| Topic: |
Science > Physics |
| User: |
"Ian Macmillan" |
| Date: |
04 Mar 2005 03:38:30 AM |
| Object: |
Centre of expanding universe |
Dear all,
I have read here that the centre of the universe is in every three
dimensional direction from us. I wonder if it would be equally valid to say
that every point is at the centre of the universe, analogous with every
point on the surface of a sphere being at the centre of its surface area.
Reading about "young" galaxies at the distance limit of observation, "not
far", it is said, "in time from the big bang" brings to mind that observers
there would see our locality similarly, and presumably also have a similar
view in the opposite direction. Is there any reason to suppose that the "big
bang" would come in to view from there any more than it does from where we
are located?
All the best
Ian Macmillan.
,
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| User: "tadchem" |
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| Title: Re: Centre of expanding universe |
04 Mar 2005 09:06:33 AM |
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Given a free-floating soap bubble: where is the center?
Hint: It is *not* on the surface of the bubble.
The surface of the soap bubble is a 2-dimensional analog to the 3
geometrical dimensions of the observable universe.
The 'center' of the observable universe is 13-point-something billion
years *in the past* from every geometrical point we can identify in the
observable universe.
Tom Davidson
Richmond, VA
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| User: "Uncle Al" |
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| Title: Re: Centre of expanding universe |
04 Mar 2005 11:39:18 AM |
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Ian Macmillan wrote:
Dear all,
I have read here that the centre of the universe is in every three
dimensional direction from us. I wonder if it would be equally valid to say
that every point is at the centre of the universe, analogous with every
point on the surface of a sphere being at the centre of its surface area.
All 4(pi)steradians point exactly at the Big Bang, everywhere. All
points in the universe are at its exact center.
Reading about "young" galaxies at the distance limit of observation, "not
far", it is said, "in time from the big bang" brings to mind that observers
there would see our locality similarly, and presumably also have a similar
view in the opposite direction. Is there any reason to suppose that the "big
bang" would come in to view from there any more than it does from where we
are located?
Correct for physical viewpoint vs. its place in time.
--
Uncle Al
http://www.mazepath.com/uncleal/
(Toxic URL! Unsafe for children and most mammals)
http://www.mazepath.com/uncleal/qz.pdf
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| User: "Sam Wormley" |
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| Title: Re: Centre of expanding universe |
04 Mar 2005 07:07:34 AM |
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Ian Macmillan wrote:
Dear all,
I have read here that the centre of the universe is in every three
dimensional direction from us. I wonder if it would be equally valid to say
that every point is at the centre of the universe, analogous with every
point on the surface of a sphere being at the centre of its surface area.
Reading about "young" galaxies at the distance limit of observation, "not
far", it is said, "in time from the big bang" brings to mind that observers
there would see our locality similarly, and presumably also have a similar
view in the opposite direction. Is there any reason to suppose that the "big
bang" would come in to view from there any more than it does from where we
are located?
No Center
http://www.astro.ucla.edu/~wright/nocenter.html
Ned Wright's Cosmology Tutorial
http://www.astro.ucla.edu/~wright/cosmolog.htm
http://www.astro.ucla.edu/~wright/cosmology_faq.html
WMAP: Foundations of the Big Bang theory
http://map.gsfc.nasa.gov/m_uni.html
WMAP: Tests of Big Bang Cosmology
http://map.gsfc.nasa.gov/m_uni/uni_101bbtest.html
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| User: "Ben Rudiak-Gould" |
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| Title: Re: Centre of expanding universe |
04 Mar 2005 04:41:01 AM |
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Ian Macmillan wrote:
I have read here that the centre of the universe is in every three
dimensional direction from us. I wonder if it would be equally valid to say
that every point is at the centre of the universe, analogous with every
point on the surface of a sphere being at the centre of its surface area.
This doesn't fit with the usual use of the word "center". Either something
has a single distinguished center, or none at all. In the case of the
universe, there's no center. (As far as anyone knows.)
One can equally well *treat* any point in space as a center of expansion,
just as one can equally well *treat* any velocity as one's standard of rest.
That's one way of expressing that the expansion is homogeneous. But that
doesn't mean that the point you choose is actually the center of anything.
I wouldn't put too much faith in the inflating balloon analogy, which has
many flaws, but in this case it does give the right idea.
Reading about "young" galaxies at the distance limit of observation, "not
far", it is said, "in time from the big bang" brings to mind that observers
there would see our locality similarly, and presumably also have a similar
view in the opposite direction. Is there any reason to suppose that the "big
bang" would come in to view from there any more than it does from where we
are located?
I think you're forgetting that we don't see distant objects directly. What
we see is light which was once emitted from those objects, and is now in our
vicinity. The farther away the object, the longer ago the light must have
been emitted, for it to reach us at this particular moment. So your question
about "observers there" is ill-posed. Perhaps you mean this: if our
telescopes were powerful enough that we could see little green men in the
distant galaxy peering through telescopes in our direction, would they see
the primeval earth through their telescopes? The answer to that is no. They
wouldn't be able to see the earth at all, or even the matter that would
later condense to form the earth, because there wouldn't have been enough
time (since the inflationary epoch) for any light from that far away to
reach them. They would, however, have a better view than us of the early
history of the universe. On the other hand, if you're talking about
observers there now (in cosmic time), then they would see the ancient earth,
but wouldn't have a better view of the early universe.
-- Ben
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