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  1. What is the space-time medium?

  2. According to this answer: "... fields are a fundamental part of the universe." Then why do we describe a gravity as being depressions in space-time?

  3. And why don't we describe weak, strong, or electromagnetic forces as such?

  4. Have we actually proved that there is no substance that makes space-time?

  5. Also is there a difference between the ideas of aether and quantum foam?

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    $\begingroup$ There are too many questions here, but each of them is either a duplicate or doesn't really make sense: For "describing electromagnetic forces as such", see Geometric interpretation of Electromagnetism. What does "describing a gravitational field as propagating through some space-time sheet" mean? What would it mean to "prove" (or disprove) that there is a "substance that makes space-time"? What exactly are you referring to when you say "quantum foam"? $\endgroup$ – ACuriousMind Mar 27 '16 at 13:09