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Solly Home

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How wide is the universe?
« on: 24/11/2010 01:30:03 »
Solly Home  asked the Naked Scientists:
   
Dear Dr. Chris,

During a recent podcast, Dr Dom. stated in response to a question about the size of the Universe, that it was approximately 13.6 billion light years.

This has intrigued me, and got my grey matter moving.  Surely if everything started from a big bang some 13.6 billion years ago, and has been expanding ever since, the universe should be 27.2 billion light years across?

I welcome your response.

Regards,

Dave Solway

What do you think?
« Last Edit: 24/11/2010 01:30:03 by _system »


 

Offline QuantumClue

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How wide is the universe?
« Reply #1 on: 24/11/2010 01:40:18 »
Solly Home  asked the Naked Scientists:
   
Dear Dr. Chris,

During a recent podcast, Dr Dom. stated in response to a question about the size of the Universe, that it was approximately 13.6 billion light years.

This has intrigued me, and got my grey matter moving.  Surely if everything started from a big bang some 13.6 billion years ago, and has been expanding ever since, the universe should be 27.2 billion light years across?

I welcome your response.

Regards,

Dave Solway

What do you think?

Yes, I do believe the universe is around 156 billion light years wide.
« Last Edit: 24/11/2010 01:44:51 by QuantumClue »
 

Offline JP

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How wide is the universe?
« Reply #2 on: 24/11/2010 03:11:32 »
This has intrigued me, and got my grey matter moving.  Surely if everything started from a big bang some 13.6 billion years ago, and has been expanding ever since, the universe should be 27.2 billion light years across?

I think it was pointed out elsewhere that the answer on the podcast might be wrong.  The usual answer is that the observable universe is 93 billion light years across, or the edge of it is ~46 billion light years away from us. 

The answer is bigger than 27.2 because the expansion of the universe appears to be accelerating are accelerating.  This means that we're seeing light arriving from distant objects that are now 46 billion light years from us, rather than 13. 

QuantumClue: where do you get the 156 billion light years from?  That's a number I haven't heard before.
 

Offline QuantumClue

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« Reply #3 on: 24/11/2010 10:59:50 »
This has intrigued me, and got my grey matter moving.  Surely if everything started from a big bang some 13.6 billion years ago, and has been expanding ever since, the universe should be 27.2 billion light years across?

I think it was pointed out elsewhere that the answer on the podcast might be wrong.  The usual answer is that the observable universe is 93 billion light years across, or the edge of it is ~46 billion light years away from us. 

The answer is bigger than 27.2 because the expansion of the universe appears to be accelerating are accelerating.  This means that we're seeing light arriving from distant objects that are now 46 billion light years from us, rather than 13. 

QuantumClue: where do you get the 156 billion light years from?  That's a number I haven't heard before.

I seem to have found five different sources which claim it to be 156 billion lightyears. I will find these sources when I return later.

bye for now.
 

Offline Pikaia

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« Reply #4 on: 24/11/2010 11:20:07 »
Quote
Surely if everything started from a big bang some 13.6 billion years ago, and has been expanding ever since, the universe should be 27.2 billion light years across?
This is the usual error of assuming that the universe began as a point. The universe seems to be infinite, and always has been. The visible universe is not the whole universe - we cannot see objects that are very far away because the light has not had time to reach us, not because the universe has an edge with us at the centre.
 

Offline peppercorn

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How wide is the universe?
« Reply #5 on: 24/11/2010 11:40:13 »
The universe seems to be infinite, and always has been.
Based on what?  All evidence since Hubble points to an expansive universe and the coalescence of galactic masses points to a finite size for it.

...not because the universe has an edge with us at the centre.
No ones claiming (except fund. religious types!) that we are at any way at its centre.
 

Offline Pikaia

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« Reply #6 on: 24/11/2010 11:57:49 »
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All evidence since Hubble points to an expansive universe
I do not deny that the universe is expanding. It is expanding, but it is also infinite.

http://www.astro.ucla.edu/~wright/infpoint.html

Quote
the coalescence of galactic masses points to a finite size for it
Please explain.

Quote
No ones claiming (except fund. religious types!) that we are at any way at its centre.
The OP seems to be under the impression that we are.
 

Offline QuantumClue

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« Reply #7 on: 24/11/2010 14:16:24 »
http://www.space.com/scienceastronomy/mystery_monday_040524.html


http://www.physicsforums.com/showthread.php?t=29208

CMB data seems to conclude it is around 156 billion lightyears. I may be wrong, but I feel this is what has been concluded. Some sources claim it is significantly less. It would be interesting to see who else has any evidence to the width, or the radius and then work out the diameter.



 

Offline Pikaia

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« Reply #8 on: 24/11/2010 14:35:37 »
To quote one of your links:
Quote
So the upshot of Cornish work is, like the u looks flat and infinite in extent in all directions and NOT like a finite ball or donut. And almost all working cosmologists quietly assume it is flat and infinite. But IF by some weird joke it should be finite, like a ball or donut then Cornish tells us that the "halfway around" size of the mother is at least 78.

People tend to confuse the issue when they talk about the Universe, when actually mean the visible Universe. The most distant objects that we can see now are certainly now much more than 13.7 billion light years away because of the expansion, but there could well be objects that are so far away that their light has not had time to reach us, and the expansion of the universe means that it never will.
 

Offline peppercorn

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« Reply #9 on: 24/11/2010 15:24:42 »
Quote
All evidence since Hubble points to an expansive universe
I do not deny that the universe is expanding. It is expanding, but it is also infinite.
http://www.astro.ucla.edu/~wright/infpoint.html
It's your use of 'seems to' that intrigues me. The page shows a theoretical explanation, for how such an infinite universe could operate, with its furthest reaches unobservable for ever.  I took 'seems to' to mean that this was proven most likely.

Quote
the coalescence of galactic masses points to a finite size for it
Please explain.
TBH, I'm not sure I can! The theory, based on observations that point to a finite universe being most likely, is more complex than I have given credit for.  I may have to leave it to one of the regulars who is expert in these matters...

Quote
No ones claiming (except fund. religious types!) that we are at any way at its centre.
The OP seems to be under the impression that we are.
Which part of what he says makes you think that?
 

Offline Pikaia

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« Reply #10 on: 24/11/2010 16:28:13 »
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I took 'seems to' to mean that this was proven most likely.
I think that is the most plausible view. It may not be proven but I don't think there is anything to contradict that view, so that is where I would put my money.
Quote
Which part of what he says makes you think that?
The OP talks about a universe 27.2 bly across, ie edge to edge. We can see objects 13.6 bly away in every direction, which would place us in the exact centre.
 

Offline peppercorn

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How wide is the universe?
« Reply #11 on: 24/11/2010 16:53:39 »
Quote
I took 'seems to' to mean that this was proven most likely.
I think that is the most plausible view. It may not be proven but I don't think there is anything to contradict that view, so that is where I would put my money.
I think most physicists find any theorem that needs an infinity in the initial conditions, generally unsettling. Of course, this is an aesthetic preference - I don;t like the idea of a universe that expands faster & faster for ever, but it may be so.

Quote
Which part of what he says makes you think that?
The OP talks about a universe 27.2 bly across, ie edge to edge. We can see objects 13.6 bly away in every direction, which would place us in the exact centre.
Maybe this is a misconception on my part, but I thought in a 4D spacetime universe there wasn;t a centre as such - like a 2d 'man' existing on the surface of a balloon being filled up.  Every directions as good as any other.
 

Offline QuantumClue

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« Reply #12 on: 24/11/2010 17:26:55 »
Quote
I took 'seems to' to mean that this was proven most likely.
I think that is the most plausible view. It may not be proven but I don't think there is anything to contradict that view, so that is where I would put my money.
I think most physicists find any theorem that needs an infinity in the initial conditions, generally unsettling. Of course, this is an aesthetic preference - I don;t like the idea of a universe that expands faster & faster for ever, but it may be so.

Quote
Which part of what he says makes you think that?
The OP talks about a universe 27.2 bly across, ie edge to edge. We can see objects 13.6 bly away in every direction, which would place us in the exact centre.
Maybe this is a misconception on my part, but I thought in a 4D spacetime universe there wasn;t a centre as such - like a 2d 'man' existing on the surface of a balloon being filled up.  Every directions as good as any other.

No, you are right. There is no centre in this universe. Every point on the spacetime map is as valid a true centre as any other.
 

Offline Bill S

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« Reply #13 on: 24/11/2010 23:09:40 »
Pikaia, as pointed out in your link, at the time of the B B, the observable Universe occupied a single point.  Possibly this, coupled with the statement that the Universe was infinite at the time of the B B, leads to confusion.

John Gribbin explains that he uses “Universe” for our observable Universe; “universe” for any other universe we might want to talk about; and, “cosmos” for anything beyond the observable Universe.  That’s from memory, I hope I am not doing him an injustice.

Using this sort of terminology, the Universe would be a finite entity within an infinite cosmos. 

Does that help?  If it seems to – think again! It leads to some weird stuff. ;D
 

Offline QuantumClue

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« Reply #14 on: 25/11/2010 03:01:48 »
Pikaia, as pointed out in your link, at the time of the B B, the observable Universe occupied a single point.  Possibly this, coupled with the statement that the Universe was infinite at the time of the B B, leads to confusion.

John Gribbin explains that he uses “Universe” for our observable Universe; “universe” for any other universe we might want to talk about; and, “cosmos” for anything beyond the observable Universe.  That’s from memory, I hope I am not doing him an injustice.

Using this sort of terminology, the Universe would be a finite entity within an infinite cosmos. 

Does that help?  If it seems to – think again! It leads to some weird stuff. ;D


It is easy to say there was a center to the point singularity, but what is that in reference too?

Better yet, there is no center to the singularity - but there is something infinite about it. Whilst it may seem like a contradiction, the mathematics of quantum mechanics and physicists alike realize that the only possible out come is a singular region with energy so dense, it of infinite values. But the greatest point, if not the true point to the OP, is that most seem to agree that the singularity is possibly an indication there has been a mathematical red-herring. And indication that our efforts have been pretty much futile and taxing.

The paradox is simple. Remove the paradox of a dogmatic thinking, and believe that Occams Razor leads us to the truth... that being that there couldn't be such a singularity if it causes such a bizarre conceptual paradox - mind you, quantum theory is wierd at best.
 

Offline JP

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« Reply #15 on: 25/11/2010 03:49:41 »
http://www.space.com/scienceastronomy/mystery_monday_040524.html


http://www.physicsforums.com/showthread.php?t=29208

CMB data seems to conclude it is around 156 billion lightyears. I may be wrong, but I feel this is what has been concluded. Some sources claim it is significantly less. It would be interesting to see who else has any evidence to the width, or the radius and then work out the diameter.

Hmm... according to wikipedia (which of course could also be wrong), 46 billion light years is the radius of the observable universe.  If the entire universe is closed, then 78 billion light years is the total possible diameter.  156 billion is an incorrect doubling of diameter.  I was a bit confused that 78 is a smaller number than the diameter observable universe at 92.  I think it comes from checking to see if light went "around" the closed universe, so that we have light from the same points coming at us from two directions, depending which path it took around the universe.  The 78 is the furthest we've checked for the kinds of repeating patterns that would develop from this.  The 92 is a theoretical calculation on how far away the furthest objects we can see are, regardless of whether the universe is closed or not... if that makes sense.

Of course, the 156 could be right, too.  I just take the numbers at face value and wouldn't know how to calculate them.
 

Offline JP

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« Reply #16 on: 25/11/2010 03:55:26 »
Pikaia, as pointed out in your link, at the time of the B B, the observable Universe occupied a single point.  Possibly this, coupled with the statement that the Universe was infinite at the time of the B B, leads to confusion.

John Gribbin explains that he uses “Universe” for our observable Universe; “universe” for any other universe we might want to talk about; and, “cosmos” for anything beyond the observable Universe.  That’s from memory, I hope I am not doing him an injustice.

Using this sort of terminology, the Universe would be a finite entity within an infinite cosmos. 

Does that help?  If it seems to – think again! It leads to some weird stuff. ;D


It is easy to say there was a center to the point singularity, but what is that in reference too?

Better yet, there is no center to the singularity - but there is something infinite about it. Whilst it may seem like a contradiction, the mathematics of quantum mechanics and physicists alike realize that the only possible out come is a singular region with energy so dense, it of infinite values. But the greatest point, if not the true point to the OP, is that most seem to agree that the singularity is possibly an indication there has been a mathematical red-herring. And indication that our efforts have been pretty much futile and taxing.

The paradox is simple. Remove the paradox of a dogmatic thinking, and believe that Occams Razor leads us to the truth... that being that there couldn't be such a singularity if it causes such a bizarre conceptual paradox - mind you, quantum theory is wierd at best.

If the universe is infinite and flat, then you could squeeze it down and it would still be infinite and flat, but matter would be more densely packed.  That's basically all the BB model is saying, as I understand it.  Since the BB, it's just been expanding, but if an infinitely large, flat object expands, its still a infinitely large and flat.  The only differences we'd see are density changes as things move apart... which is exactly what's observed.

I don't think the density at the big bang was actually infinitely dense.  The best we know is that it was denser than the Planck density, and at that point, we don't have a good theory or any experimental evidence to cover what happens.
 

Offline JP

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« Reply #17 on: 25/11/2010 03:59:25 »
Quote
Which part of what he says makes you think that?
The OP talks about a universe 27.2 bly across, ie edge to edge. We can see objects 13.6 bly away in every direction, which would place us in the exact centre.
Maybe this is a misconception on my part, but I thought in a 4D spacetime universe there wasn;t a centre as such - like a 2d 'man' existing on the surface of a balloon being filled up.  Every directions as good as any other.

The OP, I think, is confused between the idea of observable universe and size of the universe.  The observable universe is a sphere surrounding us of the points from which light has had time to reach us.  In other words, it's things we can see when we look out from earth.

The universe itself might be bigger, but if we can't see it (nothing can travel faster than light) how would we know?

As for numbers of light years, I believe they get those numbers by taking the most distant objects we can see, and computing how far away they are at this instant in time.  Clearly when we see distant objects, we're viewing them billions of years in the past, but the numbers quoted, I believe, are the current distances of the objects from us.  That's why you can see something that's 46 billion light years away, even though the universe is only ~14 billion light years old: in the time it took the light to reach us, the universe has expanded and pushed the object further from us.

 

Offline Bill S

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« Reply #18 on: 25/11/2010 15:02:56 »
I believe the Universe (cosmos) has to be bigger that the observable Universe, in fact I think it has to be infinite.  However, "believe" and "think" are the key words here.

Can anyone improve on that?  ???
 

Offline QuantumClue

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« Reply #19 on: 25/11/2010 16:53:52 »
I believe the Universe (cosmos) has to be bigger that the observable Universe, in fact I think it has to be infinite.  However, "believe" and "think" are the key words here.

Can anyone improve on that?  ???

The observable universe is the limit of our understanding. There is where theory enters, and theory is what dictates that the observable universe is either finite or infinite. Either way, we do not know, it's but a theory, a mathematical guess-work.
 

Offline QuantumClue

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« Reply #20 on: 25/11/2010 17:00:53 »
I believe the Universe (cosmos) has to be bigger that the observable Universe, in fact I think it has to be infinite.  However, "believe" and "think" are the key words here.

Can anyone improve on that?  ???
Pikaia, as pointed out in your link, at the time of the B B, the observable Universe occupied a single point.  Possibly this, coupled with the statement that the Universe was infinite at the time of the B B, leads to confusion.

John Gribbin explains that he uses “Universe” for our observable Universe; “universe” for any other universe we might want to talk about; and, “cosmos” for anything beyond the observable Universe.  That’s from memory, I hope I am not doing him an injustice.

Using this sort of terminology, the Universe would be a finite entity within an infinite cosmos. 

Does that help?  If it seems to – think again! It leads to some weird stuff. ;D


It is easy to say there was a center to the point singularity, but what is that in reference too?

Better yet, there is no center to the singularity - but there is something infinite about it. Whilst it may seem like a contradiction, the mathematics of quantum mechanics and physicists alike realize that the only possible out come is a singular region with energy so dense, it of infinite values. But the greatest point, if not the true point to the OP, is that most seem to agree that the singularity is possibly an indication there has been a mathematical red-herring. And indication that our efforts have been pretty much futile and taxing.

The paradox is simple. Remove the paradox of a dogmatic thinking, and believe that Occams Razor leads us to the truth... that being that there couldn't be such a singularity if it causes such a bizarre conceptual paradox - mind you, quantum theory is wierd at best.

If the universe is infinite and flat, then you could squeeze it down and it would still be infinite and flat, but matter would be more densely packed.  That's basically all the BB model is saying, as I understand it.  Since the BB, it's just been expanding, but if an infinitely large, flat object expands, its still a infinitely large and flat.  The only differences we'd see are density changes as things move apart... which is exactly what's observed.

I don't think the density at the big bang was actually infinitely dense.  The best we know is that it was denser than the Planck density, and at that point, we don't have a good theory or any experimental evidence to cover what happens.

It's an epistemological paradox. Afterall all, it depends on two things, whether the universe is closed or open. If closed there is no paradox. If open, there is a finite beginning but one which extends into an infinity of reality. Which end is right? This is why I believe the universe must be closed.
« Last Edit: 25/11/2010 17:13:34 by QuantumClue »
 

Offline Bill S

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How wide is the universe?
« Reply #21 on: 25/11/2010 18:17:34 »
Quote from: Q C
If open, there is a finite beginning but one which extends into an infinity of reality.

That's why I prefer "boundless" in this sort of situation.  It doesn't carry the implication that something finite can become infinite.   
 

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