Middle of the universe

[StringJunky]

Sorry, but I don't understand. If the universe is expanding, doesn't that mean the edge of it, is moving. How can it move, unless there's some space for it to move in?

 

I should work through what's in Martin's thread on Cosmo Basics to get yourself up to speed:

 

http://www.scienceforums.net/topic/33180-cosmo-basics/

[Incendia]

Let's get rid of the "Balloon Analogy" and start using "The Doughnut Analogy" or, even better, "The Inflatable Ring Analogy" then we can get rid of the middle!

 

 

http://www.cosmosmag...e.com/node/1566

 

The link goes into the differences between topology and geometry amongst other things

 

I already think of the universe as donut shaped thing. Even then it has a centre. (My thinking is it's either a donut or the centre is constantly spitting out matter &/or energy. As it's probably less likely that the centre is constantly spitting out matter/energy then it must be a donut because as matter moves no other matter fills it's place. Either that only part of the universe is still expanding or we really are the centre; which are both probably less likely than a donut shaped universe.)

 

Even a 1 faced donut has a middle and centre.

 

The centre of the donut would be the middle of the gap inside the hole of the donut.

The middle would be a ring equally distant from the part of the face closest to the centre and the part of the face furthest away.

 

Even though the centre isn't real, as nothing exists outside the universe because there is no outside, the middle is real.

 

Of-coarse you could say that the centre is a ring which is the part of the face closest to what could be considered an inside.

 

Edited June 11, 2011 by Incendia

[between3and26characterslon]

Excellent presentation between! I especially like the part about what's beyond the edge of the Universe..."NOTHING - not even space (or therefore distance)...." However, if there was no distance between someone and any part of the "sphere" you would end up just inside the edge. How do you leap all the way back to the center?

 

Does cosmic inflation imply the possibility of infinite speed of expansion? Or just beyond the speed of light, but a finite speed?

 

You get back to the centre because the surface area of the outside of the Universe is necessarily zero, for you to be just inside the edge would imply there is still distance from the edge of the Universe to the centre of your head. But the entire surface of the outside of the Universe, which has zero area, would be a point of no dimension right at the centre of your head. As far as you were concerned you would be at the centre of the Universe.

 

This whole arguement means there is no edge or absolute centre to the Universe.

[Incendia]

You get back to the centre because the surface area of the outside of the Universe is necessarily zero, for you to be just inside the edge would imply there is still distance from the edge of the Universe to the centre of your head. But the entire surface of the outside of the Universe, which has zero area, would be a point of no dimension right at the centre of your head. As far as you were concerned you would be at the centre of the Universe.

 

This whole arguement means there is no edge or absolute centre to the Universe.

 

 

The centre is irrelevant. The OP was talking about the middle of the universe.

 

The centre is something equally far away from the edge of something.

The middle is something equally distance from the centre and edge.

 

 

Please refer to my post about how a donut universe would still have a middle, but no centre.

Edited June 12, 2011 by Incendia

[insane_alien]

The centre is irrelevant. The OP was talking about the middle of the universe.

 

The centre is something equally far away from the edge of something.

The middle is something equally distance from the centre and edge.

 

 

Please refer to my post about how a donut universe would still have a middle, but no centre.

 

the center is relevant as you yourself define middle to be equidistant from center and edge.

 

therefore if it has no center then it cannot have a middle. doughnuts have a center, it is just outside the bounds of the torus.

 

its all moot anyway, the universe does not have what would be called an edge or a center so it is equally impossible to be equidistant from both.

[Incendia]

the center is relevant as you yourself define middle to be equidistant from center and edge.

 

therefore if it has no center then it cannot have a middle. doughnuts have a center, it is just outside the bounds of the torus.

 

its all moot anyway, the universe does not have what would be called an edge or a center so it is equally impossible to be equidistant from both.

 

A hollow sphere has no edges and it's centre is absent; However it has a face. This means it can have a middle. I can prove it too. You yourself said that a doughnut has a centre. A cross section of a hollow sphere is a ring...which is the shape of a doughnut. ...and I already showed you what the middle of a ring/doughnut would be in a diagram.

 

 

Unless you can prove the universe has no face, you can't say it lacks a middle. ...you also said that a doughnut has a centre so as long as the universe has a face it has both a middle and centre.

 

(I was simplifying my definition of a middle. It doesn't have to be equidistant from an edge or centre. Could be the part equidistant from the two parts of the face furthest from each other.)

[between3and26characterslon]

The centre is irrelevant. The OP was talking about the middle of the universe.

 

The centre is something equally far away from the edge of something.

The middle is something equally distance from the centre and edge.

 

 

Please refer to my post about how a donut universe would still have a middle, but no centre.

 

Centre or middle neither are correct, the point I was making is that either case would imply an edge to the Universe and therefore an outside. However this model of the Universe, by definition, does not have any space outside of it. Even a toroidal Universe would not have any space outside of it, if you were to travel to the outside of a toroidal then every part of the surface of this Universe would be zero distance from you, you would think you were just somewhere in deep space. The logical consequence of this is that everywhere is the centre/middle and there is no edge I was trying to dispell the notion that there is an edge or middle/centre point. So like insane_alien said it's all moot.

 

The torus Universe is a little simplistic I think, perhaps the Universe is a 4 dimensional sphere and its shadow in 3 dimensions looks like a torus where, like in the baloon analogy, the entire volume of the 3 dimensional Universe is represented in 2 dimensions as the surface of the torus. But who knows?

 

However my belief, and current theory, is that the Universe is infinite.

 

So why don't we see infinite stars and amounts of radiation and gravity etc...? Because we wouldn't be here to see it, by this I mean the Universe has ways of making things work and it's the SOL that makes this model of the Universe work. Every point in the Universe is limited as to how much of the Universe it can ever experience, always less and never more, meaning there is an observable edge beyond which we can not see but not a physical edge.

[Incendia]

The universe is not infinite. Steady State theory is nonsense and wrong!

[insane_alien]

The universe is not infinite. Steady State theory is nonsense and wrong!

 

an infintely sized universe does not imply steady state.

 

i'm sure you won't find anyone here that believes in steady state universe theory as it is obvious from the evidence that it is expanding.

[between3and26characterslon]

The universe is not infinite.

 

That's quite a bold statement

 

Steady State theory is nonsense and wrong!

 

That may well be true.

 

I've just had a quick skim through of the wikki page on steady state theory and one of the things it requires is the production of matter to keep the average density of the Universe constant.

 

I thought the latest emerging theory is that the Universe is infinite in size but, due to the SOL etc..., we are only able to experience 13.7bn years X the SOL X the hubble constant. This is how much of the infinite Universe we can see. Anything beyond this we can not experience.

 

A Galaxy 5bn Ly from us would be able to see objects that are too far away for us to see and we can see objects too far away for them to see. If we were to travel to this other Galaxy we would only be able to do so at a maximum of light speed, so in the 5bn years it would take us to get there the Universe would have expanded and we wouldn't be able to see any more than we can now.

 

Is this not current theory, I'm sure I read it somewhere like in New Scientist or something.

[michel123456]

its not expanding into anything. its just expanding.

 

Well.

Back to the balloon analogy:

The 2D surface of the balloon represents 3D space. A dimension has been eliminated to make the analogy work.

In the analogy, the surface of the balloon is embedded into 3D space. And because the balloon is expanding, there is a change in time so that the whole analogy is embedded in spacetime. It is thus a 4D concept. That is what makes the analogy comprehensible: it works because it is embedded in the same space-time reality we are living in.

 

But if you want to transform this analogy into a model, you have to put back the dimension that was eliminated. Then you obtain a 4D model +1: a 5D model.

 

So one could propose that the Universe is expanding into the 5th dimension. And not that "its not expanding into anything.".

Edited June 12, 2011 by michel123456

[between3and26characterslon]

Sorry, but I don't understand. If the universe is expanding, doesn't that mean the edge of it, is moving. How can it move, unless there's some space for it to move in?

 

It's a bit like the Tardis, it's bigger on the inside than it is on the outside but the Universe viewed from the outside (whatever that means) would have no size at all. The Universe is expanding internally.

 

EDIT: Just to be clear I don't think the Universe is a closed and finite space. In the closed and finite model of the Universe the notion of being outside it is meaningless - there is no outside. In the infinite and open Universe the notion of being outside it is also meaningless - you would just be in a part of a much bigger Universe. The closed and finite model contradicts itself IMO in that when you get to the edge you end up in the middle, so how do you know your not already there?

Edited June 12, 2011 by between3and26characterslon

[Incendia]

It's a bit like the Tardis, it's bigger on the inside than it is on the outside but the Universe viewed from the outside (whatever that means) would have no size at all. The Universe is expanding internally.

 

EDIT: Just to be clear I don't think the Universe is a closed and finite space. In the closed and finite model of the Universe the notion of being outside it is meaningless - there is no outside. In the infinite and open Universe the notion of being outside it is also meaningless - you would just be in a part of a much bigger Universe. The closed and finite model contradicts itself IMO in that when you get to the edge you end up in the middle, so how do you know your not already there?

 

It doesn't say that when you get to the edge you end up in the middle. It doesn't say anything of the sort. There is no edge.

[between3and26characterslon]

It doesn't say that when you get to the edge you end up in the middle. It doesn't say anything of the sort. There is no edge.

 

That's my point.

 

 

What I'm saying is, to anyone who thinks there is an edge, IF and I'll say again IF there was an edge and IF you were to pass beyond this "edge" of the Universe then you would enter a 'place' where there is no space or distance and therefore no distance between you and any part of the outside edge of the Universe. You would, as far as you're concerned, appear to be in the middle (figuratively speaking not literally) of the Universe. It's entirely possible you would appear to be exactly where you are now.

 

It's a logical arguement to refute the notion of an edge to the Universe. It's not something that would or could happen.

[Incendia]

That's my point.

 

 

What I'm saying is, to anyone who thinks there is an edge, IF and I'll say again IF there was an edge and IF you were to pass beyond this "edge" of the Universe then you would enter a 'place' where there is no space or distance and therefore no distance between you and any part of the outside edge of the Universe. You would, as far as you're concerned, appear to be in the middle (figuratively speaking not literally) of the Universe. It's entirely possible you would appear to be exactly where you are now.

 

It's a logical arguement to refute the notion of an edge to the Universe. It's not something that would or could happen.

 

You are forgetting that there is no outside and so you couldn't leave even if there was an edge, which there isn't.

[DrRocket]

The closed and finite model contradicts itself IMO in that when you get to the edge you end up in the middle, so how do you know your not already there?

 

No, it does not.

 

"Closed" in the theory of manifolds means compact without boundary. "Without boundary" means without an edge.

 

The surface of a sphere is a closed 2-manifold.

[J.C.MacSwell]

an infintely sized universe does not imply steady state.

i'm sure you won't find anyone here that believes in steady state universe theory as it is obvious from the evidence that it is expanding.

 

The steady state theory could not account well for the CMBR, but it was not inconsistent with expansion after hypothesizing matter production.

 

The Big Bang seems to have less problems though I would not rule some form of either (or neither) in or out.

 

A lot of assumptions are made for each, and the Big Bang's seem the most reasonable but even expansion is a stretch (pun intended) as we only get data from our one little point on an unknown Cosmos/Metric/Manifold/Whateveritis.

Edited June 12, 2011 by J.C.MacSwell

[Dekan]

I'd like to thank StringJunky for post#51, pointing me to Martin's "Cosmo Basics" thread.

 

I've had a go at reading it, but it's above my head. The thing that struck me about it, was the mention of "wriggling photons".

 

These seem reminiscent of the "swerving atoms" that Lucretius envisaged in his "On the Nature of the Universe", written some 2,000 years ago.

 

Plus ca change.... and all that!

[between3and26characterslon]

You are forgetting that there is no outside and so you couldn't leave even if there was an edge, which there isn't.

 

No, it does not.

 

"Closed" in the theory of manifolds means compact without boundary. "Without boundary" means without an edge.

 

The surface of a sphere is a closed 2-manifold.

 

I understand what 'closed' means and 'without boundary' and I am not forgetting anything. Someone asked what the Universe was expanding into and could not envisage a Universe where the edge wasn't moving away from the centre. I am saying the terms 'edge' and 'outside' are meaningless and was providing an arguement that if you start from the premise there is an edge and outside then, by resonable deduction, you will arrive at the conclusion that there is no edge or outside. It's a thought experiment.

 

EDIT: Having re-read my earlier post I meant to say the middle/edge model of The Universe rather than the closed/finite model. My Bad!

Edited June 13, 2011 by between3and26characterslon

[Airbrush]

If the universe is everything, everywhere, then it is NOT correct to say the "universe is expanding". All we can say is the observable unverse is expanding. Beyond the observable universe there may be regions of the universe which are not expanding. Dark flow gives a hint at this. The entire universe, or multiverse if you prefer, is like an infinite tub of soap bubbles. Some bubbles, such as our observable universe or Big Bang, are expanding, other bubbles are shrinking, popping, budding off others, or whatever.

[DrRocket]

The entire universe, or multiverse if you prefer, is like an infinite tub of soap bubbles. Some bubbles, such as our observable universe or Big Bang, are expanding, other bubbles are shrinking, popping, budding off others, or whatever.

 

Prove it.

[Airbrush]

I cannot prove this of course, but you cannot prove the entire universe is expanding. Only the observable universe is expanding.

[DrRocket]

I cannot prove this of course, but you cannot prove the entire universe is expanding. Only the observable universe is expanding.

 

You lack understanding of the burden of proof. You have made an unqualified assertion. The burden of proof is on you.

 

The expansion of the (entire) universe is based on several things 1) the observed red shift 2) general relativity and 3) the cosmological principle which asserts the homogeneity and isotropy of the universe on the largest scale. The first two are veery well supported by evidence. The cosmological principle is an outright assumption that is consistent with what is observed. All of this is consistent with the big bang model based on general relativity. It may or may not ultimately be true, but unless the accelerated expansion of everything that we can detect stops, it doesn't matter as it applies to everything with which we are or ever will be causally connected.

 

As soon as you violate the cosmological principle, there are a great many (really infinitely many) cosmological models available since you are then free to change physics willy-nilly as a function of space. That sells books, but it violates the basic requirement of good science -- falsifiability in principle. Michu Kaku is a poor source.

 

Now, back up your assertion. Fair warning, I am quite aware of such speculations and of the very shaky basis for them. The fact that that you may have read such stuff in popularizations is not adequate basis to assert the truth or even likelihood of it. There are huge gaps in those models.

Edited June 13, 2011 by DrRocket

[Airbrush]

You lack understanding of the burden of proof. You have made an unqualified assertion. The burden of proof is on you.

Now, back up your assertion.

 

Fair warning, I am quite aware of such speculations and of the very shaky basis for them. The fact that that you may have read such stuff in popularizations is not adequate basis to assert the truth or even likelihood of it. There are huge gaps in those models.

 

Sorry for the misunderstanding. I did not intend my "tub of soap bubbles" as a model. I only vaguely remember something like that on an episode of THC's "The Universe". I suppose for someone to explain how the entire universe is supposed to be expanding at an accelerating rate, because the observable universe is doing that, is quite beyond my understanding.

[DrRocket]

Sorry for the misunderstanding. I did not intend my "tub of soap bubbles" as a model. I only vaguely remember something like that on an episode of THC's "The Universe". I suppose for someone to explain how the entire universe is supposed to be expanding at an accelerating rate, because the observable universe is doing that, is quite beyond my understanding.

 

See the post above. It is all based on the, reasonable, assumption that the universe is pretty much the same everywhere. That assumption is quite reasonable, but it is indeed an assumption.

 

You can also assume that the universe, and the laws of physics themselves, vary. But that too is an assumption, and there is not the slightest bit of empirical evidence to support it. It is great for selling books, and advertising time on TV programs, but then so is magic.