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Miketmbt
2007-Jan-09, 09:08 PM
Is everywhere is the center of the universe? Does that meant that if you look far enough in any direction you will see the same thing?

Sam5
2007-Jan-09, 09:28 PM
Is everywhere is the center of the universe? Does that meant that if you look far enough in any direction you will see the same thing?


I wouldn't say that everywhere is the center, I would say that everything came from the center..... if the universe started at a point and expanded outward in 3 dimensions.

If the universe is infinite, then I guess it doesn't have a center. If it turns out to have more dimensions than 3, it might not have a "center".

If it is infinite, then if we look far enough in any direction we might see the same thing, assuming it is of the same density and consistancy all over, infinitely, everywhere.

Think of our galaxy. It has a definite "center", but we really can't see it from here with a regular telescope, and the stars we see in all directions are mostly within our own galaxy, and there are billions of other stars/planets that we could look out from and see just about the same thing as we see here on earth. Different "constellations", but still pretty much the same thing, although not exactly the same thing.

crosscountry
2007-Jan-09, 10:04 PM
I don't know about the a true center, but...


our horizon is beyond all telescopes ability, not only that due to the accelleration of the universe we are actually losing visible galaxies. In every direction we can only see so far because the rest moving away faster than the speed of light.

So, using the term "visible universe" we are the center.

Sam5
2007-Jan-09, 10:10 PM
So, using the term "visible universe" we are the center.

Right, and you can carry that right on down to yourself as an individual. YOU are the center of your own visible universe.

Jeff Root
2007-Jan-09, 10:19 PM
Mike,

The statement that "everywhere is the center" is misleading and
not an expression I would use. There is no indication of any center
or edge in the part of the Universe that we can see. There is no
indication whether the Universe is finite or infinite. Even if it is
finite, it is definitely much bigger than the part we can see, so it
might have a center, but be too big for us to ever determine where
the center is. Or it could be finite, yet not have a center. If it is
infinite then of course it has no center.

The overall "curvature" of space appears to be flat, so nomatter
how far you look, you can't see the same galaxy in different
directions. If space were strongly curved in the positive direction,
like a sphere, that might be possible. There are local curvatures
caused by variations in gravity, from variations in the density of
matter, but overall the visible part of the Universe is flat.

-- Jeff, in Minneapolis

Sam5
2007-Jan-09, 10:19 PM
I don't know about the a true center, but...
our horizon is beyond all telescopes ability,


I love this picture....

http://tinypic.com/jsdbhc.jpg

That guy’s just like us, trying to see beyond what he actually can see, and since the artists doesn’t know what’s out there beyond the stars, he has to make up some stuff.

Note Ezekiel’s “wheels”, way out in outer space.

max8166
2007-Jan-17, 05:52 PM
If everywhere is the center of the universe? Does that meant that if you look far enough in any direction you will see the same thing?
Yes and No.
Yes, if you look far enough in any direction all you will see is the past.
No, if you look far enough in any direction you will not see duplicate galaxies.
-------------------------------------------------------
Everything I say is in my opinion (IMO)

Argos
2007-Jan-17, 06:11 PM
if you look far enough in any direction you will see the same thing?

Yes, namely the Cosmic Microwave Background. ;)

Amber Robot
2007-Jan-17, 06:24 PM
our horizon is beyond all telescopes ability, not only that due to the accelleration of the universe we are actually losing visible galaxies. In every direction we can only see so far because the rest moving away faster than the speed of light.

I thought we could see to higher redshifts than those that would have the calculated recessional velocity greater than the speed of light. :confused:

crosscountry
2007-Jan-17, 08:31 PM
then we would have to rethink General Relativity, and I that hasn't changed in a few years.

Amber Robot
2007-Jan-17, 08:45 PM
then we would have to rethink General Relativity, and I that hasn't changed in a few years.

According to the article Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the universe (http://arxiv.org/pdf/astro-ph/0310808):


Recession velocities exceed the speed of light in all viable cosmological models for objects with redshifts greater than z~1.5

I know that we have observed objects at redshifts higher than 1.5

Ken G
2007-Jan-17, 09:23 PM
Yes, it is very strange, but we can see galaxies that are receding from us faster than light if we wait long enough. This is tantamount to saying that an ant can eventually crawl across a sheet of rubber, even if you stretch the end of rubber faster than the ant can walk. That's because as the ant makes progress across the rubber, at first that stretching you were doing was leaving it behind, but as it puts more rubber behind it, eventually the stretching is actually giving the ant a turbo boost! Try it yourself, if you have some rubber and a willing ant.

Also, if the expansion is accelerating, then it is true that we won't get light from galaxies past a certain point, and that point is including more and more galaxies-- they are indeed "dropping out" of observability, but it's not their speed, it is the acceleration of the expansion that is doing it, just like with the ant and the rubber.

Jeff Root
2007-Jan-18, 01:31 AM
Ken,

Regarding an ant crawling over a stretching rubber sheet...

I made this animation for another thread:

http://www.freemars.org/jeff2/expand2a.gif

It is based on a similar animation at the Atlas of the Universe
website. That animation shows slowing expansion. Mine shows
constant expansion. There are 4 galaxies and 3 light pulses, so
you can see the effect of the events taking place in different
parts of the god's field of view. The three light pulses are
identical (made so by copying and pasting), but positioning the
first one was part measurement and part guesstimation.

I tried to make each pulse always have the same speed relative
to the grid line that it is crossing over. If there were more
lines between those actually shown (say 1/4, 1/2, and 3/4 of
the way between), then the light pulses would have the same
speed relative to them, too.

What can you say about the animation and how well it does or
does not model reality?

-- Jeff, in Minneapolis

Ken G
2007-Jan-18, 04:03 AM
Yeah, that's a good animation for the point!

crosscountry
2007-Jan-18, 09:11 AM
According to the article Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the universe (http://arxiv.org/pdf/astro-ph/0310808):



I know that we have observed objects at redshifts higher than 1.5


so it does. I think that first statement you quoted was a little mixed up. I should have stopped about halfway through.