From Wikipedia, the free encyclopedia

This article is about the astronomical concept. For other uses of the word, see Meridian.

The meridian is the outer orange circle which Z, the zenith, lies on. O is the observer.

In the sky, a meridian is an imaginary great circle on the celestial sphere. It passes through the north point on the horizon, through the celestial pole, up to the zenith, through the south point on the horizon, and through the nadir, and is perpendicular to the local horizon.

Because it is fixed to the local horizon, stars will appear to drift past the local meridian as the earth spins. You can use an object's right ascension and the local sidereal time to determine when it will cross your local meridian, or culminate (see hour angle).

The upper meridian is the half above the horizon, the lower meridian the half below it.

.............We have a lot to do...... lets Begin...

From Wikipedia, the free encyclopedia

The prime meridian at Greenwich, England

A meridian (or line of longitude) is an imaginary arc on the Earth's surface from the North Pole to the South Pole that connects all locations running along it with a given longitude. The position of a point on the meridian is given by the latitude. Each meridian is perpendicular to all circles of latitude at the intersection points. Each is also the same size, being half of a great circle on the Earth's surface and therefore measuring 20,003.93 km.

Since the meridian that passes through Greenwich, England, establishes the meaning of zero degrees of longitude, or the Prime Meridian, any other meridian is identified by the angle, referenced to the center of the earth as vertex, between where it and the prime meridian cross the equator. As there are 360 degrees in a circle, the meridian on the opposite side of the earth from Greenwich (which forms the other half of a circle with the two through Greenwich) is 180° longitude, and the others lie between 0° and 180° of West longitude in the Western Hemisphere (west of Greenwich) and between 0° and 180° of East longitude in the Eastern Hemisphere (east of Greenwich). You can see the lines of longitude on most maps.

The term "meridian" comes from the Latin meridies, meaning "midday"; the sun crosses a given meridian midway between the times of sunrise and sunset on that meridian. The same Latin stem gives rise to the terms A.M. (Ante Meridian) and P.M. (Post Meridian) used to disambiguate hours of the day when using the 12-hour clock.

The magnetic meridian is an equivalent imaginary line connecting the magnetic south and north poles and can be taken as the magnetic force lines along the surface of the earth^[1]. That is, a compass needle will be parallel to the magnetic meridian. The angle between the magnetic and the true meridian is the Magnetic declination, which is relevant for navigating with a compass.^[2]

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From Wikipedia, the free encyclopedia

From left to right, the square, the cube, and the tesseract. The square is bounded by 1-dimensional lines, the cube by 2-dimensional areas, and the tesseract by 3-dimensional volumes. A projection of the cube is given since it is viewed on a two-dimensional screen. The same applies to the tesseract, which additionally can only be shown as a projection even in three-dimensional space.

A diagram showing the first four spatial dimensions.

In mathematics and physics, the dimension of a space or object is informally defined as the minimum number of coordinates needed to specify each point within it.^[1][2] Thus a line has a dimension of one because only one coordinate is needed to specify a point on it. A surface such as a plane or the surface of a cylinder or sphere has a dimension of two because two coordinates are needed to specify a point on it (for example, to locate a point on the surface of a sphere you need both its latitude and its longitude). Cubes, cylinders and spheres are three-dimensional.

The concept of dimension is not restricted to physical objects. High-dimensional spaces occur in mathematics and the sciences for many reasons, frequently as configuration spaces such as in Lagrangian or Hamiltonian mechanics; these are abstract spaces, independent of the physical space we live in. The state-space of quantum mechanics is an infinite-dimensional function space. Some physical theories are also by nature high-dimensional, such as the 4-dimensional general relativity and higher-dimensional string theories.

[edit] In mathematics

In mathematics, the dimension of an object is an intrinsic property, independent of the space in which the object may happen to be embedded. For example: a point on the unit circle in the plane can be specified by two Cartesian coordinates but one can make do with a single coordinate (the polar coordinate angle), so the circle is 1-dimensional even though it exists in the 2-dimensional plane. This intrinsic notion of dimension is one of the chief ways in which the mathematical notion of dimension differs from its common usages.

The dimension of Euclidean n-space Eⁿ is n. When trying to generalize to other types of spaces, one is faced with the question “what makes Eⁿ n-dimensional?" One answer is that in order to cover a fixed ball in Eⁿ by small balls of radius ε, one needs on the order of ε⁻ⁿ such small balls. This observation leads to the definition of the Minkowski dimension and its more sophisticated variant, the Hausdorff dimension. But there are also other answers to that question. For example, one may observe that the boundary of a ball in Eⁿ looks locally like E^{n − 1} and this leads to the notion of the inductive dimension. While these notions agree on Eⁿ, they turn out to be different when one looks at more general spaces.

A tesseract is an example of a four-dimensional object. Whereas outside of mathematics the use of the term "dimension" is as in: "A tesseract has four dimensions," mathematicians usually express this as: "The tesseract has dimension 4," or: "The dimension of the tesseract is 4."

Although the notion of higher dimensions goes back to René Descartes, substantial development of a higher-dimensional geometry only began in the 19th century, via the work of Arthur Cayley, William Rowan Hamilton, Ludwig Schläfli and Bernhard Riemann. Riemann's 1854 Habilitationsschrift, Schlafi's 1852 Theorie der vielfachen Kontinuität, Hamilton's 1843 discovery of the quaternions and the construction of the Cayley Algebra marked the beginning of higher-dimensional geometry.

The rest of this section examines some of the more important mathematical definitions of dimension.

[edit] Hamel dimension

For vector spaces, there is a natural concept of dimension, namely the cardinality of a basis.

[edit] Manifolds

A connected topological manifold is locally homeomorphic to Euclidean n-space, and the number n is called the manifold's dimension. One can show that this yields a uniquely defined dimension for every connected topological manifold.

The theory of manifolds, in the field of geometric topology, is characterized by the way dimensions 1 and 2 are relatively elementary, the high-dimensional cases n > 4 are simplified by having extra space in which to 'work'; and the cases n = 3 and 4 are in some senses the most difficult. This state of affairs was highly marked in the various cases of the Poincaré conjecture, where four different proof methods are applied.

[edit] Lebesgue covering dimension

For any normal topological space X, the Lebesgue covering dimension of X is defined to be n if n is the smallest integer for which the following holds: any open cover has an open refinement (a second open cover where each element is a subset of an element in the first cover) such that no point is included in more than n + 1 elements. In this case we write dim X = n. For X a manifold, this coincides with the dimension mentioned above. If no such integer n exists, then the dimension of X is said to be infinite, and we write dim X = ∞. Note also that we say X has dimension −1, i.e. dim X = −1 if and only if X is empty. This definition of covering dimension can be extended from the class of normal spaces to all Tychonoff spaces merely by replacing the term "open" in the definition by the term "functionally open".

[edit] Inductive dimension

An inductive definition of dimension can be created as follows. Consider a discrete set of points (such as a finite collection of points) to be 0-dimensional. By dragging a 0-dimensional object in some direction, one obtains a 1-dimensional object. By dragging a 1-dimensional object in a new direction, one obtains a 2-dimensional object. In general one obtains an n+1-dimensional object by dragging an n dimensional object in a new direction.

The inductive dimension of a topological space may refer to the small inductive dimension or the large inductive dimension, and is based on the analogy that (n + 1)-dimensional balls have n dimensional boundaries, permitting an inductive definition based on the dimension of the boundaries of open sets.

[edit] Hausdorff dimension

For sets which are of a complicated structure, especially fractals, the Hausdorff dimension is useful. The Hausdorff dimension is defined for all metric spaces and, unlike the Hamel dimension, can also attain non-integer real values.^[3] The box dimension or Minkowski dimension is a variant of the same idea. In general, there exist more definitions of fractal dimensions that work for highly irregular sets and attain non-integer positive real values.

[edit] Hilbert spaces

Every Hilbert space admits an orthonormal basis, and any two such bases for a particular space have the same cardinality. This cardinality is called the dimension of the Hilbert space. This dimension is finite if and only if the space's Hamel dimension is finite, and in this case the above dimensions coincide.

[edit] In physics

[edit] Spatial dimensions

A three-dimensional Cartesian coordinate system.

Classical physics theories describe three physical dimensions: from a particular point in space, the basic directions in which we can move are up/down, left/right, and forward/backward. Movement in any other direction can be expressed in terms of just these three. Moving down is the same as moving up a negative distance. Moving diagonally upward and forward is just as the name of the direction implies; i.e., moving in a linear combination of up and forward. In its simplest form: a line describes one dimension, a plane describes two dimensions, and a cube describes three dimensions. (See Space and Cartesian coordinate system.)

[edit] Time

A temporal dimension is a dimension of time. Time is often referred to as the "fourth dimension" for this reason, but that is not to imply that it is a spatial dimension. A temporal dimension is one way to measure physical change. It is perceived differently from the three spatial dimensions in that there is only one of it, and that we cannot move freely in time but subjectively move in one direction.

The equations used in physics to model reality do not treat time in the same way that humans perceive it. The equations of classical mechanics are symmetric with respect to time, and equations of quantum mechanics are typically symmetric if both time and other quantities (such as charge and parity) are reversed. In these models, the perception of time flowing in one direction is an artifact of the laws of thermodynamics (we perceive time as flowing in the direction of increasing entropy).

The best-known treatment of time as a dimension is Poincaré and Einstein's special relativity (and extended to general relativity), which treats perceived space and time as components of a four-dimensional manifold, known as spacetime, and in the special, flat case as Minkowski space.

[edit] Additional dimensions

Theories such as string theory and M-theory predict that physical space in general has in fact 10 and 11 dimensions, respectively. The extra dimensions are spacelike. We perceive only three spatial dimensions, and no physical experiments have confirmed the reality of additional dimensions. A possible explanation that has been suggested is that space acts as if it were "curled up" in the extra dimensions on a subatomic scale, possibly at the quark/string level of scale or below. Another less-held fringe view asserts that dimensions beyond the fourth progressively condense timelines and universes into single spatial points in the above dimension, until the tenth, where a 0-dimensional point equates to all possible timelines in all possible universes.^[4]

[edit] Literature

Perhaps the most basic way in which the word dimension is used in literature is as a hyperbolic synonym for feature, attribute, aspect, or magnitude. Frequently the hyperbole is quite literal as in he's so 2-dimensional, meaning that one can see at a glance what he is. This contrasts with 3-dimensional objects which have an interior that is hidden from view, and a back that can only be seen with further examination.

Science fiction texts often mention the concept of dimension, when really referring to parallel universes, alternate universes, or other planes of existence. This usage is derived from the idea that in order to travel to parallel/alternate universes/planes of existence one must travel in a spatial direction/dimension besides the standard ones. In effect, the other universes/planes are just a small distance away from our own, but the distance is in a fourth (or higher) spatial dimension, not the standard ones.

One of the most heralded science fiction novellas regarding true geometric dimensionality, and often recommended as a starting point for those just starting to investigate such matters, is the 1884 novel Flatland by Edwin A. Abbott. Isaac Asimov, in his foreword to the Signet Classics 1984 edition, described Flatland as "The best introduction one can find into the manner of perceiving dimensions."

Another reference would be the novel "A Wrinkle In Time" which uses the 5th Dimension as a way for Tesseracting the universe. Or in a better sense, folding the universe in half to move across it quickly.

[edit] Philosophy

In 1783, Kant wrote: "That everywhere space (which is not itself the boundary of another space) has three dimensions and that space in general cannot have more dimensions is based on the proposition that not more than three lines can intersect at right angles in one point. This proposition cannot at all be shown from concepts, but rests immediately on intuition and indeed on pure intuition a priori because it is apodictically (demonstrably) certain."^[5]

^{..............................Let the GROUND FLOOR Be our foundation...........}

^{..............................and let us build in all Dimensions of peace.....}

From Wikipedia, the free encyclopedia

A 1967 Soviet Union 16 kopeks postage stamp, with a satellite from an imagined extraterrestrial civilization.

Extraterrestrial life is defined as life which does not originate from planet Earth. It is the subject of astrobiology and its existence remains hypothetical since to date no credible evidence of extraterrestrial life has been discovered which has been generally accepted by the mainstream scientific community. Hypotheses regarding the origin(s) of extraterrestrial life, if it indeed exists, are as follows: one proposes that it may have emerged, independently, from different places in the universe. An alternative hypothesis is panspermia, which holds that life emerges from one location, then spreads between habitable planets. These two hypotheses are not mutually exclusive. The study and theorization of extraterrestrial life is known as astrobiology, exobiology or xenobiology. Speculated forms of extraterrestrial life range from life at the scale of bacteria to sapient or sentient beings.

Suggested locations which might have once developed, or presently continue to host life similar to our own, include the planets Venus^[1] and Mars, moons of Jupiter and Saturn (e.g. Europa,^[2] Enceladus and Titan) and Gliese 581 c and d, recently discovered to be near Earth-mass extrasolar planets apparently located in their star's habitable zone, and with the potential to have liquid water.^[3]

[edit] Possible basis of extraterrestrial life

Several theories have been proposed about the possible basis of alien life from a biochemical, evolutionary or morphological viewpoint.

[edit] Biochemistry

All life on Earth requires carbon, hydrogen, oxygen, nitrogen, sulfur and phosphorus as well as numerous other elements in smaller amounts, notably minerals; it also requires water as the solvent in which biochemical reactions take place. Sufficient quantities of carbon and the other major life-forming elements, along with water, may enable the formation of living organisms on other planets with a chemical make-up and average temperature similar to that of Earth. Because Earth and other planets are made up of "star dust", i.e. relatively abundant chemical elements formed from stars which have ended their lives as supernovae, it is very probable that other planets may have been formed by elements of a similar composition to the Earth's. The combination of carbon and water in the chemical form of carbohydrates (e.g. sugar) can be a source of chemical energy on which life depends, and can also provide structural elements for life (such as ribose, in the molecules DNA and RNA, and cellulose in plants). Plants derive energy through the conversion of light energy into chemical energy via photosynthesis. Life requires carbon in both reduced (methane derivatives) and partially-oxidized (carbon oxides) states. It also requires nitrogen as a reduced ammonia derivative in all proteins, sulfur as a derivative of hydrogen sulfide in some necessary proteins, and phosphorus oxidized to phosphates in genetic material and in energy transfer. Adequate water as a solvent supplies adequate oxygen as constituents of biochemical substances.

Pure water is useful because it has a neutral pH due to its continued dissociation between hydroxide and hydronium ions. As a result, it can dissolve both positive metallic ions and negative non-metallic ions with equal ability. Furthermore, the fact that organic molecules can be either hydrophobic (repelled by water) or hydrophilic (soluble in water) creates the ability of organic compounds to orient themselves to form water-enclosing membranes. The fact that solid water (ice) is less dense than liquid water also means that ice floats, thereby preventing Earth's oceans from slowly freezing. Without this quality, the oceans could have frozen solid during the Snowball Earth episodes. Additionally, the Van der Waals forces between water molecules give it an ability to store energy with evaporation, which upon condensation is released. This helps to moderate the climate, cooling the tropics and warming the poles, helping to maintain the thermodynamic stability needed for life.

Carbon is fundamental to terrestrial life for its immense flexibility in creating covalent chemical bonds with a variety of non-metallic elements, principally nitrogen, oxygen and hydrogen. Carbon dioxide and water together enable the storage of solar energy in sugars, such as glucose. The oxidation of glucose releases biochemical energy needed to fuel all other biochemical reactions.

The ability to form organic acids (–COOH) and amine bases (–NH₂) gives rise to the possibility of neutralization dehydrating reactions to build long polymer peptides and catalytic proteins from monomer amino acids, and with phosphates to build not only DNA (the information-storing molecule of inheritance), but also ATP (the principal energy "currency" of cellular life).

Due to their relative abundance and usefulness in sustaining life, many have hypothesized that lifeforms elsewhere in the universe would also utilize these basic materials. However, other elements and solvents could also provide a basis for life. Silicon is most often deemed to be the probable alternative to carbon. Silicon lifeforms are proposed to have a crystalline morphology, and are theorized to be able to exist in high temperatures, such as on planets which are very close to their star. Life forms based in ammonia (rather than water) have also been suggested, though this solution appears less optimal than water.^[4]

When looked at from a chemical perspective, life is fundamentally a self-replicating reaction, but one which could arise under a great many conditions and with various possible ingredients, though carbon-oxygen within the liquid temperature range of water seems most conducive. Suggestions have even been made that self-replicating reactions of some sort could occur within the plasma of a star, though it would be highly unconventional.^[5]

Several pre-conceived ideas about the characteristics of life outside of Earth have been questioned. For example, NASA scientists believe that the color of photosynthesizing pigments on extrasolar planets might not be green.^[6]

[edit] Evolution and morphology

In addition to the biochemical basis of extraterrestrial life, many have also considered evolution and morphology. Science fiction has often depicted extraterrestrial life with humanoid and/or reptilian forms. Aliens have often been depicted as having light green or grey skin, with a large head, as well as four limbs — i.e. fundamentally humanoid. Other subjects, such as felines and insects, have also occurred in fictional representations of aliens.

A division has been suggested between universal and parochial (narrowly restricted) characteristics. Universals are features which are thought to have evolved independently more than once on Earth (and thus, presumably, are not too difficult to develop) and are so intrinsically useful that species will inevitably tend towards them. These include flight, sight, photosynthesis and limbs, all of which are thought to have evolved several times here on Earth. There is a huge variety of eyes, for example, and many of these have radically different working schematics and different visual foci: the visual spectrum, infrared, polarity and echolocation. Parochials, however, are essentially arbitrary evolutionary forms. These often have little inherent utility (or at least have a function which can be equally served by dissimilar morphology) and probably will not be replicated. Intelligent aliens could communicate through gestures, as deaf humans do, or by sounds created from structures unrelated to breathing, which happens on Earth when, for instance, cicadas vibrate their wings, or crickets rub their legs.

Attempting to define parochial features challenges many taken-for-granted notions about morphological necessity. Skeletons, which are essential to large terrestrial organisms according to the experts of the field of Gravitational biology, are almost assured to be replicated elsewhere in one form or another. Many also conjecture as to some type of egg-laying amongst extraterrestrial creatures, but mammalian mammary glands might be a singular case.

The assumption of radical diversity amongst putative extraterrestrials is by no means settled. While many exobiologists do stress that the enormously heterogeneous nature of life on Earth foregrounds an even greater variety in space, others point out that convergent evolution may dictate substantial similarities between Earth and extraterrestrial life. These two schools of thought are called "divergionism" and "convergionism" respectively.^[5]

[edit] Beliefs in extraterrestrial life

[edit] Ancient and early modern ideas

Beliefs in extraterrestrial life may have been present in ancient Babylon, Assyria, Sumer, Egypt, Arabia, China, India, and South America, although in these societies, cosmology was often associated with the supernatural, and the notion of alien life is difficult to distinguish from that of gods, demons, and such. The first important Western thinkers to argue systematically for a universe full of other planets and, therefore, possible extraterrestrial life were the ancient Greek writer Thales and his student Anaximander in the 7th and 6th centuries B.C. The atomists of Greece took up the idea, arguing that an infinite universe ought to have an infinity of populated worlds. Ancient Greek cosmology worked against the idea of extraterrestrial life in one critical respect, however: the geocentric universe. Championed by Aristotle and codified by Ptolemy, it favored the Earth and Earth-life (Aristotle denied that there could be a plurality of worlds) and seemingly rendered extraterrestrial life philosophically untenable. Lucian, in his novels, described inhabitants of the Moon and other celestial bodies as humanoids, but significantly different from humans.

Authors of Jewish sources also considered extraterrestrial life. The Talmud states that there are at least 18,000 other worlds, but provides little elaboration on the nature of those worlds, or on whether they are physical or spiritual. Based on this, however, the 18th century exposition "Sefer HaB'rit" posits that extraterrestrial creatures exist, and that some may well possess intelligence. It adds that human beings should not expect creatures from another world to resemble earthly life any more than sea creatures resemble land animals.^[7][8]

Hindu beliefs of endlessly repeated cycles of life have led to descriptions of multiple worlds in existence and their mutual contacts (Sanskrit word Sampark (सम्पर्क) means 'contact' as in Mahasamparka (महासम्पर्क) = the great contact). According to Hindu scriptures, there are innumerable universes created by God to facilitate the fulfillment of the separated desires of innumerable living entities. However, the purpose of such creations is to bring back the deluded souls to correct understanding about the purpose of life. Aside from the innumerable universes which are material, there is also the unlimited spiritual world, where the purified living entities live with perfect conception about life and ultimate reality. The life of these purified beings is centered on loving devotional services to God. The spiritually aspiring saints and devotees, as well as thoughtful men of the material world, have been getting guidance and help from these purified living entities of the spiritual world from time immemorial. However, the relevance of such descriptions has to be evaluated in the context of a correct understanding of geography and science at those times.

Within Islam, the statement of the Qur'an "All praise belongs to God, Lord of all the worlds" indicates multiple universal bodies, and maybe even multiple universes, which may indicate extraterrestrial and even extradimensional life. Surat Al-Jinn also mentioned a statement from a Jinn regarding the current status and ability of his group in the heavens.

According to Ahmadiyya Islam a more direct reference from the Quran is presented by Mirza Tahir Ahmad as a proof that life on other planets may exist according to the Quran. In his book, Revelation, Rationality, Knowledge & Truth, he quotes verse 42:29 "And among His Signs is the creation of the heavens and the earth, and of whatever living creatures (da'bbah) He has spread forth in both..."; according to this verse there is life in heavens. According to the same verse "And He has the power to gather them together (jam-'i-him) when He will so please"; indicates the bringing together the life on Earth and the life elsewhere in the universe. The verse does not specify the time or the place of this meeting but rather states that this event will most certainly come to pass whenever God so desires. It should be pointed out that the Arabic term Jam-i-him used to express the gathering event can imply either a physical encounter or a contact through communication.^[9]

When Christianity spread throughout the West, the Ptolemaic system became very widely accepted, and although the Church never issued any formal pronouncement on the question of alien life^[10], at least tacitly, the idea was aberrant. In 1277, the Bishop of Paris, Étienne Tempier, did overturn Aristotle on one point: God could have created more than one world (given His omnipotence). Taking a further step, and arguing that aliens actually existed, remained rare. Notably, Cardinal Nicholas of Cusa speculated about aliens on the moon and sun.

Giordano Bruno, De l'Infinito, Universo e Mondi, 1584

There was a dramatic shift in thinking initiated by the invention of the telescope and the Copernican assault on geocentric cosmology. Once it became clear that the Earth was merely one planet amongst countless bodies in the universe, the extraterrestrial idea moved towards the scientific mainstream. God's omnipotence, it could be argued, not only allowed for other worlds and other life; on some level, it necessitated them. The best known early-modern proponent of such ideas was the Italian philosopher Giordano Bruno, who argued in the 16th century for an infinite universe in which every star is surrounded by its own solar system. Bruno's thoughts about God and the universe led to his eventual condemnation as a heretic by the Catholic church, as a result of which he was burned at the stake.

In the early 17th century the Czech astronomer Anton Maria Schyrleus of Rheita mused that "if Jupiter has (...) inhabitants (...) they must be larger and more beautiful than the inhabitants of the Earth, in proportion to the [characteristics] of the two spheres".^[11] Dominican monk Tommaso Campanella wrote about a Solarian alien race in his Civitas Solis. The Catholic Church has not made a formal ruling on existence of extraterrestrials. However, writing in the Vatican newspaper, the astronomer, Father José Gabriel Funes, director of the Vatican Observatory near Rome, said in 2008 that intelligent beings created by God could exist in outer space.^[12]

Such comparisons also appeared in poetry of the era. In "The Creation: a Philosophical Poem in Seven Books" (1712), Sir Richard Blackmore observed: "We may pronounce each orb sustains a race / Of living things adapted to the place". The didactic poet Henry More took up the classical theme of the Greek Democritus in "Democritus Platonissans, or an Essay Upon the Infinity of Worlds" (1647). With the new relative viewpoint that the Copernican revolution had wrought, he suggested "our world's sunne / Becomes a starre elsewhere". Fontanelle's "Conversations on the Plurality of Worlds" (translated into English in 1686) offered similar excursions on the possibility of extraterrestrial life, expanding, rather than denying, the creative sphere of a Maker.

The possibility of extraterrestrials remained a widespread speculation as scientific discovery accelerated. William Herschel, the discoverer of Uranus, was one of many 18th-19th century astronomers convinced that our Solar System, and perhaps others, would be well-populated by alien life. Other luminaries of the period who championed "cosmic pluralism" included Immanuel Kant and Benjamin Franklin. At the height of the Enlightenment, even the Sun and Moon were considered candidates for extraterrestrial inhabitants.

[edit] Extraterrestrials and the modern era

The Arecibo message is a digital message sent to globular star cluster M13, and is a well-known symbol of human attempts to contact extraterrestrials.

This enthusiasm toward the possibility of alien life continued well into the 20th century. Indeed, the (roughly) three centuries from the Scientific Revolution through to the beginning of the modern era of solar system probes were essentially the zenith for belief in extraterrestrials in the West. Many astronomers and other secular thinkers, at least some religious thinkers, and much of the general public were largely satisfied that aliens were a reality. This trend was finally tempered as actual probes visited potential alien abodes in the solar system. The moon was decisively ruled out as a possibility, while Venus and Mars, long the two main candidates for extraterrestrials, showed no obvious evidence of current life. The other large moons of our system which have been visited appear similarly lifeless, though the interesting geothermic forces observed (Io's volcanism, Europa's ocean, Titan's thick atmosphere) have underscored how broad the range of potentially habitable environments may be. Although the hypothesis of a deliberate cosmic silence of advanced extraterrestrials is also a possibility,^[13] the failure of the SETI program to detect anything resembling an intelligent radio signal after four decades of effort has at least partially dimmed the prevailing optimism of the beginning of the space age. Notwithstanding, the unproven belief in extraterrestrial beings is voiced (not as a hypothesis) in pseudoscience, conspiracy theories in popular folklore like about 'Area 51' and legends. Emboldened critics^[who?] view the search for extraterrestrials as unscientific, despite the fact that the SETI program is not the result of a continuous, dedicated search, but instead utilizes what resources and manpower it can, when it can. Furthermore, the SETI program only searches a limited range of frequencies at any one time.^[14]

Thus, the three decades preceding the turn of the second millennium saw a crossroads reached in beliefs in alien life. The prospect of ubiquitous, intelligent, space-faring civilizations in our galaxy appears increasingly dubious to many scientists. Still, in the words of SETI's Frank Drake, "All we know for sure is that the sky is not littered with powerful microwave transmitters".^[15] Drake has also noted that it is entirely possible that advanced technology results in communication being carried out in some way other than conventional radio transmission. At the same time, the data returned by space probes, and giant strides in detection methods, have allowed science to begin delineating habitability criteria on other worlds, and to confirm that at least other planets are plentiful, though aliens remain a question mark. The Wow! signal, from SETI, remains a speculative debate.

In 2000, geologist and paleontologist Peter Ward and astrobiologist Donald Brownlee published a book entitled Rare Earth: Why Complex Life is Uncommon in the Universe.^[16] In it, they discussed the Rare Earth hypothesis, in which they claim that Earth-like life is rare in the universe, while microbial life is common. Ward and Brownlee are open to the idea of evolution on other planets which is not based on essential Earth-like characteristics (such as DNA and carbon).

The possible existence of primitive (microbial) life outside of Earth is much less controversial to mainstream scientists, although, at present, no direct evidence of such life has been found. Indirect evidence has been offered for the current existence of primitive life on Mars. However, the conclusions that should be drawn from such evidence remain in debate.

[edit] Scientific search for extraterrestrial life

The NASA Kepler Mission for the search of extrasolar planets.

The scientific search for extraterrestrial life is being carried both directly and indirectly.

[edit] Direct search

Scientists are directly searching for evidence of unicellular life within the solar system, carrying out studies on the surface of Mars and examining meteors which have fallen to Earth. A mission is also proposed to Europa, one of Jupiter's moons with a possible liquid water layer under its surface, which might contain life.

There is some limited evidence that microbial life might possibly exist (or have existed) on Mars.^[17] An experiment on the Viking Mars lander reported gas emissions from heated Martian soil that some argue are consistent with the presence of microbes. However, the lack of corroborating evidence from other experiments on the Viking indicates that a non-biological reaction is a more likely hypothesis. Independently, in 1996, structures resembling nanobacteria were reportedly discovered in a meteorite, ALH84001, thought to be formed of rock ejected from Mars. This report is also controversial, and scientific debate continues.

Electron micrograph of martian meteorite ALH84001 showing structures that some scientists think could be fossilized bacteria-like lifeforms

In February 2005, NASA scientists reported that they had found strong evidence of present life on Mars.^[18] The two scientists, Carol Stoker and Larry Lemke of NASA's Ames Research Center, based their claims on methane signatures found in Mars' atmosphere resembling the methane production of some forms of primitive life on Earth, as well as on their own study of primitive life near the Rio Tinto river in Spain. NASA officials soon denied the scientists' claims, and Stoker herself backed off from her initial assertions.^[19]

Though such findings are still very much in debate, support among scientists for the belief in the existence of life on Mars seems to be growing. In an informal survey conducted at the conference at which the European Space Agency presented its findings, 75 percent of the scientists in attendance were reported to believe that life once existed on Mars, and 25 percent reported a belief that life currently exists there.^[20]

The Gaia hypothesis stipulates that any planet with a robust population of life will have an atmosphere not in chemical equilibrium, which is relatively easy to determine from a distance by spectroscopy. However, significant advances in the ability to find and resolve light from smaller rocky worlds near to their star are necessary before this can be used to analyze extrasolar planets.

[edit] Indirect search

Terrestrial Planet Finder - A planned Infrared interferometer for finding Earth-like extrasolar planets (as of 2009^[update], it has not received the funding from NASA which it needs — that funding is going towards the Kepler mission).

It is theorized that any technological society in space will be transmitting information, although this is arguable, as there are generally no human systems intentionally, randomly, transmitting information into deep space, so there is no guarantee that any other species would do so, either. Also, the length of time required for a signal to travel across the vastness of space means that any signal detected or not detected would come from the distant past.
Nevertheless, Projects such as SETI are conducting an astronomical search for radio activity which would confirm the presence of intelligent life. A related suggestion is that aliens might broadcast pulsed and continuous laser signals in the optical, as well as infrared, spectrum;^[21] laser signals have the advantage of not "smearing" in the interstellar medium, and may prove more conducive to communication between the stars. While other communication techniques, including laser transmission and interstellar spaceflight, have been discussed seriously and may well be feasible, the measure of effectiveness is the amount of information communicated per unit cost, resulting with radio as the method of choice.

[edit] Extrasolar planets

Astronomers also search for extrasolar planets that they believe would be conducive to life, such as Gliese 581 c, Gliese 581 d and OGLE-2005-BLG-390Lb, which have been found to have Earth-like qualities.^[22][23] Current radiodetection methods have been inadequate for such a search, as the resolution afforded by recent technology is inadequate for a detailed study of extrasolar planetary objects. Future telescopes should be able to image planets around nearby stars, which may reveal the presence of life — either directly or through spectrography which would reveal key information, such as the presence of free oxygen in a planet's atmosphere:

Artist's Impression of Gliese 581 c, the first extrasolar planet discovered within its star's habitable zone.

• Darwin is an ESA mission designed to find Earth-like planets and analyze their atmosphere.
• The COROT mission, initiated by the French Space Agency, was launched in 2006, and is currently looking for extrasolar planets; it is the first of its kind.
• The Terrestrial Planet Finder was supposed to have been launched by NASA, but as of 2009, budget cuts have caused it to be delayed indefinitely.
• The Kepler Mission, largely replacing the Terrestrial Planet Finder, was launched in March 2009.

It has been argued that Alpha Centauri, the closest star system to Earth, may contain planets which could be capable of sustaining life.^[24]

On April 24, 2007, scientists at the European Southern Observatory in La Silla, Chile said they had found the first Earth-like planet. The planet, known as Gliese 581 c, orbits within the habitable zone of its star Gliese 581, a red dwarf star which is a scant 20.5 light years (194 trillion km) from the Earth. It was initially thought that this planet could contain liquid water, but recent computer simulations of the climate on Gliese 581c by Werner von Bloh and his team at Germany's Institute for Climate Impact Research suggest that carbon dioxide and methane in the atmosphere would create a runaway greenhouse effect. This would warm the planet well above the boiling point of water (100 degrees Celsius/212 degrees Fahrenheit), thus dimming the hopes of finding life. As a result of greenhouse models, scientists are now turning their attention to Gliese 581 d, which lies just outside of the star's traditional habitable zone.^[25]

On May 29, 2007, the Associated Press released a report stating that scientists identified twenty-eight new extra-solar planetary bodies. One of these newly-discovered planets is said to have many similarities to Neptune.^[26]

To date, 349 extrasolar planets have been discovered (with 37 multi-planet systems), and new discoveries occur monthly.^[27]

[edit] Drake equation

In 1961, University of California, Santa Cruz astronomer and astrophysicist Dr. Frank Drake devised the Drake equation. This controversial equation multiplied estimates of the following terms together:

• The rate of formation of suitable stars.

• The fraction of those stars which contain planets.

• The number of Earth-like worlds per planetary system.

• The fraction of planets where intelligent life develops.

• The fraction of possible communicative planets.

• The “lifetime” of possible communicative civilizations.

Drake used the equation to estimate that there are approximately 10,000 planets containing intelligent life, with the possible capability of communicating with Earth in the Milky Way galaxy.^[28]

Based on observations from the Hubble Space Telescope, there are at least 125 billion galaxies in the universe. It is estimated that at least ten percent of all sun-like stars have a system of planets^[29], there are 6.25^*10¹⁸ stars with planets orbiting them in the universe. If even a billionth of these stars have planets supporting life, there are some 6.25 billion life-supporting solar systems in the universe.

[edit] Extraterrestrial life in the Solar System

This planetary habitability chart shows where life might exist on extrasolar planets, based on our own Solar System and life on Earth.

Europa, due to the possibility of an ocean under its icy crust, might host some form of microbial life.^[2][30]

Many bodies in the Solar System have been suggested as being capable of containing conventional organic life. The most commonly suggested ones are listed below; of these, five of the ten are moons, and are thought to have large bodies of underground liquid (streams), where life may have evolved in a similar fashion to deep sea vents.

• Mars - Life on Mars has been long speculated. Liquid water is widely thought to have existed on Mars in the past, and there may still be liquid water beneath the surface. Methane was found in the atmosphere of Mars. By July 2008, laboratory tests aboard NASA's Phoenix Mars Lander had identified water in a soil sample. The lander's robotic arm delivered the sample to an instrument which identifies vapors produced by the heating of samples. Recent photographs from the Mars Global Surveyor show evidence of recent (i.e. within 10 years) flows of a liquid on the Red Planet's frigid surface.^[31]
• Mercury - The MESSENGER expedition to Mercury has discovered that a large amount of water exists in its exosphere.
• Europa - Europa may contain liquid water beneath its thick ice layer. It is possible that vents on the bottom of the ocean warm the ice, so liquid could exist beneath the ice layer, perhaps capable of supporting microbes and simple plants, just like in Earth's hydrothermal vents.^[2]
• Jupiter - Carl Sagan and others in the 1960s and 70s computed conditions for hypothetical amino acid-based macroscopic life in Jupiter's atmosphere, based on observed conditions of this atmosphere. These investigations inspired some science fiction stories.
• Ganymede - Possible underground ocean (see Europa).
• Callisto - Possible underground ocean (see Europa).
• Enceladus - Geothermal activity, water vapor. Possible under-ice oceans heated by tidal effects.
• Titan (Saturn's largest moon) - The only known moon with a significant atmosphere was recently visited by the Huygens probe. Latest discoveries indicate there is no global or widespread ocean, but that small and/or seasonal liquid hydrocarbon lakes are present on the surface (the first liquid lakes discovered outside of Earth).^[32][33][34]
• Venus - Recently, scientists have speculated on the existence of microbes in the stable cloud layers 50 km above the surface, evidenced by hospitable climates and chemical disequilibrium.^[35]

Numerous other bodies have been suggested as potential hosts for microbial life. Fred Hoyle has proposed that life might exist on comets, as some Earth microbes managed to survive on a lunar probe for many years. However, it is considered highly unlikely that complex multicellular organisms of the conventional chemistry of terrestrial life (i.e. animals and plants) could exist under these living conditions.

[edit] See also

Events and objects

• ALH84001 - a Mars meteorite with disputed seemingly microbial formations
• Ceres (dwarf planet)
• Gliese 581 c, d, and e
• Wow! signal

Searches for extraterrestrial life

• Rejection of chemical evolution
• Communication with Extraterrestrial Intelligence
• Darwin - an ESA mission designed to find Earth-like planets and analyze their atmosphere for signs of life.
• SETI (Search for Extra-Terrestrial Intelligence)
• Allen Telescope Array

Subjects

Theories

From Wikipedia, the free encyclopedia

Zener cards used in the early twentieth century for experimental research into ESP

Extrasensory perception (ESP) involves reception of information not gained through the recognized senses and not inferred from previous experience. The term was coined by German psychical researcher, Rudolf Tischner, and adopted by Duke University psychologist J. B. Rhine to denote psychic abilities such as telepathy and clairvoyance, and their trans-temporal operation as precognition or retrocognition. ESP is also sometimes casually referred to as a sixth sense, gut instinct or hunch. The term implies acquisition of information by means external to the basic limiting assumptions of science, such as that organisms can only receive information from the past to the present.

Parapsychology is the study of paranormal psychic phenomena, including ESP. Parapsychologists generally regard such tests as the ganzfeld experiment as providing compelling evidence for the existence of ESP. The scientific community does not accept this due to the disputed evidence base, the lack of a theory which would explain ESP, and the lack of experimental techniques which can provide reliably positive results.^{[1][2][3][4][5][6]}

[edit] History of ESP

The notion of extrasensory perception existed in antiquity. In many ancient cultures, such powers were ascribed to people who purported to use them for second sight or communicate with deities, ancestors, spirits, and the like.

[edit] J.B. Rhine

In the 1930s, at Duke University in North Carolina, J. B. Rhine and his wife Louisa tried to develop psychical research into an experimental science. To avoid the connotations of hauntings and the seance room, they renamed it "parapsychology." While Louisa Rhine concentrated on collecting accounts of spontaneous cases, J. B. Rhine worked largely in the laboratory, carefully defining terms such as ESP and psi and designing experiments to test them. A simple set of cards was developed, originally called Zener cards^[7] (after their designer)—now called ESP cards. They bear the symbols circle, square, wavy lines, cross, and star; there are five cards of each in a pack of 25.

In a telepathy experiment the "sender" looks at a series of cards while the "receiver" guesses the symbols. To try to observe clairvoyance, the pack of cards is hidden from everyone while the receiver guesses. To try to observe precognition, the order of the cards is determined after the guesses are made.

In all such experiments the order of the cards must be random so that hits are not obtained through systematic biases or prior knowledge. At first the cards were shuffled by hand, then by machine. Later, random number tables were used and, nowadays, computers. An advantage of ESP cards is that statistics can easily be applied to determine whether the number of hits obtained is higher than would be expected by chance. Rhine used ordinary people as subjects and claimed that, on average, they did significantly better than chance expectation. Later he used dice to test for psychokinesis and also claimed results that were better than chance.

In 1940, Rhine, J.G. Pratt, and others at Duke authored a review of all card-guessing experiments conducted internationally since 1882. Titled Extra-Sensory Perception After Sixty Years, it has become recognised as the first meta-analysis in science.^[8] It included details of replications of Rhine's studies. Through these years, 50 studies were published, of which 33 were contributed by investigators other than Rhine and the Duke University group; 61% of these independent studies reported significant results suggestive of ESP.^[9] Among these were psychologists at Colorado University and Hunter College, New York, who completed the studies with the largest number of trials and the highest levels of significance.^[10][11] Replication failures encouraged Rhine to further research into the conditions necessary to experimentally produce the effect. He maintained, however, that it was not replicability, or even a fundamental theory of ESP that would evolve research, but only a greater interest in unconscious mental processes and a more complete understanding of human personality.^[12]

One of the first statistical studies of ESP, using card-guessing, was conducted by Ina Jephson, in the 1920s. She reported mixed findings across two studies. More successful experiments were conducted with procedures other than card-guessing. G.N.M. Tyrrell used automated target-selection and data-recording in guessing the location of a future point of light. Whateley Carington experimented on the paranormal cognition of drawings of randomly selected words, using participants from across the globe. J. Hettinger studied the ability to retrieve information associated with token objects.^[13]

Less successful was University of London mathematician Samuel Soal in his attempted replications of the card-guessing studies. However, following a hypothesis suggested by Carington on the basis of his own findings, Soal re-analysed his data for evidence of what Carington termed displacement. Soal discovered, to his surprise, that two of his former participants, Basil Shackleton and Gloria Stewart, evidenced displacement: i.e., their responses significantly corresponded to targets for trials one removed from which they were assigned. Soal sought to confirm this finding by testing these participants in new experiments. Conducted during the war years, into the 1950s, under tightly controlled conditions, they produced highly significant results suggestive of precognitive telepathy. The findings were convincing for many other scientists and philosophers regarding telepathy and the claims of Rhine, but were also prominently critiqued as fraudulent, until, following Soal's death in 1975, support for them was largely abandoned. (For references and further information, see Samuel Soal.)

[edit] Sequence, position and psychological effects

Rhine and other parapsychologists found that some subjects, or some conditions, produced significant below-chance scoring (psi-missing); or that scores declined during testing (the "decline effect").^[14][15] Some such "internal effects" in ESP scores have also appeared to be idiosyncratic to particular participants or research methods. Most notable is the focusing effect identified in the decade-long research with Pavel Stepanek.

Personality measures have also been tested. People who believe in psi ("sheep") tend to score above chance, while those who do not believe in psi ("goats") show null results or psi-missing. This has become known as the "sheep-goat effect".^[16]

Prediction of decline and other position effects has proved challenging, although they have been often identified in data gathered for the purpose of observing other effects.^[17] Personality and attitudinal effects have shown greater predictability, with meta-analysis of parapsychological databases showing the sheep-goat effect, and other traits, to have significant and reliable effects over the accumulated data.^[18][19]

[edit] Cognitive and humanistic research

In the 1960s, in line with the development of cognitive psychology and humanistic psychology, parapsychologists became increasingly interested in the cognitive components of ESP, the subjective experience involved in making ESP responses, and the role of ESP in psychological life. Memory, for instance, was offered as a better model of psi than perception. This called for experimental procedures that were not limited to Rhine's favoured forced-choice methodology. Free-response measures, such as used by Carington in the 1930s, were developed with attempts to raise the sensitivity of participants to their cognitions. These procedures included relaxation, meditation, REM-sleep, and the Ganzfeld (a mild sensory deprivation procedure). These studies have proved to be even more successful than Rhine's forced-choice paradigm, with meta-analyses evidencing reliable effects, and many confirmatory replication studies.^[20][21] Methodological hypotheses have still been raised to explain the results, while others have sought to advance theoretical development in parapsychology on their bases. Moving research out of the laboratory and into naturalistic settings, and taking advantage of naturally occurring conditions, has been a related development.

[edit] Parapsychological investigation of ESP

The study of psi phenomena such as ESP is called parapsychology. The consensus of the Parapsychological Association is that certain types of psychic phenomena such as psychokinesis, telepathy, and astral projection are well established.^[22][5][23]

A great deal of reported extrasensory perception is said to occur spontaneously in conditions which are not scientifically controlled. Such experiences have often been reported to be much stronger and more obvious than those observed in laboratory experiments. These reports, rather than laboratory evidence, have historically been the basis for the extremely widespread belief in the authenticity of these phenomena. However, it has proven extremely difficult (perhaps impossible) to replicate such extraordinary experiences under controlled scientific conditions.^[5]

Those who believe that ESP may exist point to numerous studies that appear to offer evidence of the phenomenon's existence: the work of J. B. Rhine, Russell Targ, Harold E. Puthoff and physicists at SRI International in the 1970s, and many others, are often cited in arguments that ESP exists.

The main current debate concerning ESP surrounds whether or not statistically compelling laboratory evidence for it has already been accumulated.^[5][24] The most compelling and repeatable results are all small to moderate statistical results. Some dispute the positive interpretation of results obtained in scientific studies of ESP, because they are difficult to reproduce reliably, and are small effects. Parapsychologists have argued that the data from numerous studies show that certain individuals have consistently produced remarkable results while the remainder have constituted a highly significant trend that cannot be dismissed even if the effect is small.^[25]

[edit] Extrasensory perception and hypnosis

There is a common belief that a hypnotized person would be able to demonstrate ESP. Carl Sargent, a psychology major at the University of Cambridge, heard about the early claims of a hypnosis – ESP link and designed an experiment to test whether they had merit. He recruited 40 fellow college students, none of whom identified themselves as having ESP, and then divided them into a group that would be hypnotized before being tested with a pack of 25 Zener cards, and a control group that would be tested with the same Zener cards. The control subjects averaged a score of 5 out of 25 right, exactly what chance would indicate. The subjects who were hypnotized did more than twice as well, averaging a score of 11.9 out of 25 right. Sargent's own interpretation of the experiment is that ESP is associated with a relaxed state of mind and a freer, more atavistic level of consciousness.^{[dubious – discuss][citation needed]}

[edit] Skepticism

Among scientists in the National Academy of Sciences, 96% described themselves as "skeptical" of ESP, although 2% believed in psi and 10% felt that parapsychological research should be encouraged.^[26] The National Academy of Sciences had previously sponsored the Enhancing Human Performance report on mental development programs, which was critical of parapsychology.^[27]

A scientific methodology that shows statistically significant evidence for ESP has not been documented. The lack of a viable theory of the mechanism behind ESP is also frequently cited as a source of skepticism. Historical cases in which flaws have been discovered in the experimental design of parapsychological studies, and the occasional cases of fraud marred the field.^[28]

Critics of experimental parapsychology hold that there are no consistent and agreed-upon standards by which "ESP powers" may be tested, in the way one might test for, say, electrical current or the chemical composition of a substance. It is argued that when psychics are challenged by skeptics and fail to prove their alleged powers, they assign all sorts of reasons for their failure, such as that the skeptic is affecting the experiment with "negative energy." (See: Texas sharpshooter fallacy)

[edit] See also

• Clever Hans
• Parapsychology
• Intuition
• List of basic parapsychology topics
• List of spirituality-related topics
• Silva Method
• International Zetetic Challenge
• Consciousness causes collapse
• Clairvoyance
• Remote viewing
• Precognition
• Retrocognition
• Aura reading
• Telepathy
• Out-of-body experiences
• Astral projection
• Mediumship
• Psychokinesis
• Pyrokinesis

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