Atman and Brahman are the most fundamental entities of known and unknown to understand it and their relationship with each other can be understood by Mahavaakyas and References of Upanishads like Chandogya, Brihadaranyak, and Mandukya Upanishad. The concept of the relation between Atman and Brahman can be explained using concepts of Natural Science. Metaphysics of correlation of existence and necessity of both entities can be studied using this concept.