Re: The size of the universe <= 14E+9 light years

On Sat, 29 Sep 2007 22:17:17 -0000, Friar Broccoli <EliasRK@xxxxxxxxx>
posted:

On Sep 29, 3:59 pm, catHORME...@xxxxxxxxxxxxxxx (Don Cates) wrote:
On Sat, 29 Sep 2007 11:59:17 -0000, Friar Broccoli <Elia...@xxxxxxxxx>
posted:

On Sep 29, 12:35 am, catHORME...@xxxxxxxxxxxxxxx (Don Cates) wrote:
On Sat, 29 Sep 2007 01:15:26 -0000, Friar Broccoli <Elia...@xxxxxxxxx>
posted:

On Sep 27, 1:19 pm, Jack Dominey <l...@xxxxxx> wrote:
In <1190653524.104789.89...@xxxxxxxxxxxxxxxxxxxxxxxxxxx>, Ken Denny

<k...@xxxxxxxxxxxx> wrote:
Therefore no two points in the
universe can be more than 14E+9 light years apart.

Take a look athttp://en.wikipedia.org/wiki/Universe#Size
andhttp://en.wikipedia.org/wiki/Observable_universe#Misconceptions.

I was impressed by the following comment from the article:

"Those galaxies are now about 46 billion light-years from us, but at
the time the light was emitted, that matter was only about 40 million
light-years away from the matter that would eventually become the
Earth. See comoving coordinates."

If that is correct then the universe has been expanding at a rate
that is effectively well over 99% the speed of light. I must admit
to some skepticism.

I'm curious how you calculate a 'rate of expansion' from within the
thing that is expanding. Can you show me your calculations?

Part of the statement was:

... at the time the light was emitted, that matter was only about
40 million light-years away ...

So if the universe had not been expanding it would have taken
40,000,000 years for the light to reach "earth". It actually
took say 12,000,000,000 years, which is 300 times "too long".
So the EFFECTIVE (I used the word "effectively") rate of
expansion looks like 99.66% that of light.

In reflecting further, that apparent rate is so close to C that
I began wondering if C might be a property of the space-time in
which it propagates.

I'm afraid I didn't word my concern very well.

I'll have to remember that line.

If you are looking at something at the edge of the observable
universe, then it must, by definition, have an apparent
velocity away from us at C. If you pick something closer then
the apparent velocity away from us is less than C. In neither
case is it a metric of expansion rate. An expansion rate would
be a change of volume with time, not a velocity.

There's probably something I'm missing (actually I'm certain
there is), but plowing on:

You end by saying something like: ChangeVol/Time ^= Velocity;
while they are obviously not identical a change in volume will
result in a proportional change in linear distance during some
time between two points in the volume. That looks like a duck
to me.

But the rate of change of distance is specific to the particular
distance you pick. You can get any velocity you want by choosing the
appropriate distance.

On the main point, the article appears to be saying that light
from objects we can see NOW, which was created 12,000,000,000
years ago (henceforth this time is The Period), was at the
moment of its emission 400,000,000 light years away.

That's not a period, it's a very specific time. Let's say 'At the
Time' rather than 'During the Period'. If you choose a different time
you get different results.

Let's say that the rate of expansion is constant and is such that at a
distance of 50 million LY the expansion velocity is C.
Photons emitted from an object at or beyond that distance will *never*
reach us. For photons emitted at that distance, they will always
remain at that distance. For the objects (and any photons they
subsequently emit), their distance from us increases and does so at an
ever increasing rate.

Photons emitted from closer that that distance do eventually reach us
and the closer they start the shorter the time. The objects emitting
get farther away at an increasing rate and eventually move beyond that
distance and no photons they subsequently emit ever reach us. They do
not 'wink out', they just get redder and dimmer as the photons they
did emit before passing beyond 'that distance' continue to reach us at
later and later times.

Light from objects farther away during The Period, has not yet
reached us, while light from closer objects has already passed
us by. So, as far as I can tell, this information does give us
an effective rate of expansion for the universe since The
Period.

Well... yes. It would be closely related to Hubble's Constant and it
is not a velocity.

Hmm... let's see. Using units of millions of LY.
volume 12 billion yr ago = 4/3pi*40^3 = 268083
volume now = 4/3pi*46000^3 = 407720083373088
volume increased by 1520875000 times in 12 billion yr or
about 0.127 times / year.

(Obviously the rate of expansion has decreased
dramatically over time - making my comment about C being a
property of space-time appear silly for this context).

Why is it obvious that "the rate of expansion has decreased
dramatically over time "?

Don Cates ("he's a cunning rascal" - PN)

Note that though I am not deliberately hiding anything, I am
interested in seeing if this rascal is cunning enough to sort
this mess out in a way that is understandable to simpletons like
myself.

Cordially;

Friar Broccoli
Robert Keith Elias, Quebec, Canada Email: EliasRK (of) gmail * com
Best programmer's & all purpose text editor: http://www.semware.com

--------- I consider ALL arguments in support of my views ---------


--
Don Cates ("he's a cunning rascal" - PN)

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