The Full Wiki

Ψ: Wikis

Note: Many of our articles have direct quotes from sources you can cite, within the Wikipedia article! This article doesn't yet, but we're working on it! See more info or our list of citable articles.


(Redirected to Psi (letter) article)

From Wikipedia, the free encyclopedia

Psi uc lc.svg
Greek alphabet
Αα Alpha Νν Nu
Ββ Beta Ξξ Xi
Γγ Gamma Οο Omicron
Δδ Delta Ππ Pi
Εε Epsilon Ρρ Rho
Ζζ Zeta Σσς Sigma
Ηη Eta Ττ Tau
Θθ Theta Υυ Upsilon
Ιι Iota Φφ Phi
Κκ Kappa Χχ Chi
Λλ Lambda Ψψ Psi
Μμ Mu Ωω Omega
Obsolete letters
Ϝϝ Digamma Ϙϙ Qoppa
Ϻϻ San Ϡϡ Sampi
Other characters
Ϛϛ Stigma Ϸϸ Sho
Ͱͱ Heta

Greek diacritics
For other uses, see Psi.

Psi (uppercase Ψ, lowercase ψ; pronounced in English as sigh) is the 23rd letter of the Greek alphabet and has a numeric value of 700. In both Classical and Modern Greek, the letter indicates the combination /ps/ (like in English "lapse"). The letter was adopted into the Old Italic alphabet, and its shape is continued into the Algiz rune of the Elder Futhark. Psi was also adopted into the early Cyrillic alphabet as Ѱ. 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/.

The letter psi is commonly used in physics for representing a wavefunction in quantum mechanics, particularly with the Schrödinger equation and bra-ket notation: \langle\phi|\psi\rangle. It is also used to represent the (generalized) positional states of a qubit in a quantum computer.

Psi is also used as the symbol for the polygamma function, defined by

 \psi_n(x) = \frac{d^{(n)}}{dx^{(n)}}\frac{\Gamma '(x)}{\Gamma (x)}\,\!

where Γ(x) is the gamma function.

The letters Ψ or ψ can also be a symbol for:

See also


Up to date as of January 15, 2010

Definition from Wiktionary, a free dictionary

The Universal Character Set
Greek uc psi.png
Codepoint U+03A8
χ ← Greek and Coptic → Ω
See also Ѱ, ѱ, and





  1. sometimes used instead of for Neptune.

See also



Ψ (uppercase, lowercase ψ)

  1. The upper case letter psi (ψι), the 23rd letter of the modern Greek alphabet.



  1. The number 700 in Greek numerals.

  1. The number 700,000 in Greek numerals.


  • Ѱ, ѱ

See also

Got something to say? Make a comment.
Your name
Your email address