Ψ

Psi in a capital letter Etymologicum Magnum (1499).

Psi (uppercase Ψ, lowercase ψ; Ancient Greek call ψ(ε) ῖ ps(e)î /psêː, psîː/, in Modern Greek ψι psi /psi/) is the twentieth third letter of the Greek alphabet. It was transliterated with the digraph ps by the Romans into words such as psalmus, psalterium and psyche (psalm, psalter). and psyche).

In the Greek numeral system it has a value of 700 (Ψʹ).

History

Epigraphic variants

In archaic epigraphic sources the following variants appear:

Use

The meaning arises from the association of the letter Psi with the Greek word “Psyche”, which originally had the meaning of “butterfly” (in fact we can easily assimilate the shape of the letter with the stylized drawing of a butterfly with wings outstretched). Later the term came to be used with the senses of "breeze breath", "breath", "mood" and, finally, "soul" or "mind".

This is the origin of the name “Psychology” (behavioral science) and the use of the letter Psi to represent it. The Greeks believed that when a person died and breathed his last, the soul flew out of the body in the form of a butterfly. Greek mythology represents the goddess "Psyche" or "Psyche" as an adolescent with butterfly wings, being the youngest of the three daughters of the king of Anatolia, the most beautiful of them and the representation of the human soul.

• is used as a symbol of Psychology and Psychiatry, since the etymology of the word is associated to the psyche or psycho (from the Greek ANTEχ psyche: soul or mental activity).

• represents the digomma function in mathematics:

END END (x)=Interpreter Interpreter ♫(x)Interpreter Interpreter (x){displaystyle psi (x)={frac {Gamma '(x)}{Gamma (x)}}}{,!}, with Interpreter Interpreter (x){displaystyle Gamma (x)} the gamma function;

• represents the polygamma function, also in mathematics:

END END (m)(z)=(ddz)mEND END (z)=(ddx)m+1log Interpreter Interpreter (z){displaystyle psi ^{(m)}(z)=left({frac {d}{dz}}}}right)^{m}psi (z)=left({frac {d}{dx}}}}{m+1}log Gamma (z)}

• represents the wave function in quantum mechanics.
• In the Greek numeration system it has a value of 700 (∫.

Unicode

• Greek

• Cyrillic

• Maths