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View Full Version : Where is the universes center of gravity?

Profpat
2007-Jul-13, 07:06 PM
Hi again everyone;

I have a new question regarding the universes' center of gravity.

It's my understanding that for every REAL THING there is a center of gravity albeit imaginary.but of real importance. This is true for a proton, me, and I would assume the universe.

I heard that the universe is boundless with no center. Indeed I heard there is no inside or outside. ( A very confusing concept )

Well using the baloon analogy the center would be inside the baloon.

Can somebody help me I'm confused.

Thank you

Profpaqt

01101001
2007-Jul-13, 07:43 PM
Where is the universes center of gravity?

On the tip of your nose. And the tip of mine. And every other point in the universe. All points are the center. Or, if you wish, none are.

Sean Carroll's Preposterous Universe Cosmology Primer FAQ (http://preposterousuniverse.com/writings/cosmologyprimer/faq.html#center)

Does the universe have a center?
No. Our observable universe looks basically the same from the point of view of any observer. We see galaxies moving away from us in all directions, but an astronomer living in any one of those galaxies would also see all the galaxies (including our own) moving away from them. In particular, the Big Bang is not an explosion that happened at some particular point in space; according to the Big Bang model, the entire universe came into existence expanding at every point all at once.

That covers expansion.

As for center of mass, there is no requirement that the universe have a single center of mass.

The balloon is an analogy. The real situation is up a dimension, or several. Not all features apply.

If you were in a balloon-universe, you'd be stuck on the balloon, and all points possible would be on the balloon with you, so hypothesizing a center of the ballon that wasn't on the surface of the balloon would be a... stretch.

Don't let the balloon be too real. It's a tool, not a model.

Sean Carroll treads briefly on the balloon here: Cosmology Primer: The Expanding Universe (http://preposterousuniverse.com/writings/cosmologyprimer/expanding.html)

In thinking about the expanding universe, it is tempting to appeal to some sort of simile: distant galaxies are like raisins in a baking loaf of bread, or dots drawn on the surface of a balloon. But the universe is a unique place, and similes tend not to do it justice (or worse, to suggest something misleading). It's actually best just to think about the universe itself, and what it looks like.

Aristocrates
2007-Jul-13, 07:46 PM
Also, we can't actually even see the whole universe right now (if I understand correctly), so even if we assumed a flat topology, we wouldn't be able to figure out the center of mass.

01101001
2007-Jul-13, 07:56 PM
Some other BAUT topics:
Center of the Universe (http://www.bautforum.com/astronomical-observing-equipment-accessories/20965-center-universe.html)
Is there a "center" to the universe? (http://www.bautforum.com/questions-answers/27122-there-center-universe.html#post526770)

Fire up the search engine. There are plenty.

Ken G
2007-Jul-14, 03:50 AM
Also, we can't actually even see the whole universe right now (if I understand correctly), so even if we assumed a flat topology, we wouldn't be able to figure out the center of mass.
Yes, I think the answer to the OP is actually "no one has any idea, but at the moment there does not appear to be any good reason to postulate that the universe has a meaningful center of mass, and science doesn't make postulates that it doesn't need."

Profpat
2007-Jul-14, 04:59 PM
Thank you everyone for your responses and references.

Knowledge_Seeker
2007-Jul-15, 03:55 AM
I kind of have the same question but did not want to re-post it. If early galaxies were formed when a small group of stars attracted individual stars to form large galaxies, shouldn't there be a place where everything is moving to a large mass? (or does dark energy stop this from happening?)

01101001
2007-Jul-15, 04:15 AM
If early galaxies were formed when a small group of stars attracted individual stars to form large galaxies, shouldn't there be a place where everything is moving to a large mass?

Stars didn't attract other stars to form galaxies. Stuff attracted stuff.

Cosmology Primer: The Early Universe (http://preposterousuniverse.com/writings/cosmologyprimer/early.html)

The smooth, slightly perturbed early universe visible in the CMB anisotropies grew into the lumpier universe of stars and galaxies we see today. This should come as no surprise. The hot and cold spots of the CMB correspond to regions of slightly higher or lower density than average. In the regions that were overdense, the pull of gravity brought matter closer together, further emptying out the regions that were less dense. The evolution of the universe under the influence of gravity thus acts to increase the contrast of the matter distribution, from a nearly featureless plasma to an intricate collection of galaxies. This process takes longer over larger distances, which is why the universe remains approximately smooth on very large scales.