivial solution". Soliton stability is due to topological constraints, rather than integrability of the field equations. The constraints arise almost always because the differential equations must obey a set of boundary conditions, and the boundary has a nontrivial homotopy group, preserved by the differential equations. Thus, the differential equation solutions can be classified into homotopy classes.

No continuous transformation maps a solution in one homotopy class to another. The solutions are truly distinct, and maintain their integrity, even in the face of extremely powerful forces. Examples of topological solitons include the screw dislocation in a crystalline lattice, the Dirac string and the magnetic monopole in electromagnetism, the Skyrmion and the Wess–Zumino–Witten model in quantum field theory, the magnetic skyrmion in condensed matter physics, and cosmic strings and domain walls in cosmology.

History

A plaque marking the workshop of John Scott Russell at 8 Stafford Street in Edinburgh.

In 1834, John Scott Russell describes his wave of translation. The discovery is described here in Scott Russell's own words:

I was observing the motion of a boat which was rapidly drawn along a narrow channel by a pair of horses, when the boat suddenly stopped – not so the mass of water in the channel which it had put in motion; it accumulated round the prow of the vessel in a state of violent agitation, then suddenly leaving it behind, rolled forward with great velocity, assuming the form of a large solitary elevation, a rounded, smooth and well-defined heap of water, which continued its course along the channel apparently without change of form or diminution of speed. I followed it on horseback, and overtook it still rolling on at a rate of some eight or nine miles an hour, preserving its original figure some thirty feet long and a foot to a foot and a half in height. Its height gradually diminished, and after a chase of one or two miles I lost it in the windings of the channel. Such, in the month of August 1834, was my first chance interview with that singular and beautiful phenomenon which I have called the Wave of Translation.

Scott Russell spent some time making practical and theoretical investigations of these waves. He built wave tanks at his home and noticed some key properties:

• The waves are stable, and can travel over very large distances (normal waves would tend to either flatten out, or steepen and topple over)
• The speed depends on the size of the wave, and its width on the depth of water.
• Unlike normal waves they will never merge – so a small wave is overtaken by a large one, rather than the two combining.
• If a wave is too big for the depth of water, it splits into two, one big and one small.

Scott Russell's experimental work seemed at odds with Isaac Newton's and Daniel Bernoulli's theories of hydrodynamics. George Biddell Airy and George Gabriel Stokes had difficulty accepting Scott Russell's experimental observations because they could not be explained by the existing water wave theories. Their contemporaries spent some time attempting to extend the theory but it would take until the 1870s before Joseph Boussinesq and Lord Rayleigh published a theoretical treatment and solutions. In 1895 Diederik Korteweg and Gustav de Vries provided what is now known as the Korteweg–de Vries equation, including solitary wave and periodic cnoidal wave solutions.

An animation of the overtaking of two solitary waves according to the Benjamin–Bona–Mahony equation – or BBM equation, a model equation for (among others) long surface gravity waves. The wave heights of the solitary waves are 1.2 and 0.6, respectively, and their velocities are 1.4 and 1.2.

The upper graph is for a frame of reference moving with the average velocity of the solitary waves.

The lower graph (with a different vertical scale and in a stationary frame of reference) shows the oscillatory tail produced by the interaction. Thus, the solitary wave solutions of the BBM equation are not solitons.

In 1965 Norman Zabusky of Bell Labs and Martin Kruskal of Princeton University first demonstrated soliton behavior in media subject to the Korteweg–de Vries equation (KdV equation) in a computational investigation using a finite difference approach. They also showed how this behavior explained the puzzling earlier work of Fermi, Pasta, Ulam, and Tsingou.

In 1967, Gardner, Greene, Kruskal and Miura discovered an inverse scattering transform enabling analytical solution of the KdV equation. The work of Peter Lax on Lax pairs and the Lax equation has since extended this to solution of many related soliton-generating systems.

Note that solitons are, by definition, unaltered in shape and speed by a collision with other solitons. So solitary waves on a water surface are near-solitons, but not exactly – after the interaction of two (colliding or overtaking) solitary waves, they have changed a bit in amplitude and an oscillatory residual is left behind.

Solitons are also studied in quantum mechanics, thanks to the fact that they could provide a new foundation of it through de Broglie's unfinished program, known as "Double solution theory" or "Nonlinear wave mechanics". This theory, developed by de Broglie in 1927 and revived in the 1950s, is the natural continuation of his ideas developed between 1923 and 1926, which extended the wave-particle duality introduced by Albert Einstein for the light quanta, to all the particles of matter. In 2019, researchers from Tel-Aviv university measured an accelerating surface gravity water wave soliton by using an external hydrodynamic linear potential. They also managed to excite ballistic solitons and measure their corresponding phases.

In fiber optics

See also: Soliton (optics)

Much experimentation has been done using solitons in fiber optics applications. Solitons in a fiber optic system are described by the Manakov equations. Solitons' inherent stability make long-distance transmission possible without the use of repeaters, and could potentially double transmission capacity as well.

Year	Discovery
1973	Akira Hasegawa of AT&T Bell Labs was the first to suggest that solitons could exist in optical fibers, due to a balance between self-phase modulation and anomalous dispersion. Also in 1973 Robin Bullough made the first mathematical report of the existence of optical solitons. He also proposed the idea of a soliton-based transmission system to increase performance of optical telecommunications.
1987	Emplit et al. (1987) – from the Universities of Brussels and Limoges – made the first experimental observation of the propagation of a dark soliton, in an optical fiber.
1988	Linn F. Mollenauer and his team transmitted soliton pulses over 4,000 kilometers using a phenomenon called the Raman effect, named after Sir C. V. Raman who first described it in the 1920s, to provide optical gain in the fiber.
1991	A Bell Labs research team transmitted solitons error-free at 2.5 gigabits per second over more than 14,000 kilometers, using erbium optical fiber amplifiers (spliced-in segments of optical fiber containing the rare earth element erbium). Pump lasers, coupled to the optical amplifiers, activate the erbium, which energizes the light pulses.
1998	Thierry Georges and his team at France Telecom R&D Center, combining optical solitons of different wavelengths (wavelength-division multiplexing), demonstrated a composite data transmission of 1 terabit per second (1,000,000,000,000 units of information per second), not to be confused with Terabit-Ethernet. The above impressive experiments have not translated to actual commercial soliton system deployments however, in either terrestrial or submarine systems, chiefly due to the Gordon–Haus (GH) jitter. The GH jitter requires sophisticated, expensive compensatory solutions that ultimately makes dense wavelength-division multiplexing (DWDM) soliton transmission in the field unattractive, compared to the conventional non-return-to-zero/return-to-zero paradigm. Further, the likely future adoption of the more spectrally efficient phase-shift-keyed/QAM formats makes soliton transmission even less viable, due to the Gordon–Mollenauer effect. Consequently, the long-haul fiberoptic transmission soliton has remained a laboratory curiosity.
2000	Steven Cundiff predicted the existence of a vector soliton in a birefringence fiber cavity passively mode locking through a semiconductor saturable absorber mirror (SESAM). The polarization state of such a vector soliton could either be rotating or locked depending on the cavity parameters.
2008	D. Y. Tang et al. observed a novel form of higher-order vector soliton from the perspectives of experiments and numerical simulations. Different types of vector solitons and the polarization state of vector solitons have been investigated by his group.

In biology

Solitons may occur in proteins and DNA. Solitons are related to the low-frequency collective motion in proteins and DNA.

A recently developed model in neuroscience proposes that signals, in the form of density waves, are conducted within neurons in the form of solitons. Solitons can be described as almost lossless energy transfer in biomolecular chains or lattices as wave-like propagations of coupled conformational and electronic disturbances.

In material physics

Solitons can occur in materials, such as ferroelectrics, in the form of domain walls. Ferroelectric materials exhibit spontaneous polarization, or electric dipoles, which are coupled to configurations of the material structure. Domains of oppositely poled polarizations can be present within a single material as the structural configurations corresponding to opposing polarizations are equally favorable with no presence of external forces. The domain boundaries, or “walls”, that separate these local structural configurations are regions of lattice dislocations. The domain walls can propagate as the polarizations, and thus, the local structural configurations can switch within a domain with applied forces such as electric bias or mechanical stress. Consequently, the domain walls can be described as solitons, discrete regions of dislocations that are able to slip or propagate and maintain their shape in width and length. 

In recent literature, ferroelectricity has been observed in twisted bilayers of van der Waal materials such as MoS₂ and graphene. The moiré superlattice that arises from the relative twist angle between the van der Waal monolayers generates regions of different stacking orders of the atoms within the layers. These regions exhibit inversion symmetry breaking structural configurations that enable ferroelectricity at the interface of these monolayers. The domain walls that separate these regions are composed of partial dislocations where different types of stresses, and thus, strains are experienced by the lattice. It has been observed that soliton or domain wall propagation across a moderate length of the sample (order of nanometers to micrometers) can be initiated with applied stress from an AFM tip on a fixed region. The soliton propagation carries the mechanical perturbation with little loss in energy across the material, which enables domain switching in a domino-like fashion.

It has also been observed that the type of dislocations found at the walls can affect propagation parameters such as direction. For instance, STM measurements showed four types of strains of varying degrees of shear, compression, and tension at domain walls depending on the type of localized stacking order in twisted bilayer graphene. Different slip directions of the walls are achieved with different types of strains found at the domains, influencing the direction of the soliton network propagation.

Nonidealities such as disruptions to the soliton network and surface impurities can influence soliton propagation as well. Domain walls can meet at nodes and get effectively pinned, forming triangular domains, which have been readily observed in various ferroelectric twisted bilayer systems. In addition, closed loops of domain walls enclosing multiple polarization domains can inhibit soliton propagation and thus, switching of polarizations across it. Also, domain walls can propagate and meet at wrinkles and surface inhomogeneities within the van der Waal layers, which can act as obstacles obstructing the propagation.

In magnets

In magnets, there also exist different types of solitons and other nonlinear waves. These magnetic solitons are an exact solution of classical nonlinear differential equations — magnetic equations, e.g. the Landau–Lifshitz equation, continuum Heisenberg model, Ishimori equation, nonlinear Schrödinger equation and others.

In nuclear physics

Atomic nuclei may exhibit solitonic behavior. Here the whole nuclear wave function is predicted to exist as a soliton under certain conditions of temperature and energy. Such conditions are suggested to exist in the cores of some stars in which the nuclei would not react but pass through each other unchanged, retaining their soliton waves through a collision between nuclei.

The Skyrme Model is a model of nuclei in which each nucleus is considered to be a topologically stable soliton solution of a field theory with conserved baryon number.

Bions

The bound state of two solitons is known as a bion, or in systems where the bound state periodically oscillates, a breather. The interference-type forces between solitons could be used in making bions. However, these forces are very sensitive to their relative phases. Alternatively, the bound state of solitons could be formed by dressing atoms with highly excited Rydberg levels. The resulting self-generated potential profile features an inner attractive soft-core supporting the 3D self-trapped soliton, an intermediate repulsive shell (barrier) preventing solitons’ fusion, and an outer attractive layer (well) used for completing the bound state resulting in giant stable soliton molecules. In this scheme, the distance and size of the individual solitons in the molecule can be controlled dynamically with the laser adjustment.

In field theory bion usually refers to the solution of the Born–Infeld model. The name appears to have been coined by G. W. Gibbons in order to distinguish this solution from the conventional soliton, understood as a regular, finite-energy (and usually stable) solution of a differential equation describing some physical system. The word regular means a smooth solution carrying no sources at all. However, the solution of the Born–Infeld model still carries a source in the form of a Dirac-delta function at the origin. As a consequence it displays a singularity in this point (although the electric field is everywhere regular). In some physical contexts (for instance string theory) this feature can be important, which motivated the introduction of a special name for this class of solitons.

On the other hand, when gravity is added (i.e. when considering the coupling of the Born–Infeld model to general relativity) the corresponding solution is called EBIon, where "E" stands for Einstein.

Alcubierre drive

Erik Lentz, a physicist at the University of Göttingen, has theorized that solitons could allow for the generation of Alcubierre warp bubbles in spacetime without the need for exotic matter, i.e., matter with negative mass.