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The Geezer
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If the far flung reaches of the universe are many light ...

Resolved Question:

If the far flung reaches of the universe are many light years away presumably we only assume they are still there, we only receive signals at the speed of light.
My question is - Do we know the universe is still there?
Submitted: 7 years ago.
Category: General
Expert:  The Geezer replied 7 years ago.
Actually this is a fine philosophical point.

Following is something I recently wrote about the distance to the edge of the known universe. But, considering that the light has taken so long to get here, are the things we see "still there"?

There is something missing from phrasing the question like that. It really means "are the things we see the there now" ... and it is the "NOW" that causes the philosophical question to arise.

"Now" implies "now as in at the same TIME we are asking the question". Einstein would answer this point by noting that "now here" is not "now there" when you are talking about interstellar distances.

Let's do one of his famous "thought" experiments. Consider an observer halfway between "here" and "there". When that observer sees light from "here" and light from "there" at the same TIME, that observer can say "they WERE both THERE at the same TIME".

But that observer can't tell us even that NOW because it will take TIME for his message, even traveling at the speed of light, to get to us.

But we won't be THERE. Perhaps our descendants will, but we won't. Humbling, isn't it, to consider the limits on what we can know across interstellar distances.

Too bad. If the things we see are not THERE right NOW what happens to their contribution to gravity, the balance of mass in the known universe, whether the universe is "closed" or "open", whether the cosmic constants change, will there be a "big crunch" or continued expansion... my mind is tired, I need a beer!

*********

The edge of the known universe is at least 12.3 billion light years away. See this article from last year:

"...Date:      May 8, 2006
     
Astronomers Find Molecular Hydrogen At Edge Of Universe

Science Daily — Using a quasar located 12.3 billion light-years away as a beacon, a team of astronomers detected the presence of molecular hydrogen in the farthest system ever, an otherwise invisible galaxy that we observe when the Universe was less than 1.5 billion years old, that is, about 10% of its present age.

Spectrum of the quasar PSS J 1443+2724, revealing the otherwise invisible galaxy at a redshift of 4.224. The velocity profiles of selected transition lines from some rotational levels of H2 are shown...

...The astronomers find that there is about one hydrogen molecule for 250 hydrogen atoms. A similar set of observations for two other quasars, together with the most precise laboratory measurements, allows scientists to infer..."

Source: http://www.sciencedaily.com/releases/2006/05/060508112217.htm

12.3 billion is a considerable fraction of the estimated age of the universe (about 14 billion years is the consensus estimate for now):

"...Light takes billions of years to travel back from such immense distances, so objects at the edge of the Universe viewed through telescopes appear as they were when the Universe was young.

The Universe is estimated to be about 14 billion years old, yet the astronomers estimate they are seeing this stellar system less than one billion years after the big bang...."

Source: http://www.newscientist.com/article.ns?id=dn1379

The second cited article, despite claiming that the stellar system that was observed dates from less than one billion years after the big bang, doesn't actually give a light-year distance to that system. The first article does.

But THIS article goes even farther:

"...      
Galaxy spotted near edge of universe

March 15, 2002 Posted: 7:26 PM EST (0026 GMT)
The arrow marks the vicinity of the most distant galaxy in this red optical and infrared picture.
The arrow marks the vicinity of the most distant galaxy in this red optical and infrared picture.
(go to the link below to see the image)     

By Richard Stenger
CNN

(CNN) -- The new titleholder of most distant known object -- a galaxy -- has pushed our celestial view much closer to the edge of the cosmos, a team of international scientists announced.

The galaxy, which could be more than 14 billion light-years away, offers the earliest glimpse into the universe when galaxies and stars formed. ..."

Source: http://archives.cnn.com/2002/TECH/space/03/15/distant.object/index.html

Note that if this particular object is actually more than 14 billion light-years away, either the universe is older than that OR our theories of how to estimate the age and distance of galactic objects needs to be revised!

It would be safe to conclude that the current estimated distance to the edge of the known universe is between 12 and 14 billion light years.
The Geezer, Successful careers
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Experience: Retired Civil Engineer, USC Professor & Realtor, financier
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