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Author Topic: Is the universe infinite?  (Read 21710 times)

Offline PhysBang

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Re: Is the universe infinite?
« Reply #50 on: 24/03/2015 19:20:03 »
The idea that the shear-stress component of the field equation play a role in cosmology at the largest scales is a relic of the electric universe or plasma universe theories. These theories do not currently have serious and sane proponents.

The standard cosmological model sets these components to 0, because the ideal particles of the model (galaxy clusters) do not interact except for with gravity.
 

Offline yor_on

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Re: Is the universe infinite?
« Reply #51 on: 24/03/2015 19:24:43 »
PhysBang, you're one of the clearest minds here,  as far as I know it at least. And John, the difference is the one between expecting 'measurable force' and mathematics. Using mathematics is one thing, it's 'ideal', defining a relation. Expecting the universe to be a 'force' is another.
 

Offline yor_on

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Re: Is the universe infinite?
« Reply #52 on: 24/03/2015 19:51:17 »
The point is that you don't need 'elastics' to define reality. You do need logics though. When those take you into paths not seen you have you to ask yourself what is most correct, the mathematics, or my preconceptions of how 'it is'? I will go for the mathematics, as long as they make sense :) That means that they need to fit what we already know. It doesn't guarantee that you can translate them into 'measurable forces' though, as with the Einstein stress energy tensor. That's actually a challenge I think you're trying to answer John. But you're still stuck with 'forces', as far as I can see?
 

Offline Bill S

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Re: Is the universe infinite?
« Reply #53 on: 24/03/2015 20:17:53 »
This is reminiscent of that song by The Fortunes:  “Here it Comes Again”.  I suppose discussions about infinity will always be with us, and frequently they will be about the question as to whether or not the universe is infinite.

Why will they never go away, or reach any reasonable conclusion?

The answer, I believe, is that different people mean different things by “infinite” and “universe”.  It seems that, in general scientists avoid trouble by treating “infinite” as though it were synonymous with “unbounded”; and if that works so well and good.  If your ladder reaches the roof, why grumble that it is not 6ft longer?

John Gribbin’s suggested usage of “Universe”, “universe” and “cosmos”, to avoid confusion, has not caught on in the almost 20 years since he published it.  Could this be because scientists always specify exactly what they mean when they talk of the universe?  I’m not hazarding any guesses about that.
 

Offline Bill S

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Re: Is the universe infinite?
« Reply #54 on: 24/03/2015 20:41:42 »
John, I have spent a lot of time on forums trying to come to grips with what seemed logical and inevitable to me, and comparing it with what seemed logical and inevitable to others.  Most often, these viewpoints were very different when infinity was involved.  What was the outcome? 

On the basic issues, I would say: no real change.  However, what was really important to me was not so much trying to establish who was right, and who wrong, as trying to understand why those other people thought as they did.  I like to think I have made some progress on that front.

Have you tried looking at answers to a few questions while varying your terminology?

Consider, for example:

Can something finite become infinite?  No.
Can something small and expanding always have been infinite?  No.

Can something finite become boundless?  Yes.
Can something small and expanding always have been boundless?  Yes.

If you regard “infinite” and “unbounded as synonymous, do the answers to those questions remain the same?  No:  all the answers can become “Yes”.
« Last Edit: 24/03/2015 20:43:27 by Bill S »
 

Offline JohnDuffield

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Re: Is the universe infinite?
« Reply #55 on: 24/03/2015 20:49:26 »
Did Cornish discuss the universe as a whole? Yes. Did Cornish claim that the universe as a whole was a sphere of a certain size? No, he explicitly said something about the visible universe (given a certain definition).
No, he didn't explicitly say something about the visible universe. Here's the article again:

http://www.cnn.com/2004/TECH/space/05/24/universe.wide/

He was talking about the universe, not the visible universe. I'm not cherry-picking, I'm giving the reference, and you're trying to claim the cosmologist said something he didn't.

Quote from: yor_on
The point is that you don't need 'elastics' to define reality...
No, but when we're talking about space, it's good to look at things like the stress-energy-momentum tensor. 

Quote from: Bill S
...It seems that, in general scientists avoid trouble by treating “infinite” as though it were synonymous with “unbounded”; and if that works so well and good.
It isn't true Bill. The Planck mission found no evidence of the toroidal universe that is finite but unbounded. That's like the old asteroids game, where you go thataway and end up coming back thisaway. In that scenario there's no edge to the universe, it is unbounded, but it has a finite size. The infinite universe is very different. Again there's no edge and it is unbounded, but it goes on and on. From your latest post:

Quote from: Bill S
Can something finite become infinite?  No.
Can something small and expanding always have been infinite?  No.
That's my point.

Quote from: Bill S
Can something finite become boundless?  Yes.
Can something small and expanding always have been boundless?  Yes.
Agreed. Again this is the toroidal universe akin to the asteroids game. But there's no evidence for it, or for any kind of intrinsic curvature in wherein you go thataway and end up coming thisaway.

Quote from: Bill S
If you regard “infinite” and “unbounded as synonymous, do the answers to those questions remain the same?  No:  all the answers can become “Yes”.
But they aren't synonymous. The surface of a sphere is boundless but not infinite. And if the universe started small 13.8 billion years ago, it can't be infinite. It could be boundless, but we have no evidence for it. So we surely have to consider that it might be bounded. 
 

Offline Ethos_

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Re: Is the universe infinite?
« Reply #56 on: 24/03/2015 21:17:24 »
This is reminiscent of that song by The Fortunes:  “Here it Comes Again”.  I suppose discussions about infinity will always be with us, and frequently they will be about the question as to whether or not the universe is infinite.

Why will they never go away, or reach any reasonable conclusion?

I might suggest that they don't go away because; like the universe, opinions have an infinite character.
« Last Edit: 24/03/2015 21:20:52 by Ethos_ »
 

Offline Bill S

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Re: Is the universe infinite?
« Reply #57 on: 24/03/2015 21:26:29 »
John, you missed the point I was trying to make.

When I said: 
Quote
It seems that, in general scientists avoid trouble by treating “infinite” as though it were synonymous with “unbounded”
I was not referring to the toroidal universe or the asteroids game.  I was simply saying that by treating the two (incorrectly, in my view) as though they were synonymous, one could make claims about infinity that you and I might take issue with.

Similarly, when I said:
Quote
If you regard “infinite” and “unbounded as synonymous, do the answers to those questions remain the same?  No:  all the answers can become “Yes”.
I was not advocating considering them as synonymous; just pointing out that holding that view could be considered to “justify” answering any of those questions: “Yes”.
 

Offline yor_on

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Re: Is the universe infinite?
« Reply #58 on: 24/03/2015 21:28:43 »
Ethos, you're one of the most emphatic minds I've meet. Go for it.
 

Offline yor_on

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Re: Is the universe infinite?
« Reply #59 on: 24/03/2015 21:30:55 »
As well as I would hate TNS to be a place where we color people to our purpose, I want it to be a place where we have room to breath, all of us.
 

Offline Bill S

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Re: Is the universe infinite?
« Reply #60 on: 24/03/2015 21:31:16 »
An interesting thought, Ethos.  I'm not going to be drawn into considering infinite thoughts in a finite population.  :)
 

Offline JohnDuffield

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Re: Is the universe infinite?
« Reply #61 on: 24/03/2015 21:40:27 »
John, you missed the point I was trying to make.
Sorry Bill.

When I said: 
Quote
It seems that, in general scientists avoid trouble by treating “infinite” as though it were synonymous with “unbounded”
I was not referring to the toroidal universe or the asteroids game.  I was simply saying that by treating the two (incorrectly, in my view) as though they were synonymous, one could make claims about infinity that you and I might take issue with.
Agreed.

Similarly, when I said:
Quote
If you regard “infinite” and “unbounded as synonymous, do the answers to those questions remain the same?  No:  all the answers can become “Yes”.
I was not advocating considering them as synonymous; just pointing out that holding that view could be considered to “justify” answering any of those questions: “Yes”.
OK noted. The thing with all this is that you can read articles like this: Is the universe infinite, or finite? How big is the universe? Only they totally duck the issue. Here's an excerpt:

"But a spatially flat universe can be characteristic of either a finite or an infinite universe. When we say that space is “flat,” we mean it obeys Euclidean geometry: parallel lines never intersect, and the angles of a triangle always add up to 180 degrees. We can imagine the universe in two dimensions as a plane, which is flat and infinite (like an infinite piece of paper). But we can also imagine taking that paper and rolling it into a cylinder, then rolling it again into a torus (doughnut shape). The surface of the torus is spatially flat, like the piece of paper, but finite."

Get a piece of paper. Grab hold of it. Hold it out flat. What's it got? An edge. But it just doesn't feature in articles like the above. See the interview with Joe Silk? See this bit?

"So you have two possibilities for a flat Universe: one infinite, like a plane, and one finite, like a torus, which is also flat."

What about a third possibility?
 

Offline yor_on

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Re: Is the universe infinite?
« Reply #62 on: 24/03/2015 21:44:43 »
Not bad Billl, it seems we all think in different terms, some brave souls actually working in the field we try to explore. I will need to read you later.
 

Offline yor_on

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Re: Is the universe infinite?
« Reply #63 on: 24/03/2015 22:02:52 »
As I'm on  a 'discovery' tonight, and furthermore, I'm sure we've all been there, one time or another. Let me tell you that I think that we all, no matter how kooky someone might find thoughts. It's what makes TNS a special place. a place where wee will try to understand, and answer to the best of our abilities. It does not guarantee that the answers will be made into stone though, and sometimes we will argue. Ok, most times :) But, it is a place to breath.
 

Offline Ethos_

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Re: Is the universe infinite?
« Reply #64 on: 24/03/2015 23:27:17 »
Ethos, you're one of the most emphatic minds I've meet. Go for it.
Thank you sir, and as for going for it, like many others here I resist being drawn into the debate about infinities. However, I will offer one personal comment about this issue.

Because the pros and cons concerning universal infinity balance so very closely on the scale of likelihoods, I feel reasonably free to choose the one that offers me the greatest degree of cerebral comfort.

For that reason, I choose infinity. When thinking about the concept of space, the word finite demands limitations. And if science continues to deem space as flat, I find it irrational to set limits on it.



« Last Edit: 24/03/2015 23:31:03 by Ethos_ »
 

Offline yor_on

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Re: Is the universe infinite?
« Reply #65 on: 25/03/2015 00:12:15 »
:)

Quite so Sir.
 

Offline PhysBang

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Re: Is the universe infinite?
« Reply #66 on: 25/03/2015 13:57:05 »
Did Cornish discuss the universe as a whole? Yes. Did Cornish claim that the universe as a whole was a sphere of a certain size? No, he explicitly said something about the visible universe (given a certain definition).
No, he didn't explicitly say something about the visible universe.
Mr. Duffield has a pattern of writing the same falsehoods about the articles that he cites over and over again, even when the truth of the matter is explicitly quoted in response to his claims.

This could be, sadly, because he is simply incapable of recognizing his errors for some reason.
Quote
Here's the article again:

http://www.cnn.com/2004/TECH/space/05/24/universe.wide/

He was talking about the universe, not the visible universe. I'm not cherry-picking, I'm giving the reference, and you're trying to claim the cosmologist said something he didn't.
Sadly, I will direct the reader once again to the passage in that article where Neil Cornish is explicitly talking about the visible universe.

Quote from: CNN.com, Mr. Duffield's source for science
"All the distance covered by the light in the early universe gets increased by the expansion of the universe," explains Neil Cornish, an astrophysicist at Montana State University. "Think of it like compound interest."

Need a visual? Imagine the universe just a million years after it was born, Cornish suggests. A batch of light travels for a year, covering one light-year. "At that time, the universe was about 1,000 times smaller than it is today," he said. "Thus, that one light-year has now stretched to become 1,000 light-years."

All the pieces add up to 78 billion-light-years. The light has not traveled that far, but "the starting point of a photon reaching us today after traveling for 13.7 billion years is now 78 billion light-years away," Cornish said. That would be the radius of the universe, and twice that -- 156 billion light-years -- is the diameter. That's based on a view going 90 percent of the way back in time, so it might be slightly larger.
Note that here the radius being discussed is the radius of the points in the early universe that sent light that could have reached the Earth. I do not expect Mr. Duffield to recognize his mistake, at least not explicitly, though he may attempt to mislead his readers by switching to another source that he feels he can cherry-pick a quotation from with better results.

Additionally, rather than simply telling you to "google" for more information (information that never supports Mr. Duffield's position, in my past experience), I will direct you to a copy of the paper Neil Cornish is discussing, so that you can read more clearly that Cornish is discussing the visible universe. http://arxiv.org/abs/1312.4877

Quote
Quote from: Bill S
Can something finite become infinite?  No.
Can something small and expanding always have been infinite?  No.
That's my point.
Indeed, that is Mr. Duffield's point. He creates a strawman argument of the scientific papers he criticizes, none of which claim that a finite space became infinite. Then, because of his dogma, he merely declares that the standard cosmological model does not include the possibility of a universe that was always infinite.

I cannot accept the religion of Mr. Duffield and will not join his particular cult of the worship of two sentences from Albert Einstein.
 

Offline PhysBang

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Re: Is the universe infinite?
« Reply #67 on: 25/03/2015 13:59:52 »
"So you have two possibilities for a flat Universe: one infinite, like a plane, and one finite, like a torus, which is also flat."

What about a third possibility?
I would be interested in seeing this third possibility, but I know that Mr. Duffield will never commit to providing the details of such a possibility, since it is doubtful that these details could match the available observations. As such, his discussion remains interesting fantasy when it does not involve insulting practicing scientists and attempting to foster his particular religion.
 

Offline JohnDuffield

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Re: Is the universe infinite?
« Reply #68 on: 25/03/2015 16:15:29 »
...I would be interested in seeing this third possibility...
The relevant paragraph is where Joe Silk gives a 2D analogy:

"No. We do not know whether the Universe is finite or not. To give you an example, imagine the geometry of the Universe in two dimensions as a plane. It is flat, and a plane is normally infinite. But you can take a sheet of paper [an 'infinite' sheet of paper] and you can roll it up and make a cylinder, and you can roll the cylinder again and make a torus [like the shape of a doughnut]. The surface of the torus is also spatially flat, but it is finite. So you have two possibilities for a flat Universe: one infinite, like a plane, and one finite, like a torus, which is also flat."

See the bit that says you can take a sheet of paper. A piece of paper isn't infinite. All the way around, it has an edge.  The third possibility is that the universe is finite but doesn't wrap around on itself. Because it has an edge. 
 

Offline PhysBang

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Re: Is the universe infinite?
« Reply #69 on: 25/03/2015 18:51:08 »
...I would be interested in seeing this third possibility...
The relevant paragraph is where Joe Silk gives a 2D analogy:

"No. We do not know whether the Universe is finite or not. To give you an example, imagine the geometry of the Universe in two dimensions as a plane. It is flat, and a plane is normally infinite. But you can take a sheet of paper [an 'infinite' sheet of paper] and you can roll it up and make a cylinder, and you can roll the cylinder again and make a torus [like the shape of a doughnut]. The surface of the torus is also spatially flat, but it is finite. So you have two possibilities for a flat Universe: one infinite, like a plane, and one finite, like a torus, which is also flat."

See the bit that says you can take a sheet of paper. A piece of paper isn't infinite. All the way around, it has an edge.  The third possibility is that the universe is finite but doesn't wrap around on itself. Because it has an edge.
This reply is one that makes me wonder if there is some mental block that Mr. Duffield has or whether he is deliberately deceptive. In a post where I note that Mr. Duffield never gives details, he cherry-picks one sentence of my post and then proceeds to give a very vague answer, avoiding once again giving details.

Perhaps Mr. Duffield is simply a very sophisticated trolling bot.
 

Offline yor_on

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Re: Is the universe infinite?
« Reply #70 on: 26/03/2015 17:38:09 »
Thnks Phybang, that citation made Neils idea understandable in simple way. And yes, that's how I imagine a inflation too, and a expansion.
 

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Re: Is the universe infinite?
« Reply #70 on: 26/03/2015 17:38:09 »

 

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