Sublunary sphere in the context of "Aristotelian physics"

According to ancient and medieval science, aether (/ˈiːθər/, alternative spellings include æther, aither, and ether), also known as the fifth element or quintessence, is the material that fills the region of the universe beyond the terrestrial sphere. The concept of aether was used in several theories to explain several natural phenomena, such as the propagation of light and gravity. In the late 19th century, physicists postulated that aether permeated space, providing a medium through which light could travel in a vacuum, but evidence for the presence of such a medium was not found in the Michelson–Morley experiment, and this result has been interpreted to mean that no luminiferous aether exists.

The microcosm–macrocosm analogy (or, equivalently, macrocosm–microcosm analogy) refers to a historical view that posited a structural similarity between the human being (the microcosm, i.e., the small order or the small universe) and the cosmos as a whole (the macrocosm, i.e., the great order or the great universe). Given this fundamental analogy, truths about the nature of the cosmos as a whole may be inferred from truths about human nature, and vice versa.

One important corollary of this view is that the cosmos as a whole may be considered to be alive, and thus to have a mind or soul (the world soul), a position advanced by Plato in his Timaeus. Moreover, this cosmic mind or soul was often thought to be divine, most notably by the Stoics and those who were influenced by them, such as the authors of the Hermetica. Hence, it was sometimes inferred that the human mind or soul was divine in nature as well.

The astral plane, also called the astral realm, or the astral world, or the soul realm, or the spirit realm, is a plane of existence postulated by classical, medieval, oriental, esoteric, and New Age philosophies and mystery religions. It is the world of the celestial spheres, crossed by the soul in its astral body on the way to being born and after death, and is generally believed to be populated by angels, spirits, or other immaterial beings. In the late 19th and early 20th century, the term was popularised by Theosophy and neo-Rosicrucianism.

Another view holds that the astral plane or world, rather than being some kind of boundary area crossed by the soul, is the entirety of spirit existence or spirit worlds to which those who die on Earth go, and where they live out their non-physical lives. It is understood by adherents that all consciousness resides in the astral plane. Some writers conflate this realm with heaven or paradise or union with God itself, while others do not. Paramahansa Yogananda wrote in Autobiography of a Yogi (1946), "The astral universe ... is hundreds of times larger than the material universe ... [with] many astral planets, teeming with astral beings."

In esoteric cosmology, a plane is conceived as a subtle state, level, or region of reality, each plane corresponding to some type, kind, or category of being.

The concept may be found in religious and esoteric teachings which propound the idea of a whole series of subtle planes or worlds or dimensions which, from a center, interpenetrate themselves and the physical planet in which we live, the solar systems, and all the physical structures of the universe. This interpenetration of planes culminates in the universe itself as a physical structured, dynamic and evolutive expression emanated through a series of steadily denser stages, becoming progressively more materialized, and embodied.