Effort to get us all on the same page (balloon analogy)

[marcus]

What was the density of the universe [matter per unit of space] at the time of the BB?

Harry, when we talk about all getting on the same page it is the standard cosmo model. Everybody should at least know the basics of the standard model, even though people are working on various alternative improvements.

The standard model is based on vintage 1915 non-quantum General Relativity and it breaks down at t=0.
It blows up and gives meaningless answers like "infinite curvature" and the usual thing is when a theory crashes at some point then people don't trust it near that point. At some point as you go back they figure it probably just doesn't match reality---so it has a limited range of applicability.

The breakdown is called a singularity. In the past theories with singularities have been replaced or fixed so as to get rid of the singularity (the word doesn't mean "point" it means mathematical failure).

People are working on quantum versions of Gen Rel that will lead to quantum versions of the cosmo model---that won't have this singularity.
In some of these models one can run a computer sim of conditions leading up to the BB and one can actually say what the max density is, in those models of the universe.

Until those models are tested that is just a number produced by some model. Can't say it is right.
The max density that comes out in a lot of computer runs is about 41% of Planck density.
Planck density = one Planck mass per Planck volume. You can look it up in Wikipedia.
It is an almost inconceivably high density (compared to say water at room temperature and normal atmosphere pressure)

But at least it isn't infinite!

I think gravitational time dilation is where there are two different points at different potential. The observer in the weaker field sees the other guy slowed down. In these BB models the whole universe is very high density. I don't see how you could get two observers into different situations so that time dilation could occur. Anyway, the models of the BB that they run don't have a time dilation effect like what you suggested. Maybe someone else would like to explain more about that. If you want some quantum cosmology links, say. The models where they fix the singularity (but still pretty speculative, work in progress.)

 

[Ich]

Anyway, the models of the BB that they run don't have a time dilation effect like what you suggested. Maybe someone else would like to explain more about that.

Time dilation is a coordinate-dependent concept. It means "http://en.wikipedia.org/wiki/Proper_time" ".
In cosmology, one uses coordinates where the time coordinate equals by definition the proper time of a comoving observer, so there can't possibly be time dilation in these coordinates.

 

[HarryWertM]

Very pleased to see Marcus adding to 'same page effort', and very helpful to have 'same page' more clearly delimited.

I think this question regards 'same page' cosmology. If expansion is very roughly constant at a rate of 1/140 percent per million years [from Marcus' post 11], then it would seem we could compute expansion as if it were interest, i.e., 1.00714 to the power 13700. I get 2.2 x 10e42. Two objects 1 kilometer apart 13.7 giga years ago are now 10e42 km apart? What did I do wrong?

 

[HarryWertM]

On further reflection, I think the result of my computation in last post is so absurd it is not worth examining.

But I would like to know how these numbers are derived:
-45 billion light years distance to CMB
-1090 redshift for CMB.
I understand these numbers are related, but where did either one start?

Also, I do not understand the figure of 41 million light years distance to the CMB at the time of emmision. It sounds logical that the 3000K radiation at the time of last scattering should have come from everywhere, meaning from zero light years away.

And finally, what do 2.7K and 3000K mean in frequencies? About 30 Ghz and...?

 

[HarryWertM]

From Marcus' post no. 141:

Anyway, the models of the BB that they run don't have a time dilation effect like what you suggested.

Just when I think I understand something, like there is no gravitational time shift due to increased mass density in early universe, I find something puzzling. Like:
http://www.newscientist.com/article/dn13792-cosmic-time-warp-revealed-in-slowmotion-supernovae.html"

So there is a time dilation connected with expansion?? Maybe should be mentioned in any 'same page' FAQ.

 

[marcus]

Harry, the New Scientist journalism is badly distorting. Here is the original scientific paper
http://arxiv.org/abs/0804.3595
It says nothing remarkable. The journalist jazzed it up and made it sound exciting.

The original paper says in effect that a clock at the supernova was ticking just at the same rate as a clock whould have ticked here. And the explosion happened on exactly the same schedule as a nearby supernova explosion would.

An explosion of that type takes several days to run thru some characteristic known stages and those distant SN they reported observing were proceeding exactly on schedule.

However of course the signal gets stretched out on its way by exactly the same factor as the wavelengths of the colors get stretched out. And exactly the same factor that the universe expanded and distances got stretched during the years the light was traveling. That's just the expected effect of expansion.

So we get the news slower. the stretch out factor is z+1. So if the redshift z = 2, the stretch factor is 2+1 = 3. That means the wavelengths from particular chemical elements glowing are three times longer.
And also the explosion appears to take longer. The stages appear to go by slower because the whole wavetrain got stretched in transit. The universe expanded 3-fold while the light was traveling to us.

So out at the explosion time was passing just fine exactly like here. But when we watch the explosion it is going to take 3 days to watch it go thru a stage which happens in 1 day both in a nearby SN and in fact DID happen in 24 hours out there.

All the slo-mo is in the eyes of the beholder.

===========
"stretching" is just a visualization tool, to help imagine the effect. If you want to think physically about it, try this. News of the second day events had farther to travel, to get to us, than news of the first day events. Because the distance is constantly increasing, and even one day can make a difference. So the second day pictures because they had farther to travel took longer to get here. They came in more than 24 hours afterward. That is physical reasoning. But the overall result can be imagined as the effect of taking the whole wavetrain and stretching it.

 

[hurk4]

Harry, when we talk about all getting on the same page it is the standard cosmo model. Everybody should at least know the basics of the standard model, even though people are working on various alternative improvements.

The standard model is based on vintage 1915 non-quantum General Relativity and it breaks down at t=0.
It blows up and gives meaningless answers like "infinite curvature" and the usual thing is when a theory crashes at some point then people don't trust it near that point. At some point as you go back they figure it probably just doesn't match reality---so it has a limited range of applicability.

The breakdown is called a singularity. In the past theories with singularities have been replaced or fixed so as to get rid of the singularity (the word doesn't mean "point" it means mathematical failure).

People are working on quantum versions of Gen Rel that will lead to quantum versions of the cosmo model---that won't have this singularity.
In some of these models one can run a computer sim of conditions leading up to the BB and one can actually say what the max density is, in those models of the universe.

Until those models are tested that is just a number produced by some model. Can't say it is right.
The max density that comes out in a lot of computer runs is about 41% of Planck density.
Planck density = one Planck mass per Planck volume. You can look it up in Wikipedia.
It is an almost inconceivably high density (compared to say water at room temperature and normal atmosphere pressure)

But at least it isn't infinite!

I think gravitational time dilation is where there are two different points at different potential. The observer in the weaker field sees the other guy slowed down. In these BB models the whole universe is very high density. I don't see how you could get two observers into different situations so that time dilation could occur. Anyway, the models of the BB that they run don't have a time dilation effect like what you suggested. Maybe someone else would like to explain more about that. If you want some quantum cosmology links, say. The models where they fix the singularity (but still pretty speculative, work in progress.)

Harry, when we talk about all getting on the same page it is the standard cosmo model. Everybody should at least know the basics of the standard model, even though people are working on various alternative improvements.

The standard model is based on vintage 1915 non-quantum General Relativity and it breaks down at t=0.
It blows up and gives meaningless answers like "infinite curvature" and the usual thing is when a theory crashes at some point then people don't trust it near that point. At some point as you go back they figure it probably just doesn't match reality---so it has a limited range of applicability.

The breakdown is called a singularity. In the past theories with singularities have been replaced or fixed so as to get rid of the singularity (the word doesn't mean "point" it means mathematical failure).

People are working on quantum versions of Gen Rel that will lead to quantum versions of the cosmo model---that won't have this singularity.
In some of these models one can run a computer sim of conditions leading up to the BB and one can actually say what the max density is, in those models of the universe.

Until those models are tested that is just a number produced by some model. Can't say it is right.
The max density that comes out in a lot of computer runs is about 41% of Planck density.
Planck density = one Planck mass per Planck volume. You can look it up in Wikipedia.
It is an almost inconceivably high density (compared to say water at room temperature and normal atmosphere pressure)

But at least it isn't infinite!

I think gravitational time dilation is where there are two different points at different potential. The observer in the weaker field sees the other guy slowed down. In these BB models the whole universe is very high density. I don't see how you could get two observers into different situations so that time dilation could occur. Anyway, the models of the BB that they run don't have a time dilation effect like what you suggested. Maybe someone else would like to explain more about that. If you want some quantum cosmology links, say. The models where they fix the singularity (but still pretty speculative, work in progress.)

Dear Marcus,
I think that it is more or less accepted that the most dense black hole is a Planck particle which is at the same time the smallest particle (outside a BH). Larger black holes have densities inverse to their mass. Now my question: in the models, you are referring to, is it assumed there that inside a (black)hole, or inside the eventhorizon of the related universe at tht time (instead of a singularity) there exist a pit having the total mass of the BH with 40% of the Planck-density?
Kind regards,
hurk4

 

[TheDonk]

I'm sorry if someone's asked something like this but I couldn't read all 10 pages (so far) of this post.
Assuming the universe is finite, do we know what will happen when our observable universe becomes the whole universe?
In what ways does the balloon analogy break down at and after that point?
Do we continue to see background radiation from objects we've already seen from earlier WMAP-like observations?

 

[marcus]

Donk it is not clear that our observable ever will extend to the whole universe (even assuming a simple finite universe like the 3-sphere (the "hypersphere" which is 3D analog of the 2d balloon surface).

the catch is the "cosmological constant" denoted Lambda.

The bestfit cosmo model (the one everybody uses) is called LambdaCDM because it assumes a small constant positive Lamba, the slow acceleration. CDM stands for cold dark matter. "cold" means drifting clouds, not whizzing at relativistic speeds

I'm not being evasive. The answer to your question is your assumption that observable will extend to whole is NOT RIGHT. If you take the standard cosmo model that everyone uses, it has accelerated expansion that eventually forces a horizon of about 15 billion LY because light from beyond that can't get to us and eventually the light from farther away that was already inside that range (and so will reach us) becomes so redshifted that it is worthless as a signal.

In the far distant future the LambdaCDM universe is a lousy place to do astronomy because of this continued slow acceleration caused by Lambda.

My reservation about this is that math models are only good where they fit the data. extrapolating with a model beyond where you can check is speculation. How do we know that Lambda really is constant? they keep checking it with more and more data and it keeps looking constant, but what if 20 billion years from now it began to change noticeably?

suppose this current observed acceleration slows and stops,etc etc. then all bets are off.
You just have to realize that these very long range predictions are based on a specific math model.

that said. I see no reason not to use the conventional mainstream model as the best we have, and trust it to a reasonable extent.
a longterm picture of the LCDM future is written up by Larry Krauss. the PDF is free
http://arxiv.org/abs/0704.0221 and also they made a SciAm article about it
http://www.scientificamerican.com/article.cfm?id=the-end-of-cosmology
the idea is the U keeps on expanding, but it LOOKS static because future astronomers will not be able to see anything receding from us (all the stuff will have gone out past the horizon) we will only have our own galaxy (held together by its gravity)

I may not have answered your main question. Feel free to keep asking and asking. I just gave you a random bunch of stuff for starters.

 

[budrap]

So out at the explosion time was passing just fine exactly like here. But when we watch the explosion it is going to take 3 days to watch it go thru a stage which happens in 1 day both in a nearby SN and in fact DID happen in 24 hours out there.

All the slo-mo is in the eyes of the beholder.

===========
"stretching" is just a visualization tool, to help imagine the effect. If you want to think physically about it, try this. News of the second day events had farther to travel, to get to us, than news of the first day events. Because the distance is constantly increasing, and even one day can make a difference. So the second day pictures because they had farther to travel took longer to get here. They came in more than 24 hours afterward. That is physical reasoning. But the overall result can be imagined as the effect of taking the whole wavetrain and stretching it.

That's effectively the same as gravitational redshifting/time dilation isn't it?

 

[marcus]

That's effectively the same as gravitational redshifting/time dilation isn't it?

I would say not, Bud. Instead I'd say it is effectively the same (in fact exactly the same) effect as the ordinary cosmological redshift. Little or no gravitational effect needs to be factored in.

The distance to the supernova was expanding, so the news report gets spread out over more days, by exactly the same ratio as the wavelengths of the light get extended.

 

[budrap]

I would say not, Bud. Instead I'd say it is effectively the same (in fact exactly the same) effect as the ordinary cosmological redshift. Little or no gravitational effect needs to be factored in.

The distance to the supernova was expanding, so the news report gets spread out over more days, by exactly the same ratio as the wavelengths of the light get extended.

I guess what I meant was couldn't a properly structured gravitational field produce the same effect?

 

[marcus]

I guess what I meant was couldn't a properly structured gravitational field produce the same effect?

Keep in mind that the same redshift (and spreading out of the news) is affecting every other star that we can see in the galaxy where the supernova lives. So you would have to "properly structure" a humongous gravitational field in order to imitate the natural effect of expanding distance.

It's hard to imagine how such a field could be set up. But sure, in individual cases, say by placing a supermassive black hole near the star about to go supernova, one should be able to get enough gravitational redshift. The star's own gravity would hardly suffice not for the size redshift typically observed. And then one would be able to observe the effects of the supermassive BH or whatever was causing the deep potential well in which the supernova was occurring.

I don't see this as a helpful speculation here in this thread which is aimed at being of general usefulness/relevance. Let's drop the discussion. Please do start a separate thread on your own to speculate about the affects of gravitational redshift on supernovae.

 

[marcus]

In another thread, one of the PF mentors happened to give an especially concise statement of what I think is the general policy on PF's Cosmology forum topics and content:
https://www.physicsforums.com/showthread.php?p=3004403#post3004403
It was in connection with closing the other thread, where the content had gotten away from professionally researched mainstream cosmology and gone too much in the personal, philosophical and amateur direction.

It's a clear "mission statement" about Cosmo forum so I want to keep tabs on it by saving the link in this thread (we may eventually lose track of the other thread.)

 

[Farahday]

It would seem to me that the mathematical incongruities of almost ANY falsely premised theory could easily be reconciled by the use of additional falsely premised assumptions and calculations that were reverse engineered to force correct results from the flawed hypothesis.

Hypothetical dark energy and matter are crucial to the expansion hypothesis and blind acceptance of the expansion model is, itself, crucial to the reconciliation of observations that the rate of recession of the more distant galaxies appears to be exceeding the speed of light.

 

[marcus]

We still don't know whether the start of expansion was a big bounce or something else. We don't know if the U was spatially infinite at the start of expansion, or finite 3D volume.
But the balloon analogy, which assumes a finite volume at the start, is a good conceptual introduction. The assumed finiteness of space is a convenience that makes it easier to think about.

So to help myself picture the U as an expanding 3D hypersphere I would like to know WHAT IS THE MINIMUM PRESENTDAY SIZE it could have consistent with the latest data. The latest WMAP report (WMAP7, the 7 year data) gave a 95% confidence interval for Omega_k which was
[-0.0133, 0.0084].

This means that the SMALLEST RADIUS OF CURVATURE she could have, with 95% confidence, is 13.2/sqrt(0.0133) = 114 billion lightyears.

Actually 114.5 if we postpone rounding off. It's all approximate anyway. Multiply by 2 PI and you get 719 billion lightyears. So that is the present circumference of the 3D hypersphere we live in, the smallest that it could be (95% confidence). If you could stop expansion now and set off at the speed of light it would take you 719 billion years to circumnavigate. Minimum. 95% certain.

If you want to use a more precise figure for the Hubble radius than my simple 13.2, feel free, but it is all just approximate anyway. WMAP7 Komatsu et al used a figure of 74.2 for presentday Hubble and I'm trying to keep consistent with them.

Now we know the redshift of the Ancient Light that we see is 1090. So we can ask a simple question about this minimum-size Universe namely how big was the universe when the fog cleared and the ancient light escaped and set out on its way everywhere in all directions along the surface of the balloon/.

719 billion/1090 = 660 million
114.5 billion/1090 = 105 million

OK. We won't talk about the radius of curvature because it is a math convention. You coudn't TRAVEL it. Because there is no inside or outside of the balloon. Existence is concentrated on the balloon surface and there are no directions pointing off the surface. But the circumference is a real physical distance that you could travel. At the moment that transparency occurred the circumference of the hypersphere was 660 million lightyears. Minimum.

There were no stars or galaxies yet. There was just hot gas filling all space. Around 3000 Kelvin. Glowing hot. Hotter than the inside of a pottery kiln or blast furnace. But thinned out enough to be transparent. It hadn't started to condense into stars yet.

That hot hypersphere uniformly filled with gas is what you start by imagining when you watch its little 2D animated cousin at Ned Wright's website. The little blue wiggly things are the photons. The galaxies aren't even separated from each other yet--their material is still spread out as gas. Even someone who has watched it before can probably learn something by thoughtfully watching the animation again:

Google "wright balloon model" or just go to
http://www.astro.ucla.edu/~wright/Balloon2.html

As time goes on the photon wigglers get longer and change color---reminding us about redshift, the stretching out of wavelengths.

 

[v2kkim]

On TV science channel, I heard the actual univ. size is about 20% larger that the visual univ. to us.

 

[marcus]

If anyone wants technical sources for my post, see page 4 table 2 of
http://arxiv.org/abs/0803.0547
Komatsu et al, the official NASA report on cosmo implications of the WMAP5 data.
Look at note g of that table for a formula for the radius of curvature.

I took the figure of 0.0133 from the more recent WMAP7 report.
http://arxiv.org/abs/1001.4538
See page 17 section 4.3.
Or look at their page 3 table 2 rightmost column labeled "WMAP+BAO+H₀"
============
In case anyone is interested in comparing SIZES, in this minimum size U consistent with the data, since the circumf is about 720, the most distant matter from us is about 360 billion lightyears from here. Now thinking of the VISIBLE PATCH, the most distant matter we have gotten light from is currently about 45 billion lightyears from us. That is the matter that emitted the ancient light that we are now receiving. Now the ratio of those two distances is 360/45 = 8. So you could say that the actual real U is at least 8 times larger than the currently visible portion. But that is a comparison of linear sizes, like comparing the circumference of the whole balloon with the diameter of a disk-like patch on one side of it.

Maybe some people would prefer to compare VOLUMES analogous to comparing the area of the whole balloon with the area of a disk-shaped patch. Now in terms of the obvious volume units, the 3D VOLUME of the hypersphere which is our minimum-sized U is 2 pi² 114³=29,240,000
and the 3D volume of our visible portion is 4 pi/3 45³=380,000
so the ratio of volumes is 29,240/380 = 77
So in volume terms the smallest the U could be would still be 77 times the volume of what we can see.

Comparing the distance from here to the most distant matter is perhaps a bit more comfortable. 8 times. The most distant visible matter is 1/8 as far as the most distant matter in the smallest U compatible with the data.

Linear distance and volume are two very different ways of comparing "size".

 

[Farahday]

On TV science channel, I heard the actual univ. size is about 20% larger that the visual univ. to us.

Why would you assume existence is the result of cause and effect (creation) and why would you assume the universe has a size - especially a finite one?

 

[marcus]

Caveat: Ordinarily we don't use philosophical arguments here in Cosmo forum. Our main job is understanding professional cosmology. We keep pretty much focused on that: Asking and answering questions about standard cosmo. Steering clear of speculation. And not getting off into philosophical issues.

Nevertheless this was a cogent argument that one should not attribute a beginning to existence.
https://www.physicsforums.com/showthread.php?p=3182621#post3182621
Without getting mired in abstract discussion, I want to keep tabs on that.

I think people often confuse the start of expansion with "beginning of time"---when they should not, since there is no scientific reason to equate the two. Vintage 1915 General Rel breaks down at the start of expansion, but alternative models that do not break down are being studied, and some reproduce standard cosmology and fit the data just as well. We are not forever committed to using a model that breaks and cannot extend back before the start of expansion.

So personally I try to avoid using the overpopularized term Big Bang because of naive misconceptions associated with it.

That said, these issues are not what this thread is supposed to be about. So if you want, you can start a new thread. Or write me a PM explaining the topic you have in mind--and I might start a thread.

About SIZE, Farahday, a spatially finite universe is one case that we can consider. We don't have enough information to exclude either the finite or the infinite case. So we are free to estimate a minimum size in the case that it is finite. We can say IF it is finite then it cannot be smaller than suchandsuch.

This also seemed like an astute comment---about "proclivities" of our local cultural tradition:
https://www.physicsforums.com/showpost.php?p=3190572&postcount=94
You might be able to start a discussion of that in the HUMANITIES forum. I post there sometime. But it doesn't seem to work in Cosmo forum.

 

[marcus]

Yenchin pointed us to a nice discussion here
http://blogs.discovermagazine.com/cosmicvariance/2010/02/22/energy-is-not-conserved/
about the nonconservation of energy when geometry is changing, as in Gen Rel. and therefore in cosmology.

 

[RayYates]

I am new to this forum, but it has already cleared up some of my misconceptions. As an addendum to the balloon analogy I find my self visualizing two points (pennies if you will) on the balloon and would like to contribute this analogy.

I'm sitting on a rubber surface holding a marble forty one steps away from a target. I flick my marble at light speed toward the target and at the same time the rubber starts stretching faster than the marble is rolling. Even though the marble is rolling on the surface at light speed it is moving away from the target.*

Eventually the stretching slows down and when the marble finally hits the target it has actually traveled for a very long time and I am now sitting 4500 steps away.

However, even though the distance between me and the target has grown, I am the same size, because I'm self contained.

Does this seem correct?

 

[Farahday]

Sounds silly, doesn't it?

There is an axiom which is not Newtonian or Einsteinian, it is simple logic (without which there would be no science): Before something can change, before something can act or be acted upon, it must exist.

Since any who might dissent must believe in things that don't exist the confidence factor of this precept approaches 100%.

What is the significance of this axiom?

If existence is required in order for change to occur, then cause and effect is a function of existence, something derived from the phenomenon of being. No phenomenon can be the product of its own subordinate derivative, so existence is the source of cause and effect, not the result of it. Existence is not the product of creation - whether it is posed in the form of Genesis or Big Bang.

While it may be tempting to defer to the ostensibly superior knowledge of scholarly pundits with names suffixed with magna cum laudinous strings of academic labels, the sad truth is that modern versions of creation are based upon the central ancient Judeo-Christian theological misperception that still prowls the dawn of human enlightenment - CREATION.

The mathematical incongruities of any falsely premised theory can easily be reconciled by the use of additional false premises and calculations reverse engineered to force the correct results, and in order to justify their theories de jure, these pundits are reverse engineering mathematical formulae to include implausible existences (dark matter or energy - two conditions of the same thing) and illogical conclusions (the universe is expanding when it is already infinite).

Conventional cosmology is so far off track it may take centuries before they realize they are chasing stampeding Unicorns.

 

[derek101]

i am new to this forum.when i try to vizualize balloon analogy,i start with the big bang,matter and energy expanding away from a singularity.then at some point matter and energy begins to clump to together forming black holes and galaxies.with all the energy funneling in excelerating the matter awy from the surface.
my balloon now looks like the shell of a conker(covered in spikes)where the spikes represent the black holes.
am i going wrong?

 

[logics]

==quote oldman (with emphasis)==
Cosmologists have no option but to rely on a huge body of circumstantial *evidence
==endquote==
...*Gallileo is supposed to have said "E pur' si muove." And we can take the lesson of dynamic geometry seriously and say likewise
"E pur' si bende---e pur' si stretche---e pur' si expande." Eh!

hi, marcus, thanks for this fabulous thread.

I wouldn't like to put my first foot wrong, but I think the analogy * doesn't help you: Galileo was refuting strong evidence, universal everyday experience that is: "appearance that Earth does not move"
In your case you have no hard facts, your *"evidence" is just radiation that has traveled much longer than fatamorgana : you are not refuting it, not even doubting it.
In real world you can take the straw out of the glass and see it is not broken or travel on, and find out there is no "fake water". In cosmology you just can't, ergo: refuting should be the rule, and,a fortiori , whenever "evidence" is "appearance in contrast with the experimented laws of physics". There might be a dozen of unknown reasons why radiation should "get tired" after such a long journey, after being reflected, refracted, bent and...what else

Am I wrong?, if I am, I apologize.

You say that (during BB and) in some regions "universe (*space, *geometry[Hubble's law]) is *expanding *faster than light".
Well, relativity has built up a fortune on the invariance of C, speed of light is the only sure thing [constant] in this world, am I allowed to say:
wouldn't prudence suggest you entertain a dozen doubts, suspicions before venturing such extreme deductions? are you perhaps trusting a mirage?

 

[marcus]

Hello Mr or Ms Logics and welcome. Here is the context you quoted from.

...

This statement I like very much, so will highlight in blue:
==quote oldman (with emphasis)==

Cosmologists have no option but to rely on a huge body of circumstantial evidence that has been accumulated over the years, much of which confirms predictions of the model, to validate their imagined model of the universe. This evidence is very persuasive indeed, and the LCDM model, based on the best description of gravity we have, is the best description of our mysterious universe so far invented.

But there remain puzzles...

==endquote==

Perhaps one thing that needs to be mentioned here is that this best description of gravity we have teaches us that we have no right to expect distances to remain the same and triangles to add up to 180 degrees inside. Gravity is geometry and geometry is something that evolves dynamically---this may cause Joe Plumber and the rest of us some qualms when we first confront it. But "General Geometrivity" is verified by experiment right here in the solar system---we must grin and bear it.

Gallileo is supposed to have said "E pur' si muove." And we can take the lesson of dynamic geometry seriously and say likewise
"E pur' si bende---e pur' si stretche---e pur' si expande." Eh!

Logics, you sound as if you may be confused about something. It sounds as if you think the evidence is limited to REDSHIFT observations. So it seems like you think that if you could explain away the redshift as resulting from the light getting "tired" then the evidence would go away
But there would still be a whole bunch left. Oldman was serious when he said there was a huge body of evidence. The geometric law of gravity has been checked over the past 90 years again and again in a lot of different ways.

It is almost certainly wrong (or at least improvable by quantizing to apply to extreme density conditions) but it is impressively accurate and definitely the best we have so far. Every time somebody thinks of a new way to test it using a new kind of measurement, people do it. Part of the excitement of science is always trying to catch the law in an error and then striving to improve the law to get a better fit.

Anyway distance expansion is part and parcel of the whole dynamic geometry package. If you know of a better law of gravity that fits all the experimental data---including earthbound, and right here in solar system, and within our own galaxy with pulsars and all---then please let the world know. I can't keep track of all the experimental tests.

BTW you sounded conditionally apologetic at one point in your post and there is definitely no need for that! It is good to ask questions!

 

[logics]

numbers,bold added

1) Hello Mr Logics and welcome. 3) It sounds as if you think the evidence is limited. 4) But there would still be a whole bunch left.
2) If you know of a better law of gravity that fits all the experimental data---then please let the world know. 1b) no need for that! It is good to ask questions!

1) Thanks, marcus for warm welcome. I like your style, you are not dogmatic, that's why I ventured my first post here! You responded to my bantering premise and overlooked the main question, (1b) I am glad you can take my questions, when I am sure you can take my answers I'll respond seriously to (2) your banter (or sarcasm^?) and tell you, not my law, but whose law and ideas, can help you find the truth, the answer to your problems.

3) What I think is not important, but if you recall the logical and epistemological premises of our issue, you'll see there is no evidence, and cannot be any for " BB theory (model) ". No scientific theory can be verified, proven; to make things worse, BB is a one-off event and is not even within the jurisdiction of scientific method, the more prudent "circumstantial evidence" of your quote is just some concrete data (I hope you'll specify: redshift ..and...4) what else?). From these data you make a long chain of(educated-)guesses and deductions. I am chiefly going to question, (if you allow me), to probe the logical validity of these deductions and to compare your statements with valid laws of physics.
I usually try to avoid cumbersome quotes, so, probably it was not clear I was referring to this:

... never say that space expands. Distances between widely separated observers each at rest relative to the Background do increase. That is Hubble law.

The trouble with BB is that you never know what is the current version, you can read everywhere that: "...during BB there was no explosion, space expanded, inflated faster than light...". Probably theorists realized, at last, that space cannot expand and even if could expand could no-way drag matter and planets. That's good news, but out of the frying pan... now it is geometry [Hubble's law] that makes distances increase. That is the key issue, and the weak point of the theory: explosion requires energy, try, now, to explain, justify that celestial bodies ar moving apart without (kinetic)energy!

You say that (during BB and) in some regions "universe (*space, *geometry[Hubble's law]) is *expanding *faster than light". Well, relativity has built up a fortune on the invariance of C...

probably, (for member who do not read signatures), I must specify that * means "gratis", "not proven/defined", "gratis negatur"
My request was and is, please say what are the concrete data and the logical deductions that justify that conclusion: universe is expanding without energy being spent, speed may be faster than C.
(P.S. just in case this is my last post)
Please, marcus, do not abandon the balloon analogy, it is the only logical, geometrical, topological, physical possible model, the one that can drive you bang to the truth

 

[logics]

Read the first 10 or 20 posts on this thread. 1) I never say that space expands. Distances between widely separated observers each at rest relative to the Background do increase. That is 2b) Hubble law. It's about 2) geometry, not about some substance called "space"..

Hi, marcus, to save time (I visited the ucla site you call your "country" in your profile and) I read your posts from 2007 and was happy to see that: you never said that space expands, at least from that date. But, the pdf [(page 5) they recommend at FAQ (brockwell) http://www.mso.anu.edu.au/~charley/papers/LineweaverDavisSciAm.pdf" ] clearly says: "it was an explosion of space itself", now

1) Is yours a different view, is it only your personal opinion ?
2) is 'geometry' referred only to space (geometry package)? (in post #166, is the following sentence " If you know a better law a gravity..." related to "geometry package", or its position there is only casual ?)
2b) is 'geometry' referred to Hubble law? Can Hubble law be the reason or a proof of the expansion?

(P.S. When I say "speed faster than C", naturally I mean speed of particles, bodies.
Of course relative speed , usually 2 x C, if universe is expanding must be updated to over 3 x C
(Does news from CERN affect our issue?))

 

[Lost in Space]

Isn't the balloon analogy too simplistic? A balloon has to be contained in a bigger dimensional space. So if our universe is expanding doesn't this mean that it has to be expanding into something? Not only this, but on an expanding balloon all points on the surface expand at the same rate. Therefore, galaxies on the surface of the balloon would be expanding in size proportionately to the space between them, so is there any real expansion at all to someone sitting inside one of these galaxies and making observations?

I've argued this point with others on this forum previously but have been told by mentors etc. that the space inside galaxies doesn't expand as fast as the space between the galaxies.

 

[RayYates]

...So if our universe is expanding doesn't this mean that it has to be expanding into something?

The balloon surface is 2D. You have to envision the entire universe as the 3D surface of the balloon. In 3D, no matter what direction you point you can't get off the surface of the balloon. Also consider the inside of the balloon as the past, and the outside of the balloon as the future. so the balloon actually is expanding into something; the future. There may be other balloons, they may bump into each other. But that's another theory.

Not only this, but on an expanding balloon all points on the surface expand at the same rate. Therefore, galaxies on the surface of the balloon would be expanding in size proportionately to the space between them, so is there any real expansion at all to someone sitting inside one of these galaxies and making observations? I've argued this point with others on this forum previously but have been told by mentors etc. that the space inside galaxies doesn't expand as fast as the space between the galaxies.

As I understand it, the force that binds the galaxies together gravity, mostly from Dark Matter, causes them to be "self contained" and less affected by the expansion of cosmic space-time. You have to consider the balloon surface in that context. Three dimensions of space (the surface of the balloon is the entire universe) and one of time (in the past it was smaller) and finally gravity that binds the pennies (galaxies) together and resists the expansion.

 

[marcus]

Thanks RayYates! I was busy with other stuff and forgot to check this thread---didn't see the new posts until just now. You said everything needed I think---at any rate I agree.

 

[DaveC426913]

...on an expanding balloon all points on the surface expand at the same rate. Therefore, galaxies on the surface of the balloon would be expanding in size proportionately to the space between them, so is there any real expansion at all to someone sitting inside one of these galaxies and making observations?

In the balloon analogy I use, galaxies are represented by pennies glued to the balloon. You can see that the pennies do not grow as the balloon's expansion pulls adjacent galaxies apart. Problem solved.

The pennies addition has one other bonus thing in the process.

Whenever discussing the expansion of universe, the very next question is almost inevitably asked is: so is the Earth is getting farther from the Sun, and are atoms are spreading out in our bodies?

Using pennies glued to a balloon, we see that the pennies obviously don't get ripped apart. We know a penny's cohesion can easily overcome any expansive force by the glue. So now it is intuitively obvious why the gravitational cohesion of a galaxy, solar system, or atomic object easily overcomes any expansive force of the universe. Like the glue, the expansive is simply far too weak.

 

[marcus]

...
(P.S. When I say "speed faster than C", naturally I mean speed of particles, bodies.
Of course relative speed , usually 2 x C, if universe is expanding must be updated to over 3 x C
(Does news from CERN affect our issue?))

Hi Logics, the neutrino news is most likely due to an experimental error and the result will not be confirmed. We just have to wait and see---avoid drawing conclusions.

Metaphors like "explosion of space itself" can be misleading. The Lineweaver SciAm article isn't perfect, but it has helped a lot of people understand expansion cosmology.

If the "Charley" article really does not work for you, I can offer a different catechism, a different set of words, and we can try that. Mathematical realities can be dressed in different suits of verbal clothes. Don't worry if my words are different from Lineweaver's. It's the same math model just presented in different verbiage. see if it works.

Our law of gravity is the GR equation. It describes motions much more precisely than Newton, motions of satellites, gyroscopes, the progress of clocks the spiraling of pulsar stars etc. It has been checked and rechecked---amazingly precise.

In GR space has no objective material existence. What exists is geometry, a bunch of distances.
The GR equation (the best-working law of gravity) is a law of DYNAMIC GEOMETRY descrbing how geometry changes with time, and how it is affected by matter, and how it has curvature.

The GR equation strongly hints that largescale distances ought to be either expanding (and large enough ones expanding at a rate faster than c) or else contracting (and again the large enough ones contracting faster than c).
You can't throw GR out because we have no more precise reliable law of gravity. But if you accept GR then you have to acknowledge that in the simplest most natural solutions of the GR equation the very large distances will be expanding. Or in the other case contracting.

This is not motion. It does not get anybody anywhere. It simply means that on a very large scale things (eg clusters of galaxies) are getting farther apart.
Since nobody is going anywhere(except into the future )nobody is breaking any speed limit.

In a world where geometry changes dynamically with time (according to the meticulously checked law of gravity) it is only natural for largescale distances to be expanding at rates faster than c. This is what relativity tells us to expect.

==================
Logics since you have been reading up, I assume you know that the distance concept used here is proper distance---the actual distance at a certain moment that you would measure with whatever conventional device if you could freeze the expansion process at that moment, so it wouldn't change on you while you were measuring. This is the most convenient type and is what is used in defining cosmic models and formulating stuff like Hubble law etc.

If you are working on grasping the mathematical reality instead of just the words, then you will have noticed that in the Wright balloon model you can actually see galaxies receding from each other at rates faster than c. You just have to watch the simulation. You will see distances (between two widely separated galaxies) which are growing faster than the little photons are moving. If you did not notice, it might be worth going back and concentrating on it. things like that can help build understanding at a nonverbal level, or so I think.

Thanks for reminding me to update my Profile! I changed the "country" to be the balloon model animation

 

[logics]

consider the inside of the balloon as the *past, and the outside of the balloon as the *future. so the balloon actually is expanding into something; the future.

You said everything needed I think---at any rate I agree.

I changed the "country" to be the *balloon model animation

I'll discuss analogy first, hoping there will be no need to discuss "SR, gravity, geometry..."

If we want to make an analogy of the standard [or any] model we must be sure that scale model shares its key properties. Yes, I have been reading a lot before starting posting, I noticed your peculiar style [of challenging davids]. I'll not quote wiki or other, [because anything could be doubted], but FAQ's, written by our best cosmologist(s):
"...universe is very nearly flat.[Komatsu]...", "...and flat types have infinite spatial volume...", "...time and space did *not exist before the BB...", "...BB happened uniformly, everywhere and at once" ., "...only points on the 2D surface of the balloon represent actual points in space."

Standars model : Ω = 1, flavour = flat, space = infinite,, time = 13blyr, origin = everywhere, present = surface
analogy* : Ω > 1, type = curved/sphere, space = finite, origin = point/ *center of sphere, present = pennies into *future

So, our analogy is not even a bad, false analogy, it is not at all an analogy, it is the analogy of a completely different model
Analogy is used also to make a trivial (in)formal fallacy http://en.wikipedia.org/wiki/equivocation" , exchanging expand=inflate of the explosion [which is therewith negated] with expand= "si stretche" of the rubber surface.
FAQ has, among others, these contradictions:a) if time and space did not exist before BB then $\rightarrow$ laws of physics did not exist/work,[actually nothing existed because time/space are categories of being, pre-requisites for existence], so $\rightarrow$ BB couldn't happen, and $\rightarrow$ everywhere did not exist; b) if time and space began 13blyr ago [then]$\rightarrow$ space/universe cannot be infinite, unless speed of expansion is infinite, etc..

But analogy *'s most dangerous fallacy, that opens a Pandora's box of "geometric" fallacies is the floating "pennies". In any model you can imagine, galaxies are not pennies or ants walking on the balloon, but are the rubber molecules of the balloon.

I reminded you that thin ice is cracking under the feet of anyone who attempts to make a theory about a one-off event, but if the theory itself is incoherent, has internal contradictions or fallacies it falsify itself and "gratis negatur" _Euclid. I did not negate it gratis, I presented some arguments, and I can present many more.

I apologize in advance if I misquoted, made any mistakes,etc..: I'll immediately accept corrections, but the main logical argument remains valid.

 

[marcus]

Logics, you seem to want to critique standard cosmology! Maybe you should start a separate thread where you can explain your arguments that it is logically inconsistent.