Speed of water and relation to light

[Serge58]

Nobody knows what "space" or "vacuum" is, except that it's not mere nothingness. The only thing we know is the equations that describe its properties (it's those space-time equations that have "curvature" etc.). And concerning gravitational fields, I linked you in post #18 to a clear example of how nearby matter affects those properties in nearby areas.
Einstein phrased it in 1920 as follows: "the metrical qualities of the continuum of space-time [..] are partly conditioned by the matter existing outside of the territory under consideration."

Very nice quote from Einstein. I will start a new topic since this discussion is too far way from the original subject. Thanks