Buddhism

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Standing Buddha statue at the Tokyo National Museum. One of the earliest known representations of the Buddha, 1st–2nd century CE.

 

Buddhism is the world's fourth-largest religion with over 520 million followers, or over 7% of the global population, known as Buddhists. Buddhism encompasses a variety of traditions, beliefs and spiritual practices largely based on original teachings attributed to the Buddha and resulting interpreted philosophies. Buddhism originated in ancient India as a Sramana tradition sometime between the 6th and 4th centuries BCE, spreading through much of Asia. Two major extant branches of Buddhism are generally recognized by scholars: Theravada (Pali: "The School of the Elders") and Mahayana (Sanskrit: "The Great Vehicle"). 

Most Buddhist traditions share the goal of overcoming suffering and the cycle of death and rebirth, either by the attainment of Nirvana or through the path of Buddhahood. Buddhist schools vary in their interpretation of the path to liberation, the relative importance and canonicity assigned to the various Buddhist texts, and their specific teachings and practices. Widely observed practices include taking refuge in the Buddha, the Dharma and the Sangha, observance of moral precepts, monasticism, meditation, and the cultivation of the Paramitas (virtues). 

Theravada Buddhism has a widespread following in Sri Lanka and Southeast Asia such as Myanmar and Thailand. Mahayana, which includes the traditions of Pure Land, Zen, Nichiren Buddhism, Shingon and Tiantai (Tendai), is found throughout East Asia.

Vajrayana, a body of teachings attributed to Indian adepts, may be viewed as a separate branch or as an aspect of Mahayana Buddhism. Tibetan Buddhism, which preserves the Vajrayana teachings of eighth-century India, is practiced in the countries of the Himalayan region, Mongolia, and Kalmykia.

Life of the Buddha

Buddha in Sarnath Museum (Dhammajak Mutra)

Buddhism is an Indian religion attributed to the teachings of the Buddha, supposedly born Siddhārtha Gautama, and also known as the Tathāgata ("thus-gone") and Sakyamuni ("sage of the Sakyas"). Early texts have his personal name as "Gautama" or "Gotama" (Pali) without any mention of "Siddhārtha," ("Achieved the Goal") which appears to have been a kind of honorific title when it does appear. The details of Buddha's life are mentioned in many Early Buddhist Texts but are inconsistent, and his social background and life details are difficult to prove, the precise dates uncertain.

The evidence of the early texts suggests that he was born as Siddhārtha Gautama in Lumbini and grew up in Kapilavasthu, a town in the plains region of the modern Nepal-India border, and that he spent his life in what is now modern Bihar and Uttar Pradesh. Some hagiographic legends state that his father was a king named Suddhodana, his mother was Queen Maya, and he was born in Lumbini gardens. However, scholars such as Richard Gombrich consider this a dubious claim because a combination of evidence suggests he was born in the Shakyas community – one that later gave him the title Shakyamuni, and the Shakya community was governed by a small oligarchy or republic-like council where there were no ranks but where seniority mattered instead. Some of the stories about Buddha, his life, his teachings, and claims about the society he grew up in may have been invented and interpolated at a later time into the Buddhist texts.

"The Great Departure", relic depicting Gautama leaving home, first or second century (Musée Guimet)

 

According to the Buddhist sutras, Gautama was moved by the innate suffering of humanity and its endless repetition due to rebirth. He set out on a quest to end this repeated suffering. Early Buddhist canonical texts and early biographies of Gautama state that Gautama first studied under Vedic teachers, namely Alara Kalama (Sanskrit: Arada Kalama) and Uddaka Ramaputta (Sanskrit: Udraka Ramaputra), learning meditation and ancient philosophies, particularly the concept of "nothingness, emptiness" from the former, and "what is neither seen nor unseen" from the latter.

The gilded "Emaciated Buddha statue" in an Ubosoth in Bangkok representing the stage of his asceticism

 

Finding these teachings to be insufficient to attain his goal, he turned to the practice of asceticism. This too fell short of attaining his goal, and then he turned to the practice of dhyana, meditation. He famously sat in meditation under a Ficus religiosa tree now called the Bodhi Tree in the town of Bodh Gaya in the Gangetic plains region of South Asia. He gained insight into the workings of karma and his former lives, and attained enlightenment, certainty about the Middle Way (Skt. madhyamā-pratipad) as the right path of spiritual practice to end suffering (dukkha) from rebirths in Saṃsāra. As a fully enlightened Buddha (Skt. samyaksaṃbuddha), he attracted followers and founded a Sangha (monastic order). Now, as the Buddha, he spent the rest of his life teaching the Dharma he had discovered, and died at the age of 80 in Kushinagar, India.

Buddha's teachings were propagated by his followers, which in the last centuries of the 1st millennium BCE became over 18 Buddhist sub-schools of thought, each with its own basket of texts containing different interpretations and authentic teachings of the Buddha; these over time evolved into many traditions of which the more well known and widespread in the modern era are Theravada, Mahayana and Vajrayana Buddhism.

The problems of life: dukkha and saṃsāra

Four Noble Truths – dukkha and its ending

The Buddha teaching the Four Noble Truths. Sanskrit manuscript. Nalanda, Bihar, India.

 

The Four Truths express the basic orientation of Buddhism: we crave and cling to impermanent states and things, which is dukkha, "incapable of satisfying" and painful. This keeps us caught in saṃsāra, the endless cycle of repeated rebirth, dukkha and dying again. But there is a way to liberation from this endless cycle to the state of nirvana, namely following the Noble Eightfold Path.

The truth of dukkha is the basic insight that life in this mundane world, with its clinging and craving to impermanent states and things is dukkha, and unsatisfactory. Dukkha can be translated as "incapable of satisfying," "the unsatisfactory nature and the general insecurity of all conditioned phenomena"; or "painful." Dukkha is most commonly translated as "suffering," but this is inaccurate, since it refers not to episodic suffering, but to the intrinsically unsatisfactory nature of temporary states and things, including pleasant but temporary experiences. We expect happiness from states and things which are impermanent, and therefore cannot attain real happiness. 

In Buddhism, dukkha is one of the three marks of existence, along with impermanence and anattā (non-self). Buddhism, like other major Indian religions, asserts that everything is impermanent (anicca), but, unlike them, also asserts that there is no permanent self or soul in living beings (anattā). The ignorance or misperception (avijjā) that anything is permanent or that there is self in any being is considered a wrong understanding, and the primary source of clinging and dukkha.

Dukkha arises when we crave (Pali: tanha) and cling to these changing phenomena. The clinging and craving produces karma, which ties us to samsara, the round of death and rebirth. Craving includes kama-tanha, craving for sense-pleasures; bhava-tanha, craving to continue the cycle of life and death, including rebirth; and vibhava-tanha, craving to not experience the world and painful feelings.

Dukkha ceases, or can be confined, when craving and clinging cease or are confined. This also means that no more karma is being produced, and rebirth ends. Cessation is nirvana, "blowing out," and peace of mind.

By following the Buddhist path to moksha, liberation, one starts to disengage from craving and clinging to impermanent states and things. The term "path" is usually taken to mean the Noble Eightfold Path, but other versions of "the path" can also be found in the Nikayas. The Theravada tradition regards insight into the four truths as liberating in itself.

The cycle of rebirth

Traditional Tibetan Buddhist Thangka depicting the Wheel of Life with its six realms

Saṃsāra

Saṃsāra means "wandering" or "world", with the connotation of cyclic, circuitous change. It refers to the theory of rebirth and "cyclicality of all life, matter, existence", a fundamental assumption of Buddhism, as with all major Indian religions. Samsara in Buddhism is considered to be dukkha, unsatisfactory and painful, perpetuated by desire and avidya (ignorance), and the resulting karma.

The theory of rebirths, and realms in which these rebirths can occur, is extensively developed in Buddhism, in particular Tibetan Buddhism with its wheel of existence (Bhavacakra) doctrine. Liberation from this cycle of existence, nirvana, has been the foundation and the most important historical justification of Buddhism.

The later Buddhist texts assert that rebirth can occur in six realms of existence, namely three good realms (heavenly, demi-god, human) and three evil realms (animal, hungry ghosts, hellish). Samsara ends if a person attains nirvana, the "blowing out" of the desires and the gaining of true insight into impermanence and non-self reality.

Rebirth

Ramabhar Stupa in Kushinagar, Uttar Pradesh, India is regionally believed to be Buddha's cremation site.

Rebirth refers to a process whereby beings go through a succession of lifetimes as one of many possible forms of sentient life, each running from conception to death. In Buddhist thought, this rebirth does not involve any soul, because of its doctrine of anattā (Sanskrit: anātman, no-self doctrine) which rejects the concepts of a permanent self or an unchanging, eternal soul, as it is called in Hinduism and Christianity. According to Buddhism there ultimately is no such thing as a self in any being or any essence in any thing.

The Buddhist traditions have traditionally disagreed on what it is in a person that is reborn, as well as how quickly the rebirth occurs after each death. Some Buddhist traditions assert that "no self" doctrine means that there is no perduring self, but there is avacya (inexpressible) self which migrates from one life to another. The majority of Buddhist traditions, in contrast, assert that vijñāna (a person's consciousness) though evolving, exists as a continuum and is the mechanistic basis of what undergoes rebirth, rebecoming and redeath. The rebirth depends on the merit or demerit gained by one's karma, as well as that accrued on one's behalf by a family member.

Each rebirth takes place within one of five realms according to Theravadins, or six according to other schools – heavenly, demi-gods, humans, animals, hungry ghosts and hellish.

In East Asian and Tibetan Buddhism, rebirth is not instantaneous, and there is an intermediate state (Tibetan "bardo") between one life and the next. The orthodox Theravada position rejects the wait, and asserts that rebirth of a being is immediate. However there are passages in the Samyutta Nikaya of the Pali Canon that seem to lend support to the idea that the Buddha taught about an intermediate stage between one life and the next.

Karma

In Buddhism, karma (from Sanskrit: "action, work") drives saṃsāra – the endless cycle of suffering and rebirth for each being. Good, skilful deeds (Pāli: kusala) and bad, unskilful deeds (Pāli: akusala) produce "seeds" in the unconscious receptacle (ālaya) that mature later either in this life or in a subsequent rebirth. The existence of karma is a core belief in Buddhism, as with all major Indian religions, it implies neither fatalism nor that everything that happens to a person is caused by karma.

A central aspect of Buddhist theory of karma is that intent (cetanā) matters and is essential to bring about a consequence or phala "fruit" or vipāka "result". However, good or bad karma accumulates even if there is no physical action, and just having ill or good thoughts creates karmic seeds; thus, actions of body, speech or mind all lead to karmic seeds. In the Buddhist traditions, life aspects affected by the law of karma in past and current births of a being include the form of rebirth, realm of rebirth, social class, character and major circumstances of a lifetime. It operates like the laws of physics, without external intervention, on every being in all six realms of existence including human beings and gods.

A notable aspect of the karma theory in Buddhism is merit transfer. A person accumulates merit not only through intentions and ethical living, but also is able to gain merit from others by exchanging goods and services, such as through dāna (charity to monks or nuns). Further, a person can transfer one's own good karma to living family members and ancestors.

Liberation

Mahabodhi Temple in Bodh Gaya, India, where Gautama Buddha attained nirvana under the Bodhi Tree (left)

The cessation of the kleshas and the attainment of nirvana (nibbāna), with which the cycle of rebirth ends, has been the primary and the soteriological goal of the Buddhist path for monastic life since the time of the Buddha. The term "path" is usually taken to mean the Noble Eightfold Path, but other versions of "the path" can also be found in the Nikayas. In some passages in the Pali Canon, a distinction is being made between right knowledge or insight (sammā-ñāṇa), and right liberation or release (sammā-vimutti), as the means to attain cessation and liberation.

Nirvana literally means "blowing out, quenching, becoming extinguished". In early Buddhist texts, it is the state of restraint and self-control that leads to the "blowing out" and the ending of the cycles of sufferings associated with rebirths and redeaths. Many later Buddhist texts describe nirvana as identical with anatta with complete "emptiness, nothingness". In some texts, the state is described with greater detail, such as passing through the gate of emptiness (sunyata) – realizing that there is no soul or self in any living being, then passing through the gate of signlessness (animitta) – realizing that nirvana cannot be perceived, and finally passing through the gate of wishlessness (apranihita) – realizing that nirvana is the state of not even wishing for nirvana.

The nirvana state has been described in Buddhist texts partly in a manner similar to other Indian religions, as the state of complete liberation, enlightenment, highest happiness, bliss, fearlessness, freedom, permanence, non-dependent origination, unfathomable, and indescribable. It has also been described in part differently, as a state of spiritual release marked by "emptiness" and realization of non-self.

While Buddhism considers the liberation from saṃsāra as the ultimate spiritual goal, in traditional practice, the primary focus of a vast majority of lay Buddhists has been to seek and accumulate merit through good deeds, donations to monks and various Buddhist rituals in order to gain better rebirths rather than nirvana.

The path to liberation: Bhavana (practice, cultivation)

While the Noble Eightfold Path is best-known in the west, a wide variety of practices and stages have been used and described in the Buddhist traditions. Basic practices include sila (ethics), samadhi (meditation, dhyana) and prajna (wisdom), as described in the Noble Eightfold Path. An important additional practice is a kind and compassionate attitude toward every living being and the world. Devotion is also important in some Buddhist traditions, and in the Tibetan traditions visualizations of deities and mandalas are important. The value of textual study is regarded differently in the various Buddhist traditions. It is central to Theravada and highly important to Tibetan Buddhism, while the Zen tradition takes an ambiguous stance.

Refuge in the Three Jewels

Relic depicting a footprint of the Buddha with Dharmachakra and Triratna, first century CE, Gandhāra

Traditionally, the first step in most Buddhist schools requires taking Three Refuges, also called the Three Jewels (Sanskrit: triratna, Pali: tiratana) as the foundation of one's religious practice. Pali texts employ the Brahmanical motif of the triple refuge, found in the Rigveda 9.97.47, Rigveda 6.46.9 and Chandogya Upanishad 2.22.3–4. Tibetan Buddhism sometimes adds a fourth refuge, in the lama. The three refuges are believed by Buddhists to be protective and a form of reverence.

The Three Jewels are:

• The Gautama Buddha, the historical Buddha, the Blessed One, the Awakened with true knowledge
• The Dharma, the precepts, the practice, the Four Truths, the Eightfold Path
• The Sangha, order of monks, the community of Buddha's disciples

Reciting the three refuges is considered in Buddhism not as a place to hide, rather a thought that purifies, uplifts and strengthens.

The Buddhist path

Theravada – Noble Eightfold Path

The Dharmachakra represents the Noble Eightfold Path.

An important guiding principle of Buddhist practice is the Middle Way (madhyamapratipad). It was a part of Buddha's first sermon, where he presented the Noble Eightfold Path that was a 'middle way' between the extremes of asceticism and hedonistic sense pleasures. In Buddhism, states Harvey, the doctrine of "dependent arising" (conditioned arising, pratītyasamutpāda) to explain rebirth is viewed as the 'middle way' between the doctrines that a being has a "permanent soul" involved in rebirth (eternalism) and "death is final and there is no rebirth" (annihilationism).

In the Theravada canon, the Pali-suttas, various often irreconcilable sequences can be found. According to Carol Anderson, the Theravada canon lacks "an overriding and comprehensive structure of the path to nibbana." Nevertheless, the Noble Eightfold Path, or "Eightfold Path of the Noble Ones", has become an important description of the Buddhist path. It consists of a set of eight interconnected factors or conditions, that when developed together, lead to the cessation of dukkha. These eight factors are: Right View (or Right Understanding), Right Intention (or Right Thought), Right Speech, Right Action, Right Livelihood, Right Effort, Right Mindfulness, and Right Concentration. 

This Eightfold Path is the fourth of the Four Noble Truths, and asserts the path to the cessation of dukkha (suffering, pain, unsatisfactoriness). The path teaches that the way of the enlightened ones stopped their craving, clinging and karmic accumulations, and thus ended their endless cycles of rebirth and suffering.

The Noble Eightfold Path is grouped into three basic divisions, as follows:

Division	Eightfold factor	Sanskrit, Pali	Description
Wisdom (Sanskrit: prajñā, Pāli: paññā)	1. Right view	samyag dṛṣṭi, sammā ditthi	The belief that there is an afterlife and not everything ends with death, that Buddha taught and followed a successful path to nirvana; according to Peter Harvey, the right view is held in Buddhism as a belief in the Buddhist principles of karma and rebirth, and the importance of the Four Noble Truths and the True Realities.
	2. Right intention	samyag saṃkalpa, sammā saṅkappa	Giving up home and adopting the life of a religious mendicant in order to follow the path; this concept, states Harvey, aims at peaceful renunciation, into an environment of non-sensuality, non-ill-will (to lovingkindness), away from cruelty (to compassion).
Moral virtues (Sanskrit: śīla, Pāli: sīla)	3. Right speech	samyag vāc, sammā vāca	No lying, no rude speech, no telling one person what another says about him, speaking that which leads to salvation;
	4. Right action	samyag karman, sammā kammanta	No killing or injuring, no taking what is not given; no sexual acts in monastic pursuit, for lay Buddhists no sensual misconduct such as sexual involvement with someone married, or with an unmarried woman protected by her parents or relatives.
	5. Right livelihood	samyag ājīvana, sammā ājīva	For monks, beg to feed, only possessing what is essential to sustain life. For lay Buddhists, the canonical texts state right livelihood as abstaining from wrong livelihood, explained as not becoming a source or means of suffering to sentient beings by cheating them, or harming or killing them in any way.
Meditation (Sanskrit and Pāli: samādhi)	6. Right effort	samyag vyāyāma, sammā vāyāma	Guard against sensual thoughts; this concept, states Harvey, aims at preventing unwholesome states that disrupt meditation.
	7. Right mindfulness	samyag smṛti, sammā sati	Never be absent minded, conscious of what one is doing; this, states Harvey, encourages mindfulness about impermanence of the body, feelings and mind, as well as to experience the five skandhas, the five hindrances, the four True Realities and seven factors of awakening.
	8. Right concentration	samyag samādhi, sammā samādhi	Correct meditation or concentration (dhyana), explained as the four jhānas.

Mahayana – Bodhisattva-path and the six paramitas

Dāna or charitable giving to monks is a virtue in Buddhism, leading to merit accumulation and better rebirths.

 

Mahāyāna Buddhism is based principally upon the path of a Bodhisattva. A Bodhisattva refers to one who is on the path to buddhahood. The term Mahāyāna was originally a synonym for Bodhisattvayāna or "Bodhisattva Vehicle."

In the earliest texts of Mahayana Buddhism, the path of a bodhisattva was to awaken the bodhicitta. Between the 1st and 3rd century CE, this tradition introduced the Ten Bhumi doctrine, which means ten levels or stages of awakening. This development was followed by the acceptance that it is impossible to achieve Buddhahood in one (current) lifetime, and the best goal is not nirvana for oneself, but Buddhahood after climbing through the ten levels during multiple rebirths. Mahayana scholars then outlined an elaborate path, for monks and laypeople, and the path includes the vow to help teach Buddhist knowledge to other beings, so as to help them cross samsara and liberate themselves, once one reaches the Buddhahood in a future rebirth. One part of this path are the Pāramitā (perfections, to cross over), derived from the Jatakas tales of Buddha's numerous rebirths.

The Mahayana texts are inconsistent in their discussion of the Paramitas, and some texts include lists of two, others four, six, ten and fifty-two. The six paramitas have been most studied, and these are:

1. Dāna pāramitā: perfection of giving; primarily to monks, nuns and the Buddhist monastic establishment dependent on the alms and gifts of the lay householders, in return for generating religious merit; some texts recommend ritually transferring the merit so accumulated for better rebirth to someone else
2. Śīla pāramitā: perfection of morality; it outlines ethical behaviour for both the laity and the Mahayana monastic community; this list is similar to Śīla in the Eightfold Path (i.e. Right Speech, Right Action, Right Livelihood)
3. Kṣānti pāramitā: perfection of patience, willingness to endure hardship
4. Vīrya pāramitā: perfection of vigour; this is similar to Right Effort in the Eightfold Path
5. Dhyāna pāramitā: perfection of meditation; this is similar to Right Concentration in the Eightfold Path
6. Prajñā pāramitā: perfection of insight (wisdom), awakening to the characteristics of existence such as karma, rebirths, impermanence, no-self, dependent origination and emptiness; this is complete acceptance of the Buddha teaching, then conviction, followed by ultimate realization that "dharmas are non-arising".

In Mahayana Sutras that include ten Paramitas, the additional four perfections are "skillful means, vow, power and knowledge". The most discussed Paramita and the highest rated perfection in Mahayana texts is the "Prajna-paramita", or the "perfection of insight". This insight in the Mahayana tradition, states Shōhei Ichimura, has been the "insight of non-duality or the absence of reality in all things".

Śīla – Buddhist ethics

Statue of Gautama Buddha, first century CE, Gandhara, present-day Pakistan (Guimet Museum)

 

Śīla (Sanskrit) or sīla (Pāli) is the concept of "moral virtues", that is the second group and an integral part of the Noble Eightfold Path. It consists of right speech, right action and right livelihood.

Śīla appear as ethical precepts for both lay and ordained Buddhist devotees. It includes the Five Precepts for laypeople, Eight or Ten Precepts for monastic life, as well as rules of Dhamma (Vinaya or Patimokkha) adopted by a monastery.

Precepts

Buddhist scriptures explain the five precepts (Pali: pañcasīla; Sanskrit: pañcaśīla) as the minimal standard of Buddhist morality. It is the most important system of morality in Buddhism, together with the monastic rules. The five precepts apply to both male and female devotees, and these are:

1. Abstain from killing (Ahimsa);
2. Abstain from stealing;
3. Abstain from sensual (including sexual) misconduct;
4. Abstain from lying;
5. Abstain from intoxicants.

Undertaking and upholding the five precepts is based on the principle of non-harming (Pāli and Sanskrit: ahiṃsa). The Pali Canon recommends one to compare oneself with others, and on the basis of that, not to hurt others. Compassion and a belief in karmic retribution form the foundation of the precepts. Undertaking the five precepts is part of regular lay devotional practice, both at home and at the local temple. However, the extent to which people keep them differs per region and time. They are sometimes referred to as the śrāvakayāna precepts in the Mahāyāna tradition, contrasting them with the bodhisattva precepts.

The five precepts are not commandments and transgressions do not invite religious sanctions, but their power has been based on the Buddhist belief in karmic consequences and their impact in the afterlife. Killing in Buddhist belief leads to rebirth in the hell realms, and for a longer time in more severe conditions if the murder victim was a monk. Adultery, similarly, invites a rebirth as prostitute or in hell, depending on whether the partner was unmarried or married. These moral precepts have been voluntarily self-enforced in lay Buddhist culture through the associated belief in karma and rebirth. Within the Buddhist doctrine, the precepts are meant to develop mind and character to make progress on the path to enlightenment.

The monastic life in Buddhism has additional precepts as part of patimokkha, and unlike lay people, transgressions by monks do invite sanctions. Full expulsion from sangha follows any instance of killing, engaging in sexual intercourse, theft or false claims about one's knowledge. Temporary expulsion follows a lesser offence. The sanctions vary per monastic fraternity (nikaya).

Lay people and novices in many Buddhist fraternities also uphold eight (asta shila) or ten (das shila) from time to time. Four of these are same as for the lay devotee: no killing, no stealing, no lying, and no intoxicants. The other four precepts are:

1. No sexual activity;
2. Abstain from eating at the wrong time (e.g. only eat solid food before noon);
3. Abstain from jewellery, perfume, adornment, entertainment;
4. Abstain from sleeping on high bed i.e. to sleep on a mat on the ground.

All eight precepts are sometimes observed by lay people on uposatha days: full moon, new moon , the first and last quarter following the lunar calendar. The ten precepts also include to abstain from accepting money.

In addition to these precepts, Buddhist monasteries have hundreds of rules of conduct, which are a part of its patimokkha.

Vinaya

Monks performing a ceremony in Hangzhou, China

Vinaya is the specific code of conduct for a sangha of monks or nuns. It includes the Patimokkha, a set of 227 offences including 75 rules of decorum for monks, along with penalties for transgression, in the Theravadin tradition. The precise content of the Vinaya Pitaka (scriptures on the Vinaya) differs in different schools and tradition, and different monasteries set their own standards on its implementation. The list of pattimokkha is recited every fortnight in a ritual gathering of all monks. Buddhist text with vinaya rules for monasteries have been traced in all Buddhist traditions, with the oldest surviving being the ancient Chinese translations.

Monastic communities in the Buddhist tradition cut normal social ties to family and community, and live as "islands unto themselves". Within a monastic fraternity, a sangha has its own rules. A monk abides by these institutionalized rules, and living life as the vinaya prescribes it is not merely a means, but very nearly the end in itself. Transgressions by a monk on Sangha vinaya rules invites enforcement, which can include temporary or permanent expulsion.

Samadhi (dhyana) – meditation

Bhikkhus in Thailand

A wide range of meditation practices has developed in the Buddhist traditions, but "meditation" primarily refers to the practice of dhyana c.q. jhana. It is a practice in which the attention of the mind is first narrowed to the focus on one specific object, such as the breath, a concrete object, or a specific thought, mental image or mantra. After this initial focusing of the mind, the focus is coupled to mindfulness, maintaining a calm mind while being aware of one's surroundings. The practice of dhyana aids in maintaining a calm mind, and avoiding disturbance of this calm mind by mindfulness of disturbing thoughts and feelings.

Origins

The earliest evidence of yogis and their meditative tradition, states Karel Werner, is found in the Keśin hymn 10.136 of the Rigveda. While evidence suggests meditation was practised in the centuries preceding the Buddha, the meditative methodologies described in the Buddhist texts are some of the earliest among texts that have survived into the modern era. These methodologies likely incorporate what existed before the Buddha as well as those first developed within Buddhism.

According to Bronkhorst, the Four Dhyanas was a Buddhist invention. Bronkhorst notes that the Buddhist canon has a mass of contradictory statements, little is known about their relative chronology, and "there can be no doubt that the canon – including the older parts, the Sutra and Vinaya Pitaka – was composed over a long period of time". Meditative practices were incorporated from other sramanic movements; the Buddhist texts describe how Buddha learnt the practice of the formless dhyana from Brahmanical practices, in the Nikayas ascribed to Alara Kalama and Uddaka Ramaputta. The Buddhist canon also describes and criticizes alternative dhyana practices, which likely mean the pre-existing mainstream meditation practices of Jainism and Hinduism.

Buddha added a new focus and interpretation, particularly through the Four Dhyanas methodology, in which mindfulness is maintained. Further, the focus of meditation and the underlying theory of liberation guiding the meditation has been different in Buddhism. For example, states Bronkhorst, the verse 4.4.23 of the Brihadaranyaka Upanishad with its "become calm, subdued, quiet, patiently enduring, concentrated, one sees soul in oneself" is most probably a meditative state. The Buddhist discussion of meditation is without the concept of soul and the discussion criticizes both the ascetic meditation of Jainism and the "real self, soul" meditation of Hinduism.

Four rupa-jhāna and four arupa-jhāna

Buddhist monuments in the Horyu-ji Area

 

For Nirvana, Buddhist texts teach various meditation methodologies, of which rupa-jhana (four meditations in the realm of form) and arupa-jhana (four meditations in the formless realm) have been the most studied. These are described in the Pali Canon as trance-like states in the world of desirelessness. The four dhyanas under rupa-jhanas are:

1. First dhyana: detach from all sensory desires and sinful states that are a source of unwholesome karma. Success here is described in Buddhist texts as leading to discursive thinking, deliberation, detachment, sukha (pleasure) and priti (rapture).
2. Second dhyana: cease deliberation and all discursive thoughts. Success leads to one-pointed thinking, serenity, pleasure and rapture.
3. Third dhyana: lose feeling of rapture. Success leads to equanimity, mindfulness and pleasure, without rapture.
4. Fourth dhyana: cease all effects, lose all happiness and sadness. Success in the fourth meditation stage leads to pure equanimity and mindfulness, without any pleasure or pain.

The arupa-jhanas (formless realm meditation) are also four, which are entered by those who have mastered the rupa-jhanas (Arhats). The first formless dhyana gets to infinite space without form or colour or shape, the second to infinity of perception base of the infinite space, the third formless dhyana transcends object-subject perception base, while the fourth is where he dwells in nothing-at-all where there are no feelings, no ideas, nor are there non-ideas, unto total cessation. The four rupa-dhyanas in Buddhist practice lead to rebirth in successfully better rupa Brahma heavenly realms, while arupa-dhyanas lead into arupa heavens.

Richard Gombrich notes that the sequence of the four rupa-jhanas describes two different cognitive states. The first two describe a narrowing of attention, while in the third and fourth jhana attention is expanded again. Alexander Wynne further explains that the dhyana-scheme is poorly understood. According to Wynne, words expressing the inculcation of awareness, such as sati, sampajāno, and upekkhā, are mistranslated or understood as particular factors of meditative states, whereas they refer to a particular way of perceiving the sense objects.

Meditation and insight

Statue of the Buddha in meditation position, Haw Phra Kaew, Vientiane, Laos

The Buddhist tradition has incorporated two traditions regarding the use of dhyāna (meditation, Pali jhāna). There is a tradition that stresses attaining prajñā (insight, bodhi, kenshō, vipassana) as the means to awakening and liberation. But it has also incorporated the yogic tradition, as reflected in the use of jhana, which is rejected in other sutras as not resulting in the final result of liberation. Lambert Schmithausen, a professor of Buddhist Studies, discerns three possible roads to liberation as described in the suttas, to which Vetter adds the sole practice of dhyana itself. According to Vetter and Bronkhorst, the earliest Buddhist path consisted of a set of practices which culminate in the practice of dhyana, leading to a calm of mind which according to Vetter is the liberation which is being sought. Frauwallner notes that the Buddha regarded tanha, "thirst," craving, to be the cause of suffering, not ignorance. But this was in contradiction to the Indian traditions of the time, and posed a problem, which was then also incorporated into the Buddhis teachings. Later on, "liberating insight" came to be regarded as equally liberating. This "liberating insight" came to be exemplified by prajna, or the insight in the "four truths," but also by other elements of the Buddhist teachings.

The Brahma-vihara

Statue of Buddha in Wat Phra Si Rattana Mahathat, Phitsanulok, Thailand

The four immeasurables or four abodes, also called Brahma-viharas, are virtues or directions for meditation in Buddhist traditions, which helps a person be reborn in the heavenly (Brahma) realm. These are traditionally believed to be a characteristic of the deity Brahma and the heavenly abode he resides in.

The four Brahma-vihara are:

1. Loving-kindness (Pāli: mettā, Sanskrit: maitrī) is active good will towards all;
2. Compassion (Pāli and Sanskrit: karuṇā) results from metta; it is identifying the suffering of others as one's own;
3. Empathetic joy (Pāli and Sanskrit: muditā): is the feeling of joy because others are happy, even if one did not contribute to it; it is a form of sympathetic joy;
4. Equanimity (Pāli: upekkhā, Sanskrit: upekṣā): is even-mindedness and serenity, treating everyone impartially.

According to Peter Harvey, the Buddhist scriptures acknowledge that the four Brahmavihara meditation practices "did not originate within the Buddhist tradition". The Brahmavihara (sometimes as Brahmaloka), along with the tradition of meditation and the above four immeasurables are found in pre-Buddha and post-Buddha Vedic and Sramanic literature. Aspects of the Brahmavihara practice for rebirths into the heavenly realm have been an important part of Buddhist meditation tradition.

According to Gombrich, the Buddhist usage of the brahma-vihāra originally referred to an awakened state of mind, and a concrete attitude toward other beings which was equal to "living with Brahman" here and now. The later tradition took those descriptions too literally, linking them to cosmology and understanding them as "living with Brahman" by rebirth in the Brahma-world. According to Gombrich, "the Buddha taught that kindness – what Christians tend to call love – was a way to salvation."

Visualizations: deities, mandalas

Mandala are used in Buddhism for initiation ceremonies and visualization.

 

Idols of deity and icons have been a part of the historic practice, and in Buddhist texts such as the 11th-century Sadanamala, a devotee visualizes and identifies himself or herself with the imagined deity as part of meditation. This has been particularly popular in Vajrayana meditative traditions, but also found in Mahayana and Theravada traditions, particularly in temples and with Buddha images.

In Tibetan Buddhism tradition, mandala are mystical maps for the visualization process with cosmic symbolism. There are numerous deities, each with a mandala, and they are used during initiation ceremonies and meditation. The mandalas are concentric geometric shapes symbolizing layers of the external world, gates and sacred space. The meditation deity is in the centre, sometimes surrounded by protective gods and goddesses. Visualizations with deities and mandalas in Buddhism is a tradition traceable to ancient times, and likely well established by the time the 5th-century text Visuddhimagga was composed.

Practice: monks, laity

According to Peter Harvey, whenever Buddhism has been healthy, not only ordained but also more committed lay people have practised formal meditation. Loud devotional chanting however, adds Harvey, has been the most prevalent Buddhist practice and considered a form of meditation that produces "energy, joy, lovingkindness and calm", purifies mind and benefits the chanter.

Throughout most of Buddhist history, meditation has been primarily practised in Buddhist monastic tradition, and historical evidence suggests that serious meditation by lay people has been an exception. In recent history, sustained meditation has been pursued by a minority of monks in Buddhist monasteries. Western interest in meditation has led to a revival where ancient Buddhist ideas and precepts are adapted to Western mores and interpreted liberally, presenting Buddhism as a meditation-based form of spirituality.

Prajñā – insight

Monks debating at Sera Monastery, Tibet

Prajñā (Sanskrit) or paññā (Pāli) is insight or knowledge of the true nature of existence. The Buddhist tradition regards ignorance (avidyā), a fundamental ignorance, misunderstanding or mis-perception of the nature of reality, as one of the basic causes of dukkha and samsara. By overcoming ignorance or misunderstanding one is enlightened and liberated. This overcoming includes awakening to impermanence and the non-self nature of reality, and this develops dispassion for the objects of clinging, and liberates a being from dukkha and saṃsāra. Prajñā is important in all Buddhist traditions, and is the wisdom about the dharmas, functioning of karma and rebirths, realms of samsara, impermanence of everything, no-self in anyone or anything, and dependent origination.

Origins

The origins of "liberating insight" are unclear. Buddhist texts, states Bronkhorst, do not describe it explicitly, and the content of "liberating insight" is likely not original to Buddhism. According to Vetter and Bronkhorst, this growing importance of "liberating insight" was a response to other religious groups in India, which held that a liberating insight was indispensable for moksha, liberation from rebirth.

Bronkhorst suggests that the conception of what exactly constituted "liberating insight" for Buddhists developed over time. Whereas originally it may not have been specified as an insight, later on the Four Noble Truths served as such, to be superseded by pratityasamutpada, and still later, in the Hinayana schools, by the doctrine of the non-existence of a substantial self or person.

Other descriptions of this "liberating insight" exist in the Buddhist canon: that the five Skandhas are impermanent, disagreeable, and neither the Self nor belonging to oneself"; "the contemplation of the arising and disappearance (udayabbaya) of the five Skandhas"; "the realisation of the Skandhas as empty (rittaka), vain (tucchaka) and without any pith or substance (asaraka).

— Lambert Schmithausen

In the Pali Canon liberating insight is attained in the fourth dhyana. However, states Vetter, modern scholarship on the Pali Canon has uncovered a "whole series of inconsistencies in the transmission of the Buddha's word", and there are many conflicting versions of what constitutes higher knowledge and samadhi that leads to the liberation from rebirth and suffering. Even within the Four Dhyana methodology of meditation, Vetter notes that "penetrating abstract truths and penetrating them successively does not seem possible in a state of mind which is without contemplation and reflection." According to Vetter, dhyāna itself constituted the original "liberating practice".

Carol Anderson notes that insight is often depicted in the Vinaya as the opening of the Dhamma eye, which sets one on the Buddhist path to liberation.

Theravada

Shwezigon Pagoda near Bagan, Myanmar

 

Temple of the Tooth, Kandy, Sri Lanka

Vipassanā

In Theravada Buddhism, but also in Tibetan Buddhism, two types of meditation Buddhist practices are being followed, namely samatha (Pāli; Sanskrit: śamatha; "calm") and vipassana (insight). Samatha is also called "calming meditation", and was adopted into Buddhism from pre-Buddha Indian traditions. Vipassanā meditation was added by Buddha, and refers to "insight meditation". Vipassana does not aim at peace and tranquillity, states Damien Keown, but "the generation of penetrating and critical insight (panna)".

The focus of Vipassana meditation is to continuously and thoroughly know impermanence of everything (annica), no-Self in anything (anatta) and the dukkha teachings of Buddhism.

Contemporary Theravada orthodoxy regards samatha as a preparation for vipassanā, pacifying the mind and strengthening the concentration in order to allow the work of insight, which leads to liberation. In contrast, the Vipassana Movement argues that insight levels can be discerned without the need for developing samatha further due to the risks of going out of the course when strong samatha is developed.

Dependent arising

Pratityasamutpada, also called "dependent arising, or dependent origination", is the Buddhist theory to explain the nature and relations of being, becoming, existence and ultimate reality. Buddhism asserts that there is nothing independent, except the state of nirvana. All physical and mental states depend on and arise from other pre-existing states, and in turn from them arise other dependent states while they cease.

The 'dependent arisings' have a causal conditioning, and thus Pratityasamutpada is the Buddhist belief that causality is the basis of ontology, not a creator God nor the ontological Vedic concept called universal Self (Brahman) nor any other 'transcendent creative principle'. However, the Buddhist thought does not understand causality in terms of Newtonian mechanics, rather it understands it as conditioned arising. In Buddhism, dependent arising is referring to conditions created by a plurality of causes that necessarily co-originate a phenomenon within and across lifetimes, such as karma in one life creating conditions that lead to rebirth in one of the realms of existence for another lifetime.

Buddhism applies the dependent arising theory to explain origination of endless cycles of dukkha and rebirth, through its Twelve Nidānas or "twelve links" doctrine. It states that because Avidyā (ignorance) exists Saṃskāras (karmic formations) exists, because Saṃskāras exists therefore Vijñāna (consciousness) exists, and in a similar manner it links Nāmarūpa (sentient body), Ṣaḍāyatana (six senses), Sparśa (sensory stimulation), Vedanā (feeling), Taṇhā (craving), Upādāna (grasping), Bhava (becoming), Jāti (birth), and Jarāmaraṇa (old age, death, sorrow, pain).

By breaking the circuitous links of the Twelve Nidanas, Buddhism asserts that liberation from these endless cycles of rebirth and dukkha can be attained.

Mahayana

The Great Statue of Amitābha in Kamakura, Japan

Emptiness

Śūnyatā, or "emptiness", is a central concept in Nagarjuna's Madhyamaka school, and widely attested in the Prajñāpāramitā sutras. It brings together key Buddhist doctrines, particularly anatta and dependent origination, to refute the metaphysics of Sarvastivada and Sautrāntika (extinct non-Mahayana schools). Not only sentient beings are empty of ātman; all phenomena (dharmas) are without any svabhava (literally "own-nature" or "self-nature"), and thus without any underlying essence, and "empty" of being independent; thus the heterodox theories of svabhava circulating at the time were refuted on the basis of the doctrines of early Buddhism.

Representation-ony c.q. mind-only

Sarvastivada teachings, which were criticized by Nāgārjuna, were reformulated by scholars such as Vasubandhu and Asanga and were adapted into the Yogachara school. One of the main features of Yogācāra philosophy is the concept of vijñapti-mātra. It is often used interchangeably with the term citta-mātra, but they have different meanings. The standard translation of both terms is "consciousness-only" or "mind-only." Several modern researchers object to this translation, and the accompanying label of "absolute idealism" or "idealistic monism". A better translation for vijñapti-mātra is representation-only, while an alternative translation for citta (mind, thought) mātra (only, exclusively) has not been proposed. 

While the Mādhyamaka school held that asserting the existence or non-existence of any ultimately real thing was inappropriate, some later exponents of Yogachara asserted that the mind and only the mind is ultimately real (a doctrine known as cittamatra). Vasubandhu and Asanga however did not assert that mind was truly existent, or the basis of all reality.

These two schools of thought, in opposition or synthesis, form the basis of subsequent Mahayana metaphysics in the Indo-Tibetan tradition.

Buddha-nature

Buddha-nature is a concept found in some 1st-millennium CE Buddhist texts, such as the Tathāgatagarbha sūtras. This concept has been controversial in Buddhism, but has a following in East Asian Buddhism. These Sutras suggest, states Paul Williams, that 'all sentient beings contain a Tathagata' as their 'essence, core inner nature, Self'. The Tathagatagarbha doctrine, at its earliest probably appeared about the later part of the 3rd century CE, and it contradicts the Anatta doctrine (non-Self) in a vast majority of Buddhist texts, leading scholars to posit that the Tathagatagarbha Sutras were written to promote Buddhism to non-Buddhists. However, the Buddhist text Ratnagotravibhāga states that the "Self" implied in Tathagatagarbha doctrine is actually "not-Self".

Devotion

Bhatti (devotion) at a Buddhist temple, Tibet. Chanting during Bhatti Puja (devotional worship) is often a part of the Theravada Buddhist tradition.

 

Devotion is an important part of the practice of most Buddhists. Devotional practices include ritual prayer, prostration, offerings, pilgrimage, and chanting. In Pure Land Buddhism, devotion to the Buddha Amitabha is the main practice. In Nichiren Buddhism, devotion to the Lotus Sutra is the main practice. Bhakti (called Bhatti in Pali) has been a common practice in Theravada Buddhism, where offerings and group prayers are made to deities and particularly images of Buddha. According to Karel Werner and other scholars, devotional worship has been a significant practice in Theravada Buddhism, and deep devotion is part of Buddhist traditions starting from the earliest days.

Guru devotion is a central practice of Tibetan Buddhism. The guru is considered essential and to the Buddhist devotee, the guru is the "enlightened teacher and ritual master" in Vajrayana spiritual pursuits.

For someone seeking Buddhahood, the guru is the Buddha, the Dhamma and the Sangha, wrote the 12th-century Buddhist scholar Sadhanamala. The veneration of and obedience to teachers is also important in Theravada and Zen Buddhism.

Buddhist texts

Buddhist monk Geshe Konchog Wangdu reads Mahayana sutras from an old woodblock copy of the Tibetan Kanjur.

Buddhism, like all Indian religions, was an oral tradition in ancient times. The Buddha's words, the early doctrines and concepts, and the interpretations were transmitted from one generation to the next by the word of mouth in monasteries, and not through written texts. The first Buddhist canonical texts were likely written down in Sri Lanka, about 400 years after the Buddha died. The texts were part of the Tripitakas, and many versions appeared thereafter claiming to be the words of the Buddha. Scholarly Buddhist commentary texts, with named authors, appeared in India, around the 2nd century CE. These texts were written in Pali or Sanskrit, sometimes regional languages, as palm-leaf manuscripts, birch bark, painted scrolls, carved into temple walls, and later on paper.

Unlike what the Bible is to Christianity and the Quran is to Islam, but like all major ancient Indian religions, there is no consensus among the different Buddhist traditions as to what constitutes the scriptures or a common canon in Buddhism. The general belief among Buddhists is that the canonical corpus is vast. This corpus includes the ancient Sutras organized into Nikayas, itself the part of three basket of texts called the Tripitakas. Each Buddhist tradition has its own collection of texts, much of which is translation of ancient Pali and Sanskrit Buddhist texts of India. The Chinese Buddhist canon, for example, includes 2184 texts in 55 volumes, while the Tibetan canon comprises 1108 texts—all claimed to have been spoken by the Buddha—and another 3461 texts composed by Indian scholars revered in the Tibetan tradition. The Buddhist textual history is vast; over 40,000 manuscripts—mostly Buddhist, some non-Buddhist—were discovered in 1900 in the Dunhuang Chinese cave alone.

Pāli Tipitaka

The Pāli Tipitaka (Sanskrit: Tripiṭaka, three pitakas), which means "three baskets", refers to the Vinaya Pitaka, the Sutta Pitaka, and the Abhidhamma Pitaka. These constitute the oldest known canonical works of Buddhism. The Vinaya Pitaka contains disciplinary rules for the Buddhist monasteries. The Sutta Pitaka contains words attributed to the Buddha. The Abhidhamma Pitaka contain expositions and commentaries on the Sutta, and these vary significantly between Buddhist schools. 

The Pāli Tipitaka is the only surviving early Tipitaka. According to some sources, some early schools of Buddhism had five or seven pitakas. Much of the material in the Canon is not specifically "Theravadin", but is instead the collection of teachings that this school preserved from the early, non-sectarian body of teachings. According to Peter Harvey, it contains material at odds with later Theravadin orthodoxy. He states: "The Theravadins, then, may have added texts to the Canon for some time, but they do not appear to have tampered with what they already had from an earlier period."

Theravada texts

In addition to the Pali Canon, the important commentary texts of the Theravada tradition include the 5th-century Visuddhimagga by Buddhaghosa of the Mahavihara school. It includes sections on shila (virtues), samadhi (concentration), panna (wisdom) as well as Theravada tradition's meditation methodology.

Mahayana sutras

The Tripiṭaka Koreana in South Korea, an edition of the Chinese Buddhist canon carved and preserved in over 81,000 wood printing blocks

 

The Mahayana sutras are a very broad genre of Buddhist scriptures that the Mahayana Buddhist tradition holds are original teachings of the Buddha. Some adherents of Mahayana accept both the early teachings (including in this the Sarvastivada Abhidharma, which was criticized by Nagarjuna and is in fact opposed to early Buddhist thought) and the Mahayana sutras as authentic teachings of Gautama Buddha, and claim they were designed for different types of persons and different levels of spiritual understanding. 

The Mahayana sutras often claim to articulate the Buddha's deeper, more advanced doctrines, reserved for those who follow the bodhisattva path. That path is explained as being built upon the motivation to liberate all living beings from unhappiness. Hence the name Mahāyāna (lit., the Great Vehicle). The Theravada school does not treat the Mahayana Sutras as authoritative or authentic teachings of the Buddha.

Generally, scholars conclude that the Mahayana scriptures were composed from the 1st century CE onwards: "Large numbers of Mahayana sutras were being composed in the period between the beginning of the common era and the fifth century".

Śālistamba Sutra

Many ancient Indian texts have not survived into the modern era, creating a challenge in establishing the historic commonalities between Theravada and Mahayana. The texts preserved in the Tibetan Buddhist monasteries, with parallel Chinese translations, have provided a breakthrough. Among these is the Mahayana text Śālistamba Sutra which no longer exists in a Sanskrit version, but does in Tibetan and Chinese versions. This Mahayana text contains numerous sections which are remarkably the same as the Theravada Pali Canon and Nikaya Buddhism. The Śālistamba Sutra was cited by Mahayana scholars such as the 8th-century Yasomitra to be authoritative. This suggests that Buddhist literature of different traditions shared a common core of Buddhist texts in the early centuries of its history, until Mahayana literature diverged about and after the 1st century CE.

History

Historical roots

The Buddhist "Carpenter's Cave" at Ellora in Maharashtra, India

 

Historically, the roots of Buddhism lie in the religious thought of Iron Age India around the middle of the first millennium BCE. This was a period of great intellectual ferment and socio-cultural change known as the "Second urbanisation", marked by the composition of the Upanishads and the historical emergence of the Sramanic traditions.

New ideas developed both in the Vedic tradition in the form of the Upanishads, and outside of the Vedic tradition through the Śramaṇa movements. The term Śramaṇa refers to several Indian religious movements parallel to but separate from the historical Vedic religion, including Buddhism, Jainism and others such as Ājīvika.

Several Śramaṇa movements are known to have existed in India before the 6th century BCE (pre-Buddha, pre-Mahavira), and these influenced both the āstika and nāstika traditions of Indian philosophy. According to Martin Wilshire, the Śramaṇa tradition evolved in India over two phases, namely Paccekabuddha and Savaka phases, the former being the tradition of individual ascetic and the latter of disciples, and that Buddhism and Jainism ultimately emerged from these. Brahmanical and non-Brahmanical ascetic groups shared and used several similar ideas, but the Śramaṇa traditions also drew upon already established Brahmanical concepts and philosophical roots, states Wiltshire, to formulate their own doctrines. Brahmanical motifs can be found in the oldest Buddhist texts, using them to introduce and explain Buddhist ideas. For example, prior to Buddhist developments, the Brahmanical tradition internalized and variously reinterpreted the three Vedic sacrificial fires as concepts such as Truth, Rite, Tranquility or Restraint. Buddhist texts also refer to the three Vedic sacrificial fires, reinterpreting and explaining them as ethical conduct.

The Śramaṇa religions challenged and broke with the Brahmanic tradition on core assumptions such as Atman (soul, self), Brahman, the nature of afterlife, and they rejected the authority of the Vedas and Upanishads. Buddhism was one among several Indian religions that did so.

Rock-cut Lord Buddha statue at Bojjanakonda near Anakapalle in the Visakhapatnam district of Andhra Pradesh, India

Indian Buddhism

The history of Indian Buddhism may be divided into five periods: Early Buddhism (occasionally called pre-sectarian Buddhism), Nikaya Buddhism or Sectarian Buddhism: The period of the early Buddhist schools, Early Mahayana Buddhism, later Mahayana Buddhism, and Vajrayana Buddhism. 

Sanchi Stupa

Pre-sectarian Buddhism

According to Lambert Schmithausen Pre-sectarian Buddhism is "the canonical period prior to the development of different schools with their different positions."

The early Buddhist Texts include the four principal Nikāyas (and their parallel Agamas) together with the main body of monastic rules, which survive in the various versions of the patimokkha. However, these texts were revised over time, and it is unclear what constitutes the earliest layer of Buddhist teachings. One method to obtain information on the oldest core of Buddhism is to compare the oldest extant versions of the Theravadin Pāli Canon and other texts. The reliability of the early sources, and the possibility to draw out a core of oldest teachings, is a matter of dispute. According to Vetter, inconsistencies remain, and other methods must be applied to resolve those inconsistencies.

According to Schmithausen, three positions held by scholars of Buddhism can be distinguished:

1. "Stress on the fundamental homogeneity and substantial authenticity of at least a considerable part of the Nikayic materials;"
2. "Scepticism with regard to the possibility of retrieving the doctrine of earliest Buddhism;"
3. "Cautious optimism in this respect."

Core teachings

Buddhist Chakras at ASI Museum, Amaravathi

 

According to Mitchell, certain basic teachings appear in many places throughout the early texts, which has led most scholars to conclude that Gautama Buddha must have taught something similar to the Four Noble Truths, the Noble Eightfold Path, Nirvana, the three marks of existence, the five aggregates, dependent origination, karma and rebirth. Yet critical analysis reveals discrepancies, which point to alternative possibilities.

Bruce Matthews notes that there is no cohesive presentation of karma in the Sutta Pitaka, which may mean that the doctrine was incidental to the main perspective of early Buddhist soteriology. Schmithausen has questioned whether karma already played a role in the theory of rebirth of earliest Buddhism. According to Vetter, "the Buddha at first sought "the deathless" (amata/amrta), which is concerned with the here and now. Only later did he become acquainted with the doctrine of rebirth." Bronkhorst disagrees, and concludes that the Buddha "introduced a concept of karma that differed considerably from the commonly held views of his time." According to Bronkhorst, not physical and mental activities as such were seen as responsible for rebirth, but intentions and desire.

Another core problem in the study of early Buddhism is the relation between dhyana and insight. Schmithausen states that the four noble truths as "liberating insight", may be a later addition to texts such as Majjhima Nikaya 36.

According to both Bronkhorst and Anderson, the Four Noble Truths became a substitution for prajna, or "liberating insight", in the suttas in those texts where "liberating insight" was preceded by the four jhānas. The four truths may not have been formulated in earliest Buddhism, and did not serve in earliest Buddhism as a description of "liberating insight". Gotama's teachings may have been personal, "adjusted to the need of each person."

The three marks of existence – Dukkha, Annica, Anatta – may reflect Upanishadic or other influences. K.R. Norman supposes that these terms were already in use at the Buddha's time, and were familiar to his hearers. According to Vetter, the description of the Buddhist path may initially have been as simple as the term "the middle way". In time, this short description was elaborated, resulting in the description of the eightfold path. Similarly nibbāna is the common term for the desired goal of this practice, yet many other terms can be found throughout the Nikāyas, which are not specified.

Early Buddhist schools

Buddha at Xumishan Grottoes, ca. 6th century CE

 

According to the scriptures, soon after the parinirvāṇa (from Sanskrit: "highest extinguishment") of Gautama Buddha, the first Buddhist council was held. As with any ancient Indian tradition, transmission of teaching was done orally. The primary purpose of the assembly was to collectively recite the teachings to ensure that no errors occurred in oral transmission. Richard Gombrich states that the monastic assembly recitations of the Buddha's teaching likely began during Buddha's lifetime, similar to the First Council, that helped compose Buddhist scriptures.

The Second Buddhist council resulted in the first schism in the Sangha, probably caused by a group of reformists called Sthaviras who split from the conservative majority Mahāsāṃghikas. After unsuccessfully trying to modify the Vinaya, a small group of "elderly members", i.e. sthaviras, broke away from the majority Mahāsāṃghika during the Second Buddhist council, giving rise to the Sthavira Nikaya.

The Sthaviras gave rise to several schools, one of which was the Theravada school. Originally, these schisms were caused by disputes over monastic disciplinary codes of various fraternities, but eventually, by about 100 CE if not earlier, schisms were being caused by doctrinal disagreements too. Buddhist monks of different fraternities became distinct schools and stopped doing official Sangha business together, but continued to study each other's doctrines.

Following (or leading up to) the schisms, each Saṅgha started to accumulate their own version of Tripiṭaka (Pali Canons, triple basket of texts). In their Tripiṭaka, each school included the Suttas of the Buddha, a Vinaya basket (disciplinary code) and added an Abhidharma basket which were texts on detailed scholastic classification, summary and interpretation of the Suttas. The doctrine details in the Abhidharmas of various Buddhist schools differ significantly, and these were composed starting about the third century BCE and through the 1st millennium CE. Eighteen early Buddhist schools are known, each with its own Tripitaka, but only one collection from Sri Lanka has survived, in a nearly complete state, into the modern era.

Early Mahayana Buddhism

A Buddhist triad depicting, left to right, a Kushan, the future buddha Maitreya, Gautama Buddha, the bodhisattva Avalokiteśvara, and a monk. Second–third century. Guimet Museum

 

Several scholars have suggested that the Mahayana Buddhist tradition started in south India (modern Andhra Pradesh), and it is there that Prajnaparamita sutras, among the earliest Mahayana sutras, developed among the Mahāsāṃghika along the Kṛṣṇa River region about the 1st century BCE.

There is no evidence that Mahayana ever referred to a separate formal school or sect of Buddhism, but rather that it existed as a certain set of ideals, and later doctrines, for bodhisattvas. Initially it was known as Bodhisattvayāna (the "Vehicle of the Bodhisattvas"). Paul Williams states that the Mahāyāna never had nor ever attempted to have a separate Vinaya or ordination codes from the early schools of Buddhism. Records written by Chinese monks visiting India indicate that both Mahāyāna and non-Mahāyāna monks could be found in the same monasteries, with the difference that Mahayana monks worshipped figures of Bodhisattvas, while non-Mahayana monks did not.

Much of the early extant evidence for the origins of Mahāyāna comes from early Chinese translations of Mahāyāna texts. These Mahayana teachings were first propagated into China by Lokakṣema, the first translator of Mahayana sutras into Chinese during the 2nd century CE. Some scholars have traditionally considered the earliest Mahāyāna sūtras to include the very first versions of the Prajnaparamita series, along with texts concerning Akṣobhya, which were probably composed in the 1st century BCE in the south of India.

Late Mahayana Buddhism

During the period of Late Mahāyāna, four major types of thought developed: Madhyamaka, Yogachara, Tathagatagarbha, and Buddhist logic as the last and most recent. In India, the two main philosophical schools of the Mahayana were the Madhyamaka and the later Yogachara. According to Dan Lusthaus, Madhyamaka and Yogachara have a great deal in common, and the commonality stems from early Buddhism. There were no great Indian teachers associated with tathagatagarbha thought.

Vajrayana (Esoteric Buddhism)

Scholarly research concerning Esoteric Buddhism is still in its early stages and has a number of problems that make research difficult:

1. Vajrayana Buddhism was influenced by Hinduism, and therefore research must include exploring Hinduism as well.
2. The scriptures of Vajrayana have not yet been put in any kind of order.
3. Ritual must be examined as well, not just doctrine.

Spread of Buddhism

The spread of Buddhism within South Asia and beyond.

 

Buddhism may have spread only slowly in India until the time of the Mauryan emperor Ashoka, who was a public supporter of the religion. The support of Aśoka and his descendants led to the construction of more stūpas (Buddhist religious memorials) and to its spread throughout the Maurya empire and into neighbouring lands such as Central Asia and to the island of Sri Lanka. These two missions, in opposite directions, would ultimately lead, in the first case to the spread of Buddhism into China, Korea and Japan, and in the second case, to the emergence of Sinhalese Theravāda Buddhism and its spread from Sri Lanka to much of Southeast Asia.

This period marks the first known spread of Buddhism beyond India. According to the edicts of Aśoka, emissaries were sent to various countries west of India to spread Buddhism (Dharma), particularly in eastern provinces of the neighbouring Seleucid Empire, and even farther to Hellenistic kingdoms of the Mediterranean. It is a matter of disagreement among scholars whether or not these emissaries were accompanied by Buddhist missionaries.

Coin depicting Indo-Greek king Menander, who, according to Buddhist tradition records in the Milinda Panha, converted to the Buddhist faith and became an arhat in the 2nd century BCE (British Museum)

 

In central and west Asia, Buddhist influence grew, through Greek-speaking Buddhist monarchs and ancient Asian trade routes. An example of this is evidenced in Chinese and Pali Buddhist records, such as Milindapanha and the Greco-Buddhist art of Gandhāra. The Milindapanha describes a conversation between a Buddhist monk and the 2nd-century BCE Greek king Menander, after which Menander abdicates and himself goes into monastic life in the pursuit of nirvana. Some scholars have questioned the Milindapanha version, expressing doubts whether Menander was Buddhist or just favourably disposed to Buddhist monks.

The Kushans (mid 1st–3rd century CE) came to control the Silk Road trade through Central and South Asia, which brought them to interact with ancient Buddhist monasteries and societies involved in trade in these regions. They patronized Buddhist institutions, and Buddhist monastery influence, in turn, expanded into a world religion, according to Xinru Liu. Buddhism spread to Khotan and China, eventually to other parts of the far east.

Some of the earliest written documents of the Buddhist faith are the Gandharan Buddhist texts, dating from about the 1st century CE, and connected to the Dharmaguptaka school. These texts are written in the Kharosthi script, a script that was predominantly used in the Greco-Bactrian and Indo-Greek kingdoms of northern India and that played a prominent role in the coinage and inscriptions of their kings.

The Islamic conquest of the Iranian Plateau in the 7th-century, followed by the Muslim conquests of Afghanistan and the later establishment of the Ghaznavid kingdom with Islam as the state religion in Central Asia between the 10th- and 12th-century led to the decline and disappearance of Buddhism from most of these regions.

To East and Southeast Asia

White Horse Temple (est. 68 CE), traditionally held to be at the origin of Chinese Buddhism.

 

Angkor Thom build by Khmer King Jayavarman VII (c. 1120–1218).

 

The Silk Road transmission of Buddhism to China is most commonly thought to have started in the late 2nd or the 1st century CE, though the literary sources are all open to question. The first documented translation efforts by foreign Buddhist monks in China were in the 2nd century CE, probably as a consequence of the expansion of the Kushan Empire into the Chinese territory of the Tarim Basin.

The first documented Buddhist texts translated into Chinese are those of the Parthian An Shigao (148–180 CE). The first known Mahāyāna scriptural texts are translations into Chinese by the Kushan monk Lokakṣema in Luoyang, between 178 and 189 CE. From China, Buddhism was introduced into its neighbors Korea (4th century), Japan (6th–7th centuries), and Vietnam (c. 1st–2nd centuries).

During the Chinese Tang dynasty (618–907), Chinese Esoteric Buddhism was introduced from India and Chan Buddhism (Zen) became a major religion. Chan continued to grow in the Song dynasty (960–1279) and it was during this era that it strongly influenced Korean Buddhism and Japanese Buddhism. Pure Land Buddhism also became popular during this period and was often practiced together with Chan. It was also during the Song that the entire Chinese canon was printed using over 130,000 wooden printing blocks.

During the Indian period of Esoteric Buddhism (from the 8th century onwards), Buddhism spread from India to Tibet and Mongolia. Johannes Bronkhorst states that the esoteric form was attractive because it allowed both a secluded monastic community as well as the social rites and rituals important to laypersons and to kings for the maintenance of a political state during succession and wars to resist invasion. During the Middle Ages, Buddhism slowly declined in India, while it vanished from Persia and Central Asia as Islam became the state religion.

The Theravada school arrived in Sri Lanka sometime in the 3rd century BCE. Sri Lanka became a base for its later spread to southeast Asia after the 5th century CE (Myanmar, Malaysia, Indonesia, Thailand, Cambodia and coastal Vietnam). Theravada Buddhism was the dominant religion in Burma during the Mon Hanthawaddy Kingdom (1287–1552). It also became dominant in the Khmer Empire during the 13th and 14th centuries and in the Thai Sukhothai Kingdom during the reign of Ram Khamhaeng (1237/1247–1298).

Schools and traditions

Distribution of major Buddhist traditions

 

Buddhists generally classify themselves as either Theravada or Mahayana. This classification is also used by some scholars and is the one ordinarily used in the English language. An alternative scheme used by some scholars divides Buddhism into the following three traditions or geographical or cultural areas: Theravada, East Asian Buddhism and Tibetan Buddhism. 

Young monks in Cambodia

 

Some scholars use other schemes. Buddhists themselves have a variety of other schemes. Hinayana (literally "lesser or inferior vehicle") is used by Mahayana followers to name the family of early philosophical schools and traditions from which contemporary Theravada emerged, but as the Hinayana term is considered derogatory, a variety of other terms are used instead, including Śrāvakayāna, Nikaya Buddhism, early Buddhist schools, sectarian Buddhism and conservative Buddhism.

Not all traditions of Buddhism share the same philosophical outlook, or treat the same concepts as central. Each tradition, however, does have its own core concepts, and some comparisons can be drawn between them:

• Both Theravada and Mahayana traditions accept the Buddha as the founder, Theravada considers him unique, but Mahayana considers him one of many Buddhas
• Both accept the Middle Way, dependent origination, the Four Noble Truths, the Noble Eightfold Path and the three marks of existence
• Nirvana is attainable by the monks in Theravada tradition, while Mahayana considers it broadly attainable; Arhat state is aimed for in the Theravada, while Buddhahood is aimed for in the Mahayana
• Religious practice consists of meditation for monks and prayer for laypersons in Theravada, while Mahayana includes prayer, chanting and meditation for both
• Theravada has been a more rationalist, historical form of Buddhism; while Mahayana has included more rituals, mysticism and worldly flexibility in its scope.

Theravada school

A young bhikkhu in Sri Lanka

The Theravada tradition traces its roots to the words of the Buddha preserved in the Pali Canon, and considers itself to be the more orthodox form of Buddhism.

Theravada flourished in south India and Sri Lanka in ancient times; from there it spread for the first time into mainland southeast Asia about the 11th century into its elite urban centres. By the 13th century, Theravada had spread widely into the rural areas of mainland southeast Asia, displacing Mahayana Buddhism and some traditions of Hinduism which had arrived in places such as Thailand, Cambodia, Vietnam, Indonesia and Malaysia around the mid-1st millennium CE. The later traditions were well established in south Thailand and Java by the 7th century, under the sponsorship of the Srivijaya dynasty. The political separation between Khmer and Sukhothai led the Sukhothai king to welcome Sri Lankan emissaries, helping them establish the first Theravada Buddhist sangha in the 13th century, in contrast to the Mahayana tradition of Khmer earlier.

Sinhalese Buddhist reformers in the late nineteenth and early twentieth centuries portrayed the Pali Canon as the original version of scripture. They also emphasized Theravada being rational and scientific.

Theravāda is primarily practised today in Sri Lanka, Burma, Laos, Thailand, Cambodia as well as small portions of China, Vietnam, Malaysia and Bangladesh. It has a growing presence in the west.

Mahayana traditions

The ideas of the 2nd century scholar Nagarjuna helped shape the Mahayana traditions.

 

Mahayana schools consider the Mahayana Sutras as authoritative scriptures and accurate rendering of Buddha's words. These traditions have been the more liberal form of Buddhism allowing different and new interpretations that emerged over time.

Mahayana flourished in India from the time of Ashoka, through to the dynasty of the Guptas (4th to 6th-century). Mahāyāna monastic foundations and centres of learning were established by the Buddhist kings, and the Hindu kings of the Gupta dynasty as evidenced by records left by three Chinese visitors to India. The Gupta dynasty, for example, helped establish the famed Nālandā University in Bihar. These monasteries and foundations helped Buddhist scholarship, as well as studies into non-Buddhist traditions and secular subjects such as medicine, host visitors and spread Buddhism into East and Central Asia.

Native Mahayana Buddhism is practised today in China, Japan, Korea, Singapore, parts of Russia and most of Vietnam (also commonly referred to as "Eastern Buddhism"). The Buddhism practised in Tibet, the Himalayan regions, and Mongolia is also Mahayana in origin, but is discussed below under the heading of Vajrayana (also commonly referred to as "Northern Buddhism"). There are a variety of strands in Eastern Buddhism, of which "the Pure Land school of Mahayana is the most widely practised today.". In most of this area however, they are fused into a single unified form of Buddhism. In Japan in particular, they form separate denominations with the five major ones being: Nichiren, peculiar to Japan; Pure Land; Shingon, a form of Vajrayana; Tendai, and Zen. In Korea, nearly all Buddhists belong to the Chogye school, which is officially Son (Zen), but with substantial elements from other traditions.

Vajrayana traditions

7th-century Potala Palace in Lhasa valley symbolizes Tibetan Buddhism and is a UNESCO world heritage site.

 

The goal and philosophy of the Vajrayāna remains Mahāyānist, but its methods are seen by its followers as far more powerful, so as to lead to Buddhahood in just one lifetime. The practice of using mantras was adopted from Hinduism, where they were first used in the Vedas.

Various classes of Vajrayana literature developed as a result of royal courts sponsoring both Buddhism and Saivism. The Mañjusrimulakalpa, which later came to classified under Kriyatantra, states that mantras taught in the Saiva, Garuda and Vaisnava tantras will be effective if applied by Buddhists since they were all taught originally by Manjushri. The Guhyasiddhi of Padmavajra, a work associated with the Guhyasamaja tradition, prescribes acting as a Saiva guru and initiating members into Saiva Siddhanta scriptures and mandalas. The Samvara tantra texts adopted the pitha list from the Saiva text Tantrasadbhava, introducing a copying error where a deity was mistaken for a place.

Tibetan Buddhism preserves the Vajrayana teachings of eighth-century India. Tantric Buddhism is largely concerned with ritual and meditative practices. A central feature of Buddhist Tantra is deity yoga which includes visualization and identification with an enlightened yidam or meditation deity and its associated mandala. Another element of Tantra is the need for ritual initiation or empowerment (abhiṣeka) by a Guru or Lama. Some Tantras like the Guhyasamāja Tantra features new forms of antinomian ritual practice such as the use taboo substances like alcohol, sexual yoga, and charnel ground practices which evoke wrathful deities.

Zen

Ginkaku-ji, a Zen temple in Kyoto, Japan

 

Zen Buddhism (禅), pronounced Chán in Chinese, seon in Korean or zen in Japanese (derived from the Sanskrit term dhyāna, meaning "meditation") is a form of Mahayana Buddhism found in China, Korea and Japan. It lays special emphasis on meditation, and direct discovery of the Buddha-nature.

Zen Buddhism is divided into two main schools: Rinzai (臨済宗) and Sōtō (曹洞宗), the former greatly favouring the use in meditation on the koan (公案, a meditative riddle or puzzle) as a device for spiritual break-through, and the latter (while certainly employing koans) focusing more on shikantaza or "just sitting".

Zen Buddhism is primarily found in Japan, with some presence in South Korea and Vietnam. The scholars of Japanese Soto Zen tradition in recent times have critiqued the mainstream Japanese Buddhism for dhatu-vada, that is assuming things have substantiality, a view they assert to be non-Buddhist and "out of tune with the teachings of non-Self and conditioned arising", states Peter Harvey.

Buddhism in the modern era

Buryat Buddhist monk in Siberia

Colonial era

Buddhism has faced various challenges and changes during the colonization of Buddhist states by Christian countries and its persecution under modern states. Like other religions, the findings of modern science has challenged its basic premises. One response to some of these challenges has come to be called Buddhist modernism. Early Buddhist modernist figures such as the American convert Henry Olcott (1832– 1907) and Anagarika Dharmapala (1864–1933) reinterpreted and promoted Buddhism as a scientific and rational religion which they saw as compatible with modern science.

East Asian Buddhism meanwhile suffered under various wars which ravaged China during the modern era, such as the Taiping rebellion and the World War II (which also affected Korean Buddhism). During the Republican period (1912–49), a new movement called Humanistic Buddhism was developed by figures such as Taixu (1899–1947), and though Buddhist institutions were destroyed during the Cultural Revolution (1966–76), there has been a revival of the religion in China after 1977. Japanese Buddhism also went through a period of modernization during the Meiji period. In Central Asia meanwhile, the arrival of Communist repression to Tibet (1966–1980) and Mongolia (between 1924–1990) had a strong negative impact on Buddhist institutions, though the situation has improved somewhat since the 80s and 90s.

Buddhism in the West

1893 World Parliament of Religions in Chicago

 

While there were some encounters of Western travelers or missionaries such as St. Francis Xavier and Ippolito Desideri with Buddhist cultures, it was not until the 19th century that Buddhism began to be studied by Western scholars. It was the work of pioneering scholars such as Eugène Burnouf, Max Müller, Hermann Oldenberg and Thomas William Rhys Davids that paved the way for modern Buddhist studies in the West. The English words such as Buddhism, "Boudhist", "Bauddhist" and Buddhist were coined in the early 19th-century in the West, while in 1881, Rhys Davids founded the Pali Text Society – an influential Western resource of Buddhist literature in the Pali language and one of the earliest publisher of a journal on Buddhist studies. It was also during the 19th century that Asian Buddhist immigrants (mainly from China and Japan) began to arrive in Western countries such as the United States and Canada, bringing with them their Buddhist religion. This period also saw the first Westerners to formally convert to Buddhism, such as Helena Blavatsky and Henry Steel Olcott. An important event in the introduction of Buddhism to the West was the 1893 World Parliament of Religions, which for the first time saw well-publicized speeches by major Buddhist leaders alongside other religious leaders. 

The 20th century saw a prolific growth of new Buddhist institutions in Western countries, including the Buddhist Society, London (1924), Das Buddhistische Haus (1924) and Datsan Gunzechoinei in St Petersburg. The publication and translations of Buddhist literature in Western languages thereafter accelerated. After the second world war, further immigration from Asia, globalization, the secularization on Western culture as well a renewed interest in Buddhism among the 60s counterculture led to further growth in Buddhist institutions. Influential figures on post-war Western Buddhism include Shunryu Suzuki, Jack Kerouac, Alan Watts, Thích Nhất Hạnh, and the 14th Dalai Lama. While Buddhist institutions have grown, some of the central premises of Buddhism such as the cycles of rebirth and Four Noble Truths have been problematic in the West. In contrast, states Christopher Gowans, for "most ordinary [Asian] Buddhists, today as well as in the past, their basic moral orientation is governed by belief in karma and rebirth". Most Asian Buddhist laypersons, states Kevin Trainor, have historically pursued Buddhist rituals and practices seeking better rebirth, not nirvana or freedom from rebirth.

Buddhas of Bamiyan, Afghanistan in 1896 (top) and after destruction in 2001 by the Taliban Islamists.

 

Buddhism has spread across the world, and Buddhist texts are increasingly translated into local languages. While Buddhism in the West is often seen as exotic and progressive, in the East it is regarded as familiar and traditional. In countries such as Cambodia and Bhutan, it is recognized as the state religion and receives government support. 

In certain regions such as Afghanistan and Pakistan, militants have targeted violence and destruction of historic Buddhist monuments.

Neo-Buddhism movements

A number of modern movements in Buddhism emerged during the second half of the 20th century. These new forms of Buddhism are diverse and significantly depart from traditional beliefs and practices.

In India, B.R. Ambedkar launched the Navayana tradition – literally, "new vehicle". Ambedkar's Buddhism rejects the foundational doctrines and historic practices of traditional Theravada and Mahayana traditions, such as monk lifestyle after renunciation, karma, rebirth, samsara, meditation, nirvana, Four Noble Truths and others. Ambedkar's Navayana Buddhism considers these as superstitions and re-interprets the original Buddha as someone who taught about class struggle and social equality. Ambedkar urged low caste Indian Dalits to convert to his Marxism-inspired reinterpretation called the Navayana Buddhism, also known as Bhimayana Buddhism. Ambedkar's effort led to the expansion of Navayana Buddhism in India.

The Thai King Mongkut (r. 1851–68), and his son King Chulalongkorn (r. 1868–1910), were responsible for modern reforms of Thai Buddhism. Modern Buddhist movements include Secular Buddhism in many countries, Won Buddhism in Korea, the Dhammakaya movement in Thailand and several Japanese organizations, such as Shinnyo-en, Risshō Kōsei Kai or Soka Gakkai.

Some of these movements have brought internal disputes and strife within regional Buddhist communities. For example, the Dhammakaya movement in Thailand teaches a "true self" doctrine, which traditional Theravada monks consider as heretically denying the fundamental anatta (not-self) doctrine of Buddhism.

Demographics

Buddhism is practised by an estimated 488 million, 495 million, or 535 million people as of the 2010s, representing 7% to 8% of the world's total population. 

Percentage of Buddhists by country, according to the Pew Research Center, as of 2010

 

China is the country with the largest population of Buddhists, approximately 244 million or 18.2% of its total population. They are mostly followers of Chinese schools of Mahayana, making this the largest body of Buddhist traditions. Mahayana, also practised in broader East Asia, is followed by over half of world Buddhists.

According to a demographic analysis reported by Peter Harvey (2013): Mahayana has 360 million adherents; Theravada has 150 million adherents; and Vajrayana has 18.2 million adherents. 

According to Johnson and Grim (2013), Buddhism has grown from a total of 138 million adherents in 1910, of which 137 million were in Asia, to 495 million in 2010, of which 487 million are in Asia. Over 98% of all Buddhists live in the Asia-Pacific and South Asia region. North America had about 3.9 million Buddhists, Europe 1.3 million, while South America, Africa and the Middle East had an estimated combined total of about 1 million Buddhists in 2010.

Buddhism is the dominant religion in Bhutan, Myanmar, Cambodia, Tibet, Laos, Mongolia, Sri Lanka and Thailand. Large Buddhist populations live in China (18%), Japan (36%), Taiwan (35%), Macau (17%), North Korea (14%), Nepal (11%), Vietnam (10%), Singapore (33%), Hong Kong (15%) and South Korea (23%).

Buddhism is also growing by conversion. In United States, only about a third (32%) of Buddhists in the United States are Asian; a majority (53%) are white. Buddhism in the America is primarily made up of native-born adherents, whites and converts. In New Zealand, about 25%-35% of the total Buddhists are converts to Buddhism. 

After China, where nearly half of the worldwide Buddhists live, the 10 countries with the largest Buddhist population densities are:

Buddhism by percentage as of 2010

Country	Estimated Buddhist population	Buddhists as % of total population
Cambodia	13,701,660	96.9%
Thailand	64,419,840	93.2%
Burma	38,415,960	80.1%
Bhutan	563,000	74.7%
Sri Lanka	14,455,980	69.3%
Laos	4,092,000	66.0%
Mongolia	1,520,760	55.1%
Japan	45,807,480 or 84,653,000	36.2% or 67%
Singapore	1,725,510	33.9%
Taiwan	4,945,600 or 8,000,000	21.1% or 35%
China	185,000,000+	15.9%

Planet Nine

From Wikipedia, the free encyclopedia

Planet Nine

Artist's impression of Planet Nine eclipsing the central Milky Way, with the Sun in the distance; Neptune's orbit is shown as a small ellipse around the Sun
Orbital characteristics
Semi-major axis	400–800 AU
Eccentricity	0.2–0.5
Inclination	15°–25°
Argument of perihelion	150° (est.)
Physical characteristics
Mass	5–10 M⊕ (est.)
Apparent magnitude	>22.5 (est.)

Planet Nine is a hypothetical planet in the outer region of the Solar System. Its gravitational effects could explain the unusual clustering of orbits for a group of extreme trans-Neptunian objects (eTNOs), bodies beyond Neptune that orbit the Sun at distances averaging more than 250 times that of the Earth. These eTNOs tend to make their closest approaches to the Sun in one sector, and their orbits are similarly tilted. These improbable alignments suggest that an undiscovered planet may be shepherding the orbits of the most distant known Solar System objects.

This undiscovered super-Earth-sized planet would have a predicted mass of five to ten times that of the Earth, and an elongated orbit 400 to 800 times as far from the Sun as the Earth. Konstantin Batygin and Michael E. Brown suggest that Planet Nine could be the core of a giant planet that was ejected from its original orbit by Jupiter during the genesis of the Solar System. Others propose that the planet was captured from another star, was once a rogue planet, or that it formed on a distant orbit and was pulled into an eccentric orbit by a passing star.

As of the end of 2018, no observation of Planet Nine had been announced. While sky surveys such as Wide-field Infrared Survey Explorer (WISE) and Pan-STARRS did not detect Planet Nine, they have not ruled out the existence of a Neptune-diameter object in the outer Solar System. The ability of these past sky surveys to detect Planet Nine were dependent on its location and characteristics. Further surveys of the remaining regions are ongoing using NEOWISE and the 8-meter Subaru Telescope. Unless Planet Nine is observed, its existence is purely conjectural. Several alternative theories have been proposed to explain the observed clustering of TNOs.

History

Following the discovery of Neptune in 1846, there was considerable speculation that another planet might exist beyond its orbit. The best-known of these theories predicted the existence of a distant planet that was influencing the orbits of Uranus and Neptune. After extensive calculations Percival Lowell predicted the possible orbit and location of the hypothetical trans-Neptunian planet and began an extensive search for it in 1906. He called the hypothetical object Planet X, a name previously used by Gabriel Dallet. Clyde Tombaugh continued Lowell's search and in 1930 discovered Pluto, but it was soon determined to be too small to qualify as Lowell's Planet X. After Voyager 2's flyby of Neptune in 1989, the difference between Uranus' predicted and observed orbit was determined to have been due to the use of a previously inaccurate mass of Neptune.

Attempts to detect planets beyond Neptune by indirect means such as orbital perturbation date back to before the discovery of Pluto. Among the first was George Forbes who postulated the existence of two trans-Neptunian planets in 1880. One would have an average distance from the Sun, or semi-major axis, of 100 astronomical units (AU), 100 times that of the Earth. The second would have a semimajor axis of 300 AU. His work is considered similar to more recent Planet Nine theories in that the planets would be responsible for a clustering of the orbits of several objects, in this case the aphelion distances of periodic comets similar to that of the Jupiter-family comets.

The discovery of Sedna's peculiar orbit in 2004 led to speculation that it had encountered a massive body other than one of the eight known planets. Sedna's orbit is detached, with a perihelion distance of 76 AU that is too large to be due to gravitational interactions with Neptune. Several authors proposed that Sedna entered this orbit after encountering an unknown planet on a distant orbit, a member of the open cluster that formed with the Sun, or another star that later passed near the Solar System. The announcement in March 2014 of the discovery of a second sednoid with a perihelion distance of 80 AU, 2012 VP113, in a similar orbit led to renewed speculation that an unknown super-Earth remained in the distant Solar System.

At a conference in 2012, Rodney Gomes proposed that an undetected planet was responsible for the orbits of some eTNOs with detached orbits and the large semi-major axis Centaurs, small Solar System bodies that cross the orbits of the giant planets. The proposed Neptune-massed planet would be in a distant (1500 AU), eccentric (eccentricity 0.4), and inclined (inclination 40°) orbit. Like Planet Nine it would cause the perihelia of objects with semi-major axes greater than 300 AU to oscillate, delivering some into planet-crossing orbits and others into detached orbits like that of Sedna. An article by Gomes, Soares, and Brasser was published in 2015, detailing their arguments.

In 2014, astronomers Chad Trujillo and Scott S. Sheppard noted the similarities in the orbits of Sedna and 2012 VP₁₁₃ and several other eTNOs. They proposed that an unknown planet in a circular orbit between 200 and 300 AU was perturbing their orbits. Later, in 2015, Raúl and Carlos de la Fuente Marco argued that two massive planets in orbital resonance were necessary to produce the similarities of so many orbits.

Batygin and Brown hypothesis

One hypothetical path through the sky of Planet Nine near aphelion crossing Orion west to east with about 2,000 years of motion. It is derived from that employed in the artistic conception on Brown's blog.

 

In early 2016, California Institute of Technology's Batygin and Brown described how the similar orbits of six eTNOs could be explained by Planet Nine and proposed a possible orbit for the planet. This hypothesis could also explain eTNOs with orbits perpendicular to the inner planets and others with extreme inclinations, and had been offered as an explanation of the tilt of the Sun's axis.

Orbit

Planet Nine is hypothesized to follow an elliptical orbit around the Sun with an eccentricity of 0.2 to 0.5. The planet's semi-major axis is estimated to be 400 AU to 800 AU, roughly 13 to 26 times the distance from Neptune to the Sun. Its inclination to the ecliptic, the plane of the Earth's orbit, is projected to be 15° to 25°. The aphelion, or farthest point from the Sun, would be in the general direction of the constellation of Taurus, whereas the perihelion, the nearest point to the Sun, would be in the general direction of the southerly areas of Serpens (Caput), Ophiuchus, and Libra. Brown thinks that if Planet Nine is confirmed to exist, a probe could reach it in as little as 20 years by using a powered slingshot trajectory around the Sun.

Mass and radius

The planet is estimated to have 5 to 10 times the mass of Earth and a radius of 2 to 4 times Earth's. Brown thinks that if Planet Nine exists, its mass is sufficient to clear its orbit of large bodies in 4.6 billion years, the age of the Solar System, and that its gravity dominates the outer edge of the Solar System, which is sufficient to make it a planet by current definitions. Astronomer Jean-Luc Margot has also stated that Planet Nine satisfies his criteria and would qualify as a planet if and when it is detected.

Origin

Several possible origins for Planet Nine have been examined including its ejection from the neighborhood of the known giant planets, capture from another star, and in situ formation. In their initial article, Batygin and Brown proposed that Planet Nine formed closer to the Sun and was ejected into a distant eccentric orbit following a close encounter with Jupiter or Saturn during the nebular epoch. The gravity of a nearby star, or drag from the gaseous remnants of the Solar nebula, then reduced the eccentricity of its orbit. This raised its perihelion, leaving it in a very wide but stable orbit beyond the influence of the other planets. Had it not been flung into the Solar System's farthest reaches, Planet Nine could have accreted more mass from the proto-planetary disk and developed into the core of a gas giant. Instead, its growth was halted early, leaving it with a lower mass than Uranus or Neptune.

Dynamical friction from a massive belt of planetesimals could also enable Planet Nine's capture in a stable orbit. Recent models propose that a 60–130 Earth mass disk of planetesimals could have formed as the gas was cleared from the outer parts of the proto-planetary disk. As Planet Nine passed through this disk its gravity would alter the paths of the individual objects in a way that reduced Planet Nine's velocity relative to it. This would lower the eccentricity of Planet Nine and stabilize its orbit. If this disk had a distant inner edge, 100–200 AU, a planet encountering Neptune would have a 20% chance of being captured in an orbit similar to that proposed for Planet Nine, with the observed clustering more likely if the inner edge is at 200 AU. Unlike the gas nebula, the planetesimal disk is likely to have been long lived, potentially allowing a later capture.

Planet Nine could have been captured from outside the Solar System during a close encounter between the Sun and another star. If a planet was in a distant orbit around this star, three-body interactions during the encounter could alter the planet's path, leaving it in a stable orbit around the Sun. A planet originating in a system without Jupiter-massed planets could remain in a distant eccentric orbit for a longer time, increasing its chances of capture. The wider range of possible orbits would reduce the odds of its capture in a relatively low inclination orbit to 1–2 percent. This process could also occur with rogue planets, but the likelihood of their capture is much smaller, with only 0.05–0.10% being captured in orbits similar to that proposed for Planet Nine.

An encounter with another star could also alter the orbit of a distant planet, shifting it from a circular to an eccentric orbit. The in situ formation of a planet at this distance would require a very massive and extensive disk, or the outward drift of solids in a dissipating disk forming a narrow ring from which the planet accreted over a billion years. If a planet formed at such a great distance while the Sun was in its original cluster, the probability of it remaining bound to the Sun in a highly eccentric orbit is roughly 10%. A previous article reported that if the massive disk extended beyond 80 AU some objects scattered outward by Jupiter and Saturn would have been left in high inclination (inc > 50°), low eccentricity orbits which have not been observed. An extended disk would also have been subject to gravitational disruption by passing stars and by mass loss due to photoevaporation while the Sun remained in the open cluster where it formed.

Evidence

The gravitational influence of Planet Nine would explain four peculiarities of the Solar System:

• The clustering of the orbits of eTNOs;
• The high perihelia of objects like 90377 Sedna that are detached from Neptune's influence;
• The high inclinations of eTNOs with orbits roughly perpendicular to the orbits of the eight known planets;
• High-inclination trans-Neptunian objects (TNOs) with semi-major axis less than 100 AU.

Planet Nine was initially proposed to explain the clustering of orbits, via a mechanism that would also explain the high perihelia of objects like Sedna. The evolution of some of these objects into perpendicular orbits was unexpected, but found to match objects previously observed. The orbits of some objects with perpendicular orbits were later found to evolve toward smaller semimajor axes when the other planets were included in simulations. Although other mechanisms have been offered for many of these peculiarities, the gravitational influence of Planet Nine is the only one that explains all four. The gravity of Planet Nine could also increase the inclinations of other objects that cross its orbit, however, leaving the short-period comets with a broader inclination distribution than is observed. Previously Planet Nine was hypothesized to be responsible for the 6 degree tilt of the Sun's axis relative to the orbits of the planets. Recent updates to its predicted orbit and mass limit this shift to ~1 degree.

Observations: Orbital clustering of high perihelion objects

Diagram illustrating the true anomaly, argument of periapsis, longitude of ascending node, and inclination of a celestial body.

 

The clustering of the orbits of TNOs with large semi-major axes was first described by Trujillo and Sheppard, who noted similarities between the orbits of Sedna and 2012 VP₁₁₃. Without the presence of Planet Nine, these orbits should be distributed randomly, without preference for any direction. Upon further analysis, Trujillo and Sheppard observed that the arguments of perihelion of 12 TNOs with perihelia greater than 30 AU and semi-major axes greater than 150 AU were clustered near zero degrees, meaning that they rise through the ecliptic when they are closest to the sun. Trujillo and Sheppard proposed that this alignment was caused by a massive unknown planet beyond Neptune via the Kozai mechanism. For objects with similar semi-major axes the Kozai mechanism would confine their arguments of perihelion to near 0 or 180 degrees. This confinement allows objects with eccentric and inclined orbits to avoid close approaches to the planet because they would cross the plane of the planet's orbit at their closest and farthest points from the Sun, and cross the planet's orbit when they are well above or below its orbit. Trujillo and Sheppard's hypothesis about how the objects would be aligned by the Kozai mechanism has been supplanted by further analysis and evidence.

Batygin and Brown, looking to refute the mechanism proposed by Trujillo and Sheppard, also examined the orbits of the TNOs with large semi-major axes. After eliminating the objects in Trujillo and Sheppard's original analysis that were unstable due to close approaches to Neptune or were affected by Neptune's mean-motion resonances, Batygin and Brown determined that the arguments of perihelion for the remaining six objects (Sedna, 2012 VP₁₁₃, 2004 VN₁₁₂, 2010 GB174, 2000 CR₁₀₅, and 2010 VZ₉₈) were clustered around 318°±8°. This finding did not agree with how the Kozai mechanism would tend to align orbits with arguments of perihelion at 0° or 180°.

Orbital correlations among six distant trans-Neptunian objects led to the hypothesis.

 

Batygin and Brown also found that the orbits of the six eTNOs with semi-major axes greater than 250 AU and perihelia beyond 30 AU (Sedna, 2012 VP₁₁₃, 2004 VN₁₁₂, 2010 GB₁₇₄, 2007 TG422, and 2013 RF98) were aligned in space with their perihelia in roughly the same direction, resulting in a clustering of their longitudes of perihelion, the location where they make their closest approaches to the Sun. The orbits of the six objects were also tilted with respect to that of the ecliptic and approximately coplanar, producing a clustering of their longitudes of ascending nodes, the directions where they each rise through the ecliptic. They determined that there was only a 0.007% likelihood that this combination of alignments was due to chance. These six objects had been discovered by six different surveys on six different telescopes. That made it less likely that the clumping might be due to an observation bias such as pointing a telescope at a particular part of the sky. The observed clustering should be smeared out in a few hundred million years due to the locations of the perihelia and the ascending nodes changing, or precessing, at differing rates due to their varied semi-major axes and eccentricities. This indicates that the clustering could not be due to an event in the distant past, such as a passing star, and is most likely maintained by the gravitational field of an object orbiting the Sun.

Two of the six objects (2013 RF₉₈ and 2004 VN₁₁₂) also have very similar orbits and spectra. This has led to the suggestion that they were a binary object disrupted near aphelion during an encounter with a distant object. The disruption of a binary would require a relatively close encounter, which becomes less likely at large distances from the Sun.

In a later article Trujillo and Sheppard noted a correlation between the longitude of perihelion and the argument of perihelion of the TNOs with semi-major axes greater than 150 AU. Those with a longitude of perihelion of 0–120° have arguments of perihelion between 280–360°, and those with longitude of perihelion between 180° and 340° have arguments of perihelion between 0° and 40°. The statistical significance of this correlation was 99.99%. They suggested that the correlation is due to the orbits of these objects avoiding close approaches to a massive planet by passing above or below its orbit.

A 2017 article by Carlos and Raul de la Fuente Marcos noted that distribution of the distances to the ascending nodes of the eTNOs, and those of centaurs and comets with large semi-major axes, may be bimodal. They suggest it is due to the eTNOs avoiding close approaches to a planet with a semi-major axis of 300–400 AU.

The extreme trans-Neptunian object orbits

Six original and eight additional eTNO objects orbits with current positions near their perihelion in purple, with hypothetical Planet Nine orbit in green

 

Close up view of 13 eTNO current positions

Simulations: Observed clustering reproduced

The clustering of the orbits of eTNOs and raising of their perihelia is reproduced in simulations that include Planet Nine. In simulations conducted by Batygin and Brown, swarms of objects with large semi-major axes that began with random orientations were sculpted into roughly collinear and coplanar groups of spatially confined orbits by a massive distant planet in a highly eccentric orbit. The objects' perihelia tended to point in the same direction and the objects' orbits tended to align in the same plane. Many of these objects entered high-perihelion orbits like Sedna and, unexpectedly, some entered perpendicular orbits that Batygin and Brown later noticed had been previously observed.

In their original analysis Batygin and Brown found that the distribution of the orbits of the first six eTNOs was best reproduced in simulations using a 10 Earth mass planet in the following orbit:

• Semi-major axis a ≈ 700 AU (orbital period 700^1.5=18,520 years)
• Eccentricity e ≈ 0.6, (perihelion ≈ 280 AU, aphelion ≈ 1,120 AU)
• Inclination i ≈ 30° to the ecliptic
• Longitude of the ascending node Ω ≈ 94°.
• Argument of perihelion ω ≈ 141° and longitude of perihelion ϖ = 235°±12°

These parameters for Planet Nine produce different simulated effects on TNOs. Objects with semi-major axis greater than 250 AU are strongly anti-aligned with Planet Nine, with perihelia opposite Planet Nine's perihelion. Objects with semi-major axes between 150 AU and 250 AU are weakly aligned with Planet Nine, with perihelia in the same direction as Planet Nine's perihelion. Little effect is found on objects with semi-major axes less than 150 AU. The simulations also revealed that objects with semimajor axis greater than 250 AU could have stable, aligned orbits if they had lower eccentricities. These objects have yet to be observed.

Other possible orbits for Planet Nine were also examined, with semi-major axes between 400 AU and 1500 AU, eccentricites up to 0.8, and a wide range of inclinations. These orbits yield varied results. Batygin and Brown found that orbits of the eTNOs were more likely to have similar tilts if Planet Nine had a higher inclination, but anti-alignment also decreased. Simulations by Becker et al. showed that their orbits were more stable if Planet Nine had a smaller eccentricity, but that anti-alignment was more likely at higher eccentricities. Lawler et al. found that the population captured in orbital resonances with Planet Nine was smaller if it had a circular orbit, and that fewer objects reached high inclination orbits. Investigations by Cáceres et al. showed that the orbits of the eTNOs were better aligned if Planet Nine had a lower perihelion orbit, but its perihelion would need to be higher than 90 AU. Later investigations by Batygin et al. found that higher eccentricity orbits reduced the average tilts of the eTNOs orbits. While there are many possible combinations of orbital parameters and masses for Planet Nine, none of the alternative simulations have been better at predicting the observed alignment of objects in the Solar System. The discovery of additional distant Solar System objects would allow astronomers to make more accurate predictions about the orbit of the hypothesized planet. These may also provide further support for, or refutation of, the Planet Nine hypothesis.

Dynamics: How Planet Nine modifies the orbits of eTNOs

Long term evolution of eTNOs induced by Planet Nine for objects with semi-major axis of 250 AU. Blue: anti-aligned, Red: aligned, Green: metastable, Orange: circulating. Crossing orbits above black line.

Planet Nine modifies the orbits of eTNOs via a combination of effects. On very long timescales Planet Nine exerts a torque on the orbits of the eTNOs that varies with the alignment of their orbits with Planet Nine's. The resulting exchanges of angular momentum cause the perihelia to rise, placing them in Sedna-like orbits, and later fall, returning them to their original orbits after several hundred million years. The motion of their directions of perihelion also reverses when their eccentricities are small, keeping the objects anti-aligned, see blue curves on diagram, or aligned, red curves. On shorter timescales mean-motion resonances with Planet Nine provides phase protection, which stabilizes their orbits by slightly altering the objects' semi-major axes, keeping their orbits synchronized with Planet Nine's and preventing close approaches. The gravity of Neptune and the other giant planets, and the inclination of Planet Nine's orbit, weaken this protection. This results in a chaotic variation of semi-major axes as objects hop between resonances, including high order resonances such as 27:17, on million-year timescales. The mean-motion resonances may not be necessary for the survival of eTNOs if they and Planet Nine are both on inclined orbits. The orbital poles of the objects precess around, or circle, the pole of the Solar System's Laplace plane. At large semi-major axes the Laplace plane is warped toward the plane of Planet Nine's orbit. This causes orbital poles of the eTNOs on average to be tilted toward one side and their longitudes of ascending nodes to be clustered.

Objects in perpendicular orbits with large semi-major axis

The orbits of the five objects with high-inclination orbits (nearly perpendicular to the ecliptic) are shown here as cyan ellipses with the hypothetical Planet Nine in orange.

 

Planet Nine can deliver eTNOs into orbits roughly perpendicular to the ecliptic. Several objects with high inclinations, greater than 50°, and large semi-major axes, above 250 AU, have been observed. These orbits are produced when some low inclination eTNOs enter a secular resonance with Planet Nine upon reaching low eccentricity orbits. The resonance causes their eccentricities and inclinations to increase, delivering the eTNOs into perpendicular orbits with low perihelia where they are more readily observed. The eTNOs then evolve into retrograde orbits with lower eccentricities, after which they pass through a second phase of high eccentricity perpendicular orbits, before returning to low eccentricity and inclination orbits. The secular resonance with Planet Nine involves a linear combination of the orbit's arguments and longitudes of perihelion: Δϖ – 2ω. Unlike the Kozai mechanism this resonance causes objects to reach their maximum eccentricities when in nearly perpendicular orbits. In simulations conducted by Batygin and Morbidelli this evolution was relatively common, with 38% of stable objects undergoing it at least once. The arguments of perihelion of these objects are clustered near or opposite Planet Nine's and their longitudes of ascending node are clustered around 90° in either direction from Planet Nine's when they reach low perihelia. This is in rough agreement with observations with the differences attributed to distant encounters with the known giant planets.

Orbits of high-inclination objects

A population of high-inclination TNOs with semi-major axes less than 100 AU may be generated by the combined effects of Planet Nine and the other giant planets. The eTNOs that enter perpendicular orbits have perihelia low enough for their orbits to intersect those of Neptune or the other giant planets. An encounter with one of these planets can lower an eTNO's semi-major axis to below 100 AU, where the object's orbits is no longer controlled by Planet Nine, leaving it in an orbit like 2008 KV42. The predicted orbital distribution of the longest lived of these objects is nonuniform. Most would have orbits with perihelia ranging from 5 AU to 35 AU and inclinations below 110 degree; beyond a gap with few objects are would be others with inclinations near 150 degrees and perihelia near 10 AU. Previously it was proposed that these objects originated in the Oort Cloud, a theoretical cloud of icy planetesimals surrounding the Sun at distances of 2,000 to 200,000 AU.

Oort cloud and comets

Planet Nine would alter the source regions and the inclination distribution of comets. In simulations of the migration of the giant planets described by the Nice model fewer objects are captured in the Oort cloud when Planet Nine is included. Other objects would be captured in a cloud of objects dynamically controlled by Planet Nine. This Planet Nine cloud, made up of the eTNOs and the perpendicular objects, would extend from semimajor axes of 200 AU to 3000 AU and contain roughly 0.3–0.4 Earth masses. When the perihelia of objects in the Planet Nine cloud drop low enough for them to encounter the other planets some would be scattered into orbits that enter the inner Solar System where they could be observed as comets. If Planet Nine exists these would make up roughly one third of the Halley-type comets. Planet Nine would also alter the orbits of the scattering disk objects, those with semi-major axes greater than 50 AU and perihelia near Neptune's orbit, that cross its orbit, increasing their inclinations. This would increase the inclinations of the Jupiter-family comets derived from that population leaving them with a broader inclination distribution than is observed. Recent estimates of a smaller mass and eccentricity for Planet Nine would reduce its effect on these inclinations.

Reception

Batygin was cautious in interpreting the results of the simulation developed for his and Brown's research article, saying, "Until Planet Nine is caught on camera it does not count as being real. All we have now is an echo." Brown put the odds for the existence of Planet Nine at about 90%. Greg Laughlin, one of the few researchers who knew in advance about this article, gives an estimate of 68.3%. Other skeptical scientists demand more data in terms of additional KBOs to be analyzed or final evidence through photographic confirmation. Brown, though conceding the skeptics' point, still thinks that there is enough data to mount a search for a new planet.

The Planet Nine hypothesis is supported by several astronomers and academics. Jim Green, director of NASA's Science Mission Directorate, said, "the evidence is stronger now than it's been before". But Green also cautioned about the possibility of other explanations for the observed motion of distant eTNOs and, quoting Carl Sagan, he said, "extraordinary claims require extraordinary evidence." Massachusetts Institute of Technology Professor Tom Levenson concluded that, for now, Planet Nine seems the only satisfactory explanation for everything now known about the outer regions of the Solar System. Astronomer Alessandro Morbidelli, who reviewed the research article for The Astronomical Journal, concurred, saying, "I don't see any alternative explanation to that offered by Batygin and Brown."

Astronomer Renu Malhotra remains agnostic about Planet Nine, but noted that she and her colleagues have found that the orbits of eTNOs seem tilted in a way that is difficult to otherwise explain. "The amount of warp we see is just crazy," she said. "To me, it's the most intriguing evidence for Planet Nine I've run across so far."

Other authorities have varying degrees of skepticism. American astrophysicist Ethan Siegel, who previously speculated that planets may have been ejected from the Solar System during an early dynamical instability, is skeptical of the existence of an undiscovered planet in the Solar System. In a 2018 article discussing a survey that did not find evidence of clustering of the eTNOs' orbits he suggests the previously observed clustering could have been the result of observing bias and claims most scientists think Planet Nine does not exist. Planetary scientist Hal Levison thinks that the chance of an ejected object ending up in the inner Oort cloud is only about 2%, and speculates that many objects must have been thrown past the Oort cloud if one has entered a stable orbit.

Alternative hypotheses

Temporary or coincidental clustering

The results of the Outer Solar System Survey (OSSOS) suggest that the observed clustering is the result of a combination of observing bias and small number statistics. OSSOS, a well-characterized survey of the outer Solar System with known biases, observed eight objects with semi-major axis > 150 AU with orbits oriented on a wide range of directions. After accounting for the observational biases of the survey, no evidence for the arguments of perihelion (ω) clustering identified by Trujillo and Sheppard was seen, and the orientation of the orbits of the objects with the largest semi-major axis was statistically consistent with random. This result differed from an analysis of discovery biases in the previously observed eTNOs by Mike Brown. He found that after observing biases were accounted for the clustering of longitudes of perihelion of 10 known eTNOs would be observed only 1.2% of the time if their actual distribution was uniform. When combined with the odds of the observed clustering of the arguments of perihelion the probability was 0.025%. A later analysis of the discovery biases of 14 eTNOs by Brown and Batygin found a probability of the observed clustering of the longitudes of perihelion and the orbital pole locations of 0.2%.

Simulations of 15 known objects evolving under the influence of Planet Nine also revealed differences with observations. Cory Shankman and his colleagues included Planet Nine in a simulation of many clones (objects with similar orbits) of 15 objects with semi-major axis more than 150 AU and perihelion more than 30 AU. While they observed alignment of the orbits opposite that of Planet Nine's for the objects with semi-major axis greater than 250 AU, clustering of the arguments of perihelion was not seen. Their simulations also showed that the perihelia of the eTNOs rose and fell smoothly, leaving many with perihelion distances between 50 AU and 70 AU where none had been observed, and predicted that there would be many other unobserved objects. These included a large reservoir of high-inclination objects that would have been missed due to most observations being at small inclinations, and a large population of objects with perihelia so distant that they would be too faint to observe. Many of the objects were also ejected from the Solar System after encountering the other giant planets. The large unobserved populations and the loss of many objects led Shankman et al. to estimate that the mass of the original population was tens of Earth masses, requiring that a much larger mass had been ejected during the early Solar System.^[L] Shankman et al. concluded that the existence of Planet Nine is unlikely and that the currently observed alignment of the existing eTNOs is a temporary phenomenon that will disappear as more objects are detected.

Inclination instability in a massive disk

Ann-Marie Madigan and Michael McCourt postulate that an inclination instability in a distant massive belt is responsible for the alignment of the arguments of perihelion of the eTNOs. An inclination instability could occur in a disk of particles with high eccentricity orbits (e>0.6) around a central body, such as the Sun. The self-gravity of this disk would cause its spontaneous organization, increasing the inclinations of the objects and aligning the arguments of perihelion, forming it into a cone above or below the original plane. This process would require an extended time and significant mass of the disk, on the order of a billion years for a 1–10 Earth-mass disk. While an inclination instability could align the arguments of perihelion and raise perihelia, producing detached objects, it would not align the longitudes of perihelion. Mike Brown considers Planet Nine a more probable explanation, noting that current surveys have not revealed a large enough scattered-disk to produce an "inclination instability". In Nice model simulations of the Solar System that included the self-gravity of the planetesimal disk an inclination instability did not occur. Instead, the simulation produced a rapid precession of the objects' orbits and most of the objects were ejected on too short of a timescale for an inclination instability to occur.

Shepherding by a massive disk

Antranik Sefilian and Jihad Touma propose that a massive disk of moderately eccentric TNOs is responsible for the clustering of the longitudes of perihelion of the eTNOs. Their predicted 10 Earth-mass disk would contain TNOs with aligned orbits and eccentricities that increased with their semimajor axes ranging from zero to 0.165. The gravitational effects of this disk would offset the forward precession driven by the giant planets so that the orbital orientations of its individual objects are maintained. The orbits of objects with high eccentricities, such as the observed eTNOs, would be stable and have roughly fixed orientations, or longitudes of perihelion, if their orbits were anti-aligned with this disk. Although Brown thinks the proposed disk could explain the observed clustering of the eTNOs, he finds it implausible that the disk could survive over the age of the Solar System. Batygin thinks that there is insufficient mass in the Kuiper belt to explain the formation of the disk and asks "why would the protoplanetary disk end near 30 AU and restart beyond 100 AU?"

Planet in lower eccentricity orbit

The Planet Nine hypothesis includes a set of predictions about the mass and orbit of the planet. An alternative theory predicts a planet with different orbital parameters. Malhotra, Kathryn Volk, and Xianyu Wang have proposed that the four detached objects with the longest orbital periods, those with perihelia beyond 40 AU and semi-major axes greater than 250 AU, are in n:1 or n:2 mean-motion resonances with a hypothetical planet. Two other objects with semi-major axes greater than 150 AU are also potentially in resonance with this planet. Their proposed planet could be on a lower eccentricity, low inclination orbit, with eccentricity e less than 0.18 and inclination i ≈ 11°. The eccentricity is limited in this case by the requirement that close approaches of 2010 GB₁₇₄ to the planet are avoided. If the eTNOs are in periodic orbits of the third kind, with their stability enhanced by the libration of their arguments of perihelion, the planet could be in a higher inclination orbit, with i ≈ 48°. Unlike Batygin and Brown, Malhotra, Volk and Wang do not specify that most of the distant detached objects would have orbits anti-aligned with the massive planet.

Alignment due to the Kozai mechanism

Trujillo and Sheppard argued in 2014 that a massive planet in a circular orbit with an average distance between 200 AU and 300 AU was responsible for the clustering of the arguments of perihelion of twelve TNOs with large semi-major axes. Trujillo and Sheppard identified a clustering near zero degrees of the arguments of perihelion of the orbits of twelve TNOs with perihelia greater than 30 AU and semi-major axes greater than 150 AU. After numerical simulations showed that the arguments of perihelion should circulate at varying rates, leaving them randomized after billions of years, they suggested that a massive planet in a circular orbit at a few hundred astronomical units was responsible for this clustering. This massive planet would cause the arguments of perihelion of the TNOs to librate about 0° or 180° via the Kozai mechanism so that their orbits crossed the plane of the planet's orbit near perihelion and aphelion, the closest and farthest points from the planet. In numerical simulations including a 2–15 Earth mass body in a circular low-inclination orbit between 200 AU and 300 AU the arguments of perihelia of Sedna and 2012 VP₁₁₃ librated around 0° for billions of years (although the lower perihelion objects did not) and underwent periods of libration with a Neptune mass object in a high inclination orbit at 1,500 AU. Another process such as a passing star would be required to account for the absence of objects with arguments of perihelion near 180°.

These simulations showed the basic idea of how a single large planet can shepherd the smaller TNOs into similar types of orbits. They were basic proof of concept simulations that did not obtain a unique orbit for the planet as they state there are many possible orbital configurations the planet could have. Thus they did not fully formulate a model that successfully incorporated all the clustering of the eTNOs with an orbit for the planet. But they were the first to notice there was a clustering in the orbits of TNOs and that the most likely reason was from an unknown massive distant planet. Their work is very similar to how Alexis Bouvard noticed Uranus' motion was peculiar and suggested that it was likely gravitational forces from an unknown 8th planet, which led to the discovery of Neptune.

Raúl and Carlos de la Fuente Marcos proposed a similar model but with two distant planets in resonance. An analysis by Carlos and Raúl de la Fuente Marcos with Sverre J. Aarseth confirmed that the observed alignment of the arguments of perihelion could not be due to observational bias. They speculated that instead it was caused by an object with a mass between that of Mars and Saturn that orbited at some 200 AU from the Sun. Like Trujillo and Sheppard they theorized that the TNOs are kept bunched together by a Kozai mechanism and compared their behavior to that of Comet 96P/Machholz under the influence of Jupiter. They also struggled to explain the orbital alignment using a model with only one unknown planet, and therefore suggested that this planet is itself in resonance with a more-massive world about 250 AU from the Sun. In their article, Brown and Batygin noted that alignment of arguments of perihelion near 0° or 180° via the Kozai mechanism requires a ratio of the semi-major axes nearly equal to one, indicating that multiple planets with orbits tuned to the data set would be required, making this explanation too unwieldy.

Detection attempts

Visibility and location

Due to its extreme distance from the Sun, Planet Nine would reflect little sunlight, potentially evading telescope sightings. It is expected to have an apparent magnitude fainter than 22, making it at least 600 times fainter than Pluto. If Planet Nine exists and is close to perihelion, astronomers could identify it based on existing images. At aphelion, the largest telescopes would be required, but if the planet is currently located in between, many observatories could spot Planet Nine. Statistically, the planet is more likely to be closer to its aphelion at a distance greater than 600 AU. This is because objects move more slowly when near their aphelion, in accordance with Kepler's second law. Planet Nine is predicted to be brighter, magnitude 21–22, if it is near the small end of its estimated mass range because it would need to be closer to have the same dynamical effect.

Searches of existing data

The search of databases of stellar objects by Batygin and Brown has already excluded much of the sky along Planet Nine's predicted orbit. The remaining regions include the direction of its aphelion, where it would be too faint to be spotted by these surveys, and near the plane of the Milky Way, where it would be difficult to distinguish from the numerous stars. This search included the archival data from the Catalina Sky Survey to magnitude c. 19, Pan-STARRS to magnitude 21.5, and infrared data from the Wide-field Infrared Survey Explorer (WISE) satellite.

Other researchers have been conducting searches of existing data. David Gerdes, who helped develop the camera used in the Dark Energy Survey, claims that software designed to identify distant Solar System objects such as 2014 UZ224 could find Planet Nine if it was imaged as part of that survey, which covered a quarter of the southern sky. Michael Medford and Danny Goldstein, graduate students at the University of California, Berkeley, are also examining archived data using a technique that combines images taken at different times. Using a supercomputer they will offset the images to account for the calculated motion of Planet Nine, allowing many faint images of a faint moving object to be combined to produce a brighter image. A search combining multiple images collected by WISE and NEOWISE data has also been conducted without detecting Planet Nine. This search covered regions of the sky away from the galactic plane at the "W1" wavelength (the 3.4 μm wavelength used by WISE) and is estimated to be able to detect a 10-Earth mass object out to 800–900 AU.

Ongoing searches

Because the planet is predicted to be visible in the Northern Hemisphere, the primary search is expected to be carried out using the Subaru Telescope, which has both an aperture large enough to see faint objects and a wide field of view to shorten the search. Two teams of astronomers—Batygin and Brown, as well as Trujillo and Sheppard—are undertaking this search together, and both teams expect the search to take up to five years. Brown and Batygin initially narrowed the search for Planet Nine down to roughly 2,000 square degrees of sky near Orion, a swath of space that Batygin thinks could be covered in about 20 nights by the Subaru Telescope. Subsequent refinements by Batygin and Brown have reduced the search space to 600–800 square degrees of sky. In December 2018, they spent 4 half–nights and 3 full nights observing with the Subaru Telescope.

Radiation

Although a distant planet such as Planet Nine would reflect little light, it would still be radiating the heat from its formation as it cools due to its large mass. At its estimated temperature of 47 K (−226.2 °C) the peak of its emissions would be at infrared wavelengths. This radiation signature could be detected by Earth-based submillimeter telescopes, such as ALMA, and a search could be conducted by cosmic microwave background experiments operating at mm wavelengths. Jim Green of NASA's Science Mission Directorate is optimistic that it could be observed by the James Webb Space Telescope, the successor to the Hubble Space Telescope, that is expected to be launched in 2021.

Citizen science

The Zooniverse Backyard Worlds project, started in February 2017, is using archival data from the WISE spacecraft to search for Planet Nine. The project will also search for substellar objects like brown dwarfs in the neighborhood of the Solar System. 32,000 animations of four images each, which constitute 3 per cent of the WISE data, have been uploaded to the Backyard Worlds website. By looking for moving objects in the animations, citizen scientists might find Planet Nine.

In April 2017, using data from the SkyMapper telescope at Siding Spring Observatory, citizen scientists on the Zooniverse platform reported four candidates for Planet Nine. These candidates will be followed up on by astronomers to determine their viability. The project, which started on 28 March 2017, completed their goals in less than three days with around five million classifications by more than 60,000 individuals.

Attempts to predict location

Cassini measurements of Saturn's orbit

Precise observations of Saturn's orbit using data from Cassini suggest that Planet Nine could not be in certain sections of its proposed orbit because its gravity would cause a noticeable effect on Saturn's position. This data neither proves nor disproves that Planet Nine exists.

An initial analysis by Fienga, Laskar, Manche, and Gastineau using Cassini data to search for Saturn's orbital residuals, small differences with its predicted orbit due to the Sun and the known planets, was inconsistent with Planet Nine being located with a true anomaly, the location along its orbit relative to perihelion, of −130° to −110° or −65° to 85°. The analysis, using Batygin and Brown's orbital parameters for Planet Nine, suggests that the lack of perturbations to Saturn's orbit is best explained if Planet Nine is located at a true anomaly of 117.8°+11°
−10°. At this location, Planet Nine would be approximately 630 AU from the Sun, with right ascension close to 2^h and declination close to −20°, in Cetus. In contrast, if the putative planet is near aphelion it would be located near right ascension 3.0^h to 5.5^h and declination −1° to 6°.

A later analysis of Cassini data by astrophysicists Matthew Holman and Matthew Payne tightened the constraints on possible locations of Planet Nine. Holman and Payne developed a more efficient model that allowed them to explore a broader range of parameters than the previous analysis. The parameters identified using this technique to analyze the Cassini data was then intersected with Batygin and Brown's dynamical constraints on Planet Nine's orbit. Holman and Payne concluded that Planet Nine is most likely to be located within 20° of RA = 40°, Dec = −15°, in an area of the sky near the constellation Cetus.

William Folkner, a planetary scientist at the Jet Propulsion Laboratory (JPL), has stated that the Cassini spacecraft is not experiencing unexplained deviations in its orbit around Saturn. An undiscovered planet would affect the orbit of Saturn, not Cassini. This could produce a signature in the measurements of Cassini, but JPL has seen no unexplained signatures in Cassini data.

Analysis of Pluto's orbit

An analysis in 2016 of Pluto's orbit by Holman and Payne found perturbations much larger than predicted by Batygin and Brown's proposed orbit for Planet Nine. Holman and Payne suggested three possible explanations: systematic errors in the measurements of Pluto's orbit; an unmodeled mass in the Solar System, such as a small planet in the range of 60–100 AU (potentially explaining the Kuiper cliff); or a planet more massive or closer to the Sun instead of the planet predicted by Batygin and Brown.

Orbits of nearly parabolic comets

An analysis of the orbits of comets with nearly parabolic orbits identifies five new comets with hyperbolic orbits that approach the nominal orbit of Planet Nine described in Batygin and Brown's initial article. If these orbits are hyperbolic due to close encounters with Planet Nine the analysis estimates that Planet Nine is currently near aphelion with a right ascension of 83–90° and a declination of 8–10°. Scott Sheppard, who is skeptical of this analysis, notes that many different forces influence the orbits of comets.

Attempts to predict semimajor axis

An analysis by Sarah Millholland and Gregory Laughlin identified a pattern of commensurabilities (ratios between orbital periods of pairs of objects consistent with both being in resonance with another object) of the eTNOs. They identify five objects that would be near resonances with Planet Nine if had a semi-major axis of 654 AU: Sedna (3:2), 2004 VN112 (3:1), 2012 VP₁₁₃ (4:1), 2000 CR105 (5:1), and 2001 FP185 (5:1). They identify this planet as Planet Nine but propose a different orbit with an eccentricity e ≈ 0.5, inclination i ≈ 30°, argument of perihelion ω ≈ 150°, and longitude of ascending node Ω ≈ 50° (the last differs from Brown and Batygin's value of 90°).

Carlos and Raul de la Fuente Marcos also note commensurabilities among the known eTNOs similar to that of the Kuiper belt, where accidental commensurabilities occur due to objects in resonances with Neptune. They find that some of these objects would be in 5:3 and 3:1 resonances with a planet that had a semi-major axis of ≈700 AU.

Three objects with smaller semi-major axes near 172 AU (2013 UH15, 2016 QV89 and 2016 QU89) have also been proposed to be in resonance with Planet Nine. These objects would be in resonance and anti-aligned with Planet Nine if it had a semi-major axis of 315 AU, below the range proposed by Batygin and Brown. Alternatively, they could be in resonance with Planet Nine, but have orbital orientations that circulate instead of being confined by Planet Nine if it had a semi-major axis of 505 AU.

A later analysis by Elizabeth Bailey, Michael Brown and Konstantin Batygin found that if Planet Nine is in an eccentric and inclined orbit the capture of many of the eTNOs in higher order resonances and their chaotic transfer between resonances prevent the identification of Planet Nine's semi-major axis using current observations. They also determined that the odds of the first six objects observed being in N/1 or N/2 period ratios with Planet Nine are less than 5% if it has an eccentric orbit.

Naming

Planet Nine does not have an official name and will not receive one unless its existence is confirmed via imaging. Only two planets, Uranus and Neptune, have been discovered in recorded history. However, a great many minor planets, including dwarf planets, asteroids, and comets have been discovered and named. Consequently, there is a well-established process for naming newly discovered solar system objects. If Planet Nine is observed, the International Astronomical Union will certify a name, with priority usually given to a name proposed by its discoverers. It is likely to be a name chosen from Roman or Greek mythology.

In their original article, Batygin and Brown simply referred to the object as "perturber", and only in later press releases did they use "Planet Nine". They have also used the names "Jehoshaphat" and "George" for Planet Nine. Brown has stated: "We actually call it Phattie when we're just talking to each other."

In 2018, planetary scientist Alan Stern objected to the name Planet Nine, saying, "It is an effort to erase Clyde Tombaugh's legacy and it's frankly insulting", suggesting the name Planet X until its discovery. He signed a statement with 34 other scientists saying, "We further believe the use of this term [Planet Nine] should be discontinued in favor of culturally and taxonomically neutral terms for such planets, such as Planet X, Planet Next, or Giant Planet Five." According to Brown, "'Planet X' is not a generic reference to some unknown planet, but a specific prediction of Lowell's which led to the (accidental) discovery of Pluto. Our prediction is not related to this prediction."