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Friday, August 15, 2014

Homosexuality

Homosexuality

From Wikipedia, the free encyclopedia
 
Homosexuality (from Ancient Greek ὁμός, meaning "same", and Latin sexus, meaning "sex") is romantic attraction, sexual attraction or sexual behavior between members of the same sex or gender. As a sexual orientation, homosexuality is "an enduring pattern of emotional, romantic, and/or sexual attractions" primarily or exclusively to people of the same sex. It "also refers to a person's sense of identity based on those attractions, related behaviors, and membership in a community of others who share those attractions."[1][2]

Along with bisexuality and heterosexuality, homosexuality is one of the three main categories of sexual orientation within the heterosexual–homosexual continuum.[1] There is no consensus among scientists about why a person develops a particular sexual orientation;[1] however, biologically-based theories for the cause of sexual orientation are favored by experts,[3] which point to genetic factors, the early uterine environment, or both in combination.[4] There is no substantive evidence which suggests parenting or early childhood experiences play a role when it comes to sexual orientation;[4] when it comes to same-sex sexual behavior, shared or familial environment plays no role for men and minor role for women.[5] While some hold the view that homosexual activity is unnatural,[6][7] research has shown that homosexuality is an example of a normal and natural variation in human sexuality and is not in and of itself a source of negative psychological effects.[1][8] Most people experience little or no sense of choice about their sexual orientation.[1] There is insufficient evidence to support the use of psychological interventions to change sexual orientation.[9]
The most common terms for homosexual people are lesbian for females and gay for males, though gay is also used to refer generally to both homosexual males and females. The number of people who identify as gay or lesbian and the proportion of people who have same-sex sexual experiences are difficult for researchers to estimate reliably for a variety of reasons, including many gay people not openly identifying as such due to homophobia and heterosexist discrimination.[10] Homosexual behavior has also been documented and is observed in many non-human animal species.[11][12][13][14][15]

Many gay and lesbian people are in committed same-sex relationships, though only recently have census forms and political conditions facilitated their visibility and enumeration.[16][17][18][19][20][21][22][23][24] These relationships are equivalent to heterosexual relationships in essential psychological respects.[2] Homosexual relationships and acts have been admired, as well as condemned, throughout recorded history, depending on the form they took and the culture in which they occurred.[25] Since the end of the 19th century, there has been a global movement towards increased visibility, recognition, and legal rights for homosexual people, including the rights to marriage and civil unions, adoption and parenting, employment, military service, equal access to health care, and the introduction of anti-bullying legislation to protect gay minors.

Etymology

 

The word homosexual is a Greek and Latin hybrid, with the first element derived from Greek ὁμός homos, "same"(not related to the Latin homo, "man", as in Homo sapiens), thus connoting sexual acts and affections between members of the same sex, including lesbianism.[26][27] The first known appearance of homosexual in print is found in an 1869 German pamphlet by the Austrian-born novelist Karl-Maria Kertbeny, published anonymously,[28] arguing against a Prussian anti-sodomy law.[28][29] In 1886, Richard von Krafft-Ebing used the terms homosexual and heterosexual in his book Psychopathia Sexualis. Krafft-Ebing's book was so popular among both laymen and doctors that the terms "heterosexual" and "homosexual" became the most widely accepted terms for sexual orientation.[30][31] As such, the current use of the term has its roots in the broader 19th-century tradition of personality taxonomy.

Many modern style guides in the U.S. recommend against using homosexual as a noun, instead using gay man or lesbian.[32] Similarly, some recommend completely avoiding usage of homosexual as it has a negative, clinical history and because the word only refers to one's sexual behavior (as opposed to romantic feelings) and thus it has a negative connotation.[32] Gay and lesbian are the most common alternatives. The first letters are frequently combined to create the initialism LGBT (sometimes written as GLBT), in which B and T refer to bisexual and transgender people.

Gay generally refers to male homosexuality,[citation needed] but may be used in a broader sense to refer to all LGBT people. In the context of sexuality, lesbian refers only to female homosexuality. The word "lesbian" is derived from the name of the Greek island Lesbos, where the poet Sappho wrote largely about her emotional relationships with young women.[33][34]

Although early writers also used the adjective homosexual to refer to any single-sex context (such as an all-girls school), today the term is used exclusively in reference to sexual attraction, activity, and orientation. The term homosocial is now used to describe single-sex contexts that are not specifically sexual. There is also a word referring to same-sex love, homophilia.

Some synonyms for same-sex attraction or sexual activity include men who have sex with men or MSM (used in the medical community when specifically discussing sexual activity) and homoerotic (referring to works of art).[35][36] Pejorative terms in English include queer, faggot, fairy, poof, and homo.[37][38][39][40] Beginning in the 1990s, some of these have been reclaimed as positive words by gay men and lesbians, as in the usage of queer studies, queer theory, and even the popular American television program Queer Eye for the Straight Guy.[41] The word homo occurs in many other languages without the pejorative connotations it has in English.[42] As with ethnic slurs and racial slurs, however, the misuse of these terms can still be highly offensive; the range of acceptable use depends on the context and speaker.[43] Conversely, gay, a word originally embraced by homosexual men and women as a positive, affirmative term (as in gay liberation and gay rights),[44] has come into widespread pejorative use among young people.[45]

History

Societal attitudes towards same-sex relationships have varied over time and place, from expecting all males to engage in same-sex relationships, to casual integration, through acceptance, to seeing the practice as a minor sin, repressing it through law enforcement and judicial mechanisms, and to proscribing it under penalty of death.

In a detailed compilation of historical and ethnographic materials of Preindustrial Cultures, "strong disapproval of homosexuality was reported for 41% of 42 cultures; it was accepted or ignored by 21%, and 12% reported no such concept. Of 70 ethnographies, 59% reported homosexuality absent or rare in frequency and 41% reported it present or not uncommon."[46]

In cultures influenced by Abrahamic religions, the law and the church established sodomy as a transgression against divine law or a crime against nature. The condemnation of anal sex between males, however, predates Christian belief. It was frequent in ancient Greece; "unnatural" can be traced back to Plato.[47]

Many historical figures, including Socrates, Lord Byron, Edward II, and Hadrian,[48] have had terms such as gay or bisexual applied to them; some scholars, such as Michel Foucault, have regarded this as risking the anachronistic introduction of a contemporary construction of sexuality foreign to their times,[49] though others challenge this.[50]

In social science, there has been a dispute between "essentialist" and "constructionist" views of homosexuality. The debate divides those who believe that terms such as "gay" and "straight" refer to objective, culturally invariant properties of persons from those who believe that the experiences they name are artifacts of unique cultural and social processes. "Essentialists" typically believe that sexual preferences are determined by biological forces, while "constructionists" assume that sexual desires are learned.[51] The social constructionist approach, which is influenced by Foucault, has been criticized for being based on a selective reading of the historical record, and for confusing the fact that homosexual people exist with the fact that society labels such people and treats them in distinctive ways.[52]

Africa

The first record of possible homosexual couple in history is commonly regarded as Khnumhotep and Niankhkhnum, an ancient Egyptian male couple, who lived around 2400 BCE. The pair are portrayed in a nose-kissing position, the most intimate pose in Egyptian art, surrounded by what appear to be their heirs. Anthropologists Stephen Murray and Will Roscoe reported that women in Lesotho engaged in socially sanctioned "long term, erotic relationships" called motsoalle.[53] E. E. Evans-Pritchard also recorded that male Azande warriors in the northern Congo routinely took on young male lovers between the ages of twelve and twenty, who helped with household tasks and participated in intercrural sex with their older husbands.[54]

Americas

Dance to the Berdache
Sac and Fox Nation ceremonial dance to celebrate the two-spirit person. George Catlin (1796–1872); Smithsonian Institution, Washington, DC

Among indigenous peoples of the Americas prior to European colonization, a common form of same-sex sexuality centered around the figure of the Two-Spirit individual. Typically this individual was recognized early in life, given a choice by the parents to follow the path and, if the child accepted the role, raised in the appropriate manner, learning the customs of the gender it had chosen. Two-Spirit individuals were commonly shamans and were revered as having powers beyond those of ordinary shamans. Their sexual life was with the ordinary tribe members of the same sex.

Homosexual and transgender individuals were also common among other pre-conquest civilizations in Latin America, such as the Aztecs, Mayans, Quechuas, Moches, Zapotecs, and the Tupinambá of Brazil.[55][56]

The Spanish conquerors were horrified to discover sodomy openly practiced among native peoples, and attempted to crush it out by subjecting the berdaches (as the Spanish called them) under their rule to severe penalties, including public execution, burning and being torn to pieces by dogs.[57]

East Asia

A woman spying on a pair of male lovers. China, Qing Dynasty.

In East Asia, same-sex love has been referred to since the earliest recorded history.

Homosexuality in China, known as the passions of the cut peach and various other euphemisms has been recorded since approximately 600 BCE. Homosexuality was mentioned in many famous works of Chinese literature. The instances of same-sex affection and sexual interactions described in the classical novel Dream of the Red Chamber seem as familiar to observers in the present as do equivalent stories of romances between heterosexual people during the same period. Confucianism, being primarily a social and political philosophy, focused little on sexuality, whether homosexual or heterosexual. Ming Dynasty literature, such as Bian Er Chai (弁而釵/弁而钗), portray homosexual relationships between men as more enjoyable and more "harmonious" than heterosexual relationships.[58] Writings from the Liu Song Dynasty by Wang Shunu claimed that homosexuality was as common as heterosexuality in the late 3rd century.[59]

Opposition to homosexuality in China originates in the medieval Tang Dynasty (618–907), attributed to the rising influence of Christian and Islamic values,[60] but did not become fully established until the Westernization efforts of the late Qing Dynasty and the Republic of China.[61]

South Asia

The Laws of Manu, the foundational work of Hindu law, mentions a "third sex", members of which may engage in nontraditional gender expression and homosexual activities.[62]

Europe

Classical period

The earliest Western documents (in the form of literary works, art objects, and mythographic materials) concerning same-sex relationships are derived from ancient Greece.

In regard to male homosexuality such documents depict a world in which relationships with women and relationships with youths were the essential foundation of a normal man's love life. Same-sex relationships were a social institution variously constructed over time and from one city to another. The formal practice, an erotic yet often restrained relationship between a free adult male and a free adolescent, was valued for its pedagogic benefits and as a means of population control, though occasionally blamed for causing disorder. Plato praised its benefits in his early writings[63] but in his late works proposed its prohibition.[64] Aristotle, in the Politics, dismissed Plato's ideas about abolishing homosexuality (2.4); he explains that barbarians like the Celts accorded it a special honor (2.6.6), while the Cretans used it to regulate the population (2.7.5).[65]
Female youths are depicted surrounding Sappho in this painting of Lafond "Sappho sings for Homer", 1824.

Little is known of female homosexuality in antiquity. Sappho, born on the island of Lesbos, was included by later Greeks in the canonical list of nine lyric poets. The adjectives deriving from her name and place of birth (Sapphic and Lesbian) came to be applied to female homosexuality beginning in the 19th century.[66][67] Sappho's poetry centers on passion and love for various personages and both genders. The narrators of many of her poems speak of infatuations and love (sometimes requited, sometimes not) for various females, but descriptions of physical acts between women are few and subject to debate.[68][69]
Sappho reading to her companions on an Attic vase of c. 435 BC.

In Ancient Rome the young male body remained a focus of male sexual attention, but relationships were between older free men and slaves or freed youths who took the receptive role in sex. All the emperors with the exception of Claudius took male lovers. The Hellenophile emperor Hadrian is renowned for his relationship with Antinous, but the Christian emperor Theodosius I decreed a law on 6 August 390, condemning passive males to be burned at the stake. Justinian, towards the end of his reign, expanded the proscription to the active partner as well (in 558), warning that such conduct can lead to the destruction of cities through the "wrath of God". Notwithstanding these regulations, taxes on brothels of boys available for homosexual sex continued to be collected until the end of the reign of Anastasius I in 518.

Renaissance

During the Renaissance, wealthy cities in northern ItalyFlorence and Venice in particular — were renowned for their widespread practice of same-sex love, engaged in by a considerable part of the male population and constructed along the classical pattern of Greece and Rome.[70][71] But even as many of the male population were engaging in same-sex relationships, the authorities, under the aegis of the Officers of the Night court, were prosecuting, fining, and imprisoning a good portion of that population.

From the second half of the 13th century, death was the punishment for male homosexuality in most of Europe.[72] The eclipse of this period of relative artistic and erotic freedom was precipitated by the rise to power of the moralizing monk Girolamo Savonarola. In northern Europe the artistic discourse on sodomy was turned against its proponents by artists such as Rembrandt, who in his Rape of Ganymede no longer depicted Ganymede as a willing youth, but as a squalling baby attacked by a rapacious bird of prey.

The relationships of socially prominent figures, such as King James I and the Duke of Buckingham, served to highlight the issue, including in anonymously authored street pamphlets: "The world is chang'd I know not how, For men Kiss Men, not Women now;...Of J. the First and Buckingham: He, true it is, his Wives Embraces fled, To slabber his lov'd Ganimede" (Mundus Foppensis, or The Fop Display'd, 1691).

Modern period

Love Letters Between a Certain Late Nobleman and the Famous Mr. Wilson was published in 1723 in England and was presumed by some modern scholars to be a novel. The 1749 edition of John Cleland's popular novel Fanny Hill includes a homosexual scene, but this was removed in its 1750 edition. Also in 1749, the earliest extended and serious defense of homosexuality in English, Ancient and Modern Pederasty Investigated and Exemplified, written by Thomas Cannon, was published, but was suppressed almost immediately. It includes the passage, "Unnatural Desire is a Contradiction in Terms; downright Nonsense. Desire is an amatory Impulse of the inmost human Parts."[73] Around 1785 Jeremy Bentham wrote another defense, but this was not published until 1978.[74] Executions for sodomy continued in the Netherlands until 1803, and in England until 1835.

Between 1864 and 1880 Karl Heinrich Ulrichs published a series of twelve tracts, which he collectively titled Research on the Riddle of Man-Manly Love. In 1867, he became the first self-proclaimed homosexual person to speak out publicly in defense of homosexuality when he pleaded at the Congress of German Jurists in Munich for a resolution urging the repeal of anti-homosexual laws.[10] Sexual Inversion by Havelock Ellis, published in 1896, challenged theories that homosexuality was abnormal, as well as stereotypes, and insisted on the ubiquity of homosexuality and its association with intellectual and artistic achievement.[75]

Although medical texts like these (written partly in Latin to obscure the sexual details) were not widely read by the general public, they did lead to the rise of Magnus Hirschfeld's Scientific-Humanitarian Committee, which campaigned from 1897 to 1933 against anti-sodomy laws in Germany, as well as a much more informal, unpublicized movement among British intellectuals and writers, led by such figures as Edward Carpenter and John Addington Symonds. Beginning in 1894 with Homogenic Love, Socialist activist and poet Edward Carpenter wrote a string of pro-homosexual articles and pamphlets, and "came out" in 1916 in his book My Days and Dreams. In 1900, Elisar von Kupffer published an anthology of homosexual literature from antiquity to his own time, Lieblingminne und Freundesliebe in der Weltliteratur.

Middle East

Further information: LGBT in Islam, LGBT rights in Israel
Shah Abbas I of Persia with a boy. By Muhammad Qasim (1627).[76]

There are a handful of accounts by Arab travelers to Europe during the mid-1800s. Two of these travelers, Rifa'ah al-Tahtawi and Muhammad as-Saffar, show their surprise that the French sometimes deliberately mistranslated love poetry about a young boy, instead referring to a young female, to maintain their social norms and morals.[77]

Israel is considered the most tolerant country in the Middle East and Asia to homosexuals[78] with Tel Aviv being named "the gay capital of the Middle East",[79] and is considered one of the most gay friendly cities in the world.[80] The annual Pride Parade in support of homosexuality takes place in Tel Aviv.[81]

On the other hand, many governments in the Middle East often ignore, deny the existence of, or criminalize homosexuality. Homosexuality is illegal in almost all Muslim countries.[82] Same-sex intercourse officially carries the death penalty in several Muslim nations: Saudi Arabia, Iran, Mauritania, northern Nigeria, Sudan, and Yemen.[83] Iranian President Mahmoud Ahmadinejad, during his 2007 speech at Columbia University, asserted that there were no gay people in Iran.
However, the probable reason is that they keep their sexuality a secret for fear of government sanction or rejection by their families.[84]

Pre-Islamic period

In ancient Assyria, homosexuality was present and common; it was also not prohibited, condemned, nor looked upon as immoral or disordered. Some religious texts contain prayers for divine blessings on homosexual relationships.[85][86] The Almanac of Incantations contained prayers favoring on an equal basis the love of a man for a woman, of a woman for a man, and of a man for man.[87]

In Greater Iran, homosexuality and homoerotic expressions were tolerated in numerous public places, from monasteries and seminaries to taverns, military camps, bathhouses, and coffee houses. In the early Safavid dynasty (1501–1723), male houses of prostitution (amrad khane) were legally recognized and paid taxes.

Some scholars argue that there are examples of homosexual love in ancient literature, like in the Mesopotamian Epic of Gilgamesh as well as in the Biblical story of David and Jonathan. In the Epic of Gilgamesh, the relationship between the main protagonist Gilgamesh and the character Enkidu has been seen by some to be homosexual in nature.[88][89][90][91] Similarly, David's love for Jonathan is "greater than the love of women."[92]

South Pacific

In many societies of Melanesia, especially in Papua New Guinea, same-sex relationships were an integral part of the culture until the middle of the last century. The Etoro and Marind-anim for example, even viewed heterosexuality as sinful and celebrated homosexuality instead. In many traditional Melanesian cultures a prepubertal boy would be paired with an older adolescent who would become his mentor and who would "inseminate" him (orally, anally, or topically, depending on the tribe) over a number of years in order for the younger to also reach puberty. Many Melanesian societies, however, have become hostile towards same-sex relationships since the introduction of Christianity by European missionaries.[93]

Sexuality and identity

Kinsey scale

The Kinsey scale, also called the Heterosexual-Homosexual Rating Scale,[94] attempts to describe a person's sexual history or episodes of his or her sexual activity at a given time. It uses a scale from 0, meaning exclusively heterosexual, to 6, meaning exclusively homosexual. In both the Male and Female volumes of the Kinsey Reports, an additional grade, listed as "X", was used for asexuality.[95][96]

Orientation and behavior

The American Psychological Association, the American Psychiatric Association, and the National Association of Social Workers identify sexual orientation as "not merely a personal characteristic that can be defined in isolation. Rather, one's sexual orientation defines the universe of persons with whom one is likely to find the satisfying and fulfilling relationships":[2]
Sexual orientation is commonly discussed as a characteristic of the individual, like biological sex, gender identity, or age. This perspective is incomplete because sexual orientation is always defined in relational terms and necessarily involves relationships with other individuals. Sexual acts and romantic attractions are categorized as homosexual or heterosexual according to the biological sex of the individuals involved in them, relative to each other. Indeed, it is by acting—or desiring to act—with another person that individuals express their heterosexuality, homosexuality, or bisexuality. This includes actions as simple as holding hands with or kissing another person. Thus, sexual orientation is integrally linked to the intimate personal relationships that human beings form with others to meet their deeply felt needs for love, attachment, and intimacy. In addition to sexual behavior, these bonds encompass nonsexual physical affection between partners, shared goals and values, mutual support, and ongoing commitment.[2]

Coming out of the closet

Jóhanna Sigurðardóttir, the former Prime Minister of Iceland, was the first openly gay head of government in modern times.[97]

Coming out (of the closet) is a phrase referring to one's disclosure of their sexual orientation or gender identity, and is described and experienced variously as a psychological process or journey.[98]
Generally, coming out is described in three phases. The first phase is that of "knowing oneself", and the realization emerges that one is open to same-sex relations.[99] This is often described as an internal coming out. The second phase involves one's decision to come out to others, e.g. family, friends, or colleagues. The third phase more generally involves living openly as an LGBT person.[100] In the United States today, people often come out during high school or college age. At this age, they may not trust or ask for help from others, especially when their orientation is not accepted in society. Sometimes their own families are not even informed.

According to Rosario, Schrimshaw, Hunter, Braun (2006), "the development of a lesbian, gay, or bisexual (LGB) sexual identity is a complex and often difficult process. Unlike members of other minority groups (e.g., ethnic and racial minorities), most LGB individuals are not raised in a community of similar others from whom they learn about their identity and who reinforce and support that identity. Rather, LGB individuals are often raised in communities that are either ignorant of or openly hostile toward homosexuality."[101]

Outing is the practice of publicly revealing the sexual orientation of a closeted person.[102] Notable politicians, celebrities, military service people, and clergy members have been outed, with motives ranging from malice to political or moral beliefs. Many commentators oppose the practice altogether,[103] while some encourage outing public figures who use their positions of influence to harm other gay people.[104]

Gender identity

Early 20th-century writers on a homosexual orientation usually understood it to be intrinsically linked to the subject's own sex. For example, it was thought that a typical female-bodied person who is attracted to female-bodied persons would have masculine attributes, and vice versa.[105] However, this understanding as sexual inversion was disputed at the time, and through the second half of the 20th century, gender identity came to be increasingly seen as a phenomenon distinct from sexual orientation.

Transgender and cisgender people may be attracted to men, women or both, although the prevalence of different sexual orientations is quite different in these two populations (see sexual orientation of transwomen). An individual homosexual, heterosexual or bisexual person may be masculine, feminine, or androgynous, and in addition, many members and supporters of lesbian and gay communities now see the "gender-conforming heterosexual" and the "gender-nonconforming homosexual" as negative stereotypes. However, studies by J. Michael Bailey and K.J. Zucker have found that a majority of gay men and lesbians report being gender-nonconforming during their childhood years.[106]

Same-sex relationships

 
Male homosexuality symbol

People with a homosexual orientation can express their sexuality in a variety of ways, and may or may not express it in their behaviors.[1] Many have sexual relationships predominately with people of their own gender identity, though some have sexual relationships with those of the opposite gender, bisexual relationships, or none at all (celibate).[1] The Kinsey scale attempts to describe a person's sexual history or episodes of their sexual activity at a given time. It uses a scale from 0, meaning exclusively heterosexual, to 6, meaning exclusively homosexual. It is based on actual sexual behavior surveys. Research indicates that many lesbians and gay men want, and succeed in having, committed and durable relationships. For example, survey data indicate that between 40% and 60% of gay men and between 45% and 80% of lesbians are currently involved in a romantic relationship.[107] Survey data also indicate that between 18% and 28% of gay couples and between 8% and 21% of lesbian couples in the U.S. have lived together ten or more years.[107] Studies have found same-sex and opposite-sex couples to be equivalent to each other in measures of satisfaction and commitment in relationships, that age and gender are more reliable than sexual orientation as a predictor of satisfaction and commitment to a relationship, and that people who are heterosexual or homosexual share comparable expectations and ideals with regard to romantic relationships.[108][109][110]

Demographics

 
Jason Collins became the first active male professional athlete in major American professional sports leagues to publicly come out as gay.[111]

Reliable data as to the size of the gay and lesbian population are of value in informing public policy.[112] For example, demographics would help in calculating the costs and benefits of domestic partnership benefits, of the impact of legalizing gay adoption, and of the impact of the U.S. military's Don't Ask Don't Tell policy.[112] Further, knowledge of the size of the "gay and lesbian population holds promise for helping social scientists understand a wide array of important questions—questions about the general nature of labor market choices, accumulation of human capital, specialization within households, discrimination, and decisions about geographic location."[112]

Measuring the prevalence of homosexuality presents difficulties. It is necessary to consider the measuring criteria that is used, the cutoff point and the time span taken to define a sexual orientation.[10] Many people, despite having same-sex attractions, may be reluctant to identify themselves as gay or bisexual. The research must measure some characteristic that may or may not be defining of sexual orientation. The number of people with same-sex desires may be larger than the number of people who act on those desires, which in turn may be larger than the number of people who self-identify as gay, lesbian, or bisexual.[112]

In 1948 and 1953, Alfred Kinsey reported that nearly 46% of the male subjects had "reacted" sexually to persons of both sexes in the course of their adult lives, and 37% had had at least one homosexual experience.[113][114] Kinsey's methodology was criticized by John Tukey for using convenience samples and not random samples.[115][116] A later study tried to eliminate the sample bias, but still reached similar conclusions.[117] LeVay cites these Kinsey results as an example of the caution needed to interpret demographic studies, as they may give quite differing numbers depending on what criteria are used to conduct them, in spite of using sound scientific methods.[10]

According to major studies, 2% to 11% of people have had some form of same-sex sexual contact within their lifetime;[118][119][120][121][122][123][124][125][126][127] this percentage rises to 16–21% when either or both same-sex attraction and/or behavior are reported.[127] In a 2006 study, 20% of respondents anonymously reported some homosexual feelings, although only 2–3% identified themselves as homosexual.[128] A 1992 study reported that 6.1% of males in Britain have had a homosexual experience, while in France the number was reported at 4.1%.[129] According to a 2008 poll, 13% of Britons have had some form of same-sex sexual contact while only 6% of Britons identify themselves as either homosexual or bisexual.[130] In contrast, a survey by the UK Office for National Statistics (ONS) in 2010 found that 95% of Britons identified as heterosexual, 1.5% of Britons identified themselves as homosexual or bisexual, and the last 3.5% gave more vague answers such as "don't know," "other," or did not respond to the question.[114][131]

In the United States, according to a The Williams Institute report in April 2011, only 3.5% or approximately 9 million of the adult population are lesbian, gay, or bisexual.[132][133] According to the 2000 United States Census there were about 601,209 same-sex unmarried partner households.[134]

Psychology

Psychology was one of the first disciplines to study a homosexual orientation as a discrete phenomenon.[citation needed] The first attempts to classify homosexuality as a disease were made by the fledgling European sexologist movement in the late 19th century. In 1886 noted sexologist Richard von Krafft-Ebing listed homosexuality along with 200 other case studies of deviant sexual practices in his definitive work, Psychopathia Sexualis. Krafft-Ebing proposed that homosexuality was caused by either "congenital [during birth] inversion" or an "acquired inversion". In the last two decades of the 19th century, a different view began to predominate in medical and psychiatric circles, judging such behavior as indicative of a type of person with a defined and relatively stable sexual orientation. In the late 19th century and early 20th century, pathological models of homosexuality were standard.
The American Psychological Association, the American Psychiatric Association, and the National Association of Social Workers state:

In 1952, when the American Psychiatric Association published its first Diagnostic and Statistical Manual of Mental Disorders, homosexuality was included as a disorder. Almost immediately, however, that classification began to be subjected to critical scrutiny in research funded by the National Institute of Mental Health. That study and subsequent research consistently failed to produce any empirical or scientific basis for regarding homosexuality as a disorder or abnormality, rather than a normal and healthy sexual orientation. As results from such research accumulated, professionals in medicine, mental health, and the behavioral and social sciences reached the conclusion that it was inaccurate to classify homosexuality as a mental disorder and that the DSM classification reflected untested assumptions based on once-prevalent social norms and clinical impressions from unrepresentative samples comprising patients seeking therapy and individuals whose conduct brought them into the criminal justice system. In recognition of the scientific evidence,[135] the American Psychiatric Association removed homosexuality from the DSM in 1973, stating that "homosexuality per se implies no impairment in judgment, stability, reliability, or general social or vocational capabilities." After thoroughly reviewing the scientific data, the American Psychological Association adopted the same position in 1975, and urged all mental health professionals "to take the lead in removing the stigma of mental illness that has long been associated with homosexual orientations." The National Association of Social Workers has adopted a similar policy.
Thus, mental health professionals and researchers have long recognized that being homosexual poses no inherent obstacle to leading a happy, healthy, and productive life, and that the vast majority of gay and lesbian people function well in the full array of social institutions and interpersonal relationships.[2]
 
[4] The longstanding consensus of research and clinical literature demonstrates that same-sex sexual and romantic attractions, feelings, and behaviors are normal and positive variations of human sexuality.[136] There is now a large body of research evidence that indicates that being gay, lesbian or bisexual is compatible with normal mental health and social adjustment.[4] The World Health Organization's ICD-9 (1977) listed homosexuality as a mental illness; it was removed from the ICD-10, endorsed by the Forty-third World Health Assembly on 17 May 1990.[137][138][139] Like the DSM-II, the ICD-10 added ego-dystonic sexual orientation to the list, which refers to people who want to change their gender identities or sexual orientation because of a psychological or behavioral disorder (F66.1). The Chinese Society of Psychiatry removed homosexuality from its Chinese Classification of Mental Disorders in 2001 after five years of study by the association.[140] According to the Royal College of Psychiatrists "This unfortunate history demonstrates how marginalisation of a group of people who have a particular personality feature (in this case homosexuality) can lead to harmful medical practice and a basis for discrimination in society.[4] There is now a large body of research evidence that indicates that being gay, lesbian or bisexual is compatible with normal mental health and social adjustment. However, the experiences of discrimination in society and possible rejection by friends, families and others, such as employers, means that some LGB people experience a greater than expected prevalence of mental health difficulties and substance misuse problems. Although there have been claims by conservative political groups in the USA that this higher prevalence of mental health difficulties is confirmation that homosexuality is itself a mental disorder, there is no evidence whatever to substantiate such a claim."[141]

Most lesbian, gay, and bisexual people who seek psychotherapy do so for the same reasons as heterosexual people (stress, relationship difficulties, difficulty adjusting to social or work situations, etc.); their sexual orientation may be of primary, incidental, or no importance to their issues and treatment. Whatever the issue, there is a high risk for anti-gay bias in psychotherapy with lesbian, gay, and bisexual clients.[142] Psychological research in this area has been relevant to counteracting prejudicial ("homophobic") attitudes and actions, and to the LGBT rights movement generally.[143]

The appropriate application of affirmative psychotherapy is based on the following scientific facts:[136]
  • Same-sex sexual attractions, behavior, and orientations per se are normal and positive variants of human sexuality; in other words, they are not indicators of mental or developmental disorders.
  • Homosexuality and bisexuality are stigmatized, and this stigma can have a variety of negative consequences (e.g., Minority Stress) throughout the life span (D'Augelli & Patterson, 1995; DiPlacido, 1998; Herek & Garnets, 2007; Meyer, 1995, 2003).
  • Same-sex sexual attractions and behavior can occur in the context of a variety of sexual orientations and sexual orientation identities (Diamond, 2006; Hoburg et al., 2004; Rust, 1996; Savin-Williams, 2005).
  • Gay men, lesbians, and bisexual individuals can live satisfying lives as well as form stable, committed relationships and families that are equivalent to heterosexual relationships in essential respects (APA, 2005c; Kurdek, 2001, 2003, 2004; Peplau & Fingerhut, 2007).
  • There are no empirical studies or peer-reviewed research that support theories attributing same-sex sexual orientation to family dysfunction or trauma (Bell et al., 1981; Bene, 1965; Freund & Blanchard, 1983; Freund & Pinkava, 1961; Hooker, 1969; McCord et al., 1962; D. K. Peters & Cantrell, 1991; Siegelman, 1974, 1981; Townes et al., 1976).

Cause

General

Science has looked at the causes of homosexuality, and more generically the causes of human sexual orientation, with the general conclusions being related to biological and environmental factors. The biological factors that have been researched are genetic and hormonal, particularly during the fetal developmental period, that influence the resulting brain structure, and other characteristics such as handedness.[3][4] There are a wide range of environmental factors (sociological, psychological, or early uterine environment), and various biological factors, that may influence sexual orientation; though many researchers believe that it is caused by a complex interplay between nature and nurture, they favor biological models for the cause.[1][3]

The American Academy of Pediatrics stated in Pediatrics in 2004:

Sexual orientation probably is not determined by any one factor but by a combination of genetic, hormonal, and environmental influences. In recent decades, biologically based theories have been favored by experts. [...] Although there continues to be controversy and uncertainty as to the genesis of the variety of human sexual orientations, there is no scientific evidence that abnormal parenting, sexual abuse, or other adverse life events influence sexual orientation. Current knowledge suggests that sexual orientation is usually established during early childhood.[3][144]
 
The American Psychological Association, American Psychiatric Association, and National Association of Social Workers stated in 2006:

Currently, there is no scientific consensus about the specific factors that cause an individual to become heterosexual, homosexual, or bisexual—including possible biological, psychological, or social effects of the parents' sexual orientation. However, the available evidence indicates that the vast majority of lesbian and gay adults were raised by heterosexual parents and the vast majority of children raised by lesbian and gay parents eventually grow up to be heterosexual.[2]
 
The Royal College of Psychiatrists stated in 2007:

Despite almost a century of psychoanalytic and psychological speculation, there is no substantive evidence to support the suggestion that the nature of parenting or early childhood experiences play any role in the formation of a person's fundamental heterosexual or homosexual orientation. It would appear that sexual orientation is biological in nature, determined by a complex interplay of genetic factors and the early uterine environment. Sexual orientation is therefore not a choice.[4]
 
The American Psychological Association states "there are probably many reasons for a person's sexual orientation and the reasons may be different for different people", and says most people's sexual orientation is determined at an early age.[1] Research into how sexual orientation in males may be determined by genetic or other prenatal factors plays a role in political and social debates about homosexuality, and also raises concerns about genetic profiling and prenatal testing.[145]
Professor Michael King states: "The conclusion reached by scientists who have investigated the origins and stability of sexual orientation is that it is a human characteristic that is formed early in life, and is resistant to change. Scientific evidence on the origins of homosexuality is considered relevant to theological and social debate because it undermines suggestions that sexual orientation is a choice."[146]

Garcia-Falgueras and Swaab state in the abstract of their 2010 study, "The fetal brain develops during the intrauterine period in the male direction through a direct action of testosterone on the developing nerve cells, or in the female direction through the absence of this hormone surge. In this way, our gender identity (the conviction of belonging to the male or female gender) and sexual orientation are programmed or organized into our brain structures when we are still in the womb. There is no indication that social environment after birth has an effect on gender identity or sexual orientation."[147]

Evolutionary perspectives

The authors of a 2008 study stated "there is considerable evidence that human sexual orientation is genetically influenced, so it is not known how homosexuality, which tends to lower reproductive success, is maintained in the population at a relatively high frequency". They hypothesized that "while genes predisposing to homosexuality reduce homosexuals' reproductive success, they may confer some advantage in heterosexuals who carry them". Their results suggested that "genes predisposing to homosexuality may confer a mating advantage in heterosexuals, which could help explain the evolution and maintenance of homosexuality in the population".[148] A 2009 study also suggested a significant increase in fecundity in the females related to the homosexual people from the maternal line (but not in those related from the paternal one).[149]

A review paper by Bailey and Zuk looking into studies of same-sex sexual behaviour in animals challenges the view that such behaviour lowers reproductive success, citing several hypotheses about how same-sex sexual behavior might be adaptive; these hypotheses vary greatly among different species. Bailey and Zuk also suggest future research needs to look into evolutionary consequences of same-sex sexual behaviour, rather than only looking into origins of such behaviour.[150]

Lesbian narratives and sexual orientation awareness

Annise Parker is the openly gay mayor of Houston.[151]

Lesbians often experience their sexuality differently from gay men, and have different understandings about etiology from those derived from studies focused mostly on men. For information specific to female homosexuality, see Lesbian.

In a U.S.-based 1970s mail survey by Shere Hite, lesbians self-reported their reasons for being lesbian. This is the only major piece of research into female sexuality that has looked at how women understand being homosexual since Kinsey in 1953. The research yielded information about women's general understanding of lesbian relationships and their sexual orientation. Women gave various reasons for preferring sexual relations with women to sexual relations with men, including finding women more sensitive to other people's needs.[152]

Since Hite carried out her study she has acknowledged that some women may have chosen the political identity of a lesbian. Julie Bindel, a UK journalist, reaffirmed that "political lesbianism continues to make intrinsic sense because it reinforces the idea that sexuality is a choice, and we are not destined to a particular fate because of our chromosomes." as recently as 2009.[153]

Sexual orientation change efforts

There are no studies of adequate scientific rigor to conclude whether sexual orientation change efforts work to change a person's sexual orientation. Those efforts have been controversial due to tensions between the values held by some faith-based organizations, on the one hand, and those held by LGBT rights organizations and professional and scientific organizations and other faith-based organizations, on the other.[9] The longstanding consensus of the behavioral and social sciences and the health and mental health professions is that homosexuality per se is a normal and positive variation of human sexual orientation, and therefore not a mental disorder.[9] The American Psychological Association says that "most people experience little or no sense of choice about their sexual orientation".[154]
Some individuals and groups have promoted the idea of homosexuality as symptomatic of developmental defects or spiritual and moral failings and have argued that sexual orientation change efforts, including psychotherapy and religious efforts, could alter homosexual feelings and behaviors. Many of these individuals and groups appeared to be embedded within the larger context of conservative religious political movements that have supported the stigmatization of homosexuality on political or religious grounds.[9]

No major mental health professional organization has sanctioned efforts to change sexual orientation and virtually all of them have adopted policy statements cautioning the profession and the public about treatments that purport to change sexual orientation. These include the American Psychiatric Association, American Psychological Association, American Counseling Association, National Association of Social Workers in the USA,[155] the Royal College of Psychiatrists,[156] and the Australian Psychological Society.[157] The American Psychological Association and the Royal College of Psychiatrists expressed concerns that the positions espoused by NARTH are not supported by the science and create an environment in which prejudice and discrimination can flourish.[156][158]
The American Psychological Association "encourages mental health professionals to avoid misrepresenting the efficacy of sexual orientation change efforts by promoting or promising change in sexual orientation when providing assistance to individuals distressed by their own or others' sexual orientation and concludes that the benefits reported by participants in sexual orientation change efforts can be gained through approaches that do not attempt to change sexual orientation".[9]

Fluidity of orientation

The American Psychiatric Association (APA) has stated "some people believe that sexual orientation is innate and fixed; however, sexual orientation develops across a person's lifetime".[159] A report from the Centre for Addiction and Mental Health states: "For some people, sexual orientation is continuous and fixed throughout their lives. For others, sexual orientation may be fluid and change over time".[160] One study has suggested "considerable fluidity in bisexual, unlabeled, and lesbian women's attractions, behaviors, and identities".[161][162]

Gender and fluidity

In a 2004 study, the female subjects (both gay and straight women) became sexually aroused when they viewed heterosexual as well as lesbian erotic films. Among the male subjects, however, the straight men were turned on only by erotic films with women, the gay ones by those with men. The study's senior researcher said that women's sexual desire is less rigidly directed toward a particular sex, as compared with men's, and it's more changeable over time.[163]

Parenting

Scientific research has been generally consistent in showing that lesbian and gay parents are as fit and capable as heterosexual parents, and their children are as psychologically healthy and well-adjusted as children reared by heterosexual parents.[164][165][166] According to scientific literature reviews, there is no evidence to the contrary.[2][167][168][169][170]

A review study suggested that the children with lesbian or gay parents appear less traditionally gender-typed and are more likely to be open to homoerotic relationships, partly due to genetic (80% of the children being raised by same-sex couples in the US are not adopted and most are the result of heterosexual marriages)[171]) and family socialization processes (children grow up in relatively more tolerant school, neighborhood, and social contexts, which are less heterosexist), even though majority of children raised by same-sex couples identify as heterosexual.[172] A 2005 review by Charlotte J. Patterson for the American Psychological Association found that the available data did not suggest higher rates of homosexuality among the children of lesbian or gay parents.[173] One study suggested that children of gay and lesbian parents were more likely to adopt non-heterosexual identities, especially daughters of lesbian parents (inter-generational transfer was not significant in some analyses for sons).[174]

Health

Physical

Blood donation policies for men who have sex with men
  Men who have sex with men may donate blood; No deferral
  Men who have sex with men may donate blood; Temporary deferral
  Men who have sex with men may not donate blood; Permanent deferral1
  No Data
1No restriction in Israel and the United States of America if last MSM activity was before 1977.

The terms "Men who have sex with men" (MSM) and "women who have sex with women" (WSW) refer to people who engage in sexual activity with others of the same sex regardless of how they identify themselves—as many choose not to accept social identities as lesbian, gay and bisexual.[175][176][177][178][179] These terms are often used in medical literature and social research to describe such groups for study, without needing to consider the issues of sexual self-identity. The terms are seen as problematic, however, because they "obscure social dimensions of sexuality; undermine the self-labeling of lesbian, gay, and bisexual people; and do not sufficiently describe variations in sexual behavior".[180] MSM and WSW are sexually active with each other for a variety of reasons with the main ones arguably sexual pleasure, intimacy and bonding. In contrast to its benefits, sexual behavior can be a disease vector. Safe sex is a relevant harm reduction philosophy.[181] The United States currently prohibits men who have sex with men from donating blood "because they are, as a group, at increased risk for HIV, hepatitis B and certain other infections that can be transmitted by transfusion." Many European countries have the same prohibition.[182]

Public health

These safer sex recommendations are agreed upon by public health officials for women who have sex with women to avoid sexually transmitted infections (STIs):
  • Avoid contact with a partner’s menstrual blood and with any visible genital lesions.
  • Cover sex toys that penetrate more than one person's vagina or anus with a new condom for each person; consider using different toys for each person.
  • Use a barrier (e.g., latex sheet, dental dam, cut-open condom, plastic wrap) during oral sex.
  • Use latex or vinyl gloves and lubricant for any manual sex that might cause bleeding.[183]
These safer sex recommendations are agreed upon by public health officials for men who have sex with men to avoid sexually transmitted infections:
  • Avoid contact with a partner's bodily fluids and with any visible genital lesions.
  • Use condoms for anal and oral sex.
  • Use a barrier (e.g., latex sheet, dental dam, cut-open condom) during anal–oral sex.
  • Cover sex toys that penetrate more than one person with a new condom for each person; consider using different toys for each person and use latex or vinyl gloves and lubricant for any sex that might cause bleeding.[184][185]

Mental

When it was first described in medical literature, homosexuality was often approached from a view that sought to find an inherent psychopathology as its root cause. Much literature on mental health and homosexual patients centered on their depression, substance abuse, and suicide. Although these issues exist among people who are non-heterosexual, discussion about their causes shifted after homosexuality was removed from the Diagnostic and Statistical Manual (DSM) in 1973. Instead, social ostracism, legal discrimination, internalization of negative stereotypes, and limited support structures indicate factors homosexual people face in Western societies that often adversely affect their mental health.[186] Stigma, prejudice, and discrimination stemming from negative societal attitudes toward homosexuality lead to a higher prevalence of mental health disorders among lesbians, gay men, and bisexuals compared to their heterosexual peers.[187] Evidence indicates that the liberalization of these attitudes over the past few decades is associated with a decrease in such mental health risks among younger LGBT people.[188]

Gay and lesbian youth

Gay and lesbian youth bear an increased risk of suicide, substance abuse, school problems, and isolation because of a "hostile and condemning environment, verbal and physical abuse, rejection and isolation from family and peers".[189] Further, LGBT youths are more likely to report psychological and physical abuse by parents or caretakers, and more sexual abuse. Suggested reasons for this disparity are that (1) LGBT youths may be specifically targeted on the basis of their perceived sexual orientation or gender non-conforming appearance, and (2) that "risk factors associated with sexual minority status, including discrimination, invisibility, and rejection by family members...may lead to an increase in behaviors that are associated with risk for victimization, such as substance abuse, sex with multiple partners, or running away from home as a teenager."[190] A 2008 study showed a correlation between the degree of rejecting behavior by parents of LGB adolescents and negative health problems in the teenagers studied:
Higher rates of family rejection were significantly associated with poorer health outcomes. On the basis of odds ratios, lesbian, gay, and bisexual young adults who reported higher levels of family rejection during adolescence were 8.4 times more likely to report having attempted suicide, 5.9 times more likely to report high levels of depression, 3.4 times more likely to use illegal drugs, and 3.4 times more likely to report having engaged in unprotected sexual intercourse compared with peers from families that reported no or low levels of family rejection.[191]
Crisis centers in larger cities and information sites on the Internet have arisen to help youth and adults.[192] The Trevor Helpline, a suicide prevention helpline for gay youth, was established following the 1998 airing on HBO of the Academy Award winning short film Trevor.

Law and politics

Legality

 
Worldwide laws regarding homosexual
relationships and expression
    Same-sex marriage    Restricted freedom of expression
    Other type of partnership or unregistered cohabitation    Unenforced penalty
    Marriage recognized but not performed    Imprisonment
    Marriage recognized federally but not performed    Up to life in prison
    Same-sex unions not recognized    Death penalty
Click on map to view an enlarged version where rings in various locations become visible. These indicate places with local and/or case-by-case applications of law.
Decriminalization of Homosexuality by country or territory
  1790–1799
  1800–1869
  1870–1929
  1930–1939
  1940–1949
  1950–1959
  1960–1969
  1970–1979
  1980–1989
  1990–1999
  2000–2009
  2010+
  Same-sex sexual activity illegal
  Male same-sex sexual activity illegal

Most nations do not prohibit consensual sex between unrelated persons above the local age of consent. Some jurisdictions further recognize identical rights, protections, and privileges for the family structures of same-sex couples, including marriage. Some nations mandate that all individuals restrict themselves to heterosexual relationships; that is, in some jurisdictions homosexual activity is illegal. Offenders can face the death penalty in some fundamentalist Muslim areas such as Iran and parts of Nigeria. There are, however, often significant differences between official policy and real-world enforcement. See Violence against LGBT people.

Although homosexual acts were decriminalized in some parts of the Western world, such as Poland in 1932, Denmark in 1933, Sweden in 1944, and the United Kingdom in 1967, it was not until the mid-1970s that the gay community first began to achieve limited civil rights in some developed countries. A turning point was reached in 1973 when the American Psychiatric Association removed homosexuality from the Diagnostic and Statistical Manual of Mental Disorders, thus negating its previous definition of homosexuality as a clinical mental disorder. In 1977, Quebec became the first state-level jurisdiction in the world to prohibit discrimination on the grounds of sexual orientation.
During the 1980s and 1990s, most developed countries enacted laws decriminalizing homosexual behavior and prohibiting discrimination against lesbian and gay people in employment, housing, and services. On the other hand, many countries today in the Middle East and Africa, as well as several countries in Asia, the Caribbean and the South Pacific, outlaw homosexuality. On 11 December 2013, homosexuality was criminalized in India by a Supreme Court ruling.[193] The Section 377 of the colonial-era Indian Penal Code which criminalizes homosexuality remains in effect in many former colonies.[194] In six countries, homosexual behavior is punishable by life imprisonment; in ten others, it carries the death penalty.[195]

Laws against sexual orientation discrimination

United States

  • Employment discrimination refers to discriminatory employment practices such as bias in hiring, promotion, job assignment, termination, and compensation, and various types of harassment. In the United States there is "very little statutory, common law, and case law establishing employment discrimination based upon sexual orientation as a legal wrong."[196] Some exceptions and alternative legal strategies are available. President Bill Clinton's Executive Order 13087 (1998) prohibits discrimination based on sexual orientation in the competitive service of the federal civilian workforce,[197] and federal non-civil service employees may have recourse under the Due Process Clause of the U.S. Constitution.[198] Private sector workers may have a Title VII action under a quid pro quo sexual harassment theory,[199] a "hostile work environment" theory,[200] a sexual stereotyping theory,[201] or others.[196]
  • Housing discrimination refers to discrimination against potential or current tenants by landlords. In the United States, there is no federal law against such discrimination on the basis of sexual orientation or gender identity, but at least thirteen states and many major cities have enacted laws prohibiting it.[202]
  • Hate crimes (also known as bias crimes) are crimes motivated by bias against an identifiable social group, usually groups defined by race (human classification), religion, sexual orientation, disability, ethnicity, nationality, age, gender, gender identity, or political affiliation. In the United States, 45 states and the District of Columbia have statutes criminalizing various types of bias-motivated violence or intimidation (the exceptions are AZ, GA, IN, SC, and WY). Each of these statutes covers bias on the basis of race, religion, and ethnicity; 32 of them cover sexual orientation, 28 cover gender, and 11 cover transgender/gender-identity.[203] In October 2009, the Matthew Shepard and James Byrd, Jr. Hate Crimes Prevention Act, which "...gives the Justice Department the power to investigate and prosecute bias-motivated violence where the perpetrator has selected the victim because of the person's actual or perceived race, color, religion, national origin, gender, sexual orientation, gender identity or disability", was signed into law and makes hate crime based on sexual orientation, amongst other offenses, a federal crime in the United States.[204]

European Union

In the European Union, discrimination of any type based on sexual orientation or gender identity is illegal under the Charter of Fundamental Rights of the European Union.[205]

Political activism

 
Barbara Gittings picketing Independence Hall 4 July 1966. Photo taken by Kay Lahusen.

Since the 1960s, many LGBT people in the West, particularly those in major metropolitan areas, have developed a so-called gay culture. To many,[who?] gay culture is exemplified by the gay pride movement, with annual parades and displays of rainbow flags. Yet not all LGBT people choose to participate in "queer culture", and many gay men and women specifically decline to do so. To some[who?] it seems to be a frivolous display, perpetuating gay stereotypes. To some others,[who?] the gay culture represents heterophobia and is scorned as widening the gulf between gay and non-gay people.
With the outbreak of AIDS in the early 1980s, many LGBT groups and individuals organized campaigns to promote efforts in AIDS education, prevention, research, patient support, and community outreach, as well as to demand government support for these programs.

The bewildering death toll wrought by the AIDS epidemic at first seemed to slow the progress of the gay rights movement, but in time it galvanized some parts of the LGBT community into community service and political action, and challenged the heterosexual community to respond compassionately. Major American motion pictures from this period that dramatized the response of individuals and communities to the AIDS crisis include An Early Frost (1985), Longtime Companion (1990), And the Band Played On (1993), Philadelphia (1993), and Common Threads: Stories from the Quilt (1989).
Publicly gay politicians have attained numerous government posts, even in countries that had sodomy laws in their recent past. Examples include Guido Westerwelle, Germany's Vice-Chancellor; Peter Mandelson, a British Labour Party cabinet minister and Per-Kristian Foss, formerly Norwegian Minister of Finance.

LGBT movements are opposed by a variety of individuals and organizations. Some social conservatives believe that all sexual relationships with people other than an opposite-sex spouse undermine the traditional family[206] and that children should be reared in homes with both a father and a mother.[207][208] Some opponents of gay rights say that such rights may conflict with individuals' freedom of speech,[209][210][211][212][213] religious freedoms in the workplace,[214][215] the ability to run churches,[216] charitable organizations[217][218] and other religious organizations[219] in accordance with one's religious views, and that the acceptance of homosexual relationships by religious organizations might be forced through threatening to remove the tax-exempt status of churches whose views do not align with those of the government.[220][221][222][223]

Critics charge[weasel words] that political correctness has led to the association of sex between males and HIV being downplayed.[224][225]

Military service

U.S. President Barack Obama signs into law the Don't Ask, Don't Tell Repeal Act of 2010

Policies and attitudes toward gay and lesbian military personnel vary widely around the world. Some countries allow gay men, lesbians, and bisexual people to serve openly and have granted them the same rights and privileges as their heterosexual counterparts. Many countries neither ban nor support LGB service members. A few countries continue to ban homosexual personnel outright.

Most Western military forces have removed policies excluding sexual minority members. Of the 26 countries that participate militarily in NATO, more than 20 permit openly gay, lesbian and bisexual people to serve. Of the permanent members of the United Nations Security Council, three (United Kingdom, France and United States) do so. The other two generally do not: China bans gay and lesbian people outright, Russia excludes all gay and lesbian people during peacetime but allows some gay men to serve in wartime (see below). Israel is the only country in the Middle East region that allows openly LGB people to serve in the military.

While the question of homosexuality in the military has been highly politicized in the United States, it is not necessarily so in many countries. Generally speaking, sexuality in these cultures is considered a more personal aspect of one's identity than it is in the United States.

According to American Psychological Association empirical evidence fails to show that sexual orientation is germane to any aspect of military effectiveness including unit cohesion, morale, recruitment and retention.[226] Sexual orientation is irrelevant to task cohesion, the only type of cohesion that critically predicts the team's military readiness and success.[227]

Society and sociology

Public opinion

2013 Pew Global Research Poll: Should homosexuality be accepted in society? Percentage of responders that answered accept:
  81% – 90%
  71% – 80%
  61% – 70%
  51% – 60%
  41% – 50%
  31% – 40%
  21% – 30%
  11% – 20%
  1% – 10%
  No data

Societal acceptance of non-heterosexual orientations such as homosexuality is lowest in Asian and African countries, and is highest in Europe, Australia, and the Americas. Western society has become increasingly accepting of homosexuality over the past few decades.

Relationships

In 2006, the American Psychological Association, American Psychiatric Association and National Association of Social Workers stated in an amicus brief presented to the Supreme Court of the State of California: "Gay men and lesbians form stable, committed relationships that are equivalent to heterosexual relationships in essential respects. The institution of marriage offers social, psychological, and health benefits that are denied to same-sex couples. By denying same-sex couples the right to marry, the state reinforces and perpetuates the stigma historically associated with homosexuality. Homosexuality remains stigmatized, and this stigma has negative consequences. California's prohibition on marriage for same-sex couples reflects and reinforces this stigma". They concluded: "There is no scientific basis for distinguishing between same-sex couples and heterosexual couples with respect to the legal rights, obligations, benefits, and burdens conferred by civil marriage."[2]

Religion

Though the relationship between homosexuality and religion can vary greatly across time and place, within and between different religions and sects, and regarding different forms of homosexuality and bisexuality, current authoritative bodies and doctrines of the world's largest religions generally view homosexuality negatively. This can range from quietly discouraging homosexual activity, to explicitly forbidding same-sex sexual practices among adherents and actively opposing social acceptance of homosexuality. Some teach that homosexual orientation itself is sinful,[228] others state that only the sexual act is a sin,[229] others are completely accepting of gays and lesbians,[230] while some encourage homosexuality.[231] Some claim that homosexuality can be overcome through religious faith and practice. On the other hand, voices exist within many of these religions that view homosexuality more positively, and liberal religious denominations may bless same-sex marriages. Some view same-sex love and sexuality as sacred, and a mythology of same-sex love can be found around the world.[232] Regardless of their position on homosexuality, many people of faith look to both sacred texts and tradition for guidance on this issue.[citation needed]

Discrimination

Gay bullying

Gay bullying can be the verbal or physical abuse against a person who is perceived by the aggressor to be lesbian, gay, bisexual or transgender, including persons who are actually heterosexual or of non-specific or unknown sexual orientation. In the US, teenage students heard anti-gay slurs such as “homo”, “faggot” and “sissy” about 26 times a day on average, or once every 14 minutes, according to a 1998 study by Mental Health America (formerly National Mental Health Association).[233]

Heterosexism and homophobia

 
Protests in New York City against Uganda's Anti-Homosexuality Bill.

In many cultures, homosexual people are frequently subject to prejudice and discrimination. A 2011 Dutch study concluded that 49% of Holland's youth and 58% of youth foreign to the country reject homosexuality.[234] Similar to other minority groups they can also be subject to stereotyping. These attitudes tend to be due to forms of homophobia and heterosexism (negative attitudes, bias, and discrimination in favor of opposite-sex sexuality and relationships). Heterosexism can include the presumption that everyone is heterosexual or that opposite-sex attractions and relationships are the norm and therefore superior. Homophobia is a fear of, aversion to, or discrimination against homosexual people. It manifests in different forms, and a number of different types have been postulated, among which are internalized homophobia, social homophobia, emotional homophobia, rationalized homophobia, and others.[235] Similar is lesbophobia (specifically targeting lesbians) and biphobia (against bisexual people). When such attitudes manifest as crimes they are often called hate crimes and gay bashing.

Negative stereotypes characterize LGB people as less romantically stable, more promiscuous and more likely to abuse children, but there is no scientific basis to such assertions. Gay men and lesbians form stable, committed relationships that are equivalent to heterosexual relationships in essential respects.[2] Sexual orientation does not affect the likelihood that people will abuse children.[236][237][238] Claims that there is scientific evidence to support an association between being gay and being a pedophile are based on misuses of those terms and misrepresentation of the actual evidence.[237]

Violence against gays and lesbians

In the United States, the FBI reported that 20.4% of hate crimes reported to law enforcement in 2011 were based on sexual orientation bias. 56.7% of these crimes were based on anti-male homosexual bias. 11.1% were based on anti-female homosexual bias. 29.6% were based on anti-homosexual bias without regard to gender.[239] The 1998 murder of Matthew Shepard, a gay student, is a notorious such incident in the U.S. LGBT people, especially lesbians, may become the victims of "corrective rape", a violent crime with the supposed aim of making them heterosexual. In certain parts of the world, LGBT people are also at risk of "honor killings" perpetrated by their families or relatives.[240][241][242]

Homosexual behavior in other animals

 
Roy and Silo, two New York Central Park Zoo male Chinstrap Penguins similar to those pictured, became internationally known when they coupled and later were given an egg that needed hatching and care, which they successfully did.[243]

Homosexual, bisexual and transgender behaviors occur in a number of other animal species. Such behaviors include sexual activity, courtship, affection, pair bonding, and parenting,[14] and are widespread; a 1999 review by researcher Bruce Bagemihl shows that homosexual behavior has been observed in close to 1500 species, ranging from primates to gut worms, and is well documented for 500 of them.[14][15] Animal sexual behavior takes many different forms, even within the same species.
The motivations for and implications of these behaviors have yet to be fully understood, since most species have yet to be fully studied.[244] According to Bagemihl, "the animal kingdom [does] it with much greater sexual diversity—including homosexual, bisexual and nonreproductive sex—than the scientific community and society at large have previously been willing to accept".[245]

Molecule

Molecule

From Wikipedia, the free encyclopedia
 

3D (left and center) and 2D (right) representations of the terpenoid molecule atisane

A molecule /ˈmɒlɪkjuːl/ is an electrically neutral group of two or more atoms held together by chemical bonds.[1][2][3][4][5][6] Molecules are distinguished from ions by their lack of electrical charge. However, in quantum physics, organic chemistry, and biochemistry, the term molecule is often used less strictly, also being applied to polyatomic ions.

In the kinetic theory of gases, the term molecule is often used for any gaseous particle regardless of its composition. According to this definition, noble gas atoms are considered molecules despite being composed of a single non-bonded atom.[7]

A molecule may be homonuclear, that is, it consists of atoms of a single chemical element, as with oxygen (O2); or it may be a chemical compound composed of more than one element, as with water (H2O). Atoms and complexes connected by non-covalent bonds such as hydrogen bonds or ionic bonds are generally not considered single molecules.[8]

Molecules as components of matter are common in organic substances (and therefore biochemistry). They also make up most of the oceans and atmosphere. However, the majority of familiar solid substances on Earth, including most of the minerals that make up the crust, mantle, and core of the Earth, contain many chemical bonds, but are not made of identifiable molecules. Also, no typical molecule can be defined for ionic crystals (salts) and covalent crystals (network solids), although these are often composed of repeating unit cells that extend either in a plane (such as in graphene) or three-dimensionally (such as in diamond, quartz, or sodium chloride). The theme of repeated unit-cellular-structure also holds for most condensed phases with metallic bonding, which means that solid metals are also not made of molecules. In glasses (solids that exist in a vitreous disordered state), atoms may also be held together by chemical bonds without presence of any definable molecule, but also without any of the regularity of repeating units that characterises crystals.

Molecular science

The science of molecules is called molecular chemistry or molecular physics, depending on whether the focus is on chemistry or physics. Molecular chemistry deals with the laws governing the interaction between molecules that results in the formation and breakage of chemical bonds, while molecular physics deals with the laws governing their structure and properties. In practice, however, this distinction is vague. In molecular sciences, a molecule consists of a stable system (bound state) composed of two or more atoms. Polyatomic ions may sometimes be usefully thought of as electrically charged molecules. The term unstable molecule is used for very reactive species, i.e., short-lived assemblies (resonances) of electrons and nuclei, such as radicals, molecular ions, Rydberg molecules, transition states, van der Waals complexes, or systems of colliding atoms as in Bose–Einstein condensate.

History and etymology

 

John Dalton

According to Merriam-Webster and the Online Etymology Dictionary, the word "molecule" derives from the Latin "moles" or small unit of mass.
  • Molecule (1794) – "extremely minute particle", from Fr. molécule (1678),[citation needed] from modern Latin. molecula, diminutive of Latin moles "mass, barrier". A vague meaning at first; the vogue for the word (used until late 18th century only in Latin form) can be traced to the philosophy of Descartes.
The definition of the molecule has evolved as knowledge of the structure of molecules has increased. Earlier definitions were less precise, defining molecules as the smallest particles of pure chemical substances that still retain their composition and chemical properties.[9] This definition often breaks down since many substances in ordinary experience, such as rocks, salts, and metals, are composed of large crystalline networks of chemically bonded atoms or ions, but are not made of discrete molecules.

Molecular size

Most molecules are far too small to be seen with the naked eye, but there are exceptions. DNA, a macromolecule, can reach macroscopic sizes, as can molecules of many polymers. Molecules commonly used as building blocks for organic synthesis have a dimension of a few angstroms (Å) to several dozen Å. Single molecules cannot usually be observed by light (as noted above), but small molecules and even the outlines of individual atoms may be traced in some circumstances by use of an atomic force microscope. Some of the largest molecules are macromolecules or supermolecules.

Smallest molecule diameter

The smallest molecule is the diatomic hydrogen (H2), with a bond length of 0.74 Å.[10]

Largest molecule diameter

Mesoporous silica have been produced with a diameter of 1000 Å (100 nm)[11]

Radius

Effective molecular radius is the size a molecule displays in solution.[12][13] The table of permselectivity for different substances contains examples.

Molecular formula

A compound's empirical formula is the simplest integer ratio of the chemical elements that constitute it. For example, water is always composed of a 2:1 ratio of hydrogen to oxygen atoms, and ethyl alcohol or ethanol is always composed of carbon, hydrogen, and oxygen in a 2:6:1 ratio. However, this does not determine the kind of molecule uniquely – dimethyl ether has the same ratios as ethanol, for instance. Molecules with the same atoms in different arrangements are called isomers. Also carbohydrates, for example, have the same ratio (carbon:hydrogen:oxygen = 1:2:1) (and thus the same empirical formula) but different total numbers of atoms in the molecule.

The molecular formula reflects the exact number of atoms that compose the molecule and so characterizes different molecules. However different isomers can have the same atomic composition while being different molecules.

The empirical formula is often the same as the molecular formula but not always. For example, the molecule acetylene has molecular formula C2H2, but the simplest integer ratio of elements is CH.
The molecular mass can be calculated from the chemical formula and is expressed in conventional atomic mass units equal to 1/12 of the mass of a neutral carbon-12 (12C isotope) atom. For network solids, the term formula unit is used in stoichiometric calculations.

Molecular geometry

Molecules have fixed equilibrium geometries—bond lengths and angles— about which they continuously oscillate through vibrational and rotational motions. A pure substance is composed of molecules with the same average geometrical structure. The chemical formula and the structure of a molecule are the two important factors that determine its properties, particularly its reactivity. Isomers share a chemical formula but normally have very different properties because of their different structures. Stereoisomers, a particular type of isomers, may have very similar physico-chemical properties and at the same time different biochemical activities.

Molecular spectroscopy

Molecular spectroscopy deals with the response (spectrum) of molecules interacting with probing signals of known energy (or frequency, according to Planck's formula). Molecules have quantized energy levels that can be analyzed by detecting the molecule's energy exchange through absorbance or emission.[14] Spectroscopy does not generally refer to diffraction studies where particles such as neutrons, electrons, or high energy X-rays interact with a regular arrangement of molecules (as in a crystal).

Theoretical aspects

The study of molecules by molecular physics and theoretical chemistry is largely based on quantum mechanics and is essential for the understanding of the chemical bond. The simplest of molecules is the hydrogen molecule-ion, H2+, and the simplest of all the chemical bonds is the one-electron bond. H2+ is composed of two positively charged protons and one negatively charged electron, which means that the Schrödinger equation for the system can be solved more easily due to the lack of electron–electron repulsion. With the development of fast digital computers, approximate solutions for more complicated molecules became possible and are one of the main aspects of computational chemistry.
When trying to define rigorously whether an arrangement of atoms is "sufficiently stable" to be considered a molecule, IUPAC suggests that it "must correspond to a depression on the potential energy surface that is deep enough to confine at least one vibrational state".[1] This definition does not depend on the nature of the interaction between the atoms, but only on the strength of the interaction. In fact, it includes weakly bound species that would not traditionally be considered molecules, such as the helium dimer, He2, which has one vibrational bound state[15] and is so loosely bound that it is only likely to be observed at very low temperatures.

Whether or not an arrangement of atoms is "sufficiently stable" to be considered a molecule is inherently an operational definition. Philosophically, therefore, a molecule is not a fundamental entity (in contrast, for instance, to an elementary particle); rather, the concept of a molecule is the chemist's way of making a useful statement about the strengths of atomic-scale interactions in the world that we observe.

Fundamental interactions (forces)

Fundamental interaction

From Wikipedia, the free encyclopedia
   
The Standard Model of elementary particles, with the fermions in the first three columns, the gauge bosons in the fourth column and the Higgs boson in the fifth column.

Fundamental interactions or fundamental forces or interactive forces are modeled in fundamental physics as patterns of relations in physical systems, evolving over time, whose objects appear not reducible to more basic entities. Conventionally accepted are four fundamental interactions—gravitational, electromagnetic, strong nuclear, and weak nuclear—each understood as the dynamics of a field. The gravitational is modeled as continuous, one classical field. Manifesting a measurable unit or elementary particle, each of the other three is modeled as discrete, a quantum field.

Gravitation and electromagnetism act over potentially infinite distance—across the universe—and mediate everyday phenomena of human experience. The other two fields act over minuscule, subatomic distances. Synthesizing chemical elements via nuclear fusion within stars and quasars, the strong binds the atomic nucleus—the force released during nuclear fission as in detonation of a nuclear bomb—whereas the weak mediates radioactive decay.

Modest gravitational effects are conventionally predicted via refinements of the theory of universal gravitation (UG). Yet the gravitational phenomenon itself is conventionally explained as a consequence of spacetime's dynamic geometry "curving" in the vicinity of mass, and is modeled by the general theory of relativity (GR). UG and GR comprise classical mechanics. As energy alters spatial and temporal relations—effects notable at vast energy levels—such relativistic effects on space and time are modeled in relativistic mechanics, whose relativity theory extends classical mechanics via GR and special theory of relativity (SR).[1]

Experimentally detected phenomena of elementary particles were first modeled in quantum mechanics (QM). For predictive accuracy at high energy, however, QM was set to SR,[2] and yielded quantum field theory (QFT), whose first quantized the electromagnetic field, quantum electrodynamics (QED). QED was reduced along with the weak field to the QFT electroweak theory (EWT). The strong field was modeled as quantum chromodynamics (QCD). EWT together with QCD and the Higgs mechanism—which models the phenomena of some particles bearing mass—comprise particle physics' Standard Model.

Theoretical physicists working beyond the Standard Model seek to quantize the gravitational field toward predictions that particle physicists can experimentally confirm, thus yielding acceptance of a theory of quantum gravity (QG). (Phenomena suitable to model as a fifth force—perhaps an added gravitational effect—remain widely disputed.) Other theorists seek to unite the electroweak and strong fields within a Grand Unified Theory (GUT). Yet all four fundamental interactions are widely thought to align at an extremely minuscule scale, although particle accelerators cannot produce the massive energy levels to experimentally probe at that Planck scale to experimentally confirm such theories. Still, some theories, principally string theory, seek both QG and GUT within one framework, unifying all four fundamental interactions along with mass production within a theory of everything (ToE).

General relativity

In his 1687 theory, Newton postulated space as an infinite and unalterable physical structure existing before, within, and around all objects while their states and relations unfold at a constant pace everywhere, thus absolute space and time. Inferring that all objects bearing mass approach at a constant rate, but collide by impact proportional to their masses, Newton inferred that matter exhibits an attractive force. His law of universal gravitation mathematically stated it to span the entire universe instantly (despite absolute time), or, if not actually a force, to be instant interaction among all objects (despite absolute space). As conventionally interpreted, Newton's theory of motion modeled a central force without a communicating medium.[3] Newton's thus theory violated the first principle of mechanical philosophy, as stated by Descartes, No action at a distance. Conversely, during the 1820s, when explaining magnetism, Michael Faraday inferred a field filing space and transmitting that force. Faraday conjectured that ultimately, all forces unified into one.

In the early 1870s, James Clerk Maxwell unified electricity and magnetism as effects of an electromagnetic field whose third consequence was light, traveling at constant speed in a vacuum. The electromagnetic field theory contradicted predictions of Newton's theory of motion, unless physical states of the luminiferous aether—presumed to fill all space whether within matter or in a vacuum and to manifest the electromagnetic field—were aligning all phenomena and thereby holding valid the Newtonian principle relativity or invariance. Disfavoring hypotheses at unobservables,
Einstein discarded the aether, and aligned electrodynamics with relativity by denying absolute space and time, and stating relative space and time. The two phenomena altered in the vicinity of an object measured in to be motion—length contraction and time dilation for the object experienced to be in relative motion—Einstein's principle special relativity, published in 1905.

Accepted as theory, too, special relativity rendered Newton's theory of motion apparently untenable, especially since Newtonian physics postulated an object's mass to be constant. A consequence of special relativity is mass being a variant form of energy, condensed into an object. By the equivalence principle, published by Einstein in 1907, gravitation is indistinguishable from acceleration, perhaps two phenomena sharing a mechanism. That year, Hermann Minkowski modeled special relativity to a unification of space and time, 4D spacetime. So stretching the three spatial dimensions onto the single dimension of time's arrow, Einstein arrived at general theory of relativity in 1915.[4] Einstein interpreted space as a substance, Einstein aether, whose physical properties receive motion from an object and transmit it to other objects while modulating events' unfolding. Equivalent to energy, mass contracts space, which dilates time—events unfold more slowly—establishing local tension. The object relieves it in the likeness of a free fall at light speed along the pathway of least resistance, a straight line's equivalent on the curved surface of 4D spacetime, a pathway termed worldline.

Einstein abolished action at a distance by theorizing a gravitational field—4D spacetime—that waves while transmitting motion across the universe a light speed. All objects always travel at light speed in 4D spacetime. At zero relative speed, an object is observed to travel none through space, but age most rapidly. That is, an object at relative rest in 3D space exhibits its constant energy to an observer by exhibiting top speed along 1D time flow. Conversely, at highest relative speed, an object traverses 3D space at light speed, yet is ageless, none of its constant energy available to internal motion as flow along 1D time. Whereas Newtonian inertia is an idealized case of an object either keeping rest or holding constant velocity by hypothetical existence in a universe otherwise devoid of matter, Einsteinian inertia is indistinguishable from an object experiencing no acceleration by existing in a gravitational field possibly full of matter distributed uniformly. Conversely, even massless energy manifests gravitation—which is acceleration—on local objects by "curving" the surface of 4D spacetime. Physicists renounced belief that motion must be mediated by a force.

Standard Model

The electromagnetic, strong, and weak interactions associate with elementary particles, whose behaviors are modeled in quantum mechanics (QM). For predictive success with QM's probabilistic outcomes, particle physics conventionally models QM events across a field set to special relativity, altogether relativistic quantum field theory (QFT).[5] Force particles, called gauge bosonsforce carriers or messenger particles of underlying fields—interact with matter particles, called fermions. Everyday matter is atoms, composed of three fermion types: up-quarks and down-quarks constituting, as well as electrons orbiting, the atom's nucleus. Atoms interact, form molecules, and manifest further properties through electromagnetic interactions among their electrons absorbing and emitting photons, the electromagnetic field's force carrier, which if unimpeded traverse potentially infinite distance. Electromagnetism's QFT is quantum electrodynamics (QED).

The electromagnetic interaction was modeled with the weak interaction, whose force carriers are W and Z bosons, traversing minuscule distance, in electroweak theory (EWT). Electroweak interaction would operate at such high temperatures as soon after the presumed Big Bang, but, as the early universe cooled, split into electromagnetic and weak interactions. The strong interaction, whose force carrier is the gluon, traversing minuscule distance among quarks, is modeled in quantum chromodynamics (QCD). EWT, QCD, and the Higgs mechanism, whereby the Higgs field manifests Higgs bosons that interact with some quantum particles and thereby endow those particles with mass, comprise particle physics' Standard Model (SM). Predictions are usually made using calculational approximation methods, although such perturbation theory is inadequate to model some experimental observations (for instance bound states and solitons). Still, physicists widely accept the Standard Model as science's most experimentally confirmed theory.

Beyond the Standard Model, some theorists work to unite the electroweak and strong interactions within a Grand Unified Theory (GUT). Some attempts at GUTs hypothesize "shadow" particles, such that every known matter particle associates with an undiscovered force particle, and vice versa, altogether supersymmetry (SUSY). Other theorists seek to quantize the gravitational field by modeling behavior of its hypothetical force carrier, the graviton and achieve quantum gravity (QG). One approach to QG is loop quantum gravity (LQG). Still other theorists seek both QG and GUT within one framework, reducing all four fundamental interactions to a Theory of Everything (ToE). The most prevalent aim at a ToE is string theory, although to model matter particles, it added SUSY to force particles—and so, strictly speaking, became superstring theory. Multiple, seemingly disparate superstring theories were unified on a backbone, M theory. Theories beyond the Standard Model remain highly speculative, lacking great experimental support.

Overview of the fundamental interaction

An overview of the various families of elementary and composite particles, and the theories describing their interactions. Fermions are on the left, and Bosons are on the right.

In the conceptual model of fundamental interactions, matter consists of fermions, which carry properties called charges and spin ±12 (intrinsic angular momentum ±ħ2, where ħ is the reduced Planck constant). They attract or repel each other by exchanging bosons.

The interaction of any pair of fermions in perturbation theory can then be modeled thus:
Two fermions go in → interaction by boson exchange → Two changed fermions go out.
The exchange of bosons always carries energy and momentum between the fermions, thereby changing their speed and direction. The exchange may also transport a charge between the fermions, changing the charges of the fermions in the process (e.g., turn them from one type of fermion to another). Since bosons carry one unit of angular momentum, the fermion's spin direction will flip from +12 to −12 (or vice versa) during such an exchange (in units of the reduced Planck's constant).

Because an interaction results in fermions attracting and repelling each other, an older term for "interaction" is force.

According to the present understanding, there are four fundamental interactions or forces: gravitation, electromagnetism, the weak interaction, and the strong interaction. Their magnitude and behavior vary greatly, as described in the table below. Modern physics attempts to explain every observed physical phenomenon by these fundamental interactions. Moreover, reducing the number of different interaction types is seen as desirable. Two cases in point are the unification of:
Both magnitude ("relative strength") and "range", as given in the table, are meaningful only within a rather complex theoretical framework. It should also be noted that the table below lists properties of a conceptual scheme that is still the subject of ongoing research.
InteractionCurrent theoryMediatorsRelative strength[6]Long-distance behaviorRange (m)
StrongQuantum chromodynamics
(QCD)
gluons1038{1}
(see discussion below)
10−15
ElectromagneticQuantum electrodynamics
(QED)
photons1036\frac{1}{r^2}
WeakElectroweak Theory (EWT)W and Z bosons1025 \frac{1}{r} \ e^{-m_{W,Z} \ r}10−18
GravitationGeneral Relativity
(GR)
gravitons (hypothetical)1\frac{1}{r^2}

The modern (perturbative) quantum mechanical view of the fundamental forces other than gravity is that particles of matter (fermions) do not directly interact with each other, but rather carry a charge, and exchange virtual particles (gauge bosons), which are the interaction carriers or force mediators. For example, photons mediate the interaction of electric charges, and gluons mediate the interaction of color charges.

The interactions

Gravitation

Gravitation is by far the weakest of the four interactions. The weakness of gravity can easily be demonstrated by suspending a pin using a simple magnet (such as a refrigerator magnet). The magnet is able to hold the pin against the gravitational pull of the entire Earth.

Yet gravitation is very important for macroscopic objects and over macroscopic distances for the following reasons. Gravitation:
  • is the only interaction that acts on all particles having mass;
  • has an infinite range, like electromagnetism but unlike strong and weak interaction;
  • cannot be absorbed, transformed, or shielded against;
  • always attracts and never repels.
Even though electromagnetism is far stronger than gravitation, electrostatic attraction is not relevant for large celestial bodies, such as planets, stars, and galaxies, simply because such bodies contain equal numbers of protons and electrons and so have a net electric charge of zero. Nothing "cancels" gravity, since it is only attractive, unlike electric forces which can be attractive or repulsive. On the other hand, all objects having mass are subject to the gravitational force, which only attracts.
Therefore, only gravitation matters on the large scale structure of the universe.

The long range of gravitation makes it responsible for such large-scale phenomena as the structure of galaxies, black holes, and it retards the expansion of the universe. Gravitation also explains astronomical phenomena on more modest scales, such as planetary orbits, as well as everyday experience: objects fall; heavy objects act as if they were glued to the ground; and animals can only jump so high.

Gravitation was the first interaction to be described mathematically. In ancient times, Aristotle hypothesized that objects of different masses fall at different rates. During the Scientific Revolution, Galileo Galilei experimentally determined that this was not the case — neglecting the friction due to air resistance, and buoyancy forces if an atmosphere is present (e.g. the case of a dropped air filled balloon vs a water filled balloon) all objects accelerate toward the Earth at the same rate. Isaac Newton's law of Universal Gravitation (1687) was a good approximation of the behaviour of gravitation. Our present-day understanding of gravitation stems from Albert Einstein's General Theory of Relativity of 1915, a more accurate (especially for cosmological masses and distances) description of gravitation in terms of the geometry of space-time.

Merging general relativity and quantum mechanics (or quantum field theory) into a more general theory of quantum gravity is an area of active research. It is hypothesized that gravitation is mediated by a massless spin-2 particle called the graviton.

Although general relativity has been experimentally confirmed (at least, in the weak field or Post-Newtonian case) on all but the smallest scales, there are rival theories of gravitation. Those taken seriously by the physics community all reduce to general relativity in some limit, and the focus of observational work is to establish limitations on what deviations from general relativity are possible.

Electroweak interaction

Electromagnetism and weak interaction appear to be very different at everyday low energies. They can be modeled using two different theories. However, above unification energy, on the order of 100 GeV, they would merge into a single electroweak force.

Electroweak theory is very important for modern cosmology, particularly on how the universe evolved. This is because shortly after the Big Bang, the temperature was approximately above 1015 K. Electromagnetic force and weak force were merged into a combined electroweak force.
For contributions to the unification of the weak and electromagnetic interaction between elementary particles, Abdus Salam, Sheldon Glashow and Steven Weinberg were awarded the Nobel Prize in Physics in 1979.[7][8]

Electromagnetism

Electromagnetism is the force that acts between electrically charged particles. This phenomenon includes the electrostatic force acting between charged particles at rest, and the combined effect of electric and magnetic forces acting between charged particles moving relative to each other.

Electromagnetism is infinite-ranged like gravity, but vastly stronger, and therefore describes a number of macroscopic phenomena of everyday experience such as friction, rainbows, lightning, and all human-made devices using electric current, such as television, lasers, and computers.
Electromagnetism fundamentally determines all macroscopic, and many atomic level, properties of the chemical elements, including all chemical bonding.

In a four kilogram (~1 gallon) jug of water there are

 4000 \ \mbox{g}\,H_2 O \cdot \frac{1 \ \mbox{mol}\,H_2 O}{18 \ \mbox{g}\,H_2 O} \cdot \frac{10 \ \mbox{mol}\,e^{-}}{1 \ \mbox{mol}\,H_2 O} \cdot \frac{96,000 \ \mbox{C}\,}{1 \ \mbox{mol}\,e^{-}} = 2.1 \times 10^{8} C \ \, \

of total electron charge. Thus, if we place two such jugs a meter apart, the electrons in one of the jugs repel those in the other jug with a force of

 {1 \over 4\pi\varepsilon_0}\frac{(2.1 \times 10^{8} C)^2}{(1 m)^2} = 4.1 \times 10^{26} N.

This is larger than what the planet Earth would weigh if weighed on another Earth. The atomic nuclei in one jug also repel those in the other with the same force. However, these repulsive forces are cancelled by the attraction of the electrons in jug A with the nuclei in jug B and the attraction of the nuclei in jug A with the electrons in jug B, resulting in no net force. Electromagnetic forces are tremendously stronger than gravity but cancel out so that for large bodies gravity dominates.

Electrical and magnetic phenomena have been observed since ancient times, but it was only in the 19th century that it was discovered that electricity and magnetism are two aspects of the same fundamental interaction. By 1864, Maxwell's equations had rigorously quantified this unified interaction. Maxwell's theory, restated using vector calculus, is the classical theory of electromagnetism, suitable for most technological purposes.

The constant speed of light in a vacuum (customarily described with the letter "c") can be derived from Maxwell's equations, which are consistent with the theory of special relativity. Einstein's 1905 theory of special relativity, however, which flows from the observation that the speed of light is constant no matter how fast the observer is moving, showed that the theoretical result implied by Maxwell's equations has profound implications far beyond electro-magnetism on the very nature of time and space.

In other work that departed from classical electro-magnetism, Einstein also explained the photoelectric effect by hypothesizing that light was transmitted in quanta, which we now call photons. Starting around 1927, Paul Dirac combined quantum mechanics with the relativistic theory of electromagnetism. Further work in the 1940s, by Richard Feynman, Freeman Dyson, Julian Schwinger, and Sin-Itiro Tomonaga, completed this theory, which is now called quantum electrodynamics, the revised theory of electromagnetism. Quantum electrodynamics and quantum mechanics provide a theoretical basis for electromagnetic behavior such as quantum tunneling, in which a certain percentage of electrically charged particles move in ways that would be impossible under classical electromagnetic theory, that is necessary for everyday electronic devices such as transistors to function.

Weak interaction

The weak interaction or weak nuclear force is responsible for some nuclear phenomena such as beta decay. Electromagnetism and the weak force are now understood to be two aspects of a unified electroweak interaction — this discovery was the first step toward the unified theory known as the Standard Model. In the theory of the electroweak interaction, the carriers of the weak force are the massive gauge bosons called the W and Z bosons. The weak interaction is the only known interaction which does not conserve parity; it is left-right asymmetric. The weak interaction even violates CP symmetry but does conserve CPT.

Strong interaction

The strong interaction, or strong nuclear force, is the most complicated interaction, mainly because of the way it varies with distance. At distances greater than 10 femtometers, the strong force is practically unobservable. Moreover, it holds only inside the atomic nucleus.

After the nucleus was discovered in 1908, it was clear that a new force was needed to overcome the electrostatic repulsion, a manifestation of electromagnetism, of the positively charged protons.
Otherwise the nucleus could not exist. Moreover, the force had to be strong enough to squeeze the protons into a volume that is 10−15 of that of the entire atom. From the short range of this force, Hideki Yukawa predicted that it was associated with a massive particle, whose mass is approximately 100 MeV.

The 1947 discovery of the pion ushered in the modern era of particle physics. Hundreds of hadrons were discovered from the 1940s to 1960s, and an extremely complicated theory of hadrons as strongly interacting particles was developed. Most notably:
While each of these approaches offered deep insights, no approach led directly to a fundamental theory.

Murray Gell-Mann along with George Zweig first proposed fractionally charged quarks in 1961. Throughout the 1960s, different authors considered theories similar to the modern fundamental theory of quantum chromodynamics (QCD) as simple models for the interactions of quarks. The first to hypothesize the gluons of QCD were Moo-Young Han and Yoichiro Nambu, who introduced the quark color charge and hypothesized that it might be associated with a force-carrying field. At that time, however, it was difficult to see how such a model could permanently confine quarks. Han and Nambu also assigned each quark color an integer electrical charge, so that the quarks were fractionally charged only on average, and they did not expect the quarks in their model to be permanently confined.

In 1971, Murray Gell-Mann and Harald Fritzsch proposed that the Han/Nambu color gauge field was the correct theory of the short-distance interactions of fractionally charged quarks. A little later, David Gross, Frank Wilczek, and David Politzer discovered that this theory had the property of asymptotic freedom, allowing them to make contact with experimental evidence. They concluded that QCD was the complete theory of the strong interactions, correct at all distance scales. The discovery of asymptotic freedom led most physicists to accept QCD, since it became clear that even the long-distance properties of the strong interactions could be consistent with experiment, if the quarks are permanently confined.

Assuming that quarks are confined, Mikhail Shifman, Arkady Vainshtein, and Valentine Zakharov were able to compute the properties of many low-lying hadrons directly from QCD, with only a few extra parameters to describe the vacuum. In 1980, Kenneth G. Wilson published computer calculations based on the first principles of QCD, establishing, to a level of confidence tantamount to certainty, that QCD will confine quarks. Since then, QCD has been the established theory of the strong interactions.

QCD is a theory of fractionally charged quarks interacting by means of 8 photon-like particles called gluons. The gluons interact with each other, not just with the quarks, and at long distances the lines of force collimate into strings. In this way, the mathematical theory of QCD not only explains how quarks interact over short distances, but also the string-like behavior, discovered by Chew and Frautschi, which they manifest over longer distances.

Beyond the Standard Model

Numerous theoretical efforts have been made to systematize the existing four fundamental interactions on the model of electro-weak unification.

Grand Unified Theories (GUTs) are proposals to show that all of the fundamental interactions, other than gravity, arise from a single interaction with symmetries that break down at low energy levels. GUTs predict relationships among constants of nature that are unrelated in the SM. GUTs also predict gauge coupling unification for the relative strengths of the electromagnetic, weak, and strong forces, a prediction verified at the LEP in 1991 for supersymmetric theories.

Theories of everything, which integrate GUTs with a quantum gravity theory face a greater barrier, because no quantum gravity theories, which include string theory, loop quantum gravity, and twistor theory, have secured wide acceptance. Some theories look for a graviton to complete the Standard Model list of force carrying particles, while others, like loop quantum gravity, emphasize the possibility that time-space itself may have a quantum aspect to it.

Some theories beyond the Standard Model include a hypothetical fifth force, and the search for such a force is an ongoing line of experimental research in physics. In supersymmetric theories, there are particles that acquire their masses only through supersymmetry breaking effects and these particles, known as moduli can mediate new forces. Another reason to look for new forces is the recent discovery that the expansion of the universe is accelerating (also known as dark energy), giving rise to a need to explain a nonzero cosmological constant, and possibly to other modifications of general relativity. Fifth forces have also been suggested to explain phenomena such as CP violations, dark matter, and dark flow.

Operator (computer programming)

From Wikipedia, the free encyclopedia https://en.wikipedia.org/wiki/Operator_(computer_programmin...