View Full Version : Acceleration

2004-Jul-07, 09:36 PM

what im gonna say might sound a bit stupid,

but we always read or hear about the universe expanding, like the galaxies are moving away from us, but was does this mean exactly?

i read that the andromeda galaxy is on collision course with us''
the point is are the scientists using our galaxy as the center of everything? because as far as i know'' from what i read'' things are moving away from us, then why ar'nt we moving with them?

is andromeda on collision course with us? or visa versa....

im just puzzled.. i would like to think that we are moving as well and just not the center of everything <_<

any thoughts on that chaps?

2004-Jul-07, 10:00 PM
Hi Aquarius,

Welcome to the forum.

Andromeda is moving in our general direction. It might not be coming directly at us.

Galaxy clusters are moving away from each other. The galaxies in the clusters are bound to each other, and sometimes collide with each other. Since the universe is expanding, the space between galaxy clusters is increasing. It doesn&#39;t matter which galaxy cluster you look from, all other cluster will be moving away from you. The further away you look, the faster the galaxies are moving.

Generally, as a convenience, astronomers treat where we are as the center of measurements, but no one says we are at the only center of the universe. From any perspective but ours we are moving... We are observers, but not otherwise special.

2004-Jul-08, 08:04 PM
It might help to say that it is space itself that is expanding, and it is carrying other galaxies along with it, much like pulling a rug and having a table that&#39;s standing on it come with you.

Or, take a balloon, paint a bunch of dots on it, and blow it up. The balloon is like space and all the dots are galaxy clusters. You can see that the total area of the balloon increases in all directions, while the number of dots stays the same.

Close by galaxies, like Andromeda, are moving toward us faster than the expansion, so they aren&#39;t carried away. The break-even point where expansion beats gravity is around 5-10 million light-years. If there are galaxy clusters bigger than that, they break up and disperse.

2004-Jul-27, 11:02 AM
I&#39;ve a quick question regarding the balloon analogy. I&#39;m wondering how far we can take it.

All of the dots we drew on the surface of the balloon are moving away from one another (with no central point) as the surface area increases. What about the points *within* the balloon (the bit that&#39;s filled with air)? I&#39;m imagining these expanding also, but moving away from one another more slowly. And a point in the centre of the balloon is moving away from everything the slowest on average.

When we use the balloon analogy, are we saying that the three dimensions of space (not including time, because I don&#39;t know how to conceptualise that with the balloon), are behaving like the surface of the balloon, or are we saying it acts like the whole balloon, including the area within?

Does this make sense? :huh:

2004-Jul-27, 11:28 AM
Originally posted by virtualutopia@Jul 27 2004, 11:02 AM
When we use the balloon analogy, are we saying that the three dimensions of space, are behaving like the surface of the balloon, or are we saying it acts like the whole balloon, including the area within?
Yes, we are saying that the three spatial dimensions are analogous to the two spatial dimensions on the surface of the balloon, and that there is no thought or comparison to the contents of the balloon, except to say that it would be only a meaningful analogy if there were at least one more spatial dimension that we can&#39;t observe directly.

2004-Jul-29, 03:21 AM
hi as far as we know, in regards to our juxtposition, in relation to everything else, in the known universe at large.we may as well just throw up our hands and surrender, for all we know we may even be in the chute after being swallowed up by a giant black hole and all this we see about us might just be the floatsum & jetsum when things pass through one of those items which as we have seen are becoming more important in the scope of looking at all that exists around us.and will certainly change our concepts of the mechanics at work whereever we look
so dont worry about it the course of events, what evers gonna happen is way off in the distance.and what we think we see a&#39;commin, might look very different in a thousand years.and hey well be just a memory by then.
relax crack open a chilly one and unless you have to come up with the next theroy enjoy the view.and be glad you alive today and not a thousand years ago when the stars were pin holes in the canvas that blocked the sun at night.
and prepared to be amazed everyday by the things the fellows who do bring us all this information lay at your feet.
the stuff is comming so fast now the theorys are changing almost as they are being postulated, we can barly grasp one as it is cast asside by a more provacative and hard to grasp theory &#33;enjoy its all up there the questions and the answers.