- #71
Ibix
Science Advisor
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The "common explanation" is a best attempt at saying something that can't really be said well in natural language. The key point, in this context, is that you will never see these galaxies overtake a light pulse.skanskan said:Can anyone explain exactly how the maximum speed limit is taken into consideration here?
A loose analogy is this: turn around 360° on the spot. In your rotating frame, Alpha Centauri just traveled about 25 light years in a second or two. That's fine because the coordinate speed in this coordinate system isn't restricted to being less than 3×108m/s. And Alpha Centauri does not overtake any light pulses.
Nothing is rotating in the cosmological case, but you are forced to use curved coordinate systems in curved spacetime. This has the same result that coordinate speeds do not really mean anything physical. Local measurement of the speed of light in those distant galaxies would show it to be ##c## in all inertial frames, just as here.