The Cyrillic letter "psi" () of the Old Slavonic alphabet comes from the Greek letter "psi" - symbolizing the soul. The soul is contemplated in three forces: thinking (mind), irritable (feeling) and desirable (will).
Now the letter "psi" () is used only in Church Slavonic and physics to represent wave functions in quantum mechanics.
Now the letter "psi" () is used only in Church Slavonic and physics to represent wave functions in quantum mechanics.