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Author Topic: Is the universe infinite?  (Read 21901 times)

Offline JohnDuffield

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Re: Is the universe infinite?
« Reply #25 on: 23/03/2015 14:29:17 »
...Note that contemporary cosmology has a wealth of evidential support in the form of specific theory that can compare to measurement results (as opposed to qualitative claims and vague analogies).
Contemporary cosmology is big-bang cosmology. We have good evidence for this, and that the universe has been expanding for a finite time. But we have no evidence whatsoever that the universe expanded from a small size to an infinite size in a finite time, and we have no evidence whatsoever that the universe was already infinite when the big bang occurred.

If someone, like JohnDuffield, rejects contemporary cosmology (and especially rejects learning the relevant mathematics), then that person can't follow the reasoning. This does not mean that there isn't reasoning.
I don't reject contemporary cosmology. I'm happy with big bang cosmology. What I reject is the fairy tale notion that the universe was already infinite when the big bang occurred.   

Again, Mr. Duffield decides to stick with his own dogma
It isn't dogma to point out that there no evidence for the infinite universe and that it's at odds with big bang cosmology.
 

Offline JohnDuffield

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Re: Is the universe infinite?
« Reply #26 on: 23/03/2015 14:41:08 »
I wasn't referring to any shape John. I only used it as a analogy, and a pretty bad one too considering your response. The 'shape' of this universe is the one defined from a inside.
I don't see how. If the universe is "flat", then expansion apart, light goes straight. I take my cue here from cosmologist Neil Cornish who said he thought the universe was at least 156 billion light years wide, and that this "can be thought of as a spherical diameter is the usual sense".

I knew I should have avoided it, but I just wanted to point out one way infinity can be reached. In my idea of it you have to start with how things connect, and there we have a lot of contenders, strings and loops among them. It can't be anything else than infinite in my thoughts if what decides a universe is how it connects. And it fits all evidence I know of too.
But that's just the thing. There's no evidence for anything fancy. And yet it seems that people can't conceive of the mundane universe where space doesn't curve back round on itself, and doesn't go on forever.

What I used to get stuck on was the idea of 'sizes', that one has to go, and so has infinity actually :) They becomes meaningless terms if one keep thinking of it from a observer position 'outside a universe'...
I don't get stuck with this. I think of the wave nature of matter and waves inside a droplet of water. They can't go beyond the droplet, they undergo total internal reflection instead. Meanwhile the droplet is spherical, with a finite size. OK it isn't a perfect analogy because there's space beyond this droplet, but IMHO it's better than most.
 

Offline PhysBang

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Re: Is the universe infinite?
« Reply #27 on: 23/03/2015 18:26:11 »
...Note that contemporary cosmology has a wealth of evidential support in the form of specific theory that can compare to measurement results (as opposed to qualitative claims and vague analogies).
Contemporary cosmology is big-bang cosmology. We have good evidence for this, and that the universe has been expanding for a finite time. But we have no evidence whatsoever that the universe expanded from a small size to an infinite size in a finite time, and we have no evidence whatsoever that the universe was already infinite when the big bang occurred.
Except, of course, the evidence that is in every major cosmological paper since 1999.

I know that Mr. Duffield doesn't like this evidence and that it contradicts the contents of his self-published book, but that isn't a good reason for other people to ignore the contents of cosmology papers and textbooks and the reasoning found therein.
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If someone, like JohnDuffield, rejects contemporary cosmology (and especially rejects learning the relevant mathematics), then that person can't follow the reasoning. This does not mean that there isn't reasoning.
I don't reject contemporary cosmology. I'm happy with big bang cosmology. What I reject is the fairy tale notion that the universe was already infinite when the big bang occurred.   
Mr. Duffield clearly has a dogmatic position that he wants to stick to that leads him to refuse to acknowledge the contents of the scientific theories he supposedly accepts. People should judge him accordingly.
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Again, Mr. Duffield decides to stick with his own dogma
It isn't dogma to point out that there no evidence for the infinite universe and that it's at odds with big bang cosmology.
Here we see Mr. Duffield doing the rhetorical equivalent of sticking his fingers in his ears. One may speculate on whether it is ability or character that prompts his actions, but that is beyond the scope of this forum.
 

Offline PhysBang

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Re: Is the universe infinite?
« Reply #28 on: 23/03/2015 18:33:34 »
I wasn't referring to any shape John. I only used it as a analogy, and a pretty bad one too considering your response. The 'shape' of this universe is the one defined from a inside.
I don't see how. If the universe is "flat", then expansion apart, light goes straight. I take my cue here from cosmologist Neil Cornish who said he thought the universe was at least 156 billion light years wide, and that this "can be thought of as a spherical diameter is the usual sense".
Cornish is correct in identifying that the visible universe is a finite spherical volume. That does not mean that the entire universe is a finite spherical volume. In the standard cosmological models used today, this is true regardless of the overall curvature of the universe, flat or not.

As Cornish correctly points out, results that set a minimum size of the universe do not set a maximum or necessarily imply that the universe is infinite in size. The standard argument that the universe is, and always has been, infinite does not rely on one kind of observation or on determinations of minimum size. To claim that it does is to offer a straw man argument.
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And yet it seems that people can't conceive of the mundane universe where space doesn't curve back round on itself, and doesn't go on forever.
Indeed, it is difficult to reconcile such a universe with general relativity. Mr. Duffield refuses to offer a cosmological model of his own, with sufficient detail that it can be compared to empirical results, so one can safely ignore the idea that he has a real alternative to offer.
 

Offline yor_on

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Re: Is the universe infinite?
« Reply #29 on: 23/03/2015 19:39:09 »
I don't know John, you lose me there.  "I don't see how. If the universe is "flat", then expansion apart, light goes straight. I take my cue here from cosmologist Neil Cornish who said he thought the universe was at least 156 billion light years wide, and that this "can be thought of as a spherical diameter is the usual sense"."

That one should be defined from Earth, presuming our visionary to have spherical vision :) And then he will find this 'light sphere' all around him. It doesn't define the universe in any other way to me? Now, if this guy Neil on the other hand had stated that going to one 'edge' of his 'light sphere' would give our spherical visionary a radically new view, with some 'barrier' cutting of space outside that edge, then he would need to prove it.

"The density of the universe also determines its geometry. If the density of the universe exceeds the critical density, then the geometry of space is closed and positively curved like the surface of a sphere. This implies that initially parallel photon paths converge slowly, eventually cross, and return back to their starting point (if the universe lasts long enough). If the density of the universe is less than the critical density, then the geometry of space is open (infinite), and negatively curved like the surface of a saddle. If the density of the universe exactly equals the critical density, then the geometry of the universe is flat like a sheet of paper, and infinite in extent.

The simplest version of the inflationary theory, an extension of the Big Bang theory, predicts that the density of the universe is very close to the critical density, and that the geometry of the universe is flat, like a sheet of paper. The WMAP spacecraft can measure the basic parameters of the Big Bang theory including the geometry of the universe. If the universe were flat, the brightest microwave background fluctuations (or "spots") would be about one degree across. If the universe were open, the spots would be less than one degree across. If the universe were closed, the brightest spots would be greater than one degree across.

Recent measurements (c. 2001) by a number of ground-based and balloon-based experiments, including MAT/TOCO, Boomerang, Maxima, and DASI, have shown that the brightest spots are about 1 degree across. Thus the universe was known to be flat to within about 15% accuracy prior to the WMAP results. WMAP has confirmed this result with very high accuracy and precision. We now know (as of 2013) that the universe is flat with only a 0.4% margin of error. This suggests that the Universe is infinite in extent; however, since the Universe has a finite age, we can only observe a finite volume of the Universe. All we can truly conclude is that the Universe is much larger than the volume we can directly observe." http://map.gsfc.nasa.gov/universe/uni_shape.html

This one might be interesting too. http://www.scientificamerican.com/article/dark-energy-cosmic-distances/

And "If you have an accurate galactic ruler, it then becomes fairly easy to work out whether the universe is flat or curved, and whether the universe is static, expanding, or contracting" http://arxiv.org/abs/1312.4877

Which then means that I won't agree to your statement that "There's no evidence for anything fancy. And yet it seems that people can't conceive of the mundane universe where space doesn't curve back round on itself, and doesn't go on forever."

That doesn't mean that you can't propose other ideas, but you will have to adapt it to those experiments that exist, or prove them wrong.
 

Offline PhysBang

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Re: Is the universe infinite?
« Reply #30 on: 23/03/2015 19:59:43 »
I don't know John, you lose me there.  "I don't see how. If the universe is "flat", then expansion apart, light goes straight. I take my cue here from cosmologist Neil Cornish who said he thought the universe was at least 156 billion light years wide, and that this "can be thought of as a spherical diameter is the usual sense"."
I fear that you have been mislead by the way that Mr. Duffield placed that particular quotation. Cornish does not believe that the universe is a finite sphere, he was speaking only of the shape of the set of all points that have sent light to the Earth. That is, in every standard cosmology, a finite sphere. Cornish does not seem to believe that there is any boundary to the universe, as much as Mr. Duffield would like to quote him in support of such an idea.
 

Offline yor_on

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Re: Is the universe infinite?
« Reply #31 on: 23/03/2015 20:10:55 »
Ahh, thanks PB. Wondered a little there.

There are other ways to consider it too. Think of the statement that physics should be the same throughout a universe. That makes a lot of sense to me, but assuming a bubble I now create a situation in where one have to consider what's outside that bubble? And what 'membrane' I should presume to exist in-between those regions. There the physics can't be the same any more, you could also see it as some sort of 'regime' splitting this universe from some other. It gives way to all sorts of complications for me when we start to define the universe as something with a boundary. We have no evidence for that sort of thinking that I know of. the simplest way around it using a 'container model' is then something alike a möbius strip, but it doesn't simplify anything.
==

what I think one need to be clear on is that the definition of 'astronomic time' we find for this universe isn't about the scale of it. Not if we use a Big Bang and inflation. Because there is no singular defined point of origin for that Big Bang, it happened 'everywhere', just as I understand expansion to do. You can pick any position you want in this observable portion of a universe, just to find all other galaxies move away from you. Doesn't matter where you place yourself.
=

To see how that works think of our spherical observer. He actually sees the origin of the universe 'everywhere', simultaneously, well, sort of :) as the 'earliest light' reaching him comes from all directions, inside that 'observable light sphere' he finds around him. If there was one point of origin we should also find a direction for the in-falling light, but we don't. And that's the definition of that Big Bang, the earliest light we can observe, now put that together with a accelerating expansion, in where our spherical observer can pick any position she like, just to see the same happening, all other galaxies moving away from her. (As well as once again finding the earliest light to reach her, from all over the light sphere)
« Last Edit: 23/03/2015 21:05:07 by yor_on »
 

Offline JohnDuffield

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Re: Is the universe infinite?
« Reply #32 on: 24/03/2015 09:00:52 »
Now, if this guy Neil on the other hand had stated that going to one 'edge' of his 'light sphere' would give our spherical visionary a radically new view, with some 'barrier' cutting of space outside that edge, then he would need to prove it.
He was trying. Read the article and note the mention of the "hall of mirrors". They didn't find any evidence of it, but note stuff like this:

...All the pieces add up to 78 billion-light-years. The light has not travelled 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...

He's saying the universe is some kind of spherical thing that's at least 156 billion light years in diameter. Let's say you're in the middle of it. The obvious question is what's 78 billion light years away? Some kind of edge?

"The density of the universe also determines its geometry. If the density of the universe exceeds the critical density, then the geometry of space is closed and positively curved like the surface of a sphere. This implies that initially parallel photon paths converge slowly, eventually cross, and return back to their starting point (if the universe lasts long enough). If the density of the universe is less than the critical density, then the geometry of space is open (infinite), and negatively curved like the surface of a saddle. If the density of the universe exactly equals the critical density, then the geometry of the universe is flat like a sheet of paper, and infinite in extent.
That's from the NASA WMAP article about the shape of the universe, and it's misleading. It doesn't follow that a flat universe is an infinite universe. It's a non-sequitur, and it's at odds with big bang cosmology. 

The simplest version of the inflationary theory, an extension of the Big Bang theory
You need to be a bit wary about inflation. Not the big bang, inflation. See John Horgan's SciAm blog where you can read Physicist Paul Steinhardt Slams Inflation, Cosmic Theory He Helped Conceive.

Recent measurements (c. 2001) by a number of ground-based and balloon-based experiments, including MAT/TOCO, Boomerang, Maxima, and DASI, have shown that the brightest spots are about 1 degree across. Thus the universe was known to be flat to within about 15% accuracy prior to the WMAP results. WMAP has confirmed this result with very high accuracy and precision. We now know (as of 2013) that the universe is flat with only a 0.4% margin of error
I'm confident that the universe is flat because of what I know about general relativity and gravity. However...

This suggests that the Universe is infinite in extent
No it doesn't.

however, since the Universe has a finite age
It can't be infinite, can it? Not unless it was already infinite when it began.

we can only observe a finite volume of the Universe. All we can truly conclude is that the Universe is much larger than the volume we can directly observe."
No we can't. 

This one might be interesting too. http://www.scientificamerican.com/article/dark-energy-cosmic-distances/
I read it. It seems reasonable.

And "If you have an accurate galactic ruler, it then becomes fairly easy to work out whether the universe is flat or curved, and whether the universe is static, expanding, or contracting" http://arxiv.org/abs/1312.4877
I didn't read the whole paper, I just searched on infinite and flat. It doesn't say anything about an infinite universe, but it says plenty about a flat universe, which is fine by me. 

Which then means that I won't agree to your statement that "There's no evidence for anything fancy. And yet it seems that people can't conceive of the mundane universe where space doesn't curve back round on itself, and doesn't go on forever."
Show me the evidence for an infinite universe. There isn't any.

That doesn't mean that you can't propose other ideas, but you will have to adapt it to those experiments that exist, or prove them wrong.
I'm not saying the experiments are wrong. What I'm saying is that the idea that the universe was already infinite when it began is wrong, and that there's no evidence to support this notion.
 

Offline JohnDuffield

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Re: Is the universe infinite?
« Reply #33 on: 24/03/2015 09:12:16 »
As for PhysBang saying stuff like this:

Cornish is correct in identifying that the visible universe is a finite spherical volume.

Neil Cornish was talking about the universe, not the visible universe.  The article includes sentences like this:

But the universe has been expanding ever since the beginning of time, when theorists believe it all sprang forth from an infinitely dense point in a Big Bang...

"Our results don't rule out a hall-of-mirrors effect, but they make the possibility far less likely," Cornish said, adding that the findings have shown "no sign that the universe is finite, but that doesn't prove that it is infinite."


So we come back to the central issue, which is this: if the universe started off pointlike or small 13.8 billion years ago, how can it be infinite now? It can't. So it must be finite. And if it's finite and flat, it has to have some kind of edge.
 

Offline PhysBang

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Re: Is the universe infinite?
« Reply #34 on: 24/03/2015 13:13:27 »
Now, if this guy Neil on the other hand had stated that going to one 'edge' of his 'light sphere' would give our spherical visionary a radically new view, with some 'barrier' cutting of space outside that edge, then he would need to prove it.
He was trying.
This is the problem with Mr. Duffield's dogma-based approach: he doesn't want to understand the actual science, so he misreads all the things that he comes across and then says things that are untrue about the statements of scientists. While it is always a really, really bad idea to ignore science textbooks and empirical evidence and try to establish a scientific point through a website run by a television station, even here Mr. Duffield misrepresents the views of Cornish because he so desperately wants to find some scientists saying one thing that seems to match his own dogma.
[quoteRead the article and note the mention of the "hall of mirrors".[/quote]
The scientific investigation that Cornish is commenting upon did not search for reflections, but for light that went in a direction away from the Earth but that ended up coming in towards the Earth because it effectively wrapped around the universe. This is something that can happen in a finite universe with no boundary.

One can read about this in the actual scientific paper, here: http://arxiv.org/abs/astro-ph/0604616

You'll find the authors, including Cornish, writing, "It is possible instead that our three dimensional Universe has a finite volume without having an edge, just as the two dimensional surface of the Earth is finite but has no edge. In such a universe, it is possible that a straight path in one direction could eventually lead back to where it started."

This is the basis for the discussion Cornish is making. Someone who is interested in responsibly representing a scientific claim would look at the actual science discussed, not a website for a television station. Someone interested in only their own dogma would grab whatever cherry-picked statement they could that they imagined matched their own fantasy.
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He's saying the universe is some kind of spherical thing that's at least 156 billion light years in diameter. Let's say you're in the middle of it. The obvious question is what's 78 billion light years away? Some kind of edge?
Except that this isn't what he's saying, he is saying that all the points from which light was sent to the Earth are up to that distance away. There is no edge there, that's just how far away some of those points have reached, if we are using the time coordinates normally used to represent cosmological eras.
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That's from the NASA WMAP article about the shape of the universe, and it's misleading. It doesn't follow that a flat universe is an infinite universe. It's a non-sequitur, and it's at odds with big bang cosmology. 
SO here one has a choice to make: trust that Mr. Duffield, with his self-published book for sale and a history of misrepresenting the claims of scientists, is correct about the contents of the "Big Bang theory" or trust that NASA's page for a greater than seven year cosmology project with dozens of scientists and published papers is correct. Having read the relevant papers and reviewed them, I don't have to trust in this case, but I know what I would do.

Quote
Recent measurements (c. 2001) by a number of ground-based and balloon-based experiments, including MAT/TOCO, Boomerang, Maxima, and DASI, have shown that the brightest spots are about 1 degree across. Thus the universe was known to be flat to within about 15% accuracy prior to the WMAP results. WMAP has confirmed this result with very high accuracy and precision. We now know (as of 2013) that the universe is flat with only a 0.4% margin of error
I'm confident that the universe is flat because of what I know about general relativity and gravity.
Note that Mr. Duffield does not care for the evidence, he only cares about his personal knowledge, gleaned from his personal, perhaps mystical, understanding of the writings (but not the mathematics) of Einstein.
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And "If you have an accurate galactic ruler, it then becomes fairly easy to work out whether the universe is flat or curved, and whether the universe is static, expanding, or contracting" http://arxiv.org/abs/1312.4877
I didn't read the whole paper, I just searched on infinite and flat. It doesn't say anything about an infinite universe, but it says plenty about a flat universe, which is fine by me. 
If one is ignorant of the science, then one can miss that the paper does, in fact, discuss infinite universes. This is because the idea is so ubiquitous now, all the authors of the paper have to do is say that they are using a "minimal [Lambda]CDM model"  (pg. 30) and the educated reader knows that they are discussing the Friedmann-Lemaitre-Robertson-Walker familiy of models, which can be infinitely in size. If one bothers to read the most basic textbooks on cosmology, this is laid out clearly along with the relevant reasoning. If one, dogmatically, works to ignore the basics in the field and make claims on the basis of this willful ignorance, then one is likely to say a number of falsehoods.
 

Offline PhysBang

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Re: Is the universe infinite?
« Reply #35 on: 24/03/2015 13:18:29 »
As for PhysBang saying stuff like this:

Cornish is correct in identifying that the visible universe is a finite spherical volume.

Neil Cornish was talking about the universe, not the visible universe.
As usual, Mr. Duffield doubles down on his, to be charitable, mistakes. I know that Mr. Duffield has a difficult time reading an entire piece and that he prefers that he and his readers only read the parts that he has cherry-picked, but, unfortunately for him, I have to read the entire article.

Here is the passage from the article explaining that Cornish is discussing the visible universe:

'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.'

As always, one can believe the dogmatic position of Mr. Duffield, or one can believe the words of the scientist himself.
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So we come back to the central issue, which is this: if the universe started off pointlike or small 13.8 billion years ago, how can it be infinite now? It can't.
I'm sure that in the mind of Mr. Duffield, this is a great argument. However, that this argument can be taken seriously has been effectively abandoned since the 1920s, if not earlier.

Indeed, this issue is settled and Mr. Duffield seems to know this, given his original post in this thread. As such, this thread seems little more than a deceitful attempt for Mr. Duffield to present his own "New Theories" without having to follow the forum rules on where to post such theories. Again, this is an important factor to use in a consideration of the truth value of any statement made by Mr. Duffield.
« Last Edit: 24/03/2015 13:40:28 by PhysBang »
 

Offline JohnDuffield

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Re: Is the universe infinite?
« Reply #36 on: 24/03/2015 13:57:53 »
...As always, one can believe the dogmatic position of Mr. Duffield, or one can believe the words of the scientist himself.
Quote
So we come back to the central issue, which is this: if the universe started off pointlike or small 13.8 billion years ago, how can it be infinite now? It can't.
I'm sure that in the mind of Mr. Duffield, this is a great argument. However, that this argument can be taken seriously has been effectively abandoned since the 1920s, if not earlier. Indeed, this issue is settled...
No, it isn't settled, and it definitely isn't dogma to point out that a universe that was small 13.8 billion years ago cannot be infinite now.
 

Online chiralSPO

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Re: Is the universe infinite?
« Reply #37 on: 24/03/2015 14:25:01 »
My understanding is that, by tracing back all that makes up our current observable universe, it can be concluded that very near the time of the big bang it all must have been in a very small space (high density), but that this argument does not necessarily mean that the *entire universe* was that small.

One could imagine an infinite universe with an initially high density that expanded into the density that we observe today while remaining infinite in scope from inception onward.

If, in fact, the zero-energy universe theory is correct, then I think it would be just as possible to for an infinite amount of matter to "come into being" as it would for any finite amount.

On the other hand, I am not convinced that the universe "must be" infinite, merely because it is the simplest solution that fits with our observations. However, this is mostly a philosophic point (for now), as we can model the universe as infinite or just arbitrarily large and reach most of the same conclusions. Certainly we cannot perform any experiment that proves that the universe is finite. We could show that the universe is flat here, there, and everywhere we we can observe, but that doesn't ultimately prove that there isn't either a point beyond which the universe does curve, or a point beyond which there is some kind of "edge."

At this point, I am satisfied knowing that we don't know the answer, and hypothesizing that it is possible that we cannot know the answer. But that's just me.
 

Offline PhysBang

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Re: Is the universe infinite?
« Reply #38 on: 24/03/2015 14:47:42 »
...As always, one can believe the dogmatic position of Mr. Duffield, or one can believe the words of the scientist himself.
Quote
So we come back to the central issue, which is this: if the universe started off pointlike or small 13.8 billion years ago, how can it be infinite now? It can't.
I'm sure that in the mind of Mr. Duffield, this is a great argument. However, that this argument can be taken seriously has been effectively abandoned since the 1920s, if not earlier. Indeed, this issue is settled...
No, it isn't settled, and it definitely isn't dogma to point out that a universe that was small 13.8 billion years ago cannot be infinite now.
It is nice to see Mr. Duffield attempting to misrepresent the issue in such a ham-fisted manner that readers can clearly see his character. Rather than apologize for misrepresenting the words of Neil Cornish, he instead attempts to present a more-or-less correct inference (a small universe cannot become infinite) while neglecting to bring up his main points (the universe cannot in principle be infinite and contemporary cosmology cannot include an infinite universe). These main points are so demonstrably false that it is amazing that one can claim them and claim to have read anything on this topic without lying.
 

Offline yor_on

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Re: Is the universe infinite?
« Reply #39 on: 24/03/2015 16:49:41 »
Now John, this is a single malt day, so you have to take what I write with a pinch of salt. My view ok?

Time is a construction. Which 'ticks' macroscopically.
Life is indeed a mystery, but it make us look around and think.
Why does it exist?

Most of the things we've believed in as a species has been proved wrong. And the ones proving it wrong is us.
That makes me rather proud over us :)

Although, at no time the transition has been easy.

And yes, the universe is indeed weird. Einstein didn't expect 'black holes', they were a expression of the mathematics he defined, but he didn't expect it. We're all explorers John, you and me both :) And we have our own views. The logic is there if you want to explore it.
« Last Edit: 24/03/2015 16:51:51 by yor_on »
 

Offline yor_on

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Re: Is the universe infinite?
« Reply #40 on: 24/03/2015 17:05:13 »
PB, reading you I get a distinct impression of Neil Cornish et al defining a universe from what I define as a 'container perspective' ?
If that is so? Then it's a outdated perspective in my view.
The thing is, there is a complementary principle involved, but stretch it too long and it will break.
 

Offline yor_on

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Re: Is the universe infinite?
« Reply #41 on: 24/03/2015 17:14:36 »
And John "No, it isn't settled, and it definitely isn't dogma to point out that a universe that was small 13.8 billion years ago cannot be infinite now."

You really need to look up the logic used there. what it will tell you is that there is no 'origin', or that everywhere is the 'origin'.

Both of those statements should tell you the same. There is no origin, the universe is indeed infinite, no expansion needed. and what that should tell you is that there are different types of logic, some fitting this universe, others won't, that doesn't discuss the mathematics 'reality', just where we exist.
 

Offline PhysBang

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Re: Is the universe infinite?
« Reply #42 on: 24/03/2015 17:26:51 »
PB, reading you I get a distinct impression of Neil Cornish et al defining a universe from what I define as a 'container perspective' ?
If that is so? Then it's a outdated perspective in my view.
The thing is, there is a complementary principle involved, but stretch it too long and it will break.
I'm not sure what you mean. There are a number of ways of defining regions within the universe. One is to identify the region at a given time that can possibly send light to Earth. One is to identify a region that has once sent light to Earth. In both cases, these are not the entirety of the universe unless the universe is finite and, in one sense, small.

The CNN article was reporting on the failure of some observations to detect a signal that the universe was so small that the entire universe is within the visible universe in the second sense above.
 

Offline JohnDuffield

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Re: Is the universe infinite?
« Reply #43 on: 24/03/2015 17:36:38 »
My understanding is that, by tracing back all that makes up our current observable universe, it can be concluded that very near the time of the big bang it all must have been in a very small space (high density), but that this argument does not necessarily mean that the *entire universe* was that small.
That's what people used to say. Google on big bang singularity. Somehow we've gone from the universe used to be small to the observable universe used to be small and that non-sequitur that a flat universe must be an infinite universe. Like I was saying, Neil Cornish was talking about the universe, not just the visible universe.

One could imagine an infinite universe with an initially high density that expanded into the density that we observe today while remaining infinite in scope from inception onward.
I can't. Because from what I know of relativity, an infinite universe can't expand. IMHO the very expansion of the universe is hard scientific evidence that the universe is not infinite.

If, in fact, the zero-energy universe theory is correct
It isn't. That's a myth that arises on the mistaken idea that gravitational field energy is negative. It isn't, it's positive. See The Foundation of the General Theory of Relativity where Einstein said the energy of the gravitational field shall act gravitatively in the same way as any other kind of energy. The people who propose the zero-energy universe cannot have read this.

I think it would be just as possible to for an infinite amount of matter to "come into being" as it would for any finite amount.
I don't know how or why the big bang occurred, but I know of no infinities in nature, and I'm not comfortable with some infinite amount of space and matter and energy just popping into existence.

On the other hand, I am not convinced that the universe "must be" infinite, merely because it is the simplest solution that fits with our observations.
That's the thing - I don't think it is the simplest solution.

However, this is mostly a philosophic point (for now), as we can model the universe as infinite or just arbitrarily large and reach most of the same conclusions. Certainly we cannot perform any experiment that proves that the universe is finite.
Neil Cornish et al had a go, WMAP looked at flatness as did Planck which also looked for the toroidal topology. So never say never.

We could show that the universe is flat here, there, and everywhere we we can observe, but that doesn't ultimately prove that there isn't either a point beyond which the universe does curve, or a point beyond which there is some kind of "edge."
Agreed.

At this point, I am satisfied knowing that we don't know the answer, and hypothesizing that it is possible that we cannot know the answer. But that's just me.
Me too. Only I reject "the universe is infinite" as a non-answer that runs counter to big bang cosmology.   
 

Offline JohnDuffield

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Re: Is the universe infinite?
« Reply #44 on: 24/03/2015 17:45:34 »
You really need to look up the logic used there. what it will tell you is that there is no 'origin', or that everywhere is the 'origin'.
I take no issue with that. Space itself is expanding.

Both of those statements should tell you the same. There is no origin, the universe is indeed infinite, no expansion needed.
Sorry yor-on, but expanding space doesn't mean infinite space. And we have good evidence that space is expanding. Not only that, but look at Einstein's stress-energy-momentum tensor. See that energy-pressure diagonal? Einstein should have predicted that space had an innate "pressure" and just had to expand. He didn't, and it was his greatest blunder.

 

Offline yor_on

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Re: Is the universe infinite?
« Reply #45 on: 24/03/2015 17:50:45 »
Ok PB, I see how you define it. It doesn't answer the definitions I'm wondering about though. That means that I need a link, to see for myself I suspect :)
A 'containetr' in my view is a try for something that will 'hold it all'. And I don't expect that, what I expect are rules, and 'properties' scaling.
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Actually PhysBang, what I really expect is a symmetry.
« Last Edit: 24/03/2015 18:06:22 by yor_on »
 

Offline yor_on

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Re: Is the universe infinite?
« Reply #46 on: 24/03/2015 17:59:55 »
Ouch, I told you that a expansion isn't needed, if you use the logic, or premises, defining a Big Bang. You don't really need it, as long as you understand that our 'spherical observer' find the origin of light coming to him wherever he goes, and at a exact same 'time scale'. If that logic is correct then there is no defined origin in the usual sense, as with some force expressing itself normally (Explosion). And I better point out that I don't see your arguments as being 'less' in any way. You and me both want to discuss, And we both want to use our imagination :) Not such a bad thing in my view. Too few that dare.
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I told you John, I'm on a single malt diet today, have nothing to do with logic, just life.
« Last Edit: 24/03/2015 18:26:31 by yor_on »
 

Offline JohnDuffield

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Re: Is the universe infinite?
« Reply #47 on: 24/03/2015 18:40:19 »
I'm sorry yor_on, I don't know what you mean. We have what looks like good evidence that the universe is expanding, and from what I know of the nature of space, it just has to expand. See the stress-energy-momentum tensor above? It "describes the density and flux of energy and momentum in spacetime". See the energy-pressure diagonal? See the sheer stress? It's like space is this gin-clear ghostly elastic that can curve and wave. I kid ye not, google it. And Einstein's greatest blunder is that he talked about gravitational fields being everywhere, but he didn't think of space has having a pressure everywhere. For some reason he didn't follow his theory to its logical conclusion, and instead was convinced that the universe was static. So he didn't predict the expanding universe.
 

Offline yor_on

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Re: Is the universe infinite?
« Reply #48 on: 24/03/2015 19:10:11 »
Ok John. different definitions :)
I don't like 'shear stress' when applied on a vacuum.  Doesn't state that it must be wrong. Same as the idea of a vacuum, a vacuum according to old views is complementary. Yin and Yang.  That's a very naive interpretation naturally, doesn't mean it hasn't a logic though. I'm questioning a vacuum, as I do most everything.
 

Offline PhysBang

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Re: Is the universe infinite?
« Reply #49 on: 24/03/2015 19:17:42 »
Like I was saying, Neil Cornish was talking about the universe, not just the visible universe.
This really is all that needs to be pointed out about Mr. Duffield: he cherry-picks statements, he then uses this selective quotation to mislead his readers, then he ignores all the evidence that shows that he is misleading his reader, finally, he returns to the cherry-picked quotation.

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).

This is essentially the only technique that Mr. Duffield has to attempt to harness scientific results.
 

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Re: Is the universe infinite?
« Reply #49 on: 24/03/2015 19:17:42 »

 

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