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bjw3470
2007-Aug-14, 02:08 AM
If our universe is closed, and light bends with the shape of the universe, then shouldn't we be able to locate a galaxy far, far away and discover that we are looking at our very own Milky Way?

Ken G
2007-Aug-14, 02:49 AM
In principle, yes, but the Milky Way isn't bright enough. Anyway, there is plenty of evidence that the universe is not closed on scales that we can observe.

astromark
2007-Aug-14, 08:51 AM
Dare I ask who said it is closed?. My understanding of this is that it is not.

WaxRubiks
2007-Aug-14, 09:30 AM
I thought that you thought that it was close astomark?

closed as in finite but unbounded.

astromark
2007-Aug-14, 10:17 AM
Yes, You thought right but, finite but unbounded does imply that the amount of material available is finite and the space it exists in is expanding to infinity. Well I thought it did... Let me consider this some more.

astromark
2007-Aug-14, 10:25 AM
As Ken G has noted and I agree. This idea of bending light to the point of seeing our own galaxy as a distant object is a bit extreme. I do not think it could work like that. Over in the ATM thread we could give this another look.

Amber Robot
2007-Aug-14, 10:41 AM
Even if the universe were closed, it may not be old enough to see all the way around.

WaxRubiks
2007-Aug-14, 10:47 AM
even just after the BB, when the Universe was small, I thought that the Universe was expanding too fast for light to go all the way around.

WaxRubiks
2007-Aug-14, 10:49 AM
Yes, You thought right but, finite but unbounded does imply that the amount of material available is finite and the space it exists in is expanding to infinity. Well I thought it did... Let me consider this some more.


well, when I say "finite but unbounded" I mean, finite amount of space in a closed system with no boundaries.

So I think you mean something else.

Ken G
2007-Aug-14, 11:00 AM
even just after the BB, when the Universe was small, I thought that the Universe was expanding too fast for light to go all the way around.The universe never expands "too fast" for light to get between any two points-- that's because the light expands too. It is exactly like ants crawling on a stretching rubber sheet-- it makes no difference how fast the edges of the sheet are separating, the ants will eventually make it to the other side (surprising but true). What matters, as Amber Robot pointed out, is whether or not they have yet had enough time to do so, and you are right that rapid expansion increases the time it takes to make it around, even for a closed universe. The only way to prevent them from ever reaching the other side is to accelerate the expansion, which appears to be a relatively recent development and was not occuring in the early universe (regular gravity was causing the expansion to slow at that time).