Local Landmarks & General Relativity

[codeman_nz]

General relativity says that nothing can go faster than the speed of light when measured against local landmarks.

What counts as a local landmark? What is the boundary between a local and distant landmark?

 

[Mentz114]

The distance between such local landmarks gets smaller as the spacetime curvature around them, or between them increases. So in flat spacetime it can be any distance, but close to the sun it would be smaller. I suppose the boundary is where the nearby spacetime deviates from flatness by an amount greater than the instrumental error.