Psi is the 23rd letter of the
Greek alphabetThe Greek alphabet is the script that has been used to write the Greek language since at least 730 BC . The alphabet in its classical and modern form consists of 24 letters ordered in sequence from alpha to omega...
and has a
numericGreek numerals are a system of representing numbers using letters of the Greek alphabet. They are also known by the names Ionian numerals, Milesian numerals , Alexandrian numerals, or alphabetic numerals...
value of 700. In both Classical and
Modern GreekModern Greek refers to the varieties of the Greek language 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...
, the letter indicates the combination /ps/ (like in English "lapse"). The letter was adopted into the
Old Italic alphabetOld Italic refers to several now extinct alphabet systems used on the Italian Peninsula in ancient times for various Indo-European languages and non-Indo-European languages...
, and its shape is continued into the
AlgizThe Algiz is part of the ancient Nordic and Anglo-Saxon runic alphabet, often equated to the modern day z, however was traditionally pronounced yr. The letter has come to symbolize many neo-pagan religions and is often worn as a pendant...
rune of the
Elder FutharkThe 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 such as jewellery, amulets, tools, weapons and runestones...
. Psi was also adopted into the
early Cyrillic alphabetThe Early Cyrillic alphabet is a writing system developed in the First Bulgarian Empire in the 9th or 10th century to write the Old Church Slavonic liturgical language...
as
{{pp-semi-indef}}
{{Globalize|date=July 2010}}
{{Unreferenced|date=May 2008}}
{{Wiktionary|Ψ|ψ}}
{{Greek Alphabet|letter=psi|image=Greek alphabet psi.svg}}
Psi (uppercase Ψ, lowercase ψ; pronounced ˈsaɪ sigh) is the 23rd letter of the Greek alphabetThe Greek alphabet is the script that has been used to write the Greek language since at least 730 BC . The alphabet in its classical and modern form consists of 24 letters ordered in sequence from alpha to omega...
and has a
numericGreek numerals are a system of representing numbers using letters of the Greek alphabet. They are also known by the names Ionian numerals, Milesian numerals , Alexandrian numerals, or alphabetic numerals...
value of 700. In both Classical and
Modern GreekModern Greek refers to the varieties of the Greek language 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...
, the letter indicates the combination /ps/ (like in English "lapse"). The letter was adopted into the
Old Italic alphabetOld Italic refers to several now extinct alphabet systems used on the Italian Peninsula in ancient times for various Indo-European languages and non-Indo-European languages...
, and its shape is continued into the
AlgizThe Algiz is part of the ancient Nordic and Anglo-Saxon runic alphabet, often equated to the modern day z, however was traditionally pronounced yr. The letter has come to symbolize many neo-pagan religions and is often worn as a pendant...
rune of the
Elder FutharkThe 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 such as jewellery, amulets, tools, weapons and runestones...
. Psi was also adopted into the
early Cyrillic alphabetThe Early Cyrillic alphabet is a writing system developed in the First Bulgarian Empire in the 9th or 10th century to write the Old Church Slavonic liturgical language...
as
{{pp-semi-indef}}
{{Globalize|date=July 2010}}
{{Unreferenced|date=May 2008}}
{{Wiktionary|Ψ|ψ}}
{{Greek Alphabet|letter=psi|image=Greek alphabet psi.svg}}
Psi (uppercase Ψ, lowercase ψ; pronounced ˈsaɪ sigh) is the 23rd letter of the Greek alphabetThe Greek alphabet is the script that has been used to write the Greek language since at least 730 BC . The alphabet in its classical and modern form consists of 24 letters ordered in sequence from alpha to omega...
and has a
numericGreek numerals are a system of representing numbers using letters of the Greek alphabet. They are also known by the names Ionian numerals, Milesian numerals , Alexandrian numerals, or alphabetic numerals...
value of 700. In both Classical and
Modern GreekModern Greek refers to the varieties of the Greek language 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...
, the letter indicates the combination /ps/ (like in English "lapse"). The letter was adopted into the
Old Italic alphabetOld Italic refers to several now extinct alphabet systems used on the Italian Peninsula in ancient times for various Indo-European languages and non-Indo-European languages...
, and its shape is continued into the
AlgizThe Algiz is part of the ancient Nordic and Anglo-Saxon runic alphabet, often equated to the modern day z, however was traditionally pronounced yr. The letter has come to symbolize many neo-pagan religions and is often worn as a pendant...
rune of the
Elder FutharkThe 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 such as jewellery, amulets, tools, weapons and runestones...
. Psi was also adopted into the
early Cyrillic alphabetThe Early Cyrillic alphabet is a writing system developed in the First Bulgarian Empire in the 9th or 10th century to write the Old Church Slavonic liturgical language...
as
{{UnicodePsi is a letter in the early Cyrillic alphabet, derived from the Greek letter psi . It represents the sound /ps/, as in English naps...
. In Greek loanwords in Latin and modern languages with Latin alphabets, Psi is usually transliterated as "ps". In English, due to phonotactic constraints, its pronunciation is usually simplified to /s/ at the beginning of a word.
Meanings
The letter psi is commonly used in
physicsPhysics is a natural science that involves the study of matter and its motion through spacetime, along with related concepts such as energy and force. More broadly, it is the general analysis of nature, conducted in order to understand how the universe behaves.Physics is one of the oldest academic...
for representing a
wavefunctionNot to be confused with the related concept of the Wave equationA wave function or wavefunction is a probability amplitude in quantum mechanics describing the quantum state of a particle and how it behaves. Typically, its values are complex numbers and, for a single particle, it is a function of...
in
quantum mechanicsQuantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic...
, particularly with the
Schrödinger equationThe Schrödinger equation was formulated in 1926 by Austrian physicist Erwin Schrödinger. Used in physics , it is an equation that describes how the quantum state of a physical system changes in time....
and
bra-ket notationBra-ket notation is a standard notation for describing quantum states in the theory of quantum mechanics composed of angle brackets and vertical bars. It can also be used to denote abstract vectors and linear functionals in mathematics...
:
. It is also used to represent the (generalized) positional states of a
qubitIn quantum computing, a qubit or quantum bit is a unit of quantum information—the quantum analogue of the classical bit—with additional dimensions associated to the quantum properties of a physical atom....
in a
quantum computerA quantum computer is a device for computation that makes direct use of quantum mechanical phenomena, such as superposition and entanglement, to perform operations on data. Quantum computers are different from traditional computers based on transistors...
.
Psi is also used as the symbol for the
polygamma function, defined by
where
is the
gamma functionIn mathematics, the gamma function is an extension of the factorial function, with its argument shifted down by 1, to real and complex numbers...
.
The letters Ψ or ψ can also be a symbol for:
- psychology
Psychology is the study of the mind and behavior. Its immediate goal is to understand individuals and groups by both establishing general principles and researching specific cases. For many, the ultimate goal of psychology is to benefit society...
, psychiatryPsychiatry is the medical specialty devoted to the study and treatment of mental disorders. These mental disorders include various affective, behavioural, cognitive and perceptual abnormalities...
, and sometimes parapsychologyThe term parapsychology was coined in or around 1889 by philosopher Max Dessoir, and originates from para meaning "alongside", and psychology. The term was adopted by J.B. Rhine in the 1930s as a replacement for the term psychical research...
(involving paranormalParanormal is a general term that designates experiences that lie outside "the range of normal experience or scientific explanation" or that indicates phenomena understood to be outside of science's current ability to explain or measure...
or relating with the supernaturalThe supernatural or is that which is not subject to the laws of nature, or more figuratively, that which is said to exist above and beyond nature...
subjects, especially research into extrasensory perception).
- In mathematics, the reciprocal Fibonacci constant.
- Water potential
Water potential is the potential energy of water per unit volume relative to pure water in reference conditions. Water potential quantifies the tendency of water to move from one area to another due to osmosis, gravity, mechanical pressure, or matrix effects such as surface tension...
in movement of water between plant cells.
- In biochemistry
Biochemistry, sometimes called biological chemistry, is the study of chemical processes in living organisms, including, but not limited to, living matter. Biochemistry governs all living organisms and living processes...
, it denotes the rare nucleotideNucleotides are molecules that, when joined together, make up the structural units of RNA and DNA. In addition, nucleotides participate in cellular signaling , and are incorporated into important cofactors of enzymatic reactions...
pseudouridilic acidPseudouridine is the C-glycoside isomer of the nucleoside uridine, and it is the most prevalent of the over one hundred different modified nucleosides found in RNA. Ψ is found in all species and in many classes of RNA except mRNA...
.
- Stream function
The stream function is defined for two-dimensional flows of various kinds. The stream function can be used to plot streamlines, which represent the trajectories of particles in a steady flow. Streamlines are perpendicular to equipotential lines...
in fluid mechanicsFluid mechanics is the study of fluids and the forces on them. Fluid mechanics can be divided into fluid statics, the study of fluids at rest; fluid kinematics, the study of fluids in motion; and fluid dynamics, the study of the effect of forces on fluid motion...
defining the curve to which the flow velocityIn 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 tangentIn geometry, the tangent line to a plane curve at a given point is the straight line that "just touches" the curve at that point. More precisely, a straight line is said to be a tangent of a curve at a point on the curve if the line passes through the point on the curve and has slope where f...
.
- One of the dihedral angle
In geometry, a dihedral or torsion angle is the angle between two planes.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 is the eighth and farthest planet from the Sun in the Solar System. Named for the Roman god of the sea, it is the fourth-largest planet by diameter and the third largest by mass. Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times...
- The Schrödinger equation
The Schrödinger equation was formulated in 1926 by Austrian physicist Erwin Schrödinger. Used in physics , it is an equation that describes how the quantum state of a physical system changes in time....
and throughout quantum mechanicsQuantum mechanics, also known as quantum physics or quantum theory, is a branch of physics providing a mathematical description of much of the dual particle-like and wave-like behavior and interactions of energy and matter. It departs from classical mechanics primarily at the atomic and subatomic...
, ψ(x) stands for the wave function
- Indiana University
Indiana University is a multi-campus public university system in the state of Indiana, United States. Indiana University has a combined student body of more than 100,000 students, including approximately 42,000 students enrolled at the Indiana University Bloomington campus and approximately 37,000...
(as a superimposed II is the ninth letter and a vowel in the basic modern Latin alphabet.-History:In Semitic, the letter may have originated in a hieroglyph for an arm that represented a voiced pharyngeal fricative in Egyptian, but was reassigned to by Semites, because their word for "arm" began with that sound...
and UU is the twenty-first letter and a vowel in the basic modern Latin alphabet.-History:The letter U ultimately comes from the Semitic letter Waw by way of the letter Y. See the letter Y for details....
)
- Gangster Disciples
The Black Gangster Disciple Nation is a gang which was formed on the South-side of Chicago in the late 1960s, by David Barksdale, leader of the Black Disciples, and Larry Hoover, leader of the Supreme Gangsters. The two groups united to form the Black Gangster Disciple Nation .The gang has made...
- A Sai
The sai is a traditional Okinawan martial arts weapon. The basic form of the weapon is that of a pointed, dagger-shaped metal truncheon, with two curved prongs called yoku projecting from the handle...
, the name of which is pronounced the same way.
- Pharmacology
Pharmacology is the branch of medicine and biology concerned with the study of drug action. More specifically, it is the study of the interactions that occur between a living organism and chemicals that affect normal or abnormal biochemical function...
, general pharmacyPharmacy is the health profession that links the health sciences with the chemical sciences and it is charged with ensuring the safe and effective use of pharmaceutical drugs...
- In virology
Virology is the study of viruses and virus-like agents: their structure, classification and evolution, their ways to infect and exploit cells for virus reproduction, the diseases they cause, the techniques to isolate and culture them, and their use in research and therapy...
the ψ site is a viral packaging signal.
- The J/ψ meson, in particle physics
Particle physics is a branch of physics that studies the existence and interactions of particles that are the constituents of what is usually referred to as matter or radiation. In current understanding, particles are excitations of quantum fields and interact following their dynamics...
.
- In the computability theory
Computability theory, also called recursion theory, is a branch of mathematical logic that originated in the 1930s with the study of computable functions and Turing degrees. The field has grown to include the study of generalized computability and definability...
, 
represents the return value 
of a program 
.
- In the comic Monochrome
Monochrome describes paintings, drawings, design, or photographs in one color or shades of one color. A monochromatic object or image has colors in shades of limited colors or hues. Images using only shades of grey are called grayscale or black-and-white...
, Psi is a mentally disturbed character, though her name is usually spelled out.
- In the television show Babylon 5, Ψ is the symbol of the Psi Corps
In the fictional universe of Babylon 5, the Psi Corps is an agency of the Earth Alliance responsible for all humans with telepathic or other para-psychological abilities anywhere within Earth controlled space. All persons with Psi abilities are required to either join the Corps, face lifetime...
.
- In circadian physiology, ψ represents the phase relationship between a zeitgeber
Zeitgeber is any exogenous cue that synchronizes an organism's endogenous time-keeping system to the earth's 24-hour light/dark cycle. The strongest zeitgeber, for both plants and animals, is light...
and a biological rhythm.