Eternity

Eternity, in common parlance, means infinite time that never ends (or the quality, condition or fact of being eternal). Classical philosophy, however, defines eternity as what exists outside time - as in describing supernatural beings and forces, whereas sempiternity corresponds to the infinitely temporal, non-metaphoric definitions, as recited in requiem prayers for the dead. Thomas Hobbes (1588-1679) and many others in the Age of Enlightenment drew on the classical distinction to put forward metaphysical hypotheses such as "eternity is a permanent Now".
Eternity as infinite duration is an important concept in many religions, where the god or gods are said to endure eternally. Religious views of an afterlife may speak of it in terms of eternity.
Some thinkers, such as Aristotle, suggest the eternity of the natural cosmos in regard to both past and future eternal duration - Christian theologians may regard immutability - like the eternal Platonic forms - as essential. Today cosmologists, philosophers, and others look to analyses of the concept from across cultures and history. They debate, among other things, whether an absolute concept of eternity has real application for fundamental laws of physics - compare the issue of the arrow of time in entropy.
Philosophy.
Aristotle argued that the cosmos has no beginning. In Aristotle's Metaphysics, eternity is the unmoved mover, understood as the gradient of total synergy ("produces motion by being loved"). Boethius defined eternity as "simultaneously full and perfect possession of interminable life".
Symbolism.
Eternity is often symbolized by the endless snake, swallowing its own tail, the ouroboros (or oroboros). The circle, band or ring is also commonly used as a symbol for eternity, as is the mathematical symbol of infinity, formula_1. Symbolically these are reminders that eternity has no beginning/end. 