Galaxy at edge of universe?

[Dinosaur]

Another thread got me to thinking about conditions in a galaxy at the edge of the universe.

First: Is there a region at the leading edge of the expansion? In the expanding balloon analogy with one spatial dimension suppressed, the present 2D surface of a sphere is all the space there is and all of it is the leading edge of the expansion. Is the entire 3D space of our universe at the leading edge of the expansion?

I have never seen an article which explicitly stated that all of our 3D space is at the leading edge, but I suspect that it might be so.

If the answer to the above is that all of our 3D space is at the leading edge of the expansion, there is no point to the following.

Would an intelligent observer in a galaxy near the leading edge of the expansion have evidence that his position was different from that of other galaxies? Might he be able to detect a net gravitational force toward a more centrally located region?

I have read about some great attractor which is pulling our local galactic cluster and several others toward Centaurus at about 600 km per second.This mass migration includes the Local Group, the Virgo Cluster, the Hydra--Centaurus Supercluster, and other groups and clusters for a distance of at least 60 Mpc up and downstream from us. It is as if a great river of galaxies (including our own) is flowing with a swift current of 600 km/s toward Centaurus.

Might there be other anomalies in a region near the edge of the universe? When Big Bang cosmology included the possibility of gravity overcoming the expansion, it was suggested that our universe might be inside the Event Horizon of a huge Black Hole. In such a universe, I would expect the region inside but near the Event Horizon to be very peculiar compared to our local region.

[blobrana]

Yea, i believe that 3D space is at the leading edge ... This is the old idea of a `hyper-balloon` expanding.
This would also mean that all points on the surface of the balloon are equally `near` to the edge. So there is no unique point in our universe that is at the centre or at the edge...(the real points lie in higher dimensions..).

The great attractor is only a `local` wall of Galaxy's, (the universe seems to be frothy and full of huge bubbles), and hasn`t really anything to do with the edge of the universe...

But it has to be said that there are multi-universe theories that suggest that false vacuum bubbles exponentially grew into universes each with a `wall` or boundary, these wall would be far beyond our universes `horizon`, and we would be very unlucky to find ourselves near to one of these boundaries...
(the density of the universe would be higher at the boundaries than say the centre)

[The `horizon` of our universe lies over 13 billion LY away, and it is racing away from us at the speed of light, er, almost like a Black-hole]

Anyway the expansion of the universe isn`t going to stop, well according to the WMAP space-probe results...

[Norman]

Yea, i believe that 3D space is at the leading edge ... This is the old idea of a `hyper-balloon` expanding.
This would also mean that all points on the surface of the balloon are equally `near` to the edge. So there is no unique point in our universe that is at the centre or at the edge...(the real points lie in higher dimensions..).

The great attractor is only a `local` wall of Galaxy's, (the universe seems to be frothy and full of huge bubbles), and hasn`t really anything to do with the edge of the universe...

But it has to be said that there are multi-universe theories that suggest that false vacuum bubbles exponentially grew into universes each with a `wall` or boundary, these wall would be far beyond our universes `horizon`, and we would be very unlucky to find ourselves near to one of these boundaries...
(the density of the universe would be higher at the boundaries than say the centre)

[The `horizon` of our universe lies over 13 billion LY away, and it is racing away from us at the speed of light, er, almost like a Black-hole]

Anyway the expansion of the universe isn`t going to stop, well according to the WMAP space-probe results...

If you ever get any good observational data confirming that the edge or "horizon" of the universe or distant "wall" or "boundary" has been found, let us know.....I think it would be interesting to catch a glimpse of it using the Hubble don't you think? Or should we conclude that the Hubble would need a 3X barlow lens to see it?

Atta Boy :)

[blobrana]

If you ever get any good observational data confirming that the edge or "horizon" of the universe or distant "wall" or "boundary" has been found, let us know.....I think it would be interesting to catch a glimpse of it using the Hubble don't you think? Or should we conclude that the Hubble would need a 3X barlow lens to see it?

Atta Boy :)


Sry, i didn`t explain that very well....
The horizon is just the limiting distance that light could have travelled since the big-bang (when we look into space we look back in time)...So we sit in an expanding shell that has a radius of 13.7 billion light years (the time since the big bang). It`s our visible universe...

The `wall/boundary` is a boundary formed by the expansion of a false vacuum, and maybe 10⁵⁰ times bigger than our visible universe....

Came across a good realplayer stream describing the concepts, er, and string theory...From the guy that wrote <b>The Elegant Universe</b>,...
physicist Brian Greene developed a reputation for explaining complex scientific theories with insight and clarity.
His new book is `<b>The Fabric of the Cosmos: Space, Time, and the Texture of Reality</b>`.

http://www.npr.org/dmg/dmg.html?prgCode=FA&showDate=16-Mar-2004&segNum=1&NPRMediaPref=RM

Greene is a professor of physics and mathematics at Columbia University.
He received his undergraduate degree from Harvard and his doctorate from Oxford, where he was a Rhodes scholar.

[Dinosaur]

Blobrana: The light from the Cosmic microwave Background radiation has been traveling for 13-14 billion years, but the path is now about 45 billion light years due to expansion while the light was traveling. I am not sure what the implications are for the size of our current observable universe. I believe that our observable universe is determined by calculating the distance at which the current recession velocity is the speed of light. This seems to be a theretical distance. It suggests to me that we cannot observe the limits of our so called observable universe.

BTW: When I try to carefully analyze certain Big Bang concepts, I get confused and think I am missing some critical insights.

I do not think the balloon analogy can be taken too literally. The 3D surface of a 4D sphere would have curvature. 2D creatures on the surface of a 3D sphere could make measurements indicating that they were not on a 2D Euclidean plane. Similarly, we could (in principle) make measurements to determine if our 3D space is Euclidean. I have never heard of anybody suggesting that we attempt such measurements, suggesting to me that our 3D space is Euclidean. If so, the balloon analogy is not a good model of the space part of our space time continuum. Even if it is a good analogy, it is a counterintuitive model.

Try to imagine the situation of 2D creatures on the expanding 2D surface of a sphere. In every direction for an infinitesimal distance, they are looking along a tangent to the surface of the 2D sphere. The objects they see are actually on the surface of a smaller 2D sphere inside the surface on which they reside at any particular instant.

Nearby objects can be considered to be on the surface of their current sphere. This is a very good approximation is of their reality. Note that they see distant objects on the surface of their current sphere when they are on the surface of a larger sphere.

A cosmologically distant object is on the surface of a sphere with radius which is a fraction of the radius of their current sphere. Yet they are not looking along a radius vector (or even a straight line) from their current sphere to that very distant objct on the small sphere. Every line of sight starts in a direction tangent to their current sphere, but gets to a point on some tiny sphere far inside their current sphere.

Note that the direction perpendicular to their current sphere (a radius vector to the origin) is not a direction in which they can look. The ballon analogy tells us that the 2D creatures cannot see objects very close to them in what we consider space, but which is a time distance, not a space distance for them.

When analyzed more carefully, the balloon analogy is not as helpful as it seems at first glance.

My mind boggles when I try to think of the world line of a star ship not using some worm hole technology. It boggles more when I try to think of the worm hole or warp drive world line.

[Norman]

Blobrana: The light from the Cosmic microwave Background radiation has been traveling for 13-14 billion years, but the path is now about 45 billion light years due to expansion while the light was traveling. I am not sure what the implications are for the size of our current observable universe. I believe that our observable universe is determined by calculating the distance at which the current recession velocity is the speed of light. This seems to be a theretical distance. It suggests to me that we cannot observe the limits of our so called observable universe.

BTW: When I try to carefully analyze certain Big Bang concepts, I get confused and think I am missing some critical insights.

I do not think the balloon analogy can be taken too literally. The 3D surface of a 4D sphere would have curvature. 2D creatures on the surface of a 3D sphere could make measurements indicating that they were not on a 2D Euclidean plane. Similarly, we could (in principle) make measurements to determine if our 3D space is Euclidean. I have never heard of anybody suggesting that we attempt such measurements, suggesting to me that our 3D space is Euclidean. If so, the balloon analogy is not a good model of the space part of our space time continuum. Even if it is a good analogy, it is a counterintuitive model.

Try to imagine the situation of 2D creatures on the expanding 2D surface of a sphere. In every direction for an infinitesimal distance, they are looking along a tangent to the surface of the 2D sphere. The objects they see are actually on the surface of a smaller 2D sphere inside the surface on which they reside at any particular instant.

Nearby objects can be considered to be on the surface of their current sphere. This is a very good approximation is of their reality. Note that they see distant objects on the surface of their current sphere when they are on the surface of a larger sphere.

A cosmologically distant object is on the surface of a sphere with radius which is a fraction of the radius of their current sphere. Yet they are not looking along a radius vector (or even a straight line) from their current sphere to that very distant objct on the small sphere. Every line of sight starts in a direction tangent to their current sphere, but gets to a point on some tiny sphere far inside their current sphere.

Note that the direction perpendicular to their current sphere (a radius vector to the origin) is not a direction in which they can look. The ballon analogy tells us that the 2D creatures cannot see objects very close to them in what we consider space, but which is a time distance, not a space distance for them.

When analyzed more carefully, the balloon analogy is not as helpful as it seems at first glance.

My mind boggles when I try to think of the world line of a star ship not using some worm hole technology. It boggles more when I try to think of the worm hole or warp drive world line.


Yea...You know I think you're right about the "balloon" and expandng universe concept. It would be extremely difficult to blow up your basic balloon to the same size of the universe. You'd probably run out to breath by then anyway. However, if the scientific urge is still there and you want to give it a try, I'm sure a toy balloon salesman would be happy to sell you a few to get you going......I'm sure after a couple of light years of blowing up balloons, you'd probably lose interest in it anyway.........Give me a worm hole or warp drive anyday........Keep us posted.

Atta Boy :)

[Pete]

The word "expanding" in "expanding universe" is used in a subtly different way to the ordinary meaning of the term.

Ordinarily, we use "expanding" from an external point of view. We observe the outside of something, and note that its outside dimensions are growing.

In the case of the universe, that does not apply. We observe some points inside, and note that all those points are getting further apart from each other, and that's all that "expanding" means in this context.

To deduce from the word "expanding" that the universe has an outside surface that is growing larger is not sound, but an artefact of the way that we're used to using the word.

[Norman]

Cool.....Maybe you can pass on the exact size of the universe as it is now, plus or minus a couple of lightyears will do nicely.........Will you measure it from the inside out or from the outside in? Keep us posted.

Atta Boy

[Pete]

As far as we can tell so far, the size of the universe is unknown but probably infinite.

That makes it a bit hard to measure - especially from the outside in!

[Norman]

As far as we can tell so far, the size of the universe is unknown but probably infinite.

That makes it a bit hard to measure - especially from the outside in!


I think there's probably an end to the universe just like there was probably a beginning to it or we wouldn't keep using the term "Big Bang". It's natural to assume just because we can't measure something because we can't see the end to it doesn't mean that it doesn't have an end.......Or do you know something we don't???

Atta Boy

[Pete]

Do you know something all the world's cosmologists don't?

[Norman]

Do you know something all the world's cosmologists don't?

I was going to ask you the same question, but seeing how I have already asked it, now is your chance to give us some dimensional aspects (metric is O.K.) on how big or "infinite" as you said you think the universe really is?

Atta Boy :)

[Pete]

Why do you suggest that I think I know exactly how big the Universe is?

Let me spell it out...
When you want to know how big something is, the easiest way is to look at the edges, and see how far apart they are. Right?
When you say something is expanding, it's usually because you're looking at the edges, and they're getting further apart. Right?

This can't be done for the universe.
We can't see the edges. We don't know how far apart they are. We don't know if they're getting further apart. We don't know if there are any edges. And since the Universe is unique in our experience, there's no reason to assume one way or the other without further evidence.

Now as it happens, there is further evidence. If you spend a little time to learn some cosmology, you'll find that the best evidence suggests that there are no edges, and that the Universe stretches on forever.

So, you want to know how big I think the Universe is? I don't know, but if I had to bet, I'd say infinite (that's the same in both miles and km). Because that's what the evidence I'm aware of suggests.

Your turn, AttaBoy. What do you know that everyone else doesn't that makes you think that there's probably an end to the Universe?

[Norman]

Why do you suggest that I think I know exactly how big the Universe is?

Let me spell it out...
When you want to know how big something is, the easiest way is to look at the edges, and see how far apart they are. Right?
When you say something is expanding, it's usually because you're looking at the edges, and they're getting further apart. Right?

This can't be done for the universe.
We can't see the edges. We don't know how far apart they are. We don't know if they're getting further apart. We don't know if there are any edges. And since the Universe is unique in our experience, there's no reason to assume one way or the other without further evidence.

Now as it happens, there is further evidence. If you spend a little time to learn some cosmology, you'll find that the best evidence suggests that there are no edges, and that the Universe stretches on forever.

So, you want to know how big I think the Universe is? I don't know, but if I had to bet, I'd say infinite (that's the same in both miles and km). Because that's what the evidence I'm aware of suggests.

Your turn, AttaBoy. What do you know that everyone else doesn't that makes you think that there's probably an end to the Universe?

I'm sure the your documentary on the subject of cosmology will be included in future astronomical texts concerning the "Size of The Universe", especially the part about "We don't Know".........You must mean "I don't Know" and any of your dialogue on this part means that "You Don't Know" either.....So any opinion on the subject concerning the size of the Universe may be considered as "Possible"........

Atta Boy :)

[Pete]

No shit, Sherlock, but possible doesn't mean probable.

What do you know that everyone else doesn't that makes you think that there's probably an end to the Universe?

[crazymikey]

This can't be done for the universe.
We can't see the edges. We don't know how far apart they are. We don't know if they're getting further apart. We don't know if there are any edges. And since the Universe is unique in our experience, there's no reason to assume one way or the other without further evidence.

Now as it happens, there is further evidence. If you spend a little time to learn some cosmology, you'll find that the best evidence suggests that there are no edges, and that the Universe stretches on forever.

So, you want to know how big I think the Universe is? I don't know, but if I had to bet, I'd say infinite (that's the same in both miles and km). Because that's what the evidence I'm aware of suggests.

I was just going to make the same point, when I saw the title of the thread.
How do we say there is an edge of the universe, when we have no evidence to support it being finite. Logically, it should be infinite, because beyond a finite universe, what is there, if not more space?

[Zarkov]

There is a restaurant at the END of the Universe... Douglas Adams wrote about it!!!!

therefore there must be a beginning.......
therefore the Universe can only be really small


:rolleyes:

[Norman]

I was just going to make the same point, when I saw the title of the thread.
How do we say there is an edge of the universe, when we have no evidence to support it being finite. Logically, it should be infinite, because beyond a finite universe, what is there, if not more space?


You said the secret word......."No evidence to support it being finite"......as they say.....So who is to say it is finite??? When you say finite, or probably finite, then you and all the others are only "Guessing" that it is finite!!! Even the worlds's greatest cosmologists are only "Guessing" that the universe is finite......They have "No" evidence either and that's the bottom line.............So your guess is as good as mine!!!

Atta Boy :) :) :)

[John Connellan]

I was just going to make the same point, when I saw the title of the thread.
How do we say there is an edge of the universe, when we have no evidence to support it being finite. Logically, it should be infinite, because beyond a finite universe, what is there, if not more space?

I don't know why people still don't get it. To answer your question, there is nothing beyond this universe (which is finite) not empty space like u say :rolleyes:

[Norman]

Of course you've been there an seen it.........Right???

Atta Boy

[John Connellan]

....Right :D

[Pete]

... this universe (which is finite)...
Are you sure about that?

[Dinosaur]

I do not think there is evidence for either a finite or an infinite universe.

If Big Bang cosmology provides a reasonable description of our universe, it indicates that the matter and energy of our universe is contained in a finite but expanding volume of 3D space. Perhaps finite but expanding 4D space/time continuum might be more precise. This neither supports nor refutes a finite 3D space (or 4D continuum).

It seems reasonable to believe that matter/energy cannot exist independent of space & time. Is there any reason to suppose the converse? Can space/time exist without matter and energy? Our intuitive concepts relating to space and time make them seem independent of matter and energy, but since when does our intuition equate to evidence? We have no experimental data relating to space/time containing neither matter nor energy. It seems impossible to obtain any such data.

Relativity theory refutes some of our intuitive notions about space and time being independent of each other? Quantum Theory refutes all sorts of intuitive concepts about reality. Why trust our intuition about space and time being independent of matter & energy? Why trust our intuitive notions about space being finite or infinite? It appears that some here think space is finite, while others think it is infinite. Does anybody have evidence supporting either belief?

Was there time & space before the Big Bang? Who knows? Is there space beyond the matter and energy contained in our universe? Who knows?

[Pete]

If Big Bang cosmology provides a reasonable description of our universe, it indicates that the matter and energy of our universe is contained in a finite but expanding volume of 3D space.

I was under the understanding that Big bang cosmology does not dictate a finite volume containing the universe's mass and energy; quite the opposite if the overall curvature of space-time is negative or zero (as it appears to be).

[crazymikey]

Dinosaur,

The big bang dictates the spatial dimensions and volume of the known universe, it does not dictate the the volume of the universe in totality. The origin of the universe, if there is indeed an origin, is not explainable by a big bang. For all we know, there maybe innumerable big bangs in the universe, and we are just one of them.

My own theory is, an infinite void, in which by probabalistic chance, a finite universe emerges from the void in a cosmic explosion. In other words, there are infinite finite universes in the infinite void .

I also do not concur with you, that we have no evidence that the universe is infinite. It is only logical to assume the universe is infinite, also supported by the curvature of space time being 0. The burden of proof lies with the universe being finite. So untill unproven, the universe should be regarded as infinite. Most astronomers subscribe to this.

[John Connellan]

Jo Silk: To give you an example, imagine the geometry of the Universe in two dimensions as a plane. It is flat, and a plane is normally infinite. But you can take a sheet of paper [an 'infinite' sheet of paper] and you can roll it up and make a cylinder, and you can roll the cylinder again and make a torus [like the shape of a doughnut]. The surface of the torus is also spatially flat, but it is finite. So you have two possibilities for a flat Universe: one infinite, like a plane, and one finite, like a torus, which is also flat.

I believe the latter to be the case for the universe.

Take a look at the following link:

http://www.newscientist.com/news/news.jsp?id=ns99994250 (Newscientist)

[Pete]

I believe the latter to be the case for the universe.
Why? Without supporting evidence, it seems rather contrived.

[Dinosaur]

Pete: Big bang cosmology claims a beginning of our universe at a finite instant about 14 billion years ago. At that instant, all the matter & energy was contained in a small volume of space. 14 billion years is a long time, but it is a finite amount of time. Can you explain how any matter or energy is now beyond a large but finite volume? Did some matter or energy travel at infinite speed? Was some matter or energy already an infinite distance away when the process started?I was under the understanding that Big bang cosmology does not dictate a finite volume containing the universe's mass and energy; quite the opposite if the overall curvature of space-time is negative or zero (as it appears to be).Do you have an explanation for your understanding?

John Connellan: A cylinder, a cone, and various other surfaces have the same local geometry as a plane. They are flat or Euclidean spaces. All the laws of plane geometry apply to triangles and other geometric objects provided they are not too large and you restrict yourself to intrinsic 2D geometry. For example, the Pythagorean theorem is valid for triangles drawn with geodesics.

A torus cannot be a Euclidean or flat space. Triangles drawn with geodesics on a torus conform to neither the Pythagorean theorem nor to many other theorems of plane geometry.

Others: Our notions of space and the space/time continuum are intuitions derived from geometric concepts. These intuitions are not derived from concepts of physics nor are they supported by experimental evidence. My intuition says that the 4D space/time continuum is infinite. My intuition has been wrong on other issues, why should I trust it on this issue without any supporting evidence? I can visualize a finite unbounded 2D space (the surface of a sphere or torus). I think I can visualize an infinite 2D space (the plane and various other surfaces). I have difficulty visualizing finite unbounded 3D spaces, but they exist in the mathematical mindscape. Do they exist in the real universe?

I would trust my intuition about an infinite continuum if I had never read the following by Einstein (paraphrase, not an exact quote).Discussion of time in the absence of space is philosophy. Discussion of space in the absence of time is geometry. Physics must discuss events which occur at (x, y, z, t).

The only cosmological evidence we have supports a single universe which has been expanding for about 14 billion years. Cosmic Microwave Background radiation has been traveling for most of that 14 billion years. The path taken by the CMB is about 45 billion light years. The expansion has elongated the path. Talk of multiple big bangs, multiple universes, and universes with fundamentally different laws of physics are interesting speculations supported by no evidence.

Assuming that Big Bang cosmology is a reasonable description of our universe, the issue relating to a finite or infinite space requires answering the following question.Is the 4D space/time continuum (or at least the 3D part of it) expanding and carrying matter along with the expansion, or is matter/energy moving into already existing infinite space?I do not know how to answer that question. I would have more faith in my intuitive notion of an infinite universe if I was unaware its being based on geometric concepts of space. When I think of the (x, y, z, t) concepts of the space/time continuum of physics, I wonder if my intuition is based on insufficient insight.

I cannot imagine matter/energy existing without space & time, but I seem to be able to imagine the converse. However, do I have any evidence that there is space beyond all the matter and energy in my universe? I do not. Do I have evidence that the space/time continuum is independent of matter and energy? I do not.

Did time exist before the Big Bang? It boggles my mind to imagine that time started about 14 billion years ago. My intuition says it extends infinitely far into the past and infinitely far into the future. Should I trust this intuition in the absence of evidence? There are Quantum Theory concepts which are contrary to my intuitive notions about the real world. There are some very intelligent people who talk about time starting with the Big Bang. There are those who claim that space, time, matter, energy are inextricably intertwined. It is claimed that the separation of these concepts is an abstraction used by the mind to help our thinking about reality.

[Pete]

Pete: Big bang cosmology claims a beginning of our universe at a finite instant about 14 billion years ago. At that instant, all the matter & energy was contained in a small volume of space. 14 billion years is a long time, but it is a finite amount of time. Can you explain how any matter or energy is now beyond a large but finite volume? Did some matter or energy travel at infinite speed? Was some matter or energy already an infinite distance away when the process started?

I think you have the wrong idea of what Big Bang cosmology claims.

BB cosmology claims that the Universe was once VeryVery hot and VeryVery dense. It does not (as far as I know) claim that either the volume or the mass of the universe was ever finite. I'm willing to be corrected, of course.

[Pete]

You might want to have a look here: NASA - Foundations of Big Bang Cosmology (http://map.gsfc.nasa.gov/m_uni/uni_101bb2.html)

From that link:
The Big Bang did not occur at a single point in space as an "explosion." It is better thought of as the simultaneous appearance of space everywhere in the universe. That region of space that is within our present horizon was indeed no bigger than a point in the past. Nevertheless, if all of space both inside and outside our horizon is infinite now, it was born infinite. If it is closed and finite, then it was born with zero volume and grew from that. In neither case is there a "center of expansion" - a point from which the universe is expanding away from.

[Dinosaur]

Pete: You do not read carefully, which is a must for technical subjects. Reread the paragraph you quoted.. . . If all the space both inside and outside our horizon is infinite now . . . If it is closed and finite . . . Your expert source considers a finite universe a possibility, but apparently thinks this is an unresolved issue.

Also reconsider my claim that all the matter and energy in our universe is contained in a finite volume of space. This claim does not address the total amount of space in the universe, only the volume of space within which all the matter resides. I also claimed that Big Bang cosmology assumes that all the matter and energy was initially contained in a very tiny (zero?) volume. I probably should have stated that Big Bang cosmology implies that all the matter and energy in our universe has always been contained in a finite volume of space. This seems to me to be true even if the universe has infinite volume, which is another issue.

I also believe that Big Bang cosmology implies a finite amount of mass and energy in our universe.

[Pete]

Please note that my assertion is not that the Universe is definitely infinite. I assert that it is not certain that it is finite (ie I am asserting that your assertion is uncertain :)).
I do assert that best evidence to date indicates an infinite Universe, but do not assert that this situation is unchangeable.

Your expert source considers a finite universe a possibility, but apparently thinks this is an unresolved issue.
The source states (as I do) that Big Bang cosmology dictates neither a finite nor an infinite universe. It does dictate that globally flat space indicates an infinite universe. I'm sorry if I haven't been clear enough.

I also claimed that Big Bang cosmology assumes that all the matter and energy was initially contained in a very tiny (zero?) volume. I probably should have stated that Big Bang cosmology implies that all the matter and energy in our universe has always been contained in a finite volume of space.

I also believe that Big Bang cosmology implies a finite amount of mass and energy in our universe.

All three statements are incorrect.
Big Bang cosmology does dictate that the observable Universe was initially contained in a very tiny volume.
Big Bang cosmology does not dictate or impy that the Universe was ever finite, or that all the matter and energy in the Universe was ever contained in a finite space, or that the total mass/energy of the Universe is finite, unless the global curvature is positive (it does not appear to be).

[2inquisitive]

Pete, let me see if I understand you correctly.
(1) Big Bang cosmology does dictate that the observable Universe was initially contained in a very tiny volume. OK, that is a finite space, a point. This point was
contained within an infinite volume, the Universe, as opposed to the observable
Universe.
(2) Big Bang cosmology does not dictate or imply that the Universe (as opposed to the
observable universe) was ever finite, or that all matter and energy in the Universe was
ever contained in a finite space, etc. OK, so all matter and energy MAY not be contained within the OBSERVABLE Universe, there may be other matter or other
Universes outside our OBSERVABLE Universe, but with no way of detecting such.
If our observable universe was initially contained in a very tiny volume, then the
OBSERVABLE Universe became a part of infinite Universe at the moment of the Big
Bang. Therefore, the OBSERVABLE Universe is the one expanding INTO the volume
of the infinite Universe. The observable universe has a boundry, but the infinite
Universe does not. How can it logically be said that the OBSERVABLE Universe IS NOT
expanding from a point?

[Pete]

You appear confused on the concept of "observable Universe".

It's really an arbitrary region, being that region of the Universe which is close enough to a particular observer that light has had time to reach the observer since the Big Bang.

Note that every observer has a different observable universe. Note also that it doesn't have a physical boundary - the boundary is just an optical illusion.

Regions outside any observable Universe are in no way a different Universe.

I'm happy to agree that our observable universe is expanding around us (we are at the center) if it makes you feel better.

[2inquisitive]

Pete, I never suggested the observable universe has a physical boundary. It does,
however, have an edge, a boundary. I also said the term observable universe had a
different meaning, as it is a PART OF the entire universe, not a different universe. I
said there MAY be matter or other universes, undetectable, outside our observable
universe. The term "observable universe" is common and has a specific meaning
within cosmology.


Size of Universe and observable universe
It is not known whether the Universe is finite or infinite in spatial extent and volume, although the majority of theorists currently favor a finite Universe.

However, the observable universe, consisting of all locations that could have affected us since the Big Bang given the finite speed of light, is certainly finite. The edge of the cosmic light horizon is 14-15B light years distant. The present distance (comoving distance) to the edge of the observable universe is larger, since the universe has been expanding; it is estimated to be about 50 billion light years (4.7E23km). This would make the comoving volume, of the known universe, equal to 5E32 cubic light years (assuming this region is perfectly spherical). The observable universe contains about 7 × 1022 stars, organized in about 1010 galaxies, which themselves form clusters and superclusters. The number of galaxies may be even larger, based on the Hubble Deep Field observed with the Hubble Space Telescope.

http://www.fact-index.com/u/un/universe.html

In the cut and paste you posted above it states "In neither case is there a center of expansion - a point from which the universe is expanding away from." You then said
all three of Dinosaur's statements were incorrect. He stated "our universe" which in
observational cosmology refers to the observable universe, in which all three of his statements were correct according to Big Bang theory.
"During the second half of the 20th century, the development of observational cosmology, also called physical cosmology, led to a split in the meaning of the word Universe between observational cosmologists and theoretical cosmologists, where the former (usually) abandon the hope of observing the whole spacetime continuum, while the latter retain this hope, attempting to find the most reasonable speculations for modelling the whole of spacetime, despite the extreme difficulty in imagining any empirical constraints on these speculations and the risk of declining into metaphysics.

The terms known universe, observable universe, or visible universe are often used to describe the part of the Universe that we can see or otherwise observe. Those who believe it is impossible to observe the whole continuum may use our universe, referring only to that knowable by human beings in particular."

[Gravage]

I don't know why people still don't get it. To answer your question, there is nothing beyond this universe (which is finite) not empty space like u say :rolleyes:

Sorry,but it has to be something,it doesn't make sense that there is nothing.

[John Connellan]

Why does it not make sense? Surely the opposite does not make sense!!!

[Dinosaur]

An interesting essay on the Big Bang can be found at http://www.astronomycafe.net/cosm/bang.html

The above essay claims that neither space nor time existed prior to the Big Bang.

Another interesting article is at http://www.fact-index.com/u/un/universe.html

The above article discusses among other subjects, the size of our observable universe. It includes the followingExtrapolating this expansion back in time, one approaches a gravitational singularity, a rather abstract mathematical concept, which may or may not correspond to reality.

The time=zero of the Big Bang is estimated to have happened about 13.7 billion years ago, with an uncertainty of only 200 million years

It is not known whether the Universe is finite or infinite in spatial extent and volume, although the majority of theorists currently favor a finite Universe.

However, the observable universe, consisting of all locations that could have affected us since the Big Bang given the finite speed of light, is certainly finite. The edge of the cosmic light horizon is 14-15B light years distant. The present distance (comoving distance) to the edge of the observable universe is larger, since the universe has been expanding; it is estimated to be about 50 billion light years (4.7E23km). This would make the comoving volume, of the known universe, equal to 5E32 cubic light years (assuming this region is perfectly spherical).It seems weird that light from the Cosmic microwave background has been traveling for about 13-14 billion years, but the path it has taken is about 50 billion light years due to cosmic expansion.

I wonder if the above estimate of the size of the observable universe is the same as that defined by estimating the distance to galaxies whose recession velocity is at or slightly beyond the speed of light relative to us. If not, what would be the size of a universe defined by the distance to galaxies receding at light speed?

In theory, my observable universe is slightly different than my girlfriend’s observable universe. She is about 2 feet away from me working with her computer. Our combined observable universes have a greater volume than my observable universe. That volume gets a bit bigger if she leaves the apartment to go shopping.

Has anybody ever estimated the size of the entire universe, rather than just the observable universe? Here I am referring to the volume of space including all the matter and energy.

Does anybody here know of an estimate for the size of the universe when it became transparent to photons? That is, when atoms first formed and the universe ceased being a hot plasma?

Pete: Is English your second language? I wonder at your interpretation of my statements.

Do you understand that I am not claiming that the space of our universe is finite? Many believe that it is, but I think this is still an open question. I am only claiming that all the matter in our universe is now and was in the past contained in a finite volume of space.

Every description of Big Bang cosmology starts with our entire universe being contained in a quantum-sized volume. That sounds finite to me.

If you claim that the matter in the universe extends over an infinite volume, you are claiming that there is an infinite amount of distance between some pair of objects in the universe. This is totally contrary to Big Bang cosmology, which assumes that all the matter was originally in an extremely small volume at the beginning. Since the Big Bang claims that the universe started about 14 billion years ago, there has not been enough time for any two objects to get infinitely far apart.

[Pete]

Has anybody ever estimated the size of the entire universe, rather than just the observable universe? Here I am referring to the volume of space including all the matter and energy.
Hello? Am I talking to myself? It's infinite, according to best knowledge to date.

Does anybody here know of an estimate for the size of the universe when it became transparent to photons? That is, when atoms first formed and the universe ceased being a hot plasma?
The age of the Universe was around 300,000 years at that time. So I guess the size of any given observable Universe was either 300,000 light years or zero, depending on precise interpretation of observable.

The size of the Universe as a whole was infinite (according to current best knowledge).

Do you understand that I am not claiming that the space of our universe is finite? Many believe that it is, but I think this is still an open question. I am only claiming that all the matter in our universe is now and was in the past contained in a finite volume of space.
The claim is unfounded, as far as I know. According to best theory to date, the Universe is of uniform density on large scales. If the size is infinite, then so is the mass/energy.

Every description of Big Bang cosmology starts with our entire universe being contained in a quantum-sized volume. That sounds finite to me.
Every good description of Big Bang cosmology starts with the Universe being very very hot and very very dense. This implies that our observable Universe was contained in a small volume. However, the observable Universe and the entire Universe are often confused in pop science literature. If you read the hard science literature, or at least careful layman explanations by scientists who write the hard science literature, you'll find that the if the curvature is not positive, then the GR model indicates an infinite non-empty Universe from the moment of the Big Bang.

[Dinosaur]

Pete: You certainly have some interesting interpretations of Big Bang cosmology.The age of the Universe was around 300,000 years at that time. So I guess the size of any given observable Universe was either 300,000 light years or zero, depending on precise interpretation of observable.Your estimate of 300,000 years for the age at the time of recombination sounds about right. You seem to believe that the recession rate was the speed of light.

You seem to believe that there are at least two objects in the universe which are an infinite distance apart. Does your interpretation of Big Bang cosmology provide an explanation for how two objects might have gotten separated by an infinite distance?

The following suggests you believe that might have been the case when the Big Bang startedIf you read the hard science literature, or at least careful layman explanations by scientists who write the hard science literature, you'll find that the if the curvature is not positive, then the GR model indicates an infinite non-empty Universe from the moment of the Big Bang.You surely do not believe that the universe started with some objects separated by an infinite distance.

BTW: I do understand the difference between our observable universe and the entire universe. I am aware that there is matter beyond the limits of our observable universe. I only claim that there is no matter an infinite distance from us.

[Pete]

You surely do not believe that the universe started with some objects separated by an infinite distance.
If you'll allow me to avoiding particular niceties of talking about objects separated by infinite distances, then yes, I believe that it is possible, even likely (though not necessarily certain).

To be perfectly clear:
It is implied by Big Bang cosmology in an open Universe that in the very beginning, matter and energy existed everywhere - to infinity in all directions.

Your estimate of 300,000 years for the age at the time of recombination sounds about right. You seem to believe that the recession rate was the speed of light.
It's not about recession rate, it's about how much of the Universe has had time to send a signal to a specific point. Remember, I suggested 300,000 light years as the size of the observable Universe.

[Dinosaur]

Pete: You sure have some strange ideas about Big Bang cosmology. Size of observable universe 300,000 light years when it was 300,000 years old. That implies that it grew at the speed of light during the first 3000,000 years. I think Big Bang cosmology suggests incredible recession speed during inflation (first few seconds), but not later. I think it suggests speed of light recession rate at or beyond our current observable universe, but not when universe was 300,000 years old.

I suspect that when the universe was still opaque about 300,000 years from the start, it was a lot smaller than 300,000 light years in diameter.

Can you provide a reference for there being mass at an infinite distance from the initial cosmic egg? I find it hard to take your statements at face value.

[2inquisitive]

One of the problems describing the early universe is that it is a very complex
subject and there are many rapidly developing models. What you read in textbooks only 10 years old has already been shown to be incorrect. There
are many Big Bang models and many inflationary models. The textbook
inflation model has already been discounted, for instance, to be replaced
by other inflation models.
a cut and paste:
3.4. Single field models confront the data
3.4.1. Testing a specific inflation model:
 4
"As a prelude to showing constraints on broad classes of inflationary models, we first illustrate
the power of the data using the example of the minimally-coupledV =
 4

4 model, which is often
used as an introduction to inflationary models (Linde 1990). We show that this textbook example
is unlikely."
3.4. Single field models confront the data
3.4.1. Testing a specific inflation model:
 4
As a prelude to showing constraints on broad classes of inflationary models, we first illustrate
the power of the data using the example of the minimally-coupledV =
 4

4 model, which is often
used as an introduction to inflationary models (Linde 1990). We show that this textbook example
is unlikely."
http://lambda.gsfc.nasa.gov/product/map/pub_papers/firstyear/inflation/wmap_inflation.pdf
This is a pdf file and you have to give it a while to download if on dialup.
The paper also gives a formula for determing the size of the CMB sphere. And
yes, this early universe is depicted as a sphere (many maps show an oblong
area, but it is stated that it wraps around into a sphere and sphere are also shown) and "we" are in the CENTER of this sphere. Somewhat different than the old explanations. Only one of the things that is hard for me to grasp is,
from our position in the center to any position on the surface of the sphere
is over 13.6 billion light years. In any direction we look, it is over 13.6 billion
lyrs to this CMB radiation, which was only 379,000 years old at the time it
was formed. This infers a diameter of over 27 billion light years when the observable universe was only 379,000 years old. Since inflation is believed
to have been a very short-lived event, there must have been an almost
unbelieveable rate of expansion for the universe to have achieved this size
in so short of time. The other explaination is that the Big Bang happened
everywhere at once, not from a blackhole type singularity where everything
is in one "very small volume" at the beginning. But this begs the question
how did information travel over vast distances in an instant if it happened
"everywhere at once"? The variation in the CMB is less than a thousandth
of a degree at any point on it, about 2.73 degrees above absolute zero. It
seems the farther we look back in time the larger the universe was at that time. The latest Ultra deep field view from the Hubble has already yielded
a small galaxy believed to be at a red shift of 12. They are confirming this now, checking to make sure z=12 is correct. That would make it 13.3 billion
years old, the light leaving the object when the observable universe was only
400 million years old. After all, we are within this observable universe and it
took light 13.3 billion years to reach us from this object which is also within
the observable universe, so how small could the universe have been when
it was only 400 million years old?

[Pete]

Size of observable universe 300,000 light years when it was 300,000 years old. That implies that it grew at the speed of light during the first 3000,000 years.
We seem to be talking at cross purposes.
Are you talking about how big our observable Universe now was back then?

I was describing the size of an observable Universe then, which is unrelated to our current observable Universe. Sorry about that.

On a side note, my 300kly statement was not based on an expanding Universe at all, but simply on the propogation of light from all around. I didn't allow for inflation, or even expansion. I have no idea how that affects the outcome. Either way, I don't think I'm answering your question!

[Pete]

Can you provide a reference for there being mass at an infinite distance from the initial cosmic egg? I find it hard to take your statements at face value.

It's a deduction from a number of things.

1 - The Universe is flat
2 - A flat Universe implies infinite space
3 - The Universe is homogenous on large scales (has uniform density)

I think you agree with the possibility of 1 and 2 - correct?
But you don't agree with 3? You maintain that a positive mass/energy density locally, but that if the Universe is infinite then it has zero density at some distant region?

Have a look here: U Washington, Physics 557 Lecture 3 2002 (http://courses.washington.edu/phys55x/Physics%20557_lec3.htm)
Pay attention to the discussion on critical density.


Now!
On some further reading and thinking about inflation, I'm no longer sure about point 2.
I think that without inflation a flat universe certainly implies infinite space, but I'm getting the impression that a closed, inflated Universe would look flat out to unimaginable scales. And if the expansion is accelerating, then it will always look flat? I now have the understanding that it is unknowable whether then global Universe is finite or infinite. However, it still appears that all space is occupied, that no part of the global Universe has zero density.

This page looks particular good: Physics Central (http://www.physicscentral.com/action/action-01-4d.pdf) (American Physics Society)
In particular:
The word “observable” is key to understanding this picture, though, because while the “observable” universe can be thought of as expanding outward from an arbitrarily small volume, the same cannot necessarily be said of the entire universe, which in fact may be infinite.
...
Whether or not the entire (as opposed to just the observable) universe was “compressed” into something smaller than an atom, we do not know. What we see today, though, after inflation, is a universe that is essentially flat – meaning two rays of light sent out next to each other will remain (assuming no local gravitational influences) parallel essentially forever. Whatever curvature the universe may have had has long since been flattened away – much as a tiny ant would perceive a big beach ball it chanced to walk on. The nature of cosmic background radiation as indicated in the three findings support just such a view: the size of the cosmic background radiation variations reaching us indicates that the universe is indeed flat.

Finally, I'd like to suggest this essay from the Harvard Science Review as some background reading on the nature of Empty Space (http://hcs.harvard.edu/~hsr/pdfswinter2003/denton79-81.pdf).

[Peter2003]

The HUDF galaxies at the edge of the observable universe simply do to the big bang what CMB-radiation did to the steady-state theory.

you may more sirously consider this
http://www.world-mysteries.com/toi_esavov.htm

[Pete]

I suggest that has more to do with galactic and stellar evolution.