Quote:
On 2001-11-15 07:46, SeanF wrote:
Yeah, Rosen, ol' JW had some interesting theories, didn't he?
After reading this paper, it almost seems like these folks are taking Hubble as a given and accepting that a galaxy past a certain distance must have superluminal recession, and the paper is intended to show how this superluminal recession could exist without violating SR or causing an infinite redshift. Is that how you read it?
So now I have a more general question . . . how do we determine the distance to these galaxies?
We're obviously not using Hubble the other way (using redshift to determine the velocity and determining the distance from that), and these galaxies are certainly too far away to use parallax, so how do we know they're so far away they should be superluminal?
|
I may be able to answer your first question. I just beginning to learn GR, so one of the other more learned board members may correct me. They assume the simplest GR expanding universe model which is the FRW metric. This metric assumes that matter in the universe is homogeneous and the universe is expanding equally in all spatial directions. From what I understand these assumptions are very good.
According to this model, past the distance
d = c/H, the recession velocities are superluminal.
H is the Hubble constant which is derivable from this metric. However SR still holds locally, i.e. the observer measure light at "c".
As to how they measure distance. I thought redshift was the primary distance indicator. From redshift get recession velocity and from recession velocity get distance.
Here's a link to a couple of articles that discuss this:
Scaling The Universe ...
Supernovae, ...
Hope this helps,
<font size=-1>[ This Message was edited by: Wiley on 2001-11-15 12:45 ]</font>