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John37309
2010-May-05, 12:59 PM
Its just a simple question that i don't fully understand, can anyone help me.

1. If the observable universe started with a big bang, and the matter, stars and galaxy's are all moving away from the bang, why do we seem to be in the centre?

2. Why do we see 13 billion year old galaxy's in all directions in the sky?

3. If it started with a bang, wouldn't there be a big empty space in the middle somewhere and our MilkyWay would be roughly in a galaxy cluster somewhere on the outside edge? With one direction in the sky looking emptier than all the other directions.

Note; question 1, 2, and 3 are really all the same question.

Thanks for the help in advance,
John.

Incomplete
2010-May-05, 02:47 PM
1. Good question, but with a good answer. Imagine you're a 2D creature living on the surface of an expanding, spherical balloon. Other creatures are scattered around the surface. You'd see them expanding away from you with a Hubble law and in a symmetric way, but they would see just the same. None of you are at the "center" (or all of you are), because the surface of the balloon has no center.

2. We can't see all the way around the balloon because light hasn't had time to propagate all the way around it yet. So we just see a patch of it. If that patch is much smaller than the balloon, we might not even notice the curvature of its surface.

3. For the balloon, the "middle" is distant from you in the 3rd dimension. If you like, you can think of the big bang as the center of the universe, but it's back in time, not space.

(Small print: the universe doesn't necessarily have the topology of a sphere. But it might, and I think this is the easiest model for understanding how to answer those questions.)

Does that help?

WayneFrancis
2010-May-05, 02:51 PM
good description Incomplete

Andrew D
2010-May-05, 03:17 PM
Its just a simple question that i don't fully understand, can anyone help me.

1. If the observable universe started with a big bang, and the matter, stars and galaxy's are all moving away from the bang, why do we seem to be in the centre?

2. Why do we see 13 billion year old galaxy's in all directions in the sky?

3. If it started with a bang, wouldn't there be a big empty space in the middle somewhere and our MilkyWay would be roughly in a galaxy cluster somewhere on the outside edge? With one direction in the sky looking emptier than all the other directions.

Note; question 1, 2, and 3 are really all the same question.

Thanks for the help in advance,
John.


1. Most people who have not done any research on the big bang assume that it was an event that happened at a point within the universe we see today. However, at the time of the big bang, the universe had not yet expanded to the size it is today; in essence the universe was as small as space occupied by the energy of the big bang. In essence: all that existed was the big bang, so the big bang occurred in the entire universe, not at any one distinct point. The whole universe expanded, and now the universe that once fit only the big bang fits everything that exists today.

2. The reason we see thirteen billion year old galaxies is the same reason we see an 8 minute old sun. You could say the sun is 8 "light minutes" away; from our point of view, it takes 8 minutes for the light from the sun to reach us. Likewise, it would take light from a galaxy 13 billion light years away 13 billion years to reach us. Because of this, it is not possible to see what these galaxies look like now, as the light they are emitting now will not reach us for 13 billion years.

3. There is no empty space like the one you refer to for the reason explained in question 1. Since the big bang didn't occur in any one location, there is no point for thing to be moving away from. However, the big bang was not perfect. The fluctuations in temperature and density at the very beginning of the universe, although infinitesimally small by human standards, are very visible now due to the amount of expansion the universe has experienced. This effect, combined with gravity, causes the structure we see in the universe at large: clusters of galaxies and gas separated by large empty voids.

The implications of what you are learning are very important. The average person has no idea how the universe works at the grandest and smallest scales, and thus fails to appreciate the world we can observe. This is an excellent question, it was my first. Don't stop asking; however, know this: not only will many answers you hear be hard to accept, let alone understand- you may even find it hard to ask the right questions. Be patient, don't get ahead of yourself, and take one thing at a time. The universe is a strange and beautiful place, and it's waiting for you to discover it.

John37309
2010-May-05, 04:06 PM
Incomplete, WayneFrancis, Roobydo,
Thank you for taking the time to explain.

For the last 4 years i have heard many explanations and variations of the expanding balloon analogy. I do understand the analogy, but i can never accept it as a viable explanation for what we see. I only ever seem to see flaws in the concept. It still does not make any sense.

I understand that all astronomical images are history pictures, none of them can ever display what is there right now at this moment in time. So really we are always seeing the way stuff was in the past, not the present. This makes the balloon analogy wrong and misleading.This is why i can never make it work in my mind.

I know its a difficult one. But do you see the point i'm making.

John.

Incomplete
2010-May-05, 04:18 PM
I
I understand that all astronomical images are history pictures, none of them can ever display what is there right now at this moment in time. So really we are always seeing the way stuff was in the past, not the present. This makes the balloon analogy wrong and misleading.This is why i can never make it work in my mind.

But the balloon universe has exactly that same feature! Remember, light (in this analogy) is stuck also to the 2D surface, just like you, galaxies, and everything else. So when you look at a nearby "galaxy" (a spot on the balloon's surface some distance away), you're seeing it as it was some time before, when the balloon was smaller. The part of the balloon's surface you can see with a telescope is a disk, and as you move out along a radius of that disk, the light you're seeing from each successive ring is a slice of the balloonverse at an earlier and earlier time.

That's exactly what we see in the real 3D universe, if you replace "disk" with "ball" and "ring" with "spherical surface".

The reason you hear this analogy so much is that it's really almost exactly like the geometry we think may describe our universe. The only significant difference is that it has one less spatial dimension. But if you can put that aside for a moment, it's barely an analogy at all. So it's well worth thinking through.

John37309
2010-May-05, 04:42 PM
Yea, i understand the concept. 13.7 billion years ago all the matter we see was all inside one tiny point. Ever since, from our point of view, everything seems to be moving away. Still puts us in the centre.

This expanding balloon should still put us somewhere else other than appearing to be in the centre. The Cosmic microwave background, CMB we see today should be lob sided cos the CMB is also a time lapse image of the remnants of the big bang.. But the CMB is relatively uniform in all directions.

John.

Incomplete
2010-May-05, 04:55 PM
Yea, i understand the concept. 13.7 billion years ago all the matter we see was all inside one tiny point. Ever since, from our point of view, everything seems to be moving away. Still puts us in the centre.

I'm not sure you're grasping the analogy. Remember, we're 2D creatures stuck to the surface of the balloon. The inside doesn't exist for us at all, except in a sense as the past.


This expanding balloon should still put us somewhere else other than appearing to be in the centre. The Cosmic microwave background, CMB we see today should be lob sided cos the CMB is also a time lapse image of the remnants of the big bang.. But the CMB is relatively uniform in all directions.


And that's exactly what the ballooniverse predicts. Just as on the surface of the earth, you're always at the center of your own circular horizon (ignoring mountains, trees, etc.).

Suppose at some time when the balloon is small, every point on its surface lights up in a flash like a flashbulb. Please remember that the light emitted is "stuck" to the surface. So after that time, there are photons flying in all directions all over the surface. Those photons move at a finite speed, and assume they don't get absorbed or scattered by anything.

Wait a little after the flash, long enough to let a photon cover (say) 1/4 of the circumference of the balloon (of course the balloon is expanding, so what I mean is that a photon that originated at the flash on the equator has after this time made it to the north pole). If you then look through a telescope at those photons, what do you see?

The answer is you see them coming from every direction, isotropically. Everyone sees that, no matter where they are (because every point on the surface of the balloon is the same as every other point). This is very much like the CMB, the "flash" is really the moment when photons in the universe stopped interacting and started to propagate freely.

Andrew D
2010-May-05, 05:31 PM
Yea, i understand the concept. 13.7 billion years ago all the matter we see was all inside one tiny point. Ever since, from our point of view, everything seems to be moving away. Still puts us in the centre.

This is correct. From our point of view, we seem to be in the center of the universe and, lo, how proud we are. However, because the expansion has the characteristics that incomplete described, this appearance is not correct. All objects that are not gravitationally bound are moving away from each other at a velocity that is proportional to the distance between them. Because of this it appears that all (distant) objects are moving away from us, and in fact they are, but they are also moving away from all the other objects, so our perspective is not unique.


This expanding balloon should still put us somewhere else other than appearing to be in the centre.

For clarification, I want to point out (if it has not been addressed) that the only thing that exists in the ballooniverse (ahhem, well done) is the surface of the balloon. It doesn't grow "into" anything, because there is nothing to grow into on the surface. At any point in time, it just has more area than it did a moment before. These are familiar problems with the balloon analogy. We do appear in the center, because we can't see off the surface of the balloon. We can not infer the shape or size of the balloon (for all we know it's an infinite flat rubber sheet), we can only observe the dots around us all moving away, as could any other dot.


The Cosmic microwave background, CMB we see today should be lob sided cos the CMB is also a time lapse image of the remnants of the big bang.. But the CMB is relatively uniform in all directions.

The CMB should only be lopsided in the way you're describing if the big bang took place in any general direction relative to us. But, since it occurred 'everywhere' (remember, the whole universe expanded) we see it in every direction, and the radiation we see is very similar (although not exactly the same) no matter where we look.

Luckmeister
2010-May-05, 06:51 PM
Hi John37309, The trouble you're having is conceptualizing a fourth physical dimension and spacetime, in which our universe exists. But take heart in the fact that no one can fully conceptualize it because we don't accurately experience it. Our problem is like looking at a 3D cube drawn on a 2D piece of paper. All angles on the cube are 90 degree, but on paper they aren't. Losing a dimension causes distortion as a compromise in perception. Our only concept of the fourth dimension is our distorted 3D view of it.

I would suggest that you study 4D concepts and eventually the maths, starting with Wikipedia and other sources that will help you understand what we are missing. Remember, we all suffer the same frustration in that area to some degree.

Mike

ETA: Now here's the kicker; scientific method tells us the universe doesn't actually have dimensions. They are an analogy to the real properties of the universe. They are our invention to assist us in working with relative points in space. Our original definition and usage of dimensions works fine for the first three, but runs into problems with the fourth. That's because the fourth must take time into consideration as a necessary component, and that complicates things. Beyond the third dimension, space and time can no longer be considered separately and must be combined as spacetime. But I guess that's a subject for another thread.

Andrew D
2010-May-05, 07:39 PM
it would take light from a galaxy 13 billion light years away 13 billion years to reach us. Because of this, it is not possible to see what these galaxies look like now, as the light they are emitting now will not reach us for 13 billion years.

I'd like to clarify: this figure ignores the expansion between the two galaxies. I believe the actual figure is some 40 billion years.

John37309
2010-May-05, 08:28 PM
I follow through the thought experiments with the expanding balloon in my head, but no matter what way i play through the experiment, i still cannot get to a point where the big bang works and we see what we see in astronomical images.

This is whats inside my head; Thought experiment!

At this exact moment in time we can see nothing in the sky, the sky is black, completely empty and void of anything. The astronomical images from the worlds telescopes are simple archaeology, they are the same as digging in the soil and finding old history stuff.

So, if we could theoretically take an astronomical image of the universe, but without the 13 billion year time lapse, and look at this image on our computers, the probability of the earth being in the centre would be almost zero! So in this theoretical image, where would the earth be? Where would the Milkyway be?

{EDIT}Anyone know how to install an avatar? Or do i have to serve a time period before being allowed one? I feel nakid without one :)

John.

Luckmeister
2010-May-05, 08:44 PM
Okay, look at things in space between two points as following a vector line. In this case, it is a time line representing the shortest time between two points. When we look out from our reference point, the vector lines radiate out from us in all directions. The reason our frame of reference is the vector starting point is because everything we see is back in time and we are the only point in our view that is the present. That makes us look like the center of the universe, but only to us. Any view from anywhere else would follow its own vector lines from their "now" in time. Hope that helps.

Mike

Incomplete
2010-May-05, 08:48 PM
I follow through the thought experiments with the expanding balloon in my head, but no matter what way i play through the experiment, i still cannot get to a point where the big bang works and we see what we see in astronomical images.

Can you explain why? That is, do you agree that a 2D observer on the balloon's surface would see something isotropic, no matter where he was?



At this exact moment in time we can see nothing in the sky, the sky is black, completely empty and void of anything. The astronomical images from the worlds telescopes are simple archaeology, they are the same as digging in the soil and finding old history stuff.

The same thing is true of everything you see and hear. But ok, go on.


So, if we could theoretically take an astronomical image of the universe, but without the 13 billion year time lapse, and look at this image on our computers, the probability of the earth being in the centre would be almost zero! So in this theoretical image, where would the earth be? Where would the Milkyway be?


I think perhaps one thing you haven't wrapped your head around is that the universe doesn't have a center. Maybe we should focus on that first.

Forget the big bang, the CMB, expansion, etc. Let's just think about one moment in time as you suggest. If you don't mind, let's start with the surface of the balloon again.

Do you agree that the 2D surface of a spherical balloon doesn't have a center? That is, there is no point on the surface that can be said to be the center? And that every point on the surface is equivalent to every other point (assuming it's perfectly spherical)?

So the thing is, the universe, at a fixed instant of time, is just like that, except 3D. It doesn't have a center. Every point is equivalent to every other point.

Andrew D
2010-May-05, 08:54 PM
I follow through the thought experiments with the expanding balloon in my head, but no matter what way i play through the experiment, i still cannot get to a point where the big bang works and we see what we see in astronomical images.

This is whats inside my head; Thought experiment!

At this exact moment in time we can see nothing in the sky, the sky is black, completely empty and void of anything. The astronomical images from the worlds telescopes are simple archaeology, they are the same as digging in the soil and finding old history stuff.

So, if we could theoretically take an astronomical image of the universe, but without the 13 billion year time lapse, and look at this image on our computers, the probability of the earth being in the centre would be almost zero! So in this theoretical image, where would the earth be? Where would the Milkyway be?

John.

I'm having trouble understanding your experiment. If the skies are empty, what are the pictures of?

To answer your question: If we could see what the universe looks like at present, Earth wouldn't change as it's the only thing we observe in (close to) the present; gravity is much stronger than the expansion, so things like planets, stars, galaxies, and galaxy clusters stay together. The Milky Way would still be in the same location relative to distant galaxies, it would just be further away from all of them. We would notice, however, that the objects closer to us wouldn't have moved as far as those that are further out. The Earth would indeed not be in the center of anything, just like today.

John37309
2010-May-05, 08:58 PM
Yes, i do understand the inflating balloon concept and that at any point of the balloon, every other object or point would see themselves as being in the centre. But my problem with this is that at any given moment in time, the surface of the balloon is 2D, but our universe is always 3D + time.

In my previous thought experiment about the instant universe picture, where would the earth be? cos its really unlikely to be in the centre.

John.

Incomplete
2010-May-05, 09:09 PM
Yes, i do understand the inflating balloon concept and that at any point of the balloon, every other object or point would see themsees as being in the centre. But my problem with this is that at any given moment in time, the surface of the balloon is 2D, but our universe is always 3D + time.

In my previous thought experiment about the instant universe picture, where would the earth be? cos its really unlikely to be in the centre.


Please try reading the quote below again. If you're still confused, can you point out where it loses you? Is it that you can't imagine a 3D space with no center?



I think perhaps one thing you haven't wrapped your head around is that the universe doesn't have a center. Maybe we should focus on that first.

Forget the big bang, the CMB, expansion, etc. Let's just think about one moment in time as you suggest. If you don't mind, let's start with the surface of the balloon again.

Do you agree that the 2D surface of a spherical balloon doesn't have a center? That is, there is no point on the surface that can be said to be the center? And that every point on the surface is equivalent to every other point (assuming it's perfectly spherical)?

So the thing is, the universe, at a fixed instant of time, is just like that, except 3D. It doesn't have a center. Every point is equivalent to every other point.

pzkpfw
2010-May-05, 09:13 PM
cos its really unlikely to be in the centre.

Everything is the centre.

Earth is.
You are.
I am.

Way over there, at the furthest edge of what our most powerful telescopes can see, is a Planet orbiting some Star. On that Planet is a creature thinking "why is my Planet the centre of the Universe?".


The big bang wasn't an explosion that occured at some point in empty space and flung stuff outwards from that point.

The big bang was the expansion of the (visible) Universe. All of the (visible) Universe expanded - no one point of that Universe was the centre; it all expanded away from itself.

Andrew D
2010-May-05, 09:18 PM
Yes, i do understand the inflating balloon concept and that at any point of the balloon, every other object or point would see themselves as being in the centre. But my problem with this is that at any given moment in time, the surface of the balloon is 2D, but our universe is always 3D + time.

You are correct. But don't get hung up on this, it's just a consequence of the analogy. You have to ignore the amount of dimensions, as the purpose of the analogy it to explore the distance between the dots and how they move apart uniformly on the surface of the ballooniverse. If it helps, imagine being so small that when you stood on the balloon, it looked flat, the way the Earth looks to us. Now, imagine a grid is set up on the surface of the balloon. If the balloon were inflated, the tiny observer on the surface would just see the grid getting larger. If he were to move to any other part of the balloon and look down at the surface, he would see the exact same thing. This is the principle that Incomplete is trying to illustrate: no matter where the tiny observer is on the balloon, the expansion looks the same.


In my previous thought experiment about the instant universe picture, where would the earth be? cos its really unlikely to be in the centre.

Again, you are correct. Questions like this are hard to answer, and the answers are usually unimportant. In a universe as big as ours, you can only define things like 'location' in terms of other objects. Since expansion is uniform, the Earth would be in exactly the same location in the (larger) universe, our galactic neighborhood would just be a bit further away from everything else.

John37309
2010-May-05, 09:24 PM
Incomplete, pzkpfw,
No,i just don't understand that. I see things differently. Maybe our brains work differently. You guys are able to see logic in this and i am not.

No, i just cannot make any sense out of there being no centre, or that everyone is at the centre. Or that from everyones prospective they all think they are at the centre.

I'm only able to think in 3 dimensions. I can accept there being a time lapse in all astronomical images but i cannot accept that at any moment in time the earth and the Milkyway are in the middle.

John.

Luckmeister
2010-May-05, 09:30 PM
I'm only able to think in 3 dimensions. I can accept there being a time lapse in all astronomical images but i cannot accept that at any moment in time the earth and the Milkyway are in the middle.

John.

That's the problem. Neither of them is in the middle. Each of them sees the illusion that they are in the middle.

Incomplete
2010-May-05, 09:37 PM
No, i just cannot make any sense out of there being no centre, or that everyone is at the centre. Or that from everyones prospective they all think they are at the centre.

Well, at least now you know precisely where the problem is. You could try reading this (http://en.wikipedia.org/wiki/N-sphere) article. The case of interest is a 3-sphere (NOT a 3-ball!).

If that's too mathematical, one trick that works very well for many people is to start in lower dimensions. Start with a 1-sphere, which is just the 1D edge of a circle. It has no center, because all points on the circle are equivalent. Now imagine what you have to do to go up one dimension. That does NOT mean filling in the circle to make a disk, because that does have a center. It means rotating the 1D circle to sweep out the 2D surface of a sphere, or stacking 1D circles with decreasing radius above and below the one you started with in the right way to make a sphere.

Now try to imagine rotating the 2D surface of a sphere to sweep out a 3D space with no center and no edge (or stacking them). Good luck, it's hard :).

Incomplete
2010-May-05, 09:46 PM
By the way, there is another kind of 3D space (actually there are two other kinds, but we'll take the simplest) that has no center and no edge: infinite 3D space. Just imagine that the universe at any fixed instant is infinitely big. No matter how far you travel in any direction, you never hit an edge, or find anything very different than where you started.

As time passes the entire thing expands (even though it's infinite). That means that every observer sees everything around them moving away in a radial direction, and the farther away it is, the faster it's going (because there's more space in between to expand).

John37309
2010-May-05, 09:49 PM
Luckmeister, Roobydo, pzkpfw, Incomplete, WayneFrancis,
I want to thank you all for helping me,thank you guys for taking the time! I better just leave this topic alone for a while.

I don't accept the big bang theory, i first heard it about 15 years ago. It took me about 10 years to fully get my head around it and today, now that i know what i have learnt about physics and cosmology, i still don't accept it. I certainly cannot accept the expanding balloon analogy as a method of explaining universal expansion to my 5 year old child. At 5 years of age, my little boy has a pretty advanced understanding of higher level physics, thanks to his dad. But unfortunately i won't be explaining universal expansion to my boy with the expanding balloon theory. Nor will i be teaching him the standard model of particle physics as its way off the mark.

Its through teaching my child that i have developed a higher understanding of physics, physics is easy to understand. But we are all still infants when it comes to understanding the big picture.

Thanks for the help guys,
John in Ireland.

Geo Kaplan
2010-May-05, 09:54 PM
I'm only able to think in 3 dimensions. I can accept there being a time lapse in all astronomical images but i cannot accept that at any moment in time the earth and the Milkyway are in the middle.

John.

You seem to be ignoring what the kind folks here have written, so pardon the boldface italicized declaration:

The earth and the Milky Way are not in the middle.

(Repeat as necessary).

So there is no need to "accept that any moment...".

If it is true that you can only think in three dimensions, then it should be easier -- not harder -- for you to visualize the absence of a center. "Things flying away from other things" does not require a center at all. It's true in the 2D balloon case, and since 3D subsumes 2D, that example still holds as one of many possible center-free arrangements in which, nonetheless, each observer sees all other points moving away. Each observer sees the same thing, but no one is at the center (which, in the balloon example, does not even exist). The earth is not in a special place.

Incomplete
2010-May-05, 09:56 PM
At 5 years of age, my little boy has a pretty advanced understanding of higher level physics, thanks to his dad. But unfortunately i won't be explaining universal expansion to my boy with the expanding balloon theory. Nor will i be teaching him the standard model of particle physics as its way off the mark.

Maybe when he gets a little older he'll come to understand why these theories are so widely accepted by so many smart people, and find a way to explain them to his father?

Geo Kaplan
2010-May-05, 10:00 PM
I don't accept the big bang theory, i first heard it about 15 years ago. It took me about 10 years to fully get my head around it ...{snip}

Regrettably, your inability even to "get your head around" the simple balloon example contradicts your self-described "higher understanding of physics." I second Incomplete's optimism that your son will be able to achieve enlightenment and pass that back to his father.

John37309
2010-May-05, 10:01 PM
Maybe when he gets a little older he'll come to understand why these theories are so widely accepted by so many smart people, and find a way to explain them to his father?
LOL..... Yes Incomplete. I hope that some day the little lad will be able to teach his dad how it works. Its possible my brain is stuck in 1980's physics.

John.

Incomplete
2010-May-05, 10:04 PM
LOL..... Yes Incomplete. I hope that some day the little lad will be able to teach his dad how it works. Its possible my brain is stuck in 1980's physics.

John.

1980s?

The standard model was basically complete by the early 1970s, and its essential elements have been in place since the 50s and before. Einstein's general relativity was published in final form in 1916 or so, and the expansion of the universe was confirmed observationally in the 1920s or early 30s.

Luckmeister
2010-May-05, 10:40 PM
John37309, before you go, try to keep in mind that when you look at the night sky, you are not looking at the universe. You are not looking at today's reality. You are looking at a distorted view of what it used to be. Please reread my post #13. I added a little to try to make it a bit clearer. I think your kid will do well having you for a dad. Even if you're having trouble with admittedly difficult concepts to visualize, you're trying, and your son will benefit from your example.

Mike

Geo Kaplan
2010-May-05, 11:12 PM
Even if you're having trouble with admittedly difficult concepts to visualize, you're trying, and your son will benefit from your example.


Maybe, but only if Dad adopts a more humble attitude than "Because I personally can't understand it, it must be wrong." That's a pernicious lesson to pass on. To declare explicitly that he won't use the balloon example for the reasons he stated, makes me worried for the son. As has been said often at BAUT, "you're certainly welcome to your own opinion, but not to your own facts."

fwsocial
2010-May-05, 11:28 PM
It's not easy to understand these concepts without mathematics. Analogs only go so far. But the Copernican principle and that distant galaxies depart from each other is easily shown in any textbook.
What many have problems with is the concept of expanding space, where the expansion can be superluminal even. But reality is that General Relativity has passed all experimental tests sofar.
Another related issue is the unknown dark energy which actually accelerates the expansion. To sum up, the evidence of the expansion is very clear, distant galaxies depart without exception in accordance with
the Hubble law and the CMB is clear evidence of a big bang. And the Hubble Deep Field shows that there has been substantial galactic evolution.

pzkpfw
2010-May-06, 12:07 AM
To all: Let's have no more "analysis" of the OP or his beliefs/attitudes. Let's stick to giving answers to the question - and not worry about how those answers are taken. (Unless they are argued against - in which case this thread will get taken to ATM...).

Grashtel
2010-May-06, 01:19 AM
Perhaps this analogy will work for you:

Imagine that the actual universe is much bigger than the visible one, say a googol (http://en.wikipedia.org/wiki/Googol) light years across currently, with matter being distributed uniformly throughout it (at large scales at least). So long as our position is such that we can't see the edge of the actual universe (which given the age of the universe describes virtually all of it) the uniform distribution of matter makes it impossible to tell our relative location within it.

Probably not a very good description but hopefully it will help you visualise things.

Jens
2010-May-06, 01:34 AM
No, i just cannot make any sense out of there being no centre, or that everyone is at the centre. Or that from everyones prospective they all think they are at the centre.


Let me put a little extra meat to Jouh37309's difficulty, because I also have difficulty in a sense. In the analogy of the surface of the balloon, in fact there is a center. The center is the center of the 3D sphere that is expanding. So the way I see it is, either the analogy is incomplete in some way, or is there in fact a center of the universe in 4D, which we cannot see because we are confined to a 3D world? The 2D surface can only expand that way because it is living in a 3D universe, right?

Incomplete
2010-May-06, 01:42 AM
Let me put a little extra meat to Jouh37309's difficulty, because I also have difficulty in a sense. In the analogy of the surface of the balloon, in fact there is a center. The center is the center of the 3D sphere that is expanding. So the way I see it is, either the analogy is incomplete in some way, or is there in fact a center of the universe in 4D, which we cannot see because we are confined to a 3D world?

The analogy is not incomplete, it's simply one dimension less. As for there being a center in 4D, you can think of it that way if you like. More poetically, you can think of the balloon as being "filled" by its past selves (which were smaller), so that its "center" is the big bang t=0.

One can always embed a manifold in a higher dimensional space. Similarly, one can usually "fill in" a manifold using an extra dimension. But there is no need or reason to do so, it's purely a mathematical device.

Interestingly, there are three geometries for the spatial geometry of the universe that are considered the standard possibilities. One is the 3-sphere we've been discussing, which can be embedded in ordinary (i.e. Euclidean0 4D space. One is ordinary 3D space. The third is hyperbolic 3-space, which cannot be embedded in 4D (but perhaps it can in 5D, I'm not positive).

Which goes to show that thinking of the universe as an embedding makes everything unnecessarily complex! Better just to deal with the intrinsic 3D geometry.

DrRocket
2010-May-06, 01:45 AM
Incomplete, WayneFrancis, Roobydo,
Thank you for taking the time to explain.

For the last 4 years i have heard many explanations and variations of the expanding balloon analogy. I do understand the analogy, but i can never accept it as a viable explanation for what we see. I only ever seem to see flaws in the concept. It still does not make any sense.

I understand that all astronomical images are history pictures, none of them can ever display what is there right now at this moment in time. So really we are always seeing the way stuff was in the past, not the present. This makes the balloon analogy wrong and misleading.This is why i can never make it work in my mind.

I know its a difficult one. But do you see the point i'm making.

John.

If you don't like the balloon analogy, imagine an infinite sheet of rubber with grid lines. Now imagine that the rubber is being uniformly stretched. You get the same picture. Every point looks the same and from every point it appears that all other points are moving away, and the speed with which they are moving away is proportional to distance.

DrRocket
2010-May-06, 01:50 AM
The analogy is not incomplete, it's simply one dimension less. As for there being a center in 4D, you can think of it that way if you like. More poetically, you can think of the balloon as being "filled" by its past selves (which were smaller), so that its "center" is the big bang t=0.

One can always embed a manifold in a higher dimensional space. Similarly, one can usually "fill in" a manifold using an extra dimension. But there is no need or reason to do so, it's purely a mathematical device.

Interestingly, there are three geometries for the spatial geometry of the universe that are considered the standard possibilities. One is the 3-sphere we've been discussing, which can be embedded in ordinary (i.e. Euclidean0 4D space. One is ordinary 3D space. The third is hyperbolic 3-space, which cannot be embedded in 4D (but perhaps it can in 5D, I'm not positive).

Which goes to show that thinking of the universe as an embedding makes everything unnecessarily complex! Better just to deal with the intrinsic 3D geometry.

Careful with hyperbolic 3-manifolds. There are lots of them -- Google William Thurston. Some are compact.

I have yet to see a convincing argument why the usual three posisibilities are the only viable candidates.

I agree that embeddings get in the way. The embeddings exist, but tend to have rather high dimension in general, particularly in the semi-Riemannian case. They are an unnecessary device that obscures the basic philosophy of general relativity.

Cougar
2010-May-06, 02:03 AM
I don't accept the big bang theory, i first heard it about 15 years ago. It took me about 10 years to fully get my head around it and today, now that i know what i have learnt about physics and cosmology, i still don't accept it.

That's preposterous. In 10 years of study, one should have a pretty good understanding of general relativity, which is the theory, and not "an analogy of the theory using party favors." Much of that study would be mathematical prerequisites.

You don't "get" it? One shouldn't be surprised if you haven't taken the classes and studied general relativity!

But you "don't accept the big bang theory"? On what basis could you even make such a decision? It doesn't appear you've gotten very far into it.


But unfortunately i won't be explaining universal expansion to my boy with the expanding balloon theory. Nor will i be teaching him the standard model of particle physics as its way off the mark.

So you're a home-schooler? How are you going to explain to your charge that the observed abundances of the elements in the Universe are in the exact proportion that they would be if they originally came from an extremely hot and dense state that was expanding and cooling rapidly, leaving only a brief window for helium nuclei to fuse from hydrogen, resulting in the precise proportion we observe?

The big bang theory is not about the "point" that has been popularly explained as the beginning. It's all about after that.

WayneFrancis
2010-May-06, 02:21 AM
Incomplete, WayneFrancis, Roobydo,
Thank you for taking the time to explain.

For the last 4 years i have heard many explanations and variations of the expanding balloon analogy. I do understand the analogy, but i can never accept it as a viable explanation for what we see. I only ever seem to see flaws in the concept. It still does not make any sense.


What flaws do you see with it? It's hard because all to often people try to take the analogy to far. It is only an analogy and if you look at it to close the concept is bound to break down and unless you want to start learning the maths and physics involved with different spatial topologies and manifolds then you have to just take the experts word on it. IE if you can't understand what the actual science is saying then you really shouldn't say that it is faulty.



I understand that all astronomical images are history pictures, none of them can ever display what is there right now at this moment in time. So really we are always seeing the way stuff was in the past, not the present. This makes the balloon analogy wrong and misleading.This is why i can never make it work in my mind.

I know its a difficult one. But do you see the point i'm making.

John.

No that doesn't make the balloon analogy wrong.

1. When you look at the balloon you are looking at it from another higher order dimension.
2. There is still a difference in "time" when you look at different points on the balloon. NOTHING you see is how it is "now" because for you to see something it has to be separated from you and thus takes time for the light to get to you. So if it is 10 feet away from you then what you are "seeing" is something as it was ~10 nanoseconds ago. If you look at something 1 billion light years away then you are looking at something as it was 1 billion years ago. The concept is the same it is just the scale. In actuality no 2 objects share a common "now"

If you put yourself "on" the surface of the balloon then you're in a 2d version of our 3d universe.

WayneFrancis
2010-May-06, 02:46 AM
Yea, i understand the concept. 13.7 billion years ago all the matter we see was all inside one tiny point. Ever since, from our point of view, everything seems to be moving away. Still puts us in the centre.


But like the balloon analogy every point on the surface of the balloon appears to be the centre when looking at other points on the surface of the balloon. Remember you can't look "off the surface" of the balloon if you are in the balloon universe.



This expanding balloon should still put us somewhere else other than appearing to be in the centre.


No offence but if you have this view then you are not grasping the concept.

Ok try this 1d analogy


you have an infinitely long bungie cord.
Every 1m there is a ball the bungie cord
The bungy cord gets stretched by 2x
The balls are now 2m apart

Pick any ball on the bungie cord and it appears that all other balls are moving away from it and that they are at the centre.

Or pick a bungy cord that is a loop and you increase the circumference of the loop by 2x. Each ball could see all the other balls moving away from it. Remember the balls can not look "off" the cord.


The beautity of the balloon analogy is that it displays the harder closed universe scenario and people often have problems conceptualising infinity getting larger.



The Cosmic microwave background, CMB we see today should be lob sided cos the CMB is also a time lapse image of the remnants of the big bang.. But the CMB is relatively uniform in all directions.

John.

No the CMB should not be lop sided according to the main stream view. Again its an indication that you aren't getting the base concept right in your head.

There are tons of videos on you tube that show it.

http://www.youtube.com/watch?v=Cm8UNSHRm8c

WayneFrancis
2010-May-06, 03:01 AM
I follow through the thought experiments with the expanding balloon in my head, but no matter what way i play through the experiment, i still cannot get to a point where the big bang works and we see what we see in astronomical images.

This is whats inside my head; Thought experiment!

At this exact moment in time we can see nothing in the sky, the sky is black, completely empty and void of anything. The astronomical images from the worlds telescopes are simple archaeology, they are the same as digging in the soil and finding old history stuff.

So, if we could theoretically take an astronomical image of the universe, but without the 13 billion year time lapse, and look at this image on our computers, the probability of the earth being in the centre would be almost zero! So in this theoretical image, where would the earth be? Where would the Milkyway be?

{EDIT}Anyone know how to install an avatar? Or do i have to serve a time period before being allowed one? I feel nakid without one :)

John.

Given the mainstream view if you could pop out of the universe and look at it there are 2 possiblities

1) it is infinite in size (open)
2) it is finite in size (closed)

Either view there is no "centre". Again back to an analogy. Take a sphere and show me a place on the surface of the ball that would qualify as the centre. If you say you can pick a spot, again only on the surface, then what makes that point on the ball any more special then any other spot on the surface of the ball.

If you could freeze stuff and did the maths you would say that the furthest galaxies that Earth has seen are now actually over 40 billion light years away. Doing more calculations you would be able to tell that the view of them actually was emitted when they where only something like 4 billion light years away but that 4 billion light years was stretched to 12 billion light years during the time the light has been travelling.

Again don't look at the big bang as an explosion IN space but an explosion OF space. A real explosion is matter moving through space away from a point. The big bang is space being stretched and taking what ever is in it along for the ride.

WayneFrancis
2010-May-06, 03:12 AM
Yes, i do understand the inflating balloon concept and that at any point of the balloon, every other object or point would see themselves as being in the centre. But my problem with this is that at any given moment in time, the surface of the balloon is 2D, but our universe is always 3D + time.

In my previous thought experiment about the instant universe picture, where would the earth be? cos its really unlikely to be in the centre.

John.

Taking a real world example of what is happening. A tree.
You plant a tree and it shoots up from the ground. You are an ant on the surface and live on the surface. Where is the centre of the tree. Well for us we cut into it and can see the centre but that centre was really a layer from the past. We can "see" the past of a tree by looking at its rings.

The universe is similar but in this case...the centre of the universe is defined by time. There is no "position" as the 3 spatial dimension don't have a concept of "centre" when it comes to the universe. The only dimension that does is "time" and that "centre" is the beginning of time.

Again you can't look off of the "Surface" you are on. So yes when you look at a object you see it as it was when the balloon was smaller and that smaller is, for the balloon, the time dimension. There is no way to get to the beginning of time like you can get to a point in space. The only points in time you can get to are in your future.

WayneFrancis
2010-May-06, 03:17 AM
Incomplete, pzkpfw,
No,i just don't understand that. I see things differently. Maybe our brains work differently. You guys are able to see logic in this and i am not.

No, i just cannot make any sense out of there being no centre, or that everyone is at the centre. Or that from everyones prospective they all think they are at the centre.

I'm only able to think in 3 dimensions. I can accept there being a time lapse in all astronomical images but i cannot accept that at any moment in time the earth and the Milkyway are in the middle.

John.

Don't equate "appearing as we are in the centre" with the concept of "we are in the centre" or even "there is a centre"

That's the key. There really is NO centre in the 3 spatial dimensions. Only the "time" dimension can be even framed as having a centre.

There is no real need to introduce extra dimensions into this discussion beyond the 3 spatial and 1 time.

Incomplete
2010-May-06, 06:16 AM
Careful with hyperbolic 3-manifolds. There are lots of them -- Google William Thurston. Some are compact.

That's true, but I don't think any of them are isotropic and homogeneous except the vanilla one. There's a similar story with flat space. You can compactify it into a 3-torus, but that breaks isotropy.


I have yet to see a convincing argument why the usual three posisibilities are the only viable candidates.

It's just based on the observation that the part of the universe we can see appears to be homogeneous and isotropic. Extend that to an entire manifold, and there are just those three. Clearly that's an assumption, so I'm not convinced by it either.

Spaceman Spiff
2010-May-06, 12:38 PM
John37309:

If you're still reading any of this, ask yourself this:

what would an astronomer in a distant galaxy (say 2 billion light years away**) observe, and how would he/she/it interpret the observations? You might even imagine that this being was studying a tiny grouping of galaxies just beyond the outskirts of a major galaxy cluster. I am, of course, speaking of the Milky Way and Andromeda galaxies...



** not so far that we have to worry about the definition of distance

formulaterp
2010-May-07, 05:16 AM
Let me put a little extra meat to Jouh37309's difficulty, because I also have difficulty in a sense. In the analogy of the surface of the balloon, in fact there is a center. The center is the center of the 3D sphere that is expanding. So the way I see it is, either the analogy is incomplete in some way, or is there in fact a center of the universe in 4D, which we cannot see because we are confined to a 3D world? The 2D surface can only expand that way because it is living in a 3D universe, right?

I think you are making a similar mistake. With the balloon analogy, you are describing the center of the balloon, not the center of the SURFACE of the balloon. The distinction is vital to understanding the analogy.

Of course you are correct that the analogy is incomplete. But that is the very nature of all analogies. As it becomes closer and closer to being complete is stops being an analogy and becomes the "thing" we are trying to describe.

Geo Kaplan
2010-May-07, 05:44 AM
I think you are making a similar mistake. With the balloon analogy, you are describing the center of the balloon, not the center of the SURFACE of the balloon. The distinction is vital to understanding the analogy.

Of course you are correct that the analogy is incomplete. But that is the very nature of all analogies. As it becomes closer and closer to being complete is stops being an analogy and becomes the "thing" we are trying to describe.

Exactly. That's the problem and power of an analogy. If the OP is still perusing this thread, here's one more non-balloon analogy to ponder: Imagine a magic loaf of bread, say, with raisins distributed throughout. This magic bread expands uniformly as it's baked, and keeps expanding forever. Any particular raisin will see all the other raisins receding from it, without being at the center.

As has already been observed, it's critically important to separate "appears to be in the middle" from "it is in the middle." Appearances can be deceiving.

DrRocket
2010-May-07, 05:55 AM
That's true, but I don't think any of them are isotropic and homogeneous except the vanilla one. There's a similar story with flat space. You can compactify it into a 3-torus, but that breaks isotropy.

??

Isotropy and homogeneity are not properties of manifolds, but only of functions defined on manifolds, so I don't understand this statement. Even defining homogeneity and isotropy take a bit of work.

In the case of a flat torus, it is a quotient space of a Euclidean box, so it is pretty easy to see what isotropy and homogeneity ought to mean -- invariance under rotation and translation back in Euclidean space. So I don't immediately see how isotropy becomes "broken".

Martin C
2010-May-07, 08:30 AM
Darn, I always thought I understood the expansion of the universe because of the balloon analogy, but now it appears from this discussion that I am missing something. I have always understood that the balloon analogy explains why everything appears to be moving away from us (i.e. lots of red shift, no blue shift), yet that does not make us special: from <b>any</b> point you picked on the balloon's surface all other points on the balloon's surface would be moving away.

However when posters on this thread stated saying "there is no actual place the expansion started" then I began to go "whaaa?". I always viewed the model of the universe as effectively an infinite series of balloons within balloons, all expanding, so effectively it is a 3D space, and because the outermost balloon is expanding fastest, still any point on any balloon will be seen as moving away from any other point on any other - or the same - balloon.

But isn't it <b>still</b> a simple 3-dimensional object? An expanding solid ball (ouch, perhaps "3D" is a better word than "solid") of space, with light-emitting objects peppered throughout it, which are expanding outward from a central point, but because of their mutual outward-bound vectors, and the fact that effectively the outermost "shell" of space in any expanding object must be moving outward fastest, each point in the universe still measures each other point in the universe as receding. Parrallels with the bungy cord analogy show this too in one dimension.

This model always seemed reasonably explanatory to me, but it still has some physical basics like a "central point that the expansion must have started from". I even thought we knew roughly where the direction of that centre was ... there was a particular constellation ... Sagittarius? Or is that just the Milky Way galaxy?

Note 1. I am not considering the limits of visibility due to light-speed here, I am considering how the universe <b>is</b>, not how it appears. Imagine I am trying to make a map of the universe <b>at the present time</b> by asking all stars to report their current position ... and I'm prepared to wait billions of years for all the reports to come in.

Note 2. By the way, I accept that it's possible that you guys were simplifying the argument for the original poster, so maybe my analogy is still correct.

Note 3. I'm bright, but bright enough to accept that even if there are some things I can't get my head around, they might still be true, and if all the Einsteins of the world agree on something, I tend to accept it is probably right, even if it doesn't make any sense to me even after detailed study. Previous examples include wave vs. particle, and the Twin Paradox.

Incomplete
2010-May-07, 10:20 AM
??

Isotropy and homogeneity are not properties of manifolds, but only of functions defined on manifolds, so I don't understand this statement.


They're properties of metric spaces, which these are.



In the case of a flat torus, it is a quotient space of a Euclidean box, so it is pretty easy to see what isotropy and homogeneity ought to mean -- invariance under rotation and translation back in Euclidean space. So I don't immediately see how isotropy becomes "broken".

A torus is not invariant under rotations.

For example, take a "square" torus (modular parameter 1). Shoot a geodesic along one of the preferred axes. It forms a closed cycle with length 1. Now shoot it at angle 1/pi relative to that axis. It never closes.

Grashtel
2010-May-07, 12:44 PM
But isn't it <b>still</b> a simple 3-dimensional object? An expanding solid ball (ouch, perhaps "3D" is a better word than "solid") of space, with light-emitting objects peppered throughout it, which are expanding outward from a central point, but because of their mutual outward-bound vectors, and the fact that effectively the outermost "shell" of space in any expanding object must be moving outward fastest, each point in the universe still measures each other point in the universe as receding. Parrallels with the bungy cord analogy show this too in one dimension.
You are misunderstanding the balloon analogy, the balloon is just a three dimensional analogy to the four dimensional (or more, though there are only four we can actually interact with) nature of the actual universe. The two dimensional surface of the three dimensional balloon is analogous to the three dimensional hypersurface of the four dimensional (with time being the fourth dimension) hypersphere of the universe (the actual shape of the universe is virtually certain to be much more complex, but a simple hypersphere is more than brain hurty enough though).

This model always seemed reasonably explanatory to me, but it still has some physical basics like a "central point that the expansion must have started from". I even thought we knew roughly where the direction of that centre was ... there was a particular constellation ... Sagittarius? Or is that just the Milky Way galaxy?
That is just the centre of the galaxy, one of the major features of the balloon analogy is to explain how the universe doesn't have a centre in three dimensional space (like how the balloon doesn't have a centre on its surface). The nearest thing that the universe has to a centre is the big bang fourteen odd billion years ago, that is to say its a point in time not a point in space.

Incomplete
2010-May-07, 12:53 PM
However when posters on this thread stated saying "there is no actual place the expansion started" then I began to go "whaaa?". I always viewed the model of the universe as effectively an infinite series of balloons within balloons, all expanding, so effectively it is a 3D space, and because the outermost balloon is expanding fastest, still any point on any balloon will be seen as moving away from any other point on any other - or the same - balloon.


You're gong up a dimension in the wrong way. Suppose we started with a spatially 1D model: an expanding circle. How would we go from that 1D model to the 2D balloon model? Would we fill in the circle using a series of circles within circles? No, because that would give us a disk, not the surface of sphere.

Instead, we need to either rotate the circle through another dimension and take the surface it sweeps out, or "pile" concentric circles both above and below the one we started with in the right way (think of latitude lines).

So to go from the 2D spherical balloon model to a realistic, 3D model, you need to perform the analogue of one of those two operations. Have fun thinking about how.

DrRocket
2010-May-09, 04:13 AM
They're properties of metric spaces, which these are.



A torus is not invariant under rotations.

For example, take a "square" torus (modular parameter 1). Shoot a geodesic along one of the preferred axes. It forms a closed cycle with length 1. Now shoot it at angle 1/pi relative to that axis. It never closes.

Sorry, I don't buy this.

The fact that the space-like slices are metric spaces is not good enougn, not even when the metric is a natural result of an inherited Riemannian metric tensor. There is a some rather obscure notion of isotropy related to Riemanian manifolds ( I find is buried in one page of vol 2 of Spivak's books on differential geometry and not in any of the other many books that I have available), and it appears to be consistent with your observations regarding the flat torus, but while they are useful for abstract studies of topology, they do not reflect the usual meaning of "isotropic" in a physical sense. That is because the notions are essentially global, as with your observation that the irrational flow on the torus, produces geodesics that are not closed, while rational flows produce closed geodesics.

However, locally, and as Einstein insisted on many occasions general relativity focuses on physics as local, the flat torus is indistinguishable from ordinary flat Euclidean space, and there the O(n) symmetry is pretty clear. I would certainly imagine that were space a flat (3-) torus, then given the imense size of the universe, one would not be able to expeerimentally distinguish it from Euclidean space, in the time since the Big Bang.

I have not seen the proof of the existence of the foliation of space-time into a one-parameter family of space-like hyperspaces, so an not sure whether the assumption of istropy in the sense of differential geometry is made. I would be interested in knowing.

Martin C
2010-May-10, 06:26 AM
Darn, I was hoping for a simpler universe.

Thanks for replies.

Cougar
2010-May-10, 12:57 PM
Darn, I was hoping for a simpler universe.

You were born too late.






"...cosmologists are claiming that they can extrapolate backward in time to learn the conditions in the universe just one second after the beginning! If cosmologists are so smart, you might ask, why can't they predict the weather? The answer, I would argue, is not that cosmologists are so smart, but that the early universe is much simpler than the weather!" -- Alan Guth (http://en.wikipedia.org/wiki/Alan_Guth)

Incomplete
2010-May-10, 01:33 PM
Sorry, I don't buy this.

The fact that the space-like slices are metric spaces is not good enougn, not even when the metric is a natural result of an inherited Riemannian metric tensor. There is a some rather obscure notion of isotropy related to Riemanian manifolds ( I find is buried in one page of vol 2 of Spivak's books on differential geometry and not in any of the other many books that I have available), and it appears to be consistent with your observations regarding the flat torus, but while they are useful for abstract studies of topology, they do not reflect the usual meaning of "isotropic" in a physical sense. That is because the notions are essentially global, as with your observation that the irrational flow on the torus, produces geodesics that are not closed, while rational flows produce closed geodesics.

I don't have Spivak's book, but these notions are not that obscure. In physics language the question is whether the isometry group has a rotation subgroup. Anyway, you're correct about the lack of isotropy in the torus case being global.


However, locally, and as Einstein insisted on many occasions general relativity focuses on physics as local, the flat torus is indistinguishable from ordinary flat Euclidean space, and there the O(n) symmetry is pretty clear.

What Einstein insisted on isn't very relevant. GR is GR, regardless of what he thought about it. On top, he didn't insist GR focuses on physics as local (it sounds like you've been reading too many posts by a certain poster here). What he postulated is that if you focus on a sufficiently small region, then the physics looks like SR. But the observable universe is too big for that to hold true. We can easily detect the curvature of spacetime, for example.


I would certainly imagine that were space a flat (3-) torus, then given the imense size of the universe, one would not be able to expeerimentally distinguish it from Euclidean space, in the time since the Big Bang.

That entirely depends on the size of the cycles of the torus compared to the Hubble horizon today. If they are comparable, the effects can be detected, and had they been significantly smaller they would have had obvious effects. People have searched for those effects in data (and didn't find them).

Incidentally there are also many theories where the cycles are microscopic, and we don't see them because they are too small (although in that case of course these are extra dimensions, and physics on human scales is very anisotropic with respect to them).


I have not seen the proof of the existence of the foliation of space-time into a one-parameter family of space-like hyperspaces, so an not sure whether the assumption of istropy in the sense of differential geometry is made. I would be interested in knowing.

If you don't require anything at all of those spacelike hypersurfaces, that should always be possible. Usually though you require that they be homogeneous and isotropic, and if you impose that globally you're only left with the three possibilities I mentioned before.

Webbo
2010-May-10, 02:40 PM
The problem I have with the baloon analogy is that it must assume that when an occupier of this 2D universe travels in any direction in a straight line, they must eventually arrive back where to they started. Is this property also assumed to be true of our 3D universe?

Cougar
2010-May-10, 02:50 PM
Is this property also assumed to be true of our 3D universe?

No, but it might be.

Webbo
2010-May-10, 03:10 PM
No, but it might be.

If so, then shouldn't we be able to see some evidence of the early milky way in every direction we look? In fact any galaxy we see in one direction should have a mirror image in the opposite direction, and galaxies that are roughly half the maximum distance now (circa 7 billion ly) should have their exact inverted replica in the opposite direction at the same distance and age. Is there any such evidence?

Strange
2010-May-10, 03:27 PM
If so, then shouldn't we be able to see some evidence of the early milky way in every direction we look? In fact any galaxy we see in one direction should have a mirror image in the opposite direction, and galaxies that are roughly half the maximum distance now (circa 7 billion ly) should have their exact inverted replica in the opposite direction at the same distance and age. Is there any such evidence?

Imagine the ballon is really, really big. So big that the 2D inhabitants can't detect any curvature (e.g. if they create a big triangle, the angles add up to 180 degrees within the accuracy they can measure it). It is so big it looks like it could be a rubber sheet that possibly extends to infinity.

Or, to put it another way: no.

Incomplete
2010-May-10, 03:33 PM
If so, then shouldn't we be able to see some evidence of the early milky way in every direction we look? In fact any galaxy we see in one direction should have a mirror image in the opposite direction, and galaxies that are roughly half the maximum distance now (circa 7 billion ly) should have their exact inverted replica in the opposite direction at the same distance and age. Is there any such evidence?

That's a good question. The answer is that it depends on how big the universe is relative to how much of it we can see (which is related to what DrRocket and I were discussing above).

To see how that works, think about the balloon again. Suppose all the light you can see came from points on the balloon's surface that lie in a disk of some radius, centered on your location. If that disk is much smaller than the surface as a whole, you won't see any such mirror images. In fact you'll have difficulty even being sure whether the surface is curved or flat (just as it requires some observation to be sure the world is round).

So how big is that "disk" (which is really a 3D solid ball) in the real universe? The answer depends on the expansion history. If the ballooniverse expanded very rapidly to its current size, light had little time to travel and so the disk/ball is small. If it expanded more slowly, you get to see more. Does that make sense?

(You might get confused about the moment t=0 when the balloon had zero size, but recall that it was expanding infinitely rapidly at that time, in such a way that light only moved a finite distance around the surface.)

Webbo
2010-May-10, 05:11 PM
That's a good question. The answer is that it depends on how big the universe is relative to how much of it we can see (which is related to what DrRocket and I were discussing above).

To see how that works, think about the balloon again. Suppose all the light you can see came from points on the balloon's surface that lie in a disk of some radius, centered on your location. If that disk is much smaller than the surface as a whole, you won't see any such mirror images. In fact you'll have difficulty even being sure whether the surface is curved or flat (just as it requires some observation to be sure the world is round).

So how big is that "disk" (which is really a 3D solid ball) in the real universe? The answer depends on the expansion history. If the ballooniverse expanded very rapidly to its current size, light had little time to travel and so the disk/ball is small. If it expanded more slowly, you get to see more. Does that make sense?

(You might get confused about the moment t=0 when the balloon had zero size, but recall that it was expanding infinitely rapidly at that time, in such a way that light only moved a finite distance around the surface.)

If you place youself on the surface of this 14 billion years old baloon once you look further than 7 billion ly everything must repeat and invert. I thought we had observed galaxies older than this so there must be some potential evidence.

Actually, thinking about it, it cant be a possibility because everything beyond halfway point should amass to a single point of light. Place a light bulb at the opposite point of the balloon and no matter what direction you look you will see the bulb.

Incomplete
2010-May-10, 05:18 PM
If you place youself on the surface of this 14 billion years old baloon once you look further than 7 billion ly everything must repeat and invert. I thought we had observed galaxies older than this so there must be some potential evidence.

Actually, thinking about it, it cant be a possibility because everything beyond halfway point should amass to a single point of light. Place a light bulb at the opposite point of the balloon and no matter what direction you look you will see the bulb.

Only if the balloon/universe is 14 billion light years in circumference. But it isn't. We know for certain (from the lack of such effects) that it is at least 10 times bigger than that.

And before you ask, yes, that means the circumference expanded "faster than light" (in exactly the sense we are discussing), and no, that doesn't violate any principle of relativity.

Shaula
2010-May-10, 05:24 PM
If you place youself on the surface of this 14 billion years old baloon once you look further than 7 billion ly everything must repeat and invert. I thought we had observed galaxies older than this so there must be some potential evidence.
You may have missed what Incomplete was saying - if the size of the balloon is considerably greater than 14 billion light years then you will not see any evidence of the wrapping around. This is perfectly possible if inflation was suitably fast.

Your comments hold true for very small universes but not for large ones. You also ignore extinction and expansion as possibilities. If the cut-off point for the observable universe (the point where space is expanding so quickly light from it will never arrive - I am trying to avoid the word super-luminally here having seen the previous debate on what it means) is small compared to the size of the universe or even if there was enough dust to scatter all the light from a distant source so much that we couldn't observe it then the distant images would not be observable. As Incomplete said - the key is the ratio of the sizes of the observable and actual universes.

Edit: beaten to it...

Webbo
2010-May-10, 05:40 PM
Only if the balloon/universe is 14 billion light years in circumference. But it isn't. We know for certain (from the lack of such effects) that it is at least 10 times bigger than that.

And before you ask, yes, that means the circumference expanded "faster than light" (in exactly the sense we are discussing), and no, that doesn't violate any principle of relativity.

I'm not talking about it's physical size though. Irrespective of how large the balloon is and irrespective of how long it would take light to circumnavigate it, the fact remains the light we observe cannot be older than 14 billion years, and if we could look back that far we should see the moment of the big bang. So everything we could observe on the surface of this baloon is between 0 and 14 billion years old. As we have stated that our own position should be observable at 14 billion years (and that means we observe all the way around) then at the opposite point of the balloon (halfway around) we must observe an object that is 7 billion years old, so beyond this point it should be possible to observe the same galaxy in the opposite direction as well (and younger as it's closer). As we have looked beyond this halfway point there should be a potential to observe these inverted galaxies in opposite directions.

Cougar
2010-May-10, 06:25 PM
If so, then shouldn't we be able to see some evidence of the early milky way in every direction we look?

Though not quite as you picture it, this effect has been looked for. But it's not as simple as you might think:






The most distant objects would be visible in opposite directions, although they would be seen at different ages. Trying to spot the same galaxy in two different places "would be like trying to recognize the same person viewed at age 50 face-on, and at the age of 7 from the top of their head, in a crowd of billions," says Weeks.

So far, their search has drawn a blank. "There is a little room left for the small-Universe idea, but not much," Cornish says.

See this article (http://www.nature.com/news/2003/031006/full/news031006-8.html) in Nature News (from 2003).

DrRocket
2010-May-10, 09:01 PM
I don't have Spivak's book, but these notions are not that obscure. In physics language the question is whether the isometry group has a rotation subgroup. Anyway, you're correct about the lack of isotropy in the torus case being global.


That definition only works in Euclidean space. On a general manifold it is not clear what "rotation" means. In the case of a Riemannian manifold the isotropy group at a point is just the subgroup of the isometry group that fixes that point. That group might be only the identity.

Believe me the notin of isotropy is that obscure. You do not find it in the standard texts, including Kobyashi and Nomizu which usually has everything. You don't find it in differential topology texts either. Nor in Misner, Thorne and Wheeler.

With regard to physics being local I was not at all quoting anyone in the forum. It is a recurring theme in, for instance, Misner, Thorne and Wheeler.

In any case the global notion of isometry that you have for the flat torus, strike me as essentially untestable given the apparent size of the universe. I don't think it represents the spirit of what physicists call isotropy, which to me is local invariance under rotations, and rotations are defined locally.

I would like to see a reference for the recution of the potential manifolds to the cases that you mention. While I have seen that quoted in sources that I do not beleive, I just finished reading a piece by Geroch on the potential topology of spacetime which seems to leave out very few possibilities -- see the 1979 Centenary Survey on General Relativity edited by Hawking and Israel.

Incomplete
2010-May-10, 10:03 PM
I'm not talking about it's physical size though. Irrespective of how large the balloon is and irrespective of how long it would take light to circumnavigate it, the fact remains the light we observe cannot be older than 14 billion years, and if we could look back that far we should see the moment of the big bang. So everything we could observe on the surface of this baloon is between 0 and 14 billion years old.


Yes.



As we have stated that our own position should be observable at 14 billion years (and that means we observe all the way around)

What? No, it doesn't mean that.


then at the opposite point of the balloon (halfway around) we must observe an object that is 7 billion years old

No. If the balloon is bigger than 14 billion years around, we cannot see the opposite point at all.


so beyond this point it should be possible to observe the same galaxy in the opposite direction as well (and younger as it's closer). As we have looked beyond this halfway point there should be a potential to observe these inverted galaxies in opposite directions.

Not if it's bigger than 14 billion years in circumference.

Incomplete
2010-May-10, 10:08 PM
That definition only works in Euclidean space.

Why? Pseudo-Reimannian manifolds still have well-defined isometry groups, and so my definition seems to work just fine.


On a general manifold it is not clear what "rotation" means. In the case of a Riemannian manifold the isotropy group at a point is just the subgroup of the isometry group that fixes that point. That group might be only the identity.

Then it isn't isotropic.


Nor in Misner, Thorne and Wheeler.

Try Landau and Lifschitz.



In any case the global notion of isometry that you have for the flat torus, strike me as essentially untestable given the apparent size of the universe. I don't think it represents the spirit of what physicists call isotropy, which to me is local invariance under rotations, and rotations are defined locally.

Like I said, it's untestable only if the size is significantly larger than the size of the observable universe. In that case, isotropy is nearly restored.

That kind of global breaking of local symmetries arises all the time in physics. It's really pretty standard.


I would like to see a reference for the recution of the potential manifolds to the cases that you mention. While I have seen that quoted in sources that I do not beleive, I just finished reading a piece by Geroch on the potential topology of spacetime which seems to leave out very few possibilities -- see the 1979 Centenary Survey on General Relativity edited by Hawking and Israel.

I'm sure that statement is made in many GR books, but I don't know if that will satisfy you. I recommend L&L though, I recall they carefully classify homogeneous but not isotropic manifolds (that's the Bianchi classification), but in a fair amount of detail.

Cougar
2010-May-10, 10:21 PM
Try Landau and Lifschitz.

Which one?


L.D. Landau, E.M. Lifschitz (1976). Mechanics. Vol. 1 (3rd ed.). Butterworth-Heinemann. ISBN 978-0-750-62896-9.
L.D. Landau, E.M. Lifschitz (1975). The Classical Theory of Fields. Vol. 2 (4th ed.). Butterworth-Heinemann. ISBN 978-0-750-62768-9.
L.D. Landau, E.M. Lifschitz (1977). Quantum Mechanics: Non-Relativistic Theory. Vol. 3 (3rd ed.). Pergamon Press. ISBN 978-0-080-20940-1.
L.D. Landau, E.M. Lifschitz (1980). Statistical Physics, Part 1. Vol. 5 (3rd ed.). Butterworth-Heinemann. ISBN 978-0-750-63372-7.
L.D. Landau, E.M. Lifschitz (1987). Fluid Mechanics. Vol. 6 (1rst ed.). Butterworth-Heinemann. ISBN 978-0-080-33933-7.
L.D. Landau, E.M. Lifschitz (1986). Theory of Elasticity. Vol. 7 (3rd ed.). Butterworth-Heinemann. ISBN 978-0-750-62633-0.
L.D. Landau, E.M. Lifschitz, L.P. Pitaevskii (1984). Electrodynamics of Continuous Media. Vol. 8 (1rst ed.). Butterworth-Heinemann. ISBN 978-0-750-62634-7.

cjameshuff
2010-May-10, 10:23 PM
As we have stated that our own position should be observable at 14 billion years

This was not stated and is not true. What's visible at an age of 14 billion years are objects that are "now" some 46 billion lightyears away across the surface of the balloon (due to the expansion since the emission of that light), which could easily amount to a small circular section of the balloon.

Incomplete
2010-May-11, 12:27 AM
The Classical Theory of Fields. It's the one with GR in it.


Which one?


L.D. Landau, E.M. Lifschitz (1976). Mechanics. Vol. 1 (3rd ed.). Butterworth-Heinemann. ISBN 978-0-750-62896-9.
L.D. Landau, E.M. Lifschitz (1975). The Classical Theory of Fields. Vol. 2 (4th ed.). Butterworth-Heinemann. ISBN 978-0-750-62768-9.
L.D. Landau, E.M. Lifschitz (1977). Quantum Mechanics: Non-Relativistic Theory. Vol. 3 (3rd ed.). Pergamon Press. ISBN 978-0-080-20940-1.
L.D. Landau, E.M. Lifschitz (1980). Statistical Physics, Part 1. Vol. 5 (3rd ed.). Butterworth-Heinemann. ISBN 978-0-750-63372-7.
L.D. Landau, E.M. Lifschitz (1987). Fluid Mechanics. Vol. 6 (1rst ed.). Butterworth-Heinemann. ISBN 978-0-080-33933-7.
L.D. Landau, E.M. Lifschitz (1986). Theory of Elasticity. Vol. 7 (3rd ed.). Butterworth-Heinemann. ISBN 978-0-750-62633-0.
L.D. Landau, E.M. Lifschitz, L.P. Pitaevskii (1984). Electrodynamics of Continuous Media. Vol. 8 (1rst ed.). Butterworth-Heinemann. ISBN 978-0-750-62634-7.

Martin C
2010-May-11, 01:45 AM
1. My ballooniverse has been popped.

2. The universe is not only stranger than I imagined, it may unfortunately also be stranger than I can imagine.

3. "Pseudo-Reimannian manifolds still have well-defined isometry groups", which is a comforting thought, and one that I shall be bringing up at a dinner party in the near future.

Cougar
2010-May-11, 03:08 AM
The Classical Theory of Fields. It's the one with GR in it.
I just ran into Landau in Empire of the Stars by Arthur I. Miller. Child prodigy, PhD at 19, "a formidable scientist whose interests spanned the whole spectrum of theoretical physics...." I'll say.

DrRocket
2010-May-11, 03:49 AM
Why? Pseudo-Reimannian manifolds still have well-defined isometry groups, and so my definition seems to work just fine.

The problem is not isometry groups, the problem is lack of meaning of rotation. You have the same problem on Riemannian manifolds as on pseudo-Riemanian manifolds. As I said earlier the isotropy group at a point is just the group of isometries that fix that point. The problem is that the group may be only the identity and it may have no clear relatioinship to anything one would call a "rotation" in the normal sense of the word.

In R^n with a non-degenerate quadratic form there is not particular problem, but with a general manifold the notion of rotation become at best rather tricky.




Then it isn't isotropic.

That is a purely semantic statement.

The question is whether "independence of direction" can be defined so as to have the usual physical meaningful and therefore useful as an aprior criteria for determining if a Lorentzian manifold is a candidate for spacetime. You can impose artificial definitions and artificial criteria, but you don't have any justification for doing so. Isotropy is based on the local physical notion of independence of direction and any definition that is either different or more restrictive than that is not supportable by the observational evidence.




Try Landau and Lifschitz.

Landau and Lifschitz make the same unsupported argument that one finds elsewhere. It runs as follows. One assumes homogeneity and isotropy {translational and rotational/directional invariance without rigorous definition) which somehow resuts in a one-parameter foliation of spacetime by spacelike hypersurfaces of constant curvature and then somehow conclude that the topology is completely determined by the scalar curvature.

This argument lacks at least 2 important things: 1) justification for some sort of uniqueness of the foliation (and in general such foliations are not at all unique, and some physicists, like Geroch, know this) 2) justification for believing that the topology is determined by the curvature, which again it is not (and some physicists know this too, and Geroch is again an example).

It appears to be just another example of physicists being sloppy with the mathematics.




Like I said, it's untestable only if the size is significantly larger than the size of the observable universe. In that case, isotropy is nearly restored.

Which is my point. The size does appear to be significantly larger than the size of the observavle universe. Isotropy is restored in any local sense of the word, and global arguments restricting the topology are not testable. This ought not be surprising as the whole premist of GR is that the universe is locally Euclidean/Lorentzian or in other words a manifold. If things did not look pretty flat locally the whole theory would fail to match Newtonian gravity in the appropriate limit.


That kind of global breaking of local symmetries arises all the time in physics. It's really pretty standard. Several things that physicists do with mathematics are pretty standard -- and wrong. I have seen statements made in physics books that can be proved wrong rather easily -- examples include evaluation of integrals that don't exist to Fourier series that don't converge.




I'm sure that statement is made in many GR books, but I don't know if that will satisfy you. I recommend L&L though, I recall they carefully classify homogeneous but not isotropic manifolds (that's the Bianchi classification), but in a fair amount of detail.

I'll think about this some. The Bianchi classification is usually taken to mean a classification of 3-dimensional Lie Algebras, but that might shed some light on the matter. One can go from the Lie algebra to the Lie groups of which it is the Lie algebra, and then by looking at quotient groups to manifolds on which the groups act. That amy still be too tough to handle, but maybe it is progress. There are a several difficult steps on that path.

You are correct that the statement is made in several GR books. But it is not proved in any of them that I have seen. Wald, for instance, dismisses flat tori on the basis that the usual realization is as a quotent space -- which strikes me a pure hand waving and not at all valid.

Incomplete
2010-May-11, 04:11 AM
The problem is not isometry groups, the problem is lack of meaning of rotation. You have the same problem on Riemannian manifolds as on pseudo-Riemanian manifolds. As I said earlier the isotropy group at a point is just the group of isometries that fix that point. The problem is that the group may be only the identity and it may have no clear relatioinship to anything one would call a "rotation" in the normal sense of the word.

I'm either not understanding you, or you didn't read what I wrote.

Definition: a 4D pseudo-Riemannian manifold is isotropic if and only if its isometry group has an SO(3) subgroup.

The only problem I see with that definition is that it includes spaces like YxS2, where Y is anything. But I think those actually should be considered isotropic.



The question is whether "independence of direction" can be defined so as to have the usual physical meaningful and therefore useful as an aprior criteria for determining if a Lorentzian manifold is a candidate for spacetime. You can impose artificial definitions and artificial criteria, but you don't have any justification for doing so. Isotropy is based on the local physical notion of independence of direction and any definition that is either different or more restrictive than that is not supportable by the observational evidence.

Find me an example of a manifold for which the above definition does agree with your physical notions and we can discuss it.



You are correct that the statement is made in several GR books. But it is not proved in any of them that I have seen. Wald, for instance, dismisses flat tori on the basis that the usual realization is as a quotent space -- which strikes me a pure hand waving and not at all valid.

Torii are definitely not isotropic. The fact that the isotropy breaking would be hard to see if the cycles are much larger than the Hubble length simply means that the breaking of isotropy is hard to see, not that it's not there. You could take an isotropic region that's larger than the Hubble radius, put anything at all outside that, and the isotropy breaking would be hard to detect.

DrRocket
2010-May-11, 05:07 AM
I'm either not understanding you, or you didn't read what I wrote.

Definition: a 4D pseudo-Riemannian manifold is isotropic if and only if its isometry group has an SO(3) subgroup.



Would that not make RxSO(3) isotropic ? In that case the isotropy group at a point would be only the identity group. So you then have an isotropic space with a trivial isotropy group -- seems a bit odd.

Incomplete
2010-May-11, 01:11 PM
Would that not make RxSO(3) isotropic ? In that case the isotropy group at a point would be only the identity group. So you then have an isotropic space with a trivial isotropy group -- seems a bit odd.

Hmm, I'm not sure. What's the metric on the SO(3) group manifold? What's its full isometry group?

Anyway I think I can see what you're driving at. Perhaps in some manifolds the SO(3) isometries are better thought of as generating "translations" than "rotations"; in other words the space could be homogeneous but not necessarily isotropic. But I'm not sure at the moment whether that is actually a problem (after all, in conventional isotropic spaces one could think of the isotropy group as acting by moving points around on the sphere).

Webbo
2010-May-11, 02:03 PM
Though not quite as you picture it, this effect has been looked for. But it's not as simple as you might think:






The most distant objects would be visible in opposite directions, although they would be seen at different ages. Trying to spot the same galaxy in two different places "would be like trying to recognize the same person viewed at age 50 face-on, and at the age of 7 from the top of their head, in a crowd of billions," says Weeks.

So far, their search has drawn a blank. "There is a little room left for the small-Universe idea, but not much," Cornish says.

See this article (http://www.nature.com/news/2003/031006/full/news031006-8.html) in Nature News (from 2003).

At some point they should be the same distance in both directions. If we propose that if we look back from here in any direction we would see earth then the same galaxies must also exist all the halfway points. Therefore any galaxy or cluster recorded to be circa 7 by old must roughly the same age in the opposite direction. Surely a galaxy or cluster can't change much in a few hundred milliion years.

Webbo
2010-May-11, 02:09 PM
Yes.



What? No, it doesn't mean that.



No. If the balloon is bigger than 14 billion years around, we cannot see the opposite point at all.



Not if it's bigger than 14 billion years in circumference.

I assume you accept that the whole surface of the balloon cannot have galaxies that are older than 14 by. So, irrespective of the size of that baloon (which may now be 50 by in circumference), where on that balloon would you place a 7 billion year old galaxy that we currently observe as being 7 billion years old?

Strange
2010-May-11, 02:12 PM
I'm not talking about it's physical size though. Irrespective of how large the balloon is and irrespective of how long it would take light to circumnavigate it, the fact remains the light we observe cannot be older than 14 billion years, and if we could look back that far we should see the moment of the big bang.

The point you are missing, though, is that if the ballon is bigger than 14 billion light years in circumference then we cannot see all the way round. So we won't be able to see the same galaxy in opposite directions (or the backs of our own heads).

Webbo
2010-May-11, 02:27 PM
The point you are missing, though, is that if the ballon is bigger than 14 billion light years in circumference then we cannot see all the way round. So we won't be able to see the same galaxy in opposite directions (or the backs of our own heads).

Yes, I know that is the situation now, but if the light is able to reach us in one direction from 7 billion light years ago (when the baloon was smaller) why has the light not been able to reach us from the opposite direction also. If a galaxy were only say 5 billion light years distant in one direction it should be 9 billion in the opposite (assuming its older than 9 billion years). If an object were only half a billion distant then yes I could accept it probably wouldn't have a visible opposite. However if it's 7 billion ly distant in one direction it must be the same in the other otherwise something is blocking the light in that direction.

The relevant point is what size the balloon was 7 billion years ago when the light started it's journey, not its size now. Space expands behind the light as well as in front.

Incomplete
2010-May-11, 02:27 PM
I assume you accept that the whole surface of the balloon cannot have galaxies that are older than 14 by. So, irrespective of the size of that baloon (which may now be 50 by in circumference), where on that balloon would you place a 7 billion year old galaxy that we currently observe as being 7 billion years old?

Very near us, obviously.

Is that really what you meant to ask?

Incomplete
2010-May-11, 02:33 PM
Yes, I know that is the situation now, but if the light is able to reach us in one direction from 7 billion light years ago (when the baloon was smaller) why has the light not been able to reach us from the opposite direction also.

It has, of course. Again, what we can see lies in a disk with us at the center. There is no a priori reason for that disk to cover any significant fraction of the balloon's surface.


If a galaxy were only say 5 billion light years distant in one direction it should be 9 billion in the opposite (assuming its older than 9 billion years).

Nonsense. If Calcutta is 2000 km from Mumbai, how far is it in the opposite direction? It depends on the size of the earth, obviously.


If an object were only half a billion distant then yes I could accept it probably wouldn't have a visible opposite. However if it's 7 billion ly distant in one direction it must be the same in the other otherwise something is blocking the light in that direction.

The relevant point is what size the balloon was 7 billion years ago when the light started it's journey, not its size now. Space expands behind the light as well as in front.

Everything you say assumes the balloon must be 14 billion light years around. It's not, because the balloon expanded very fast during the 14 billion years since the big bang.

Strange
2010-May-11, 02:50 PM
what we can see lies in a disk with us at the center. There is no a priori reason for that disk to cover any significant fraction of the balloon's surface.

To put it another way, consider the light from that distant galaxy 7 billion light years away. This will form a disk with a diameter of 14 billion light years, centered on that galaxy. On one side that disk will just be touching us. The other side will only be part way round the ballon (assuming the ballon is many times larger than 14b light years).

Webbo
2010-May-11, 02:50 PM
Very near us, obviously.

Is that really what you meant to ask?

Then where would you place the oldest galaxy or first born?

Incomplete
2010-May-11, 02:53 PM
Then where would you place the oldest galaxy or first born?

There isn't one.

Where is the oldest rock on the earth's surface? Up to local variations, there are old rocks everywhere.

Webbo
2010-May-11, 02:58 PM
It has, of course. Again, what we can see lies in a disk with us at the center. There is no a priori reason for that disk to cover any significant fraction of the balloon's surface.



Nonsense. If Calcutta is 2000 km from Mumbai, how far is it in the opposite direction? It depends on the size of the earth, obviously.



Everything you say assumes the balloon must be 14 billion light years around. It's not, because the balloon expanded very fast during the 14 billion years since the big bang.

No, I'm talking about when the light started its jouney not at the end of it. What possible relevance can there between light that reaches us now, to space that's expanded behind it. It didn't travel accross that expanded space. It passed long before most of it expanded.

Incomplete
2010-May-11, 03:01 PM
No, I'm talking about when the light started its jouney not at the end of it. What possible relevance can there between light that reaches us now, to space that's expanded behind it. It didn't travel accross that expanded space. It passed long before most of it expanded.

No. It passed long after most of the expansion.

Relative to how much it expanded before galaxies formed, to first approximation the universe didn't expand at all since the time they began forming. The same statement is even true for cosmic microwave background light. Only if you want to think about some kind of non-existent light that originated at the big bang and travelled in a straight line to our telescopes today do you really need to think hard about what things were like when the balloon was small... and even then, what you're saying is wrong (because the balloon expanded so fast at first that even light was essentially frozen on its surface).

Webbo
2010-May-11, 03:59 PM
No. It passed long after most of the expansion.

Relative to how much it expanded before galaxies formed, to first approximation the universe didn't expand at all since the time they began forming.

I thought high redshifted objects were caused by the light crossing expanding space. And isn't this used to explain whay we have comoving and proper distances far greater than 14 billion years. How is this so if most expansion happened before galaxies formed?

Incomplete
2010-May-11, 04:39 PM
I thought high redshifted objects were caused by the light crossing expanding space.

The redshift is a result of that, yes.


And isn't this used to explain whay we have comoving and proper distances far greater than 14 billion years.

I'm not sure what you mean by "we have" such distances.


How is this so if most expansion happened before galaxies formed?

Look: suppose, at the time galaxies formed, the balloon was enormous. OK? Then, between that time and now it expanded more and got even more enormous. Do you understand why the most distant galaxy we can see in that case is a very small fraction of the way around the balloon?

cjameshuff
2010-May-11, 05:06 PM
At the age when the universe became transparent and light started propagating significant distances "across the balloon", the balloon was already quite large and inflating rapidly, quite easily increasing in circumference rapidly enough that none of that "first light" could ever reach its point of origin. The oldest visible galaxies are near the rim of a circular area on that balloon, the rim itself is the cosmic background radiation, our view of the universe when it became transparent. That rim is always advancing, with us seeing more and more severely redshifted light from further locations emitted at the time the universe became transparent. The first galaxies to form, whose light is now reaching us, are those that formed somewhat inward of that rim.

The background, that outer wavefront of light emitted from our location from which we are receiving the first light that was able to travel long distances through the universe, is steadily advancing at local c, but there is no reason to think it has or ever will reach the "far side of the balloon" and allow us to see the same object in multiple directions. There may be a galaxy at such a location, but its light emitted at its formation is still advancing toward us (covering another circular segment of the balloon), and the distance in front of it is increasing faster than it is advancing.

Webbo
2010-May-12, 03:15 PM
Look: suppose, at the time galaxies formed, the balloon was enormous. OK? Then, between that time and now it expanded more and got even more enormous. Do you understand why the most distant galaxy we can see in that case is a very small fraction of the way around the balloon?

Yes, I agree that is a possibility however, that would mean that the universe rapidly expanded, slowed to almost a stop and is now expanding again at an accelerating rate. If this is the accepted explanation then fair enough but to me that seems quite absurd.

Incomplete
2010-May-12, 03:20 PM
My last post in this thread.


Yes, I agree that is a possibility however, that would mean that the universe rapidly expanded, slowed to almost a stop and is now expanding again at an accelerating rate. If this is the accepted explanation then fair enough but to me that seems quite absurd.

"Slow almost to a stop" isn't very quantitative, but your characterization is otherwise pretty much OK. The latter two phases are known from direct observation. The early phase of rapid expansion (which is called "inflation") is required to resolve just the type of questions you have been asking (along with various others, most of which have a similar character). While we cannot observe inflation directly, it left a variety of highly characteristic signatures on the large scale structure of the universe. Their existence has been confirmed observationally many times over now.

Absurd? Perhaps. The world is full of surprises.

Strange
2010-May-12, 03:24 PM
but to me that seems quite absurd.

And yet, you have come to that conclusion by the application of logic. Isn't science great?

Webbo
2010-May-12, 03:31 PM
And yet, you have come to that conclusion by the application of logic. Isn't science great?

Maybe so, however, one thing I have learned thoughout life is that one should be cautious of theories that result in absurd conclusions.

Cougar
2010-May-12, 03:47 PM
that would mean that the universe rapidly expanded, slowed to almost a stop and is now expanding again at an accelerating rate. If this is the accepted explanation then fair enough but to me that seems quite absurd.

Just to be sure, the expansion did not slow to almost a stop. It's the rate of expansion that was slowing for the first ~6 billion years. The rate of expansion kept slowing until at one point the rate of expansion was neither slowing nor increasing. But soon thereafter, the rate of expansion slowly began to increase, which is also called acceleration. There was never a time when the universe was not expanding.

Grey
2010-May-12, 05:35 PM
Maybe so, however, one thing I have learned thoughout life is that one should be cautious of theories that result in absurd conclusions.When studying the universe, I find it far more dangerous to decide ahead of time what is absurd and what is likely to be true. The whole point of science is to accept that the universe may not work in a way that at first seems reasonable to us, and that we need to look at the evidence rather than making up our minds based on the way we think it should be. There are a whole host of conclusions from quantum theory, for example, that sound completely ridiculous, but applying that theory to engineering allowed people to build the computer you're typing on.

As Cougar says, the observations suggest that the rate of expansion has varied both up and down, but has not actually slowed to a halt. And the fact that sometimes the rate was increasing and other times it was decreasing fits perfectly well with the theory of how that expansion has taken place.

Webbo
2010-May-12, 05:37 PM
Just to be sure, the expansion did not slow to almost a stop. It's the rate of expansion that was slowing for the first ~6 billion years. The rate of expansion kept slowing until at one point the rate of expansion was neither slowing nor increasing. But soon thereafter, the rate of expansion slowly began to increase, which is also called acceleration. There was never a time when the universe was not expanding.

Not according to Incomplete.


Relative to how much it expanded before galaxies formed, to first approximation the universe didn't expand at all since the time they began forming.

This cleary states that the relative to the expansion prior to formation, the universe hasn't expaned "at all" (hence my use of the word stopped. I was of course talking relatively). No mention of rates. We were discussing actual size. This is necessary to place our viewable region on a relatively small piece of the balloon.

Webbo
2010-May-12, 05:51 PM
When studying the universe, I find it far more dangerous to decide ahead of time what is absurd and what is likely to be true. The whole point of science is to accept that the universe may not work in a way that at first seems reasonable to us, and that we need to look at the evidence rather than making up our minds based on the way we think it should be. There are a whole host of conclusions from quantum theory, for example, that sound completely ridiculous, but applying that theory to engineering allowed people to build the computer you're typing on.
Nothing wrong with discussing something as potentially unreasonalble. It may just need tweaking. Absurdness is an altogether different story.

And you reference quantum theory but if it's applied to engineering it must be a bit more solid than a theory. What exactly are you refering to?



As Cougar says, the observations suggest that the rate of expansion has varied both up and down, but has not actually slowed to a halt. And the fact that sometimes the rate was increasing and other times it was decreasing fits perfectly well with the theory of how that expansion has taken place.
It's the degree of expansion rate required initially compared to now thats seems absurd. What decelerated it to such a degree? Then reaccelerated it again?

Grey
2010-May-12, 07:37 PM
Nothing wrong with discussing something as potentially unreasonalble. It may just need tweaking. Absurdness is an altogether different story.It's clear you've already decided what is and is not possible, based on your preconceived ideas. Unfortunately, the universe isn't necessarily obliged to conform to your notions of what is and is not absurd.


And you reference quantum theory but if it's applied to engineering it must be a bit more solid than a theory. What exactly are you refering to?Nothing in science is more solid than a theory. Theories are all we have. Nonscientists sometimes use "theory" to mean "hypothesis" or even "off the wall guess" or "hunch", but when used in a scientific context, "theory" means a hypothesis that has already been well tested by experiment and observation. "It's only a theory" is something said by people that don't understand how the word theory is used by scientists. Quantum theory is "just a theory", but it's capable of predicting the behavior of particles to an accuracy of about ten parts in a trillion. Pretty much all of modern electronics required quantum mechanics for its development.


It's the degree of expansion rate required initially compared to now thats seems absurd. What decelerated it to such a degree? Then reaccelerated it again?After an initial period of rapid expansion (inflation), the universe settled down to a rate of expansion that was gradually slowing down due to mutual gravitation of the matter within it. However, as the universe expands, the density of matter gets weaker and so that gravitational slowing decreases. There appears to be a negative pressure contribution to the rate of expansion which stays roughly linear (dark energy), so as the gravitational effects of matter decrease, eventually, that negative pressure term comes to dominate. The idea of such a negative pressure term had been introduced by Einstein as a hypothetical possibility, but nobody really thought there would be such a term needed in reality until observations of very distant supernovae, about 12 years ago.

DrRocket
2010-May-12, 11:06 PM
Nothing in science is more solid than a theory. Theories are all we have. Nonscientists sometimes use "theory" to mean "hypothesis" or even "off the wall guess" or "hunch", but when used in a scientific context, "theory" means a hypothesis that has already been well tested by experiment and observation. "It's only a theory" is something said by people that don't understand how the word theory is used by scientists. Quantum theory is "just a theory", but it's capable of predicting the behavior of particles to an accuracy of about ten parts in a trillion. Pretty much all of modern electronics required quantum mechanics for its development.

Absolutely, positively, correct


After an initial period of rapid expansion (inflation), the universe settled down to a rate of expansion that was gradually slowing down due to mutual gravitation of the matter within it. However, as the universe expands, the density of matter gets weaker and so that gravitational slowing decreases. There appears to be a negative pressure contribution to the rate of expansion which stays roughly linear (dark energy), so as the gravitational effects of matter decrease, eventually, that negative pressure term comes to dominate. The idea of such a negative pressure term had been introduced by Einstein as a hypothetical possibility, but nobody really thought there would be such a term needed in reality until observations of very distant supernovae, about 12 years ago.

Clear and correct. Nice.

One might think this will end the discussion. I am not betting on it.

Schneibster
2010-May-13, 02:45 AM
Yes, I agree that is a possibility however, that would mean that the universe rapidly expanded, slowed to almost a stop and is now expanding again at an accelerating rate. If this is the accepted explanation then fair enough but to me that seems quite absurd.Actually, the universe rapidly expanded from the initial fluctuation due to vacuum pressure/zero point energy/Casimir pressure/cosmological constant, then when this rapid expansion, called inflation, passed a critical point the pressure dropped precipitously. The entire universe was then a fireball, which decayed into a giant thermonuclear reaction that ran for a couple hundred thousand years and then passed another critical point and became transparent; this corresponds to your "slowed almost to a stop" phase, but the speed of the initial inflation is so fast that "almost a stop" is almost inconceivably fast. Over the next seven billion years or so, the stuff in the universe expanded along with the expansion of the universe, driven (this is only partly accurate but gives the flavor of the best way to visualize this stage) by the initial energy imparted by the fireball. However, as the universe expanded, the amount of vacuum expanded, and since the vacuum contains Casimir pressure, that means that the amount of vacuum pressure/cosmological constant value was constantly increasing. At seven billion years ago, it surpassed the original expansion caused by the fireball and the universe's rate of expansion started to accelerate. It will do so until every galaxy is so far from every other one that we cannot see them with the best possible instruments.

The long-term forecast is very cold.

CaptainToonces
2010-May-13, 05:48 AM
I think what a lot of people have trouble with is, Why the extra dimension? Why does space itself have to expand, when galaxies are perfectly capable of flying away from a central point in 3 dimensions (like a firework exploding)?

Jens
2010-May-13, 08:15 AM
(You might get confused about the moment t=0 when the balloon had zero size, but recall that it was expanding infinitely rapidly at that time, in such a way that light only moved a finite distance around the surface.)

Do you really mean to say "infinitely fast"? I've never heard that before. Very fast, yes. But infinitely fast means that whatever unit you put in the denominator, the distance is going to be infinite, I think.

Shaula
2010-May-13, 01:50 PM
Why does space itself have to expand, when galaxies are perfectly capable of flying away from a central point in 3 dimensions (like a firework exploding)?
Because that would not match our observations. If everything was expanding radially from a central point then we would not see isotropic expansion in all directions. Unless we just happened to be motionless at the centre of the universe...

Webbo
2010-May-13, 02:13 PM
It's clear you've already decided what is and is not possible, based on your preconceived ideas. Unfortunately, the universe isn't necessarily obliged to conform to your notions of what is and is not absurd.
You're putting words in my mouth. I never said it wasn't possible, however in my opinion, and I'm entiltled to any opinion I like, the answer for my question seems absurd. And that's based on the mechanism proposed not on any ideas I have.



Nothing in science is more solid than a theory. Theories are all we have. Nonscientists sometimes use "theory" to mean "hypothesis" or even "off the wall guess" or "hunch", but when used in a scientific context, "theory" means a hypothesis that has already been well tested by experiment and observation. "It's only a theory" is something said by people that don't understand how the word theory is used by scientists. Quantum theory is "just a theory", but it's capable of predicting the behavior of particles to an accuracy of about ten parts in a trillion. Pretty much all of modern electronics required quantum mechanics for its development.
So, nothing specific then.

By the way, I built a fence in my garden last week and I didn't need any theories to do that either.



After an initial period of rapid expansion (inflation), the universe settled down to a rate of expansion that was gradually slowing down due to mutual gravitation of the matter within it. However, as the universe expands, the density of matter gets weaker and so that gravitational slowing decreases. There appears to be a negative pressure contribution to the rate of expansion which stays roughly linear (dark energy), so as the gravitational effects of matter decrease, eventually, that negative pressure term comes to dominate. The idea of such a negative pressure term had been introduced by Einstein as a hypothetical possibility, but nobody really thought there would be such a term needed in reality until observations of very distant supernovae, about 12 years ago.
How did gravity act on slowing the expansion, when I thought expansion only occurs in areas devoid of gravitation, and why is gravity now unable to slow this expansion? What changed? Why did gravity have the strength to slow rapid expansion and then suddenly, once it had slowed it, lost its influence to continue that effect? This is the part that seems illogical and leads to me viewing it as absurd. Gravity appears to be initially weak, then strong, then weak.

Webbo
2010-May-13, 02:18 PM
Actually, the universe rapidly expanded from the initial fluctuation due to vacuum pressure/zero point energy/Casimir pressure/cosmological constant, then when this rapid expansion, called inflation, passed a critical point the pressure dropped precipitously. The entire universe was then a fireball, which decayed into a giant thermonuclear reaction that ran for a couple hundred thousand years and then passed another critical point and became transparent; this corresponds to your "slowed almost to a stop" phase, but the speed of the initial inflation is so fast that "almost a stop" is almost inconceivably fast. Over the next seven billion years or so, the stuff in the universe expanded along with the expansion of the universe, driven (this is only partly accurate but gives the flavor of the best way to visualize this stage) by the initial energy imparted by the fireball. However, as the universe expanded, the amount of vacuum expanded, and since the vacuum contains Casimir pressure, that means that the amount of vacuum pressure/cosmological constant value was constantly increasing. At seven billion years ago, it surpassed the original expansion caused by the fireball and the universe's rate of expansion started to accelerate. It will do so until every galaxy is so far from every other one that we cannot see them with the best possible instruments.

The long-term forecast is very cold.

Is the initial inflation you mention an inflation of matter or of space?

Webbo
2010-May-13, 02:25 PM
Because that would not match our observations. If everything was expanding radially from a central point then we would not see isotropic expansion in all directions. Unless we just happened to be motionless at the centre of the universe...

Not necessarily. If you could only see a small proportion of the universe then it would still appear you were in the centre. The real stumbling block for this is that it would mean some galaxies would need to be travelling through space at speeds greater than c.

Cougar
2010-May-13, 03:53 PM
So, nothing specific then.

About what?


By the way, I built a fence in my garden last week and I didn't need any theories to do that either.

Oh, I bet you used a little Euclidean geometry and didn't even know it.


How did gravity act on slowing the expansion, when I thought expansion only occurs in areas devoid of gravitation...

Expansion occurs everywhere. It is locally imperceptible because it is totally overwhelmed by local electromagnetism (our bodies are not expanding with the expansion) and local gravity (the galaxy is not expanding with the expansion). There are no areas devoid of gravitation, which has infinite reach.


...why is gravity now unable to slow this expansion? What changed?

The universe got bigger. The distance between (distant) objects is greater. As distance increases by x times, the strength of gravity drops by x2.


Why did gravity have the strength to slow rapid expansion...

Everything was closer together then; If the distance between two objects is smaller by x times, the strength of gravity is greater by x2.


Gravity appears to be initially weak, then strong, then weak.

Well, the gravitational constant stays the same throughout the history of the universe. The ultra brief inflationary period (hypothesized to last for something like 10-32 sec.) is rather a special case. After that, the expansion was still very fast, but with everything so close together, gravity was slowing the expansion. Fortunately, the gravity of all the mass in the universe could not stop and reverse the expansion.

Dark energy, which appears to be a characteristic of space itself, is very, very weak. But its effect is additive; so when you're detecting light that has been traveling through billions of lightyears of space, the effect becomes perceptible (if you're clever enough to figure out a way to perceive it).

tommac
2010-May-13, 05:25 PM
There are no areas devoid of gravitation, which has infinite reach.

Is that true? In an expanding universe can you have areas of the universe OR slightly outside of the universe where gravity has not yet had the time to reach? Gravity only propogates at the speed of light. So assuming that the age of the universe is finite there is the possibility that parts of a universe ( non homogeneous ) may not have reached it yet???

Webbo
2010-May-13, 05:48 PM
About what?
Exactly what from quantum theory was required to build what in my PC that I’m typing on.



Oh, I bet you used a little Euclidean geometry and didn't even know it.
I didn’t need any of the theories to allow me to do it though did I. Trial and error worked fine.



Expansion occurs everywhere. It is locally imperceptible because it is totally overwhelmed by local electromagnetism (our bodies are not expanding with the expansion) and local gravity (the galaxy is not expanding with the expansion). There are no areas devoid of gravitation, which has infinite reach.
By this definition any 2 galaxies must be gravitationally influencing each other so how can expansion occur between them?



The universe got bigger. The distance between (distant) objects is greater. As distance increases by x times, the strength of gravity drops by x2.
Yes, but this was true when the universe was expanding earlier at a much higher rate yet somehow, as it’s influenced decreased, it suddenly gained strength for a while to slow expansion and then lost that strength again. Please explain how/why rather than just describing the events.



Everything was closer together then; If the distance between two objects is smaller by x times, the strength of gravity is greater by x2.
Yes it was. I have no problem with it being stronger when close and then weaker when distant but why then, when it was closer, did it have a weaker effect (rapid early expansion)? I am looking for the mechanism not another way to describe the effect.



Well, the gravitational constant stays the same throughout the history of the universe. The ultra brief inflationary period (hypothesized to last for something like 10-32 sec.) is rather a special case. After that, the expansion was still very fast, but with everything so close together, gravity was slowing the expansion. Fortunately, the gravity of all the mass in the universe could not stop and reverse the expansion.
So it’s a special case. Then maybe it’s this special case that’s absurd. You also state after the initial expansion gravity was slowing the expansion but isn’t the expansion accelerating not slowing? Which is it?

mugaliens
2010-May-13, 07:10 PM
Not necessarily. If you could only see a small proportion of the universe then it would still appear you were in the centre. The real stumbling block for this is that it would mean some galaxies would need to be travelling through space at speeds greater than c.

Not relative to their local space. It's not that galaxies are hurtling through space faster than c - that's impossible. Rather, space itself is expanding. Over great distances, this results in relative velocities beyond c. Thus, it appears we're in the exact center of the universe, but in reality, we're merely in the exact center of the observable universe, that is, the portion of it within the comoving distance. More (http://en.wikipedia.org/wiki/Friedmann-Lema%C3%AEtre-Robertson-Walker).

Cougar
2010-May-13, 07:56 PM
By this definition any 2 galaxies must be gravitationally influencing each other so how can expansion occur between them?

When the effect of expansion is greater than the effect of gravity between them.


So itís a special case. Then maybe itís this special case thatís absurd.

As previously pointed out, perceived absurdity does not falsify an idea. From 1930 to roughly 1960, most astrophysicists thought the idea of a black hole was absurd.


You also state after the initial expansion gravity was slowing the expansion but isnít the expansion accelerating not slowing? Which is it?

Ha ha. It's both. It was slowing then. Now it's accelerating.

There are books on this stuff that are certain to help your and Tommac's understanding. A few suggestions:






The Runaway Universe, the Race to Find the Future of the Cosmos [2000] -- Donald Goldsmith Big Bang, the origin of the universe [2004] -- by Simon Singh

Alpha and Omega, The search for the beginning and end of the universe [2004] -- Charles Seife

Black Holes and Time Warps, Einstein's Outrageous Legacy [1994] -- Kip Thorne

Chasing Hubble's Shadows, The Search for Galaxies at the Edge of Time [2006] -- Jeff Kanipe

Endless Universe, Beyond the Big Bang [2007] -- Paul Steinhardt and Neil Turok

Extreme Stars, At the Edge of Creation [2001] -- by James Kaler

Origins, Fourteen billion years of cosmic evolution [2004] -- Neil DeGrasse Tyson and Donald Goldsmith




and highly recommended:


The Lightness of Being, Mass, ether, and the unification of forces [2008] -- by Frank Wilczek

Grey
2010-May-13, 08:06 PM
You're putting words in my mouth. I never said it wasn't possible, however in my opinion, and I'm entiltled to any opinion I like, the answer for my question seems absurd. And that's based on the mechanism proposed not on any ideas I have.Sure, you're entitled to any opinion you like. But don't expect other people to take that opinion seriously, unless you can give better reasons than "well, that sounds absurd to me". Much of modern physics sounds absurd to those unfamiliar with it.


So, nothing specific then.Well, I didn't want to list every element of modern electronics. How about semiconductors, including diodes and transistors?


By the way, I built a fence in my garden last week and I didn't need any theories to do that either.Sure, no problem for a fence. Build a suspension bridge, and you'll need to rely on principles developed through theory. The engineers may not understand how those principles were developed, but be sure that without the theoretical underpinnings, those engineering requirements could not have been developed.


How did gravity act on slowing the expansion, when I thought expansion only occurs in areas devoid of gravitation...I don't know where you got that idea. All matter in the universe attracts all other matter, and the net result of that interaction (not considering any other effects) is to slow down the expansion. There aren't any regions devoid of gravitation. There certainly are regions (like galaxies) where the local gravitation is strong enough to overcome the global expansion, but that doesn't mean the other areas are devoid of gravity.


...and why is gravity now unable to slow this expansion? What changed?Read the paragraph again. The universe is expanding, the density of matter is getting lower. Hence, the slowing effect of gravity is getting weaker. Before the discoveries of the High-Z supernova team, the big question was, is the density of matter (compared to the rate of expansion) high enough that the universe will eventually stop expanding and start to collapse, or is it low enough that the universe will just continue expanding (though at an ever slower rate).


Why did gravity have the strength to slow rapid expansion and then suddenly, once it had slowed it, lost its influence to continue that effect? This is the part that seems illogical and leads to me viewing it as absurd. Gravity appears to be initially weak, then strong, then weak.Gravity starts out fairly strong (when everything is very close), but then gets weaker as things move apart. However, gravity isn't the only thing affecting the expansion. Dark energy tends to accelerate the expansion, but the size of that effect doesn't vary as the universe expands. So at an earlier era, gravity is the predominant effect and the expansion slows. Later, gravity's effect has weakened, but dark energy remains constant, and so it's eventually a larger effect than gravity, and the expansion accelerates. There was a similar effect during the very early inflationary period. Note that we don't know what dark energy is, or why there should be such a thing in the universe. I'll grant that it's strange. However, cosmological models that include it do a very good job of matching the observations, while models without it do not.

Shaula
2010-May-13, 09:36 PM
Not necessarily. If you could only see a small proportion of the universe then it would still appear you were in the centre. The real stumbling block for this is that it would mean some galaxies would need to be travelling through space at speeds greater than c.
I disagree. If you can only see a tiny proportion of the expanding universe then you would see a preferential direction to expansion. In essence any small enough portion of a radially expanding group of galaxies would look roughly like a linear flow of galaxies. Thus when you measured the angular distribution of the recessional velocities you'd see an anisotropy that we do not observe. Remember that redshift gives us a line of sight velocity - not a measure of the absolute speed of the target.

Jeff Root
2010-May-13, 10:37 PM
Is there actually any observational evidence that the expansion was
slowing prior to the currently-observed acceleration? We can't see
any supernovae far enough away to make any measurements of the
expansion rate that far back, can we?

-- Jeff, in Minneapolis

Infinitenight2093
2010-May-14, 04:28 AM
Its just a simple question that i don't fully understand, can anyone help me.

1. If the observable universe started with a big bang, and the matter, stars and galaxy's are all moving away from the bang, why do we seem to be in the centre?

2. Why do we see 13 billion year old galaxy's in all directions in the sky?

3. If it started with a bang, wouldn't there be a big empty space in the middle somewhere and our MilkyWay would be roughly in a galaxy cluster somewhere on the outside edge? With one direction in the sky looking emptier than all the other directions.

Note; question 1, 2, and 3 are really all the same question.

Thanks for the help in advance,
John.

As far as seeing 13 billion light years of galaxies in any direction, this is because that is the cutoff point for light. Any light coming from farther galaxies is next to nonexistent for current technology. And as far as us seeing ourselves in the middle of the universe, I believe that is because the universe is actually infinite and much older than 13.7 billion years (living in an infinite vacuum would place anything at the direct center because there will always be infinity on any side)

Webbo
2010-May-14, 03:46 PM
Ha ha. It's both. It was slowing then. Now it's accelerating.
So now you agree it was fast, then slow, then fast again. How is this possible?

Webbo
2010-May-14, 04:15 PM
Sure, you're entitled to any opinion you like. But don't expect other people to take that opinion seriously, unless you can give better reasons than "well, that sounds absurd to me". Much of modern physics sounds absurd to those unfamiliar with it.
I’m familiar with quite a lot. While I disagree with some things, as I’m sure we all do, I find very little that is actually absurd.


Well, I didn't want to list every element of modern electronics. How about semiconductors, including diodes and transistors?
Do/did all those require a quantum theory do develop & build?


Sure, no problem for a fence. Build a suspension bridge, and you'll need to rely on principles developed through theory. The engineers may not understand how those principles were developed, but be sure that without the theoretical underpinnings, those engineering requirements could not have been developed.
I’m not saying that theories are useless, only that they are not the utmost requirement of engineering. Trial and error and just pure experience based on practice can work well also.



I don't know where you got that idea. All matter in the universe attracts all other matter, and the net result of that interaction (not considering any other effects) is to slow down the expansion. There aren't any regions devoid of gravitation. There certainly are regions (like galaxies) where the local gravitation is strong enough to overcome the global expansion, but that doesn't mean the other areas are devoid of gravity.
I guess I could accept that gravity is slightly reducing the increasing rate of inflation, but I still don’t follow how it went from fast expansion, with minor influence from gravity, to slower expansion, with greater influence from gravity, and then increasing expansion again with minor influence from gravity. What’s the explanation for this?



Read the paragraph again. The universe is expanding, the density of matter is getting lower. Hence, the slowing effect of gravity is getting weaker. Before the discoveries of the High-Z supernova team, the big question was, is the density of matter (compared to the rate of expansion) high enough that the universe will eventually stop expanding and start to collapse, or is it low enough that the universe will just continue expanding (though at an ever slower rate).
My understanding was that it’s expanding at an ever increasing rate.



Gravity starts out fairly strong (when everything is very close), but then gets weaker as things move apart. However, gravity isn't the only thing affecting the expansion. Dark energy tends to accelerate the expansion, but the size of that effect doesn't vary as the universe expands. So at an earlier era, gravity is the predominant effect and the expansion slows. Later, gravity's effect has weakened, but dark energy remains constant, and so it's eventually a larger effect than gravity, and the expansion accelerates. There was a similar effect during the very early inflationary period. Note that we don't know what dark energy is, or why there should be such a thing in the universe. I'll grant that it's strange. However, cosmological models that include it do a very good job of matching the observations, while models without it do not.
Agreed but this statement doesn’t account for the sudden increase in gravity’s influence (and slowing of expansion) between initial expansion and expansion now.

Webbo
2010-May-14, 04:22 PM
I disagree. If you can only see a tiny proportion of the expanding universe then you would see a preferential direction to expansion.

If so, could this perceived as some sort of great attractor?

Strange
2010-May-14, 04:25 PM
Do/did all those require a quantum theory do develop & build?

Yes. The understanding of conduction in metals depends on understanding the (quantum mechanical) behavior of "free" electrons in the atoms of the metal. Similarly, understanding the behavior of semiconductors, and the effects of different doping atoms, is based on quantum mechanics. There are devices which depend even more explicitly on quntaum effects, such as tunneling in Josephson junctions.

And as the semiconductor manufacturing process is a photochemical process, quantum theory comes in there as well. At one level, understanding effects diffraction effects in masks of increasingly small dimension. And again when it comes to the chemicals used. If you study chemcistry, you have to udnerstand bonding between atoms, which is based on the quantum mechanical theories of electron orbitals.

And on, and on...

Having worked on the design of GPS chips, we also had to take relativity into account...

So, despite all these things being "just theories" they are fundamental to mordern electronics, chemistry and many other technologies.

Webbo
2010-May-14, 04:56 PM
Yes. The understanding of conduction in metals depends on understanding the (quantum mechanical) behavior of "free" electrons in the atoms of the metal. Similarly, understanding the behavior of semiconductors, and the effects of different doping atoms, is based on quantum mechanics. There are devices which depend even more explicitly on quntaum effects, such as tunneling in Josephson junctions.

And as the semiconductor manufacturing process is a photochemical process, quantum theory comes in there as well. At one level, understanding effects diffraction effects in masks of increasingly small dimension. And again when it comes to the chemicals used. If you study chemcistry, you have to udnerstand bonding between atoms, which is based on the quantum mechanical theories of electron orbitals.

And on, and on...

Having worked on the design of GPS chips, we also had to take relativity into account...

So, despite all these things being "just theories" they are fundamental to mordern electronics, chemistry and many other technologies.

Electronics and chemistry and predate quantum theory.

Strange
2010-May-14, 06:18 PM
Electronics and chemistry and predate quantum theory.

Yes, but we understand them both better now, and can do things that weren't possible before because of that knowlegde.

Cougar
2010-May-14, 10:39 PM
Is there actually any observational evidence that the expansion was
slowing prior to the currently-observed acceleration? We can't see
any supernovae far enough away to make any measurements of the
expansion rate that far back, can we?

Yes, we can: TYPE Ia SUPERNOVA DISCOVERIES AT Z > 1 FROM THE HUBBLE SPACE TELESCOPE: EVIDENCE FOR PAST DECELERATION AND CONSTRAINTS ON DARK ENERGY EVOLUTION [pdf] (http://www.stsci.edu/~ariess/documents/2004_Type%20Ia%20Supernova%20Discov...%20on%20Dark %20Energy%20Evolution_web.pdf) -- Adam G. Riess, et al.

Cougar
2010-May-14, 10:49 PM
As far as seeing 13 billion light years of galaxies in any direction, this is because that is the cutoff point for light. Any light coming from farther galaxies is next to nonexistent for current technology.

Er, no, there is no "cutoff point for light"... unless it runs into something.


...I believe that is because the universe is actually infinite and much older than 13.7 billion years...

Well, your belief is at odds with multiple, independent observations, a situation that normally suggests such a belief should be discarded.

Shaula
2010-May-14, 10:52 PM
If so, could this perceived as some sort of great attractor?
Not the kind that there have been stories about. That is a polar attractor - velocities seem to be biased to converge towards it in one part of the sky (or so it said in the last thing I read about this - which was some time ago). This would look different - like there was an infinitely large sheet attractor dragging us along. I think. It would not look like a classic masscon attractor. Now if they decide that there is a universal 'flow' towards a preferred direction...

Anyway, my point was that the two were distinguishable and the evidence favours the expansion of space, not the expansion into space.

Cougar
2010-May-15, 12:04 AM
It was slowing then. Now it's accelerating.
So now you agree it was fast, then slow, then fast again. How is this possible?

I believe it has been explained in more detail previously in this thread. To summarize:

Your initial "fast" is not in the same league as the subsequent "slowing" then "accelerating." Inflation is an extremely brief burst of colossal expansion near the "beginning." The universe is very small at the time, but accumulating evidence keeps supporting the idea that it doubled in size something like 50 times in some ridiculously small fraction of a second. Then it apparently came out of this frenzy, but kept expanding at a pretty good clip. Here's where the expansion is slowing. The proportion of "mass" to "space" was much higher back then, thus gravity dominated the DARK ENERGY that pervades space (but doesn't seem to "thin out" as space expands).

Dark energy, with its mysterious and barely perceptible "expansion effect" on space, is just lying in wait for the universe to expand enough so there's enough space for its effect to begin to dominate over the weakening gravitational attraction between the masses. Thus begins the acceleration. This tide turned roughly 4-5 billion years ago.

That paper I linked to provides pretty compelling support for this scenario.

Cougar
2010-May-15, 12:15 AM
I'm familiar with quite a lot.

Yes, but are you familiar with enough to realize that you are unfamiliar with quite a lot? :)

rigney
2010-May-15, 01:13 AM
Perhaps a simpler way of viewing our universe is to picture a stone being tossed into a "smooth, endless" and wind free pond. Immediately, concentrically shaped ripples will begin forming in tandem. As the first ripple moves away from the center, newer ones continue forming until the weight and size of the stone is displaced by the water. After displacement, the ripples and smoothed water behind, will continue expanding outwardly and proportionately forever, if, in fact the pond in endless.

Our universe is much like the pond, other than it being "spherical" in design and expanding out into an unobstructed, endless and pristine continuum. Somewhere behind, lies a vast and empty void moving outwardly but spherically, much as the smoothed water behind the last and innermost ripple on the pond. Time has tempered that part of our universe, but the stone at the center continues to grow, and someday will become the next "Big Bang".

Our world is not a balloon in any sense, but more of an airy, breathing cocoon. This galaxy is not on the outer shell of anything, but simply a part of the many billions of galaxies making up the ripples of this universe. And answering the question as to where we fit into the overall scheme of things would come under the heading of "Genius"?

pzkpfw
2010-May-15, 01:46 AM
rigney, the Q&A forum is not the place to make ones' own claims as to how things work. This forum is for (on topic) questions to be asked, and to get asnwers based on current scientific knowledge. If you wish to make claims of this sort, please make a post in the ATM forum, and be prepared to back them up.

Grashtel
2010-May-15, 03:44 AM
As far as seeing 13 billion light years of galaxies in any direction, this is because that is the cutoff point for light. Any light coming from farther galaxies is next to nonexistent for current technology. And as far as us seeing ourselves in the middle of the universe, I believe that is because the universe is actually infinite and much older than 13.7 billion years (living in an infinite vacuum would place anything at the direct center because there will always be infinity on any side)
While you are free to believe whatever you want the available evidence points to the Big Bang theory being the closest to being a correct interpretation of the origins and nature of the universe and is therefore what mainstream science uses. If you wish to dispute this its the sort of thing that the "Against The Mainstream" section of this forum is for, brining up non-mainstream ideas in other parts of the forum will get you in trouble and ultimately if you are sufficiently persistent in doing so banned.

rigney
2010-May-15, 02:52 PM
My apologies to the moderator. I am new at this and will likely continue making mistakes for a while, ubless you toss me out. But if you would bear with me for a bit, perhaps I can get it together. Thank You: Rigney

Schneibster
2010-May-16, 11:30 AM
Is the initial inflation you mention an inflation of matter or of space?Neither. It is a vacuum fluctuation that by pure chance exceeds the critical density to form an inflaton. Once the inflaton exists, it inflates until it undergoes vacuum decay and fills the entire universe, which has stopped inflating, with the initial fireball of the big bang. The fireball and the remaining vacuum pressure drive the expansion of the universe for the next seven billion years, after which the increase in the amount of vacuum caused by the expansion of the universe causes there to be more vacuum pressure than there is expansion from the bang, and the eventually exponential increase in the rate of expansion begins, continuing until the present day and according to current projections eventually, in a trillion years or so, resulting in a universe in which we can only see our own galaxy and perhaps the members of our local group; M31 in Andromeda, M33 in Triangulum, the Magellanic Clouds, and so forth.

It's very important to understand that prior to inflation, space as we are used to thinking of it does not exist. The universe doesn't have space yet. After inflation, it has space, and energy as well; it's filled with a gas of particles at an astronomically high temperature. That's how the Big Bang starts. The energy comes from the vacuum decay of the inflaton.

Jason Thompson
2010-May-17, 12:16 PM
Electronics and chemistry and predate quantum theory.

Semiconductor technology, microprocessors, GPS, x-ray diffraction molecular structural determination and in vitro peptide synthesis do not.

John37309
2010-May-20, 03:36 AM
So..... I went away for a while from this thread, i needed time to consider the many really good idea's that has been suggested in this thread. Some really good idea's have been discussed here.

I still find the balloon analogy confusing, but i accept that other people are happy with this explanation.

But really, i asked the original question "Why do we seem to be in the middle?".

This is the conclusion i have come to;
We are not seeing the whole picture. Our deepest image of the universe to date has been the Hubble ultra deep field IR image (HUDF-IR) - http://hubblesite.org/newscenter/archive/releases/2009/31/image/a/. Its the longest exposure we have. In the HUDF-IR image, the very oldest Galaxy's are still very blurred and very tiny and very red-shifted. When JWST is launched in 2014, if it takes an image of the same region of the sky, and we see more stuff appearing in the image that is not in the Hubble image, then we will know that we are still not seeing the very edge, or the farthest possible back in time. We will just be seeing an image that is just a tad clearer and deeper, with more stuff. Then who is to say that when we build a massive 100 meter telescope in space 50 years from now, that we won't see more new stuff appear in the exact same part of the sky.

Also, the HUDF-IR image is just one part of the sky. Even the best all-sky surveys we have today are good, but lack the clarity needed to say that we can see complete uniformity of matter in every direction. Its even hard to say if we had a HUDF-IR image for the whole sky if this would make things any clearer.

So this brings me to the conclusion that, for the time being with today's information, we are not seeing everything from the big bang. Instead it is my personal view that the big bang could well have been much larger than what we see. Or it could also mean that the big bang was just a local bang in the area we call the "observable universe". Either way, we are not seeing anywhere near the total amount of stuff that is further out or further back in time. Our biggest obstacle is getting massive telescopes into earth orbit.

So in my mind, this is why i think we seem to be in the middle. We are only seeing our part, the bit that is observable today with todays technology. Its our limiting technology and the expanding,accelerating universe that is putting us in the middle. There must be a whole pile of stuff so far red-shifted that its gone out of view cos of acceleration.

http://www.wildwildweather.com/forecastblog/wp-content/uploads/2009/03/big_bang_wmap.jpg

John.

Geo Kaplan
2010-May-20, 04:22 AM
So in my mind, this is why i think we seem to be in the middle. We are only seeing our part, the bit that is observable today with todays technology. Its our limiting technology and the expanding,accelerating universe that is putting us in the middle.

Your first sentence is presuming something that is contrary to the mainstream view. If you've really read the replies folks have offered here, we've been trying to tell you that there's no reason to believe that our corner of space is special in any way. The chance that we are in the middle (whatever that might mean) is infinitesimally small. It is only those who draw the wrong conclusion from redshift data that might believe erroneously that we are in "the middle".

The balloon analogies were offered to show how recession of raisins/ants/dots from each other does not imply that any individual raisin is at the center. Yet all raisins see the same expansion in every direction they look.

So, there is no reason to believe that we are in the middle, and therefore the question you asked originally -- "why are we in the middle?" -- presumes something that is not believed to be true in the first place.

Jens
2010-May-20, 04:36 AM
Er, no, there is no "cutoff point for light"... unless it runs into something.


Infinitenight2093 was not expressing it well, but there is in a sense a cutoff point. It's not a real cutoff point, but a point beyond which the light becomes mixed together as a wall that is not distinguishable with any technology, called the surface of last scattering. And that would be true with a non-expanding as well as an expanding universe. I think that's probably what Infinitenight2093 was referring to.

DrRocket
2010-May-20, 05:16 AM
So in my mind, this is why i think we seem to be in the middle. We are only seeing our part, the bit that is observable today with todays technology. Its our limiting technology and the expanding,accelerating universe that is putting us in the middle. There must be a whole pile of stuff so far red-shifted that its gone out of view cos of acceleration.
John.

No. The point is that the universe appears to be homogeneous and isotropic and all that other stuff is in the middle too. EVERYTHING is in the middle. Or, eqivalently, there is no middle.

John37309
2010-May-20, 07:24 AM
Found this really great video.

Millennium Simulation: "The Largest Model of Our Universe"; http://www.youtube.com/watch?v=W35SYkfdGtw

Its simple, there are no balloons in the video, its 3 dimensional and its an easy way to explain universal expansion to young kids, like my little boy who's 5. This is how i see the universe when we look at it from the outside.

John.

Hornblower
2010-May-20, 07:47 AM
Found this really great video.

Millennium Simulation: "The Largest Model of Our Universe"; http://www.youtube.com/watch?v=W35SYkfdGtw

Its simple, there are no balloons in the video, its 3 dimensional and its an easy way to explain universal expansion to young kids, like my little boy who's 5. This is how i see the universe when we look at it from the outside.

John.

I cannot see that video addressing expansion one way or the other, and I do not see anything I would call a view from the outside. It gives the appearance of wandering through an expanse that includes clusters of galaxies, filaments and sheets thereof, and voids. The whole thing just goes on and on, with no identifiable feature that could be considered the center.

Strange
2010-May-20, 08:35 AM
But really, i asked the original question "Why do we seem to be in the middle?".

This is the conclusion i have come to;
We are not seeing the whole picture.

Perhaps there are two different things here: why do we appear to be in the middle of the visible universe; and why do we appear to be in the middle of the expanding universe.

We would appear to be in the middle of the universe even if it weren't expanding. Simply because the universe is isotropic and it looks pretty much the same in all directions. Everywhere we looked we would see galaxies which get older the farther away they are - simply because of the delay caused by the speed of light. But, the same would be true for any observer on any galxy; they would see themselves surrounded by galaxies getting older the further away they were. So everyone would think they were in the middle.

As well as that, because the universe is uniformly expanding, we see the same increasing red-shift / speed of expansion in every direction. But, as has been pointed out, the same would be true for everyone else. So everyone would think they were in the middle.


So this brings me to the conclusion that, for the time being with today's information, we are not seeing everything from the big bang. Instead it is my personal view that the big bang could well have been much larger than what we see.

Clearly we are not seeing everything from the big bang. We are not even seeing everything in the visible universe. It is generally assumed that the visible universe is a tiny fraction of the whole universe. But that is irrelevant: however far out we are able to see, the universe will look the same in all directions. We will still "appear" to be in the middle. I don't understand what you think will be seen by a bigger telescope that will change that.


There must be a whole pile of stuff so far red-shifted that its gone out of view cos of acceleration.

True. But how is that relevant?

Strange
2010-May-20, 08:38 AM
Found this really great video.

Millennium Simulation: "The Largest Model of Our Universe"; http://www.youtube.com/watch?v=W35SYkfdGtw

Its simple, there are no balloons in the video, its 3 dimensional and its an easy way to explain universal expansion to young kids, like my little boy who's 5. This is how i see the universe when we look at it from the outside.

John.

This was just, as far as I could tell, an (overlong and poorly explained) attempt to show that the universe is big, but really big. It was a static "snapshot" of the universe as it is now. I fail to see the connection with the expansion of the universe, or appearing to be in the middle. Or even looking at it from "outside".

astromark
2010-May-20, 08:41 AM
The failure to understand that there is no outside to view from is secondary to the point that,.
That U tube video does not make any forward progress in this discussion. Its pretty. and might be a good representation of what you might see if you could. Its only a good representation of what you might expect to see. Its not real.
The adult human eye has a aperture of about 4.5mm. You need a massive telescope and about 100 hours of observing time to build enough light image to see images like those... yes it helps the understanding of the shear size of it. Remembering that Universe does mean all of everything. There can be no edge. . . Now there's a point. Where you realize that you have just said a stupid thing... :o
There 'could' be an edge, or end. It may however be beyond any ability to get to or see it. If that statement can be true then yes there could equally be a center... Oh dear me...:(...Yes no maybe... But we could not be so self important to suggest we are at that center point a...?

cosmocrazy
2010-May-20, 09:06 AM
I do most times enjoy reading your posts astromark although on most occasions I must admit after reading them over a few times I still fail to see your point! lol. but on this occasion I think I get the idea of what you are trying to say. ;)

DrRocket
2010-May-20, 03:14 PM
Found this really great video.

Millennium Simulation: "The Largest Model of Our Universe"; http://www.youtube.com/watch?v=W35SYkfdGtw

Its simple, there are no balloons in the video, its 3 dimensional and its an easy way to explain universal expansion to young kids, like my little boy who's 5. This is how i see the universe when we look at it from the outside.

John.

I'm glad that video did it for you. I have no idea what that model has tod do with expansion, and I think I understand what expansion means fairly well.

It does seem to give a pretty good, though highly magnified, internal picture of the structure of an air filter.

DrRocket
2010-May-20, 03:28 PM
Perhaps there are two different things here: why do we appear to be in the middle of the visible universe; and why do we appear to be in the middle of the expanding universe.

We would appear to be in the middle of the universe even if it weren't expanding. Simply because the universe is isotropic and it looks pretty much the same in all directions. Everywhere we looked we would see galaxies which get older the farther away they are - simply because of the delay caused by the speed of light.

Yes, this is the result of local isotropy. Isotropy is invariance under rotation -- so things look the same in all directions.



But, the same would be true for any observer on any galxy; they would see themselves surrounded by galaxies getting older the further away they were. So everyone would think they were in the middle.

This requires the additional assumption of homogeneity. Homogeneity is invariance under position (usually stated as invariance under translation).

Put together homogeneity and isotropy and you have what is called the cosmological principle, or Copernican principle. Things look the same in all directions from all locations.


As well as that, because the universe is uniformly expanding, we see the same increasing red-shift / speed of expansion in every direction. But, as has been pointed out, the same would be true for everyone else. So everyone would think they were in the middle.

Precisely. The result of homogeneity and isotropy. Things look the same everywhere in all directions, at least on the largest scales, so far as we know. But homogeneity and isotropy are assumptions.

Andrew D
2010-May-23, 12:48 AM
I know not everyone here likes Susskind, and I'm not endorsing any of his 'ideals', but his video lecture series "Cosmology" does a really good job explaining expansion. You can find the series in its entirety by searching "Stanford Cosmology" on YouTube. He basically uses a handful of lectures to derive the FLRW metric as simply as possible. Even if you don't understand the math (it assumes some knowledge of calculus, but you should be fine if you just look up "derivative" in the dictionary), he uses helpful visuals, and is not too difficult to follow.

rigney
2010-May-23, 03:13 AM
What if our universe is nothing more than balloons inside balloons, inside balloons, inside balloons, etc? "And each level, a mere ripple on the spherical pond of creation?

Jeff Root
2010-May-23, 09:15 AM
rigney,

Would you care to describe your understanding of the balloon
analogy for the cosmic expansion? That is, explain it to us as
if we didn't know anything about it? I think doing so might be
helpful both to you and the rest of us.

-- Jeff, in Minneapolis

astromark
2010-May-23, 09:34 AM
The only reason a balloon was ever mentioned here was to help those whom need a little help visualizing a ever expanding universe where not the velocity of galaxies but the expansion of space is attempting to be explained. Fortunately there just is not the latex available to build your modal...
and is why I would try and encourage the cooking bread as a better similarly. The fact that a 3 dimensional concept can be visualized better than a 2 dimensional image. Balloons within balloons right on down to the turtles...

Shaula
2010-May-23, 10:38 AM
The only reason a balloon was ever mentioned here was to help those whom need a little help visualizing a ever expanding universe where not the velocity of galaxies but the expansion of space is attempting to be explained. Fortunately there just is not the latex available to build your modal...
and is why I would try and encourage the cooking bread as a better similarly. The fact that a 3 dimensional concept can be visualized better than a 2 dimensional image. Balloons within balloons right on down to the turtles...
Oddly enough the reason you give is why I prefer the balloon analogy. Although the vectors of expansion are better visualised in the 3D example the actual model for it is not. When you say infinitely big people, in my experience, just think 'very very big' and don't think of the ramifications of that. So what you get is a comforting model of a 3D loaf/universe expanding into empty space. It is better to try to get them to think in 2D so that they can see that this is not what is meant, that there is no outside for it to expand into. Basically you are replacing an infinite universe expanding with an infinite bit of raisin bread expanding. You are not explaining anything about how the expansion is believed to work, just how galaxies move.

astromark
2010-May-23, 07:59 PM
Its a simple mater of perception... I would not tell you what you should believe. Just as I can not see what you see. ( The expanding surface of the balloon does work. ) The image in my mind that is a similarly. It works for me. Its not compulsory ...

Quote;" Basically you are replacing an infinite universe expanding with an infinite bit of raisin bread expanding. You are not explaining anything about how the expansion is believed to work, just how galaxies move.

I could argue that as your surface of the balloon is only two dimensional, Its not real enough.

I was never attempting to explain how it works. I do not know. Its called Dark Energy because we do not know any better. All we can hope for is a understanding of what we know. We know there is no before, We know there is no outside. We know that the Universe is expanding just like the action of expanding raisin bread...
Your preference for balloons, thats fine with me. I will not pop your balloon as you will not rise to my bread... :o mark

Shaula
2010-May-23, 09:24 PM
No worries, not trying to convert you. Just saying that the analogy used can make a difference as people often assume the model is the reality. So a 2D analogue of a 3D effect can force the mind to come closer to what is being proposed by the mainstream models than the 3D version, for the reasons I stated. When I said how it worked I didn't mean exactly how it worked - just that the balloon neatly captures the idea of a close space expanding and highlights a way that it can be expanding without being expanding into anything, which is one of the classic misconceptions we all make at first!

Whatever works for the person, though.

Jeff Root
2010-May-23, 11:00 PM
I wonder if my use of a balloon in my talk about the Big Bang in my
high school speech class mislead more than it informed. And if so,
I wonder if it made any difference to anyone or anything.

The raisin bread analogy describes some aspects of the cosmic
expansion; the balloon analogy describes other aspects. Each can
show some things that the other cannot.

-- Jeff, in Minneapolis

Jeff Root
2010-May-23, 11:12 PM
The balloon model doesn't at all demonstrate that space can be
expanding without expanding *into* anything. It doesn't do it any
better than an expanding loaf of bread, anyhow. And I would say
that whether the Universe we can see is expanding into anything
or not is completely unknown. General relativity shows that such
expansion is mathematically conceiveable and consistent with
observations, but doesn't require that it is how the expansion
actually works.

-- Jeff, in Minneapolis

Shaula
2010-May-24, 01:28 PM
The balloon model doesn't at all demonstrate that space can be
expanding without expanding *into* anything.
Um, so what bit of pre-existing 2D space is the balloon's surface expanding into? The surface is a closed 2D surface - it is not the same as a rubber sheet being stretched out in a pre-existing infinite 2D space at all AIUI. Hence it makes a great model (IMO) for a 3D universe which in not an expanding object in some greater void. As for what really is happening out there... No it is not proven but AIUI mainstream theory is that the universe is not expanding into empty space in 3D. Other explanations are possible but the one I was taught was the one I mentioned.

Jeff Root
2010-May-24, 10:24 PM
Um, so what bit of pre-existing 2D space is the balloon's surface
expanding into? The surface is a closed 2D surface - it is not the
same as a rubber sheet being stretched out in a pre-existing infinite
2D space at all AIUI. Hence it makes a great model (IMO) for a 3D
universe which in not an expanding object in some greater void.
The balloon is obviously a 3D object expanding in 3D space. The
2D surface increases in area by expanding into the space around it.

The geometry and topology of the balloon's spherical surface are
certainly different from that of a flat sheet, and the balloon analogy
takes advantage of those differences, but there is no difference
between them as far as their expansion into surrounding space.
Neither one models expansion which is not expansion into existing
space.



As for what really is happening out there... No it is not proven but
AIUI mainstream theory is that the universe is not expanding into
empty space in 3D. Other explanations are possible but the one I
was taught was the one I mentioned.
Yes, that's the preferred explanation. But observational evidence
does not favor it over an explanation which has an edge and a
center. The introduction of Inflation and the resulting size of the
Universe being vastly larger than what we see removed the
advantages of the centerless explanation by reducing the
significance of the already rather weak cosmological principle.
According to Inflation, things look pretty much the same only
in the volume affected by Inflation, and not outside that volume.
With Inflation, both bounded and unbounded descriptions work
equally well.

Even without Inflation, any mechanism for the cosmic expansion
which makes the expansion the same everywhere in a finite
volume of space would have the same effect of making the
visible Universe look pretty much the same everywhere we
can see. Since we don't know the mechanism, we don't know
whether an unbounded description is required, and a bounded
description works equally well.

-- Jeff, in Minneapolis

DrRocket
2010-May-24, 10:58 PM
The geometry and topology of the balloon's spherical surface are
certainly different from that of a flat sheet, and the balloon analogy
takes advantage of those differences, but there is no difference
between them as far as their expansion into surrounding space.
Neither one models expansion which is not expansion into existing
space.

That depends on how one regards the analogy.

If you consider the balloon, as it is intended that you do, as simply the surface without regard for the fact that it is embedded in 3-space then it is a fairly good analogy for the expansion of the "space" of the universe. The point is that the surface expands as the balloon is inflated and all points recede directly away from another with the rate of recession being proportional to the distance by which they are separated. In using this analogy it is not intended that you focus on either the center of the ball of which the balloon is the boundary or the embedding in 3-space.

Analogies are just that, analogies. They are of necessity imperfect, because they do not describe the real thing. In this case the purpose of the analogy is to express notions that really require the mathematics of manifolds without actually using that lievel of sophistication. The surface of a baloon is an excellent analogy for a 2-manifold, and it gets across the notion of "metric expansion" rather well so long as one focuses on the point being made and not the shortcomings.

The raisin bread analogy attempts to do the same thing in 3-dimensions. With that example you run into some difficulty in getting across the notion of a manifold. That is because of the "edge" which would be the crust. You either must pretend that the crust is not there, in which case you have an open subset of 3-space wth compact closure or you get a manifold-with-boundary which is not allowed in the model of spacetime as it is understood in general relativity. One also looses there any illustration of curvature. On the other hand, it you view the expanding loaf of bread as a local model for an expanding universe, not necessarily the whole things, then it is quite a good analogy for the expansion of the universe. The local picture also, of course, simple ignores the embedding.

Geo Kaplan
2010-May-24, 11:16 PM
That depends on how one regards the analogy.

If you consider the balloon, as it is intended that you do, as simply the surface without regard for the fact that it is embedded in 3-space then it is a fairly good analogy for the expansion of the "space" of the universe. The point is that the surface expands as the balloon is inflated and all points recede directly away from another with the rate of recession being proportional to the distance by which they are separated. In using this analogy it is not intended that you focus on either the center of the ball of which the balloon is the boundary or the embedding in 3-space.

Analogies are just that, analogies. They are of necessity imperfect, because they do not describe the real thing. In this case the purpose of the analogies is to express notions that really require the mathematics of manifolds without actually using that lievel of sophistication. The surface of a baloon is an excellent analogy for a 2-manifold, and it gets across the notion of "metric expansion" rather well so long as one focuses on the point being made and not the shortcomings.

The raisin bread analogy attempts to do the same thing in 3-dimensions. With that example you run into some difficulty in getting across the notion of a manifold. That is because of the "edge" which would be the crust. You either must pretend that the crust is not there, in which case you have an open subset of 3-space wth compact closure or you get a manifold-with-boundary which is not allowed in the model of spacetime as it is understood in general relativity. One also looses there any illustration of curvature. On the other hand, it you view the expanding loaf of bread as a local model for an expanding universe, not necessarily the whole things, then it is quite a good analogy for the expansion of the universe. The local picture also, of course, simple ignores the embedding.

Exactly right.

I found puzzling the complaints that this or that analogy was lacking in one or more ways. I thought folks would recognize analogies and models for what they are: Analogies and models, not the actual thing itself. To carp about the mere existence of limitations is to reveal a misunderstanding of what analogies and models are.

The balloon analogy was offered to answer the question posed by the OP, as the title to this thread. For answering that particular question, the balloon analogy does just fine. (OP: in case the answer got lost amidst the subsequent back-and-forth, we aren't in the middle. It might seem that way, but the balloon analogy shows how appearances can be deceiving.)

Thanks, DrRocket, for reminding folks what a model is, and that any model will fail at answering certain questions, because a model of a thing is not the thing itself.

Shaula
2010-May-25, 01:11 PM
And thanks, DrRocket, for getting across what I was failing to! Was going to give up on that argument (still aware I am a newbie and my physics is rusty as hell).

Jeff Root
2010-May-25, 02:07 PM
The geometry and topology of the balloon's spherical surface are
certainly different from that of a flat sheet, and the balloon analogy
takes advantage of those differences, but there is no difference
between them as far as their expansion into surrounding space.
Neither one models expansion which is not expansion into existing
space.
That depends on how one regards the analogy.

If you consider the balloon, as it is intended that you do, as simply
the surface without regard for the fact that it is embedded in 3-space
then it is a fairly good analogy for the expansion of the "space" of
the universe.
All you are saying is that you are ignoring the three-dimensionality
of the balloon. In that case, the balloon itself does not demonstrate
anything at all about whether or not the 2-dimensional surface
expands into 3-dimensional space.

If your audience does not understand that you want them to ignore
the three-dimensionality of the balloon, then you are demonstrating
to them that the two-dimensional surface expands into 3-D space.
In that regard it is no different from stretching a flat sheet.

I understand -- in a way -- what is meant by expansion without
expanding into existing space, and I'm sure a lot of other people
understand it at least as well as I do. But I don't know of any way
to make a visualization of it that actually helps. I don't think it
can be visualized. The balloon doesn't do it.



The point is that the surface expands as the balloon is inflated and all
points recede directly away from [one] another with the rate of recession
being proportional to the distance by which they are separated.
This point is one of the uses of the balloon analogy that I listed. It works
just as well with a flat sheet, except that it is physically much easier to
stretch a balloon than a flat sheet. It is a different point from the point
you and Shaula want to make that the expansion does not expand into
existing space.

-- Jeff, in Minneapolis

cosmocrazy
2010-May-25, 02:15 PM
All you are saying is that you are ignoring the three-dimensionality
of the balloon. In that case, the balloon itself does not demonstrate
anything at all about whether or not the 2-dimensional surface
expands into 3-dimensional space.

If your audience does not understand that you want them to ignore
the three-dimensionality of the balloon, then you are demonstrating
to them that the two-dimensional surface expands into 3-D space.
In that regard it is no different from stretching a flat sheet.

I understand -- in a way -- what is meant by expansion without
expanding into existing space, and I'm sure a lot of other people
understand it at least as well as I do. But I don't know of any way
to make a visualization of it that actually helps. I don't think it
can be visualized. The balloon doesn't do it.


This point is one of the uses of the balloon analogy that I listed. It works
just as well with a flat sheet, except that it is physically much easier to
stretch a balloon than a flat sheet. It is a different point from the point
you and Shaula want to make that the expansion does not expand into
existing space.

-- Jeff, in Minneapolis

This is why when an analogy is used as an example it is important to inform the people of its limits and exactly how it is meant to convey a visual understanding. I find both analogies useful but it must always be made clear with the balloon analogy that its only the 2D surface of the balloon which is representing how the expansion of space causes the separation of the distant galaxies. And that based on the current accepted mainstream model space is not expanding into or embedded in anything.

Strange
2010-May-25, 02:30 PM
If your audience does not understand that you want them to ignore
the three-dimensionality of the balloon, then you are demonstrating
to them that the two-dimensional surface expands into 3-D space.

The problem is that some people can't understand the idea that the 2D surface is the analogue for the 3D universe anyway (even if you tell them that it is only about the surface). They will always think about what is inside or outside the balloon.


In that regard it is no different from stretching a flat sheet.

Except the surface of the balloon has no edges (by definition). Whereas (as we have seen) some people will say that the sheet must have an edge (even if it is really, really big) and so must have a center.

Perhaps you need both analogies to have any chance of getting the idea across.


I don't think it can be visualized.

You may be right.


The balloon doesn't do it.

For you :)

DrRocket
2010-May-25, 02:35 PM
If your audience does not understand that you want them to ignore
the three-dimensionality of the balloon, then you are demonstrating
to them that the two-dimensional surface expands into 3-D space.
In that regard it is no different from stretching a flat sheet.

-- Jeff, in Minneapolis

Before one can explain to an audience what an analogy means, one must first understand it oneself, beyond just an analogy.

Analogies are aides to the explanatin of a deeper concept. They are not a substitute for understanding that deeper concept, particularly on the part of the one doing the explaining. If one does not understand the underlying concept there is real danger of reading way too much into the analogy.

The reason why the universe does not expand into existing space is quite simple. The universe IS existing space. It there were existing space iinto which the universe could expand that existing space would already be part of the universe -- the universe is the whole enchilada. There is no "elsewhere".

Jeff Root
2010-May-25, 03:32 PM
The reason why the universe does not expand into existing space
is quite simple. The universe IS existing space. If there were existing
space iinto which the universe could expand that existing space would
already be part of the universe -- the universe is the whole enchilada.
There is no "elsewhere".
This increases my confidence in my own determinations where they
conflict with yours. Defining one thing to be another thing doesn't
explain anything.

-- Jeff, in Minneapolis

DrRocket
2010-May-25, 03:45 PM
This increases my confidence in my own determinations where they
conflict with yours. Defining one thing to be another thing doesn't
explain anything.

-- Jeff, in Minneapolis

I have not defined anything to be anything else.

If you have some sort of ATM theory there is a forum specifically designed for such discussions.

Jeff Root
2010-May-25, 03:52 PM
You have defined the space into which the Universe is expanding
to be "the Universe". Therefore, the Universe is not and cannot be
expanding into any existing space. Pure semantic obfuscation,
with no physics involved.

-- Jeff, in Minneapolis

Shaula
2010-May-25, 04:21 PM
Whereas you seem to be defining the Universe as 'the stuff that flew out of the Big Bang' rather than the more usual definitions:
Universe: Everything that exists, including the Earth, planets, stars, galaxies, and all that they contain; the entire cosmos.
Universe: the aggregate of all existing matter, energy, and space
Universe: All matter and energy, including the earth, the galaxies, and the contents of intergalactic space, regarded as a whole.

Couldn't find a definition which said
Universe: Everything that exists except some arbitrary bits of the cosmos that the matter from the Big Bang hasn't reached yet.

DrRocket
2010-May-25, 05:17 PM
You have defined the space into which the Universe is expanding
to be "the Universe". Therefore, the Universe is not and cannot be
expanding into any existing space. Pure semantic obfuscation,
with no physics involved.

-- Jeff, in Minneapolis

Wrong. Completely wrong.

The mainstream model for cosmology is general relativity. In that model the universe is a 4-dimensional Lorentzian manifold, spacetime. I have explained to you numerous times what "expansion of space" means. It means that, given a foliation of spacetime into spacelike hypersurfaces via a single time-like parametere that the distance separating points increases as the value of the time-like parameter increases. The spacetime manifold is the universe and there is nothing into which the space-like slices expand.

You have two fundamental choices. Either you can accept the mainstream explanation, which I have given you. Or, you can be a proponent of something else. "Something else' is, by definition ATM.

The explanation that I gave you, that there is nothing else into which to expand, is part and parcel of the model based on general relativity. There is no semantic obfuscation involved. That is a figment of your imagination and your refusal to accept the mainstream model. Your assertion that is not physics is a repudiation of general relativity, which is most certainly physics.

Now, maybe the mainstream model is wrong, But it is nevertheless the best model that we have. If you have some alternative to general relativity, then the ATM forum awaits.

Jeff Root
2010-May-26, 12:59 AM
Shaula,

When I have made a distinction between the Universe as
a whole, and the portion of the Universe that was involved
in the Big Bang and is currently participating in the cosmic
expansion, I typically have done so by using wording similar
to the middle part of this long sentence. But sometimes I
enter a conversation that is already going on in which the
term "Universe" has been explicitly used to refer to that
which was involved in the Big Bang, and/or is participating
in the expansion. And other times I enter a conversation
that is already going on in which the term "Universe" has
been explicitly used to refer to everything there is, whether
it was involved in the Big Bang and is participating in the
cosmic expansion or not. So I sometimes have to switch
between those definitions. That is not much of a problem
when I only have to switch definitions between threads,
(though it *is* a problem), but it is a big problem when I
have to switch within a thread.

What DrRocket wants, though, is to define "everything that
was involved in the Big Bang and is now participating in the
cosmic expansion" as "everything there is". That is not
physics. It is semantics only.

-- Jeff, in Minneapolis

Geo Kaplan
2010-May-26, 01:34 AM
What DrRocket wants, though, is to define "everything that
was involved in the Big Bang and is now participating in the
cosmic expansion" as "everything there is". That is not
physics. It is semantics only.

Sure, it's "semantics," but it also happens to be the mainstream definition of "the universe." So, it's not so much what DrRocket "wants", it's really what you seem to want. It is becoming clear through your posts that you have a distinctly ATM view of things, so rather than feigning complaints about our explanations, please simply come out of the closet, so to speak, and just state your ATM propositions in the appropriate forum. You've been given excellent answers to your fine questions, but you clearly don't "like" them for reasons that you have not articulated.

Jeff Root
2010-May-26, 01:38 AM
The mainstream model for cosmology is general relativity.
No it isn't.

General relativity is a mathematical description of the relationship
between space and time which is used to construct cosmological
models.



In that model the universe is a 4-dimensional Lorentzian manifold,
spacetime. I have explained to you numerous times what "expansion
of space" means. It means that, given a foliation of spacetime into
spacelike hypersurfaces via a single time-like parametere that the
distance separating points increases as the value of the time-like
parameter increases.
That does not distinguish expansion of space from motion through
space, so it does not explain what "expansion of space" means.

What is actually observed does not require that "expansion of space"
be different from "motion through space".



The spacetime manifold is the universe and there is nothing into
which the space-like slices expand.
That describes one family of models.



You have two fundamental choices. Either you can accept the
mainstream explanation, which I have given you. Or, you can be
a proponent of something else. "Something else' is, by definition ATM.
I'll take choice #3: Find descriptions which fit the observations.
Your favored model is one such.



The explanation that I gave you, that there is nothing else into which
to expand, is part and parcel of the model based on general relativity.
There you put it correctly: The model is based on general relativity
(among other things).



There is no semantic obfuscation involved. That is a figment of your
imagination and your refusal to accept the mainstream model. Your
assertion that is not physics is a repudiation of general relativity, which
is most certainly physics.
You define "everything involved in the Big Bang" = "everything there is",
with no observational evidence to support such a definiton. Any model
that doesn't assume that definition, you reject out of hand, whether it
fits the observational evidence or not.

General relativity clearly is very good in describing much of what
we can see. I have no doubt that it can be used to construct an
accurate cosmological model. With the current state of knowledge,
it can be used to construct many accurate cosmological models.



Now, maybe the mainstream model is wrong,
It is certainly incomplete in very important, perhaps essential
respects. It is undoubtedly wrong in some respects because
of that incompleteness.



But it is nevertheless the best model that we have. If you have
some alternative to general relativity, then the ATM forum awaits.
I do not have any alternative to general relativity.

But, just as you can correct some of the errors that I make, I can
correct some of the errors that you make.

-- Jeff, in Minneapolis

Gomar
2010-May-26, 02:41 AM
You all seem to be forgetting that there are several different balloons(universes) which are expanding in a room. Some balloons are small and will eventually pop if their expansion isnt halted; other balloons' expansion will halt and they will recede back once the air is let out(universe's contraction back to original state); still other balloons will continue to expand and crash into the walls of the room(boundary of all there is).
It is as well possible that some balloons will crash into each other. Perhaps even merge, or destroy each other. Now as for whats beyond the walls of the room... stay tuned and I shall elighten thee in good time.

pzkpfw
2010-May-26, 03:21 AM
Now as for whats beyond the walls of the room... stay tuned and I shall elighten thee in good time.

Gomar, it's one thing to argue over the finer details (semantics) but you've moved beyond into ATM. Please keep that out of the Q&A forum.

DrRocket
2010-May-26, 03:38 AM
I do not have any alternative to general relativity.

But, just as you can correct some of the errors that I make, I can
correct some of the errors that you make.

-- Jeff, in Minneapolis

Apparently not. Since what you have said is wrong.

Try reading a real book on the subject. The largescale structure of space-time by Hawking and Ellis would be a good start.

cosmocrazy
2010-May-26, 03:22 PM
I don't understand why some people continue to argue against whats considered mainstream? Sure the current model of the BB is the best fit based on updated observation and understanding. Ok there's nothing wrong with saying "hold on a minute something is not quite right" because there are parts missing or the math doesn't quite add up under extreme conditions. But unless these people can come up with a viable alternative which can stand up to scrutiny then surely we must accept what our finest scientists like hawking and co have to offer us? Most of us on BAUT are amateur cosmologists / physicists and mathematicians, we just simply don't have the time and resources available to us that the professionals have. Hasn't it ever occurred to some of us that they might have spent years debating over the very things we discuss, actively looking at any possible alternatives?

I believe it is quite healthy to consider alternatives and then to discuss possible options. But to challenge mainstream theories requires extensive research and total understanding of any current models and the observation & math which supports them.

DrRocket
2010-May-26, 03:28 PM
I don't understand why some people continue to argue against whats considered mainstream? Sure the current model of the BB is the best fit based on updated observation and understanding. Ok there's nothing wrong with saying "hold on a minute something is not quite right" because there are parts missing or the math doesn't quite add up under extreme conditions. But unless these people can come up with a viable alternative which can stand up to scrutiny then surely we must accept what our finest scientists like hawking and co have to offer us? Most of us on BAUT are amateur cosmologists / physicists and mathematicians, we just simply don't have the time and resources available to us that the professionals have. Hasn't it ever occurred to some of us that they might have spent years debating over the very things we discuss, actively looking at any possible alternatives?

I believe it is quite healthy to consider alternatives and then to discuss possible options. But to challenge mainstream theories requires extensive research and total understanding of any current models and the observation & math which supports them.

I think it requires two things.

1) Extreme confidence in one's own conclusions and reasoning

2) Ignorance of the established theories and related mathematics and inability to understand those theories and to use the mathematical tools

It is a deadly combination.

cosmocrazy
2010-May-26, 03:36 PM
I think it requires two things.

1) Extreme confidence in one's own conclusions and reasoning

2) Ignorance of the established theories and related mathematics and inability to understand those theories and to use the mathematical tools

It is a deadly combination.

I would agree with you on the first point! In part for most of us yes I would agree on the second, but someone with very good understanding of established theories and supporting math and evidence will one day challenge or improve on what is considered mainstream. This is a must if we want to make progress. That person/s though must already have a thorougher grasp on what are currently accepted models and then demonstrate how to improve on or fix any flaws in such. No disrespect to anyone here on BAUT but i'm not confident that those person/s have come forth yet.

DrRocket
2010-May-26, 04:01 PM
I would agree with you on the first point! In part for most of us yes I would agree on the second, but someone with very good understanding of established theories and supporting math and evidence will one day challenge or improve on what is considered mainstream. This is a must if we want to make progress. That person/s though must already have a thorougher grasp on what are currently accepted models and then demonstrate how to improve on or fix any flaws in such. No disrespect to anyone here on BAUT but i'm not confident that those person/s have come forth yet.

What you are now describing is an exceptional researcher. Such a person does not argue against the mainstream. Such a person formulates and proposes a theory that extends and supplants the mainstream theory.

You will never see theories of that nature make the first appearance on BAUT or any other such public forum. Such theories would be circulated within the research community, pre-prints would appear in ArXiv, and polished papers published in serious journals.

CaptainToonces
2010-May-27, 05:13 AM
What you are now describing is an exceptional researcher. Such a person does not argue against the mainstream. Such a person formulates and proposes a theory that extends and supplants the mainstream theory.

You will never see theories of that nature make the first appearance on BAUT or any other such public forum. Such theories would be circulated within the research community, pre-prints would appear in ArXiv, and polished papers published in serious journals.

You offer this highly subjective opinion as though it were some sort of proven fact.

It is quite possible for advancements in a field to come outside of that field's established community. The key datum is the proportion of the number of total people vs. the number of people in that field's research community and it is large.

For a millennium people believed that only those of royal birth could achieve great things, but now we have a democracy that recognizes the fact that greatness can come from all minds.

DrRocket
2010-May-27, 05:22 AM
You offer this highly subjective opinion as though it were some sort of proven fact.

It is quite possible for advancements in a field to come outside of that field's established community. The key datum is the proportion of the number of total people vs. the number of people in that field's research community and it is large.

For a millennium people believed that only those of royal birth could achieve great things, but now we have a democracy that recognizes the fact that greatness can come from all minds.

So , produce an example of a major discovery in science made by such a person in the last century.

CaptainToonces
2010-May-27, 05:31 AM
So , produce an example of a major discovery in science made by such a person in the last century.
Well I don't think Einstein as a 20-something patent officer in Suisse would've been considered in the theoretical physics community at the time he released Relativity. My knowledge of the scientific biographies is not that great but i doubt highly that there are not some great contributions from men who were not technically within the established community of researchers in the fields they produced discoveries. Maybe another poster here has a better example than Einstein.

I think it is quite likely that the era of innovation from human minds is near its end though. In 20 years, all innovations in theory will come from computers.

DrRocket
2010-May-27, 06:07 AM
Well I don't think Einstein as a 20-something patent officer in Suisse would've been considered in the theoretical physics community at the time he released Relativity. My knowledge of the scientific biographies is not that great but i doubt highly that there are not some great contributions from men who were not technically within the established community of researchers in the fields they produced discoveries. Maybe another poster here has a better example than Einstein.

I think it is quite likely that the era of innovation from human minds is near its end though. In 20 years, all innovations in theory will come from computers.

Einstein had a PhD in physics, received from the University of Zuric under Alfred Kleiner, when he held that job as patent clerk and had studied physics. Although he had not particularly distinguished himself as student, he was harely an outsider in the rather small community of theoretical physicists. His "miraculous year" of 1905, whiile he was in the patent office followed immediately after his receipt of the doctorate.

Not a good example.

What you dolubt, in the absence of any hard data is not credible.

Try again.

I rather doubt that significant inventions will be the result of "computers" any time soon, if ever. Computers have done some drudge work, but have not been responsible for any creative breakthroughs.

I take it that you have never done any fundamental research. It shows.

pzkpfw
2010-May-27, 08:09 AM
At that point, can we leave the off-topic posts out please? Let's all stick the original question.

bestmann
2010-May-27, 04:34 PM
The answer is that there is no outside matter or space, we are contained within a small bubble that is expanding
spacially for us but not actually taking the space away from anywhere else.

cosmocrazy
2010-May-28, 09:17 AM
The answer is that there is no outside matter or space, we are contained within a small bubble that is expanding
spacially for us but not actually taking the space away from anywhere else.

Welcome to BAUT bestmann,

Although yes you are basically correct that is roughly part of what the current accepted model suggests, but the OP was "why are we in the middle?" . This has been answered on this thread a few times over.

Gomar
2010-Jun-01, 08:29 PM
The answer is that there is no outside matter or space, we are contained within a small bubble that is expanding spacially for us but not actually taking the space away from anywhere else.

Wow! You have such deep understanding of the universe! Please do share with us more of your brilliant conjenctures.

pzkpfw
2010-Jun-01, 09:06 PM
Wow! You have such deep understanding of the universe! Please do share with us more of your brilliant conjenctures.

Whatever you think of the post by bestmann, there's no need for the attitude displayed in your reply.

Your other post has been moved into a new thread.