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This might sound like a random question, but it came to me while I was trying to conceptualize the size of the universe and started thinking of entire galaxies resembling grands of sand floating around in the middle of the Pacific ocean. This actually did help me to truly "feel" the vastness of it. But then I started pondering if the concept could be extended to the actual dynamics of gravity and spacetime, which led me to conceptualize spacetime being "displaced" by matter rather than "curved" by it. Conversely, I thought of matter being "compressed" by space-time rather than space-time being compressed by matter. And this would imply that gravity is essentially a "pressure gradient" inside this cosmic "ocean".

So my question is: are there any theories or concepts that treat gravity and space-time more as a "fluid dynamic" or is the classical "curvature" the only real game in town?

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  • $\begingroup$ Phew, when I read sand floating on the ocean I thought that was going another direction. As for your model, how would a pressure gradient serve as an attractive force over long distances? Wouldn't the pressure only be relevant to the sand granule? Gravity is thought to act over long distances $\endgroup$
    – Obliv
    Commented Feb 21 at 4:45
  • $\begingroup$ It sounds like you are describing aether. en.wikipedia.org/wiki/Aether_theories $\endgroup$
    – Stevan V. Saban
    Commented Feb 21 at 5:28
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    $\begingroup$ When we have a working theory to explain some real phenomenon (like gravity), it's not helpful to ask "why don't we think of spacetime pressure instead of curvature" without any attempt to explain how would this pressure cause or model gravitational attraction. One of the beautiful observations of GR is that spacetime curvature (not just space curvature!) explains why two stationary objects would start to move towards each other. Can your "pressure" and "compressed matter" idea explain that? Why would two starts pull on each other because they got "compressed"? $\endgroup$
    – Nadav Har'El
    Commented Feb 21 at 8:21
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    $\begingroup$ See also: en.wikipedia.org/wiki/Mechanical_explanations_of_gravitation $\endgroup$
    – Nadav Har'El
    Commented Feb 21 at 8:23

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