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Conóceme

The Universe is commonly defined as the totality of existence,[1][2][3][4] including planets, stars, galaxies, the contents of intergalactic space, the smallest subatomic particles, and all matter and energy.[5][6] Similar terms include the cosmos, the world, reality, and nature.
The observable universe is about 46 billion light years in radius.[7] Scientific observation of the Universe has led to inferences of its earlier stages. These observations suggest that the Universe has been governed by the same physical laws and constants throughout most of its extent and history. The Big Bang theory is the prevailing cosmological model that describes the early development of the Universe, which is calculated to have begun 13.798 ± 0.037 billion years ago.[8][9] Observations of a supernovae have shown that the Universe is expanding at an accelerating rate.[10]
There are many competing theories about the ultimate fate of the universe. Physicists remain unsure about what, if anything, preceded the Big Bang. Many refuse to speculate, doubting that any information from any such prior state could ever be accessible. There are various multiverse hypotheses, in which some physicists have suggested that the Universe might be one among many universes that likewise exist.[11][12]
Contents [hide]
1 Historical observation
2 History
3 Etymology, synonyms and definitions
3.1 Broadest definition: reality and probability
3.2 Definition as reality
3.3 Definition as connected space-time
3.4 Definition as observable reality
4 Size, age, contents, structure, and laws
4.1 Fine tuning
5 Historical models
5.1 Creation
5.2 Philosophical models
5.3 Astronomical models
6 Theoretical models
6.1 General theory of relativity
6.2 Special relativity and space-time
6.3 Solving Einstein's field equations
6.4 Big Bang model
6.5 Multiverse theory
7 Shape of the Universe
8 See also
9 Notes and references
10 Bibliography
11 Further reading
12 External links
12.1 Videos
Historical observation

Hubble eXtreme Deep Field (XDF)


XDF size compared to the size of the Moon – several thousand galaxies, each consisting of billions of stars, are in this small view.

XDF (2012) view – each light speck is a galaxy – some of these are as old as 13.2 billion years[13] – the visible Universe is estimated to contain 200 billion galaxies.

XDF image shows fully mature galaxies in the foreground plane – nearly mature galaxies from 5 to 9 billion years ago – protogalaxies, blazing with young stars, beyond 9 billion years.
Throughout recorded history, several cosmologies and cosmogonies have been proposed to account for observations of the Universe. The earliest quantitative geocentric models were developed by the ancient Greek philosophers. Over the centuries, more precise observations and improved theories of gravity led to Copernicus's heliocentric model and the Newtonian model of the Solar System, respectively. Further improvements in astronomy led to the realization that the Solar System is embedded in a galaxy composed of billions of stars, the Milky Way, and that other galaxies exist outside it, as far as astronomical instruments can reach. Careful studies of the distribution of these galaxies and their spectral lines have led to much of modern cosmology. Discovery of the red shift and cosmic microwave background radiation suggested that the Universe is expanding and had a beginning.[14]
History

Main article: Chronology of the universe
According to the prevailing scientific model of the Universe, known as the Big Bang, the Universe expanded from an extremely hot, dense phase called the Planck epoch, in which all the matter and energy of the observable universe was concentrated. Since the Planck epoch, the Universe has been expanding to its present form, possibly with a brief period (less than 10−32 seconds) of cosmic inflation. Several independent experimental measurements support this theoretical expansion and, more generally, the Big Bang theory. The universe is composed of ordinary matter (5%) including atoms, stars, and galaxies, dark matter (25%) which is a hypothetical particle that has not yet been detected, and dark energy (70%), which is a kind of energy density that seemingly exists even in completely empty space.[15] Recent observations indicate that this expansion is accelerating because of dark energy, and that most of the matter in the Universe may be in a form which cannot be detected by present instruments, called dark matter.[16] The common use of the "dark matter" and "dark energy" placeholder names for the unknown entities purported to account for about 95% of the mass-energy density of the Universe demonstrates the present observational and conceptual shortcomings and uncertainties concerning the nature and ultimate fate of the Universe.[17]
On 21 March 2013, the European research team behind the Planck cosmology probe released the mission's all-sky map of the cosmic microwave background.[18][19][20][21][22] The map suggests the universe is slightly older than thought. According to the map, subtle fluctuations in temperature were imprinted on the deep sky when the cosmos was about 370,000 years old. The imprint reflects ripples that arose as early, in the existence of the universe, as the first nonillionth (10−30) of a second. Apparently, these ripples gave rise to the present vast cosmic web of galaxy clusters and dark matter. According to the team, the universe is 13.798 ± 0.037 billion years old,[9][23] and contains 4.9% ordinary matter, 26.8% dark matter and 68.3% dark energy. Also, the Hubble constant was measured to be 67.80 ± 0.77 (km/s)/Mpc.[18][19][20][22][23]
An earlier interpretation of astronomical observations indicated that the age of the Universe was 13.772 ± 0.059 billion years,[24] and that the diameter of the observable universe is at least 93 billion light years or 8.80×1026 meters.[25] According to general relativity, space can expand faster than the speed of light, although we can view only a small portion of the Universe due to the limitation imposed by light speed. Since we cannot observe space beyond the limitations of light (or any electromagnetic radiation), it is uncertain whether the size of the Universe is finite or infinite.
Etymology, synonyms and definitions

See also: Cosmos, Nature, World (philosophy), and Celestial spheres
The word Universe derives from the Old French word Univers, which in turn derives from the Latin word universum.[26] The Latin word was used by Cicero and later Latin authors in many of the same senses as the modern English word is used.[27] The Latin word derives from the poetic contraction Unvorsum — first used by Lucretius in Book IV (line 262) of his De rerum natura (On the Nature of Things) — which connects un, uni (the combining form of unus, or "one") with vorsum, versum (a noun made from the perfect passive participle of vertere, meaning "something rotated, rolled, changed").[27]
An alternative interpretation of unvorsum is "everything rotated as one" or "everything rotated by one". In this sense, it may be considered a translation of an earlier Greek word for the Universe, περιφορά, (periforá, "circumambulation"), originally used to describe a course of a meal, the food being carried around the circle of dinner guests.[28] This Greek word refers to celestial spheres, an early Greek model of the Universe. Regarding Plato's Metaphor of the sun, Aristotle suggests that the rotation of the sphere of fixed stars inspired by the prime mover, motivates, in turn, terrestrial change via the Sun. Careful astronomical and physical measurements (such as the Foucault pendulum) are required to prove the Earth rotates on its axis.
A term for "Universe" in ancient Greece was τὸ πᾶν (tò pán, The All, Pan (mythology)). Related terms were matter, (τὸ ὅλον, tò ólon, see also Hyle, lit. wood) and place (τὸ κενόν, tò kenón).[29][30] Other synonyms for the Universe among the ancient Greek philosophers included κόσμος (cosmos) and φύσις (meaning Nature, from which we derive the word physics).[31] The same synonyms are found in Latin authors (totum, mundus, natura)[32] and survive in modern languages, e.g., the German words Das All, Weltall, and Natur for Universe. The same synonyms are found in English, such as everything (as in the theory of everything), the cosmos (as in cosmology), the world (as in the many-worlds interpretation), and Nature (as in natural laws or natural philosophy).[33]
Broadest definition: reality and probability
See also: Essence–Energies distinction#Distinction between created and uncreated
The broadest definition of the Universe is found in De divisione naturae by the medieval philosopher and theologian Johannes Scotus Eriugena, who defined it as simply everything: everything that is created and everything that is not created.
Definition as reality
See also: Reality and Physics
More customarily, the Universe is defined as everything that exists, (has existed, and will exist)[citation needed]. According to our current understanding, the Universe consists of three principles: spacetime, forms of energy, including momentum and matter, and the physical laws that relate them.
Definition as connected space-time
See also: Eternal inflation
It is possible to conceive of disconnected space-times, each existing but unable to interact with one another. An easily visualized metaphor is a group of separate soap bubbles, in which observers living on one soap bubble cannot interact with those on other soap bubbles, even in principle. According to one common terminology, each "soap bubble" of space-time is denoted as a universe, whereas our particular space-time is denoted as the Universe, just as we call our moon the Moon. The entire collection of these separate space-times is denoted as the multiverse.[34] In principle, the other unconnected universes may have different dimensionalities and topologies of space-time, different forms of matter and energy, and different physical laws and physical constants, although such possibilities are purely speculative.
Definition as observable reality
See also: Observable universe and Observational cosmology
According to a still-more-restrictive definition, the Universe is everything within our connected space-time that could have a chance to interact with us and vice versa.[citation needed] According to the general theory of relativity, some regions of space may never interact with ours even in the lifetime of the Universe due to the finite speed of light and the ongoing expansion of space. For example, radio messages sent from Earth may never reach some regions of space, even if the Universe would live forever: space may expand faster than light can traverse it.
Distant regions of space are taken to exist and be part of reality as much as we are, yet we can never interact with them. The spatial region within which we can affect and be affected is the observable universe. Strictly speaking, the observable Universe depends on the location of the observer. By traveling, an observer can come into contact with a greater region of space-time than an observer who remains still. Nevertheless, even the most rapid traveler will not be able to interact with all of space. Typically, the observable Universe is taken to mean the Universe observable from our vantage point in the Milky Way Galaxy.
Size, age, contents, structure, and laws

Main articles: Observable universe, Age of the universe, and Abundance of the chemical elements
The size of the Universe is unknown; it may be infinite. The region visible from Earth (the observable universe) is a sphere with a radius of about 46 billion light years,[35] based on where the expansion of space has taken the most distant objects observed. For comparison, the diameter of a typical galaxy is 30,000 light-years, and the typical distance between two neighboring galaxies is 3 million light-years.[36] As an example, the Milky Way Galaxy is roughly 100,000 light years in diameter,[37] and the nearest sister galaxy to the Milky Way, the Andromeda Galaxy, is located roughly 2.5 million light years away.[38] There are probably more than 100 billion (1011) galaxies in the observable Universe.[39] Typical galaxies range from dwarfs with as few as ten million[40] (107) stars up to giants with one trillion[41] (1012) stars, all orbiting the galaxy's center of mass. A 2010 study by astronomers estimated that the observable Universe contains 300 sextillion (3×1023) stars.[42]


The Universe is believed to be mostly composed of dark energy and dark matter, both of which are poorly understood at present. Less than 5% of the Universe is ordinary matter, a relatively small contribution.
The observable matter is spread homogeneously (uniformly) throughout the Universe, when averaged over distances longer than 300 million light-years.[43] However, on smaller length-scales, matter is observed to form "clumps", i.e., to cluster hierarchically; many atoms are condensed into stars, most stars into galaxies, most galaxies into clusters, superclusters and, finally, the largest-scale structures such as the Great Wall of galaxies. The observable matter of the Universe is also spread isotropically, meaning that no direction of observation seems different from any other; each region of the sky has roughly the same content.[44] The Universe is also bathed in a highly isotropic microwave radiation that corresponds to a thermal equilibrium blackbody spectrum of roughly 2.725 kelvin.[45] The hypothesis that the large-scale Universe is homogeneous and isotropic is known as the cosmological principle,[46] which is supported by astronomical observations.
The present overall density of the Universe is very low, roughly 9.9 × 10−30 grams per cubic centimetre. This mass-energy appears to consist of 73% dark energy, 23% cold dark matter and 4% ordinary matter. Thus the density of atoms is on the order of a single hydrogen atom for every four cubic meters of volume.[47] The properties of dark energy and dark matter are largely unknown. Dark matter gravitates as ordinary matter, and thus works to slow the expansion of the Universe; by contrast, dark energy accelerates its expansion.
The current estimate of the Universe's age is 13.798 ± 0.037 billion years old.[9] The Universe has not been the same at all times in its history; for example, the relative populations of quasars and galaxies have changed and space itself appears to have expanded. This expansion accounts for how Earth-bound scientists can observe the light from a galaxy 30 billion light years away, even if that light has traveled for only 13 billion years; the very space between them has expanded. This expansion is consistent with the observation that the light from distant galaxies has been redshifted; the photons emitted have been stretched to longer wavelengths and lower frequency during their journey. The rate of this spatial expansion is accelerating, based on studies of Type Ia supernovae and corroborated by other data.
The relative fractions of different chemical elements — particularly the lightest atoms such as hydrogen, deuterium and helium — seem to be identical throughout the Universe and throughout its observable history.[48] The Universe seems to have much more matter than antimatter, an asymmetry possibly related to the observations of CP violation.[49] The Universe appears to have no net electric charge, and therefore gravity appears to be the dominant interaction on cosmological length scales. The Universe also appears to have neither net momentum nor angular momentum. The absence of net charge and momentum would follow from accepted physical laws (Gauss's law and the non-divergence of the stress-energy-momentum pseudotensor, respectively), if the Universe were finite.[50]


The elementary particles from which the Universe is constructed. Six leptons and six quarks comprise most of the matter; for example, the protons and neutrons of atomic nuclei are composed of quarks, and the ubiquitous electron is a lepton. These particles interact via the gauge bosons shown in the middle row, each corresponding to a particular type of gauge symmetry. The Higgs boson is believed to confer mass on the particles with which it is connected. The graviton, a supposed gauge boson for gravity, is not shown.
The Universe appears to have a smooth space-time continuum consisting of three spatial dimensions and one temporal (time) dimension. On the average, space is observed to be very nearly flat (close to zero curvature), meaning that Euclidean geometry is experimentally true with high accuracy throughout most of the Universe.[51] Spacetime also appears to have a simply connected topology, at least on the length-scale of the observable Universe. However, present observations cannot exclude the possibilities that the Universe has more dimensions and that its spacetime may have a multiply connected global topology, in analogy with the cylindrical or toroidal topologies of two-dimensional spaces.[52]
The Universe appears to behave in a manner that regularly follows a set of physical laws and physical constants.[53] According to the prevailing Standard Model of physics, all matter is composed of three generations of leptons and quarks, both of which are fermions. These elementary particles interact via at most three fundamental interactions: the electroweak interaction which includes electromagnetism and the weak nuclear force; the strong nuclear force described by quantum chromodynamics; and gravity, which is best described at present by general relativity. The first two interactions can be described by renormalized quantum field theory, and are mediated by gauge bosons that correspond to a particular type of gauge symmetry. A renormalized quantum field theory of general relativity has not yet been achieved, although various forms of string theory seem promising. The theory of special relativity is believed to hold throughout the Universe, provided that the spatial and temporal length scales are sufficiently short; otherwise, the more general theory of general relativity must be applied. There is no explanation for the particular values that physical constants appear to have throughout our Universe, such as Planck's constant h or the gravitational constant G. Several conservation laws have been identified, such as the conservation of charge, momentum, angular momentum and energy; in many cases, these conservation laws can be related to symmetries or mathematical identities.
Fine tuning
Main article: Fine-tuned Universe
It appears that many of the properties of the Universe have special values in the sense that a Universe where these properties differ slightly would not be able to support intelligent life.[14][54] Not all scientists agree that this fine-tuning exists.[55][56] In particular, it is not known under what conditions intelligent life could form and what form or shape that would take. A relevant observation in this discussion is that for an observer to exist to observe fine-tuning, the Universe must be able to support intelligent life. As such the conditional probability of observing a Universe that is fine-tuned to support intelligent life is 1. This observation is known as the anthropic principle and is particularly relevant if the creation of the Universe was probabilistic or if multiple universes with a variety of properties exist (see below).
Historical models

See also: Cosmology and Timeline of cosmology
Many models of the cosmos (cosmologies) and its origin (cosmogonies) have been proposed, based on the then-available data and conceptions of the Universe. Historically, cosmologies and cosmogonies were based on narratives of gods acting in various ways. Theories of an impersonal Universe governed by physical laws were first proposed by the Greeks and Indians. Over the centuries, improvements in astronomical observations and theories of motion and gravitation led to ever more accurate descriptions of the Universe. The modern era of cosmology began with Albert Einstein's 1915 general theory of relativity, which made it possible to quantitatively predict the origin, evolution, and conclusion of the Universe as a whole. Most modern, accepted theories of cosmology are based on general relativity and, more specifically, the predicted Big Bang; however, still more careful measurements are required to determine which theory is correct.
Creation
Main articles: Creation myth and Creator deity
Many cultures have stories describing the origin of the world, which may be roughly grouped into common types. In one type of story, the world is born from a world egg; such stories include the Finnish epic poem Kalevala, the Chinese story of Pangu or the Indian Brahmanda Purana. In related stories, the Universe is created by a single entity emanating or producing something by him- or herself, as in the Tibetan Buddhism concept of Adi-Buddha, the ancient Greek story of Gaia (Mother Earth), the Aztec goddess Coatlicue myth, the ancient Egyptian god Atum story, or the Genesis creation narrative. In another type of story, the Universe is created from the union of male and female deities, as in the Maori story of Rangi and Papa. In other stories, the Universe is created by crafting it from pre-existing materials, such as the corpse of a dead god — as from Tiamat in the Babylonian epic Enuma Elish or from the giant Ymir in Norse mythology – or from chaotic materials, as in Izanagi and Izanami in Japanese mythology. In other stories, the Universe emanates from fundamental principles, such as Brahman and Prakrti, the creation myth of the Serers,[57] or the yin and yang of the Tao.
Philosophical models
Further information: Cosmology
See also: Pre-Socratic philosophy, Physics (Aristotle), Hindu cosmology, Islamic cosmology, and Time
From the 6th century BCE, the pre-Socratic Greek philosophers developed the earliest known philosophical models of the Universe. The earliest Greek philosophers noted that appearances can be deceiving, and sought to understand the underlying reality behind the appearances. In particular, they noted the ability of matter to change forms (e.g., ice to water to steam) and several philosophers proposed that all the apparently different materials of the world are different forms of a single primordial material, or arche. The first to do so was Thales, who proposed this material is Water. Thales' student, Anaximander, proposed that everything came from the limitless apeiron. Anaximenes proposed Air on account of its perceived attractive and repulsive qualities that cause the arche to condense or dissociate into different forms. Anaxagoras, proposed the principle of Nous (Mind). Heraclitus proposed fire (and spoke of logos). Empedocles proposed the elements: earth, water, air and fire. His four element theory became very popular. Like Pythagoras, Plato believed that all things were composed of number, with the Empedocles' elements taking the form of the Platonic solids. Democritus, and later philosophers—most notably Leucippus—proposed that the Universe was composed of indivisible atoms moving through void (vacuum). Aristotle did not believe that was feasible because air, like water, offers resistance to motion. Air will immediately rush in to fill a void, and moreover, without resistance, it would do so indefinitely fast.
Although Heraclitus argued for eternal change, his quasi-contemporary Parmenides made the radical suggestion that all change is an illusion, that the true underlying reality is eternally unchanging and of a single nature. Parmenides denoted this reality as τὸ ἐν (The One). Parmenides' theory seemed implausible to many Greeks, but his student Zeno of Elea challenged them with several famous paradoxes. Aristotle responded to these paradoxes by developing the notion of a potential countable infinity, as well as the infinitely divisible continuum. Unlike the eternal and unchanging cycles of time, he believed the world was bounded by the celestial spheres, and thus magnitude was only finitely multiplicative.
The Indian philosopher Kanada, founder of the Vaisheshika school, developed a theory of atomism and proposed that light and heat were varieties of the same substance.[58] In the 5th century AD, the Buddhist atomist philosopher Dignāga proposed atoms to be point-sized, durationless, and made of energy. They denied the existence of substantial matter and proposed that movement consisted of momentary flashes of a stream of energy.[59]
The theory of temporal finitism was inspired by the doctrine of Creation shared by the three Abrahamic religions: Judaism, Christianity and Islam. The Christian philosopher, John Philoponus, presented the philosophical arguments against the ancient Greek notion of an infinite past and future. Philoponus' arguments against an infinite past were used by the early Muslim philosopher, Al-Kindi (Alkindus); the Jewish philosopher, Saadia Gaon (Saadia ben Joseph); and the Muslim theologian, Al-Ghazali (Algazel). Borrowing from Aristotle's Physics and Metaphysics, they employed two logical arguments against an infinite past, the first being the "argument from the impossibility of the existence of an actual infinite", which states:[60]
"An actual infinite cannot exist."
"An infinite temporal regress of events is an actual infinite."
"\therefore An infinite temporal regress of events cannot exist."
The second argument, the "argument from the impossibility of completing an actual infinite by successive addition", states:[60]
"An actual infinite cannot be completed by successive addition."
"The temporal series of past events has been completed by successive addition."
"\therefore The temporal series of past events cannot be an actual infinite."
Both arguments were adopted by Christian philosophers and theologians, and the second argument in particular became more famous after it was adopted by Immanuel Kant in his thesis of the first antinomy concerning time.[60]
Astronomical models
Main article: History of astronomy


Aristarchus's 3rd century BCE calculations on the relative sizes of from left the Sun, Earth and Moon, from a 10th-century AD Greek copy
Astronomical models of the Universe were proposed soon after astronomy began with the Babylonian astronomers, who viewed the Universe as a flat disk floating in the ocean, and this forms the premise for early Greek maps like those of Anaximander and Hecataeus of Miletus.
Later Greek philosophers, observing the motions of the heavenly bodies, were concerned with developing models of the Universe based more profoundly on empirical evidence. The first coherent model was proposed by Eudoxus of Cnidos. According to Aristotle's physical interpretation of the model, celestial spheres eternally rotate with uniform motion around a stationary Earth. Normal matter, is entirely contained within the terrestrial sphere. This model was also refined by Callippus and after concentric spheres were abandoned, it was brought into nearly perfect agreement with astronomical observations by Ptolemy. The success of such a model is largely due to the mathematical fact that any function (such as the position of a planet) can be decomposed into a set of circular functions (the Fourier modes). Other Greek scientists, such as the Pythagorean philosopher Philolaus postulated that at the center of the Universe was a "central fire" around which the Earth, Sun, Moon and Planets revolved in uniform circular motion.[61] The Greek astronomer Aristarchus of Samos was the first known individual to propose a heliocentric model of the Universe. Though the original text has been lost, a reference in Archimedes' book The Sand Reckoner describes Aristarchus' heliocentric theory. Archimedes wrote: (translated into English)
You King Gelon are aware the 'Universe' is the name given by most astronomers to the sphere the center of which is the center of the Earth, while its radius is equal to the straight line between the center of the Sun and the center of the Earth. This is the common account as you have heard from astronomers. But Aristarchus has brought out a book consisting of certain hypotheses, wherein it appears, as a consequence of the assumptions made, that the Universe is many times greater than the 'Universe' just mentioned. His hypotheses are that the fixed stars and the Sun remain unmoved, that the Earth revolves about the Sun on the circumference of a circle, the Sun lying in the middle of the orbit, and that the sphere of fixed stars, situated about the same center as the Sun, is so great that the circle in which he supposes the Earth to revolve bears such a proportion to the distance of the fixed stars as the center of the sphere bears to its surface.
Aristarchus thus believed the stars to be very far away, and saw this as the reason why there was no parallax apparent, that is, no observed movement of the stars relative to each other as the Earth moved around the Sun. The stars are in fact much farther away than the distance that was generally assumed in ancient times, which is why stellar parallax is only detectable with precision instruments. The geocentric model, consistent with planetary parallax, was assumed to be an explanation for the unobservability of the parallel phenomenon, stellar parallax. The rejection of the heliocentric view was apparently quite strong, as the following passage from Plutarch suggests (On the Apparent Face in the Orb of the Moon):
Cleanthes [a contemporary of Aristarchus and head of the Stoics] thought it was the duty of the Greeks to indict Aristarchus of Samos on the charge of impiety for putting in motion the Hearth of the Universe [i.e. the earth], . . . supposing the heaven to remain at rest and the earth to revolve in an oblique circle, while it rotates, at the same time, about its own axis. [1]
The only other astronomer from antiquity known by name who supported Aristarchus' heliocentric model was Seleucus of Seleucia, a Hellenistic astronomer who lived a century after Aristarchus.[62][63][64] According to Plutarch, Seleucus was the first to prove the heliocentric system through reasoning, but it is not known what arguments he used. Seleucus' arguments for a heliocentric theory were probably related to the phenomenon of tides.[65] According to Strabo (1.1.9), Seleucus was the first to state that the tides are due to the attraction of the Moon, and that the height of the tides depends on the Moon's position relative to the Sun.[66] Alternatively, he may have proved the heliocentric theory by determining the constants of a geometric model for the heliocentric theory and by developing methods to compute planetary positions using this model, like what Nicolaus Copernicus later did in the 16th century.[67] During the Middle Ages, heliocentric models may have also been proposed by the Indian astronomer, Aryabhata,[68] and by the Persian astronomers, Albumasar[69] and Al-Sijzi.[70]

Suicide (Latin suicidium, from sui caedere, "to kill oneself") is the act of intentionally causing one's own death. Suicide is often committed out of despair, the cause of which is frequently attributed to a mental disorder such as depression, bipolar disorder, schizophrenia, borderline personality disorder,[1] alcoholism, or drug abuse.[2] Stress factors such as financial difficulties or troubles with interpersonal relationships often play a role. Efforts to prevent suicide include limiting access to firearms, treating mental illness and drug misuse, and improving economic development. Although crisis hotlines are common there is little evidence for their effectiveness.[3]

The most commonly used method of suicide varies by country and is partly related to availability. Common methods include: hanging, pesticide poisoning, and firearms. Around 800,000 to a million people die by suicide every year, making it the 10th leading cause of death worldwide.[2][4] Rates are higher in men than in women, with males three to four times more likely to kill themselves than females.[5] There are an estimated 10 to 20 million non-fatal attempted suicides every year.[6] Attempts are more common in young people and females.

Views on suicide have been influenced by broad existential themes such as religion, honor, and the meaning of life. The Abrahamic religions traditionally consider suicide an offense towards God due to the belief in the sanctity of life. During the samurai era in Japan, seppuku was respected as a means of atonement for failure or as a form of protest. Sati, a now outlawed East Indian practice, expected the widow to immolate herself on her husband's funeral pyre, either willingly or under pressure from the family and society.[7]

Suicide and attempted suicide, while previously criminally punishable, is no longer in most Western countries. It remains a criminal offense in many countries. In the 20th and 21st centuries, suicide in the form of self-immolation has been used as a medium of protest, and kamikaze and suicide bombings have been used as a military or terrorist tactic.[8]

Contents [hide]
1 Definitions
2 Risk factors
2.1 Mental disorders
2.2 Substance use
2.3 Problem gambling
2.4 Medical conditions
2.5 Psychosocial states
2.6 Media
2.7 Rational
3 Methods
4 Pathophysiology
5 Prevention
5.1 Screening
5.2 Mental illness
6 Epidemiology
6.1 Gender
6.2 Age
7 History
8 Social and culture
8.1 Legislation
8.2 Religious views
8.3 Philosophy
8.4 Advocacy
8.5 Locations
8.6 Notable cases
9 Other species
10 Notes
11 Further reading
12 External links
Definitions
Main article: Suicide terminology
Suicide, also known as completed suicide, is the "act of taking one's own life".[9] Attempted suicide or non-fatal suicidal behavior is self-injury with the desire to end one's life that does not result in death.[10] Assisted suicide is when one individual helps another bring about their own death indirectly via providing either advice or the means to the end.[11] This is in contrast to euthanasia, where another person takes a more active role in bringing about a person's death.[11] Suicidal ideations is thoughts of ending one's life but not taking any active efforts to do so.[10]

Risk factors


The precipitating circumstances for suicide from 16 American states in 2008.[12]
Factors that affect the risk of suicide include psychiatric disorders, drug misuse, psychological states, cultural, family and social situations, and genetics.[13] Mental illness and substance misuse frequently co-exist.[14] Other risk factors include having previously attempted suicide,[15] the ready availability of a means to commit the act, a family history of suicide, or the presence of traumatic brain injury.[16] For example, suicide rates have been found to be greater in households with firearms than those without them.[17] Socio-economic problems such as unemployment, poverty, homelessness, and discrimination may trigger suicidal thoughts.[18][19] About 15–40% of people leave a suicide note.[20] Genetics appears to account for between 38% and 55% of suicidal behaviors.[21] War veterans have a higher risk of suicide due in part to higher rates of mental illness and physical health problems related to war.[22]

Mental disorders
Mental disorders are often present at the time of suicide with estimates ranging from 27%[23] to more than 90%.[15] Of those who have been admitted to a psychiatric unit, their lifetime risk of completed suicide is about 8.6%.[15] Half of all people who die by suicide may have major depressive disorder; having this or one of the other mood disorders such as bipolar disorder increases the risk of suicide 20-fold.[24] Other conditions implicated include schizophrenia (14%), personality disorders (14%),[25] bipolar disorder,[24] and posttraumatic stress disorder.[15] About 5% of people with schizophrenia die of suicide.[26] Eating disorders are another high risk condition.[27]

A history of previous suicide attempts is the greatest predictor of eventual completion of suicide.[15] Approximately 20% of suicides have had a previous attempt and of those who have attempted suicide 1% complete suicide within a year[15] and more than 5% commit suicide after 10 years.[27] Acts of self-harm are not usually suicide attempts and most who self-harm are not at high risk of suicide.[28] Some who self-harm, however, do still end their life by suicide, and risk for self-harm and suicide may overlap.[28]

In approximately 80% of completed suicides the individual has seen a physician within the year before their death,[29] including 45% within the prior month.[30] Approximately 25–40% of those who completed suicide had contact with mental health services in the prior year.[23][29]

Substance use


"The Drunkard's Progress", 1846 demonstrating how alcoholism can lead to poverty, crime, and eventually suicide
Substance abuse is the second most common risk factor for suicide after major depression and bipolar disorder.[31] Both chronic substance misuse as well as acute intoxication are associated.[14][32] When combined with personal grief, such as bereavement, the risk is further increased.[32] Additionally substance misuse is associated with mental health disorders.[14]

Most people are under the influence of sedative-hypnotic drugs (such as alcohol or benzodiazepines) when they commit suicide[33] with alcoholism present in between 15% and 61% of cases.[14] Countries that have higher rates of alcohol use and a greater density of bars generally also have higher rates of suicide[34] with this link being primarily related to distilled spirit use rather than total alcohol use.[14] About 2.2–3.4% of those who have been treated for alcoholism at some point in their life die by suicide.[34] Alcoholics who attempt suicide are usually male, older, and have tried to commit suicide in the past.[14] Between 3 and 35% of deaths among those who use heroin are due to suicide (approximately 14 fold greater than those who do not use).[35]

The misuse of cocaine and methamphetamines has a high correlation with suicide.[14][36] In those who use cocaine the risk is greatest during the withdrawal phase.[37] Those who used inhalants are also at significant risk with around 20% attempting suicide at some point and more than 65% considering it.[14] Smoking cigarettes is associated with the risk of suicide.[38] There is little evidence as to why this association exists; however it has been hypothesized that those who are predisposed to smoking are also predisposed to suicide, that smoking causes health problems which subsequently make people want to end their life, and that smoking affects brain chemistry causing a propensity for suicide.[38] Cannabis however does not appear to independently increase the risk.[14]

Problem gambling
Problem gambling is associated with increased suicidal ideation and attempts compared to the general population.[39] Between 12 and 24% pathological gamblers attempt suicide.[40] The rate of suicide among their spouses is three times greater than that of the general population.[40] Other factors that increase the risk in problem gamblers include mental illness, alcohol and drug misuse.[41]

Medical conditions
There is an association between suicidality and physical health problems such as[27] chronic pain,[42] traumatic brain injury,[43] cancer,[44] kidney failure (requiring hemodialysis, HIV, and systemic lupus erythematosus.[27] The diagnosis of cancer approximately doubles the subsequent risk of suicide.[44] The prevalence of increased suicidality persisted after adjusting for depressive illness and alcohol abuse. In people with more than one medical condition the risk was particularly high. In Japan, health problems are listed as the primary justification for suicide.[45]

Sleep disturbances such as insomnia[46] and sleep apnea are risk factors for depression and suicide. In some instances the sleep disturbances may be a risk factor independent of depression.[47] A number of other medical conditions may present with symptoms similar to mood disorders, including hypothyroidism, Alzheimer's, brain tumors, systemic lupus erythematosus, and adverse effects from a number of medications (such as beta blockers and steroids).[15]

Psychosocial states
A number of psychological states increase the risk of suicide including: hopelessness, loss of pleasure in life, depression and anxiousness.[24] A poor ability to solve problems, the loss of abilities one used to have, and poor impulse control also play a role.[24][48] In older adults the perception of being a burden to others is important.[49] Suicide in which the reason is that the person feels that they are not part of society is known as egoistic suicide.[50]

Recent life stresses such as a loss of a family member or friend, loss of a job, or social isolation (such as living alone) increases the risk.[24] Those who have never married are also at greater risk.[15] Being religious may reduce one's risk of suicide.[51] This has been attributed to the negative stance many religions take against suicide and to the greater connectedness religion may give.[51] Muslims, among religious people, appear to have a lower rate.[52]

Some may commit suicide to escape bullying or prejudice.[53] A history of childhood sexual abuse[54] and time spent in foster care are also risk factors.[55] Sexual abuse is believed to contribute to about 20% of the overall risk.[21]

An evolutionary explanation for suicide is that it may improve inclusive fitness. This may occur if the person committing suicide cannot have more children and takes resources away from relatives by staying alive. An objection is that deaths by healthy adolescents likely does not increase inclusive fitness. Adaptation to a very different ancestral environment may be maladaptive in the current one.[48][56]

Poverty is associated with the risk of suicide.[57] Increasing relative poverty compared to those around a person increases suicide risk.[58] Over 200,000 farmers in India have committed suicide since 1997 partly due to issues of debt.[59] In China suicide is three times as likely in rural regions as urban ones partly it is believed due to financial difficulties in this area of the country.[60]

Media


New York Daily Mirror front page heralding Marilyn Monroe's death
The media, which includes the Internet, plays an important role.[13] How it presents depiction of suicide may have a negative effect, with high volume, prominent, repetitive coverage glorifying or romanticizing suicide having the most impact.[61] When detailed descriptions of how to kill oneself by a specific means are portrayed, this method of suicide may increase in the population as a whole.[62]

This trigger of 'suicide contagion' or copycat suicide is known as the Werther effect, named after the protagonist in Goethe's The Sorrows of Young Werther who killed himself and then was emulated by many admirers of the book.[63] This risk is greater in adolescents who may romanticize death.[64] It appears that while news media has a significant effect, that of the entertainment media is equivocal.[65] The opposite of the Werther effect is the proposed Papageno effect, in which coverage of effective coping mechanisms may have a protective effect. The term is based upon a character in Mozart's opera The Magic Flute, who (fearing the loss of a loved one) had planned to kill himself until his friends helped him out.[63] When media follows recommended reporting guidelines the risk of suicides can be decreased.[61] Getting buy-in from industry, however, can be difficult, especially in the long term.[61]

Rational
Rational suicide is the reasoned taking of one's own life,[66] although some feel that suicide is never logical.[66] The act of taking one's life for the benefit of others is known as altruistic suicide.[67] An example of this is an elder ending his or her life to leave greater amounts of food for the younger people in the community.[67] Suicide in some Eskimo cultures has been seen as an act of respect, courage, or wisdom.[68]

A suicide attack is a political action where an attacker carries out violence against others which they understand will result in their own death.[69] Some suicide bombers are motivated by a desire to obtain martyrdoms.[22] Kamikaze missions were carried out as a duty to a higher cause or moral obligation.[68] Murder–suicide is an act of homicide followed within a week by suicide of the person who carried out the act.[70]

Mass suicides are often performed under social pressure where members give up autonomy to a leader.[71] Mass suicides can take place with as few as two people, often referred to as a suicide pact.[72]

In extenuating situations where continuing to live would be intolerable, some people use suicide as a means of escape.[73] Some inmates in Nazi concentration camps are known to have killed themselves by deliberately touching the electrified fences.[74]

Methods


Case fatality rate by suicide method in the United States.[17]
Main article: Suicide methods
The leading method of suicide varies between countries. The leading methods in different regions include hanging, pesticide poisoning, and firearms.[75] These differences are believed to be in part due to availability of the different methods.[62] A review of 56 countries found that hanging was the most common method in most of the countries,[76] accounting for 53% of the male suicides and 39% of the female suicides.[77]

Worldwide 30% of suicides are from pesticides. The use of this method however varies markedly from 4% in Europe to more than 50% in the Pacific region.[78] It is also common in Latin America due to easy access within the farming populations.[62] In many countries, drug overdoses account for approximately 60% of suicides among women and 30% among men.[79] Many are unplanned and occur during an acute period of ambivalence.[62] The death rate varies by method: firearms 80-90%, drowning 65-80%, hanging 60-85%, car exhaust 40-60%, jumping 35-60%, charcoal burning 40-50%, pesticides 6-75%, medication overdose 1.5-4%.[62] The most common attempted methods of suicide differ from the most common successful methods with up to 85% of attempts via drug overdose in the developed world.[27]

In United States, 57% of suicides involve the use of firearms with this method being somewhat more common in men than women.[15] The next most common cause was hanging in males and self poisoning in females.[15] Together these methods comprised about 40% of U.S. suicides.[80] In Switzerland, where nearly everyone owns a firearm, the greatest number of suicides are by hanging.[81] Jumping to one's death is common in both Hong Kong and Singapore at 50% and 80% respectively.[62] In China the consumption of pesticides is the most common method.[82] In Japan self disembowelment known as seppuku or hara-kiri still occurs[82] however hanging is the most common.[83]

Pathophysiology
There is no known unifying underlying pathophysiology for either suicide or depression.[15] It is however believed to result from an interplay of behavioral, socio-environmental and psychiatric factors.[62]

Low levels of brain-derived neurotrophic factor (BDNF) are both directly associated with suicide[84] and indirectly associated through its role in major depression, posttraumatic stress disorder, schizophrenia and obsessive–compulsive disorder.[85] Post-mortem studies have found reduced levels of BDNF in the hippocampus and prefrontal cortex, in those with and without psychiatric conditions.[86] Serotonin, a brain neurotransmitter, is believed to be low in those who commit suicide. This is partly based on evidence of increased levels of 5-HT2A receptors found after death.[87] Other evidence includes reduced levels of a breakdown product of serotonin, 5-Hydroxyindoleacetic acid, in the cerebral spinal fluid.[88] Direct evidence is however hard to gather.[87] Epigenetics, the study of changes in genetic expression in response to environmental factors which do not alter the underlying DNA, is also believed to play a role in determining suicide risk.[89]

Prevention
Main article: Suicide prevention


As a suicide prevention initiative, this sign promotes a special telephone available on the Golden Gate Bridge that connects to a crisis hotline.
Suicide prevention is a term used for the collective efforts to reduce the incidence of suicide through preventive measures. Reducing access to certain methods, such as firearms or toxins reduces the risk.[62][90] Other measures include reducing access to charcoal and barriers on bridges and subway platforms.[62][91] Treatment of drug and alcohol addiction, depression, and those who have attempted suicide in the past may also be effective.[90] Some have proposed reducing access to alcohol as a preventative strategy (such as reducing the number of bars).[14] Although crisis hotlines are common there is little evidence to support or refute their effectiveness.[3][92] In young adults who have recently thought about suicide, cognitive behavioral therapy appears to improve outcomes.[93] Economic development through its ability to reduce poverty may be able to decrease suicide rates.[57] Efforts to increase social connection especially in elderly males may be effective.[94] The World Suicide Prevention Day is observed annually on September 10 with the support of the International Association for Suicide Prevention and the World Health Organization.[95]

Screening
There is little data on the effects of screening the general population on the ultimate rate of suicide.[96][97] As there is a high rate of people who test positive via these tools that are not at risk of suicide, there are concerns that screening may significantly increase mental health care resource utilization.[98] Assessing those at high risk however is recommended.[15] Asking about suicidality does not appear to increase the risk.[15]

Mental illness
In those with mental health problems a number of treatments may reduce the risk of suicide. Those who are actively suicidal may be admitted to psychiatric care either voluntarily or involuntarily.[15] Possessions that may be used to harm oneself are typically removed.[27] Some clinicians get patients to sign suicide prevention contracts where they agree to not harm themselves if released.[15] Evidence however does not support a significant effect from this practice.[15] If a person is at low risk, out-patient mental health treatment may be arranged.[27] Short-term hospitalization has not been found to be more effective than community care for improving outcomes in those with borderline personality disorder who are chronically suicidal.[99][100]

There is tentative evidence that psychotherapy, specifically, dialectical behaviour therapy reduces suicidality in adolescents[101] as well as in those with borderline personality disorder.[102] It may also be useful in decreasing suicide attempts in adults at high risk.[103] Evidence however has not found a decrease in completed suicides.[101]

There is controversy around the benefit versus harm of antidepressants.[13] In young persons, the newer antidepressants such as SSRIs appear to increase the risk of suicidality from 25 per 1000 to 40 per 1000.[104] In older persons however they might decrease the risk.[15] Lithium appears effective at lowering the risk in those with bipolar disorder and unipolar depression to nearly the same levels as the general population.[105][106]

Epidemiology
Main article: Epidemiology of suicide


Deaths by self-inflicted injuries per 100,000 inhabitants in 2004.[107]
unknown
<3
3–6
6–9
9–12
12–15
15–18
18–21
21–24
24–27
27–30
30–33
>33
Approximately 0.5% to 1.4% of people die by suicide.[4][15] Globally, as of 2008/2009, suicide is the tenth leading cause of death[2] with about 800,000 to one million people dying annually, giving a mortality rate of 11.6 per 100,000 persons per year.[4] Rates of suicide have increased by 60% from the 1960s to 2012,[90] with these increases seen primarily in the developing world.[2] For every suicide that results in death there are between 10 and 40 attempted suicides.[15]

Suicide rates differ significantly between countries and over time.[4] As a percentage of deaths in 2008 it was: Africa 0.5%, South-East Asia 1.9% Americas 1.2% and Europe 1.4%.[4] Rates per 100,000 were: Australia 8.6, Canada 11.1, China 12.7, India 23.2, United Kingdom 7.6, United States 11.4.[108] It is ranked as the 10th leading cause of death in the United States in 2009 at about 36,000 cases a year,[109] with about 650,000 people seen in emergency departments yearly due to attempting suicide.[15] The country's rate among men in their 50's rose by nearly half in the decade 1999–2010.[110] Lithuania, Japan and Hungary have the highest rates.[4] The countries with the greatest absolute numbers of suicides are China and India accounting for over half the total.[4] In China suicide is the 5th leading cause of death.[111]

Gender
Main article: Gender differences in suicide


Suicide rate per 100,000 males (left) and female (right) (data from 1978–2008).
no data
< 1
1–5
5–5.8
5.8–8.5
8.5–12
12–19
19–22.5
22.5–26
26–29.5
29.5–33
33–36.5
>36.5
In the Western world, males die three to four times more often by means of suicide than do females, although females attempt suicide four times more often.[4][15] This has been attributed to males using more lethal means to end their lives.[112] This difference is even more pronounced in those over the age of 65 with tenfold more males committing suicide than females.[112] China has one of the highest female suicide rates in the world and is the only country where it is higher than that of men (ratio of 0.9).[4][111] In the Eastern Mediterranean suicide rates are nearly equivalent between males and females.[4] For women the highest rate of suicide is found in South Korea at 22 per 100,000, with high rates in South-East Asia and the Western Pacific generally.[4]

Age
In many countries the rate of suicide is highest in the middle-aged[113] or elderly.[62] The absolute number of suicides however is greatest in those between 15 and 29 years old due to the number of people in this age group.[4] In the United States it is greatest in caucasian men older than 80 years, even though younger people more frequently attempt suicide.[15] It is the second most common cause of death in adolescents[13] and in young males is second only to accidental death.[113] In young males in the developed world it is the cause of nearly 30% of mortality.[113] In the developing world rates are similar, but it makes up a smaller proportion of overall deaths due to higher rates of death from other types of trauma.[113] In South-East Asia in contrast to other areas of the world, deaths from suicide occur at a greater rate in young females than elderly females.[4]

History
Main article: History of suicide


The death of Seneca (1684), painting by Luca Giordano, depicting the suicide of Seneca the Younger in Ancient Rome.
In ancient Athens, a person who committed suicide without the approval of the state was denied the honours of a normal burial. The person would be buried alone, on the outskirts of the city, without a headstone or marker,[114] however, it was deemed to be an acceptable method to deal with military defeat.[115] In Ancient Rome, while suicide was initially permitted, it was later deemed a crime against the state due to its economic costs.[116]

Suicide came to be regarded as a sin in Christian Europe and was condemned at the Council of Arles in 452 as the work of the Devil. In the Middle Ages, the Church had drawn-out discussions on the edge where the search for martyrdom was suicidal, as in the case of martyrs of Córdoba. Despite these disputes and occasional official rulings, Catholic doctrine was not entirely settled on the subject of suicide until the later 17th century. A criminal ordinance issued by Louis XIV of France in 1670 was extremely severe, even for the times: the dead person's body was drawn through the streets, face down, and then hung or thrown on a garbage heap. Additionally, all of the person's property was confiscated.[117][118]

Attitudes towards suicide slowly began to shift during the Renaissance. John Donne's work Biathanatos, contained one of the first modern defences of suicide bringing proof from the conduct of Biblical figures, such as Jesus, Samson and Saul, and presenting arguments on grounds of reason and nature to sanction suicide in certain circumstances.[119]

The secularisation of society that began during The Enlightenment questioned traditional religious attitudes toward suicide and brought a more modern perspective to the issue. David Hume denied that suicide was a crime as it affected no one and was potentially to the advantage of the individual. In his 1777 Essays on Suicide and the Immortality of the Soul he rhetorically asked, "Why should I prolong a miserable existence, because of some frivolous advantage which the public may perhaps receive from me?"[119] A shift in public opinion at large can also be discerned; The Times in 1786 initiated a spirited debate on the motion "Is suicide an act of courage?"[120]

By the 19th-century, the act of suicide had shifted from being viewed as caused by sin to being caused by insanity in Europe.[118] Although suicide remained illegal during this period, it increasingly became the target of satirical comment, such as the Gilbert and Sullivan musical The Mikado that satirised the idea of executing someone who had already killed himself.

By 1879, English law began to distinguish between suicide and homicide, although suicide still resulted in forfeiture of estate.[121] In 1882, the deceased were permitted daylight burial in England[122] and by the mid 20th century, suicide had become legal in much of the western world.

Social and culture
Legislation
Main article: Suicide legislation


A tantō knife prepared for seppuku.
In most Western countries, suicide is no longer a crime,[123] it however was in most Western European countries from the Middle Ages until at least the 1800s.[121] It remains a criminal offense in most Muslim-majority nations.[52]

In Australia suicide is not a crime.[124] It however is a crime to counsel, incite, or aid and abet another in attempting to commit suicide, and the law explicitly allows any person to use "such force as may reasonably be necessary" to prevent another from committing suicide.[125] The Northern Territory of Australia briefly had legal physician-assisted suicide from 1996 to 1997.[126]

No country in Europe currently considers suicide or attempted suicide to be a crime.[127] England and Wales decriminalized suicide via the Suicide Act 1961 and the Republic of Ireland in 1993.[127] The word "commit" was used in reference to it being illegal, however many organisations have stopped it because of the negative connotation.[128][129]

In India, suicide is illegal and surviving family may face legal difficulties.[130] In Germany, active euthanasia is illegal and anyone present during suicide may be prosecuted for failure to render aid in an emergency.[131] Switzerland has recently taken steps to legalize assisted suicide for the chronically mentally ill. The high court in Lausanne, in a 2006 ruling, granted an anonymous individual with longstanding psychiatric difficulties the right to end his own life.[132]

In the United States, suicide is not illegal but may be associated with penalties for those who attempt it.[127] Physician-assisted suicide is legal in the states of Oregon[133] and Washington.[134]

Religious views
Main article: Religious views on suicide


A Hindu widow burning herself with the corpse of her husband, 1820s.
In most forms of Christianity, suicide is considered a sin, based mainly on the writings of influential Christian thinkers of the Middle Ages, such as St. Augustine and St. Thomas Aquinas; but suicide was not considered a sin under the Byzantine Christian code of Justinian, for instance.[135][136] In Catholic doctrine, the argument is based on the commandment "Thou shalt not kill" (made applicable under the New Covenant by Jesus in Matthew 19:18), as well as the idea that life is a gift given by God which should not be spurned, and that suicide is against the "natural order" and thus interferes with God's master plan for the world.[137]

However, it is believed that mental illness or grave fear of suffering diminishes the responsibility of the one completing suicide.[138] Counter-arguments include the following: that the sixth commandment is more accurately translated as "thou shalt not murder", not necessarily applying to the self; that God has given free will to humans; that taking one's own life no more violates God's Law than does curing a disease; and that a number of suicides by followers of God are recorded in the Bible with no dire condemnation.[139]

Judaism focuses on the importance of valuing this life, and as such, suicide is tantamount to denying God's goodness in the world. Despite this, under extreme circumstances when there has seemed no choice but to either be killed or forced to betray their religion, Jews have committed individual suicide or mass suicide (see Masada, First French persecution of the Jews, and York Castle for examples) and as a grim reminder there is even a prayer in the Jewish liturgy for "when the knife is at the throat", for those dying "to sanctify God's Name" (see Martyrdom). These acts have received mixed responses by Jewish authorities, regarded by some as examples of heroic martyrdom, while others state that it was wrong for them to take their own lives in anticipation of martyrdom.[140]

Suicide is not allowed in Islam.[52] In Hinduism, suicide is generally frowned upon and is considered equally sinful as murdering another in contemporary Hindu society. Hindu Scriptures state that one who commits suicide will become part of the spirit world, wandering earth until the time one would have otherwise died, had one not committed suicide.[141] However, Hinduism accepts a man's right to end one's life through the non-violent practice of fasting to death, termed Prayopavesa.[142] But Prayopavesa is strictly restricted to people who have no desire or ambition left, and no responsibilities remaining in this life.[142] Jainism has a similar practice named Santhara. Sati, or self-immolation by widows was prevalent in Hindu society during the Middle Ages.[143]

Philosophy
Main article: Philosophy of suicide


The Way Out, or Suicidal Ideation: George Grie, 2007.
A number of questions are raised within the philosophy of suicide, included what constitutes suicide, whether or not suicide can be a rational choice, and the moral permissibility of suicide.[144] Arguments as to acceptability of suicide in moral or social terms range from the position that the act is inherently immoral and unacceptable under any circumstances to a regard for suicide as a sacrosanct right of anyone who believes they have rationally and conscientiously come to the decision to end their own lives, even if they are young and healthy.

Opponents to suicide include Christian philosophers such as Augustine of Hippo and Thomas Aquinas,[144] Immanuel Kant[145] and, arguably, John Stuart Mill – Mill's focus on the importance of liberty and autonomy meant that he rejected choices which would prevent a person from making future autonomous decisions.[146] Others view suicide as a legitimate matter of personal choice. Supporters of this position maintain that no one should be forced to suffer against their will, particularly from conditions such as incurable disease, mental illness, and old age that have no possibility of improvement. They reject the belief that suicide is always irrational, arguing instead that it can be a valid last resort for those enduring major pain or trauma.[147] A stronger stance would argue that people should be allowed to autonomously choose to die regardless of whether they are suffering. Notable supporters of this school of thought include Scottish empiricist David Hume[144] and American bioethicist Jacob Appel.[132][148]

Advocacy
See also: Advocacy of suicide


In this painting by Alexandre-Gabriel Decamps, the palette, pistol, and note lying on the floor suggest that the event has just taken place; an artist has taken his own life.[149]
Advocacy of suicide has occurred in many cultures and subcultures. The Japanese military during World War II encouraged and glorified kamikaze attacks, which were suicide attacks by military aviators from the Empire of Japan against Allied naval vessels in the closing stages of the Pacific theatre of World War II. Japanese society as a whole has been described as suicide "tolerant"[150] (see Suicide in Japan).

Internet searches for information on suicide return webpages that 10-30% of the time encourage or facilitate suicide attempts. There is some concern that such sites may push those predisposed over the edge. Some people form suicide pacts online, either with preexisting friends or people than have recently encountered in chat rooms or message boards. The Internet, however, may also help prevent suicide by providing a social group for those who are isolated.[151]

Locations
See also: List of suicide sites
Some landmarks have become known for high levels of suicide attempts.[152] These include San Francisco's Golden Gate Bridge, Japan's Aokigahara Forest,[153] England's Beachy Head,[152] and Toronto's Bloor Street Viaduct.[154]

As of 2010 the Golden Gate Bridge has had more than 1,300 commit suicide by jumping since its construction in 1937.[155] Many locations where suicide is common have constructed barriers to prevent it.[156] This includes the Luminous Veil in Toronto,[154] and barriers at the Eiffel Tower in Paris and Empire State Building in New York.[156] As of 2011 a barrier is being constructed for the Golden Gate Bridge.[157] They appear to be generally very effective.[157]

Notable cases
An example of mass suicide is the 1978 Jonestown killings/suicide in which 918 members of the Peoples Temple, an American religious group led by Jim Jones, ended their lives by drinking grape Flavor Aid laced with cyanide.[158][159][160] Thousands of Japanese civilians committed suicide in the last days of the Battle of Saipan in 1944, some jumping from "Suicide Cliff" and "Banzai Cliff".[161]

The 1981 hunger strikes, led by Bobby Sands, resulted in 10 deaths. The cause of death was recorded by the coroner as "starvation, self-imposed" rather than suicide; this was modified to simply "starvation" on the death certificates after protest from the dead strikers' families.[162] Erwin Rommel during World War II was found to have foreknowledge of the July 20 Plot on Hitler's life and was threatened with public trial, execution, and reprisals on his family unless he took his own life.[163]

Other species
Main article: Animal suicide
As suicide requires a willful attempt to die, some feel it therefore cannot be said to occur in non-human animals.[115] Suicidal behavior has been observed in salmonella seeking to overcome competing bacteria by triggering an immune system response against them.[164] Suicidal defenses by workers are also noted in a Brazilian ant Forelius pusillus where a small group of ants leaves the security of the nest after sealing the entrance from the outside each evening.[165]

Pea aphids, when threatened by a ladybug, can explode themselves, scattering and protecting their brethren and sometimes even killing the ladybug.[166] Some species of termites have soldiers that explode, covering their enemies with sticky goo.[167][168]

There have been anecdotal reports of dogs, horses and dolphins killing themselves, though with little conclusive evidence.[169] There has been little scientific study of animal suicide.[170]

Notes
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^ Jump up to: a b Gullota, edited by Thomas P.; Bloom, Martin (2002). The encyclopedia of primary prevention and health promotion. New York: Kluwer Academic/Plenum. p. 1112. ISBN 978-0-306-47296-1.
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^ Jump up to: a b c "Suicide (Stanford Encyclopedia of Philosophy)". Plato.stanford.edu. Retrieved 2009-05-06.
Jump up ^ Kant, Immanuel. (1785) Kant: The Metaphysics of Morals, M. Gregor (trans.), Cambridge: Cambridge University Press, 1996. ISBN 978-0-521-56673-5. p177.
Jump up ^ Safranek John P (1998). "Autonomy and Assisted Suicide: The Execution of Freedom". The Hastings Center Report 28 (4): 33. doi:10.2307/3528611.
Jump up ^ Raymond Whiting: A natural right to die: twenty-three centuries of debate, pp. 13–17; Praeger (2001) ISBN 0-313-31474-8
Jump up ^ Wesley J. Smith, Death on Demand: The assisted-suicide movement sheds its fig leaf, The Weekly Standard, June 5, 2007
Jump up ^ "The Suicide". The Walters Art Museum.
Jump up ^ Ozawa-de Silva, C (December 2008). "Too lonely to die alone: internet suicide pacts and existential suffering in Japan". Culture, medicine and psychiatry 32 (4): 516–51. doi:10.1007/s11013-008-9108-0. PMID 18800195.
Jump up ^ Durkee, T; Hadlaczky, G; Westerlund, M; Carli, V (October 2011). "Internet pathways in suicidality: a review of the evidence". International journal of environmental research and public health 8 (10): 3938–52. doi:10.3390/ijerph8103938. PMC 3210590. PMID 22073021.
^ Jump up to: a b Robinson, edited by David Picard, Mike (2012-11-28). Emotion in motion : tourism, affect and transformation. Farnham, Surrey: Ashgate. p. 176. ISBN 978-1-4094-2133-7.
Jump up ^ Robinson, ed. by Peter; Heitmann, Sine; Dieke, Peter (2010). Research themes for tourism. Oxfordshire [etc.]: CABI. p. 172. ISBN 978-1-84593-684-6.
^ Jump up to: a b Dennis, Richard (2008). Cities in modernity : representations and productions of metropolitan space, 1840 – 1930 (Repr. ed.). Cambridge : Cambridge Univ. Press. p. 20. ISBN 978-0-521-46841-1.
Jump up ^ McDougall, Tim; Armstrong, Marie; Trainor, Gemma (2010). Helping children and young people who self-harm : an introduction to self-harming and suicidal behaviours for health professionals. Abingdon, Oxon: Routledge. p. 23. ISBN 978-0-415-49913-2.
^ Jump up to: a b Bateson, John (2008). Building hope : leadership in the nonprofit world. Westport, Conn.: Praeger. p. 180. ISBN 978-0-313-34851-8.
^ Jump up to: a b Miller, David (2011). Child and Adolescent Suicidal Behavior: School-Based Prevention, Assessment, and Intervention. p. 46. ISBN 978-1-60623-997-1.
Jump up ^ Hall 1987, p.282
Jump up ^ "Jonestown Audiotape Primary Project." Alternative Considerations of Jonestown and Peoples Temple. San Diego State University.Archived 24 January 2011 at WebCite
Jump up ^ "1978:Mass Suicide Leaves 900 Dead". Retrieved 9 November 2011.
Jump up ^ John Toland, The Rising Sun: The Decline and Fall of the Japanese Empire 1936–1945, Random House, 1970, p. 519
Jump up ^ Suicide and Self-Starvation, Terence M. O'Keeffe, Philosophy, Vol. 59, No. 229 (Jul., 1984), pp. 349–363
Jump up ^ Watson, Bruce (2007). Exit Rommel: The Tunisian Campaign, 1942–43. Stackpole Books. p. 170. ISBN 978-0-8117-3381-6.
Jump up ^ Chang, Kenneth (August 25, 2008). In Salmonella Attack, Taking One for the Team. New York Times.
Jump up ^ Tofilski,Adam; Couvillon, MJ;Evison, SEF; Helantera, H; Robinson, EJH; Ratnieks, FLW (2008). "Preemptive Defensive Self-Sacrifice by Ant Workers" (PDF). The American Naturalist 172 (5): E239–E243. doi:10.1086/591688. PMID 18928332.

Model of the Copernican Universe by Thomas Digges in 1576, with the amendment that the stars are no longer confined to a sphere, but spread uniformly throughout the space surrounding the planets.
The Aristotelian model was accepted in the Western world for roughly two millennia, until Copernicus revived Aristarchus' theory that the astronomical data could be explained more plausibly if the earth rotated on its axis and if the sun were placed at the center of the Universe.
“In the center rests the sun. For who would place this lamp of a very beautiful temple in another or better place than this wherefrom it can illuminate everything at the same time?”
—Nicolaus Copernicus, in Chapter 10, Book 1 of De Revolutionibus Orbium Coelestrum (1543)
As noted by Copernicus himself, the suggestion that the Earth rotates was very old, dating at least to Philolaus (c. 450 BC), Heraclides Ponticus (c. 350 BC) and Ecphantus the Pythagorean. Roughly a century before Copernicus, Christian scholar Nicholas of Cusa also proposed that the Earth rotates on its axis in his book, On Learned Ignorance (1440).[71] Aryabhata (476–550), Brahmagupta (598–668), Albumasar and Al-Sijzi, also proposed that the Earth rotates on its axis.[citation needed] The first empirical evidence for the Earth's rotation on its axis, using the phenomenon of comets, was given by Tusi (1201–1274) and Ali Qushji (1403–1474).[citation needed]


Johannes Kepler published the Rudolphine Tables containing a star catalog and planetary tables using Tycho Brahe's measurements.
This cosmology was accepted by Isaac Newton, Christiaan Huygens and later scientists.[72] Edmund Halley (1720)[73] and Jean-Philippe de Cheseaux (1744)[74] noted independently that the assumption of an infinite space filled uniformly with stars would lead to the prediction that the nighttime sky would be as bright as the sun itself; this became known as Olbers' paradox in the 19th century.[75] Newton believed that an infinite space uniformly filled with matter would cause infinite forces and instabilities causing the matter to be crushed inwards under its own gravity.[72] This instability was clarified in 1902 by the Jeans instability criterion.[76] One solution to these paradoxes is the Charlier Universe, in which the matter is arranged hierarchically (systems of orbiting bodies that are themselves orbiting in a larger system, ad infinitum) in a fractal way such that the Universe has a negligibly small overall density; such a cosmological model had also been proposed earlier in 1761 by Johann Heinrich Lambert.[36][77] A significant astronomical advance of the 18th century was the realization by Thomas Wright, Immanuel Kant and others of nebulae.[73]
The modern era of physical cosmology began in 1917, when Albert Einstein first applied his general theory of relativity to model the structure and dynamics of the Universe.[78]
Theoretical models



High-precision test of general relativity by the Cassini space probe (artist's impression): radio signals sent between the Earth and the probe (green wave) are delayed by the warping of space and time (blue lines) due to the Sun's mass.
Of the four fundamental interactions, gravitation is dominant at cosmological length scales; that is, the other three forces play a negligible role in determining structures at the level of planetary systems, galaxies and larger-scale structures. Because all matter and energy gravitate, gravity's effects are cumulative; by contrast, the effects of positive and negative charges tend to cancel one another, making electromagnetism relatively insignificant on cosmological length scales. The remaining two interactions, the weak and strong nuclear forces, decline very rapidly with distance; their effects are confined mainly to sub-atomic length scales.
General theory of relativity
Main articles: Introduction to general relativity, General relativity, and Einstein's field equations
Given gravitation's predominance in shaping cosmological structures, accurate predictions of the Universe's past and future require an accurate theory of gravitation. The best theory available is Albert Einstein's general theory of relativity, which has passed all experimental tests to date. However, because rigorous experiments have not been carried out on cosmological length scales, general relativity could conceivably be inaccurate. Nevertheless, its cosmological predictions appear to be consistent with observations, so there is no compelling reason to adopt another theory.
General relativity provides a set of ten nonlinear partial differential equations for the spacetime metric (Einstein's field equations) that must be solved from the distribution of mass-energy and momentum throughout the Universe. Because these are unknown in exact detail, cosmological models have been based on the cosmological principle, which states that the Universe is homogeneous and isotropic. In effect, this principle asserts that the gravitational effects of the various galaxies making up the Universe are equivalent to those of a fine dust distributed uniformly throughout the Universe with the same average density. The assumption of a uniform dust makes it easy to solve Einstein's field equations and predict the past and future of the Universe on cosmological time scales.
Einstein's field equations include a cosmological constant (Λ),[78][79] that corresponds to an energy density of empty space.[80] Depending on its sign, the cosmological constant can either slow (negative Λ) or accelerate (positive Λ) the expansion of the Universe. Although many scientists, including Einstein, had speculated that Λ was zero,[81] recent astronomical observations of type Ia supernovae have detected a large amount of "dark energy" that is accelerating the Universe's expansion.[82] Preliminary studies suggest that this dark energy corresponds to a positive Λ, although alternative theories cannot be ruled out as yet.[83] Russian physicist Zel'dovich suggested that Λ is a measure of the zero-point energy associated with virtual particles of quantum field theory, a pervasive vacuum energy that exists everywhere, even in empty space.[84] Evidence for such zero-point energy is observed in the Casimir effect.
Special relativity and space-time
Main articles: Introduction to special relativity and Special relativity


Only its length L is intrinsic to the rod (shown in black); coordinate differences between its endpoints (such as Δx, Δy or Δξ, Δη) depend on their frame of reference (depicted in blue and red, respectively).
The Universe has at least three spatial and one temporal (time) dimension. It was long thought that the spatial and temporal dimensions were different in nature and independent of one another. However, according to the special theory of relativity, spatial and temporal separations are interconvertible (within limits) by changing one's motion.
To understand this interconversion, it is helpful to consider the analogous interconversion of spatial separations along the three spatial dimensions. Consider the two endpoints of a rod of length L. The length can be determined from the differences in the three coordinates Δx, Δy and Δz of the two endpoints in a given reference frame

L^{2} = \Delta x^{2} + \Delta y^{2} + \Delta z^{2}
using the Pythagorean theorem. In a rotated reference frame, the coordinate differences differ, but they give the same length

L^{2} = \Delta \xi^{2} + \Delta \eta^{2} + \Delta \zeta^{2}.
Thus, the coordinates differences (Δx, Δy, Δz) and (Δξ, Δη, Δζ) are not intrinsic to the rod, but merely reflect the reference frame used to describe it; by contrast, the length L is an intrinsic property of the rod. The coordinate differences can be changed without affecting the rod, by rotating one's reference frame.
The analogy in spacetime is called the interval between two events; an event is defined as a point in spacetime, a specific position in space and a specific moment in time. The spacetime interval between two events is given by

s^{2} = L_{1}^{2} - c^{2} \Delta t_{1}^{2} = L_{2}^{2} - c^{2} \Delta t_{2}^{2}
where c is the speed of light. According to special relativity, one can change a spatial and time separation (L1, Δt1) into another (L2, Δt2) by changing one's reference frame, as long as the change maintains the spacetime interval s. Such a change in reference frame corresponds to changing one's motion; in a moving frame, lengths and times are different from their counterparts in a stationary reference frame. The precise manner in which the coordinate and time differences change with motion is described by the Lorentz transformation.
Solving Einstein's field equations
See also: Big Bang and Ultimate fate of the Universe
File:Closed Friedmann universe zero Lambda.ogg

Animation illustrating the metric expansion of the universe
The distances between the spinning galaxies increase with time, but the distances between the stars within each galaxy stay roughly the same, due to their gravitational interactions. This animation illustrates a closed Friedmann Universe with zero cosmological constant Λ; such a Universe oscillates between a Big Bang and a Big Crunch.
In non-Cartesian (non-square) or curved coordinate systems, the Pythagorean theorem holds only on infinitesimal length scales and must be augmented with a more general metric tensor gμν, which can vary from place to place and which describes the local geometry in the particular coordinate system. However, assuming the cosmological principle that the Universe is homogeneous and isotropic everywhere, every point in space is like every other point; hence, the metric tensor must be the same everywhere. That leads to a single form for the metric tensor, called the Friedmann–Lemaître–Robertson–Walker metric

ds^2 = -c^{2} dt^2 +
R(t)^2 \left( \frac{dr^2}{1-k r^2} + r^2 d\theta^2 + r^2 \sin^2 \theta \, d\phi^2 \right)
where (r, θ, φ) correspond to a spherical coordinate system. This metric has only two undetermined parameters: an overall length scale R that can vary with time, and a curvature index k that can be only 0, 1 or −1, corresponding to flat Euclidean geometry, or spaces of positive or negative curvature. In cosmology, solving for the history of the Universe is done by calculating R as a function of time, given k and the value of the cosmological constant Λ, which is a (small) parameter in Einstein's field equations. The equation describing how R varies with time is known as the Friedmann equation, after its inventor, Alexander Friedmann.[85]
The solutions for R(t) depend on k and Λ, but some qualitative features of such solutions are general. First and most importantly, the length scale R of the Universe can remain constant only if the Universe is perfectly isotropic with positive curvature (k=1) and has one precise value of density everywhere, as first noted by Albert Einstein. However, this equilibrium is unstable and because the Universe is known to be inhomogeneous on smaller scales, R must change, according to general relativity. When R changes, all the spatial distances in the Universe change in tandem; there is an overall expansion or contraction of space itself. This accounts for the observation that galaxies appear to be flying apart; the space between them is stretching. The stretching of space also accounts for the apparent paradox that two galaxies can be 40 billion light years apart, although they started from the same point 13.8 billion years ago[86] and never moved faster than the speed of light.
Second, all solutions suggest that there was a gravitational singularity in the past, when R goes to zero and matter and energy became infinitely dense. It may seem that this conclusion is uncertain because it is based on the questionable assumptions of perfect homogeneity and isotropy (the cosmological principle) and that only the gravitational interaction is significant. However, the Penrose–Hawking singularity theorems show that a singularity should exist for very general conditions. Hence, according to Einstein's field equations, R grew rapidly from an unimaginably hot, dense state that existed immediately following this singularity (when R had a small, finite value); this is the essence of the Big Bang model of the Universe. A common misconception is that the Big Bang model predicts that matter and energy exploded from a single point in space and time; that is false. Rather, space itself was created in the Big Bang and imbued with a fixed amount of energy and matter distributed uniformly throughout; as space expands (i.e., as R(t) increases), the density of that matter and energy decreases.
Space has no boundary – that is empirically more certain than any external observation. However, that does not imply that space is infinite... (translated, original German)
Bernhard Riemann (Habilitationsvortrag, 1854)
Third, the curvature index k determines the sign of the mean spatial curvature of spacetime averaged over length scales greater than a billion light years. If k=1, the curvature is positive and the Universe has a finite volume. Such universes are often visualized as a three-dimensional sphere S3 embedded in a four-dimensional space. Conversely, if k is zero or negative, the Universe may have infinite volume, depending on its overall topology. It may seem counter-intuitive that an infinite and yet infinitely dense Universe could be created in a single instant at the Big Bang when R=0, but exactly that is predicted mathematically when k does not equal 1. For comparison, an infinite plane has zero curvature but infinite area, whereas an infinite cylinder is finite in one direction and a torus is finite in both. A toroidal Universe could behave like a normal Universe with periodic boundary conditions, as seen in "wrap-around" video games such as Asteroids; a traveler crossing an outer "boundary" of space going outwards would reappear instantly at another point on the boundary moving inwards.


Illustration of the Big Bang theory, the prevailing model of the origin and expansion of spacetime and all that it contains. In this diagram time increases from left to right, and one dimension of space is suppressed, so at any given time the Universe is represented by a disk-shaped "slice" of the diagram.
The ultimate fate of the Universe is still unknown, because it depends critically on the curvature index k and the cosmological constant Λ. If the Universe is sufficiently dense, k equals +1, meaning that its average curvature throughout is positive and the Universe will eventually recollapse in a Big Crunch, possibly starting a new Universe in a Big Bounce. Conversely, if the Universe is insufficiently dense, k equals 0 or −1 and the Universe will expand forever, cooling off and eventually becoming inhospitable for all life, as the stars die and all matter coalesces into black holes (the Big Freeze and the heat death of the Universe). As noted above, recent data suggests that the expansion speed of the Universe is not decreasing as originally expected, but increasing; if this continues indefinitely, the Universe will eventually rip itself to shreds (the Big Rip). Experimentally, the Universe has an overall density that is very close to the critical value between recollapse and eternal expansion; more careful astronomical observations are needed to resolve the question.
Big Bang model
Main articles: Big Bang, Timeline of the Big Bang, Nucleosynthesis, and Lambda-CDM model
The prevailing Big Bang model accounts for many of the experimental observations described above, such as the correlation of distance and redshift of galaxies, the universal ratio of hydrogen:helium atoms, and the ubiquitous, isotropic microwave radiation background. As noted above, the redshift arises from the metric expansion of space; as the space itself expands, the wavelength of a photon traveling through space likewise increases, decreasing its energy. The longer a photon has been traveling, the more expansion it has undergone; hence, older photons from more distant galaxies are the most red-shifted. Determining the correlation between distance and redshift is an important problem in experimental physical cosmology.


Chief nuclear reactions responsible for the relative abundances of light atomic nuclei observed throughout the Universe.
Other experimental observations can be explained by combining the overall expansion of space with nuclear and atomic physics. As the Universe expands, the energy density of the electromagnetic radiation decreases more quickly than does that of matter, because the energy of a photon decreases with its wavelength. Thus, although the energy density of the Universe is now dominated by matter, it was once dominated by radiation; poetically speaking, all was light. As the Universe expanded, its energy density decreased and it became cooler; as it did so, the elementary particles of matter could associate stably into ever larger combinations. Thus, in the early part of the matter-dominated era, stable protons and neutrons formed, which then associated into atomic nuclei. At this stage, the matter in the Universe was mainly a hot, dense plasma of negative electrons, neutral neutrinos and positive nuclei. Nuclear reactions among the nuclei led to the present abundances of the lighter nuclei, particularly hydrogen, deuterium, and helium. Eventually, the electrons and nuclei combined to form stable atoms, which are transparent to most wavelengths of radiation; at this point, the radiation decoupled from the matter, forming the ubiquitous, isotropic background of microwave radiation observed today.
Other observations are not answered definitively by known physics. According to the prevailing theory, a slight imbalance of matter over antimatter was present in the Universe's creation, or developed very shortly thereafter, possibly due to the CP violation that has been observed by particle physicists. Although the matter and antimatter mostly annihilated one another, producing photons, a small residue of matter survived, giving the present matter-dominated Universe. Several lines of evidence also suggest that a rapid cosmic inflation of the Universe occurred very early in its history (roughly 10−35 seconds after its creation). Recent observations also suggest that the cosmological constant (Λ) is not zero and that the net mass-energy content of the Universe is dominated by a dark energy and dark matter that have not been characterized scientifically. They differ in their gravitational effects. Dark matter gravitates as ordinary matter does, and thus slows the expansion of the Universe; by contrast, dark energy serves to accelerate the Universe's expansion.
Multiverse theory
Main articles: Multiverse, Many-worlds interpretation, Bubble universe theory, and Parallel universe (fiction)


Depiction of a multiverse of seven "bubble" universes, which are separate spacetime continua, each having different physical laws, physical constants, and perhaps even different numbers of dimensions or topologies.
Some speculative theories have proposed that this Universe is but one of a set of disconnected universes, collectively denoted as the multiverse, challenging or enhancing more limited definitions of the Universe.[34][87] Scientific multiverse theories are distinct from concepts such as alternate planes of consciousness and simulated reality, although the idea of a larger Universe is not new; for example, Bishop Étienne Tempier of Paris ruled in 1277 that God could create as many universes as he saw fit, a question that was being hotly debated by the French theologians.[88]
Max Tegmark developed a four-part classification scheme for the different types of multiverses that scientists have suggested in various problem domains. An example of such a theory is the chaotic inflation model of the early Universe.[89] Another is the many-worlds interpretation of quantum mechanics. Parallel worlds are generated in a manner similar to quantum superposition and decoherence, with all states of the wave function being realized in separate worlds. Effectively, the multiverse evolves as a universal wavefunction. If the big bang that created our multiverse created an ensemble of multiverses, the wave function of the ensemble would be entangled in this sense.
The least controversial category of multiverse in Tegmark's scheme is Level I, which describes distant space-time events "in our own Universe". If space is infinite, or sufficiently large and uniform, identical instances of the history of Earth's entire Hubble volume occur every so often, simply by chance. Tegmark calculated our nearest so-called doppelgänger, is 1010115 meters away from us (a double exponential function larger than a googolplex).[90][91] In principle, it would be impossible to scientifically verify an identical Hubble volume. However, it does follow as a fairly straightforward consequence from otherwise unrelated scientific observations and theories. Tegmark suggests that statistical analysis exploiting the anthropic principle provides an opportunity to test multiverse theories in some cases. Generally, science would consider a multiverse theory that posits neither a common point of causation, nor the possibility of interaction between universes, to be an idle speculation.
Shape of the Universe

Main article: Shape of the Universe
The shape or geometry of the Universe includes both local geometry in the observable Universe and global geometry, which we may or may not be able to measure. Shape can refer to curvature and topology. More formally, the subject in practice investigates which 3-manifold corresponds to the spatial section in comoving coordinates of the four-dimensional space-time of the Universe. Cosmologists normally work with a given space-like slice of spacetime called the comoving coordinates. In terms of observation, the section of spacetime that can be observed is the backward light cone (points within the cosmic light horizon, given time to reach a given observer). If the observable Universe is smaller than the entire Universe (in some models it is many orders of magnitude smaller), one cannot determine the global structure by observation: one is limited to a small patch.
Among the Friedmann–Lemaître–Robertson–Walker (FLRW) models, the presently most popular shape of the Universe found to fit observational data according to cosmologists is the infinite flat model,[92] while other FLRW models include the Poincaré dodecahedral space[93][94] and the Picard horn.[95] The data fit by these FLRW models of space especially include the Wilkinson Microwave Anisotropy Probe (WMAP) and Planck maps of cosmic background radiation. NASA released the first WMAP cosmic background radiation data in February 2003, while a higher resolution map regarding Planck data was released by ESA in March 2013. Both probes have found almost perfect agreement with inflationary models and the standard model of cosmology, describing a flat, homogenous universe dominated by dark matter and dark energy.[9][96]
See also

Portal iconAstronomy portal
Portal iconSpace portal
Religious cosmology
Cosmic latte
Cosmology
Hindu cosmology
Dyson's eternal intelligence
Esoteric cosmology
False vacuum
Final anthropic principle
Fine-tuned Universe
Hindu cycle of the universe
Jain cosmology
Kardashev scale
The Mysterious Universe (book)
Nucleocosmochronology
Non-standard cosmology
Observable universe
Omega Point
Rare Earth hypothesis
Vacuum genesis
World view
Zero-energy Universe
Notes and references

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^ Jump up to: a b Hawking, Stephen (1988). A Brief History of Time. Bantam Books. p. 125. ISBN 0-553-05340-X.
Jump up ^ Sean Carroll, Ph.D., Cal Tech, 2007, The Teaching Company, Dark Matter, Dark Energy: The Dark Side of the Universe, Guidebook Part 1 pages 1 and 3, Accessed Oct. 7, 2013, “...only 5% of the universe is made of ordinary matter, with 25 percent being some kind of unseen dark matter and a full 70% being a smoothly distributed dark energy...”
Jump up ^ In contrast to dark energy, which is expansive ("negative pressure"), the dark matter leads to "clumping" through gravitation.
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Jump up ^ Hinshaw, Gary (December 15, 2005). "Tests of the Big Bang: The CMB". NASA WMAP. Retrieved 2007-01-09.
Jump up ^ Rindler, p. 202.
Jump up ^ Hinshaw, Gary (February 10, 2006). "What is the Universe Made Of?". NASA WMAP. Retrieved 2007-01-04.
Jump up ^ Wright, Edward L. (September 12, 2004). "Big Bang Nucleosynthesis". UCLA. Retrieved 2007-01-05.
M. Harwit, M. Spaans (2003). "Chemical Composition of the Early Universe". The Astrophysical Journal 589 (1): 53–57. arXiv:astro-ph/0302259. Bibcode:2003ApJ...589...53H. doi:10.1086/374415.
C. Kobulnicky, E. D. Skillman; Skillman (1997). "Chemical Composition of the Early Universe". Bulletin of the American Astronomical Society 29: 1329. Bibcode:1997AAS...191.7603K.
Jump up ^ "Antimatter". Particle Physics and Astronomy Research Council. October 28, 2003. Retrieved 2006-08-10.
Jump up ^ Landau and Lifshitz, p. 361.
Jump up ^ WMAP Mission: Results – Age of the Universe. Map.gsfc.nasa.gov. Retrieved 2011-11-28.
Jump up ^ Luminet, Jean-Pierre; Boudewijn F. Roukema (1999). "Topology of the Universe: Theory and Observations". Proceedings of Cosmology School held at Cargese, Corsica, August 1998. arXiv:astro-ph/9901364.
Luminet, Jean-Pierre; J. Weeks, A. Riazuelo, R. Lehoucq, J.-P. Uzan (2003). "Dodecahedral space topology as an explanation for weak wide-angle temperature correlations in the cosmic microwave background". Nature 425 (6958): 593–595. arXiv:astro-ph/0310253. Bibcode:2003Natur.425..593L. doi:10.1038/nature01944. PMID 14534579.
Jump up ^ Strobel, Nick (May 23, 2001). "The Composition of Stars". Astronomy Notes. Retrieved 2007-01-04.
"Have physical constants changed with time?". Astrophysics (Astronomy Frequently Asked Questions). Retrieved 2007-01-04.
Jump up ^ Rees, Martin (1999). Just Six Numbers. HarperCollins Publishers. ISBN 0-465-03672-4.
Jump up ^ Adams, F.C. (2008). "Stars in other universes: stellar structure with different fundamental constants". Journal of Cosmology and Astroparticle Physics 2008 (8): 010. arXiv:0807.3697. Bibcode:2008JCAP...08..010A. doi:10.1088/1475-7516/2008/08/010.
Jump up ^ Harnik, R.; Kribs, G.D. and Perez, G. (2006). "A Universe without weak interactions". Physical Review D 74 (3): 035006. arXiv:hep-ph/0604027. Bibcode:2006PhRvD..74c5006H. doi:10.1103/PhysRevD.74.035006.
Jump up ^ (Henry Gravrand, "La civilisation Sereer -Pangool") [in] Universität Frankfurt am Main, Frobenius-Institut, Deutsche Gesellschaft für Kulturmorphologie, Frobenius Gesellschaft, "Paideuma: Mitteilungen zur Kulturkunde, Volumes 43–44", F. Steiner (1997), pp. 144–5, ISBN 3515028420
Jump up ^ Will Durant, Our Oriental Heritage:
"Two systems of Hindu thought propound physical theories suggestively similar to those of Greece. Kanada, founder of the Vaisheshika philosophy, held that the world was composed of atoms as many in kind as the various elements. The Jains more nearly approximated to Democritus by teaching that all atoms were of the same kind, producing different effects by diverse modes of combinations. Kanada believed light and heat to be varieties of the same substance; Udayana taught that all heat comes from the sun; and Vachaspati, like Newton, interpreted light as composed of minute particles emitted by substances and striking the eye."
Jump up ^ Stcherbatsky, F. Th. (1930, 1962), Buddhist Logic, Volume 1, p. 19, Dover, New York:
"The Buddhists denied the existence of substantial matter altogether. Movement consists for them of moments, it is a staccato movement, momentary flashes of a stream of energy... "Everything is evanescent“,... says the Buddhist, because there is no stuff... Both systems [Sānkhya, and later Indian Buddhism] share in common a tendency to push the analysis of existence up to its minutest, last elements which are imagined as absolute qualities, or things possessing only one unique quality. They are called “qualities” (guna-dharma) in both systems in the sense of absolute qualities, a kind of atomic, or intra-atomic, energies of which the empirical things are composed. Both systems, therefore, agree in denying the objective reality of the categories of Substance and Quality,... and of the relation of Inference uniting them. There is in Sānkhya philosophy no separate existence of qualities. What we call quality is but a particular manifestation of a subtle entity. To every new unit of quality corresponds a subtle quantum of matter which is called guna “quality”, but represents a subtle substantive entity. The same applies to early Buddhism where all qualities are substantive... or, more precisely, dynamic entities, although they are also called dharmas ('qualities')."
^ Jump up to: a b c Craig, William Lane (June 1979). "Whitrow and Popper on the Impossibility of an Infinite Past". The British Journal for the Philosophy of Science 30 (2): 165–170 (165–6). doi:10.1093/bjps/30.2.165.
Jump up ^ Boyer, C. (1968) A History of Mathematics. Wiley, p. 54.
Jump up ^ Neugebauer, Otto E. (1945). "The History of Ancient Astronomy Problems and Methods". Journal of Near Eastern Studies 4 (1): 1–38. doi:10.1086/370729. JSTOR 595168. "the Chaldaean Seleucus from Seleucia"
Jump up ^ Sarton, George (1955). "Chaldaean Astronomy of the Last Three Centuries B. C". Journal of the American Oriental Society 75 (3): 166–173 (169). doi:10.2307/595168. JSTOR 595168. "the heliocentrical astronomy invented by Aristarchos of Samos and still defended a century later by Seleucos the Babylonian"
Jump up ^ William P. D. Wightman (1951, 1953), The Growth of Scientific Ideas, Yale University Press p. 38, where Wightman calls him Seleukos the Chaldean.
Jump up ^ Lucio Russo, Flussi e riflussi, Feltrinelli, Milano, 2003, ISBN 88-07-10349-4.
Jump up ^ Bartel, p. 527
Jump up ^ Bartel, pp. 527–9
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Jump up ^ Misner, Thorne and Wheeler, p. 754.
^ Jump up to: a b Misner, Thorne and Wheeler, p. 755–756.
^ Jump up to: a b Misner, Thorne and Wheeler, p. 756.
Jump up ^ de Cheseaux JPL (1744). Traité de la Comète. Lausanne. pp. 223ff.. Reprinted as Appendix II in Dickson FP (1969). The Bowl of Night: The Physical Universe and Scientific Thought. Cambridge, MA: M.I.T. Press. ISBN 978-0-262-54003-2.
Jump up ^ Olbers HWM (1826). "Unknown title". Bode's Jahrbuch 111.. Reprinted as Appendix I in Dickson FP (1969). The Bowl of Night: The Physical Universe and Scientific Thought. Cambridge, MA: M.I.T. Press. ISBN 978-0-262-54003-2.
Jump up ^ Jeans, J. H. (1902). "The Stability of a Spherical Nebula" (PDF). Philosophical Transactions of the Royal Society A 199 (312–320): 1–53. Bibcode:1902RSPTA.199....1J. doi:10.1098/rsta.1902.0012. JSTOR 90845. Retrieved 2011-03-17.
Jump up ^ Misner, Thorne and Wheeler, p. 757.
^ Jump up to: a b Einstein, A (1917). "Kosmologische Betrachtungen zur allgemeinen Relativitätstheorie". Preussische Akademie der Wissenschaften, Sitzungsberichte. 1917. (part 1): 142–152.
Jump up ^ Rindler, pp. 226–229.
Jump up ^ Landau and Lifshitz, pp. 358–359.
Jump up ^ Einstein, A (1931). "Zum kosmologischen Problem der allgemeinen Relativitätstheorie". Sitzungsberichte der Preussischen Akademie der Wissenschaften, Physikalisch-mathematische Klasse 1931: 235–237.
Einstein A., de Sitter W. (1932). "On the relation between the expansion and the mean density of the Universe". Proceedings of the National Academy of Sciences 18 (3): 213–214. Bibcode:1932PNAS...18..213E. doi:10.1073/pnas.18.3.213. PMC 1076193. PMID 16587663.
Jump up ^ Hubble Telescope news release. Hubblesite.org (2004-02-20). Retrieved 2011-11-28.
Jump up ^ "Mysterious force's long presence". BBC News. 2006-11-16.
Jump up ^ Zel'dovich YB (1967). "Cosmological constant and elementary particles". JETP Letters 6: 316–317. Bibcode:1967JETPL...6..316Z.
Jump up ^ Friedmann A. (1922). "Über die Krümmung des Raumes". Zeitschrift für Physik 10 (1): 377–386. Bibcode:1922ZPhy...10..377F. doi:10.1007/BF01332580.
Jump up ^ "Cosmic Detectives". The European Space Agency (ESA). 2013-04-02. Retrieved 2013-04-15.
Jump up ^ Munitz MK (1959). "One Universe or Many?". Journal of the History of Ideas 12 (2): 231–255. doi:10.2307/2707516. JSTOR 2707516.
Jump up ^ Misner, Thorne and Wheeler, p. 753.
Jump up ^ Linde A. (1986). "Eternal chaotic inflation". Mod. Phys. Lett. A1 (2): 81–85. Bibcode:1986MPLA....1...81L. doi:10.1142/S0217732386000129.
Linde A. (1986). "Eternally existing self-reproducing chaotic inflationary Universe" (PDF). Phys. Lett. B175 (4): 395–400. Bibcode:1986PhLB..175..395L. doi:10.1016/0370-2693(86)90611-8. Retrieved 2011-03-17.
Jump up ^ Tegmark M. (2003). "Parallel universes. Not just a staple of science fiction, other universes are a direct implication of cosmological observations". Scientific American 288 (5): 40–51. doi:10.1038/scientificamerican0503-40. PMID 12701329.
Jump up ^ Tegmark, Max (2003). "Parallel Universes". In "Science and Ultimate Reality: from Quantum to Cosmos", honoring John Wheeler's 90th birthday. J. D. Barrow, P.C.W. Davies, & C.L. Harper eds. Cambridge University Press (2003): 2131. arXiv:astro-ph/0302131. Bibcode:2003astro.ph..2131T.
Jump up ^ Will the Universe expand forever?, WMAP website at NASA.
Jump up ^ Luminet, Jean-Pierre; Jeff Weeks, Alain Riazuelo, Roland Lehoucq, Jean-Phillipe Uzan (2003-10-09). "Dodecahedral space topology as an explanation for weak wide-angle temperature correlations in the cosmic microwave background". Nature 425 (6958): 593–5. arXiv:astro-ph/0310253. Bibcode:2003Natur.425..593L. doi:10.1038/nature01944. PMID 14534579.
Jump up ^ Roukema, Boudewijn; Zbigniew Buliński, Agnieszka Szaniewska, Nicolas E. Gaudin (2008). "A test of the Poincare dodecahedral space topology hypothesis with the WMAP CMB data". Astronomy and Astrophysics 482 (3): 747. arXiv:0801.0006. Bibcode:2008A&A...482..747L. doi:10.1051/0004-6361:20078777.
Jump up ^ Aurich, Ralf; Lustig, S., Steiner, F., Then, H. (2004). "Hyperbolic Universes with a Horned Topology and the CMB Anisotropy". Classical and Quantum Gravity 21 (21): 4901–4926. arXiv:astro-ph/0403597. Bibcode:2004CQGra..21.4901A. doi:10.1088/0264-9381/21/21/010.
Jump up ^ "Planck reveals 'almost perfect' universe". Michael Banks. Physics World. 2013-03-21. Retrieved 2013-03-21.
Bibliography

Bartel (1987). "The Heliocentric System in Greek, Persian and Hindu Astronomy". Annals of the New York Academy of Sciences 500 (1): 525–545. Bibcode:1987NYASA.500..525V. doi:10.1111/j.1749-6632.1987.tb37224.x.
Landau, Lev, Lifshitz, E.M. (1975). The Classical Theory of Fields (Course of Theoretical Physics, Vol. 2) (revised 4th English ed.). New York: Pergamon Press. pp. 358–397. ISBN 978-0-08-018176-9.
Liddell, H. G. and Scott, R. A Greek-English Lexicon. Oxford University Press. ISBN 0-19-864214-8.
Misner, C.W., Thorne, Kip, Wheeler, J.A. (1973). Gravitation. San Francisco: W. H. Freeman. pp. 703–816. ISBN 978-0-7167-0344-0.
Rindler, W. (1977). Essential Relativity: Special, General, and Cosmological. New York: Springer Verlag. pp. 193–244. ISBN 0-387-10090-3.
Further reading

Weinberg, S. (1993). The First Three Minutes: A Modern View of the Origin of the Universe (2nd updated ed.). New York: Basic Books. ISBN 978-0-465-02437-7. OCLC 28746057. For lay readers.
Nussbaumer, Harry; Bieri, Lydia; Sandage, Allan (2009). Discovering the Expanding Universe. Cambridge University Press. ISBN 978-0-521-51484-2.
External links

Wikimedia Commons has media related to Universe.
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Is there a hole in the Universe? at HowStuffWorks
Stephen Hawking's Universe – Why is the Universe the way it is?
Cosmology FAQ
Cosmos – An "illustrated dimensional journey from microcosmos to macrocosmos"
Illustration comparing the sizes of the planets, the sun, and other stars
My So-Called Universe – Arguments for and against an infinite and parallel universes
The Dark Side and the Bright Side of the Universe Princeton University, Shirley Ho
Richard Powell: An Atlas of the Universe – Images at various scales, with explanations
Multiple Big Bangs
Universe – Space Information Centre
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