> Seems like it's totally possible that something could be 4 billion light years away, or 8 billion light years away, and have the same red shift. In theory, o

> Seems like it's totally possible that something could be 4 billion light years away, or 8 billion light years away, and have the same red shift. In theory, of course this is possible. But in our actual universe, that's not what happens. In our actual universe, there is a close relationship between how far away something is and its redshift. Or, to phrase it in terms of direct observables, in theory we could have an object that was 4 billion light years away and an object that was 8 billion light years away, both with the same redshift--but they would be very different in terms of other observables like apparent luminosity and angular size. So in the general case, in theory, we would not expect any particular relationship between those variables. But in our actual universe, there is a close relationship between all three of those variables: redshift, apparent luminosity, and angular size all vary in concert and are closely correlated. That kind of observation is what leads cosmologists to conclude that our universe is expanding. > I wonder if it's pretty common to observe objects that are more blue shifted than something that is clearly closer to us. It's not only not "pretty common", it never happens except for objects very close to us, cosmologically speaking--for example, the Andromeda galaxy is somewhat blueshifted, indicating that it is moving towards us, while the Magellanic Clouds, which are closer (they are satellite galaxies of our own galaxy), are not, AFAIK, blueshifted. But all of these objects are in the same local, gravitationally bound group as our galaxy, so their relative velocities don't tell us anything useful about the large scale behavior of the universe.