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Author Topic: Does the universe have an edge?  (Read 3862 times)

Offline PmbPhy

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Re: Does the universe have an edge?
« Reply #25 on: 02/06/2016 07:56:35 »
Quote from: Alan McDougall

Does the universe have an edge?

No. At least not according to current theory. Please don't confuse what is mathematically possible with what is physically "true."

The comments in your quote are quite misleading. To be exact, the comment But those analogies also carry a fatal flaw. is quite wrong. When the analogy is used it is made clear that there is no dimensions off the surface of the balloon, that the universe is not expanding into a higher dimension. That's part of using the analogy, i.e. explaining exactly what the analogy entails.

Quote from: acsinuk
The universe must have an edge because there is a limit to the red shift.
The limit to redshift is due to galaxies lying outside the Hubble sphere which means that they're traveling faster than the speed of light as measured by observers at our location. All of that simply means that the only reason why there is a limit to cosmological redshift is because those galaxies are so far away that they lie outside the Hubble sphere and for that reason we can't see them. However, different observers have a different Hubble sphere which means that those galaxies that we can't see can be seen by other observers and therefore there is a corresponding redshift associated with them.
 

Offline Alan McDougall

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Re: Does the universe have an edge?
« Reply #26 on: 02/06/2016 08:27:36 »
Quote from: Alan McDougall

Does the universe have an edge?

No. At least not according to current theory. Please don't confuse what is mathematically possible with what is physically "true."

The comments in your quote are quite misleading. To be exact, the comment But those analogies also carry a fatal flaw. is quite wrong. When the analogy is used it is made clear that there is no dimensions off the surface of the balloon, that the universe is not expanding into a higher dimension. That's part of using the analogy, i.e. explaining exactly what the analogy entails.

Quote from: acsinuk
The universe must have an edge because there is a limit to the red shift.
The limit to redshift is due to galaxies lying outside the Hubble sphere which means that they're traveling faster than the speed of light as measured by observers at our location. All of that simply means that the only reason why there is a limit to cosmological redshift is because those galaxies are so far away that they lie outside the Hubble sphere and for that reason we can't see them. However, different observers have a different Hubble sphere which means that those galaxies that we can't see can be seen by other observers and therefore there is a corresponding redshift associated with them.

OH! really you are stating your opinion as if it were factual, you do not know if the universe has an edge or not and until you do it is just at best speculation on your part?
 

Offline impyre

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Re: Does the universe have an edge?
« Reply #27 on: 02/06/2016 12:12:55 »
OH! really you are stating your opinion as if it were factual, you do not know if the universe has an edge or not and until you do it is just at best speculation on your part?
Actually, I agree with him. In his defense he did say "according to theory", which is a pretty accurate statement as far as I know. Further, he might been better off saying that the comment was over-reaching in its implication rather than flat-out wrong, but again I agree with him. Almost any analogy can work in-so-far as its intended breadth and depth; however, any analogy can be extended beyond the original intent of the person who made the analogy, and in this extension become false or outright ridiculous. This is a common structure for an argument similar to reductio ad absurdum arguments. "Well if electricity works like water... I should be able to swim in it... but I can't, so therefore this analogy is flawed." This is a classic example of an analogy simply being taken much too far. The most basic principles of electricity do very much resemble water as all the basic components are there. Pressure to voltage, current to rate of flow, resistance to resistance, etc... but even this analogy breaks down past a certain point.
 
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Offline JohnDuffield

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Re: Does the universe have an edge?
« Reply #28 on: 02/06/2016 14:37:40 »
Thank you Sir for the very interesting link to a person whom I admire in respect to his thinking. I feel I understand Albert but also feel that the curvatures in his imagination are more of ''things'' that occupy space rather than space.
It's actually a curved "metric". We call it curved spacetime, but curved spacetime isn't curved space and time, it's a curvature in your plot of measurements of distance and time . For example you place a whole lot of optical clocks at different elevations. The lower clocks go slower, and when you plot all the clock rates, there's a curve in your graph.

We as the observers could not relatively ''see'' any possible curvature of ''light''
We do. We see gravitational lensing.

So in reply to your post, what of space are you defining is stressed?
The space around the Earth. The stress-energy- momentum tensor is called what it is for a reason. It "describes the density and flux of energy and momentum in spacetime". Stress is directional pressure. In simple terms, a gravitational field is a spatial pressure gradient.

No aether exists and space is not of solidity.
You should read Einstein's Leyden Address where he described space as the aether of general relativity. Here it is:



General relativity really does treat space like a gin-clear ghostly elastic solid. Google on Einstein elastic.
 

Offline JohnDuffield

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Re: Does the universe have an edge?
« Reply #29 on: 02/06/2016 14:55:26 »
Actually, I agree with him. In his defense he did say "according to theory", which is a pretty accurate statement as far as I know.
The trouble with this is that the theory is based on the FLRW metric which "starts with the assumption of homogeneity and isotropy of space". This assumption says wherever you are, space will look the same in all directions. But it isn't scientific. For all we know, some guy 46 billion light years away sees one half of the night sky as completely black. Or as a mirror image of the other. Or something else. We just don't know.
 
Almost any analogy can work in-so-far as its intended breadth and depth...
One analogy used to explain an edge-less expanding universe is the balloon analogy. I don't like it because we have no evidence of any higher dimensions, and no evidence of any kind of curvature that would cause you to go round in great big circles. Hence I prefer the raisin-cake analogy. And I note that a raisin cake has  an edge. 
 

Offline Thebox

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Re: Does the universe have an edge?
« Reply #30 on: 02/06/2016 17:20:57 »
It's actually a curved "metric". We call it curved spacetime, but curved spacetime isn't curved space and time, it's a curvature in your plot of measurements of distance and time . For example you place a whole lot of optical clocks at different elevations. The lower clocks go slower, and when you plot all the clock rates, there's a curve in your graph.

Yes, it is arbitrary creation to represent ''curves'' that do not exist in reality.

We as the observers could not relatively ''see'' any possible curvature of ''light''
Quote from: John
We do. We see gravitational lensing.
I apologise my sentence was short, let me re-phrase for you. We as the observers could not relatively ''see'' any possible curvature of ''light'' in the relative ''empty'' space between point sources.
Gravitation lensing is a distortion of the Quanta ''whole'' , the ''whole'' is the ''gin-clear'' you observe that you are ''submerged'' in.
 




So in reply to your post, what of space are you defining is stressed?

Quote from: John
The space around the Earth. The stress-energy- momentum tensor is called what it is for a reason. It "describes the density and flux of energy and momentum in spacetime".

In space-time?  surely you just mean in space and the ''stress'' of some ''matter''?

Otherwise it sounds rather gibberish and without meaning,  maybe I do not understand, what is this ''stress'' directly related too?




No aether exists and space is not of solidity.

Quote from: John
You should read Einstein's Leyden Address where he described space as the aether of general relativity.

A space without an ether is not unthinkable.



Quote from: John
General relativity really does treat space like a gin-clear ghostly elastic solid.

''Light'' is the ghostly gin-clear  ''convertual electro-elasticity'' and the reason you ''see'' gin-clear is because you evolved to ''see through it''.

Space is absolute darkness that is interwoven with ''light'' , (but nobody listens to me and of course I am not a scientist).

« Last Edit: 02/06/2016 17:23:02 by Thebox »
 

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Re: Does the universe have an edge?
« Reply #31 on: 02/06/2016 18:12:47 »
Here I am still waiting for John to explain continuum mechanics. I thought at least he would show me how it could be used to derive general relativity but alas no. Maybe he just hasn't noticed the posts. Maybe he just doesn't know continuum mechanics and is just trying to show off using big words.
 

Offline Alan McDougall

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Re: Does the universe have an edge?
« Reply #32 on: 02/06/2016 18:23:45 »
Here I am still waiting for John to explain continuum mechanics. I thought at least he would show me how it could be used to derive general relativity but alas no. Maybe he just hasn't noticed the posts. Maybe he just doesn't know continuum mechanics and is just trying to show off using big words.

He can't Richard Feynman the great physics and scientist who was part of the Los Alamos team on the Manhattan project to create an atomic bomb once quoted and I believe him

"Now one understands quantum mechanics"
 

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Re: Does the universe have an edge?
« Reply #33 on: 02/06/2016 19:08:24 »
Did you not notice the word continuum in there? It can't be about quanta if it is continuous. Therefore no need to invoke Feynman. Careful reading skills can be a real asset.
 

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Re: Does the universe have an edge?
« Reply #34 on: 02/06/2016 19:56:52 »
Well John I'd better get back to reading the pop science by all those PhD's and their pesky textbooks. Full of all those strange symbols that I know are like kryptonite to you.
 

Offline PmbPhy

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Re: Does the universe have an edge?
« Reply #35 on: 02/06/2016 20:24:46 »
Quote from: Alan McDougall
OH! really you are stating your opinion as if it were factual, you do not know if the universe has an edge or not and until you do it is just at best speculation on your part?
I'm not stating my opinion. I'm explaining to you what is currently assumed to be the case in theory. Reread what I said very carefully
Quote from: Pmb
No. At least not according to current theory.
And it can hardly be referred to as speculation because speculation has no theory behind it.

Besides, that's what you were looking for, wasn't it? Otherwise what was the point of asking a question in which the answer cannot been known for certain?
 

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Re: Does the universe have an edge?
« Reply #36 on: 02/06/2016 20:42:53 »
Well I have had my feet up with a coffee watching John talk about light going round in circles. Very informative. Now I really know what an electron is. Is that what they mean by spinor?

https://m.youtube.com/watch?v=56w2I8fXDAw
 

Offline Alan McDougall

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Re: Does the universe have an edge?
« Reply #37 on: 02/06/2016 20:53:38 »
Quote from: Alan McDougall
OH! really you are stating your opinion as if it were factual, you do not know if the universe has an edge or not and until you do it is just at best speculation on your part?
I'm not stating my opinion. I'm explaining to you what is currently assumed to be the case in theory. Reread what I said very carefully
Quote from: Pmb
No. At least not according to current theory.
And it can hardly be referred to as speculation because speculation has no theory behind it.

Besides, that's what you were looking for, wasn't it? Otherwise what was the point of asking a question in which the answer cannot been known for certain?

That the universe is infinite has the shape of a donut, our balloon or disk shaped, is just speculation your supposed theory is just an added speculation, with out any evidence to support a real viable final fact later.

Space does not contain matter so it might have extended out into infinite an void, with Alan Guth inflation theory, keeping space time separate from the infinite void, I admit I am speculation not postulating a unprofitable so called theory

Alan
 

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Re: Does the universe have an edge?
« Reply #38 on: 02/06/2016 21:49:27 »
Actually, I agree with him. In his defense he did say "according to theory", which is a pretty accurate statement as far as I know.
The trouble with this is that the theory is based on the FLRW metric which "starts with the assumption of homogeneity and isotropy of space". This assumption says wherever you are, space will look the same in all directions. But it isn't scientific. For all we know, some guy 46 billion light years away sees one half of the night sky as completely black. Or as a mirror image of the other. Or something else. We just don't know.
 
Almost any analogy can work in-so-far as its intended breadth and depth...
One analogy used to explain an edge-less expanding universe is the balloon analogy. I don't like it because we have no evidence of any higher dimensions, and no evidence of any kind of curvature that would cause you to go round in great big circles. Hence I prefer the raisin-cake analogy. And I note that a raisin cake has  an edge.

John can you tell me why k is not treated as complex in the FLRW metric?
 

Offline PmbPhy

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Re: Does the universe have an edge?
« Reply #39 on: 02/06/2016 22:08:08 »
Quote from: Alan McDougall
OH! really you are stating your opinion as if it were factual, you do not know if the universe has an edge or not and until you do it is just at best speculation on your part?
I'm not stating my opinion. I'm explaining to you what is currently assumed to be the case in theory. Reread what I said very carefully
Quote from: Pmb
No. At least not according to current theory.
And it can hardly be referred to as speculation because speculation has no theory behind it.

Besides, that's what you were looking for, wasn't it? Otherwise what was the point of asking a question in which the answer cannot been known for certain?

That the universe is infinite has the shape of a donut, our balloon or disk shaped, is just speculation your supposed theory is just an added speculation, with out any evidence to support a real viable final fact later.

Space does not contain matter so it might have extended out into infinite an void, with Alan Guth inflation theory, keeping space time separate from the infinite void, I admit I am speculation not postulating a unprofitable so called theory

Alan
Once again, you have absolutely no idea what you're talking about. The nature of the universe is based on general relativity and the Cosmological Principle (an axiom based on observations of the distribution of galaxies in the visible universe). That's why I keep saying that this is the way is based on theory and not mere speculation. From that and the measured density of matter in the universe the shape of the universe is determined. There's no speculation involved.

Since you keep making unfounded accusations and thus appear to have no real interest in learning what theory predicts and keep claiming that predictions are all speculation I can no longer justify either reading or responding to your comments. Welcome to my ignore list. You'll be in the company of the likes of John Duffield et al.
 

Offline JohnDuffield

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Re: Does the universe have an edge?
« Reply #40 on: 02/06/2016 22:32:57 »
The nature of the universe is based on general relativity and the Cosmological Principle (an axiom based on observations of the distribution of galaxies in the visible universe).
Like I was saying above, the Cosmological Principle is "the notion that the distribution of matter in the universe is homogeneous and isotropic when viewed on a large enough scale". This is abused to claim that all observers will see galaxies all around them, and that the universe must therefore infinite. It just isn't scientific. 

Quote from: Alan McDougall
OH! really you are stating your opinion as if it were factual, you do not know if the universe has an edge or not and until you do it is just at best speculation on your part?
Since you keep making unfounded accusations and thus appear to have no real interest in learning what theory predicts and keep claiming that predictions are all speculation I can no longer justify either reading or responding to your comments. Welcome to my ignore list. You'll be in the company of the likes of John Duffield et al.
Alan, it is speculation. If it wasn't, pmb would be able to respond to what I said, and give you some references. He can't.
 

Online jeffreyH

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Re: Does the universe have an edge?
« Reply #41 on: 02/06/2016 22:49:57 »
Duh! You are on pmb's ignore list so he doesn't even see your posts. You are smart enough to know that too. You want people to believe Pete can't respond because you are right. More disinformation that I won't let you get away with John. I noticed you are on a temporary ban elsewhere is that why you have dropped in here? BTW you didn't answer the question about the value k.
 

Offline PmbPhy

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Re: Does the universe have an edge?
« Reply #42 on: 03/06/2016 03:56:02 »
Duh! You are on pmb's ignore list so he doesn't even see your posts. You are smart enough to know that too. You want people to believe Pete can't respond because you are right.
There has never been and will never been anything that John can claim that is contrary to accepted physics that I can't prove him wrong. And you're quite right, Jeff. He is on my ignore list and he knows it!!!

Jeff: What's this nonsense that John is now claiming that I can't respond to? That's really a silly claim because anybody can respond to anything so its not really a challenge when stated like that. If you'd like,. Jeff, I'll explain why John is wrong.

The people on my ignore list are on it for either or both of two reasons (1) the member is rude and/or (2) is incapable of understanding explanations given to him. John's understanding of physics is extremely bad. He actually thinks that there's no such thing as negative energy. He also thinks that just because the electric and magnetic field are parts of the EM tensor aka Faraday tensor that there's no such thing as an electric or magnetic field, which is insanely wrong. In fact its simple to see that one can't even define or measure the Faraday tensor if in fact those fields don't exist.
« Last Edit: 03/06/2016 04:04:26 by PmbPhy »
 

Offline Alan McDougall

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Re: Does the universe have an edge?
« Reply #43 on: 03/06/2016 05:07:59 »
Quote from: Alan McDougall
OH! really you are stating your opinion as if it were factual, you do not know if the universe has an edge or not and until you do it is just at best speculation on your part?
I'm not stating my opinion. I'm explaining to you what is currently assumed to be the case in theory. Reread what I said very carefully
Quote from: Pmb
No. At least not according to current theory.
And it can hardly be referred to as speculation because speculation has no theory behind it.

Besides, that's what you were looking for, wasn't it? Otherwise what was the point of asking a question in which the answer cannot been known for certain?

That the universe is infinite has the shape of a donut, our balloon or disk shaped, is just speculation your supposed theory is just an added speculation, with out any evidence to support a real viable final fact later.

Space does not contain matter so it might have extended out into infinite an void, with Alan Guth inflation theory, keeping space time separate from the infinite void, I admit I am speculation not postulating a unprofitable so called theory

Alan
Once again, you have absolutely no idea what you're talking about. The nature of the universe is based on general relativity and the Cosmological Principle (an axiom based on observations of the distribution of galaxies in the visible universe). That's why I keep saying that this is the way is based on theory and not mere speculation. From that and the measured density of matter in the universe the shape of the universe is determined. There's no speculation involved.

Since you keep making unfounded accusations and thus appear to have no real interest in learning what theory predicts and keep claiming that predictions are all speculation I can no longer justify either reading or responding to your comments. Welcome to my ignore list. You'll be in the company of the likes of John Duffield et al.

You must admit that the theory might be totally wrong?
 

Offline JohnDuffield

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Re: Does the universe have an edge?
« Reply #44 on: 03/06/2016 12:59:02 »
Jeff: What's this nonsense that John is now claiming that I can't respond to? That's really a silly claim because anybody can respond to anything so its not really a challenge when stated like that. If you'd like,. Jeff, I'll explain why John is wrong.
No you won't, because I'm not wrong. Here, let me reiterate:

The trouble with this is that the theory is based on the FLRW metric which "starts with the assumption of homogeneity and isotropy of space". This assumption says wherever you are, space will look the same in all directions. But it isn't scientific. For all we know, some guy 46 billion light years away sees one half of the night sky as completely black. Or as a mirror image of the other. Or something else. We just don't know.
 
 

Online jeffreyH

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Re: Does the universe have an edge?
« Reply #45 on: 03/06/2016 13:12:19 »
John you have no idea what the FLRW metric is. You have simply picked up a sound bite.
 

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