Eternity in common parlance is an infinitely long period of time. In classical philosophy, however, eternity is defined as what exists outside time while sempiternity is the concept that corresponds to the colloquial definition of eternity. Eternity is an important concept in many religions, where the god or gods are said to endure eternally.
Thank you for your question. Wajib al-wujud or the Necessary Existent is that existent which does not depend on any other existent for its existence. The Absolute Existent is that existent that has no limitation what so ever. These attributes and others are discussed in transcendental philosophy and mysticism.
May you always be successful
Thank you for your question. This is a scientific issue not specifically directly discussed in any scriptural sources that i know of. It is interesting as it would mean that energy is metaphysical, but it would have to be proven before any type of research into its implications would be carried out.
May you always be successful.