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Henry Krinkle
2012-May-07, 04:53 AM
Ok Im not even sure how to ask this so please excuse me if it doestn make sense. If for example we have light from a galaxy such as LBG-2377 traveling 11 billion light years away from us in a specific direction and if that is the current limit or greatest observable light being emitted in that direction could we not then try to find the distance of furthest light emitted from galaxies in all (or as many) observable directions? In doing this could we/or would we be able to get a relative sense of our position within the universe? I mean if we can observe light in a specific direction 11 billion light years away and in other directions lets say galaxies 3 billion light years away couldnt that tell us we are more towards an end/edge (if there is such a thing) of the galaxy instead of the middle?

pzkpfw
2012-May-07, 04:58 AM
Post moved from here: http://www.bautforum.com/showthread.php/132037-Galaxies-receding-from-us-and-the-Cosmological-Principle?p=2015062#post2015062

Jens
2012-May-07, 05:12 AM
Ok Im not even sure how to ask this so please excuse me if it doesn't make sense.

Don't worry, the question makes perfect sense. The answer is that we see equally far in all directions.

antoniseb
2012-May-07, 11:48 AM
Don't worry, the question makes perfect sense. The answer is that we see equally far in all directions.

... and that given that distance away also relates to time ago that the light was emitted, and that the universe seems to be expanding... that this limit is not the edge of the universe, but rather the edge of our window AKA the "observable universe". The universe could be many orders of magnitude larger than what we can see, but we haven't observed and interpreted anything to tell us how big yet.

Jeff Root
2012-May-07, 12:06 PM
The most distant stuff we can see light from is the hydrogen
gas which filled the Universe a few hundred thousand years
after the Big Bang. That light has been travelling for about
13.7 billion years. In that time the light travelled a distance
of about 13.7 billion light-years. (Naturally!) We see that
light coming from all directions around us. When it was
emitted, the hydrogen gas that emitted it was much, much
closer to us than 13.7 billion light-years. The expansion of
the Universe during the time the light has been travelling
made it have to travel so much farther.

Likewise, the light from the most distant galaxies we can
see comes from galaxies at the same distance all around
us, in every direction. Their light has travelled something
like 12 billion light-years to reach us. Those galaxies were
also much closer than that when they emitted the light,
and are now much farther away.

The view is pretty much the same nomatter where you are
in the Universe.

-- Jeff, in Minneapolis

cjameshuff
2012-May-09, 02:50 PM
... and that given that distance away also relates to time ago that the light was emitted, and that the universe seems to be expanding... that this limit is not the edge of the universe, but rather the edge of our window AKA the "observable universe". The universe could be many orders of magnitude larger than what we can see, but we haven't observed and interpreted anything to tell us how big yet.

And if we didn't see the same distance in all directions, it wouldn't necessarily indicate that we were near an edge...it could also indicate large variations in expansion, or provide clues about the topology of the universe. This would be particularly evident in the background radiation spectrum, which is literally our view of the universe at the time it became transparent, and so is the furthest source of light we can see. This turns out to be very even, providing tight constraints on the topology of the universe (it looks very flat, with no measurable curvature or other major variations).

antoniseb
2012-May-09, 07:49 PM
... it wouldn't necessarily indicate that we were near an edge...it could also indicate large variations in expansion, or provide clues about the topology of the universe. ...
Yes, thanks! nice addition.