View Single Post
Dec23-11, 12:02 PM
P: 4,201
Quote Quote by D H View Post
Ignore the expansion of space for now ... Just consider the fact that that remote galaxy and ours are and were moving apart from one another.
Do the galaxies "move apart" if we ignore the expansion of space?

Quote Quote by D H View Post
Assume that at some time when the galaxies are separated by 500 million light years and that one of the galaxies transmits a distinguishable signal toward the other. After traveling for 500 million years, that signal from that remote galaxy would have reached the distance where our galaxy was 500 million years ago. Our galaxy is no longer at that location. It has moved beyond it.
How would all that look like in the frame of "our galaxy"?

Quote Quote by D H View Post
Even assuming a simple universe, it would take a very, very long time for the light from that remote galaxy to reach ours if the two galaxies were receding at a constant velocity that is just a tiny bit smaller than the speed of light.
A signal from a source receding away from me needs longer to get to me, than a signal from a source at the same distance at rest relative to me?