If we know the universe is made up of a relativistic ether, why wouldn't gravity just be a pressure gradient of the ether? According to one of the answers to a previous question ( Can photons and gluons be holes in an aether? ), we know a relativistic ether exists.  If we are drifting in such a superfluid, why wouldn't gravity simply be understood to be essentially the pressure differences between baryonic matter and the ether at this fundamental level?  
Imagining a "universal" fluid that surrounds us to infinity for all intents and purposes.  Assuming baryonic matter by its (jittery?) nature takes up more space than the equivalent ether it displaces, wouldn't this create a pressure gradient in the ether which would attract other baryonic matter according to the amount of ether displacement?  (Similar to the way a hot air balloon rises to where the density of the air inside the balloon matches the air outside?)
 A: You are asking if gravity can be understood to be pressure waves in an ether. This is not reasonable for several reasons:


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*Gravity is universal: it acts on electrons and protons the same and on all matter the same, in a way directly proportional to mass.

*Gravity is extraordinarily weak: it does not look like other forces in order of magnitude

*Gravity is tensorial--- we know that it is sourced by pressure and forces, not just by masses.


The three properties, plus Einstein's special relativity, essentially require something close to General Relativity as the only consistent description of gravity which naturally explains the universality of gravity. The essential principle is the equivalence principle.
The ethers that we know about have the property that their excitations are all massive. This means that if you make a dimple in the ether, it will spread to a certain length scale only, and not beyond that. Gravity is long ranged. If you make a model of ether exchange, you can get long range attractive forces, but if the result doesn't break rotational or relativistic invariance, these are scalar attractive forces, due to exchange of what are called "Goldstone bosons", like the forces that bind nuclei together, in the pretty good approximation that the pion is massless.
But it is not reasonable to speculate about the structure of the ether responsible for gravity without first reviewing the known theories of gravity, in particular General Relativity. Once one is familiar with General Relativity, any mechanistic accounting for gravity along the lines you describe becomes obviously wrong.
The closest thing to a mechanistic accounting of gravity in the modern literature is Verlinde's recent attempt to understand gravity as the result of entropy changes as you bring objects closer together. The idea is interesting, but the details are not completely sound, and it is hard to know if this explanation can be made precise in a future theory.
This idea is different from yours, in that it takes into account the equivalence principle (GR), the superposition principle (QM), and the holographic principle (Strings).
