Sulphur on 15/2/2009 at 19:58
Quote Posted by suliman
Yeah, my high school level physics tell me that it makes sense for the universe to deccelerate and eventually shrink, since gravity is the only force at work here. However, this does not take into account dark energy and probably a whole lot of other things I don't know anything about. My uncle insists that the universe's expansion is accelerating, and (
http://en.wikipedia.org/wiki/Accelerating_universe) wikipedia agrees(AND WIKIPEDIA IS NEVER WRONG), which is the whole point of the question. He claims that because the universe is accelerating and because the most updated image we have of it are the galaxies nearest to us, they should logically be the ones that move the fastest.
Say there are three galaxies moving in the same direction.
1--2--3 ->
Now, say you're on galaxy #1. Hubble's law tells us that #3 should move away from you faster than #2. You see #3 further back in time than you see #2. The more recent the image of a galaxy you get, the slower it moves.
I'm not too sure what you mean, but basically I understand this is what you're trying to say:
1) The Universe - its rate of expansion - is accelerating.
2) Our pictures of galaxies nearer to us are more recent.
3) The nearer a galaxy is to us, the slower it moves.
4) But if the Universe's expansion has been accelerating since the Big Bang, then galaxies near to us should ideally be perceived as moving faster than galaxies much further away.
That right?
Okay. You're going to have to refer to Rocketman's post, because when you talk about the Universe expanding, it's actually space itself which is spreading itself thin.
The reason why you won't see nearby stars appearing to zing off into the distance and collide with neighbours 14 billion light years away is because
all of space is expanding at the same time. Like a membrane being stretched - a la dvrabel's balloon analogy - with all the Universe's starstuff represented as points on its surface.
Say Galaxy 1 is moving away from us at 100,000 km/sec. Galaxy 2 is moving away from us at 500,000 km/sec at the same time. Let's say that, 10 years from now, the Universe's rate of expansion has increased tenfold. So 10 years from now, Galaxy 1 should now be moving at 1,000,000 km/sec and Galaxy 2 at 5,000,000 km/sec, right?
Well, no. You see, if the entire Universe is expanding, and its rate of expansion is increasing (that is to say, space), then the absolute velocity of
everything contained in space - which includes
us - will also increase proportionately.
And because of relativity, since everything in the Universe is moving equally faster, from our point of view everything will appear to be moving at exactly the same speed regardless of how much more acceleration the Universe had, has, or will pick up.
suliman on 15/2/2009 at 19:58
Well, I don't really know enough about dar matter to really say anything about it.
Parallel universes... now that's where it's at:cool:
Sulfur- well, that explains it. Thanks!
jtr7 on 15/2/2009 at 20:14
Isn't dark matter the only current explanation to make up for a great deal of "missing" matter according to the math, as well as the expansion paradox?
dvrabel on 15/2/2009 at 22:02
Huh. Seems my astrophysics is 10 years out of date.
Gambit on 16/2/2009 at 02:15
You´re all wrong.
It´s elephants, over infinite turtles...
Muzman on 16/2/2009 at 11:24
Dark matter is similar to black holes in that they were a necessary ...thing to complete the theory but had not been found.
But eventually they did find them. And now there's quite a bit of evidence for dark matter as well (like space with apparently nothing in it gravitationally bending light).
It sounds more cart-before-horse than it is. They're both predictions suggested by a given theory (or set of theories).
Adam Nuhfer on 16/2/2009 at 15:18
Dark matter, Dark energy, String theory, Big Bang caused by membranes colliding into one another.
Other dimensions of both time and space. Sorry, The twilight Zone covered that.
Four "KNOWN" forces with gravity being the weakest in our realm.
Now this is a great thread. Thanks suliman.
