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PeterDonis said:What is your criterion for something being "in your frame of reference"? Is it only objects that are at rest relative to you? That seems like a very restrictive definition, which basically makes the concept of "frame of reference" useless, as ghwellsjr pointed out earlier. But alternatively, if objects that are moving relative to you can still be in your frame of reference, why can't *all* objects be in it?
No. I tried to explain what I'm saying, but it looks like I didn't do a very good job. I realize that if I only paid attention to objects that are at rest relative to myself, spacetime would be a very boring place. What I'm saying is that objects may be flying all over the place in spacetime, and that I would be able to observe and track them, but I only count the objects and coordinate systems that are at rest with respect to myself as part of my frame of reference (and, of course, I am part of their frame of reference). All other objects and coordinate systems occupy other frames of reference that, of course, share spacetime (i.e., overlap) with my own.