When we look at distant galaxies receding due to the expansion of space, everywhere, in all directions, aren't we, as the observer, the underlying frame of reference? The universe is expanding relative to us, to our position; and the same thing applies to any observer anywhere in the universe. We're all at the very centre of our own expanding observable universes. Mine is different to yours by a couple thousand miles or whatever distance separates us.
But we observers don't violate relativity; relativity always refers to our velocity through the space around us, wherever we are. The expansion of space does not add to my velocity through space because the local expansion of the space around me is tiny (it only becomes significant over vast distances when the expansion in between adds upon expansion, upon expansion... and the forces of my own particles, and gravity overcome any local expansion anyways) so I never violate relativity, and neither does anyone else, anywhere in the universe. Those distant galaxies don't move through their own local space faster than light, even though they appear to recede from us faster than light.
Did I get that right?
Here's another thought: is 'expansion' always the right term? If I understand it right, the planck length/volume/time is not expanding--so then neither is spacetime really? (Even if the planck length was expanding, we couldn't tell anyway, because our 'measuring stick' would be expanding too?) Wouldn't it be more accurate to say spacetime is 'multiplying?' In other words: planck spaces aren't expanding as such, there are just *more* of them between us and distant galaxies? If that's right--is there any way to observe it?
When you stretch a rubber band, the number of units of rubber band (rubber molecules?) doesn't increase, rather the units themselves become longer. As space expands, the number of units of space does increase, but the units themselves don't become larger. I guess its the same difference between the anaolgy of raisin bread, and the anology of adding blocks of pavement, that Pamela has used before. No raisin bread is added. The pavement doesn't get bigger. Which anology is most correct?
If space truly was 'expanding' rather than 'multiplying' wouldn't it cause the constants of the universe to change--or the properties of spacetime to be 'diluted' in some way?
Does the force of gravity (and the other fundamental forces) hold back the expansion of spacetime--or does it somehow interrupt the mechanism by which spacetime multiplies?
Last thought: Let's say I take a line of sight to a distant galaxy, and there are a certain number of galaxy clusters along that line of sight, each constricting the expansion of the universe in each local region of space. Then, I take a line of sight to a distant galaxy in a completely different direction, where
twice as many galaxy clusters are constricting the expansion of the universe along the way.
Would I observe any difference? Or would each line of sight appear the same to me today?
What about in the past: does double the galaxy clusters mean half the expansion, one line of sight compared to the other? Should I perceive my observable, expanding universe to be perfectly spherical; or is it lumpy over time?