Is the universe expanding??

[GiantOreo]

Is the universe expanding?? Or is it that the universe ITSELF is in motion?? What is evidence for the former??

All responses appreciated.

[DNAReplicator]

Everything in the universe appears to be moving away from everything else in the universe, except where objects are gravitationally bound to each other.

The evidence for this is that the electromagnetic radiation we detect from distant objects appears more red shifted than that from nearby objects. And the red-shifting appears consistant with all the observable mass in the universe having been in the same place 13.7 billion years ago.

I am not sure that the universe being 'in motion' has much meaning. After all, what could it be in motion relative to?

[GiantOreo]

Everything in the universe appears to be moving away from everything else in the universe, except where objects are gravitationally bound to each other.

The evidence for this is that the electromagnetic radiation we detect from distant objects appears more red shifted than that from nearby objects. And the red-shifting appears consistant with all the observable mass in the universe having been in the same place 13.7 billion years ago.

I am not sure that the universe being 'in motion' has much meaning. After all, what could it be in motion relative to?

Thanks for the answer! Excellent :)

For your question, I dunno. If the multiverse theory is true, maybe the universes are rotating with respect to something. Only science will find out.

[FreezBee]

Thanks for the answer! Excellent :)

For your question, I dunno. If the multiverse theory is true, maybe the universes are rotating with respect to something. Only science will find out.

Which "something"?

- FreezBee

[GiantOreo]

Which "something"?

- FreezBee

I wish I knew. We dont even know if there is a multiverse or not.

[Canard DuJour]

I am not sure that the universe being 'in motion' has much meaning. After all, what could it be in motion relative to?

I have the same problem with space 'expanding'. After all, what could it be expanding relative to?

[GiantOreo]

I have the same problem with space 'expanding'. After all, what could it be expanding relative to?

With relative to the Earth since the Doppler Shift is measured from Earth.

[Lixma]

The Universe isn't expanding, we are shrinking......

[DNAReplicator]

This is a really good article for those trying to get their heads around the big bang model.

http://www.sciam.com/article.cfm?chanID=sa006&articleID=0009F0CA-C523-1213-852383414B7F0147&pageNumber=3&catID=2

[Sultanist]

There's a young Caltech physicist named Sean Carroll who is the most communicative person since Carl Sagan when it comes to helping us get our heads around what we know about the origin and the nature of the universe.
For anyone who has even a passing interest in this I urge you to spend the cost of a fast food meal ($6.95) and download Art Bell's latest interview with him...
Carroll discussed the Big Bang, a scientific theory which proposes the universe came about from a tremendously dense and hot state about 14 billion years ago. He provided evidence for this theory, pointing out that the Big Bang model has been "established beyond reasonable doubt."

Carroll covered other cosmological and theoretical physics topics, including the accelerating expansion of the universe, how space and time came into existence, 'quantum gravity,' parallel universes, string theory, and time travel.
http://www.coasttocoastam.com/shows/2007/04/28.html#recap

http://www.preposterousuniverse.com/self.html

[Theophage]

I have the same problem with space 'expanding'. After all, what could it be expanding relative to?

Expanding relative to itself. If something is bigger now than what it was a second ago, it is expanding.

[Sultanist]

May I ask a question. And before I ask the question let me first preface it with another question...

When space is said to be "expanding", is the three-dimensional volume of space increasing in size? Yes or no?

[Canard DuJour]

Expanding relative to itself. If something is bigger now than what it was a second ago, it is expanding.

How can you tell if something is bigger now than it was a second ago?

[aguy2]

May I ask this question. And before I ask the question let me first preface it with another question...
When space is said to be "expanding", is the three-dimensional volume of space increasing in size? Yes or no?

"Yes", but current conventional wisdom says it must be expanding "spherically" from the BB event/body. If our observable universe is the result of a "jet/pulse" and not a "spherical" explosion from the BB, it is a whole different story, in that the accellation in growth over the last 3.5 billion years, would be evidence of an impending or current collapse, and not "spherical expansion".
aguy2(amen)

[Sultanist]

"Yes", but current conventional wisdom says it must be expanding "spherically" from the BB event/body. If our observable universe is the result of a "jet/pulse" and not a "spherical" explosion from the BB, it is a whole different story, in that the accellation in growth over the last 3.5 billion years, would be evidence of an impending or current collapse, and not "spherical expansion".
aguy2(amen)

Help me out with this. I have a blank dense spot between my ears like a black hole and for some reason it never wants me to understand this.
You answered "yes" to my question. Albeit with much qualification, but the answer was still "yes".
So the three-dimensional volume of space is growing larger in size.

The problem I always have with this is: how can the three-dimensional volume of space be growing larger in size, but while that is occuring nothing is being displaced by that expansion?
Let me put it another way. It seems a contradiction in terms to me to say that the three-dimensional volume of space is increasing but there is no displacement of something else as that occurs. How in the name of all that's holy (and unholy) can that be?

What am I missing?

[GenesisNemesis]

The Universe isn't expanding, we are shrinking......

Nooooooooooooooo.... (http://users.tinyonline.co.uk/chegc/kiltsite/expandin.htm)

[howardbemyname]

What am I missing?


Have you tried reading the Scientific American article linked to by
DNAReplicator above?

Start with page 1 though - the ants on the balloon thing.

[Biniam Shire]

http://www.astro.ucla.edu/~wright/cosmology_faq.html#MX

That faq should cover most of the basic questions asked here in this thread.

[GiantOreo]

Thanks guys!

What is causing the universe to expand??

[skepticalbip]

.........................
The problem I always have with this is: how can the three-dimensional volume of space be growing larger in size, but while that is occuring nothing is being displaced by that expansion?
Let me put it another way. It seems a contradiction in terms to me to say that the three-dimensional volume of space is increasing but there is no displacement of something else as that occurs. How in the name of all that's holy (and unholy) can that be?

What am I missing?Oh my, Bob. You are opening a real can of worms here. I think that the problem is that you are thinking in terms of Euclidean space (as is normal for real people instead of physics nerds) instead of in terms of 4-Space.

From what is taken to be reality, the universe is really a weird place when compared to what we live with and have come to believe is normal here on Earth. For instance the universe is believed to be expanding but if you go out at night and peek through your super telescope and look at something that is 13.5 billion light years away you are actually seeing the universe as it was 13.5 billion years ago. Now spin this super telescope around 180 degrees and look the exact opposite direction... Again at a distance of 13.5 billion light years you will see the universe as it was 13.5 billion years ago.

Now for the brain twister for those thinking in Euclidean space terms... The universe has been expanding for these 13.5 billion years so it should be "bigger" than it was 13.5 billion years ago. However, from your observations we (our current bigger universe) is in the middle of this earlier ("smaller") universe.

But to answer your question, the universe is expanding into that forth dimension (time).

bip

[gagundathar]

I particularly liked the quote, "Whereof one cannot speak, thereof one must be silent." -- Ludwig Wittgenstein

[gagundathar]

Thanks guys!

What is causing the universe to expand??

My best guess is that God is eating Giant Oreos.
But this is merely a guess.
And it IS Friday afternoon.

[DNAReplicator]

The problem I always have with this is: how can the three-dimensional volume of space be growing larger in size, but while that is occuring nothing is being displaced by that expansion?
Let me put it another way. It seems a contradiction in terms to me to say that the three-dimensional volume of space is increasing but there is no displacement of something else as that occurs. How in the name of all that's holy (and unholy) can that be?

What am I missing?

When we measure the red-shift of the mass of the universe, it appears to us that the red-shift to distance relationship is the same, whichever direction we look in. We seem to be at the centre of the expanding universe.

However, the BB it thought to have been an explosion of space itself from a dimentionless point, not an explosion into space. So all points in the universe would have been at the centre of the universe at the time of the big bang. Put simply - all places in the universe appear to be 'the centre' of the expanding universe to an observer there.

So I suspect your problem is that you are picturing the big bang as a three dimentional sphere expanding into empty space. In fact a topology where all points in the universe are the 'centre' of that universe is much, much wierder.

[Sultanist]

Have you tried reading the Scientific American article linked to by
DNAReplicator above?

Start with page 1 though - the ants on the balloon thing.

Thanks, Howard. Here's the relevant part...
The expansion of our universe is much like the inflation of a balloon. The distances to remote galaxies are increasing. Astronomers casually say that distant galaxies are "receding" or "moving away" from us, but the galaxies are not traveling through space away from us. They are not fragments of a big bang bomb. Instead the space between the galaxies and us is expanding. Individual galaxies move around at random within clusters, but the clusters of galaxies are essentially at rest. The term "at rest" can be defined rigorously. The microwave background radiation fills the universe and defines a universal reference frame, analogous to the rubber of the balloon, with respect to which motion can be measured.

This balloon analogy should not be stretched too far. From our point of view outside the balloon, the expansion of the curved two-dimensional rubber is possible only because it is embedded in three-dimensional space. Within the third dimension, the balloon has a center, and its surface expands into the surrounding air as it inflates. One might conclude that the expansion of our three-dimensional space requires the presence of a fourth dimension. But in Einstein's general theory of relativity, the foundation of modern cosmology, space is dynamic. It can expand, shrink and curve without being embedded in a higher-dimensional space.

In this sense, the universe is self-contained. It needs neither a center to expand away from nor empty space on the outside (wherever that is) to expand into. When it expands, it does not claim previously unoccupied space from its surroundings
I grasp the part about how the expansion of the 2-dimensional surface of the balloon is analogous to the expansion of space in the universe. And how the relationship between the ants standing on the surface of the balloon is changing similiarly to how the relationship between galaxies is changing within
the universe.

But then I still have a problem with this...
But in Einstein's general theory of relativity... space is dynamic. It can expand, shrink and curve without being embedded in a higher-dimensional space.

That confounds me so badly that I think I'm just going to have to say "okey dokey" and not try to comprehend it.

[Sultanist]

a topology where all points in the universe are the 'centre' of that universe is much, much wierder.
Indeed. So weird that, like the space is "bending", so is my mind. :D

[howardbemyname]

That confounds me so badly that I think I'm just going to have to say "okey dokey" and not try to comprehend it.

Actually , upon reflection I think we're in pretty much the same boat. My brain's starting to hurt too.:D

The problem, I think, is that we're trying to think that we can stand outside the universe, when in fact there is no outside, but that just begs your question.

[robto]

Aaack! Misconceptions galore! I'll try to tackle a few.


"Yes", but current conventional wisdom says it must be expanding "spherically" from the BB event/body. If our observable universe is the result of a "jet/pulse" and not a "spherical" explosion from the BB, it is a whole different story, in that the accellation in growth over the last 3.5 billion years, would be evidence of an impending or current collapse, and not "spherical expansion".
aguy2(amen)

NO! There is NO BB "event/body". The BB happens AT EVERY POINT IN THE UNIVERSE.

Secondly, although is it possible to build models in which the expansion is not spherically symmetric, we know from observation that our universe is very nearly spherically symmetric. (Although no one knows why this should be so.)


Thirdly, space is NOT expanding "into time" (or into any other dimension).

As the feller said,
One might conclude that the expansion of our three-dimensional space requires the presence of a fourth dimension. But in Einstein's general theory of relativity, the foundation of modern cosmology, space is dynamic. It can expand, shrink and curve without being embedded in a higher-dimensional space.

Imagine you were a two-dimensional creature living on the skin of the balloon. From your point of view, you could describe the whole process without using a third dimension to expand "into". Or, you COULD use a third dimension in the description.

But here's the point: it is physically impossible for you to move in the direction of the third dimension. So, from a (2-D) physicists point of view, there is point in talking about a third dimension. It is unobservable, except for the expansion thing, and we can deal with that without invoking a third dimension.

Same for us 3-D physicists. If there are no observable consequences to embedding our expanding universe in a higher-dimensional space, then there's no point in doing it. It's Occam's Razor: don't introduce new hypotheses if they don't get you anything new.

[Berthold]

George Gamov wrote a book, "Flatland", Ian Stewart expounded on the topic with "Flatterland".

Good introductions to awaken the imagination with respect to geometry.

[Draconis]

Okay, I think what is meant by expanding is that galaxies are getting further apart, but that doesn't mean that electrons are orbitting further away from their respective nuclei.

What's causing this apparent expansion? Either gravitational imbalances throughout the visible universe (the universe might be contracting elsewhere)
or whatever caused the initial inflation in the first place (see Alan Guth) or perhaps a parallel brane exerting its gravitational pull on our universe (see Lisa Randall)

or something else....(?)

[Styrofoamdeity]

Here's a pretty good description of the expanding universe and our place in it:

http://www.youtube.com/watch?v=9JSR_6qfXTg

[Ruiner]

Sultanist seems so out of his element here. :D Like a boy who lost his pup. ;)

I recently read Five Ages of the Universe by Adams and Laughlin. If what is said in that book is consensus, then this universe will just fizzle out with no grand hurrah at the end, no climactic end. Just fizzle. Kind of tragic, in a way.

[DNAReplicator]

What's causing this apparent expansion?

My limited understanding....

Inflation explains the expansion as a consequence of a very brief early period of negative pressure resulting from the breaking of the symmetry between the strong and weak nuclear forces. The expansion today is explained as a relic from this brief phase of the big bang. This is about as close to a standard view as there is in cosmology.

Ont he other hand, while it may be speculative stuff, I am informed (because I can't get my head around the maths) that string theory cannot distinguish between a singularity collapsing beyond the plank limit and a big-bang like expansion. So it could be that the universe is in fact a collapsing singularity....

Or both????

[JustinFoldsFive]

My philosophy of science professor always mentioned that there are blue-shifted galaxies, which would suggest that they are moving toward us. How would Big Bang explain these?

[premjan]

The blue-shifted galaxies are probably neighboring ones within our galactic cluster.

[Sultanist]

Sultanist seems so out of his element here. :D Like a boy who lost his pup. ;)

I recently read Five Ages of the Universe by Adams and Laughlin. If what is said in that book is consensus, then this universe will just fizzle out with no grand hurrah at the end, no climactic end. Just fizzle. Kind of tragic, in a way.
It's literally true, Ruiner. This is actually by it's very definition where I am "most out of my element". And I would argue so are we all. ;)

But the ultimate irony is the contradiction that, it is in another sense, where
we're all "most in our element".

Yes, "we" (although obviously I don't include myself in this :D) have apparently discovered something as mind-bending as this...
space is dynamic. It can expand, shrink and curve without being embedded in a higher-dimensional space.
And even though that's like Greek to me, I accept it. :D

However, here's a quote from the book review you linked us too...
Even for astronomers, University of Michigan professor Fred Adams and his former student Greg Laughlin think big--really, really big--and their planning is really, really long-term.
Baloney.
At any time you're told that anything humans are thinking now is "really really big" and "really really long-term", then you take that with a grain of salt, Ruiner.
Because I have a feeling that, in the scheme of things, what we're thinking right now is "really really small". And "really really short term". ;)

So what did I mean we're both most out of and most in "our element" at the same time with this?

It's because that "element" is our reality, Ruiner.

A reality which can be stated as follows...
1. There is a huge and inconceivable unknown whether we like it or not.
and
2. That, in a sense, is what defines who we are.

Or stated another way, co-existing with that "element" (or "unknown") is our reality. And the very fact that we're "so out of it"
also makes it an element we're "in", deeply "in" and profoundly "in".

I realize you're thinking that this is philosophy and not science. But I cannot separate the two.

[aguy2]

Aaack! Misconceptions galore! I'll try to tackle a few.
NO! There is NO BB "event/body". The BB happens AT EVERY POINT IN THE UNIVERSE.

Bullocks! There is evidence 'everywhere' in the CBR, that the BB happened from a point. It supposedly was an explosion, and not an implosion.

Secondly, although is it possible to build models in which the expansion is not spherically symmetric, we know from observation that our universe is very nearly spherically symmetric. (Although no one knows why this should be so.)

Even if the universe is roughly spherical, we could only 'see' about 1/6th of the sphere.

My conjecture is that the matter universe rerpresents a mushrooming pulse/jet of maybe 1/3 or less than it would be if it were spherical.

Thirdly, space is NOT expanding "into time" (or into any other dimension).

I don't know where you got this, but my conjecture is that 'space/extent' is expanding from a contracting 'time/change'. The presumption being that the sum of 'time/change' and 'space/extent' is a constant.

As the feller said,
Imagine you were a two-dimensional creature living on the skin of the balloon.

A 'jet/pulse' is not an expanding balloon. More like a fountain.
aguy2(amen)

[Jesse]

Bullocks! There is evidence 'everywhere' in the CBR, that the BB happened from a point. It supposedly was an explosion, and not an implosion. It was an explosion, but not an explosion from any particular point in space, according to the theory of general relativity. Think of the flatlanders on the expanding sphere--if the sphere has been expanding from an initial radius of zero, is there any point on the surface of the sphere that qualifies as the "point in (2D) space" that the Big Bang happened? Even if the universe is roughly spherical, we could only 'see' about 1/6th of the sphere. Where did you get that number? Do you understand that when people talk about the universe being "spherical", they don't mean a 3D sphere with a 2D surface like the Earth, they mean a 4D "hypersphere" whose 3D surface is the space we live in? I don't know where you got this, but my conjecture is that 'space/extent' is expanding from a contracting 'time/change'. The presumption being that the sum of 'time/change' and 'space/extent' is a constant. If your conjecture involves rejecting the theory of general relativity, you're going to have to come up with a new theory that replicates all its successful predictions (such as gravitational time dilation, gravitational lensing, the precession of Mercury's orbit, etc.)

[Jesse]

My limited understanding....

Inflation explains the expansion as a consequence of a very brief early period of negative pressure resulting from the breaking of the symmetry between the strong and weak nuclear forces. The expansion today is explained as a relic from this brief phase of the big bang. This is about as close to a standard view as there is in cosmology. It isn't actually necessary to have inflation in order to have expansion, the original cosmological models in general relativity feature an expanding universe even though they ignore the quantum processes which could give rise to inflation. Basically, I think it's just that these cosmologies are the types of solutions you get when you try to apply the theory of general relativity to the whole universe--the type of static universe (http://en.wikipedia.org/wiki/Static_universe) that was Einstein's original cosmological model was found to be unstable, as this page from John Baez's site (http://math.ucr.edu/home/baez/physics/Relativity/GR/cosConstant.html) explains: However, there is a basic flaw in this Einstein static model: it is unstable -- like a pencil balanced on its point. For imagine that the Universe grew slightly: say by 1 part per million in size. Then the vacuum energy density stays the same, but the matter energy density goes down by 3 parts per million. This gives a net negative gravitational acceleration, which makes the Universe grow even more! If instead the Universe shrank slightly, one gets a net positive gravitational acceleration, which makes it shrink more! Any small deviation gets magnified, and the model is fundamentally flawed.

[robto]

Bullocks! There is evidence 'everywhere' in the CBR, that the BB happened from a point. It supposedly was an explosion, and not an implosion.



There's no point in trying to convince anyone of your "conjecture" if you haven't understood the basic ideas of accepted BB cosmology. I suggest you do some more reading on the BB model - you are clearly clueless about it.

[Answerer]

My philosophy of science professor always mentioned that there are blue-shifted galaxies, which would suggest that they are moving toward us. How would Big Bang explain these?

Its the galactic clusters/superclusters that are moving away from each other, no contradiction with the inflation theory. Individual galaxy is as bounded to force of localized (Within the clusters) gravity as we are. Indeed, I once read that Milky Way is on a collision course with another in the distant future, one disaster that might obliterate our system.

[Sultanist]

I asked a question earlier in the thread. "Is the 3-dimensional volume of space increasing in size as the universe expands?"
The answer I received was yes. And I presume that since no one challenged that answer then we're all in agreement on this.

So then I asked "if a given 3-dimensional volume of space is increasing in size, then how can it not be displacing something as it expands?"

If I understand correctly, the answer I'm being provided for that question
is basically that "every point in the universe existed at the time of it's birth (the Big Bang) so all of the volume of space has always existed since the beginning".
Tell me if I have that right. But if I do then that seems like such a contradiction in terms. Because how could all the 3-dimensional volume of space have existed all along if the volume of space is expanding (increasing it's 3-dimensional volume)?

But, lets not even go there for the moment. And instead I'll just accept the notion that every point in the universe and all of space existed at the beginning of the universe same as it does now.
But guess what. That immediately gives rise to the question: "what is outside the universe?"
And if your answer is "nothing is outside the universe because the universe is everything" then I challenge you to provide any evidence to support such a claim as that.

[robto]

I asked a question earlier in the thread. "Is the 3-dimensional volume of space increasing in size as the universe expands?"
The answer I received was yes. And I presume that since no one challenged that answer then we're all in agreement on this.

Correct so far.

So then I asked "if a given 3-dimensional volume of space is increasing in size, then how can it not be displacing something as it expands?"

If I understand correctly, the answer I'm being provided for that question
is basically that "every point in the universe existed at the time of it's birth (the Big Bang) so all of the volume of space has always existed since the beginning".


Nope.

There are two possibilities for the overall universe (for some point in time, say, right now): finite total volume or infinite total volume. For the sake of the discussion, let's assume it's finite.

If that's true, then 5 billion years ago the universe had a smaller total volume. Yes, less volume then, more volume now. How can that be? Where did the additional volume "come from"? Answer: from nowhere. Space just stretched, making the universe more roomy.

(If, OTOH, the total volume is infinite now, then of course it was always infinite, right back to the BB. But space still stretched.)


But guess what. That immediately gives rise to the question: "what is outside the universe?"
And if your answer is "nothing is outside the universe because the universe is everything" then I challenge you to provide any evidence to support such a claim as that.

Right back atcha: provide any evidence to support the idea that there's anything outside the universe. Note: "because there must be something out there" isn't evidence.

[Sven]

Bullocks! There is evidence 'everywhere' in the CBR, that the BB happened from a point. It supposedly was an explosion, and not an implosion.
Who said anything about an implosion?
And the Big Bang happened from a point only in the sense that the observable universe was once "contained" in something we might call a point (for sizes smaller than the Planck scale, our physics becomes meaninglesse). This "point" has been expanding ever since the expansion started. The expansion of the universe is called the "Big Bang" in physics. That the everyday usage is different does not change this fact.

I don't know where you got this, but my conjecture is that 'space/extent' is expanding from a contracting 'time/change'. The presumption being that the sum of 'time/change' and 'space/extent' is a constant. :huh:
Learn some general relativity. This does not make the slightest sense.

[aguy2]

Who said anything about an implosion?
And the Big Bang happened from a point only in the sense that the observable universe was once "contained" in something we might call a point (for sizes smaller than the Planck scale, our physics becomes meaninglesse). This "point" has been expanding ever since the expansion started. The expansion of the universe is called the "Big Bang" in physics. That the everyday usage is different does not change this fact.

:huh:
Learn some general relativity. This does not make the slightest sense.

Using the Operational (conditional) definitions:
Universe = period and extent of one oscillation/cycle
Time = the period of one oscillation/cycle
Space=the extent of one oscillation/cycle

These operational definitions are constrained, concise, and cohesive, and the non-spherical cosomological models derived from them are very interesting. During a single oscillation/cycle, T goes from 1 to 0. IOW the amount of time the universe has left contracts. These same models predict that S starts at 0 and expands as T contracts. IOW time/space is 'conserved' and 'equivalent', and would appear to be the basic substrate of reality.

aguy2(amen)

[Sven]

Using the Operational (conditional) definitions:
Universe = period and extent of one oscillation/cycle
Time = the period of one oscillation/cycle
Space=the extent of one oscillation/cycle
I see, you are defining an oscillatory universe in existence? And you simply don't care what science has actually to say about this (general relativity)? Then I don't see why I should care what you have to say.

[snip inextricable, unreferenced blather]

[aguy2]

Using the Operational (conditional) definitions:
Universe = period and extent of one oscillation/cycle
Time = the period of one oscillation/cycle
Space=the extent of one oscillation/cycle

These operational definitions are constrained, concise, and cohesive, and the non-spherical cosomological models derived from them are very interesting. During a single oscillation/cycle, T goes from 1 to 0. IOW the amount of time the universe has left contracts. These same models predict that S starts at 0 and expands as T contracts. IOW time/space is 'conserved' and 'equivalent', and would appear to be the basic substrate of reality.


Sven claims the above paragragh is:
1)inextricable

I would wonder at what sense of the term "inextricable" he is using.

I really do not think he means to say the paragragh is "hopelessly intricate". Can he show me a less intricate explanation? My contention that time/space can be seen as 'conserved' and 'equivalent' deserves discussion, not dismissal.

Does Sven use the term "inextricable" in the sense that the paragraph is, "incapable of being disentangled"? Do you think he is refering to the presented conditional definitions as being 'cohesive'?

Of course my dictionary says "inextricable, adj. 1) from which one cannot extricate oneself

I would ask why, if this is the case, why is he trying?
aguy2(amen)

[Sven]

Sven claims the above paragragh is:
1)inextricable

I would wonder at what sense of the term "inextricable" he is using.

At the only sense my dictionary is telling me what the word "unentwirrbar" means in English.

I really do not think he means to say the paragragh is "hopelessly intricate". Yes, it is.

Can he show me a less intricate explanation? Hint: For giving a less intricate explanation, I would first have to understand what you are trying to say. Which I can not, because it's inextricable. :wave:

My contention that time/space can be seen as 'conserved' and 'equivalent' deserves discussion, not dismissal. Do you remember the suggestion to learn some general relativity? Even general relativity and space-time are a nice start.

Does Sven use the term "inextricable" in the sense that the paragraph is, "incapable of being disentangled"? I don't see any difference to the meaning above.

[aguy2]

in re: C3O or "Constrained, Concise, Cohesive Operational definitions

Using the Operational (conditional) definitions:
Universe = period and extent of one oscillation/cycle
Time = the period of one oscillation/cycle
Space=the extent of one oscillation/cycle

These operational definitions are constrained, concise, and cohesive, and the non-spherical cosomological models derived from them are very interesting. During a single oscillation/cycle, T goes from 1 to 0. IOW the amount of time the universe has left contracts. These same models predict that S starts at 0 and expands as T contracts. IOW time/space is 'conserved' and 'equivalent', and would appear to be the basic substrate of reality.


Sven has directed me tp the Wiki article on "spacetime", so I can get myself educated.

This article says, "Spacetime is any model that combines time and space into a single construct." My model meets this criteria.

This article says, "By combining time and sppace into a single manifold, physicists have significantly simplified a large amount of physical theory." My model meets this criteria.

This article says, "In Relativistic contexts, time cannot be separated from the 3 dimensions of space.", and goes on to say however, "How many dimensions are needed to describe the universe is still an open question."

My model meets and exceeds this criteria by claiming that timespace is not only a "single construct", a "single manifold", and "cannot be separated from one another", in certain oscillation/cycle models there is also a distinct possibility that timespace is also "conserved" and "equivalent".

It is my contention that these models deserve close scrutiny.
aguy2(amen)

[Sven]

This article says, "Spacetime is any model that combines time and space into a single construct." My model meets this criteria.

This article says, "By combining time and sppace into a single manifold, physicists have significantly simplified a large amount of physical theory." My model meets this criteria.

This article says, "In Relativistic contexts, time cannot be separated from the 3 dimensions of space.", and goes on to say however, "How many dimensions are needed to describe the universe is still an open question."

See, I was only trying to help you. Perhaps you'll follow the advice of others to educate yourself earlier next time.

Now, have you also read up on general relativity?

My model meets and exceeds this criteria by claiming that timespace is not only a "single construct", a "single manifold", and "cannot be separated from one another", in certain oscillation/cycle models there is also a distinct possibility that timespace is also "conserved" and "equivalent".
Apparently you failed to notice that the concept of space-time itself requires that time and space are in some way equivalent.

But since both time and space have expanded by manyl magnitudes since the Big Bang, they are obviously not conserved. Which is why your model is totally bogus.

[aguy2]

See, I was only trying to help you. Perhaps you'll follow the advice of others to educate yourself earlier next time.

Now, have you also read up on general relativity?


Apparently you failed to notice that the concept of space-time itself requires that time and space are in some way equivalent.

But since both time and space have expanded by manyl magnitudes since the Big Bang,

You are assuming that both 'time' and 'space' are accumulating. Why? Is it just because everyone else has?

they are obviously not conserved.

Can you show why both must accumulate? Aren't you and I both running out of time?

Which is why your model is totally bogus.

Your assumption that time is accumulating, should be reexamined very carefully.
aguy2(amen)

[Jesse]

in re: C3O or "Constrained, Concise, Cohesive Operational definitions



Sven has directed me tp the Wiki article on "spacetime", so I can get myself educated.

This article says, "Spacetime is any model that combines time and space into a single construct." My model meets this criteria.

This article says, "By combining time and sppace into a single manifold, physicists have significantly simplified a large amount of physical theory." My model meets this criteria. Spacetime is part of the structure of the theory of general relativity (http://en.wikipedia.org/wiki/General_relativity), a mathematical theory which uses equations to describe the relationship between the distribution of matter and energy and the curvature of spacetime. Because it's mathematical, it can give you precise quantitative predictions about many phenomena which can be tested experimentally (see tests of general relativity (http://en.wikipedia.org/wiki/Tests_of_general_relativity)). And it can also be used to make predictions about cosmology, such as the expanding universe.

Your "model" is just a verbal sketch of an idea, and cannot make any new quantitative predictions or replicate the experimentally-verified predictions of general relativity. So there's really no comparison--as a physicist might say, your idea is not even wrong (http://en.wikipedia.org/wiki/Not_even_wrong).

[Sven]

You are assuming that both 'time' and 'space' are accumulating. Why? Is it just because everyone else has?
Space does. See: Redshift. See: CMB.
Since space and time have to bre treated the same way (see space-time), space also does.


[snip rest - three times saying/asking the same does not add much to the discussion]

[Jesse]

Space does. See: Redshift. See: CMB.
Since space and time have to bre treated the same way (see space-time), space also does. I don't it actually makes sense to talk about spacetime expanding, or time expanding. The notion of space expanding is based on taking a "foliation" of spacetime, which basically involves slicing up the static 4D manifold into a stack of 3D "spacelike hypersurfaces" which evolve over time. In cosmology there would be a unique way of doing this slicing so that each surface was homogeneous, which corresponds to picking the rest frame of the cosmic microwave background radiation. If you divide up space and time this way, then the you can talk about space expanding over time, but spacetime as a whole is still a totally static entity. Imagine spacetime as the 2D surface of an American football, and then slice it along the axis from tip to tip into a series of cross-sections, each of which is a 1D line curved into a circle representing space at a particular moment in time--as time passes, the circles grow from a point to a maximum size, then shrink to a point again, as with a closed universe growing from a Big Bang and then collapsing to a Big Crunch.

[seven8s]

Your assumption that time is accumulating, should be reexamined very carefully.
aguy2(amen)

what he is arguing is that the rise of women is the fall of man............this is what religion argues. And we know how religion’s both modern and ancient handled women...................put a bag over their head and **** em. This is what aguy2 is arguing for................ Amazing.

[aguy2]

Your "model" is just a verbal sketch of an idea,

True.

and cannot make any new quantitative predictions

My model made a non-quantitative prediction concerning the linkage of the Virgo 'attractor' with the hapoid structure of current cbr. My model assumes our visable universe is a cone and not a sphere. Well, more like a jet/pulse of an ideal liquid. 3.5 bya the cone began to become wider at an accelerated pace. We have been interpreting this as an expansion of a sphere and not the widening of a cone. Well, more like the turbulence that ensues when a liquid pulse/jet begins to lose momentum. Imagine a fountain.

Although the model predicts that although the expansion of the cone was rather uniform for its first 10 billion years, it is becoming increasingly turbulent. With the turbulence centered on the haploid structure we are already seeing, through cbr data, from the period right after the inflationary era.

or replicate the experimentally-verified predictions of general relativity. So there's really no comparison--as a physicist might say, your idea is not even wrong (http://en.wikipedia.org/wiki/Not_even_wrong).

Right, all I am presenting is a "verbal sketch". The sketch is not nearly as parsimonious as a spherical expansion, but the only real fundamental difference between my model and the more standard oscillation/cycle models is that, "it is assumed that the initial BB displayed a great deal of angular momentum (AM)". The balance of the model rests on this assumption of initial AM.
aguy2(amen)

[aguy2]

what he is arguing is that the rise of women is the fall of man............this is what religion argues. And we know how religion’s both modern and ancient handled women...................put a bag over their head and **** em. This is what aguy2 is arguing for................ Amazing.

Well, you take a psychological risk when you see a context that is running out of time. Maybe I shouldn't have put you at risk, but if it is the case, it is the case.
aguy2(amen)

[Jesse]

My model made a non-quantitative prediction concerning the linkage of the Virgo 'attractor' with the hapoid structure of current cbr. My model assumes our visable universe is a cone and not a sphere. The Big Bang model does not say that matter is shaped like an expanding sphere, in fact it says that matter and energy are about evenly distributed through all of space, which may be infinite or finite. Of course the visible universe is a sphere with us at the center, but that's just because there's a limit to how far out we can see structures (since they've only been around for a finite time since the Big Bang, and the farther we look the closer to the Big Bang we're seeing), and this distance is the same in all directions. Well, more like a jet/pulse of an ideal liquid. 3.5 bya the cone began to become wider at an accelerated pace. And is this what general relativity would predict would naturally happen to a jet/pulse of ideal liquid? You can't just make up any behavior of matter you want in physics, you have to have some underlying theory of how matter behaves, and show that according to this theory it would behave in the way you imagine. If general relativity doesn't predict that a jet in an otherwise empty space would "become wider at an accelerated pace" (I don't see how it would, the matter's own gravity would tend to decelerate its outward movement), then you'll need a different theory of gravity, one which can replicate all of the successful predictions of general relativity. You also need to explain where this jet came from, and why the jet prediction would lead to the "Hubble law" saying that the speed that distant galaxies move away from us (as measured by their redshift) would be proportional to their distance times the Hubble constant. We have been interpreting this as an expansion of a sphere No, mainstream cosmology does not involve an expanding sphere of matter. You really need to become well-versed in existing theories, and the evidence supporting them, before you can make well-informed proposals about alternatives. Well, more like the turbulence that ensues when a liquid pulse/jet begins to lose momentum. Imagine a fountain. Turbulence in liquids is not due to loss of momentum, in fact slower-moving liquids are less turbulent than faster ones. And a jet of water will behave very differently than a giant jet of more matter than is contained in our visible universe, because the gravity of the matter will be much more important on this scale. Right, all I am presenting is a "verbal sketch". The sketch is not nearly as parsimonious as a spherical expansion, but the only real fundamental difference between my model and the more standard oscillation/cycle models is that, "it is assumed that the initial BB displayed a great deal of angular momentum (AM)". The balance of the model rests on this assumption of initial AM.
aguy2(amen) A fundamental difference which you seem not to appreciate is that you are imagining some finite clump of matter in a larger empty space, while the standard Big Bang model does not involve a finite expanding sphere of matter in a larger empty space, it involves matter being evenly distributed throughout all of space, but becoming less densely distributed because of the expansion of space. As for angular momentum, it is in fact possible to come up with a model of a "rotating universe" in general relativity where the universe has net angular momentum even though the universe has no "center" and matter is evenly distributed throughout space--see here (http://www.ettnet.se/~egils/essay/essay.html#what) for an explanation. If the angular momentum is high enough though this leads to "closed timelike curves" (time travel), and observational evidence does not support this model (see here (http://www.ettnet.se/~egils/essay/essay.html#isrot)).

[sharahan]

Expanding relative to itself. If something is bigger now than what it was a second ago, it is expanding.

If universe is expanding ; in the space which it acquired now in this second;
what was there before one second.
I mean universe is the whole stuff. Ok ,then how can we say it expand. And the universe is infinite too.Do you mean the stars are moving away ?

[Sven]

I don't it actually makes sense to talk about spacetime expanding, or time expanding. The notion of space expanding is based on taking a "foliation" of spacetime, which basically involves slicing up the static 4D manifold into a stack of 3D "spacelike hypersurfaces" which evolve over time. In cosmology there would be a unique way of doing this slicing so that each surface was homogeneous, which corresponds to picking the rest frame of the cosmic microwave background radiation. If you divide up space and time this way, then the you can talk about space expanding over time, but spacetime as a whole is still a totally static entity. Imagine spacetime as the 2D surface of an American football, and then slice it along the axis from tip to tip into a series of cross-sections, each of which is a 1D line curved into a circle representing space at a particular moment in time--as time passes, the circles grow from a point to a maximum size, then shrink to a point again, as with a closed universe growing from a Big Bang and then collapsing to a Big Crunch.
Just to make it clear - the axis perpendicular to each of these circles is time? Then I would understand why you say spacetime is static - otherwise I just would have to scratch my head.

[Sven]

If universe is expanding ; in the space which it acquired now in this second;
what was there before one second.
I mean universe is the whole stuff. Ok ,then how can we say it expand.
Expanding in the sense that distances between stuff (galaxies) become larger.

And the universe is infinite too.
Umm, this is an open question. AFAIK, most cosmologists rather favor a finite universe. (I favor an infinite one, but this does not say much)

Do you mean the stars are moving away ?
Galaxies are. Ever heard about Hubble and redshift?

[Jesse]

Just to make it clear - the axis perpendicular to each of these circles is time? Then I would understand why you say spacetime is static - otherwise I just would have to scratch my head. Right, the axis perpendicular to the circles is time in this analogy, at least for this particular 'foliation' of the football-shaped spacetime (you could foliate it differently by slicing it at a slightly different angle, so each section would look like an ellipse rather than a circle).

[epepke]

From what is taken to be reality, the universe is really a weird place when compared to what we live with and have come to believe is normal here on Earth. For instance the universe is believed to be expanding but if you go out at night and peek through your super telescope and look at something that is 13.5 billion light years away you are actually seeing the universe as it was 13.5 billion years ago. Now spin this super telescope around 180 degrees and look the exact opposite direction... Again at a distance of 13.5 billion light years you will see the universe as it was 13.5 billion years ago.

Now for the brain twister for those thinking in Euclidean space terms... The universe has been expanding for these 13.5 billion years so it should be "bigger" than it was 13.5 billion years ago. However, from your observations we (our current bigger universe) is in the middle of this earlier ("smaller") universe.

It seems to me that it follows that, as the universe is much bigger than it was 13.5 billion years ago, that what we would imagine as a sphere 13.5 billion light years in radius has a much smaller circumference. That is, let's say galaxies A and B are at opposite ends. You have a really good telescope, and you look at an astronomer in galaxy A. He is (was) measuring the distance to galaxy B. He holds up a sign with the distance, and you read it. The distance is much smaller than the 27 billion light years that we would deduce, let alone 84.8 billion light years going around the circumference.

That always seemed to me a neater explanation for the "why is the universe so uniform" than a lot of the stuff that seemed to me ad hoc and a result of mixing Euclidean and non-Euclidean ideas.

I suggested this to a cosmologist back in the 1990s, and he told me I was full of shit, and only crackpots thought that the universe was anything other than spherical, but I can't remember the explanation he used. Something about the lack of apparent curvature at large distances, but I don't see how you can measure curvature at a distance accurately without an extremely long baseline for measurments, except by making assumptions about density that may very well turn out to be wrong. Perhaps someone can explain why I am a crackpot.

[Jesse]

It seems to me that it follows that, as the universe is much bigger than it was 13.5 billion years ago, that what we would imagine as a sphere 13.5 billion light years in radius has a much smaller circumference. That is, let's say galaxies A and B are at opposite ends. You have a really good telescope, and you look at an astronomer in galaxy A. He is (was) measuring the distance to galaxy B. He holds up a sign with the distance, and you read it. The distance is much smaller than the 27 billion light years that we would deduce, let alone 84.8 billion light years going around the circumference. I don't get it, why do you say the distance is much smaller? By the way, the visible universe is not actually thought to have a radius in light-years exactly equal to its age--p. 5 of the helpful Misconceptions about the Big Bang (http://www.sciam.com/article.cfm?articleID=0009F0CA-C523-1213-852383414B7F0147) article explains: What does mark the edge of observable space? Here again there has been confusion. If space were not expanding, the most distant object we could see would now be about 14 billion light-years away from us, the distance light could have traveled in the 14 billion years since the big bang. But because the universe is expanding, the space traversed by a photon expands behind it during the voyage. Consequently, the current distance to the most distant object we can see is about three times farther, or 46 billion light-years.

The recent discovery that the rate of cosmic expansion is accelerating makes things even more interesting. Previously, cosmologists thought that we lived in a decelerating universe and that ever more galaxies would come into view. In an accelerating universe, however, we are surrounded by a boundary beyond which occur events we will never see--a cosmic event horizon. If light from galaxies receding faster than light is to reach us, the Hubble distance has to increase, but in an accelerating universe, it stops increasing. Distant events may send out light beams aimed in our direction, but this light is trapped beyond the Hubble distance by the acceleration of the expansion.

An accelerating universe, then, resembles a black hole in that it has an event horizon, an edge beyond which we cannot see. The current distance to our cosmic event horizon is 16 billion light-years, well within our observable range. Light emitted from galaxies that are now beyond the event horizon will never be able to reach us; the distance that currently corresponds to 16 billion light-years will expand too quickly. We will still be able to see events that took place in those galaxies before they crossed the horizon, but subsequent events will be forever beyond our view. That always seemed to me a neater explanation for the "why is the universe so uniform" than a lot of the stuff that seemed to me ad hoc and a result of mixing Euclidean and non-Euclidean ideas. Again, I'm not clear what your explanation is here. And all predictions in cosmology are derived from mathematical models of the universe based on general relativity, not on some vague intuitive mix of Euclidean and non-Euclidean ideas. I suggested this to a cosmologist back in the 1990s, and he told me I was full of shit, and only crackpots thought that the universe was anything other than spherical Are you talking about the visible universe, or the entire universe? Cosmologists don't think the entire universe is a sphere, that's a misconception based on imagining the Big Bang as an explosion in a preexisting space. Presumably the visible universe is a sphere with us at the center, simply because we can see the same distance in every direction--are you suggesting otherwise?

[Cheerful Charlie]

Is the universe expanding?? Or is it that the universe ITSELF is in motion?? What is evidence for the former??

All responses appreciated.


Expanding. Space itself is expanding.The Universe is 13.7 billion years old and 138 billion light years wide, give or take a few billion.

CC

[epepke]

I don't get it, why do you say the distance is much smaller?

I can say that the distance was much smaller, in terms of the idea that it was long ago. A distance in time Or I can say that it is much smaller, given that the light arrives now. A distance in space. In relativistic terms, I don't think it matters which I pick.

In any event, my story is clearer. What I can see on the card he is holding up is a much smaller number.

Again, I'm not clear what your explanation is here. And all predictions in cosmology are derived from mathematical models of the universe based on general relativity, not on some vague intuitive mix of Euclidean and non-Euclidean ideas.

Then perhaps you could recommend some papers. Not popular treatments. I'm not really that into cosmology, so I don't know what the good papers are. I do have access to several good university libraries.

Are you talking about the visible universe, or the entire universe? Cosmologists don't think the entire universe is a sphere, that's a misconception based on imagining the Big Bang as an explosion in a preexisting space.

I hope they don't. But that's what I heard from cosmologists in the 1990s.

Presumably the visible universe is a sphere with us at the center, simply because we can see the same distance in every direction--are you suggesting otherwise?

I'm suggesting that, from our point of view, it measures as a sphere. I don't know that it means that it is a sphere. I think that it would measure as a sphere for any point in the universe at our age, which would suggest to me that, topologically, it probably isn't a sphere. But as I said, my last experience with this was not particularly enlightening to me.

[skepticalbip]

It seems to me that it follows that, as the universe is much bigger than it was 13.5 billion years ago, that what we would imagine as a sphere 13.5 billion light years in radius has a much smaller circumference. That is, let's say galaxies A and B are at opposite ends. You have a really good telescope, and you look at an astronomer in galaxy A. He is (was) measuring the distance to galaxy B. He holds up a sign with the distance, and you read it. The distance is much smaller than the 27 billion light years that we would deduce, let alone 84.8 billion light years going around the circumference.

That always seemed to me a neater explanation for the "why is the universe so uniform" than a lot of the stuff that seemed to me ad hoc and a result of mixing Euclidean and non-Euclidean ideas.

I suggested this to a cosmologist back in the 1990s, and he told me I was full of shit, and only crackpots thought that the universe was anything other than spherical, but I can't remember the explanation he used. Something about the lack of apparent curvature at large distances, but I don't see how you can measure curvature at a distance accurately without an extremely long baseline for measurments, except by making assumptions about density that may very well turn out to be wrong. Perhaps someone can explain why I am a crackpot. I sorta agree but freely admit that I have never actually been able to wrap my mind around any sort of image of what the universe is really like. The post you responded to was my poor attempt to demonstrate the folly of trying to understand the universe in Euclidean terms - which is what I saw the person I was responding to was doing.

I don't see that terms like size (in the Euclidean sense) or any description of shape (in the Euclidean sense) can have any real application or even meaning with respect to the real universe. I would think that terms like density and curviture (or degree of flatness) would be much more appropriate.

[Canard DuJour]

I can just about get away with the idea that we are on (or in) the surface of a big inflating hypersphere - although I can't picture it, obviously.

What I can't get away with is the idea that, while this hypersphere -space- is expanding, there are static spatial relations between the things on/in it. Things aren't flying apart into empty space, rather space itself is dynamic ..except when it's a stable unit of local forces holding things together. Space itself is expanding, just not round here.

Sounds like having your cake and eating it with a hint of the aether.

I wouldn't dispute the evidence or the maths, I just don't think the analogies people glibly regurtitate work. Especially since the effect has been found to be accelerating.

[epepke]

I sorta agree but freely admit that I have never actually been able to wrap my mind around any sort of image of what the universe is really like. The post you responded to was my poor attempt to demonstrate the folly of trying to understand the universe in Euclidean terms - which is what I saw the person I was responding to was doing.

Well, I'm good at topology. I can visualize any combination of E, T, and P up to four dimensions. After that, it gets kind of dicey.

I kind of suck at cosmology, though. But I was in an interdisciplinary research program for 13 years, and I know something about how difficult it can be to communicate.

I don't see that terms like size (in the Euclidean sense) or any description of shape (in the Euclidean sense) can have any real application or even meaning with respect to the real universe. I would think that terms like density and curviture (or degree of flatness) would be much more appropriate.

My problem is that I cannot see how observations of the universe from a single point (well, the Earth, but it's kinda small) can say much meaningful about overall curvature.

[Jesse]

I can say that the distance was much smaller, in terms of the idea that it was long ago. A distance in time Or I can say that it is much smaller, given that the light arrives now. A distance in space. In relativistic terms, I don't think it matters which I pick.

In any event, my story is clearer. What I can see on the card he is holding up is a much smaller number. Yeah, but isn't that just because at the time he held up the sign, the distance between galaxy A and galaxy B actually was significantly smaller than the distance between them at the time the light from the sign reaches you? Why should this conflict with the standard view of cosmology? If your point is just that the distance of objects at the time they emitted the light we're seeing now was smaller than the distance they would be now, you're right--but when cosmologists talk about the size of the visible universe, they mean the distance that the furthest object we can see in the past would be now, based on extrapolating the observable rate of expansion throughout the universe's history. Then perhaps you could recommend some papers. Not popular treatments. I'm not really that into cosmology, so I don't know what the good papers are. I do have access to several good university libraries. My college textbook was Introduction to Cosmology by Matts Roos, although I think it just took certain equations from general relativity without explaining their exact derivation. If you aren't willing to take their word for it that certain equations for the expanding universe are derived from GR models of the universe as a whole, then you'll have to get a good understanding of general relativity itself--Spacetime and Geometry by Sean Carroll is supposed to be a good intro, and then there's also the big daddy of GR textbooks, Gravitation by Misner, Thorne and Wheeler. I hope they don't. But that's what I heard from cosmologists in the 1990s. I think you probably misunderstood, whenever general relativity is applied to cosmology the assumption is always that matter and energy are homogeneously distributed throughout space on the largest scales (look at part 2 (http://www.astro.ucla.edu/~wright/cosmo_02.htm) of Ned Wright's cosmology tutorial (http://www.astro.ucla.edu/~wright/cosmolog.htm) which is also very helpful as an introduction). Perhaps the cosmologist you talked to was discussing a closed universe with positive spatial curvature, which can be imagined as an expanding 4D hypersphere with its 3D surface being all of space. I'm suggesting that, from our point of view, it measures as a sphere. Again, are you talking about the entire universe or just the visible universe? Like I said, the visible universe is a sphere just because the furthest distance we can see is the same in all directions.

[sharahan]

Expanding in the sense that distances between stuff (galaxies) become larger.


Umm, this is an open question. AFAIK, most cosmologists rather favor a finite universe. (I favor an infinite one, but this does not say much)


Galaxies are. Ever heard about Hubble and redshift?

I hope it is misunderstood for "moving" means "expanding".
By stating -Galaxies are moving - it is correct.
But the- universe is expanding - is a wrong statement .
Universe is infinite.If one say it is finite I can prove it is wrong.
For exp. if some thing is contained in a vessel. We can say the thing is confined. But there is space out side that vessel. Please try to imagine this with the universe.

[sharahan]

Expanding. Space itself is expanding.The Universe is 13.7 billion years old and 138 billion light years wide, give or take a few billion.

CC

Expanding to where? What was there ( in that space universe covering)before that expansion ? Universe is 13.7 billion years old ! How exactly you mention it ? What was there before13.7 billion years ?

[aguy2]

The Big Bang model does not say that matter is shaped like an expanding sphere,

Yes it does. To an inertial observor, the standard model is a hollow sphere of galactic clusters.

Somewhat like the spheres you mentioned in your last post.

in fact it says that matter and energy are about evenly distributed through all of space, which may be infinite or finite.

Yes, the standard model presumes isometric exspansion from a single point; this translates into a hollow sphere.

Of course the visible universe is a sphere with us at the center, but that's just because there's a limit to how far out we can see structures (since they've only been around for a finite time since the Big Bang, and the farther we look the closer to the Big Bang we're seeing), and this distance is the same in all directions.

What you are describing is a light cone or event horizon. AFAIK it is real phenomenon. If the conic jet/pulse were only slightly larger than our visual horizon, it would be very difficult to tell the difference between a conic or a spherical expansion.

You have raised some good questions, and I will try to respond to the balance of your post soon.
aguy2(amen)

[Jesse]

Yes it does. To an inertial observor, the standard model is a hollow sphere of galactic clusters. Wrong. Why do you think this? Have you actually checked any outside sources to make sure you're right, or are you just going on memories? The fact is, your understanding is incorrect, so your confidence is misplaced--confidence in your own nontechnical understanding of a theory can be a major barrier to learning in science, you need to have a healthy amount of doubt in the correctness of any nonmathematical intuitive pictures you may have in your head. Yes, the standard model presumes isometric exspansion from a single point; this translates into a hollow sphere. No, it doesn't. Read Where is the centre of the universe? (http://math.ucr.edu/home/baez/physics/Relativity/GR/centre.html) from the Usenet Physics FAQ (http://math.ucr.edu/home/baez/physics/), for example: There is no centre of the universe! According to the standard theories of cosmology, the universe started with a "Big Bang" about 14 billion years ago and has been expanding ever since. Yet there is no centre to the expansion. It is the same everywhere. The Big Bang should not be visualised as an ordinary explosion. The universe is not expanding out from a centre into space. The whole universe itself is expanding and it is doing so equally at all places, as far as we can tell.

...

A good way to help visualise the expanding universe is to compare space with the surface of an expanding balloon. This analogy was used by Arthur Eddington as early as 1933 in his book The Expanding Universe. It was also used by Fred Hoyle in the 1960 edition of his popular book The Nature of the Universe. Hoyle wrote, "My non-mathematical friends often tell me that they find it difficult to picture this expansion. Short of using a lot of mathematics I cannot do better than use the analogy of a balloon with a large number of dots marked on its surface. If the balloon is blown up the distances between the dots increase in the same way as the distances between the galaxies."

The balloon analogy is very good but needs to be understood properly otherwise it can cause more confusion. As Hoyle said "There are several important respects in which it is definitely misleading." It is important to appreciate that three dimensional space is to be compared with the two dimensional surface of the balloon. The surface is homogeneous with no point which should be picked out as the centre. The centre of the balloon itself is not on the surface and should not be thought of as the centre of the universe. If it helps you can think of the radial direction in the balloon as time. This was what Hoyle suggested, but it can also be confusing. It is better to regard points off the surface as the balloon as not being part of the universe at all. As Gauss discovered at the beginning of the 19th century, properties of space such as curvature can be described in terms of intrinsic quantities which can be measured without needing to think about what it is curving in. So space can be curved without there being any other dimensions outside. Gauss even tried to determine the curvature of space by measuring the angles of a large triangle between three hill tops.
Similarly, look at this page (http://www.astro.ucla.edu/~wright/balloon0.html) on the balloon analogy from Ned Wright's cosmology tutorial (http://www.astro.ucla.edu/~wright/cosmolog.htm): The expanding balloon analogy for cosmological models is shown below at two different times. A common misconception is that the balloon is expanding into empty space that is "beyond the Universe" and that it is expanding from a single point in the center of the balloon. But the balloon analogy is a 2-dimensional model, and the center of the balloon and the space around are not part of the 2-dimensional Universe. In our 3-dimensional Universe, these points could only be reached by traveling in a 4th spatial dimension (not the time dimension of 4-D spacetime), but there is no evidence that this dimension exists. Also on Wright's website, Where was the center of the Big Bang? (http://www.astro.ucla.edu/~wright/nocenter.html) The Big Bang has no center. It is not an explosion radiating from a point. ... There is no center because all positions in the Universe are equivalent. The Universe is homogeneous, which is part of the cosmological principle. (http://www.astro.ucla.edu/~wright/cosmo_02.htm) The book Fabric of the Cosmos by physicist Brian Greene also emphasizes on p. 229 that the Big Bang was not like an explosion in a preexisting space: In 1929, Edwin Hubble, using the 100-inch telescope at the Mount Wilson observatory in Pasadena, California, found that the couple of dozen galaxies he could detect were all rushing away. In fact, Hubble found that the more distant a galaxy is, the faster its recession. ... Actually, you might not think that coming up with an explanation would be particularly difficult. After all, if you were to pass by a factory and see all sorts of material violently flying outward in all directions, you would likely think that there had been an explosion. And if you traveled backward along the paths taken by the scraps of metal and chunks of concrete, you'd find them all converging on a location that would be a likely contender for where the explosion occurred. By the same reasoning, since the view from Earth--as attested to by Hubble's and subsequent observations--shows that galaxies are rushing outward, you might think our position in space was the location of an ancient explosion that uniformly spilled ou tthe raw material of stars and galaxies. The problem with this theory, though, is that it singles out one region of space--our region--as unique by making it the universe's birthplace ... as we are highly suspect of anthropocentric explanations laced with pre-Copernican thinking, a more sophisticated interpretation of Hubble's discovery is called for, one in which our location does not occupy some special place in the cosmic order.

General relativity provides such an interpretation. With general relativity, Einstein found that space and time are flexible, not fixed, rubbery, not rigid; and he provided equations that tell us precisely how space and time respond to the presence of matter and energy. In the 1920s, the Russian mathematician and meteorologist Alexander Friedmann and the Belgian priest and astronomer Georges Lemaître independently analyzed Einstein's equations as they apply to the entire universe, and the two found something striking. Just as the gravitational pull of the earth implies that a baseball popped high above the catcher must be heading farther upward or must be heading downward but certainly cannot be staying put (except for the single moment when it reaches its highest point), Friedmann and Lemaître realized that the gravitational pull of the matter and radiation spread throughout the entire cosmos implies that the fabric of space must either be stretching or contracting, but that it could not be staying fixed in size.

...

The flexibility of space in general relativity provides a profound way to interpret Hubble's discovery. Rather than explaining the outward motion of galaxies by a cosmic version of the factory explosion, general relativity says that for billions of years space has been stretching. And as it has swelled, space has dragged the galaxies away from each other much as the black specks in a poppy seed muffin are dragged apart as the dough rises in baking. Thus, the origin of the outward motion is not an explosion that took place within space. Instead, the outward motion arises from the relentless outward swelling of space itself.

To grasp this key idea more fully, think also of the superbly useful balloon model of the expanding universe ... This analogy likens our three-dimensional space to the easier-to-visualize two-dimensional surface of a spherical balloon ... that is being blown up to larger and larger size. The galaxies are represented by numerous evenly spaced pennies glued to the balloon's surface. Notice that as the balloon expands, the pennies all move away from one another, providing a simple analogy for how expanding space drives all galaxies to separate.

An important feature of this model is that there is complete symmetry among the pennies, since the view any particular Lincoln sees is the same as the view any other Lincoln sees. To picture it, imagine shrinking yourself, lying down on a penny, and looking out in all directions across the balloon's surface (remember, in the analogy the balloon's surface represents all of space, so looking off the balloon's surface has no meaning). What will you observe? Well, you will see pennies rushing away from you in all directions as the balloon expands. And if you lie down on a different penny what will you observe? The symmetry ensures you'll see the same thing: pennies rushing away in all directions.

...

And so, unlike a factory explosion within a fixed, preexisting space, if outward motion arises because space itself is stretching, there need be no special point--no special penny, no special galaxy--that is the center of the outward motion. Every point--every penny, every galaxy--is completely on par with every other. The view from any location seems like the view from the center of an explosion: each Lincoln sees all other Lincolns rushing away; an observer, like us, in any galaxy sees all the other galaxies rushing away. But since this is true for all locations, there is no special or unique location that is the center from which the outward motion is emanating. Finally, if you'd like a more "official" source, you can't get much more official than the GR textbook Gravitation which I mentioned to epepke, which on p. 704 in the box "cosmology in brief" lists the following two basic assumptions: Uniform density. Idealize the stars and atoms as scattered like dust through the heavenes with an effective average density rho of mass-energy everywhere the same.

Geometry homogeneous and isotropic. Idealize the curvature of space to be everywhere the same. In other words, matter and energy are assumed to fill all of space with a single uniform density and creating a uniform spatial curvature, rather than your idea that they are confined to a sphere with a density of zero outside of it, and with the curvature presumably becoming greater towards the center of the sphere and approaching zero at large distances away from it (since it is mass and energy that curve space in general relativity).

[Sven]

I hope it is misunderstood for "moving" means "expanding".
By stating -Galaxies are moving - it is correct.
But the- universe is expanding - is a wrong statement .
If everything moves apart from everything else - how can this not be an expansion?

Universe is infinite.If one say it is finite I can prove it is wrong. Ever heard about the burden of proof? :rolleyes:

For exp. if some thing is contained in a vessel. We can say the thing is confined. But there is space out side that vessel. Please try to imagine this with the universe. Please stop thinking in 3D. The universe as a whole can not be described this way. We've known this for nearly a century.

[sharahan]

If everything moves apart from everything else - how can this not be an expansion?

Ever heard about the burden of proof? :rolleyes:

Please stop thinking in 3D. The universe as a whole can not be described this way. We've known this for nearly a century.

Proof means I thought of an example to substantiate my opinion.
If I have to stop thinking in 3D, please let me know then which is the other way ?
Arguing is just to understand the fact in which I have a special interst for years.

[Sven]

Proof means I thought of an example to substantiate my opinion.
If I have to stop thinking in 3D, please let me know then which is the other way ?
4D. See the posts by Jesse.

[JamesBannon]

What gets me is that when I look out at the stars is that I'm looking at something that might not even be there.

[Tears In The Rain]

Expanding to where? What was there ( in that space universe covering)before that expansion ? Universe is 13.7 billion years old ! How exactly you mention it ? What was there before13.7 billion years ?

What's north of the North Pole?

[singularapathy]

Is the universe expanding?? Or is it that the universe ITSELF is in motion?? What is evidence for the former??

All responses appreciated.

Yes. Redshift. (Tried to make it short and sweet :D)

[epepke]

Yeah, but isn't that just because at the time he held up the sign, the distance between galaxy A and galaxy B actually was significantly smaller than the distance between them at the time the light from the sign reaches you?

Yes, if you pick the "was" interpretation.

Why should this conflict with the standard view of cosmology? If your point is just that the distance of objects at the time they emitted the light we're seeing now was smaller than the distance they would be now, you're right--but when cosmologists talk about the size of the visible universe, they mean the distance that the furthest object we can see in the past would be now, based on extrapolating the observable rate of expansion throughout the universe's history.

I don't know that it does conflict with the standard model of cosmology, whatever that is. Since I'm not a specialist, I don't know the good papers. And the only thing I know to do is talk to people. Which I'm doing. But when I did back in the 1990s, cosmologists said things to me like, "well, the light from galaxy A can't possibly have traveled to galaxy B, because they are 2 * 14.5 billion light years away, meaning that they are 29 billion light years away, and that's too long for light to have gotten there, so why is the universe so uniform? There must have been something weird happening." And then I said stuff like, "Well, the light didn't actually have to go that far, because it was a long time ago, and the distances weren't that far. So we can't naively use a sphere 14.5 billion light years in radius to determine the time. And so, if we were to reinterpret it in terms of a sphere at the present moment, determined by a constant age, what we would reconstruct as the path of travel wouldn't be a straight line." And then they started jumping up and down and waving their arms and telling me that there is no overall curvature in spacetime and telling me stuff about galaxy density. And then they told me that 29 light years was the real number, because it's really a sphere, and only idiots and crackpots think otherwise.

At this point, I kind of get lost. I think it's probably more of an anthropological problem than a problem of the physical sciences. But I make great effort to explain things to people who don't get the things that I understand, and I kind of hope that there are others who will do this for me. Perhaps that be a futile and stupid hope, but it doesn't cost me much to ask.

My college textbook was Introduction to Cosmology by Matts Roos, although I think it just took certain equations from general relativity without explaining their exact derivation. If you aren't willing to take their word for it that certain equations for the expanding universe are derived from GR models of the universe as a whole, then you'll have to get a good understanding of general relativity itself--Spacetime and Geometry by Sean Carroll is supposed to be a good intro, and then there's also the big daddy of GR textbooks, Gravitation by Misner, Thorne and Wheeler.

I have a pretty good understanding of GR. I like Dirac's little book. I just don't understand how doubling 14.5 billion light years is a valid thing to do, unless there is a weird conflation of GR and Galilean ideas.

I think you probably misunderstood, whenever general relativity is applied to cosmology the assumption is always that matter and energy are homogeneously distributed throughout space on the largest scales (look at part 2 (http://www.astro.ucla.edu/~wright/cosmo_02.htm) of Ned Wright's cosmology tutorial (http://www.astro.ucla.edu/~wright/cosmolog.htm) which is also very helpful as an introduction). Perhaps the cosmologist you talked to was discussing a closed universe with positive spatial curvature, which can be imagined as an expanding 4D hypersphere with its 3D surface being all of space. Again, are you talking about the entire universe or just the visible universe?

I don't know.

Like I said, the visible universe is a sphere just because the furthest distance we can see is the same in all directions.

That's what I have a problem with. I don't know that the fact that the visible universe can be measured as a sphere means that it is a sphere. The Earth can be measured as a disc about three miles in radius. Does that mean that the Earth is a disc?

I'd like to understand these things, and I don't, so I ask questions.

[Jesse]

Yes, if you pick the "was" interpretation. What do you mean by "the 'was' interpretation? What other interpretation are you contrasting it with? I don't know that it does conflict with the standard model of cosmology, whatever that is. Since I'm not a specialist, I don't know the good papers. And the only thing I know to do is talk to people. Which I'm doing. But when I did back in the 1990s, cosmologists said things to me like, "well, the light from galaxy A can't possibly have traveled to galaxy B, because they are 2 * 14.5 billion light years away, meaning that they are 29 billion light years away, and that's too long for light to have gotten there, so why is the universe so uniform? There must have been something weird happening." This sounds familiar--if they are talking about how distant galaxies couldn't have affected each other and worrying about how the universe could be homogenous in all directions, then it sounds like they were talking about the "horizon problem" which inflation was invented to solve--look at the bottom section of this page (http://www.astro.ucla.edu/~wright/cosmo_03.htm) from Ned Wright's cosmology tutorial, along with the discussion of inflation on the next page (http://www.astro.ucla.edu/~wright/cosmo_04.htm). But I think they were leaving out some steps in their explanation in order to make it more accessible, any detailed formulation of the horizon problem is based on projecting the past light cones of distant galaxies backwards in time according to the best models of cosmological expansion, and showing that these past light cones never would have overlapped at any time back until the Big Bang (meaning there was never an event where if light was sent in different directions at that moment, it would have been able to reach both galaxies at the age they were when they sent out the light we're seeing now. But if you allow the universe to have undergone a period of very rapid expansion shortly after the Big Bang, an idea that is made plausible by certain ideas from quantum field theory, then distant regions could have been much closer at early times than would be suggested by the non-inflationary cosmological model, so this is a possible explanation for the homogeneity. And then I said stuff like, "Well, the light didn't actually have to go that far, because it was a long time ago, and the distances weren't that far. Yes, that's understood. But when the distances were shorter, the amount of time since the Big Bang was also less so light couldn't have gotten as far since the Big Bang. Look at the "conformal spacetime diagram" from Ned Wright's discussion of the horizon problem:

http://www.astro.ucla.edu/~wright/horizon.gif

The red lines are the past light cone of our current position and time, the black line at the bottom is the Big Bang, and the blue line is the moment of "recombination" when the universe first became transparent to light, which is the furthest back in time we can see anything since before that any light emitted would almost immediately be scattered or absorbed. The tips of the two yellow triangles represent two events at the time of recombination on the opposite side of the sky where the light from both events would just be reaching us now (both as photons from the cosmic microwave backround radiation), and the yellow triangles are the past light cones of these events--you can see that the cones don't come close to intersecting, so there's no common cause that could explain why the CMBR would appear to have the same temperature on opposite sides of the sky. But inflation could solve the problem, because as the next page of Ned Wright's tutorial explains, "he future lightcone of an event that happens before inflation is expanded to a huge region by the growth during inflation." Here's an image depicting this (the green region is the inflationary period, and the future light cones of events immediately before and immediately after inflation are shown:

http://www.astro.ucla.edu/~wright/cosmo250.gif

So we can't naively use a sphere 14.5 billion light years in radius to determine the time. And so, if we were to reinterpret it in terms of a sphere at the present moment, determined by a constant age, what we would reconstruct as the path of travel wouldn't be a straight line." And then they started jumping up and down and waving their arms and telling me that there is no overall curvature in spacetime and telling me stuff about galaxy density. Well, why did you say "what we would reconstruct as the path of travel wouldn't be a straight line"? In a spatially flat expanding universe, I believe light would always move in straight lines--why do you think it wouldn't? The expansion of space wouldn't cause the path of light to bend although it would cause its frequency to change (redshift). When they talked about galaxy density, perhaps they were explaining the evidence that the universe is very close to spatially flat (see the top of p. 3 (http://www.astro.ucla.edu/~wright/cosmo_03.htm) of Ned Wright's cosmology tutorial for a discussion of the different possible curvatures), although I don't know how strong the evidence for this was in the 1990s. And then they told me that 29 light years was the real number, because it's really a sphere, and only idiots and crackpots think otherwise. Well, it's obvious from the context above that both you and they were talking about the observable universe--the set of all objects for which signals moving at the speed of light (including signals which aren't actually electromagnetic, like gravitational waves) would have had the chance to reach us if the object emitted it in our direction any time after the Big Bang. Again, this is a sphere just because light-speed signals could have traveled the same distance in all directions, but this isn't saying anything about the shape of the universe as a whole, just the part that could possibly have had a causal influence on us today.

And as for the size of the visible universe being 29 light-years, either you misunderstood or they forgot that because of the expansion of space the radius in light-years is not just equal to the time in years since the Big Bang. For example, this paper (http://arxiv.org/abs/astro-ph/0310233) established a lower bound on the diameter of the observable universe as being about 24 Gigaparsecs or 78 light-years, so the radius must be at least 39 light-years. That's what I have a problem with. I don't know that the fact that the visible universe can be measured as a sphere means that it is a sphere. The Earth can be measured as a disc about three miles in radius. Does that mean that the Earth is a disc?

I'd like to understand these things, and I don't, so I ask questions. But that's what the "observable universe" means, the part that you could possibly see, the actual universe could be much larger, possibly infinite. If we talked about the "observable Earth" then yes, it might make sense to say "the observable Earth is a disc about three miles in radius". The only difference is that in the case of the Earth "observable" is a practical matter involving line-of-sight issues, whereas anything outside the observable universe could not send a signal to us in principle unless FTL were possible, since if an object is outside the observable universe that means even if it sent a signal towards us at the speed of light an arbitrarily short time after the Big Bang, the signal still would not have been able to reach us by today because of the expansion of space between ourselves and the object.

[aguy2]

in re: "Is the standard model a hollow sphere?"

Wrong. Why do you think this? Have you actually checked any outside sources to make sure you're right, or are you just going on memories? The fact is, your understanding is incorrect, so your confidence is misplaced--confidence in your own nontechnical understanding of a theory can be a major barrier to learning in science, you need to have a healthy amount of doubt in the correctness of any nonmathematical intuitive pictures you may have in your head. No, it doesn't. Read Where is the centre of the universe? (http://math.ucr.edu/home/baez/physics/Relativity/GR/centre.html) from the Usenet Physics FAQ (http://math.ucr.edu/home/baez/physics/), for example:

The conclusion the above article draws is that, "IOW although the standard BB models describe an expanding universe with no centre, and this is consistent with all observations, there is still a possibility that these models are not accurate on scales larger than we can observe. Our ignorance about the real answer to the question, "Where is the centre of the universe?" is complete."

Whether the standard model is seen as a sphere with no center, is moot insofar as my model goes. My model presumes there is a center. A reduced but still extant BB event/body, that we have been interpreting as 'dark energy'.

I have a question though. If we presume ours is not the 1st oscillation/cycle, does the standard model assume the previously created space 'contracted' in a BC?

Similarly, look at this page (http://www.astro.ucla.edu/~wright/balloon0.html) on the balloon analogy from Ned Wright's cosmology tutorial (http://www.astro.ucla.edu/~wright/cosmolog.htm): Also on Wright's website, Where was the center of the Big Bang? (http://www.astro.ucla.edu/~wright/nocenter.html)

IOW words, 'a balloon (hollow sphere) with no center'.

In other words, matter and energy are assumed to fill all of space with a single uniform density and creating a uniform spatial curvature, rather than your idea that they are confined to a sphere with a density of zero outside of it, and with the curvature presumably becoming greater towards the centre of the sphere and approaching zero at large distances away from it (since it is mass and energy that curve space in general relativity).

Where did you get this? My model proposes no "spheres".
aguy2(amen)

[sharahan]

What's north of the North Pole?

It could be answered only if some one give answer for- what is that south of south pole?
And also -why it is not mentioned as east pole & west pole ?
:huh:

[sharahan]

4D. See the posts by Jesse.

We made only a dimensional analogy to imagine the universe.
Then we assume that universe is contained in a hypersphere.
So the word "universe" means that which we imagined to be confined in a hypersphere and in that case it proved to be finite and expanding. Because an infinity will not be increasing.
Which is the largest whole number?
Which is the smallest fraction?
If we can send an imaginary space ship of speed of 1000 billion light years per hour for an expedition; up to what extent it will go?

[Sven]

We made only a dimensional analogy to imagine the universe.
Then we assume that universe is contained in a hypersphere.
No, we don't make this assumption.
As I said: Read Jesse's posts and follow the links.

Because an infinity will not be increasing.
Which is the largest whole number? Wrong. Take all integers. There's an infinite number of them.
Multiply all of them by two. The distance between each number has doubled, but there's still the same number of them. With the universe, it could be the same.

If we can send an imaginary space ship of speed of 1000 billion light years per hour for an expedition; up to what extent it will go? As far as I understand it, for certain geometries of space you'll eventually return to from where you've started, even though you'Ve travelled in a straight line.

[Jesse]

The conclusion the above article draws is that, "IOW although the standard BB models describe an expanding universe with no centre, and this is consistent with all observations, there is still a possibility that these models are not accurate on scales larger than we can observe. Our ignorance about the real answer to the question, "Where is the centre of the universe?" is complete." We are talking about the standard model of cosmology. It is true that GR could allow us to model a spherical explosion with a center, but this is not the standard model. Also notice that the spherical explosion wouldn't be an ordinary explosion, it'd be a gigantic white hole (see the bottom part of this section (http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/universe.html) from the same FAQ), a time-reversed version of a black hole that spews out matter from a singularity rather than absorbing matter falling in to a singularity. Although white holes are valid solutions in GR, they are considered unlikely on thermodynamic grounds. Also, if your "jet" did not arise from an initial singularity, I doubt it would be possible in GR, because I don't see how a time-reversed version of an expanding jet the size of the universe (ie one where you reverse the momenta of all the particles making it up) could avoid collapsing into a singularity as all those particles converge on the position the jet originated. And if you are proposing a jet shooting out from a singularity, this would be a weird sort of white hole that only spewed out matter in a certain direction, you'd have to check that this is actually compatible with GR. Whether the standard model is seen as a sphere with no center The standard model of a closed universe is a the surface of a hypersphere with no center--a hypersphere is the 4-dimensional analogue of a sphere, whose surface is 3-dimensional, in just the same way that a 3-dimensional sphere has a 2-dimensional surface (any point on the surface can be specified with 2 coordinates).

Note that there are actually 3 possible curvatures for space in the standard model of cosmology--closed, flat, and open (positive curvature, zero curvature, and negative curvature). The balloon model is just a 2-dimensional analogue for the closed universe with positive curvature. If the universe was flat instead, a 2D analogy for this would be an infinite plane, and if you drew a grid on this plane like a chessboard, all the squares would be simultaneously growing at the same rate, while the amount of matter/energy in each square would stay constant (you could represent as a chesspiece which stays the same size as the squares grow), so that the density is constantly decreasing. Again, this is just an analogy with one dimension taken away, the surface of the 2D plane actually represents our 3D space. An open universe with negative curvature is a bit harder to picture with a 2-dimensional analogy, but it's usually drawn as a sort of saddle-shape, and again, if you drew squares on it they'd be constantly expanding. The top of part 3 of Ned Wright's cosmology tutorial (http://www.astro.ucla.edu/~wright/cosmo_03.htm) explains about these three types of curvature and illustrates 2D analogues for each one:

http://www.astro.ucla.edu/~wright/3geomtrs.gif

Current observational evidence actually favors a flat universe, not a closed one. I have a question though. If we presume ours is not the 1st oscillation/cycle, does the standard model assume the previously created space 'contracted' in a BC? General relativity on its own does not predict any sort of oscillation, proposals about oscillatory universes invoke quantum effects that might prevent a Big Crunch from collapsing into a final singularity once its density reaches the Planck scale, and instead cause it to reinflate in a new Big Bang. But this is very speculative, without a theory of quantum gravity physicists don't know if there's any justification for such a "bounce". Another idea which has developed from the notion of inflation is that of "chaotic inflation" or "eternal inflation" (see here (http://www.astro.ucla.edu/~wright/CMB-MN-03/inflating_bubble.html) and here (http://arxiv.org/abs/hep-th/0702178) and here (http://www.physicsforums.com/archive/index.php/t-13701.html)), where new universes can randomly inflate from very small patches of older universes, which doesn't require the older universe to have collapsed into a Big Crunch. IOW words, 'a balloon (hollow sphere) with no center'. No, didn't you read all the comments that the balloon model is an analogy where the 2D surface of the sphere represents 3D space? Again, the actual model involves a 4D hypersphere whose surface is our 3D space, and matter and energy are homogeneously distributed throughout all of 3D space (all of the 'surface'). In other words, matter and energy are assumed to fill all of space with a single uniform density and creating a uniform spatial curvature, rather than your idea that they are confined to a sphere with a density of zero outside of it, and with the curvature presumably becoming greater towards the centre of the sphere and approaching zero at large distances away from it (since it is mass and energy that curve space in general relativity). Where did you get this? My model proposes no "spheres". When I referred to "your idea", I was talking about your mistaken idea about the standard model of cosmology, not your idea about the jet.

[aguy2]

in re: standard model vs. jet/pulse model

We are talking about the standard model of cosmology. It is true that GR could allow us to model a spherical explosion with a center, but this is not the standard model. Also notice that the spherical explosion wouldn't be an ordinary explosion, it'd be a gigantic white hole (see the bottom part of this section (http://math.ucr.edu/home/baez/physics/Relativity/BlackHoles/universe.html) from the same FAQ), a time-reversed version of a black hole that spews out matter from a singularity rather than absorbing matter falling in to a singularity. Although white holes are valid solutions in GR, they are considered unlikely on thermodynamic grounds. Also, if your "jet" did not arise from an initial singularity,

We can presume it does arise from an initial singularity, while keeping in mind that everything past the inflationary epoch is conjecture.

I doubt it would be possible in GR, because I don't see how a time-reversed version of an expanding jet the size of the universe (ie one where you reverse the momenta of all the particles making it up)

Are 'time-reversed' and 'momenta reversed' necessarily conflated? The jet/pulse model supports conserved/equivalent timespace, in that 'new' space is being created right up to the BC, or "till our universe has run out time".

could avoid collapsing into a singularity as all those particles converge on the position the jet originated.

The jet/pulse model assumes collapse is the norm.

And if you are proposing a jet shooting out from a singularity, this would be a weird sort of white hole that only spewed out matter in a certain direction, you'd have to check that this is actually compatible with GR.

The jet/pulse model assumes the inflationary epoch was akin to a polar jet/pulse ejected from a BB event/body that displays a high degree of AM. It assumes an anti-matter jet/pulse was also ejected from the other pole.

The standard model of a closed universe is a the surface of a hypersphere with no center--a hypersphere is the 4-dimensional analogue of a sphere, whose surface is 3-dimensional, in just the same way that a 3-dimensional sphere has a 2-dimensional surface (any point on the surface can be specified with 2 coordinates).

Note that there are actually 3 possible curvatures for space in the standard model of cosmology--closed, flat, and open (positive curvature, zero curvature, and negative curvature).

The jet/pulse model assumes we are currently in the early stages of a turbulence supported 'hang time', where we could expect observation would see a 'flat' condition.

The balloon model is just a 2-dimensional analogue for the closed universe with positive curvature. If the universe was flat instead, a 2D analogy for this would be an infinite plane, and if you drew a grid on this plane like a chessboard, all the squares would be simultaneously growing at the same rate, while the amount of matter/energy in each square would stay constant (you could represent as a chesspiece which stays the same size as the squares grow), so that the density is constantly decreasing. Again, this is just an analogy with one dimension taken away, the surface of the 2D plane actually represents our 3D space. An open universe with negative curvature is a bit harder to picture with a 2-dimensional analogy, but it's usually drawn as a sort of saddle-shape, and again, if you drew squares on it they'd be constantly expanding. The top of part 3 of Ned Wright's cosmology tutorial (http://www.astro.ucla.edu/~wright/cosmo_03.htm) explains about these three types of curvature and illustrates 2D analogues for each one:

http://www.astro.ucla.edu/~wright/3geomtrs.gif

Current observational evidence actually favors a flat universe, not a closed one.

See above.

General relativity on its own does not predict any sort of oscillation, proposals about oscillatory universes invoke quantum effects that might prevent a Big Crunch from collapsing into a final singularity once its density reaches the Planck scale, and instead cause it to reinflate in a new Big Bang. But this is very speculative, without a theory of quantum gravity physicists don't know if there's any justification for such a "bounce". Another idea which has developed from the notion of inflation is that of "chaotic inflation" or "eternal inflation" (see here (http://www.astro.ucla.edu/~wright/CMB-MN-03/inflating_bubble.html) and here (http://arxiv.org/abs/hep-th/0702178) and here (http://www.physicsforums.com/archive/index.php/t-13701.html)), where new universes can randomly inflate from very small patches of older universes, which doesn't require the older universe to have collapsed into a Big Crunch.

The jet/pulse model sees the inflationary epoch as a polar ejection from a BB event/body, that due to its high degree of AM could only expand slowly.

No, didn't you read all the comments that the balloon model is an analogy where the 2D surface of the sphere represents 3D space?

My jet/pulse 'fountain' is an analogy to.

Again, the actual model involves a 4D hypersphere whose surface is our 3D space, and matter and energy are homogeneously distributed throughout all of 3D space (all of the 'surface').

Is this standard model presumption holding up to observation?

When I referred to "your idea", I was talking about your mistaken idea about the standard model of cosmology, not your idea about the jet.

Yes, I may have refered to the jet/pulse model presuming a 'center of the universe', and you may have thought I was talking about your balloon (hollow sphere) analogy.

You are asking good questions. I am hoping that you will continue.
aguy2(amen)

[pG4]

I may have just found a problem with expansion.

It takes force to move bodies apart. Unless space exerts some kind of force on bodies, why wouldn't it just expand leaving everything right where it is. It's not like bodies are attached to space like dots on a balloon?

[Jesse]

Are 'time-reversed' and 'momenta reversed' necessarily conflated? The jet/pulse model supports conserved/equivalent timespace, in that 'new' space is being created right up to the BC, or "till our universe has run out time". Well, GR is a time-symmetric theory, which means that if you have a valid solution to GR, then you'll always be able to find another solution whose time-evolution in the forward direction looks just like a reversed film of the first solution. Newtonian mechanics is also time-symmetric, and if you start a system off at time t0 and let it evolve to some time t1, then freeze it at t1 and create a new system just like that except with all the instaneous momenta reversed, this new system's future evolution will be a reversed version of the first system. I can't say for sure that reversing momentum 4-vectors is sufficient to find the reversed version of a system's time-evolution in GR, but I would think so. The jet/pulse model assumes the inflationary epoch was akin to a polar jet/pulse ejected from a BB event/body that displays a high degree of AM. It assumes an anti-matter jet/pulse was also ejected from the other pole. Again, you'd have to verify that GR actually allows a white hole that shoots out matter in two jets like that--it might, but it's not obvious. And you should also consider the fact that white holes would be able to massively violate the 2nd law of thermodynamics--since the 2nd law is a statistical one, and since the initial low entropy of the universe in the standard cosmological model is a bit of a mystery, this shouldn't totally rule out white holes, but it is a reason to be doubtful about them. The jet/pulse model assumes we are currently in the early stages of a turbulence supported 'hang time', where we could expect observation would see a 'flat' condition. Maybe that makes sense in terms of your mental picture, but to verify that the jet would indeed resemble an expanding flat universe as seen from within, you'd need some actual calculations. My jet/pulse 'fountain' is an analogy to. But the balloon model is an analogy for a preexisting verified solution of GR, whereas you start off with an analogy and hope that it will correspond to something that's actually allowed by GR. Again, the actual model involves a 4D hypersphere whose surface is our 3D space, and matter and energy are homogeneously distributed throughout all of 3D space (all of the 'surface') Is this standard model presumption holding up to observation? As I noted earlier, the balloon analogy is just meant to represent a closed universe with positive curvature, whereas the standard model allows other possible curvatures. Currently observations suggest the curvature is as close to "flat" as measurement techniques allow physicists to verify, and I think the evidence for this close-to-flatness is pretty strong, as well as the evidence for homogeneity on large scales. Yes, I may have refered to the jet/pulse model presuming a 'center of the universe', and you may have thought I was talking about your balloon (hollow sphere) analogy. I was thinking of these quotes: To an inertial observor, the standard model is a hollow sphere of galactic clusters. and Yes, the standard model presumes isometric exspansion from a single point; this translates into a hollow sphere. I interpreted "hollow sphere" to have its ordinary 3-dimensional meaning, and "expansion from a single point" to mean "from a single point in space", i.e. a center. Are you saying that you were actually referring to a 4D hypersphere in these quotes, and that you understood that no physical meaning is assigned to points outside its "surface"?

[Sven]

I may have just found a problem with expansion.

It takes force to move bodies apart. Unless space exerts some kind of force on bodies, why wouldn't it just expand leaving everything right where it is. It's not like bodies are attached to space like dots on a balloon?
You look at this thw wrong way: Things are not moving apart, space is expanding!

And what you forgot to take into account is the initial velocity of all bodies - the forces just act to slow down the bodies. If the initial velocities are large enough for the expansion to continue forever is an open question.

[aguy2]

in re: "time reversals"

Well, GR is a time-symmetric theory, which means that if you have a valid solution