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#### mph

##### Guest
Everyone speaks of the shape of the universe in terms of the surface of a balloon, it has no center and no edge, the only problem is it's 2-dimensional. So when asked for an analogy in 3 dimensions the proverbial loaf of bread laced with raisins is used. Is the fact that the loaf of bread has both an edge and a center a failing of the analogy?

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#### MeteorWayne

##### Guest
Well, to be better, you need to imagine a loaf in no bread pan.

It really doesn't have a "center"...there is a central point, but the point of the analogy is that all the raisins move away from each other, and even a raisin near the edge sees all the other raisins moving away from it.

Since the Universe started from a very small area and is expanding, there is an "edge" out there....it's just that there's nothing on the other side of the edge.

The purpose of analogies is not to reproduce the reality, it's to help understand specific concepts...they are not intended to represent how things actually look. As such they are limited in their usefulness, and cannot be taken too literally.

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#### SpeedFreek

##### Guest
I see the raisin bread analogy as follows.

You are a raisin and you have the ability to detect other raisins through dough, but only at the speed of smell. From your observations you work out that the further you can smell, the faster a raisin seems to recede from you. You work out that the raisins are not moving through the dough, but the dough is expanding between the raisins. But you can only smell a certain distance, due to the age of the bread. You smell raisins all the way to that distance, so you cannot tell whether there is an edge to the loaf.

:lol:

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#### dangineer

##### Guest
I wonder if there is a Drake equation for how many intelligent raisins would exist on any given loaf of bread.

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#### FlatEarth

##### Guest
mph":15bdgrhy said:
Everyone speaks of the shape of the universe in terms of the surface of a balloon, it has no center and no edge, the only problem is it's 2-dimensional. So when asked for an analogy in 3 dimensions the proverbial loaf of bread laced with raisins is used. Is the fact that the loaf of bread has both an edge and a center a failing of the analogy?
mph, I share your question of the use of this analogy, but I think it's the best one.

I must confess the proclamation that the universe "has no center" doesn't seem logical to me. If we are to believe that the Big Bang did happen, and everything expanded symmetrically from one point, then that point is the center of the universe. It's just that we can't detect it because everything is expanding at an equally accelerating rate away from us, and our depth of view is limited by the speed of light. Perhaps one day we will overcome this limitation.

Where the analogy falls short is the concept of "no edge", one I'm also having a hard time with but must accept as true. I suppose the universe is still expanding beyond light speed, and the edge could never be reached, but properties of space-time (not unlike the distortion of S-T around a massive object) would redirect a warp speed raisin back into normal space anyway. If we create a rule that states no raisin can escape the expanding dough, then the analogy is good!

Flat

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#### SpeedFreek

##### Guest
Hi there FlatEarth, welcome to the SDC (space dot com) forums!

Here is a link that might help you understand the expansion of the universe and its implications:

Misconceptions about the Big Bang (direct link to a PDF file that explains the current model of the Big Bang very well)

Have a read of it and then feel free to ask more questions.

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#### FlatEarth

##### Guest
SpeedFreek":2f699j07 said:
Hi there FlatEarth, welcome to the SDC (space dot com) forums!

Here is a link that might help you understand the expansion of the universe and its implications:

Misconceptions about the Big Bang (direct link to a PDF file that explains the current model of the Big Bang very well)

Have a read of it and then feel free to ask more questions.
Hey SpeedFreek, I've noticed your comments in the article section for some time and it's my pleasure to meet you here. Thanks much for the article, which was a fun read.

Unfortunately, I still take issue with the 'no center of the universe' idea, even though I understand the difference between an explosion and expansion. The universe by virtue of its three dimensions had a geometric center at gestation, and should continue to today despite its current vastness and continued expansion. That being said, I don't believe the geometric center is of any special consequence or has unique properties, but it would be an interesting discovery. I'm sure my opinion will leave experts in the field shaking their heads saying, "Why bother trying" and they would be correct.

Recently I commented on SDC that the phenomena of galaxies moving apart at an accelerating rate should be attributed to the accelerating expansion rate of the universe, rather than "dark energy" driving the galaxies apart. I didn't get much of a response to that idea, but I wonder what you think? The article "Misconceptions..." seems to support that thought.

A side note related to the article: I didn't realize that they have measured galaxies receding at greater than the speed of light. How amazing is that?

BTW, I got a kick out of your earlier post.

Flat

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#### ramparts

##### Guest
"Dark energy" is just an explanation for the accelerated expansion of the universe - we know the expansion is accelerating, so dark energy isn't an alternative to that

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#### SpeedFreek

##### Guest
FlatEarth":11p57hbm said:
Unfortunately, I still take issue with the 'no center of the universe' idea, even though I understand the difference between an explosion and expansion. The universe by virtue of its three dimensions had a geometric center at gestation, and should continue to today despite its current vastness and continued expansion. That being said, I don't believe the geometric center is of any special consequence or has unique properties, but it would be an interesting discovery. I'm sure my opinion will leave experts in the field shaking their heads saying, "Why bother trying" and they would be correct.
The idea of a geometric centre relies on the idea of the universe having an edge. This may not be the case and even if it were, you would need to find opposite edges in order to find a centre. With the edge of the observable universe currently receding from us at more than 3 times the speed of light and accelerating, and the high probability that all we can see is not all there is, it seems that the point is moot. The observable universe may only be a fraction of the whole thing.

FlatEarth":11p57hbm said:
Recently I commented on SDC that the phenomena of galaxies moving apart at an accelerating rate should be attributed to the accelerating expansion rate of the universe, rather than "dark energy" driving the galaxies apart. I didn't get much of a response to that idea, but I wonder what you think? The article "Misconceptions..." seems to support that thought.
Dark energy is simply the "placeholder" for that which causes the expansion of the universe to accelerate. The acceleration of the expansion of the universe causes clusters of galaxies to recede from each other at an accelerated rate. So you are right in one way, but we need to know why the rate of expansion is accelerating. We have given that "why" the name dark energy, for want of a better word.

If objects in motion stay in motion, something else must be responsible for those objects accelerating apart - some form of energy is possibly required to "fuel" that acceleration.

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#### FlatEarth

##### Guest
ramparts and SpeedFreek,

Thanks for your replies. To tell the truth, I find the answer to the Dark Energy issue to be somewhat perplexing and a point of frustration. Why are we trying to determine what is driving the expansion of the universe (even if it is accelerating), when this process was initiated at the Big Bang and is merely continuing today? It seems we are losing sight of the principles of expansion by trying to explain it with an unknown force. In other words, I don't believe expansion is the manifestation of a force. Unless it is. :?

Regarding the issue of the center of the universe, regardless of whether it can be measured or determined, I do believe it exists because it must! Perhaps it is possible to look back in time to see the gestation of our own galaxy, but we would need to know what part of the universe we expanded from to do that.

Flat

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#### matthewota

##### Guest
The way I see it is that the center of the universe is everywhere, since it all started as a singularity taking up zero volume.

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#### SpeedFreek

##### Guest
FlatEarth":a7q5egcs said:
To tell the truth, I find the answer to the Dark Energy issue to be somewhat perplexing and a point of frustration. Why are we trying to determine what is driving the expansion of the universe (even if it is accelerating), when this process was initiated at the Big Bang and is merely continuing today? It seems we are losing sight of the principles of expansion by trying to explain it with an unknown force. In other words, I don't believe expansion is the manifestation of a force. Unless it is. :?
Ahh, but the acceleration of the rate of expansion was not initiated at the Big-Bang. Our observations tell us that the rate of expansion was incredibly fast to begin with, but immediately slowed down. The rate of expansion continued to slow down for billions of years (presumably due to the effects of gravity) and until recently we thought the rate of expansion should still be slowing down today. But around 10 years ago we found that, sometime around 5 billion years ago, the rate of expansion levelled out and then started to accelerate!

The rate of expansion was slowing for around 9 billion years and only started accelerating around 5 billion years ago. This is why dark energy (whatever it is) is required.

FlatEarth":a7q5egcs said:
Regarding the issue of the center of the universe, regardless of whether it can be measured or determined, I do believe it exists because it must! Perhaps it is possible to look back in time to see the gestation of our own galaxy, but we would need to know what part of the universe we expanded from to do that.
Why must it have a centre? Consider the surface of the Earth. Does the surface of the Earth have a centre? If the surface of the Earth has no edge, it has no centre - you can cross the surface of the Earth until you find yourself back where you started. Perhaps the universe is a similar case, but using more dimensions.

What if the three dimensions we perceive for the universe are "wrapped" onto a four dimensional sphere. This way, whenever you plot a straight line in three dimensions, your straight line is actually part of a four dimensional curve. The universe might be finite, but have no edge - it might simply "wrap around" on itself.

Or what if the universe is infinite in extent?

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#### FlatEarth

##### Guest
SpeedFreek":2a1az57e said:
Ahh, but the acceleration of the rate of expansion was not initiated at the Big-Bang. Our observations tell us that the rate of expansion was incredibly fast to begin with, but immediately slowed down. The rate of expansion continued to slow down for billions of years (presumably due to the effects of gravity) and until recently we thought the rate of expansion should still be slowing down today. But around 10 years ago we found that, sometime around 5 billion years ago, the rate of expansion levelled out and then started to accelerate!

The rate of expansion was slowing for around 9 billion years and only started accelerating around 5 billion years ago. This is why dark energy (whatever it is) is required.
Here's a possible explanation: The conclusion that the expansion rate of the universe slowed down was only partially correct. Perhaps what actually happened was that space-time continued to expand at an incredible rate, but gravity kept the galaxies from being carried off because of their proximity to each other. The visible universe did not expand at the same rate as space-time. After a period of slowing expansion (of the galaxies), a point was reached where gravity could no longer slow the spread, and the trend transitioned from a slowing rate to an accelerating rate. The expansion of space-time accelerated from day one, never slowed down, and continues unabated today. With this explanation, no additional energy is required, and I can get a good nights sleep! :!:

SpeedFreek":2a1az57e said:
Why must it have a centre? Consider the surface of the Earth. Does the surface of the Earth have a centre? If the surface of the Earth has no edge, it has no centre - you can cross the surface of the Earth until you find yourself back where you started. Perhaps the universe is a similar case, but using more dimensions.

What if the three dimensions we perceive for the universe are "wrapped" onto a four dimensional sphere. This way, whenever you plot a straight line in three dimensions, your straight line is actually part of a four dimensional curve. The universe might be finite, but have no edge - it might simply "wrap around" on itself.

Or what if the universe is infinite in extent?
I say the universe must have a center because, based on observations of the cosmos, it appears to be a volume that can be measured in all directions. The Big Bang implies it has finite dimensions despite the mind boggling expansion. The universe certainly cannot have an edge as we understand it, but perhaps the "wrap around" concept is in play. Measuring the universe would require the ability to determine where this happens. Unlikely, but theoretically possible for the Borg.

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#### SpeedFreek

##### Guest
FlatEarth":bzl8sw5o said:
SpeedFreek":bzl8sw5o said:
Ahh, but the acceleration of the rate of expansion was not initiated at the Big-Bang. Our observations tell us that the rate of expansion was incredibly fast to begin with, but immediately slowed down. The rate of expansion continued to slow down for billions of years (presumably due to the effects of gravity) and until recently we thought the rate of expansion should still be slowing down today. But around 10 years ago we found that, sometime around 5 billion years ago, the rate of expansion levelled out and then started to accelerate!

The rate of expansion was slowing for around 9 billion years and only started accelerating around 5 billion years ago. This is why dark energy (whatever it is) is required.
Here's a possible explanation: The conclusion that the expansion rate of the universe slowed down was only partially correct. Perhaps what actually happened was that space-time continued to expand at an incredible rate, but gravity kept the galaxies from being carried off because of their proximity to each other. The visible universe did not expand at the same rate as space-time. After a period of slowing expansion (of the galaxies), a point was reached where gravity could no longer slow the spread, and the trend transitioned from a slowing rate to an accelerating rate. The expansion of space-time accelerated from day one, never slowed down, and continues unabated today. With this explanation, no additional energy is required, and I can get a good nights sleep! :!:
I like the way you think!

In fact, it seems like we are actually describing the same thing, in essence. The currently favoured model has dark energy in existence as a "background effect", but its effects only became noticeable once galaxies were far enough apart for the rate of acceleration it causes to beat their gravitational attraction.

The problem comes when considering that the effect of acceleration seems to imply that whatever causes it is a constant. We can work out, from our observations, how much of an effect it has, and it is not nearly enough to drive all the mass in the universe apart during its early stages. The effect is incredibly weak, many magnitudes less than the value given to Einsteins cosmological constant. This becomes apparent when you actually do the maths involved.

But what might interest you is a possible link between dark energy and cosmic inflation. During the inflationary epoch, everything in the universe was driven apart faster than light, even at the smallest scales imaginable. This epoch only lasted a fraction of a second and after it ended everything was moving so fast that gravity could only very weakly start to slow down the rate of expansion.

If the force that caused the initial "superluminal" expansion had continued unabated, no structure would ever been able to form.

So it seems like the inflationary force (whatever it is) only happened for a very short time indeed. Then the expansion continued without that force, and gravity could gradually slow the expansion. The original impetus for the expansion was not there anymore, but a remnant of it might have been left behind as a background force that we call dark energy.

Your idea is a good one, but unfortunately it cannot be fitted to our observations.

FlatEarth":bzl8sw5o said:
I say the universe must have a center because, based on observations of the cosmos, it appears to be a volume that can be measured in all directions. The Big Bang implies it has finite dimensions despite the mind boggling expansion. The universe certainly cannot have an edge as we understand it, but perhaps the "wrap around" concept is in play. Measuring the universe would require the ability to determine where this happens. Unlikely, but theoretically possible for the Borg.
We can only measure the volume relative to us, and it extends the same distance in all directions due to the age of the universe meaning that light can only have been travelling towards us for a finite time. So we are at the centre of our observable universe.

Whilst our observable universe has a finite volume, there is nothing to say that the whole universe is finite - the Big Bang certainly does not imply it. The universe might have been infinite all along. You can have expanding infinity, and our observable part of the universe might just be an infinitesimally small part of the whole. We can track the expansion of our observable universe back towards a singularity that is point-like for our finite portion of the universe, but in an infinite universe, the "singularity" was everywhere. All the singularity really means is that everything was a lot closer together, so much so that General Relativity cannot predict what happens anymore. This happens well before we reach a planck length, and an infinite set of planck lengths is still infinite.

There might be galaxies countless billions of light-years away, and their Big Bang was in a totally different part of the universe from ours.

On the other hand, in a finite universe which "wraps around", we would never be able to detect where it does so. It would be like asking where the surface of the Earth wraps around - the edge of the map is wherever you choose. It could be right here!

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#### FlatEarth

##### Guest
SpeedFreek":svuee2kb said:
FlatEarth":svuee2kb said:
Here's a possible explanation: The conclusion that the expansion rate of the universe slowed down was only partially correct. Perhaps what actually happened was that space-time continued to expand at an incredible rate, but gravity kept the galaxies from being carried off because of their proximity to each other. The visible universe did not expand at the same rate as space-time. After a period of slowing expansion (of the galaxies), a point was reached where gravity could no longer slow the spread, and the trend transitioned from a slowing rate to an accelerating rate. The expansion of space-time accelerated from day one, never slowed down, and continues unabated today. With this explanation, no additional energy is required, and I can get a good nights sleep! :!:
I like the way you think!

In fact, it seems like we are actually describing the same thing, in essence. The currently favoured model has dark energy in existence as a "background effect", but its effects only became noticeable once galaxies were far enough apart for the rate of acceleration it causes to beat their gravitational attraction.

The problem comes when considering that the effect of acceleration seems to imply that whatever causes it is a constant. We can work out, from our observations, how much of an effect it has, and it is not nearly enough to drive all the mass in the universe apart during its early stages. The effect is incredibly weak, many magnitudes less than the value given to Einsteins cosmological constant. This becomes apparent when you actually do the maths involved.

But what might interest you is a possible link between dark energy and cosmic inflation. During the inflationary epoch, everything in the universe was driven apart faster than light, even at the smallest scales imaginable. This epoch only lasted a fraction of a second and after it ended everything was moving so fast that gravity could only very weakly start to slow down the rate of expansion.

If the force that caused the initial "superluminal" expansion had continued unabated, no structure would ever been able to form.

So it seems like the inflationary force (whatever it is) only happened for a very short time indeed. Then the expansion continued without that force, and gravity could gradually slow the expansion. The original impetus for the expansion was not there anymore, but a remnant of it might have been left behind as a background force that we call dark energy.

Your idea is a good one, but unfortunately it cannot be fitted to our observations.
It's possible that the idea of no dark energy could fit into the model if the theory evolves to accommodate it. (Am I being unreasonable here?!) Consider that there was more going on during the inflationary epoch than "just" expansion of space-time. Another force may have been in play, but was quickly exhausted allowing the first stars and galaxies to form. It's the expansion of space-time that continues, but not the primal expansion of matter. I believe that observations do support this idea, but theory of what happened in those first moments does not.

Clearly this would take involved mathematical studies to prove, so my thoughts amount to only babble (as I am often accused). I do have a better understanding of what dark energy is thanks to you, but I still would like to see the need for it to go away!

SpeedFreek":svuee2kb said:
We can only measure the volume relative to us, and it extends the same distance in all directions due to the age of the universe meaning that light can only have been travelling towards us for a finite time. So we are at the centre of our observable universe.

Whilst our observable universe has a finite volume, there is nothing to say that the whole universe is finite - the Big Bang certainly does not imply it. The universe might have been infinite all along. You can have expanding infinity, and our observable part of the universe might just be an infinitesimally small part of the whole. We can track the expansion of our observable universe back towards a singularity that is point-like for our finite portion of the universe, but in an infinite universe, the "singularity" was everywhere. All the singularity really means is that everything was a lot closer together, so much so that General Relativity cannot predict what happens anymore. This happens well before we reach a planck length, and an infinite set of planck lengths is still infinite.

There might be galaxies countless billions of light-years away, and their Big Bang was in a totally different part of the universe from ours.

On the other hand, in a finite universe which "wraps around", we would never be able to detect where it does so. It would be like asking where the surface of the Earth wraps around - the edge of the map is wherever you choose. It could be right here!
I'm not referring to alternate concepts of a larger eternal mega-universe, even though intuitively I believe the universe is far grander and more complex than we can imagine. My reference to a center refers to the only universe we know of and can observe: the one created in the Big Bang. The expansion of the universe over time does imply that 13.5 to 14 billion years ago it was finite to the ultimate degree: a singularity. And so I must conclude we live in a universe that is defined and therefore has a center, despite being impossible to determine. I will admit you lost me on some of your points, and have resorted to drinking heavily to compensate.

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#### SpeedFreek

##### Guest
FlatEarth":3lughihi said:
It's possible that the idea of no dark energy could fit into the model if the theory evolves to accommodate it. (Am I being unreasonable here?!) Consider that there was more going on during the inflationary epoch than "just" expansion of space-time. Another force may have been in play, but was quickly exhausted allowing the first stars and galaxies to form. It's the expansion of space-time that continues, but not the primal expansion of matter. I believe that observations do support this idea, but theory of what happened in those first moments does not.

Clearly this would take involved mathematical studies to prove, so my thoughts amount to only babble (as I am often accused). I do have a better understanding of what dark energy is thanks to you, but I still would like to see the need for it to go away!
Without a cosmological constant there are only 3 possibilities. Either the rate of expansion tends towards a constant rate, as objects become distant enough from each other for gravity to cease to be a factor, or the rate of expansion is forever slowed towards a halt but never quite makes it, or the rate of expansion slows to a halt and it all starts contracting. It all depends on the average mass density.

So, without any other forces involved, expansion either slows towards a constant rate, slows towards a halt or halts and then everything contracts.

An accelerating expansion requires either a background force/energy (like the cosmological constant), or a force/energy somehow building up with time (like quintessence).

FlatEarth":3lughihi said:
I'm not referring to alternate concepts of a larger eternal mega-universe, even though intuitively I believe the universe is far grander and more complex than we can imagine. My reference to a center refers to the only universe we know of and can observe: the one created in the Big Bang. The expansion of the universe over time does imply that 13.5 to 14 billion years ago it was finite to the ultimate degree: a singularity. And so I must conclude we live in a universe that is defined and therefore has a center, despite being impossible to determine. I will admit you lost me on some of your points, and have resorted to drinking heavily to compensate.
I am not referring to a meta-verse either, I am only referring to the universe which we are part of. The universe created in the Big-Bang can be infinite in extent, if not in time. I was talking purely in terms of our own universe being infinite in extent. Our observable part of the whole universe might have tended towards a singularity 13.7 billion years ago, even if that whole universe was infinte in extent as soon as it "appeared".

It might have started out infinite and full of matter, and then expanded. If it did, we would still see exactly what we do see, 13.7 billion years later.

Or perhaps, the universe is embedded in a higher dimension. If so, what shape would our universe have if it was embedded in a four dimensional space?

Imagine a 2 dimensional universe. In this 2D universe the only directions are forwards, backwards, left and right. There is no up or down!

Beings in this 2D universe would think they live on a 2D plane that was totally flat. They would have no perception of any 3rd dimension. But their 2D universe might be wrapped onto a 3D shape of which they are unaware, as they have no ability to see in 3D. In that 3rd dimension, their universe is a sphere and they are moving across its 2D surface. If they were able to circumnavigate it, they would work out that their apparently flat universe is actually finite, but it has no edge or centre!

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#### darkmatter4brains

##### Guest
SpeedFreek":2rivrik8 said:
Beings in this 2D universe would think they live on a 2D plane that was totally flat. They would have no perception of any 3rd dimension. But their 2D universe might be wrapped onto a 3D shape of which they are unaware, as they have no ability to see in 3D. In that 3rd dimension, their universe is a sphere and they are moving across its 2D surface. If they were able to circumnavigate it, they would work out that their apparently flat universe is actually finite, but it has no edge or centre!
I've always loved this analogy.

I've been under the impression that the idea of an infinite Universe died along with the Steady State theory a long time ago. I'm not too sure people working in cosmology today consider the Universe infinite in any respect. I know it was definitely never taught (or even brought up) in the astrophysics courses I took. However, I'm not exactly "up" on the latest and greatest in cosmology anymore so maybe something has changed in the last ten years?

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#### darkmatter4brains

##### Guest
FlatEarth":22jckp96 said:
... and have resorted to drinking heavily to compensate.
Best idea I've heard all day!

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#### SpeedFreek

##### Guest
darkmatter4brains":26jst6qh said:
I've been under the impression that the idea of an infinite Universe died along with the Steady State theory a long time ago. I'm not too sure people working in cosmology today consider the Universe infinite in any respect. I know it was definitely never taught (or even brought up) in the astrophysics courses I took. However, I'm not exactly "up" on the latest and greatest in cosmology anymore so maybe something has changed in the last ten years?
A universe infinite in extent is still one of the valid possibilities, but most cosmologists tend towards a universe that is finite but has no edge, like the 3-Torus.

This is an except from "The infinite cosmos: questions from the frontiers of cosmology" by Joseph Silk, Savillian Professor of Astronomy at Oxford University, 2006.

Is the universe infinite or finite?

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#### Jalapenopopper

##### Guest
MeteorWayne":k9u7zgos said:
.

Since the Universe started from a very small area and is expanding, there is an "edge" out there....it's just that there's nothing on the other side of the edge.
So this raises a more interesting question.... If there is nothing on the other side of the edge...Then what is there? Isn't it impossible to have "nothing"? There is always something out there so I don't understand how there is "nothing" on the other side.

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#### FlatEarth

##### Guest
darkmatter4brains":2w7dqyb0 said:
FlatEarth":2w7dqyb0 said:
... and have resorted to drinking heavily to compensate.
Best idea I've heard all day!
Cheers!

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#### FlatEarth

##### Guest
SpeedFreek":2vsfjph9 said:
Without a cosmological constant there are only 3 possibilities. Either the rate of expansion tends towards a constant rate, as objects become distant enough from each other for gravity to cease to be a factor, or the rate of expansion is forever slowed towards a halt but never quite makes it, or the rate of expansion slows to a halt and it all starts contracting. It all depends on the average mass density.

So, without any other forces involved, expansion either slows towards a constant rate, slows towards a halt or halts and then everything contracts.

An accelerating expansion requires either a background force/energy (like the cosmological constant), or a force/energy somehow building up with time (like quintessence).
And so we have come full circle! The idea that we need a force or energy to drive expansion is what I believe to be incorrect. Analogous to gravity not actually being force but a distortion in space-time, the expansion of space-time is not force-driven. Remember that the galaxies are really not moving through space but are more or less in a fixed position as space-time expands around them, and this expansion is always accelerating. Einstein was right to drop the c constant!

SpeedFreek":2vsfjph9 said:
A universe infinite in extent is still one of the valid possibilities, but most cosmologists tend towards a universe that is finite but has no edge, like the 3-Torus.
This is the universe I picture when stating that it has a center. I never said we could find that center!

Whether I am right or wrong on either point, I think it's important that the scientific community continues to challenge and question what has become accepted as indisputable fact. Perhaps experiments at the LHC will uncover new evidence that will force some of these pillars of truths to be reconsidered. Whatever happens, God I hope they don't find dark energy! :shock:

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#### SpeedFreek

##### Guest
Jalapenopopper":28rk8qar said:
MeteorWayne":28rk8qar said:
.

Since the Universe started from a very small area and is expanding, there is an "edge" out there....it's just that there's nothing on the other side of the edge.
So this raises a more interesting question.... If there is nothing on the other side of the edge...Then what is there? Isn't it impossible to have "nothing"? There is always something out there so I don't understand how there is "nothing" on the other side.
I don't think Wayne meant that statement to come out as it did. There is no edge to universe. There is no place where the galaxies stop and then there is nothing beyond.

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#### SpeedFreek

##### Guest
FlatEarth":3bl2jac8 said:
And so we have come full circle! The idea that we need a force or energy to drive expansion is what I believe to be incorrect.
You keep confusing expansion, which was one of the initial conditions of the Big Bang, with accelerating expansion, which requires a separate cause. I am talking about the acceleration of that expansion, which is the reason dark energy is required.

FlatEarth":3bl2jac8 said:
Analogous to gravity not actually being force but a distortion in space-time, the expansion of space-time is not force-driven. Remember that the galaxies are really not moving through space but are more or less in a fixed position as space-time expands around them, and this expansion is always accelerating. Einstein was right to drop the c constant!
I see where you are going wrong now - you misunderstand what accelerating expansion means. Do you think it is the fact that the further away a galaxy is, the faster it is receding, means the expansion is accelerating? If so, you are incorrect!

The increase in recession speed with distance comes from expansion, whatever the expansion is doing, even if it is decelerating.

Let's make a model.

Now to model an expanding space we need to assign coordinates within that space. For the moment, forget about any edges to that space, we don't need edges, we just need coordinates in order to measure the expansion of space. Galaxies come later, so for now just imagine a 3 dimensional grid. At each grid intersection we will assign a coordinate, a point, a dot. Let's say each intersection point is 1 meter apart.

Put yourself on a point somewhere in this space. Whatever axis you look along you see neighbouring points 1, 2, 3, 4, 5 etc meters away, receding off into the distance. Then we introduce some expansion. Let's say the space grows to 10 times its original size in 1 second! That seems fast perhaps, but this is just a model with easy numbers. The key thing to remember is that the grid expands with the space.

So, here we are, still sitting on our point (but it could have been any point) 1 second later. Now lets look along an axis. We see those neighbouring points are now 10, 20, 30, 40, 50 etc meters away. The space increased to 10 times its original size, and so did the distance between each intersection point on that grid.

Our nearest neighbouring point has receded from 1 to 10 meters in 1 second, so it has receded at 9 meters per second. The next point away has receded from 2 to 20 meters in 1 second, so that point receded at 18 meters per second. The fifth point has moved from 5 to 50 meters away in 1 second, so that one has receded at 45 meters per second. The further away you look, the faster a point will seem to have receded!

And the view would be the same, whatever viewpoint you choose in the grid! There is no "centre" of expansion, no origin point within that grid - the whole thing, the whole space has expanded from something where the spaces between things were really small to something where the spaces between things are much larger. The expansion of that space has carried matter and energy along for the ride.

Remember I said the grid of points receded off into the distance.. well a point that was initially 33,000,000 meters away will have moved away to 330,000,000 meters in 1 one second, meaning that it has receded at 300,000,000 meters per second - the speed of light! Any point initially more distant than 33,000,000 meters away from another point will have receded from that point faster than the speed of light. That is the distance were an object recedes at light speed in this "little" model of expansion. If you look at a point that has receded at the speed of light, then from that point, the point you are on has receded at the speed of light. But no object would be moving through space faster than light, no photon would ever overtake another photon, it all just gets carried along by the cosmic flow.

The above simply describes a constant rate of expansion. The further away you look, the faster an object recedes, and the relationship is linear.

Now then, if the rate of expansion were to be accelerating, then we would observe those closer grid boxes would be getting slightly larger, compared to the distant ones. Put into normal terms, it was the observation that as we looked at closer and closer supernovae, they were further away than we thought they should be, relative to the distant supernovae, if the expansion were still decelerating like we had originally thought. This is because we see the distances between the distant objects as they were before the acceleration started, 5 billion years ago. The relationship is not linear, as the rate of expansion has changed.

In an expanding universe, the further you look the faster an object recedes. If that expansion is accelerating, the closer you look, the further away an object would be in relation to where it should be if the rate had remained constant. If you plot the recession speeds, with constant expansion the line is straight, with decelerating expansion the line curves one way and with accelerating expansion it curves the other. But the recession speed is always increasing along that line, in all three cases.

I hope this clears up the big difference between increasing recession speeds over distance, and the acceleration of the expansion.

FlatEarth":3bl2jac8 said:
SpeedFreek":3bl2jac8 said:
A universe infinite in extent is still one of the valid possibilities, but most cosmologists tend towards a universe that is finite but has no edge, like the 3-Torus.
This is the universe I picture when stating that it has a center. I never said we could find that center!

Whether I am right or wrong on either point, I think it's important that the scientific community continues to challenge and question what has become accepted as indisputable fact. Perhaps experiments at the LHC will uncover new evidence that will force some of these pillars of truths to be reconsidered. Whatever happens, God I hope they don't find dark energy! :shock:
The "geometric" centre of the 3-Torus is in a different dimension! All we are concerned about is the three-dimensional surface of that torus, which has no edge or centre. Wrap my grid model from above onto the surface of that 3-Torus and hopefully you will see what I mean. No part of our universe is in the hole in the centre of the Torus - it is a four dimensional shape!

Z

#### ZenGalacticore

##### Guest
Speedy- "Probably" true, that is, within the framework of the cosmology and physics of our time. But, let's be honest, we really don't know. We're not even really sure how far-and therefore how old- our own "Universe" extends.

Just some thoughts man!

I personally and insightfully(totally subjectively) believe that our universe is a 'result' of a reverse super-duper-massive black hole. And eventually, 10 to the 125 power years or so from now, the expansion of spacetime and matter and energy will cease, contract, and lead to another, yet 'obverse' black hole and new 'universe'.

All the 'while', there are infinite 'branes' or 'slices' of 'bread' in the multi-dimensional "omniverse"!

And then, what is beyond that?

The main point I'm trying to get at is that, despite the total lack of evidence, I for one believe that there are higher dimensions beyond our three dimensional universe that is most likely warped into a fourth physical dimension. And we are most likely 'trapped' in it.

But just because we are prisoners within that "universe" or, more precisely, "sub-(uni)verse", doesn't mean that there aren't multi-verses beyond ours, or even an "Omniverse" beyond that!!! And beyond that...

Don't you just love cosmology and the ultimate questions?

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