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According to one of the answers to a previous question ( Can photons be holes in an ether? ), 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?)

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To clarify: By specifying baryonic matter I don't mean to exclude everything else from being affected by or producing gravitational fields. (Though it's my understanding that matter in energy form, free electrons and photons, create a repulsive pressure than an attractive pressure.) Also, my attempt here is to specifically frame the pressure differences without referring to mass, but only by the displacement of one-another and the waves that might be created as they jostle for space. –  user6817 Dec 24 '11 at 18:41
    
This seems to be what I'm asking about: en.wikipedia.org/wiki/Superfluid_vacuum_theory –  user6817 Dec 25 '11 at 7:10
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What's a "relativistic ether"? The usual interpretation is that special relativity and the luminiferous ether theory are incompatible, and experiments such as the Michelson-Morley experiment (en.wikipedia.org/wiki/Michelson%E2%80%93Morley_experiment) were therefore seen as pretty conclusive evidence that there is no ether. –  Nathaniel Jan 23 '12 at 9:34

1 Answer 1

You are asking if gravity can be understood to be pressure waves in an ether. This is not reasonable for several reasons:

  • 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).

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Thanks. Why would pressure differences have to be strong? I would expect all fields to have some underlying mechanism (like electron hole-flow). If not a mechanistic process, what are the other options? I (probably naively) think I have a good grasp of general relativity. I guess I'm unclear on where this necessarily breaks with it. –  user6817 Dec 24 '11 at 18:35
    
@user6817: General relativity gives gravity by tensor perturbations, while this stuff would be scalar perturbations (if it were there). The scalar theory of gravity is due to Nordstrom and predated GR, and does not have light-bending by gravity. The pressure difference wouldn't be "strong" in the sense of being big, it would be strong in the sense of coupling to protons and neutrons differently from electrons. The tensor nature of gravity is central to GR, and it is this makes gravity different from other forces. –  Ron Maimon Dec 25 '11 at 4:58

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