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

[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.

 

[DaveC426913]

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.

Oops. I see the pennies feature has been introduced here weeks ago.

 

[Lost in Space]

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.

The pennies analogy is a good one, although using this analogy, surely the galaxies would have been much closer together and more gravitationally tied to each other in the past as well as being effectively larger in comparison to the total volume of space? Shouldn't they now be more closer together than they are?

 

[Lost in Space]

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.

If the universe is expanding into the future doesn't this imply that the future already exists?

 

[DaveC426913]

The pennies analogy is a good one, although using this analogy, surely the galaxies would have been much closer together and more gravitationally tied to each other in the past as well as being effectively larger in comparison to the total volume of space? Shouldn't they now be more closer together than they are?

Any analogy only goes so far. This is an analogy in qualities, not in quantities. It demonstrates the principle, not the execution.

 

[Lost in Space]

Any analogy only goes so far. This is an analogy in qualities, not in quantities. It demonstrates the principle, not the execution.

Yes, I appreciate the limitations of analogy. So does this mean that the expansion energy of space must have been much greater in the past than the gravity binding the galaxies together, even though they were a lot closer to each other? I've discussed this before on other threads because of local effects such as superclusters and galactic collision. Does it mean that the expansion is not uniform, and could it have something to do with the uneven distribution of mass in the early universe?

 

[RayYates]

...Does it mean that the expansion is not uniform, and could it have something to do with the uneven distribution of mass in the early universe?

I've wondered that myself and hope someone can clarify that point.

More specifically I have less problem with the notion of Dark Energy than Dark Matter; in that I wonder if the "Dark Matter" binding galaxies together is a space-time effect of the rotation. Like a whirl pool in the cosmic stream keeping the debris together and to an observer, moving too fast.

If this is flat wrong, please tell me how so I can get this picture out of my head.

 

[DaveC426913]

I've wondered that myself and hope someone can clarify that point.

More specifically I have less problem with the notion of Dark Energy than Dark Matter; in that I wonder if the "Dark Matter" binding galaxies together is a space-time effect of the rotation. Like a whirl pool in the cosmic stream keeping the debris together and to an observer, moving too fast.

If this is flat wrong, please tell me how so I can get this picture out of my head.

There are several independent sources of evidence of Dark Matter. Some have nothing to do with rotating galaxies. Look up the Bullet Cluster.

 

[Farahday]

On the expanding balloon there is a point within a finite distance from any given origin at which motion in any direction will not increase the distance between the two points. Are you saying this is the case with the "expanding Universe"?

 

[RayYates]

There are several independent sources of evidence of Dark Matter. Some have nothing to do with rotating galaxies. Look up the Bullet Cluster.

Thanks. Fascinating reading.

 

[Lost in Space]

On the expanding balloon there is a point within a finite distance from any given origin at which motion in any direction will not increase the distance between the two points. Are you saying this is the case with the "expanding Universe"?

A balloon can only expand so far before it bursts as its composition is finite. It's an interesting thought however, that some claim the universe can seemingly expand forever. If so spacetime has a beginning but no apparent end therefore it might or might not say something about the infinite. It's hard to imagine that in the very distant future after protons and quarks have decayed whether anything will be left to define the passing of time as we now understand it. According to quantum theory any form of matter left including strings would be unable to completely stop vibrating so the universe will never reach a temperature of absolute zero. But then again what about leakage of energy due to quantum effects? If the vacuum is caused by quantum fluctuations would these define the passing of time alone or would vibrating strings that still survive define the passing of time even if they were dispersed by cosmic distances?

 

[DaveC426913]

On the expanding balloon there is a point within a finite distance from any given origin at which motion in any direction will not increase the distance between the two points.

What point is that?

Are you saying this is the case with the "expanding Universe"?

Not until I grant your assertion above.

[ Aside ]
I may be misunderstanding, but if I take your question literally, there are an infinite number of points that meet your criteria.

Here's what you wrote:

... there is a point within a finite distance from any given origin at which motion in any direction will not increase the distance between the two points.

So: point B - which is one light year distant from point A - is completely free to move anywhere on a sphere one light year in radius from point A. i.e. Motion of B in any direction does not increase the distance between A and B. that meets your criteria. An infinite number of points do.

Since this is a trivial case, I assume it's not what you meant. So what did you mean?
[/ Aside ]

 

[RayYates]

If increasing gravity slows time then time inside galaxies is slower than time between galaxies. If this assumption is correct, how would it affect red shift used to calculate the recession of galaxies?

 

[marcus]

If increasing gravity slows time then time inside galaxies is slower than time between galaxies. If this assumption is correct, how would it affect red shift used to calculate the recession of galaxies?

Hi Ray, you and Dave have been having a good Q/A conversation (good concise Q's and A's) so I'm reluctant to jump in. Maybe Dave will confirm my rough estimate that the grav. redshift effect would typically be so slight as to be lost in the noise. You can look up "grav. redshift" on Wkpd and do the numbers.

The effect was only measured in the radiation from a star sometime in 1955-65. It is so faint it is very hard to detect.

And it is proportional to M/R the mass divided by the distance from center where the photon is emitted. If it is emitted farther from center the effect is less.

The mass of a galaxy might be 10¹¹ times the mass of a star. But a typical light source in the galaxy could be at a distance of 10,000 lightyears from center which is about 10¹¹ times the radius of a star.

So a photon emitted from a star at a moderate distance from center will suffer a grav. redshift from the galaxy gravity which is roughly the same size as what it suffers from the star itself.

And that effect (of the star's gravity) is so tiny that it took sophisticated technique to measure. It was a standing challenge for many years, finally overcome around 1960.

Practically speaking that slight effect would be all smeared out because spectral lines are fuzzy and the light from a galaxy comes from billions of stars at all different distances from center and contributing random motion doppler effects and so on.

In the CMB, the grav redshift (socalled Sachs-Wolfe effect) is about 10^-5 or one thousandth of one percent. This is a rare case where fortunate circumstances allow it to be measured. It is interesting, but it doesn't compete in size with the cosmological redshift which for a typical galaxy is several hundred percent. In other words, recession effect overwhelms gravity effect.

 

[Lost in Space]

In the CMB, the grav redshift (socalled Sachs-Wolfe effect) is about 10^-5 or one thousandth of one percent. This is a rare case where fortunate circumstances allow it to be measured. It is interesting, but it doesn't compete in size with the cosmological redshift which for a typical galaxy is several hundred percent. In other words, recession effect overwhelms gravity effect.

If increased redshift is due to greater distance and gravity is of little consequence as you seem to be sayng, is this also true of the redshift of two comparable galaxies of the same distance in which one has been Einstein lensed? In other words will the lensed galaxy be more redshifted than the one that isn't or will there be no difference and if there was a difference would it be dependent on the strength of the gravity field of the lensing object? Would the distance of the source subject be significant? If there is a difference would it be more noticeable with a similar example being observed at a greater distance as the redshift increases?

Just wondered as spacetime is curved due to the intervening lensing object whether a black hole or galaxy etc. I would have thought that the lensing objects would affect time within their influence and the light from the source object would have to travel further as well. Surely if the light has to travel further, won't it be more redshifted?

 

[marcus]

Hi LiS, the conventional formula for the cosmological redshift has it depend on the proportion that distances have increased during the time the light was in transit.

z + 1 = a(now)/a(then)

a(t) is the scale factor. Most basic function in cosmology. It is what theFriedman equation tells you about.

a(now)/a(then) = 3 would mean that largescale distances were now 3X what they were when the light was emitted and set out on its journey to us.

And then z + 1 = 3 so we would say that z = 2.

So if two bunches of light arrive today, having traveled across open space to us from distant places, then the one that has traveled longest time will be the most redshifted.

Simply because distances will have expanded more while it was in transit for the longer time.

But the lensing you talk about only has a very slight effect on the total path and on the travel time, as a rule. I don't imagine it would make much of a difference.

Still the principle you suggest holds, I think. Bent path means longer travel time. Longer transit time means more time for distances to expand. More expansion means more redshift.

I just came across an interesting paper on dimensionless cosmology. Don't know where to park the link so I'll leave it here for the time being:
http://arxiv.org/abs/1109.0492
Popular account of possible varying alpha constant:
http://astronomy.swin.edu.au/~mmurphy/res.html
Technical paper about it in Physical Review Letters
http://arxiv.org/abs/1008.3907
Douglas Scott (UBC Vancouver) looks like someone to watch on this one.

 

[Mathbrain]

I have read the entire post, and I still have some questions:

1 - Given two galaxy clusters A and B that lie on a line L at time T, where A and B are moving perpendiculr to L as time goes by. At some future time F, we can draw a diagon line D from A at T to B at F. If D is a constant distance, light from A at T will reach B at F. If we can predict the location of B at F, then we can calculate D. My question is given that A and B are moving perpendicular to L at a predictible rate, can we predict D, or will the distance D change by some variables?

2 - Are all instances of CMB from the Big Bang? If so, how is it that we can constantly sense CMB? They would need to be moving at different speeds, or bouncing off something.

WRT baloon analogy.
I think that readers of this forum should be aware that the 2D skin of the baloon is meant to represent a 3D space. Furthermore the baloon analogy is incapable of showing the curvature of space, as an extra dimension is require to express curvature in a geometric manner. That is you can't show 2D space being curved in a 2D space, only a 2D representation of 3D space. I think readers should also be informed that a dimension needs to be perpendicular to all other dimensions, and that a dimension is not an alternate reality.

I'm not saying that the baloon analogy is flawed, I'm just saying that it's limitations should be expressed. Thanks for your post you've help answer a lot of my questions.

 

[marcus]

Periodically I try a new way of explaining expansion to myself (and anybody else for whom the explanation works.) Here is the current explanation.

We are talking about a pattern of expanding distances between observers who are stationary relative to the ancient light that fills the universe.

Barring minor differences in their gravitational potential these observers all perceive time the same way---universe time. They can synchronize their clocks, agree on the age of the universe, agree on the average temperature of the ancient light, and so on. The reason they can do all that is because they are stationary---in effect at rest relative to the original hot gas that filled space before it began to coalesce and fall together. This uniformly distributed matter is a kind of landmark. Or rather its GLOW, the relic light it emitted, is a landmark.
One can be at rest relative to that ancient matter, or its light.

A shared criterion of rest is what allows a shared idea of time, and allows us to talk about distances between observers at a particular moment in time. These are called proper distances and they are what you would measure by any conventional means if you could freeze expansion at that moment (to give yourself time to measure without the distance changing.)

So I would say let's try not to say "expanding universe" or "expanding space" too much because it may engrave the wrong idea on people's brains What we are talking about it a pattern of expanding distances between stationary observers.

The current percentage rate is 1/140 % per million years. This is barely noticeable unless the distance we are talking about is very very large.

In this uniform pattern of expansion, nobody gets anywhere---it does not bring anybody closer to some imagined destination. It doesn't correspond with anything like usual motion. The usual ideas about energy-of-motion and speed limits etc etc do not apply to it.

Notice that the scheme is approximate because the ancient light is not perfectly uniform and the idea of being at rest is only approximate (up to about 1/1000 of a percent.) There is a slight 1/1000 of a percent variation in the temperature of the CMB that can't be gotten rid of, so the idea of being at rest is not perfectly precise.

If anybody reads this and finds things that they think are wrong or that don't work, or other things good or bad to remark on, comments are welcome.

I'm trying to get away from the analogy of space as a "material". The balloon analogy is not meant to suggest that space is a material, it is a way of showing geometric relationships among the galaxies and the photons. There is no rubber. There is only the expanding geometry, a web of real (and imagined what-if) measurements.

Also in response to one of the other posters, curvature does not require an extra dimension. Gauss back in 1820 and Riemann back in 1850 got that all settled Curvature can be experienced intrinsically. There does not have to be an inside or outside of the balloon in order for 2D creatures living in the balloon surface to experience and measure the curvature of their world. It has been almost 300 years now since Carl Gauss realized that.

 

[Mathbrain]

My point wasn't that you need an extra dimension for curvature to exist, I was saying that you need an extra dimension to represent curvature. It isn't enough to say "space is curved". Is it spaced by the inverse square law, as an exponential function, or what?

I am still waiting for my question to be answered.

 

[marcus]

I am still waiting for my question to be answered.

I started a special "Mathbrain questions" thread to respond. Please check it out and, if you have further questions or more to say, continue this discussion there:
https://www.physicsforums.com/showthread.php?t=554838

 

[derek101]

If the balloon analogy is a good analogy,I have a question,because the galaxies are expanding away from each other,what is the fastest galaxy that we know to be traveling away from us,and how far can we see around to the other side of the balloon?

 

[marcus]

If the balloon analogy is a good analogy,I have a question,because the galaxies are expanding away from each other,what is the fastest galaxy that we know to be traveling away from us,and how far can we see around to the other side of the balloon?

I like your question, except I think it's a bad idea to talk of galaxies "traveling away from us", or to think of them as doing that.
In a uniform pattern of distance expansion nobody is traveling in the usual sense because nobody gets anywhere.

It is not motion. It is a change in geometry.

That's a big reason WHY the balloon analogy has generally been helpful to the people who have actually gone and looked at the short movie. Google "wright balloon model"

The thing it does is it shows each galaxy staying fixed at the same latitude longitude place, while photons of light actually travel between and among them. The photons of light always travel at the same speed. You can check that by watching the movie.

And yet a photon of light even though you can see it traveling always at the same speed, does not necessarily get to its destination at that rate. The distance between it and where it is going can actually increase for a while (until the expansion rate slows).

It is a helpful model because you can learn a lot by watching carefully and you can learn a lot which SOUNDS paradoxical when said in words but is actually quite reasonable.

So I hope you have watched that movie or will do so before you start discussing the balloon analogy here.
======================

In direct answer to your questions. We can see the light from matter that is NOW 45.5 billion LY from us. It didn't use to be so far away when it emitted the light which we are not getting from it. But NOW the matter we are looking at, the farthest, is 45.5 billion LY from here, so that is how far we can see.
I am using the definition of distance called proper distance which means what you would measure by conventional means like radar or a long string, if you could just stop the expansion process NOW to give yourself time to measure.

The latest NASA estimate of the circumference of the U, the MINIMUM circumf that it could be now, if it is finite at all, is about 600 billion LY. (Again proper distance)

You asked how far we can see and is that around to the other side and the answer is no it is not around to the other side, the 45 is only a little ways compared with the 600.
And the 600 is only a minimum, a lower bound estimate. It might be much bigger. They did not give any estimate of upper bound.

You asked what rate the distance to the most distant galaxy (so far) is increasing. I believe it is about 2.3 times c. we see other more distant stuff, that is receding at 3 times c. But that stuff has not cooled and condensed into galaxies yet. If you have further questions I hope you will start a thread and ask them. The most distant galaxy is, I believe, UDFj-39546284
If you google it you find that the estimated redshift is 10.3.

Then follow the "morgans" link in my sig to morgan's calculator. Or simply google "cosmos calculator".
Put in the 3 standard parameters (.27 for matter, .73 for cosmo constant, 71 for Hubble rate) and then put in 10.3 and press calculate. It will tell you the current distance and the current rate that distance is increasing which is 2.3c.

 

[megacal]

Hi Marcus, et al =)

I have a Microbiology background, and only have undergraduate math & physics understanding, but am intrigued by cosmology.

I'm sorry I haven't had time yet to go through all the posts in this thread to catch up, but
did see the Balloon Analogy simulation. I get it, and don't have a problem with it.

Can someone please tell me:

1) Do we see the same density of galaxies (eg the Deep Field) regardless where we look?
(edited to reflect previous post...i.e. that we can only see 45 LY across the estimated 600 LY
of the Universe if it's finite).

2) According to Greg Bernhardt in this https://www.physicsforums.com/showthread.php?t=506991 for this forum:

Therefore the best evidence is that the Big Bang happened uniformly, everywhere at once.
Since realistic cosmological models are homogeneous, every point in space has the same properties as every other point, and therefore the models don't have a center.

That appears to be illogical, imho...IF the BB started at an infintesimally small point, it would
by definition have to have a center i.e. point of origin.

3) Prior to the BB (or most recent one), is it possible all the mass was contained in a sphere
the size of e.g. the sun or even the Milky Way vs an infinitely small point?

I can't conceive an infinitely small point containing all the mass of the observable universe
being stabile much less possible. Even though you can mathematically extrapolate backwards to a point, it doesn't necessarily mean that it had to originate from an infinitely small point, but may have from a reasonably large "point".

Also I see it asserted (don't have a ref) that all the matter expanded to the size of the Milky Way in a bazzilionth of a second...waaaay > than C! =O ?

Thanks in advance for the reply!
Cal McGaugh

 

[marcus]

Hi Megacal,

That appears to be illogical, imho...IF the BB started at an infintesimally small point, it would
by definition have to have a center i.e. point of origin.

Think about the balloon analogy. at whatever time the 2d balloon surface is ALL THE SPACE THERE IS AT THAT TIME and all existence is concentrated in that 2d world.

So when the balloon started expanding it was not at a point in today's space.

In our 3D space, by analogy, THERE IS NO POINT OF ORIGIN in today's space.

1) Do we see the same density of galaxies (eg the Deep Field) regardless where we look?
(edited to reflect previous post...i.e. that we can only see 45 LY across the estimated 600 LY
of the Universe if it's finite).

YES. That is approximately right. Roughly the same density profile in every direction of our 3D space. This is the same as what you get with the balloon analogy. think of a 2D creature on the surface.

And density depends also on the redshift or lookback time, because earlier universe was much denser. the density profile is the same in all directions but it also depends on depth how deep in that direction you look.

I can't conceive an infinitely small point containing all the mass of the observable universe
being stabile much less possible.

The classical theory breaks down at the very beginning of expansion. People are working on an improved model that does not develop a singularity. when that is done and tested they will have to try to figure out what matter fields could exist at the start of expansion.

Maybe at some point matter is born out of geometry. Maybe at some very high density matter and geometry are the same quantum thing. we do not have a good theory of how things could have been right at the very start.

People are working hard on this. at least 20 good researchers. This is not what you hear about, like LHC etc etc etc. But the work is going ahead. Inside of 10 years we might have a much better understanding.

I agree if you try to imagine very very high density using ordinary ideas of geometry and matter it does not make sense. Something must be different about this very very high density state. I am resolved to be patient, but I watch the ongoing research in this area with considerable interest.

 

[megacal]

Hi Marcus,

Think about the balloon analogy. at whatever time the 2d balloon surface is ALL THE SPACE THERE IS AT THAT TIME and all existence is concentrated in that 2d world.

So when the balloon started expanding it was not at a point in today's space.

In our 3D space, by analogy, THERE IS NO POINT OF ORIGIN in today's space.

But the balloon and the space inside it is 3D, right? Just because the balloon has expanded doesn't negate the volume. The point of origin still exists (somewhere).

Sorry, but don't understand the model.

 

[DaveC426913]

Hi Marcus,



But the balloon and the space inside it is 3D, right? Just because the balloon has expanded doesn't negate the volume. The point of origin still exists (somewhere).

Sorry, but don't understand the model.

This is where the balloon analogy does not hold. Wwe looka the 2D surfaceof the balloon expanding, and the balloon fills a 3D volume, and we know here its centre is.

But in 3D, it works without there having to be a 4th dimension through which it is expanding.