The material world is only a shadow representation of the anti-material world, and intelligent men who are clean in heart and habit will be able to learn, in a nutshell, all the details of the anti-material world from the text of the Bhagavad-gītā, and these are in actuality more exhaustive than material details. The basic details are as follows:
The presiding Deity of the anti-material world is Śrī Kṛṣṇa, who exists in His original personality as well as in His many plenary expansions. This personality and His plenary expansions can be known only by anti-material activities commonly known as bhakti-yoga, or devotional service. The Personality of Godhead is the supreme truth, and He is the whole anti-material principle. The material principle as well as the anti-material principle is an emanation from His person. He is the root of the complete tree. When water is poured onto the root of a tree, the branches and leaves are nourished automatically. And in the same way, when Śrī Kṛṣṇa, the Personality of Godhead, is worshiped, all details of the material worlds are enlightened, and the heart of the devotee is nourished without his having to work in a materialistic way. This is the secret of the Bhagavad-gītā.
The process of entering into the anti-material worlds differs from materialistic processes. The individual living being can very easily enter the anti-material world by practicing anti-material activities while residing in the material world. But those who are truly gross materialists, who depend on the limited strength of experimental thought, mental speculation and materialistic science, find great difficulty in entering the anti-material worlds. The gross materialist may try to approach the anti-material worlds by endeavoring with spaceships, satellites, rockets, etc., which he throws into outer space, but by such means he cannot even approach the material planets in the higher regions of the material sky, and what to speak of those planets situated in the anti-material sky, which is far beyond the material universe. Even the yogīs who have perfectly controlled mystic powers have great difficulty entering into that region. Master yogīs who control the anti-material particle within the material body by practice of mystic powers can give up their material bodies at will at a certain opportune moment and can thus enter the anti-material worlds through a specific thoroughfare which connects the material and anti-material worlds. If they are at all able, they act in accordance with the prescribed method given in the Bhagavad-gītā:
Those who have realized the Transcendence can reach the anti-material world by leaving their material bodies during the period of uttarāyana, that is, when the sun is on its northern path, or during auspicious moments in which the deities of fire and effulgence control the atmosphere.