size of the universe

[mrbean_phillip]

Originally Posted by cbwolf

I'm sure you're aware, but there is a great distinction between dark matter and dark energy - completely different things.

Dark energy as per my above description is highly theoretical.

Dark matter on the other hand is so commonly accepted because it's effects can be directly measured, and the idea of matter that doesn't react with light isn't a stretch and it's gravitational effects on nearby objects is clearly evident.

Heya Mate, I am aware, thanx

Which brings us to the next point, as to are we moving at a relatively hefty pace in our own bubble in the universe, scewing our measurements into tricking us thinking the universe is expanding, while in reality it is slowing down to an eventual halt, to start shrinking again? As would be 'logical' considering the effect of gravity?

At least Cosmologist Tsagas is having a go at this dark-flow theory, in which our part of the uiniverse is moving rather rapidly at 2million kn/hr, and leaving us with the impression that universe is expanding.....so, we could either have dark energy, or dark flow, but not both....and the dark-flow theory is by far the least mysterious...

Google for it, a pretty interesting read anyway.

Appreciate everyone's feedback, great to share ideas and debate these issues.

[twinhardballers]

Originally Posted by mrbean_phillip

Which brings us to the next point, as to are we moving at a relatively hefty pace in our own bubble in the universe, scewing our measurements into tricking us thinking the universe is expanding, while in reality it is slowing down to an eventual halt, to start shrinking again? As would be 'logical' considering the effect of gravity?

From what I have read, the red shift is the experimental evidence that all points around us are expanding at the same acceleration rates considering their distance away from us, there is not enough matter in the universe to slow/halt expansion and force a 'big crunch' that we can see, I mean, the dark matter itself only barely holds galaxies together, as there otherwise wouldn't be enough mass to pool together and form.

[Zylatis]

You don't need dark matter on the galaxy scale to keep them together, cosmic expansion isn't able to overcome gravity on that scale. It's only on the distances between galaxies and clusters that you have appreciable expansion of space.

As for the formation stage, i'm not sure.

[twinhardballers]

Originally Posted by Zylatis

You don't need dark matter on the galaxy scale to keep them together, cosmic expansion isn't able to overcome gravity on that scale. It's only on the distances between galaxies and clusters that you have appreciable expansion of space.

As for the formation stage, i'm not sure.

http://www.uslhc.us/LHC_Science/Ques...se/Dark_Matter

Most of the matter in the universe is dark. Without dark matter, galaxies and stars would not have formed and life would not exist. It holds the universe together. What is it?

[vladesch]

Originally Posted by hlokk

It is 46.5 billion light years to the edge of the observable universe. (This is called the comoving distance btw)
This makes the observable universe a sphere 93 billion light years in diameter.

This is something I have trouble understanding. The way my fuzzy logic views this is that any light that was emitted further than 13.7 billion light years away would not have had time to reach us yet, therefore the edge of the observable universe should be 13.7 B light years.

Now I know I am wrong, but despite reading some web pages about this, it still doesn't make sense to me.

[Zylatis]

@twinhardballers: dark matter plays a role in galaxy formation, not in keeping them together. On the galaxy scale you only need it to account for rotation curves.

I've changed my "i don't know" to "I have a rough idea" after reading up a bit =)
http://chronicle.uchicago.edu/060713/darkmatter.shtml
http://www.unexplained-mysteries.com....php?id=201183

This is something I have trouble understanding. The way my fuzzy logic views this is that any light that was emitted further than 13.7 billion light years away would not have had time to reach us yet, therefore the edge of the observable universe should be 13.7 B light years.

Now I know I am wrong, but despite reading some web pages about this, it still doesn't make sense to me.

Ok, let's say space isn't expanding. Then the observable universe would be 13.7b Ly in radius, right? If you now have space expanding while the light travels from the 'edge' (surface of last scattering) the distances are now larger. Don't think about it as an edge though, just think about expanding concentric spheres, the outer sphere representing the shell of matter that was present at the big bang.

[twinhardballers]

I agree with the fact that dark matter affects, galaxy rotation curves, however I am still gunna say it holds them together as well.

nowadays dark matter is a firmly established concept in modern astrophysics. It pretty much has to exist, in fact, to explain why individual galaxies spin as fast as they do without flying apart,

http://www.time.com/time/health/arti...052614,00.html

That is from the article you linked ^^

The first person to provide evidence and infer the presence of dark matter was Dutch astronomer Jan Oort, a pioneer in radio astronomy, in 1932.[12] Oort was studying stellar motions in the local galactic neighbourhood and found that the mass of the galactic plane must be more than the material that could be seen. His discovery was followed by Swiss astrophysicist Fritz Zwicky in 1933, while working at the California Institute of Technology, who studied clusters of galaxies.[13] Zwicky applied the virial theorem to the Coma cluster of galaxies and obtained evidence of unseen mass. Zwicky estimated the cluster's total mass based on the motions of galaxies near its edge and compared that estimate to one based on the number of galaxies and total brightness of the cluster. He found that there was about 400 times more estimated mass than was visually observable. The gravity of the visible galaxies in the cluster would be far too small for such fast orbits, so something extra was required. This is known as the "missing mass problem". Based on these conclusions, Zwicky inferred that there must be some non-visible form of matter which would provide enough of the mass and gravity to hold the cluster together.

http://en.wikipedia.org/wiki/Dark_matter

I did a little reading about rotation curves, and I think I understand the concept. For those of you playing at home, basically the further away from the center of a galaxy (similar to a solar system) the slower your rotation around that system should be. So things further away from the center of our galaxy should go slower than things closer to the center, HOWEVER what we have observed is uniform motion throughout the galaxy, which means that there is much more gravity producing mass (i.e. dark matter) than we can see, what would cause this effect.

If you removed the dark matter from the galaxy (which is 95% of the gravity in a galaxy remember), there wouldn't be enough gravity to hold the stars in orbit around its center, and therefore they would fly off into deep space. If the galaxy kept going the way it does without dark matter (all the velocities were the same) then the stuff at the edge of the galaxy would fly out as it's going too fast to be held in be the expected gravity of visible matter in the galaxy

[RobRoySyd]

Did this get a mention?
http://en.wikipedia.org/wiki/Big_Rip