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Buddy Posted on 9/11 14:39
Is there a cosmologist in the house?

I know there are one or two in that sort of area, so let's see if anyone can explain this to me.

I quite often read and hear scientists talking about capturing light from the oldest galaxies in the universe. The argument is that this light is 12.5bn years old and because the universe formed 13.5bn years ago these galaxies must be some of the oldest things going.

What puzzles me is, surely this only works if you look at the Earth as being at the centre of the universe. Surely if the universe has been expanding for 13.5bn years, the maximum distance between two points in it is 13.5bn times whatever the annual rate of expansion is, and therefore a light source on one side could be more than 13.5bn light years from a light receptor on the other?

captain5 Posted on 9/11 14:41
re: Is there a cosmologist in the house?

Don't think Stary comes on any more.

Buddy Posted on 9/11 14:42
re: Is there a cosmologist in the house?


Capybara Posted on 9/11 14:47
re: Is there a cosmologist in the house?

I think 7_The_Informer's yer man. The explanation is probably because once you get to around the speed of light all kinds of weird stuff starts kicking off. That's according to that Einstein gadge.

Capybara BSc (Hons) Physics.

Buddy Posted on 9/11 14:50
re: Is there a cosmologist in the house?

Could be that the annual rate of expansion is slightly slower than a 1971 Hillman Imp, I suppose.

BoroMutt Posted on 9/11 14:55
re: Is there a cosmologist in the house?

I'm no cosmo, but I would imagine that we all started from the same place with "The Big Bang" when all matter came into being at a single point. From that point/date the universe has been expanding so the galaxies furthest from us are not the oldest but the same age as us but because we are seeing the light they shone 12.5bn years ago what we see is the stars in the position they were 12.5bn years ago. Those stars are now may billions of light years from that position.

Durham_Red Posted on 9/11 15:04
re: Is there a cosmologist in the house?

Not quite sure what the problem with your argument is, although it is certainly true that for models of the universe, isotropy and homogeneity are presumed. (ie that the universe looks the same from every point and in every direction)

Buddy Posted on 9/11 15:34
re: Is there a cosmologist in the house?

Exactly Mutt, but these discoveries are written up as evidence that galaxy formation started much earlier in the history of the universe than was first thought.

BoroMutt Posted on 9/11 19:22
re: Is there a cosmologist in the house?

No. Because the light from these galaxies has taken 12.5bn years to catch up with us, what we are seeing is what happened 12.5bn years ago. Those galaxies are no longer where they appear to be. Take the closest star Proxima Centauri is we could observe a planet orbitting Proxima Centauri we might watch it pass in front of it's star. However, if we could jump instantaneously to that star system we would find that that event happened over four years ago.

So, in the case of these distant galaxies we can see that 12.5bn years ago they had formed into a recognizable galaxy therefore validating the hypothesis that Galaxies formed relatively (poor choice of word I know) quickly after the "Big Bang".

I think.