Aether and Gravitation

Aether has been used in various gravitational theories as a medium to help explain gravitation and what causes it. It was used in one of Sir <a href="https://en.wikipedia.org/wiki/Isaac_Newton" title="Isaac Newton">Isaac Newton</a>'s first published theories of gravitation, <a href="https://en.wikipedia.org/wiki/Philosophi%C3%A6_Naturalis_Principia_Mathematica" title="Philosophiæ Naturalis Principia Mathematica">Philosophiæ Naturalis Principia Mathematica</a> (the Principia). He based the whole description of planetary motions on a theoretical law of dynamic interactions. He renounced standing attempts at accounting for this particular form of interaction between distant bodies by introducing a mechanism of propagation through an intervening medium.<a href="https://en.wikipedia.org/wiki/Aether%28classical_element%29#cite_note-Rosenfeld1969-21">[21]</a> He calls this intervening medium aether. In his aether model, 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.<a href="https://en.wikipedia.org/wiki/Aether%28classical_element%29#cite_note-Rosenfeld1969-21">[21]</a> This theory described different aether densities, creating an aether density gradient. His theory also explains that aether was dense within objects and rare without them. As particles of denser aether interacted with the rare aether they were attracted back to the dense aether much like cooling vapors of water are attracted back to each other to form water.<a href="https://en.wikipedia.org/wiki/Aether%28classical_element%29#cite_note-newton1679-22">[22]</a> In the Principia he attempts to explain the elasticity and movement of aether by relating aether to his static model of fluids. This elastic interaction is what caused the pull of gravity to take place, according to this early theory, and allowed an explanation for action at a distance instead of action through direct contact. Newton also explained this changing rarity and density of aether in his letter to <a href="https://en.wikipedia.org/wiki/Robert_Boyle" title="Robert Boyle">Robert Boyle</a> in 1679.<a href="https://en.wikipedia.org/wiki/Aether%28classical_element%29#cite_note-newton1679-22">[22]</a> He illustrated aether and its field around objects in this letter as well and used this as a way to inform Robert Boyle about his theory.[<a href="https://en.wikipedia.org/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed">citation needed</a>] Although Newton eventually changed his theory of gravitation to one involving force and the laws of motion, his starting point for the modern understanding and explanation of gravity came from his original aether model on gravitation.[<a href="https://en.wikipedia.org/wiki/Wikipedia:Citation_needed" title="Wikipedia:Citation needed">citation needed</a>]