It was believed in ancient and medieval times that aether, also commonly spelled ether, was a mysterious material that filled the region of the cosmos above the terrestrial sphere.
It was a mysterious element, and the concept of ether was used to describe a number of natural phenomena, including light and how it traveled, as well as gravity.
It was believed in the past that aether was one of the primordial elements of the cosmos. In fact, in the late nineteenth century, scientists postulated that aether permeated all throughout space, allowing a medium through which light traveled in the vacuum.
However, later experiments failed to prove this.
In ancient Greek mythology, Ether was referred to as the pure essence that the gods breathed, filling the space where they lived, analogous to the air breathed by mortals.
Plato makes mention of Aether in his work as well.
If we take a look at Timaeus—where Plato mentions the existence of Atlantis—the Greek philosopher speaks about air and explains that “there is the most translucent kind which is called by the name of aether (αίθηρ)”
The term appears both in Aristotelian physics and in the old electromagnetic theory of the late nineteenth century.
For Aristotle (384-322 BC) the ether was the material of which the so-called supralunar world was composed, while the sublunary world is made up of the known four elements: earth, water, air, and fire.
Unlike these, ether was, for Aristotle, a more subtle and lighter element, more perfect than the other four (Aristotle’s physics is qualitative, rather than quantitative) and, above all, its natural movement is circular, unlike the natural movement of the other four, which is rectilinear.
The element was also mentioned in Ancient Hindu philosophy.
In India, the ether is known as akasha. In Sankhya cosmology, the pañcha mahā bhūta (five main elements) is spoken of, each one eight times more subtle than the previous one: Earth (bhumi) Water (apu). Fire (agní). Air (vāyu). Ether (ākāśa). Samkhya or Sankhya is one of the six āstika schools of Hindu philosophy, mostly related to the Yoga school of Hinduism.
Nikola Tesla, one of the greatest minds to ever live on Earth, also made reference to Aether saying: “All matter comes from a primary substance, the luminiferous ether”.
It was widely disseminated in China and India, where it forms the basis of both Buddhism and Hinduism.
During the Middle Ages the term aether, precisely because it is the fifth material element recognized by Aristotle, began to be called the fifth element, or also qüinta essentia, from which comes the expression quintessence (used in the current cosmology to refer to dark energy).
Aether was also heavily connected to Gravitation.
In fact, it was used in one of Sir Isaac Newton’s first published theories of gravitation, called the Philosophiæ Naturalis Principia Mathematica (the Principia). In his work, Sir Isaac Newton based the entire description of planetary motion on a theoretical law of dynamic interactions. As noted in “Newton’s views on Aether and Gravitation,” Newton renounced standing attempts at accounting for this particular form of interaction between distant bodies by introducing a mechanism of propagation through an intervening medium and called this intervening medium the Aether.
In addition, Newton describes aether as a medium that “flows” continually downward toward the Earth’s surface and is partially absorbed and partially diffused. This “circulation” of aether is what he associated the force of gravity with to help explain the action of gravity in a non-mechanical fashion.