Size of the universe
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02-07-2013, 07:53 AM
RE: Size of the universe
(02-07-2013 07:46 AM)Humakt Wrote:  
(02-07-2013 07:33 AM)Logisch Wrote:  See above post.

OK, watched that, everything is moving away from each other, but if everything is moving away from a central point (the detonation point) then the circumference of the universe would be getting bigger, thus the area of the universe would also be increasing, thus the observable result would that the distance between point would increase.

But, from what I understand of stuff, that makes sense. However, I dont get how there isnt a center somewhere from which this expansion is happening. If the is no center, how is it we can hold to the idea that the universe is expanding from the point of origin?

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02-07-2013, 08:01 AM
RE: Size of the universe
(02-07-2013 07:46 AM)Humakt Wrote:  
(02-07-2013 07:33 AM)Logisch Wrote:  See above post.

OK, watched that, everything is moving away from each other, but if everything is moving away from a central point (the detonation point) then the circumference of the universe would be getting bigger, thus the area of the universe would also be increasing, thus the observable result would that the distance between point would increase.

But, from what I understand of stuff, that makes sense. However, I dont get how there isnt a center somewhere from which this expansion is happening. If the is no center, how is it we can hold to the idea that the universe is expanding from the point of origin?

I think you may be fundamentally misunderstanding sort of how the universe is from a larger perspective. I think people imagine the big bang happening from a central point, and then everything sort of stems out specifically from this central point. This is easy to do because we're used to learning that things revolve around other things, or seeing things stemming out from the center of other things.

The big bang should really be called "the big expansion" because it wasn't an explosion and then matter just spattered out from that central point. Instead, it was a very rapid and exponential expansion of space itself. Since it was an expansion of space, it continues expanding everywhere. So really, the center is an irrelevant thing to contemplate Wink





Does your brain hurt yet? I know mine did when I started contemplating this stuff.

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02-07-2013, 08:26 AM
RE: Size of the universe
See, this is where my head is exploding. We talk about the expansion of space, but isn't space "nothing"? How does nothing expand? Doesn't "nothing" expand because two things in that nothing are, in fact, moving away from each other? The balloon analogy only goes so far: within a balloon, we know there is an outer edge, a boundary. There is no such boundary in space, right? I mean, if there's an outer edge of nothing, what lies beyond it? More nothing?

I fail to see (and this is my failure, make no mistake) how a discussion of the expansion of space itself leads to objects (galaxies) that are so far away from us that we should not be able to see them because not enough time has elapsed since the Big Bang, yet we see them. Is it because we are only seeing where they were, and we are extrapolating where they must be by now when we calculate their current distance from us?

In other words, when we say that we see galaxy X, which is 35 billion light years away, are we really saying galaxy X is that far away NOW, but the light we are seeing from it originated when galaxy X was much closer to us? Because that would make some sense to my decidedly unsophisticated finite little brain.
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02-07-2013, 09:10 AM
RE: Size of the universe
(02-07-2013 08:26 AM)TwoCultSurvivor Wrote:  See, this is where my head is exploding. We talk about the expansion of space, but isn't space "nothing"? How does nothing expand? Doesn't "nothing" expand because two things in that nothing are, in fact, moving away from each other? The balloon analogy only goes so far: within a balloon, we know there is an outer edge, a boundary. There is no such boundary in space, right? I mean, if there's an outer edge of nothing, what lies beyond it? More nothing?

I fail to see (and this is my failure, make no mistake) how a discussion of the expansion of space itself leads to objects (galaxies) that are so far away from us that we should not be able to see them because not enough time has elapsed since the Big Bang, yet we see them. Is it because we are only seeing where they were, and we are extrapolating where they must be by now when we calculate their current distance from us?

In other words, when we say that we see galaxy X, which is 35 billion light years away, are we really saying galaxy X is that far away NOW, but the light we are seeing from it originated when galaxy X was much closer to us? Because that would make some sense to my decidedly unsophisticated finite little brain.

This is great because it means you're contemplating it in ways you previously misunderstood. The issue is that most people misunderstand it to a great degree. Unfortunately, since our understanding has changed exponentially over the years, but education in regular public schools remain "very basic" people tend to only pick this stuff up either in college or from bothering to go look it up or research it to learn more.

Are you ready to fuck your brain even more? Space is not necessarily "nothing" but actually could be thought of as almost as a fabric, a dimension. See minute 26 http://video.pbs.org/video/2163057527/ Brian Greene talks on it and has some fantastic analogies that might help you make sense of "what space is"...

Some people think of space as nothing more than a distance. So when people think of distance expanding, they tend to imagine an object itself moving further away from another. However, imagine a central point... with some other points around it, we'll imagine these being galaxies in space.

These are "galaxies" and the lines, the space between them..
O-----O-----O

Now if we go off of the understanding of how space itself expands, we can imagine the objects themselves not necessarily moving, but the space between them stretching/expanding. Imagine a bunch of marbles on a giant piece of latex and imagine not moving the marbles, but just stretching the latex on a flat surface. This is pretty much the baloon analogy, but a bit easier to picture. The marbles aren't moving, the space they sit on and exist in is expanding.

O-<||||>-O-<||||>-O

You can imagine the dash marks the space being stretched in the middle.

But let's add MORE galaxies and do it again.... Just to kind of "strike the point home", you might imagine these galaxies "moving away from each other" but if you were on the OTHER side of the galaxy, it would appear to be moving the OTHER way... away from you. But if the galaxy is not actually "moving away" this leaves what? The space between expanding.

O-<||||>-O-<|||||>-O-<|||||>-O-<|||||>-O

If you were at the 1st galaxy in, the 2nd, 3rd, 4th and 5th galaxies would appear to be moving away from you. If you were at the second galaxy in, the first, 3rd, 4th and 5th galaxy would appear to be moving away on your sides. If you were in the middle, the galaxies in all directions are moving away, almost apparently from a central point.. so on and so forth.

Now imagine that it appears this way from any galaxy, no matter where you are at in the universe, unless you're in the local cluster of course, and something like andromeda is about to collide with you... in which case, imminent blue shift doom is apparent.

And to a large degree, yes, what we see is the light from those galaxies generally from billions of years ago. NOT as they are now. Eventually, as space expands and those objects get more distant, it would eventually appear "blank" as it would take too long for light to travel to us to see those. In fact, there are plenty of galaxies that exist this way. This is why we talk about the "observable universe" - there are things out there that have expanded so far, so fast, we'll never potentially see or understand the existence of those objects/galaxies.

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02-07-2013, 09:21 AM
RE: Size of the universe
(02-07-2013 08:26 AM)TwoCultSurvivor Wrote:  See, this is where my head is exploding. We talk about the expansion of space, but isn't space "nothing"? How does nothing expand? Doesn't "nothing" expand because two things in that nothing are, in fact, moving away from each other? The balloon analogy only goes so far: within a balloon, we know there is an outer edge, a boundary. There is no such boundary in space, right? I mean, if there's an outer edge of nothing, what lies beyond it? More nothing?

It pretty clear that space is not nothing. Space seems to have an underlying structure or reality that make it not nothing.

Quote:I fail to see (and this is my failure, make no mistake) how a discussion of the expansion of space itself leads to objects (galaxies) that are so far away from us that we should not be able to see them because not enough time has elapsed since the Big Bang, yet we see them. Is it because we are only seeing where they were, and we are extrapolating where they must be by now when we calculate their current distance from us?

No, if it is more than 13.7 light years away, we can't see it.

Quote:In other words, when we say that we see galaxy X, which is 35 billion light years away, are we really saying galaxy X is that far away NOW, but the light we are seeing from it originated when galaxy X was much closer to us? Because that would make some sense to my decidedly unsophisticated finite little brain.

You keep saying this - where are you getting this idea? We cannot see anything further than 13.7 billion light years from us.

If we look in opposite directions and see Galaxy A and Galaxy Z, then the distance between those two galaxies is as much as 27.4 billion light years, but neither can be seen from the other other.

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02-07-2013, 09:24 AM
RE: Size of the universe
Remember Abbott and Costello's "Who's on First" bit? At a certain point, Costello tries to make sense of what he's being told, and he accurately describes a hypothetical play on the field, to which Abbott basically says "yes, that's it, you've got it."

Costello responds: "I don't even know what I'm TALKING about!"

That's what just happened here, I think. It looks like I got something right, but I can't for the life of me figure out what it is.

Smile

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02-07-2013, 09:28 AM
RE: Size of the universe
(02-07-2013 08:26 AM)TwoCultSurvivor Wrote:  See, this is where my head is exploding. We talk about the expansion of space, but isn't space "nothing"? How does nothing expand? Doesn't "nothing" expand because two things in that nothing are, in fact, moving away from each other?

In a technical sense, that is true (except that space is not 'nothing', but a churning sea of virtual particle pairs). We say that space is expanding, because things are becoming farther apart (that is a very solid, observable fact), and we know of no other way to explain that. Everything is moving away from us - and, we may assume, from everything else. So the expansion cannot be from a centre point, but must be from 'everywhere' (it is universal, as it were).

How do we know it is the space between them that is expanding? Because the distance increases uniformly in every direction. If it were caused by motion, there would be relative motion, and the motion of distant objects would not be uniform.

(02-07-2013 08:26 AM)TwoCultSurvivor Wrote:  The balloon analogy only goes so far: within a balloon, we know there is an outer edge, a boundary. There is no such boundary in space, right? I mean, if there's an outer edge of nothing, what lies beyond it? More nothing?

The balloon has a closed topology. It is a two-dimensional surface streched 'into' (if you like) a sphere - travel far enough in one direction, and you return to where you started. So it is boundless (it... can also be infintely large at the same time).

The universe itself? Well, we aren't sure of its shape. It may be likewise closed. It may not be. The alternatives are open (hyperbolic) or flat (kind of - it is of course not two-dimensional, as those analogous models are).

But then - the only meaningful sense in which it may be said to have an edge is the limits of interaction. There is a hard limit to what we can perceive - we can only 'see' the area in which expansion has been sufficiently small that photons within it may reach us. That is the edge, so far as we can ever be concerned.

As to what else there may or may not be - we don't know. An observer at any point would see the cosmos as we do - surrounded by ever further, ever older objects, due to the (so far as we know) uniform expansion of the universe.

(02-07-2013 08:26 AM)TwoCultSurvivor Wrote:  I fail to see (and this is my failure, make no mistake) how a discussion of the expansion of space itself leads to objects (galaxies) that are so far away from us that we should not be able to see them because not enough time has elapsed since the Big Bang, yet we see them. Is it because we are only seeing where they were, and we are extrapolating where they must be by now when we calculate their current distance from us?

In other words, when we say that we see galaxy X, which is 35 billion light years away, are we really saying galaxy X is that far away NOW, but the light we are seeing from it originated when galaxy X was much closer to us? Because that would make some sense to my decidedly unsophisticated finite little brain.

Distance does not exist as you are using it. It's relative!

What we can measure is (roughly) how far light has travelled when we observe it. Knowing how far it has gone, we can more or less say that's how long it was travelling for.

Distances, as we intuitively understand them, have no meaning at a cosmological level.
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02-07-2013, 09:29 AM
RE: Size of the universe
Chas, I'm sorry I keep ignoring you on this point, but it appears you are mistaken. I am WAY out of my league in trying to explain it, but I would not have asked the question if I had not already determined that we can, in fact, see things that are farther away.

Let me invite you to read this article (and if others here take issue with this article, please feel free to weigh in. I don't want to become an expert or anything. I just want to grasp it on some level so that it makes sense.

http://en.wikipedia.org/wiki/Observable_universe
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02-07-2013, 09:34 AM
RE: Size of the universe
maybe the problem is my use of the word "see"?
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02-07-2013, 09:38 AM
RE: Size of the universe
(02-07-2013 09:29 AM)TwoCultSurvivor Wrote:  I don't want to become an expert or anything. I just want to grasp it on some level so that it makes sense.

I'd say you have grasped it. Certainly well enough to ask about it.

The problem is that it fundamentally does not, and will not, make intuitive 'sense' to you, because the colossally macroscopic universe (and the infinitesimally microscopic universe) operate in ways that are not governed by the rules that shape the mid-scale universe (which is where our intuition comes from).
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