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bricks41
2010-Jul-01, 04:10 AM
Sorry but I will try to be as concise as possible.

Using red shift, radiation and other methods used to determine how fast objects are moving away from each other, isn't there a way to determine where the approximate "start" of the universe is located?

Meaning, the "accepted" age is some 13.5 billion years old, but does this include the expansion on the other end of the explosion?? Say galaxies in our galactic neighborhood are moving away from each other as say 400k km per hour. Shouldn't there be galaxies that are moving away from us at say 1.2 million km per hour? This would be because they are on the "opposite" side of the expansion and therefore would have a drastically higher red shift.

Along this same thought, couldn't one trace back the "start"? Granted we may ultimately be limited by the capabilities of our instruments.

Sorry if this doesn't make sense or has been asked previously.

Sticks
2010-Jul-01, 05:01 AM
I think this may have been covered in Astronomy Cast you may want to hunt there as well.

BTW bricks41, welcome to BAUT, I have approved this post for you as it was caught in the moderation queue by the forum software

01101001
2010-Jul-01, 05:08 AM
Welcome.


Sorry if this doesn't make sense or has been asked previously.

Yeah, it's kind of asked frequently.

Sean Carroll: Cosmology Primer FAQ :: Does the universe have a center? (http://preposterousuniverse.com/writings/cosmologyprimer/faq.html#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.

Jens
2010-Jul-01, 05:09 AM
Along this same thought, couldn't one trace back the "start"? Granted we may ultimately be limited by the capabilities of our instruments.


As a pretty stock answer, the reality apparently is that wherever you are in the universe, you will appear to be the center. Observationally, we appear to be at the center. So from that you can draw two possible conclusions: one is that we really are the center. But that would be tremendously egocentric. The second is to assume that wherever you are, you appear at the center. The second is almost certainly the correct choice.

Infinitenight2093
2010-Jul-01, 05:30 AM
Sorry but I will try to be as concise as possible.

Using red shift, radiation and other methods used to determine how fast objects are moving away from each other, isn't there a way to determine where the approximate "start" of the universe is located?

Meaning, the "accepted" age is some 13.5 billion years old, but does this include the expansion on the other end of the explosion?? Say galaxies in our galactic neighborhood are moving away from each other as say 400k km per hour. Shouldn't there be galaxies that are moving away from us at say 1.2 million km per hour? This would be because they are on the "opposite" side of the expansion and therefore would have a drastically higher red shift.

Along this same thought, couldn't one trace back the "start"? Granted we may ultimately be limited by the capabilities of our instruments.

Sorry if this doesn't make sense or has been asked previously.

The question, Where did the big bang, bang? is useless because the universe started everywhere. Once you trace all expanding matter back into it's original spot, the actual "explosion" would happen everywhere in the universe at once. This is also because there is no understandable "outside" of the universe to actually put a location into perspective

WayneFrancis
2010-Jul-01, 05:50 AM
Sorry but I will try to be as concise as possible.

Using red shift, radiation and other methods used to determine how fast objects are moving away from each other, isn't there a way to determine where the approximate "start" of the universe is located?

Meaning, the "accepted" age is some 13.5 billion years old, but does this include the expansion on the other end of the explosion?? Say galaxies in our galactic neighborhood are moving away from each other as say 400k km per hour. Shouldn't there be galaxies that are moving away from us at say 1.2 million km per hour? This would be because they are on the "opposite" side of the expansion and therefore would have a drastically higher red shift.

Along this same thought, couldn't one trace back the "start"? Granted we may ultimately be limited by the capabilities of our instruments.

Sorry if this doesn't make sense or has been asked previously.

Hi bricks41,
The question is a common one...if you search for "centre of the universe" you'll probably get many hits.
It seems you have the idea that we are moving through space when actually it is space that is expanding.
It isn't like a normal explosion that ejects stuff from the point of the explosion through the air.
It is an explosion where all the fragments stay where they are but the amount of space between the fragments increases.
This has an added effect that if you try to think of expansion as an actual explosion then every point in space is the centre and this breaks down when you look at the details of an actual explosion which has very different dynamics then what we observe in cosmological expansion. The centre of the universe is better described as a point in time and not as a point in space.

Infinitenight2093
2010-Jul-01, 09:06 AM
It helps to think of the Big Bang as an explosion OF space, not an explosion IN space

Andrew D
2010-Jul-03, 01:54 AM
Sorry but I will try to be as concise as possible.

Using red shift, radiation and other methods used to determine how fast objects are moving away from each other, isn't there a way to determine where the approximate "start" of the universe is located?

Meaning, the "accepted" age is some 13.5 billion years old, but does this include the expansion on the other end of the explosion?? Say galaxies in our galactic neighborhood are moving away from each other as say 400k km per hour. Shouldn't there be galaxies that are moving away from us at say 1.2 million km per hour? This would be because they are on the "opposite" side of the expansion and therefore would have a drastically higher red shift.

Along this same thought, couldn't one trace back the "start"? Granted we may ultimately be limited by the capabilities of our instruments.

Sorry if this doesn't make sense or has been asked previously.

It is a great first question. It was my first, and I've learned quite a bit since then.

It may seem counter intuitive, but the big bang actually occurred everywhere: way back then, the universe in its entirety was infinitely small and infinitely dense. Mainstream science isn't sure why, but at some point, the infinitesimal universe began to expand very rapidly. The next question, of course, is "what was the universe expanding into?" The answer is: nothing; I assure you it's much less confusing if you don't worry about whats outside of the universe (questions like that can not be answered by science), but imagine that the universe at the time of the big bang rapidly began to contain more space. Still now, it follows this trend, at each moment containing more space than the moment before.

You are very correct in your assumption that the galaxies move away faster the farther they are from us, and indeed, the furthest galaxies are red-shifted the most. This makes it look to us as though our position in the universe is special, and we are in the center. But from what we understand about how the universe works, we know that all locations share the same quality, anywhere you were in the universe, you would see galaxies farther away moving fast from you, and closer galaxies moving away not so fast.

Be sure to read Ned Wright's Cosmology Tutorial (http://www.astro.ucla.edu/~wright/cosmolog.htm) and these wikipedia pages:

http://en.wikipedia.org/wiki/CMBR
http://en.wikipedia.org/wiki/Big_bang
http://en.wikipedia.org/wiki/Large-scale_structure_of_the_cosmos#Large-scale_structure
http://en.wikipedia.org/wiki/Metric_expansion_of_space
http://en.wikipedia.org/wiki/Hubble%27s_law
http://en.wikipedia.org/wiki/Inflation_%28cosmology%29
http://en.wikipedia.org/wiki/FLRW_metric (this one is math-heavy, just focus on the descriptions if you're not ready for the mathematics yet)

and watch this video series:

http://www.youtube.com/watch?v=32wIKaLkvc4&feature=related (this is the URL for just the first video, you can link to the others from it)

good luck, and welcome.

Somes J
2010-Jul-04, 01:27 AM
The way I like to think of this that makes it more intuitive is that we're sort of like somebody standing on the edge of a giant balloon that's being blown full of air, with lots of Xs drawn on it (the Xs representing galaxies). If you stand on one X you will see all the other X marks moving away from you. Move to a different X and you will see the same thing. Just as an expanding sphere would have no center or edge of the expansion on its surface, the universe has no center or edge of expansion.

bunker9603
2010-Jul-04, 12:15 PM
Roobydo


You are very correct in your assumption that the galaxies move away faster the farther they are from us, and indeed, the furthest galaxies are red-shifted the most.

This question has probably been asked also, but I couldn't find the answer. Since galaxies are moving/expanding, how is it the the Milkyway and the Andromeda galaxies are going to collide in the future? Are galaxies expanding in all directions?

Hornblower
2010-Jul-04, 12:24 PM
Roobydo



This question has probably been asked also, but I couldn't find the answer. Since galaxies are moving/expanding, how is it the the Milkyway and the Andromeda galaxies are going to collide in the future? Are galaxies expanding in all directions?

There are local irregularities, including the case of these two large galaxies that are close together. Their mutual gravitation overpowers the tendency to recede. Over longer distances the cosmic expansion becomes dominant.

caveman1917
2010-Jul-04, 03:39 PM
Roobydo



This question has probably been asked also, but I couldn't find the answer. Since galaxies are moving/expanding, how is it the the Milkyway and the Andromeda galaxies are going to collide in the future? Are galaxies expanding in all directions?

It basically has to do with the fact that gravity tries to pull everything together, while cosmic expansion pushes everything away from eachother. Since gravity is stronger at smaller scales (inverse square) and cosmic expansion grows stronger at longer scales (linear), you can imagine a 'line' where the two cancel out and expansion starts winning from gravity, inside this line gravity wins. Therefore there are structures in space which are close enough together for gravity to win (gravitationally bound structures), but between those structures expansion wins. This usually happens at the supercluster scale. So everything in our local supercluster will simply remain bound by gravity, the galaxies orbiting/colliding etc, and expansion wins at the scale between different superclusters.

While not technically correct, an easy way to think of it is that gravity only works within a supercluster, and expansion only works between superclusters.

Andrew D
2010-Jul-04, 06:54 PM
The way I like to think of this that makes it more intuitive is that we're sort of like somebody standing on the edge of a giant balloon that's being blown full of air, with lots of Xs drawn on it (the Xs representing galaxies). If you stand on one X you will see all the other X marks moving away from you. Move to a different X and you will see the same thing. Just as an expanding sphere would have no center or edge of the expansion on its surface, the universe has no center or edge of expansion.

This analogy has been used in the past, but can create more confusion than it alleviates. I think its best to skip the analogies and examine expansion with a mild level of technicality to develop a casual understanding. The video series I linked to in my previous post does this well, and requires only an elementary knowledge of mathematics.