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Psi (letter)
 
 
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For other uses, see Psi
Psi

Psi may refer to:...
.
Psi (uppercase ?, lowercase ?) is the 23rd letter of the Greek alphabet
Greek alphabet

The Greek alphabet is a set of twenty-four letters that has been used to write the Greek language since the late 9th century BC or early 8th century BCE....
 and has a numeric
Greek numerals

Greek numerals are a numeral system using letters of the Greek alphabet. They are also known by the names Milesian numerals, Alexandrian numerals, or alphabetic numerals....
 value of 700. In both Classical and Modern Greek
Modern Greek

Modern Greek refers the varieties of Greek spoken in the modern era. The beginning of the "modern" period of the language is often symbolically assigned to the fall of the Byzantine Empire in 1453, even though that date marks no clear linguistic boundary and many characteristic modern features of the language had been present centuries earli...
, the letter indicates the combination /ps/ (like in English "lapse"). In Greek, this consonant cluster can occur in the syllable initial position, as in the Greek word "????" [psári (=fish)]. However, in some languages (including English) this combination is not possible at the beginning of a syllable.






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For other uses, see Psi
Psi

Psi may refer to:...
.
Psi (uppercase ?, lowercase ?) is the 23rd letter of the Greek alphabet
Greek alphabet

The Greek alphabet is a set of twenty-four letters that has been used to write the Greek language since the late 9th century BC or early 8th century BCE....
 and has a numeric
Greek numerals

Greek numerals are a numeral system using letters of the Greek alphabet. They are also known by the names Milesian numerals, Alexandrian numerals, or alphabetic numerals....
 value of 700. In both Classical and Modern Greek
Modern Greek

Modern Greek refers the varieties of Greek spoken in the modern era. The beginning of the "modern" period of the language is often symbolically assigned to the fall of the Byzantine Empire in 1453, even though that date marks no clear linguistic boundary and many characteristic modern features of the language had been present centuries earli...
, the letter indicates the combination /ps/ (like in English "lapse"). In Greek, this consonant cluster can occur in the syllable initial position, as in the Greek word "????" [psári (=fish)]. However, in some languages (including English) this combination is not possible at the beginning of a syllable. In Latin
Latin

Latin is an Italic language, historically spoken in Latium and Ancient Rome. Through the Military history of the Roman Empire, Latin spread throughout the Mediterranean and a large part of Europe....
, Greek words beginning with psi are transcribed by ps-, but seem to have been pronounced simply as s-, with a quiescent p. This pronunciation has affected that of Greek loanwords beginning with the letter in several languages. In English, for example, psychology is pronounced with a silent p, and the name of the letter is often pronounced ("sigh"), although this is not always the case. The letter was adopted into the Old Italic alphabet
Old Italic alphabet

Old Italic refers to several now extinct alphabet systems used on the Italian Peninsula in ancient times for various Indo-European and non-Indo-European languages....
, and its shape is continued into the Algiz
Algiz

*Algiz, sometimes *Elhaz, is the Linguistic reconstruction Proto-Germanic name for the Runic alphabet, representing the Proto-Germanic terminal -z ....
 rune of the Elder Futhark
Elder Futhark

The Elder Futhark is the oldest form of the runic alphabet, used by Germanic tribes for Northwest Germanic and Migration period Germanic dialects of the 2nd to 8th centuries for inscriptions on artifacts and runestones....
.

The letter may have originated from the practice of writing the sigma
Sigma

Sigma is the eighteenth letter of the Greek alphabet, and carries the /s/ sound. In the system of Greek numerals it has a value of 200. When used at the end of a word, and the word is not all upper case, the final form is used....
 over the pi
Pi (letter)

Pi is the sixteenth letter of the Greek alphabet. In the system of Greek numerals it has a value of 80. Letters that arose from pi include Cyrillic Pe ....
, eventually making the combination into a single letter. Psi was also adopted into the early Cyrillic alphabet
Early Cyrillic alphabet

The old Cyrillic alphabet was a writing system developed in the First Bulgarian Empire in the tenth century to write the Old Church Slavonic liturgical language....
. See psi (Cyrillic)
Psi (Cyrillic)

Psi is a letter in the early Cyrillic alphabet, derived from the Greek language letter Psi . It represents the sound /ps/, as in English naps....
 (). This may have also been since the letter, both in lower case and uppercase form, resembles the trident
Trident

A trident , also called a leister or gig, is a three-tine spear. It is used for spear fishing and was formerly also a military weapon....
 wielded by Poseidon
Poseidon

In Greek mythology, Poseidon was the god of the sea and, as "Earth-Shaker," of earthquakes. The name of the god Nethuns in Etruscan mythology was adopted in Latin for Neptune in Roman mythology: both were sea gods analogous to Poseidon....
, the Greek god of water/ocean.

The letter psi is commonly used in physics
Physics

Physics is the natural science which examines basic concepts such as energy, force, and spacetime and all that derives from these, such as mass, charge, matter and its Motion ....
 for representing a wavefunction
Wavefunction

A wave function or wavefunction is a mathematical tool used in quantum mechanics to describe any physical system. It is a function from a mathematical space that maps the possible states of the system into the complex numbers....
 in quantum mechanics
Quantum mechanics

Quantum mechanics is a set of principles underlying the most fundamental known description of all physical systems at the microscopic scale . Notable amongst these principles are both a dual wave-like and particle-like behavior of matter and radiation, and prediction of probabilities in situations where classical physics predicts certaintie...
, particularly with the Schrödinger equation
Schrödinger equation

In physics, especially quantum mechanics, the Schr?dinger equation is an equation that describes how the quantum state of a physical system changes in time....
 and bra-ket notation
Bra-ket notation

Bra-ket notation is a standard notation for describing quantum states in the theory of quantum mechanics composed of bracket and vertical bars....
: . It is also used to represent the (generalized) positional states of a qubit
Qubit

A quantum bit or qubit is a unit of quantum information. That information is described by a Quantum state in a Two-state quantum system, which is formally equivalent to a two-dimensional vector space over the complex numbers....
 in a quantum computer
Quantum computer

A quantum computer is a device for computation that makes direct use of quantum mechanical phenomena, such as quantum superposition and quantum entanglement, to perform operations on data....
.

Psi is also used as the symbol for the polygamma function
Polygamma function

In mathematics, the polygamma function of order m is defined as the thderivative of the logarithm of the gamma function:Hereis the digamma function and is the gamma function....
, defined by where is the gamma function
Gamma function

In mathematics, the Gamma function is an extension of the factorial function to real number and complex number numbers. For a complex number z with positive real part the Gamma function is defined by...
.

The letters ? or ? can also be a symbol for:
  • psychology
    Psychology

    Psychology is an academic and applied science discipline involving the science study of human mental functions and behavior. Occasionally it also relies on symbolic hermeneutics and critical theory, although these traditions are less pronounced than in other social sciences such as sociology....
    , psychiatry
    Psychiatry

    Psychiatry is a Medicine Specialty devoted to the Treatment of mental disorders, Biomedical research and Prevention of mental disorder. The term was first coined by the German physician Johann Christian Reil in 1808....
    , and sometimes parapsychology
    Parapsychology

    Parapsychology is a discipline that seeks to investigate the existence and causes of psychic abilities and Survivalism using the scientific method....
     (involving paranormal
    Paranormal

    Paranormal is a general term that describes unusual experiences that lack a scientific explanation, or phenomena alleged to be outside of science's current ability to explain or measure....
     or relating with the supernatural
    Supernatural

    The term supernatural or supranatural pertains to an order of existence beyond the scientifically visible universe. Religious miracles are typically supernatural claims, as are Spell and curses, divination, the belief that there is an afterlife for the dead, and innumerable others....
     subjects).
  • In mathematics, the number of the "Supergolden Ratio", approximately 1.4 and the solution to the cubic equation x³ = x² + 1.
  • Water potential
    Water potential

    Water potential is the potential energy of water relative to pure free water in reference conditions. It quantifies the tendency of water to move from one area to another due to osmosis, gravity, mechanical pressure, or matrix effects including surface tension....
     in movement of water between plant cells.
  • Stream function
    Stream function

    The stream function is defined for two-dimensional flows of various kinds. The stream function can be used to plot Streamlines, streaklines, and pathliness, which represent the trajectories of particles in a steady flow....
     in fluid mechanics
    Fluid mechanics

    Fluid mechanics is the study of how fluids move and the forces on them. Fluid mechanics can be divided into fluid statics, the study of fluids at rest, and fluid dynamics, the study of fluids in motion....
     defining the curve to which the flow velocity
    Flow velocity

    In fluid dynamics the flow velocity, or velocity field, of a fluid is a vector field which is used to mathematically describe the motion of a fluid....
     is always tangent
    Tangent

    In geometry, the tangent line to a curve at a given Point is the straight line that "just touches" the curve at that point . As it passes through the point of tangency, the tangent line is "going in the same direction" as the curve, and in this sense it is the best straight-line approximation to the curve at that point....
    .
  • One of the dihedral angle
    Dihedral angle

    In geometry, the angle between two Plane s is called their dihedral or torsion angle.The dihedral angle of two planes can be seen by looking at the planes "edge on", i.e., along their line of intersection....
    s in the backbones of proteins
  • The planet Neptune
    NEPTUNE

    =Overview=The project, along with sister project, VENUS, offers a unique approach to ocean science. Traditionally, ocean scientists have relied on infrequent ship cruises or space-based satellites to carry out their research....
  • The Schrodinger Equation and throughout quantum mechanics
    Quantum mechanics

    Quantum mechanics is a set of principles underlying the most fundamental known description of all physical systems at the microscopic scale . Notable amongst these principles are both a dual wave-like and particle-like behavior of matter and radiation, and prediction of probabilities in situations where classical physics predicts certaintie...
    , ?(x) stands for the wave function
  • Indiana University
    Indiana University

    Indiana University, founded in 1820, is a nine-campus university system in the state of Indiana. The IU system includes the following campuses:...
     (as a superimposed I
    I

    I is the ninth Letter of the Latin alphabet. Its English language name is i ....
     and U
    U

    U is the twenty-first letter in the modern Latin alphabet. Its name in English language is spelled u ....
    )
  • Gangster Disciples
    Gangster Disciples

    The Black Gangster Disciple Nation was formed on the South-side of Chicago in the late 1960s, by David Barksdale, leader of the Gonzanto Disciples, and Larry Hoover, leader of the Supreme Disciples....
  • Crips
    Crips

    The Crips are a primarily, but not exclusively, African American gang founded in Los Angeles, California in 1971 mainly by 15-year-old Raymond Washington and Stanley Williams....
  • A Sai
    Sai (weapon)

    Sai is the Ryukyuan languages name for a traditional Okinawan weapon.The basic form of the weapon is that of a pointed, dagger-shaped truncheon, with two curved prongs projecting from the Handle ....
    , the name of which is pronounced the same way.
  • Pharmacology
    Pharmacology

    Pharmacology is the study of drug action. More specifically it is the study of the interactions that occur between a living organism and exogenous chemicals that alter normal biochemical function....
    , general pharmacy
    Pharmacy

    Pharmacy is the health profession that links the health sciences with the chemistrys, and it is charged with ensuring the safe and effective use of medication....
  • In virology
    Virology

    Virology is the study of virus : their structure, classification and evolution, their ways to infect and exploit cell for virus reproduction, the diseases they cause, the techniques to isolate and culture them, and their use in research and therapy....
     the ? site is a viral packaging signal.
  • The J/? meson, in particle physics
    Particle physics

    Particle physics is a branch of physics that studies the elementary particle constituents of matter and radiation, and the interactions between them....
    .
  • In the manga Monochrome
    Monochrome

    Monochrome comes from the Greek language ?????????? , meaning ?of one color?, which is a combination of ????? , meaning ?alone? or ?solitary?, and ????a , meaning ?color?....
    , Psi is a mentally disturbed character, though her name is usually spelled out.