How long is eternity?

Eternity is a term that refers to an unlimited amount of time that never ends (or the quality, condition or fact of being eternal). Classical philosophy, on the other hand, defines eternity as something that exists outside of time, as in describing supernatural creatures and energies, whereas sempiternity relates to indefinitely temporal, non-metaphoric meanings, as in requiem prayers for the dead. [more clarification is required] Many Enlightenment thinkers, like Thomas Hobbes (1588-1679), used the classical distinction to propose philosophical theories such "eternity is a permanent Now."