Eternity (or forever) is endless time. In philosophy and mathematics, an infinite duration is also called sempiternity, or everlasting. Eternity is an important concept in many religions, where the immortality of God (or the gods) is said to endure eternally. Some, such as Aristotle, would say the same about the natural cosmos in regard to both past and future eternal duration, and like the eternal Platonic Forms, immutability was considered essential.
