Matter outside of the territory under consideration. Where are we?

[Serge58]

After an analogy with air and water waves, which are limited in speed by the density of the medium in which they travel, I was wondering if there were variations in the "density" of the vacuum of space which might cause light, or any electromagnetic waves for this matter, to vary in speed.

In reply to this comment harrylin cleverley quoted Einstein from 1920:

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."

Therefore, Where are we today with the understanding of this matter outside of the territory under consideration?

 

[Nugatory]

Therefore, Where are we today with the understanding of this matter outside of the territory under consideration?

There's no great mystery here. Suppose that the "territory under consideration" is the space near a massive body; the massive body produces gravitational effects within that area. A near-trivial example would be the Schwarzschild solution - it's a vacuum solution so applies in the empty space around the matter that's responsible for the gravitational field.

 

[bcrowell]

After an analogy with air and water waves, which are limited in speed by the density of the medium in which they travel, I was wondering if there were variations in the "density" of the vacuum of space which might cause light, or any electromagnetic waves for this matter, to vary in speed.

The equivalence principle basically says that this can never be the case.

What Einstein probably had in mind was spacetime curvature, not the speed of light. (But it would be helpful to have some more context.)

 

[Serge58]

I think i didn't write my question properly. I'll try again on a new tread.