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what is the universe expanding into?


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if the universe is expanding, then it has to expand into something. just because we dont know why its doing this doesnt mean it doesnt make sense.

 

Maybe the question should be is the universe infinite or finite and if it is finite, what is past the edge. Seems like there is a long thread about that.

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if the universe is expanding, then it has to expand into something.

 

That doesn't follow. All that is meant by "universe expanding" is that distances between objects are increasing*.

 

That can happen without there being any space outside of the usual space we know.

 

Maybe the question should be is the universe infinite or finite and if it is finite, what is past the edge.

 

It doesn't follow that there should be an edge. If all existence were concentrated on a 2d spherical surface, the area would be finite, but space would have no edge.

 

*A point to be aware of is that there is a criterion for when an object is at rest with respect to the microwave background, before the background was discovered we used to say at rest with respect to the expansion process itself meaning the same thing, but now having the background makes it easier to grasp. If an observer is stationary w.r.t. background then he doesn't see any doppler hotspot in the microwave sky.

 

Our theory of gravity is also our theory of geometry---namely GR--and it teaches us not to expect distances between stationary objects to stay the same. Given some fairly easily satisfied conditions it teaches us to expect a pattern of largescale distances increasing, pretty much as we observe.

 

Distances to nearby galaxies bound to ours by gravity are not part of this pattern, nor are any more local distances. The pattern (called Hubble Law) only covers largescale distances between remote galaxies not bound together by gravity in clusters. The actual letter of the law only applies to objects which are not moving.

 

It says that the distance between two widely separated stationary objects is currently increasing at a percentage rate of 1/140 percent every million years.


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Expand into? That makes no sense. It would mean that "outside of space" wouldn't be meaningless.

 

ydoaPs has it right. "Outside of space" is meaningless.

"Expand into" makes no sense.

 

The universe should not be imagined as an object. It is a context. It's geometry is simply the distance-relations between objects. We know it from inside only and can exclude the idea of an outside almost by definition, or by Occam razor as an unnecessary complication.

 

Seems like there is a long thread about that.

The long thread that comes to mind contains a lot of junk. Crackpot ideas. Personally I wouldn't recommend it to anyone.

Edited by Martin
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i agree, and where is this thread at? i havent seen it yet, id like to read it.

 

Where Does Space End? It Must End Somewhere!

http://www.scienceforums.net/forum/showthread.php?t=6390

 

Martin warned you and I agree with him. However, you may learn something if you can wade through the trash.

 

I should have said if the universe is finite and flat, there may be an edge. "The universe" program on the History channel says so far the laser measurements say it is flat. Even if it is a 2d spherical surface it could be getting larger like the Hubble balloon. It is expanding into...


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I think you still might have to explain your point a bit more...

I am glad that I am not the only one.


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map=space=metric

territory=reality

 

reality=????

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... "The universe" program on the History channel says so far the laser measurements say it is flat...

 

NTWK, I'd warn against taking History channel literally! All the comment I heard about their "The Universe" program was that it was embarrassingly inaccurate. Didn't watch it myself. As a general rule it's a good idea to be mistrustful of pop media and both History and Discovery channels in particular. Not reliable authority to be quoting here at SFN.

 

The latest figures on largescale curvature are the 5th year WMAP* reports that came out in 2008.

 

No one can honestly say curvature is zero. What we can say is that it is near zero and within certain bounds with 95% confidence. And those measurements use other stuff than lasers.

 

Curvature measured here in the solar system is meaningless as far as cosmology goes. It could be affected by local things like the mass of the sun and planets in ways that are irrelevant to the overall curvature of space.

 

So they were misleading the public if they implied that meaningful measurements were made with lasers. Lasers can be used to detect gravity waves, but that's a different topic.

====================================

 

*I added a post to Cosmo Basics thread about this:

http://www.scienceforums.net/forum/showthread.php?p=463641#post463641

 

It explains how to get the best currently available figures from the WMAP report, how to interpret, and some other stuff relevant to this discussion.

Edited by Martin
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That doesn't follow. All that is meant by "universe expanding" is that distances between objects are increasing*.

 

That can happen without there being any space outside of the usual space we know.

 

no, it cant, its either the universe is compressing somewhere far off, or that its expanding. i dont see how anything can part away from itself without expaning or compressing.


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but i can see if the distance between galaxies are moving away from eich other, into already established space, but that brings up another q, whats making them do this?

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NTWK, I'd warn against taking History channel literally! All the comment I heard about their "The Universe" program was that it was embarrassingly inaccurate. Didn't watch it myself...

From a layman's point of view there are good and bad episodes. Some is pure speculation but they do not misrepresent what they say. Some seems factual but I do not have your eye for it. They did peek my interest and that is why you are having to put up with me. :D

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The problem IMO with this kind of discussion is that humans are very set in their ways, we know that when things expand they need somewhere to expand into because that's what we ALWAYS observe in our day to day life. Unfortunately the universe itself doesn't care much for what we observe in our day to day lives and doesn't play by those rules, so trying to apply that kind of logic to things such as this doesn't really work and you MUST rely on the maths and it's results.

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... They did peek my interest and that is why you are having to put up with me. :D

 

Then the Discovery channel producers did us a favor. I may have to revise my opinion (which was based on hear-say.)

 

The problem IMO with this kind of discussion is that humans are very set in their ways, we know that when things expand they need somewhere to expand into because that's what we ALWAYS observe in our day to day life. Unfortunately the universe itself doesn't care much for what we observe in our day to day lives and doesn't play by those rules, so trying to apply that kind of logic to things such as this doesn't really work and you MUST rely on the maths and it's results.

 

True, Klaynos!

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no, it cant, its either the universe is compressing somewhere far off, or that its expanding. i dont see how anything can part away from itself without expaning or compressing.

 

Yes, it can, and it does. You don't see how it works because nothing in everyday experience behaves that way and our brains aren't really built for that kind of visualization, but as Klaynos said, that doesn't really matter. It's what observation and the mathematics tells us, and it doesn't care whether we can visualize it.

 

Luckily, you can visualize it, sort of. There are a few imperfect analogies that are commonly used, most often the "surface of the balloon" analogy: imagine the universe is the surface of a balloon. This would be a 2 dimensional universe (just the surface) instead of a 3D one like ours. On the surface are fixed points, representing stars, galaxies, etc. Note that this "universe" has a finite area (possibly but not necessarily the case with ours) but no edges. If you keep going in a straight line you'll only end up back where you started. Now, inflate the balloon farther. The area of the universe increases, and all the fixed points get farther apart, even though they aren't moving. It is space itself which is expanding, and not a collection of objects moving apart within space.

 

The same thing (more or less) is happening with our universe, it just has an extra dimension and so is a lot harder to visualize.

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Sisyphus, that says it very well. It's not clear why this has to be explained to people. In case it might be helpful I set out a toy model that shows a simplified version of space not expanding into. To make it easy to visualize the space is 1D rather than 3D.

 

Since space is a system of distances, not an object, what expansion refers to is not the expansion of a substance or an object, but instead the general pattern according to which the distances increase.

 

Once one realizes this it should be fairly obvious that this doesn't require any surroundings. There is no physical, logical, or mathematical reason why it should!

 

Here's a link to that illustrative "toy model" thread.

http://www.scienceforums.net/forum/showthread.php?t=38006

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what is the universe expanding into?

 

This question is almost the same as asking, "What is the universe contained in?" or "What is outside the universe?". The generally accepted answer is that the universe is self-contained and there is probably nothing outside of it, and furthermore "outside the universe" might not even make sense.

 

it has to all go somewhere, whether it be compress the outside while inplode the inside, or simply expand into some sort of space between spaces, where does this giant terrarium we live in expace to?

any ideas?

 

The balloon analogy might fit. Consider if you are a two dimensional person on the surface of a balloon. If the balloon is inflated, the distance between two points on the balloon increases. However, this requires your space to be curved, and I think that requires another dimension.

 

Martin, can you help me? Would it be correct to say that the universe is expanding into "later" (ie, the time dimension)?

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Who is to say that the universe is expanding...

Perhaps we are just shrinking in a fixed sized universe.

Entropy...

I cite my checking account balance as proof.

Anywho how can something that has no boundaries and no center be said to expand,

You don't get the luxury of a reference point.

One only gets to say that time and space are working together in a way to make things far away appear to be moving away from us.

So someone calls it expansion, not bad for the lack of a better word.

~minus

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Most of what you say is right, Mr. S, but there's a mistake here:

... this requires your space to be curved, and I think that requires another dimension.

Curvature is a mathematically defined thing and it does not require an extra dimension.

 

Curvature is a property of the metric, the system of distances. It can be perceived and measured from within---it's intrinsic. This was worked out around 1850 by people like Carl Gauss and Bernard Riemann. It's one reason they are great. Einstein rode on their coat-tails. :D

 

The past 150 years have seen the growth of a huge body of math research precisely about this kind of thing---spaces which are curved without being immersed in larger spaces with more dimensions. I would urge anyone including yourself to free your mind from the illusion that curvature needs another dimension. It's time to catch up with Carl and Bernie :D

 

Martin, can you help me? Would it be correct to say that the universe is expanding into "later" (ie, the time dimension)?

 

Correct, I don't know. But some people like to think of it that way. It's whether it helps you visualize and get an intuitive grasp.

I haven't found it helps me. It seems to fit the balloon model, I realize, but that is a fairly restricted situation, very uniform. When I try to picture a realistically dynamic metric----maybe overall distances are expanding but locally they may be collapsing to make a black hole or wobbling and rippling as a pair of compact stars orbit---so there is a lot of expanding and contracting going on. When I try to picture something more realistic than the simple overall Hubble law pattern, using time the way you suggest doesn't seem to work. It gets in the way.

 

Logically since the idea of expanding space doesn't NEED any surround to expand into, you can be sure to get into some trouble if you pretend that it is expanding into something. Better to keep it clean. Shave with Occam razor. Don't try to fake something not necessary in the first place. You get the idea.

 

My imagination works better if I keep time clear and unencumbered---avoid using it as a jerry-rig extra space dimension. But in the simple balloon picture it seems like a neat visual ploy, and if it works for people I'm not going to knock it.

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so its like space is stretching, i understand, and i like it. but when you inflate a balloon it gets bigger, hence expanding into something, like the space around it.

and the idea that we just dont have the "equipment" to visualize space, although legit, seems to me like sheer laziness.

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