Closed Universe?

[Anjruu]

What with the recent support for the neutrino mass, even if it is very very small, I was wondering if this gives us enough mass in the universe to close it. I think closed is the right term, when there is enough mass in the universe to have the expansion of the universe slow down and reverse because of the pull of gravity. I thought we had like, 85% of the mass necessary to have such a universe. Does the neutrino mass give us any?

[m4rc]

I don't think that the recent discovery of neutrinos mass will change estimates of the mass of the universe. This is because astronomers can estimate the mass of galaxies by observing their rates of rotation (or something like that). For a long time it astronomers came to the conclusion that there was mass could not be accounted for by considering only the visible stars. Therefore they proposed that the galaxies contain a certain amount of unseen matter which they called dark matter. By discovering that neutrinos have mass, they have found an explanation for the dark matter. I'm not sure if this would explain all the dark matter.

[Norman Albers]

I recall that on some measure observable mass and energies are only like one-third of what is called for. Is it the same to talk of closure density as to talk of galactic dynamics? Clustering requires something. I don't know dark energy from mass in the sense of what we think might fill which voids in our theories.

[aguy2]

Is it the same to talk of closure density as to talk of galactic dynamics?

 

A very good question. You might want to animate figure 3 at this site: http://www.physics.nmt.edu/~dynamo/PJRX/Results.html

 

The animation is of a hydro-pulse and was in no way ment as an attempt to model an all-matter, cosmological 'pulse'. For example, the experiment was set up so as the hydro-pulse transited almost immediately from a laminar (even) flow to a turbulent condition, nonetheless I would contend that it is possible to visually follow the development of a "dipole/octipole-like" prefered direction indicated by some interpertations of the 3 year WMAP data.

 

Do you think I am "broken pottery shards" or just another "cracked pot"?

aguy2

[bascule]

The important measurement made in this regard recently is the value range for omega calculated from WMAP's CMBR measurements. Right now things are looking like the universe is closed...

[Severian]

The important measurement made in this regard recently is the value range for omega calculated from WMAP's CMBR measurements. Right now things are looking like the universe is closed...

 

The first statement is correct, but the second is not. The WMAP data imply the universe is spacially flat, and temporally open. So (if they are correct) there will be no big crunch.

 

The flatness measure is not a measure of the mass/energy density - it is an actual measurement of the geometry. Then one asks what mass/energy density is required to provide this geometry, which leads to the need for dark matter (and dark energy). The neutrino masses are far too small to provide the required dark matter, but there could be a sterile (right-handed) neutrino with a much larger mass which could do it.

[Martin]

The first statement is correct' date=' but the second is not. The WMAP data imply the universe is spacially flat, and temporally open. So (if they are correct) there will be no big crunch.

 

The flatness measure is not a measure of the mass/energy density - it is an actual measurement of the geometry. Then one asks what mass/energy density is required to provide this geometry, which leads to the need for dark matter (and dark energy). The neutrino masses are far too small to provide the required dark matter, but there could be a sterile (right-handed) neutrino with a much larger mass which could do it.[/quote']

 

I agree with temporally open---no big crunch.

 

As for spatially flat versus spatially "nearly flat" (with possibly closed spatial cross-sections) I think there is a nuanced shift going on in how leaders in the mainstream community discuss the issue.

 

The WMAP3 data is certainly consistent with either interpretation. I will get some page references to Spergel et al the "wmap3 implications for cosmology" paper.

 

the subtle shift is in how seriously mainstream people seem to be taking the alternatives. I will get some quotes from George Ellis (co-author of Hawking) and Ned Wright (one of the principal investigators in WMAP and co-author of the recent Spergel et al paper).

 

I think what is going on as regards the exactly flat versus "nearly flat" with possibly spatial closure is interesting to watch.

[Martin]

... I think closed is the right term, when there is enough mass in the universe to have the expansion of the universe slow down and reverse because of the pull of gravity...

 

You are possibly confused. A revolution in cosmology occurred in 1998 with the discovery that expansion was accelerating. The mainstream consensus model ("LambdaCDM") has no chance of "crunch".

 

One has to postulate exotic weird stuff that there is no evidence for, in order to get something that will eventually collapse in a crunch, so average working cosmologists usually dont bother with crunch scenarios.

 

but CLOSED can refer to spatially closed----one case being a slight positive curvature and a spatially finite universe that is not destined for a big crunch.

 

If you have been reading out-dated books, this may sound like a contradiction to you. It used to be, before 1998, when a cosmologist said "closed" he or she meant both spatially and temporally closed, because they mistakenly thought that one implied the other. A lot of books were written portraying three alternatives "closed, flat, open". These books are now MISLEADING AND CONFUSING.

 

It is probably safer to stick to recent source material like post 2002. I dont know what to recommend. Have you checked out Ned Wright's online cosmology tutorial and the related FAQ? You might find it useful. Just google Ned Wright.

[Severian]

The WMAP3 data is certainly consistent with either interpretation. I will get some page references to Spergel et al the "wmap3 implications for cosmology" paper.

 

Yes' date=' the data will never [b']prove[/b] that the universe is flat - there will always be some error on the measurement. But the error is already small enough in my opinion to require any 'nearly flat' scenario to explain the fine-tuning required.

[Norman Albers]

A revolution in cosmology occurred in 1998 with the discovery that expansion was accelerating. The mainstream consensus model ("LambdaCDM") has no chance of "crunch".

Is this the rebirth of the cosmological constant?

[Martin]

Yes, the data will never prove[/b'] that the universe is flat - there will always be some error on the measurement. But the error is already small enough in my opinion to require any 'nearly flat' scenario to explain the fine-tuning required.

 

My attitude is that Spergel and Wright etc are the experts (they conducted WMAP and wrote the "implic. for cosm." paper) and THEY said "nearly flat" in their conclusions paragraph. So I tend to think, well, they are the mainstream experts so I will try to listen carefully and catch their drift.

 

You say in your opinion it is the "nearly flat" scenario that has a fine-tuning burden, but George Ellis appears to disagree with you in his recent Elsevier handbook article. I will get the reference. He points to a fine-tuning burden is on the other side: the "exactly flat" side. But issues around fine-tuning are unresolved and I think your opinion is a reasonable one to hold. If it is merely your opinion there is little need to discuss, other people can have different opinions.

 

You say: "the data will never prove that the universe is flat - there will always be some error on the measurement." And I certainly agree!

But you cannot similarly dismiss the possibility that the data will prove that the universe is NOT flat.

 

A high confidence error bar for Omega around 1, like [0.999, 1.001] would still include the possibility that Omega = 1.001 and the universe is not flat.

 

However a high confidence error bar bounded away from 1, say something around 1.03, like [1.029, 1.031] would arguably prove that it was NOT flat.

 

And then one could certainly bring up fine-tuning issues and ask "how in the world did it ever get that way?!!" but that's another matter. My point is that future data could arguably prove non-flatness-----although as you point out the data could not prove flatness.

 

(I think you will agree that the inability of data to prove flatness should not be used to suggest that the universe really is flat but we simply lack the means to show it.)

 

thanks for discussing these questions with me Severian! I find them very interesting. Ned Wright had some good stuff to say about this recently----I will get the link as soon as I have a free moment.

[Severian]

You say in your opinion it is the "nearly flat" scenario that has a fine-tuning burden' date=' but George Ellis appears to disagree with you in his recent Elsevier handbook article. I will get the reference. He points to a fine-tuning burden is on the other side: the "exactly flat" side. But issues around fine-tuning are unresolved and I think your opinion is a reasonable one to hold. If it is merely your opinion there is little need to discuss, other people can have different opinions.[/quote']

 

I would like to see that reference because that is certainly not the philosophy which is adopted in other fields. Generally, when an observable takes on a special value (e.g. omega = 1) then it can be quite easily explained by some symmetry argument. The clasic case is the Higgs mass - if it were zero one would simply assert that the Higgs boson was the Goldstone boson of some global symmetry, but the fact that is 'nearly zero' means that the Standard Model is fine tuned. If you (or George Ellis) can explain to me why omega nearly one is not fine tuned, then I should be able to do the same for the Higgs mass, and throw away the principal motivation for low energy supersymmetry....

 

Edit: Oh dear... Is George Ellis the same Ellis who proposed the so called 'Christian Anthropic Principle' in which he uses fine tuning to support ID?

[Martin]

... Oh dear... Is George Ellis the same Ellis who proposed the so called 'Christian Anthropic Principle' in which he uses fine tuning to support ID?

 

a standard reference:

http://www.amazon.com/gp/product/0521099064/002-2154608-8065610?v=glance&n=283155

 

The Large Scale Structure of Space-Time (Cambridge Monographs on Mathematical Physics)

by S. W. Hawking, G. F. R. Ellis

 

some 30-odd Ellis papers on arxiv:

http://arxiv.org/find/astro-ph/1/au:+Ellis_G/0/1/0/all/0/1

(much of his scholarly output was published before arxiv started, so is not available online, but these are)

 

Elsevier asked him to provide the "Issues in Cosmology" chapter for a handbook to be published I think this year. His contribution:

http://arxiv.org/abs/astro-ph/0602280

Issues in the Philosophy of Cosmology

 

I am sure that any Ellis writings about religion are separate from his profession output as a cosmologist. Offhand I can't say if he is the author of the Christian essay you mention. I hope you are not dismayed by the thought that he might write purely scientific articles on the one hand and religious speculation or moralizing on the other. You say "oh dear!" as if dismayed by the prospect:-) Perhaps you are being ironical. Anyway as long as he keeps it separate it's fine with me! I believe he belongs to the Society of Friends (the "Quakers"). Perhaps as a Presbyterian you can sympathize.;-)

[Martin]

I would like to see that reference

 

In Ellis "Issues" essay check out pages 18 and 25, if I remember right.

http://arxiv.org/abs/astro-ph/0602280

When I have a moment I will get you a quote from page 18

[Severian]

In Ellis "Issues" essay check out pages 18 and 25' date=' if I remember right.

http://arxiv.org/abs/astro-ph/0602280

When I have a moment I will get you a quote from page 18

 

Don't get me wrong, I have no problem with a scientist having an opinion on religious matters, or indeed having religious beliefs. After all, I am 'religious' and a scientist myself. But I do take issue with scientists presenting non-scientific arguments in their scientific work, and this is what Ellis is doing.

 

His position, which he expounds in his papers, is that there may not be any scientifically observable explanation of 'why' the universe is the way it is. So for example, there may be no problem with having fine tuning in the physical world because it simply 'is'. He interprets this as some sort of divine fixing of the parameters; God simply set up the universe to behave in the way he wants.

 

I have no problem with this idea (and even have some sympathy for it), but it is not a scientific notion. Science makes the initial assumption that the laws of physics exhist absolutely and are testable, and furthermore that they stem from some central principle. In other words, once we have this principle, we should be able to derive all the laws of physics from it.

 

Of course, this may not be true - it could be that the universe has no central principal and so we can never find out what it is, but science should not be asking this question. Science should be asking how do we find out what this principle is, assuming it exists. If science does not do this then it stops being science because it stops trying to explain the phenomena we see by physical laws.

 

I am actually writing a paper on fine tuning at the moment (I have a PhD student working on it) and the attitute which a scientist must take is that fine tuning is not coincidental. The cosmological constant appears to be fine-tuned to one part in 10¹²⁰, and if this is true it must have a reason. It may be that that reason is 'God', but science can never test that, and it is the responsibility of science to come up with some alternate explanation.

[Martin]

... He interprets this as some sort of divine fixing of the parameters; God simply set up the universe to behave in the way he wants.

...

 

that is curious, I hadnt noticed anything like that in Ellis essay

 

What papers do you mean?

 

Could you please give a link and a page reference?

[Martin]

In any case Ellis is not the issue. what I was responding to was what you said in post #6

The WMAP data imply the universe is spacially flat...

 

 

Saying "imply spatially flat" in my view over-interprets the data and goes against what the top WMAP people said in the conclusions section of their report "WMAP3 data: implications for cosmology".

 

these people are Spergel and Ned Wright and others of that caliber and they planned and ran WMAP and they just reported on the threeyear data and one should, I think, pay close attention.

 

In their conclusions they did not say "flat" they said "nearly flat"

and they did not say "imply", they said "consistent with"

 

Spergel et al Figure 17 gives a 68% confidence interval which says Omega greater than one.

Going by what they say there, on page 54, the interval for Omega is [1.008, 1.037].

That is consistent with a NEARLY flat universe---spatially finite with positive curvature.

 

Ned Wright, in the paper he posted last week, says cosmologists should NOT assume Omega = 1 (the flat case) in doing their analysis in future. His Figure 1 points out why thinks assuming the flat case is bad science.

 

Wright's paper

http://arxiv.org/abs/astro-ph/0603750

 

Actually I think talking about God is not germane. God and fine-tuning are not the main issues. The issue is how to interpret the WMAP3 data. I urge you to take a serious look at Wright's paper.

[Severian]

Saying "imply spatially flat" in my view over-interprets the data and goes against what the top WMAP people said in the conclusions section of their report "WMAP3 data: implications for cosmology".

 

OK - fair enough. Maybe I am being too much of a theorist. Let me withdraw the word 'implies' and say instead: The new WMAP data is consistant with a flat universe.

 

Notice that I still don't say 'nearly flat'. I admit it is also consistant with a 'nearly flat' universe, but you must also admit that it is consistant with a perfectly flat one too.

[Martin]

OK - fair enough. Maybe I am being too much of a theorist. Let me withdraw the word 'implies' and say instead: The new WMAP data is consistant with a flat universe.

 

Notice that I still don't say 'nearly flat'. I admit it is also consistant with a 'nearly flat' universe' date=' but you must also admit that it is consistant with a perfectly flat one too.[/quote']

 

Yes!

 

I certainly do say this!

 

the data is consistent with BOTH a spatially finite positive curved universe AND with one absolutely flat at large scale (of which the easiest case to imagine is that space is infinite). the finite versus infinite space issue has not been decided.

 

I am very glad that we can agree about this.

[luc]

I'd be happy if some expert could estimate the volume of a closed Universe (we all agree that a closed universe has a finite volume). I've spent the last months trying to find this information, to no avail.

 

The possibility of a closed and finite Universe is exciting, I wonder if we could ever find a way to map it in its totality. (I mean, create a map containing the localization of each galaxy in the whole Universe). If the expansion continues its accelerated pace this would be impossible, but if the Universe starts to contract, then maybe...

[Norman Albers]

Is there any out-of-doors? (I love that term.) I recall reading that the manifold of spacetime is 'unbounded'. What of this? Can things be finite yet unbounded? In a wraparound topology you can come back in on the far side of the 'screen'. Which of these concepts is still possibly part of solutions?