Psi (Greek)

The Greek alphabet on a black-figure pottery vessel, with an archaic chickenfoot-shaped psi.

Psi Template:IPAc-en Template:Respell<ref>Template:Cite book</ref> (uppercase Template:Lang, lowercase Template:Lang or Template:Lang; Template:Langx psi Template:IPA) is the twenty-third and penultimate letter of the Greek alphabet and is associated with a numeric value of 700. In both Classical and Modern Greek, the letter indicates the combination Template:IPA (as in English word "lapse").

For Greek loanwords in Latin and modern languages with Latin alphabets, psi is usually transliterated as "ps".

The letter's origin is uncertain. It may or may not derive from the Phoenician alphabet. It appears in the 7th century BC, expressing Template:IPA in the Eastern alphabets, but Template:IPA in the Western alphabets (the sound expressed by Χ in the Eastern alphabets). In writing, the early letter appears in an angular shape (). There were early graphical variants that omitted the stem ("chickenfoot-shaped psi" as: or ).Template:Citation needed

The Western letter (expressing Template:IPA, later Template:IPA) was adopted into the Old Italic alphabets, and its shape is also continued into the Algiz rune <ᛉ> of the Elder Futhark.

Psi, or its Arcadian variant Template:GrGl or Template:GrGl was adopted in the Latin alphabet in the form of "Antisigma" (Ↄ, ↃC, or 𐌟) during the reign of Emperor Claudius as one of the three Claudian letters.<ref name="oliver">Template:Cite journal</ref> However, it was abandoned after his death.Template:Citation needed

The classical Greek letter was adopted into the early Cyrillic alphabet as "Ѱ".

Use as a symbol

The symbol Ψ or ψ has many uses across different academic and informal contexts:

• Wave functions in quantum mechanics
• The generalized positional states of a qubit in a quantum computer
• The polygamma function<ref>Template:Cite web</ref>

• The fields of psychology, psychiatry, and sometimes parapsychology<ref>Template:Cite web</ref>
• The reciprocal Fibonacci constant,<ref>Template:Cite web</ref> the division polynomials, and the supergolden ratio
• The second Chebyshev function<ref>Template:Cite web</ref>
• Water potential in movement of water between plant cells<ref>Template:Cite journal</ref>
• In biochemistry, it denotes pseudouridine, an uncommon nucleoside<ref>Template:Cite journal</ref>
• A stream function in fluid mechanics
• One of the dihedral angles in the backbones of proteins<ref>Template:Cite web</ref>
• Indiana University (as a superimposed I and U)<ref>Although the university itself refers to its logo as a trident, not the Greek letter psi: Template:Cite web</ref>
• A sai, whose name is pronounced the same way in English
• Pharmacology, general pharmacy
• The retroviral psi packaging element<ref>Template:Cite journal</ref>
• The J/psi meson in particle physics<ref>Template:Cite web</ref>
• The return value of a program in computability theory
• The phase relationship between a zeitgeber and a biological rhythm<ref>Template:Cite journal</ref>
• In building, to represent an adjustment to a U-value, accounting for thermal bridge effects
• The ordinal collapsing function and notation<ref>Template:Cite journal</ref>
• In Biblical studies, as an abbreviation for the book of Psalms<ref>Gesenius' Hebrew Grammar</ref>

Unicode

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See also

• Psi and phi type figurine
• Psi (Cyrillic)

Notes and references

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