Expansion of space and apparent age problem.?

Question

People always tell you, like in this wikipedia article (http://en.wikipedia.org/wiki/Horizon_problem#Basic_concept), that a galaxy that is 10 bn ly distant appears as it was 10 bn ly ago.
Now lets say that the galaxy is presently at a dist of 10 bn ly. The light emmitted carries the image of the galaxy as it is say at t=0. But, since the space between the galaxy and earth is expanding, it will take that light not 10 bn years but more, say 12 bn years to reach earth. Since the information regarding its distance can only be obtained from this light, although it would appear to us to be 10 bn ly distant, its current age would be 12 bn years, much like how the radius of the observable universe is not 13.5 bn ly but larger. Am i right?

Answer 1

Yes, pretty much you are right. The light that is getting to us now, was emitted when the galaxy was (for example) 8 billion light years away. As the light traveled toward us, the space it had to go through expanded, so the light took 10 billion years to get to us. On average over that time, the light was 5 billion light-years away.



Meanwhile, the galaxy-to-Earth distance was expanding (not just the space "in front" of the light). So now the galaxy is 13 billion light years away from us.



Questions like this have been asked and answered by experts for over 80 years. The definitions of "distance" and "now" on these scales become very precise, with terms like comoving distance, proper time, coordinate time, spacelike geodestic, etc. Since these are strange concepts in ordinary language, scientists prefer to use equations.

Answer 2

Statements of the age of the Universe do take expansion into account.

Answer 3

Hubble's constant is how they judge the "current" distance as it pertains to the observer in relation to are relative motion.

This only...only pertains to our horizon (CMB)

D/T/a(r)