The age-old question of whether there is a mechanical cause of gravity has not yet been answered with a theory that has gained general acceptance in the scientific community. In the words of Richard Feynman in The Feynman Lectures on Physics:

“What about the machinery of it? All we have done is to describe how the earth moves around the sun, but we have not said what makes it go. Newton made no hypotheses about this; he was satisfied to find out what it did without getting into the machinery of it. No one has since given any machinery.”

The articles cited below propose a conceptual model of flowing aether as the physical cause of gravity.

The Cause of Gravity: A Concept, Phys. Essays 25, 66 (2012), proposes the concept of gravity being caused by the ram (pushing) force of aether cells that flow into cosmic bodies and collide with atomic matter, less the pushing force of constituent particles that flow back into space. The one-way-force aspect of gravity is explained by inflowing aether cells being larger than the outflowing particles and therefore more likely to collide with the structure of atomic matter.  The accelerating-force aspect of gravity is explained by convergence of the flow of aether from the wide expanse of space into the relatively small areas occupied by cosmic bodies.  The fact that gravity between the Sun and the Earth appears to be instantaneous action-at-a-distance is explained by the flow of aether from space into the solar system moving directly toward the Sun at the instant when it collides with the Earth and pushes it toward the Sun..

Flowing Aether: A Concept, Phys. Essays 26, 523 (2013), adopts the concept of aether having gaseous and liquid states.  The size difference between inflow droplets and outflow cells explains why gravity is a one-way force.  This replaces the previous explanation based upon the size difference between aether cells and their constituent particles.

Outflowing Aether, Phys. Essays 29, 4 (2016), deals with the outflow of aether into space.  It posits that vaporization of incoming liquid aether produces gaseous aether and that gaseous aether travels into space by way of convection and diffusion. A comparison is made with the rain cycle on Earth, that is, the evaporation of water molecules, flow of the molecules by way of diffusion and convection into the atmosphere, condensation of the molecules into droplets, and return to the Earth as rain.

The following is a summary of the flowing aether concept of gravity:

• The gravity process is cyclic. It involves aether from cosmic bodies flowing into space and aether from space flowing into from bodies.
• Outflowing aether and inflowing aether are different states of aether. Outflowing aether consists of aether cells in a gaseous state. Inflowing aether consists of groups of aether cells that have condensed into liquid-state droplets, each of which is comprised of numerous cells.
• Inflowing liquid-state aether collides with matter that is in its path. The collisions push matter toward cosmic bodies. THE INFLOW COLLISIONS ARE POSITED AS THE DIRECT CAUSE OF GRAVITY.
• The heat generated by the collisions of inflowing liquid-state aether with cosmic bodies causes liquid-state aether to vaporize into gaseous state aether.
• Outflowing aether cells are considerably smaller than incoming droplets and tend to pass on through the matter of cosmic bodies. Thus, whatever collisional force outflowing aether has on the matter of cosmic bodies is negligible compared to the collisional force exerted by inflowing aether.
• The predominance of the collisional force of inflowing aether over the collisional force of outflowing aether on the matter of cosmic bodies explains why gravity is a one-way force.
• As aether flows from the expanse of space into the relatively small target of a cosmic body, the flow converges. The convergence causes the flow to accelerate: Bernoulli’s principle and the Venturi effect. This explains why gravity is an accelerating force.
• Gaseous-state aether in space condenses into liquid state aether. A rough analog is gaseous water molecules evaporating from the surface of the Earth, rising into the Earth’s atmosphere, condensing into liquid droplets and returning to the Earth’s surface as rain.
• What causes inflow and outflow? The answer lies in the science of fluid mechanics. Substances that comprise fluids seek equilibrium of concentration. This occurs by way of diffraction, that is, the random movement of gases and liquids from areas of higher concentration to areas of lower concentration. In regard to inflowing aether, the level of concentration of its droplets in the vicinity of cosmic bodies is constantly reduced below its level in space by vaporization of droplets caused by collisions with cosmic bodies. In regard to outflowing aether, its level of concentration of gaseous aether cells in space is constantly reduced by condensation of its aether cells into droplets of liquid aether. Each state of aether seeks its own equilibrium of concentration, with gaseous aether flowing into space and liquid aether flowing toward cosmic bodies. They flow through each other by diffusion and convection, each seeking –but never reaching –its own equilibrium of concentration.
• Similar two-way diffusion of fluids is described in the textbook, An Introduction to Fluid Mechanics, by G. K. Batchelor, Cambridge University Press, (1970), at pp. 28-29.
• The energy that drives the flows lies in the constant movements of the aether cells and droplets — their collisions and rebounding –their elasticity – their vibrations — their Brownian movements.
• Does the energy that causes these movements diminish and run out? Not according to the law of conservation of energy. The energy in space is constantly replenished by the outflow of aether from cosmic bodies in the gravity process and by discharges from nuclear reactions in stars and from supernovae. It is a fair assumption that the aether medium that pervades the universe will remain in overall energy equilibrium.

EXPERIMENTAL SUPPORT

In 2020, an article on levitation entitled Floating Under a Levitating Liquid was published in Nature, 585, 48 (2020).  It dealt with a most unusual experiment.  High frequency vibrations caused a layer of glycerol to levitate with a miniature sailboat floating on the topside of the layer of glycerol and a second miniature sailboat floating upside-down on the underside of the glycerol.  A photo of this result, provided by the authors of the levitation experiment is shown below.

The possibility that the levitation experiment might have some application to the flowing aether concept of gravity prompted me to carry out further research. This led to finding a series of papers that deal with experiments involving simulated gravity.

Based upon the results of these experiments (including the levitation experiment), I prepared the article, Experimental Support for the Flowing Aether Concept of Gravity, Phys. Essays, 34, 538 (2021).  The article concludes that the experiments provide evidence that supports the proposition that gravity is a pushing force that is transmitted by vibrations.  Further, the experiments provide observations that are consistent with numerous details of the flowing aether concept.  The observations include the pushing nature of the observed force, Brownian collisions, high speed vibrations, flows of fluids in gaseous and liquid states, transitions between the gaseous and liquid states of fluids, concentration differences, porosity of atomic matter, the one-way elements of the force, its cyclic nature, buoyancy, horizontal phenomena, and stabilization of the force.