Where is the center of the universe?

[thetexan]

There must be a center or someplace close to the center of the universe.

The actual universe can be contained in a physically describable bounding box. This box will have a center. Or, everything emminated from a center, the singularity and the position of that place where the singularity once existed is a fact, even though most will protest that it is unknowable. The point is, there must be some place, maybe known only to God where the center is. If it does exist then there must be some way to extrapolate how and where to find it.

The proof that it does exist or that people were quite happy to conceed that it exists is found in many television shows like Universe where noted scientists always note that, prior to the discovery that the universe is accelerating faster outward, everyone accepted that the universe would collapse back into a singularity. In other words, the big bang was ballistic in nature and will be so in the reverse when gravity brings it all back to a common center point.

So...why doesn't anyone try to figure out where that point is or was?

tex

 

[alexg]

No there is no center. You are trying to apply the logic of the everyday physical universe you perceive in a realm where it is not applicable.

The proof that it does exist or that people were quite happy to conceed that it exists is found in many television shows

 

[Chalnoth]

There must be a center or someplace close to the center of the universe.

Why would you think that? Take, for instance, a ball. What is the center of the surface of that ball? Which point on the surface is the center of that surface?

 

[salvestrom]

It's everywhere and nowhere, baby. That's where it's at. Riding down a geometrical distortion in spacetime owing to the presence of a large body of matter... in a Hippy Hat.

It has a ring.

If you're serious about understanding the universe as science currently thinks it to be, you need to first understand that no scientist is going to appear on a show like Universe and actually talk to you like he would his colleagues. What you think you have understood, should be treated with caution. Look around a little; at this forum, at the stars. I like stars.

 

[thetexan]

It's everywhere and nowhere, baby. That's where it's at. Riding down a geometrical distortion in spacetime owing to the presence of a large body of matter... in a Hippy Hat.

It has a ring.

If you're serious about understanding the universe as science currently thinks it to be, you need to first understand that no scientist is going to appear on a show like Universe and actually talk to you like he would his colleagues. What you think you have understood, should be treated with caution. Look around a little; at this forum, at the stars. I like stars.

I am serious and you haven't addressed the question. In a mind experiment, if I could stand off some distance from the universe I could point and say...'there it is' and there would be some central area to that thing. Or, using a different approach...since everything in the universe blasted from the singularity it is obvious that the parts of the universe, including space itself is accelerating outward from that initial start. If it isn't then from what are all the elements of the universe accellerating? IF we could play the tape backward we could easily pinpoint the location of the origination point. Just because we cant, or have difficulty figuring out how to locate the point doesn't mean it doesn't exist. And since it DID once exist...that being the point of the big bang...by what logic do you determine that it immediately is lost and can't be found?

It seems that everything is accelerating from somewhere common otherwise everything would be accelerating from different origins. Just because everything seems to be accelerating from our vantage point only means we can't tell where the origin is. That does not mean it doesn't exist.

Unless you are willing to argue that every body is accelerating from different origins then they must be sharing a common origin. Where?

tex

 

[salvestrom]

IF we could play the tape backward we could easily pinpoint the location of the origination point.

Playing the tape backward, we eventually arrive at a point where the energy of the universe is in a very small region of the space of the universe. Think of it as each point of space having a point of energy. Now shrink and expand the universe at will. Each point of energy moves away from every other point as you swell the universe and rushes toward every other point as you shrink it.

Your conception relies on a finite universe that has a boundary. This isn't considered an option even in M-theory, which allows for multiple universes beyond our own. No edge: no middle.

I couldn't tell you why it's not an option, other than an accepted assumption that there is nothing special about our own viewpoint in the universe. Hopefully someone else can provide an unconfusing answer.

 

[minio]

Unless you are willing to argue that every body is accelerating from different origins then they must be sharing a common origin. Where?

Well as I see it, the universe started to expand some 14 biliony years ago from singularity. So position of this singularity is the center of the universe. And its position is about 14 bilions years ago from any point in our observable universe.

 

[thetexan]

http://longviewbluegrass.com/expansion.jpg

 

[minio]

In balloon analogy your origin of expansion would be in the center of the balloon where once expanded is actually nothig and our present universe would be on surface of that balloon. So you cannot pinpoint center of expansion in 3 dimensions of our universe.

 

[alexg]

If all stars are expanding from a central point, and that point is not us, we would not see the homogeneous universal expansion in all directions.x

The observed rate of and size of the expansion is the same in every direction. So either WE are at the center of the universe, or there is no center.

It's a concept that many cannot fathom due to their experience with the limitations of slow, small local space. And the balloon analogy doesn't really help because most people can't deal with analogies without thinking the map is the territory.

 

[DaveC426913]

thetexan, examine the balloon analogy.

You and all your friends are ants, living shoulder to shoulder on the 2 dimensional surface of a small spherical balloon. Your entire world is 2-dimensional.

Then the balloon inflates to ten times its size.

You watch as all your friends recede from you until they are ten times further away, and getting farther every moment. Your entire universe has expanded by ten-fold.

Which of you can lay claim to being at the centre of your universe? Which one of you did not move as the balloon expanded?

Answer: everyone and no one. Every ant experiences the same thing: all the other ants receding from it, yet none of them is on a privileged position; none of them can claim to be at the centre (more accurately, all of them can claim to be at the centre, since what was the centre is now everywhere).

 

[thetexan]

No one can lay claim to the center, of course.

This does not address whether THERE IS a center to lay claim to.

My point is that, at least intuitively (and I see nothing to refute the intuitive inference) that there must be a center from which everything is expanding. Here are my reasons...

1. At the moment of the explosion (and it certainly was balistic in the sense that everything imminated from that singularity outward) everything began moving outward directly away from it according to all explanations I have heard. This is supported by the fact that everytime I hear an explanation of the expansion I see it defended by showing animations and graphs of an explosion-like event. This is furthur supported by the fact that these same people play the tape backwards to show what would happen if it all fell back inward (this is before acceleration was proven).

2. Assuming Earth is not the actual center, everything must either be
a. accelerating away from a common point, or
b. accelerating way from different points

even though everything appears to be accelerating from our vantage point, earth.

3. If the big bang was the cause to the expansion effect we observe then what was its input to that expansion we observe if not the force impetus for that expansion. And if the big bang did not provide that expansive force then what did?

4. It is argued that space is expanding and that is the cause, not an explosive event. That would not account for the idea of all mass being compacted into a tiny space in the very beginning. There must have been a lot of mass stuffed into a small measurable space. This compaction was why in the very beginning of expansion there was a soup of indeterminate particles and forces. This suggest that it was crowded in the beginning and not so crowded later on. The very definition acknowledges that there is a mass/size relationship at the very instant of the bang.

5. If there is a center from which everything imminated and you could be a far-off onlooker you could point to it and say 'there it is' and everything would, to you, seem to be moving from it.

6. Anyone on a vantage point inside the system would think they are at the center due to the reasons given already.

Yes, no ant or any observer can lay claim to being at the center. But, if there IS a center there must be some way we haven't thought of yet to point to where it actually is. Simply stating that we cant, YET, lay claim to it doesn't refute it or get us any closer to the idea of discovering it. The question is how. And my simple question was this...

If there is a definable center (which would be the point from which everything is expanding as seen theoretically from a far off vantage point) is there any way to calculate the various trajectories of the expanding stars that would tend to point to it. In other words, we have run up to a brick wall called the 'dots on the balloon' principle and it SEEMS insurmountable as to using trajectories and velocities to point to any origin other than the individual vantage point. Then it seems we therefore just accept that there MUST NOT BE a real center.

If the answer is this, 'if there is a center we can't prove it' then I accept that. If the answer is 'there is no center because we can't prove it due to the dots on the balloon principle' then I don't accept that.

tex

 

[alexg]

1. At the moment of the explosion (and it certainly was balistic in the sense that everything imminated from that singularity outward) everything began moving outward directly away from it according to all explanations I have heard.

No. Everything did not begin moving outward. Stuff did not fly away from someplace. There was an increasing amount of space between everything, everywhere.

2. Assuming Earth is not the actual center, everything must either be
a. accelerating away from a common point, or
b. accelerating way from different points

Nothing accelerated away from anywhere. There was more space between everything.

3. If the big bang was the cause to the expansion effect we observe then what was its input to that expansion we observe if not the force impetus for that expansion. And if the big bang did not provide that expansive force then what did?

It was the cause, but the expansion was not stuff being flung, but space being created between everything.

4. It is argued that space is expanding and that is the cause, not an explosive event. That would not account for the idea of all mass being compacted into a tiny space in the very beginning. There must have been a lot of mass stuffed into a small measurable space. This compaction was why in the very beginning of expansion there was a soup of indeterminate particles and forces. This suggest that it was crowded in the beginning and not so crowded later on. The very definition acknowledges that there is a mass/size relationship at the very instant of the bang.

All energy in the universe (too hot and dense for matter yet) was in a tiny space. The space itself expanded. If this were a ballistic explosion originating at a particular point, there wouldn't be any matter at the 'center' Again, that's not what we see when we look at the universe.

5. If there is a center from which everything imminated and you could be a far-off onlooker you could point to it and say 'there it is' and everything would, to you, seem to be moving from it.

Yes. But that's not what we see when we look at the universe. We don't see everything moving away from somewhere. We see everything moving away from us. Equally, in all directions. So either WE are the center, (most highly unllikely), or there is no center.

 

[thetexan]

5. If there is a center from which everything imminated and you could be a far-off onlooker you could point to it and say 'there it is' and everything would, to you, seem to be moving from it.


Yes. But that's not what we see when we look at the universe. We don't see everything moving away from somewhere. We see everything moving away from us. Equally, in all directions. So either WE are the center, (most highly unllikely), or there is no center.

You say there are only two alternatives...either...

1. we are the center...
2. or there is no center

There could be a third...

3. there is a center but because of the 'dots on the balloon' principle we can't determine it. So far there is nothing to refute the possibility of the third alternative.

Even if it is space that expands, it is expanding from a beginning with a very small space. Take the balloon for example. When you breath in more air it gets bigger. But I can approximate the center of the balloon. And if space is finite and has shape then by definition it should have a geographic center or something close to that definition.

For there not to be, space would have to in reality infinite. If you subscribe at all to the idea that space is expanding then you define it as finite in your premise and thus it is theorectically able to be contained in a big box and therefore capable of having a center.

But I go farther than that. Not only do I suspect that there is a 3 deminsional bounding box within which the universe can be contained I suspect that it IS expanding from a center. Just like a raisin which happens to be in the center of a loaf of bread as it expands during baking. The raisin sees its entire universe moving away from it because it is indeed at the center of its universe. However another raisin thinks the same thing since its observation leads it to believe that it is at the center. Only we as outside observers know which raisin is actually in the center. The fact that the second raisin concludes he is at the center does not allow him to deduce that there must be no ACTUAL center. Not based on that alone.

Any finite object must have a center. Otherwise it is either infinite or we can't deduce which. What we can't do is deduce that there MUST NOT BE a center.

By the way. I am not trying to come down one way or the other. I just can't buy that we can prove there IS NO center from our observations and explanations with balloons and loaves of bread. While they do explain what we see, they, by themselves do not EXPLAIN AWAY the idea of a center. And if we can't prove it then there is left the possibility that there is, and if so where is the center and how can we figure out how to find it. That's all. Just old fashioned curiosity and determination.

This is not unlike the sun revolving around the Earth theory. Sure they explained quite adaquately what they saw with the sun revolving around the Earth theory. But their explanations never DISPROVED the possibility of the Earth revolving around the sun. Everyone bought off on the plausible explanation and were satisfied. Right up until they discovered new facts.

tex

 

[Nabeshin]

You say there are only two alternatives...either...

1. we are the center...
2. or there is no center

There could be a third...

3. there is a center but because of the 'dots on the balloon' principle we can't determine it. So far there is nothing to refute the possibility of the third alternative.

Even if it is space that expands, it is expanding from a beginning with a very small space. Take the balloon for example. When you breath in more air it gets bigger. But I can approximate the center of the balloon. And if space is finite and has shape then by definition it should have a geographic center or something close to that definition.

For there not to be, space would have to in reality infinite. If you subscribe at all to the idea that space is expanding then you define it as finite in your premise and thus it is theorectically able to be contained in a big box and therefore capable of having a center.

But I go farther than that. Not only do I suspect that there is a 3 deminsional bounding box within which the universe can be contained I suspect that it IS expanding from a center. Just like a raisin which happens to be in the center of a loaf of bread as it expands during baking. The raisin sees its entire universe moving away from it because it is indeed at the center of its universe. However another raisin thinks the same thing since its observation leads it to believe that it is at the center. Only we as outside observers know which raisin is actually in the center. The fact that the second raisin concludes he is at the center does not allow him to deduce that there must be no ACTUAL center. Not based on that alone.

Any finite object must have a center. Otherwise it is either infinite or we can't deduce which. What we can't do is deduce that there MUST NOT BE a center.

By the way. I am not trying to come down one way or the other. I just can't buy that we can prove there IS NO center from our observations and explanations with balloons and loaves of bread. While they do explain what we see, they, by themselves do not EXPLAIN AWAY the idea of a center. And if we can't prove it then there is left the possibility that there is, and if so where is the center and how can we figure out how to find it. That's all. Just old fashioned curiosity and determination.

This is not unlike the sun revolving around the Earth theory. Sure they explained quite adaquately what they saw with the sun revolving around the Earth theory. But their explanations never DISPROVED the possibility of the Earth revolving around the sun. Everyone bought off on the plausible explanation and were satisfied. Right up until they discovered new facts.

tex

Unfortunately, you have completely missed the point of the balloon analogy, which is leading you to the incorrect conclusions.

In the balloon analogy (or raisin bread analogy), it is ABSOLUTELY CRUCIAL to remember that you are only taking about THE SURFACE of the object. That is, only THE SURFACE of the balloon is meant to be considered in the balloon analogy. This surface is a 2-dimensional space. Indeed, when we imagine it, we think of it as a 2-dimensional surface of a 3-dimensional object, namely a sphere, which of course has a geometric center in 3-dimensional space. But really, we're talking ONLY about the 2-dimensional surface, precisely because in a mathematical sense, it is not necessary to refer to the full 3-dimensional sphere to talk about its surface -- the surface exists as a geometrical object quite in its own right. The full sphere is merely a convenience introduced by us (3-d human beings) to visualize the situation.

So, with that said, you have to consider just the surface. Now begin to inflate the balloon, what do you see? The distance between ALL points of the balloon increases. Any particular point sees all the other points receding from himself, and might naively claim to be at the 'center' of the perceived expansion. But any other point would reach the same conclusion. So where is the center of this expansion? Clearly, it is nowhere (or everywhere). (Do not say that it is the center of the balloon in 3-dimensions! Remember, in the balloon analogy, this 3-dimensional object is merely a convenience). THIS is the lesson of the balloon analogy.

I hope that that clears up the balloon analogy, and you see that in such a toy model, there is no center to the expansion of such a universe. Well then, how about our own universe?

What we observe is precisely the effect we see in the balloon case: all points (at sufficient cosmological distances to nullify proper motion) are receding from us. Based on this alone we might conclude we are at the center of some grand expansion, or else, it is precisely as in the balloon analogy. But the expansion is even more remarkable than that -- the velocity of recession of any given point is proportional to its distance away from us! This is patently false in any kind of normal ballistic explosion. So a theory that posits that space has always existed and that something merely exploded, sending matter flying away is immediately falsified.

What are we left with then? Well, we are brought back to the case of the expanding balloon, which has both of the features I just described that we observe in our universe. So, as a model, this kind of scale factor expansion, whereby the distances between adjacent points increases, fits our universe remarkably well. This is why we use the balloon analogy, and why it is a good description of our universe.

(Note, the same principle applies even if the universe has zero or negative curvature, and we can go through that as well. If you understand the concept of scale factor expansion, it's a straightforward generalization, although a bit harder to visualize, since both spaces are by necessity infinite.)

If any of this hasn't made sense, what specifically is it?

 

[thetexan]

In the balloon analogy (or raisin bread analogy), it is ABSOLUTELY CRUCIAL to remember that you are only taking about THE SURFACE of the object. That is, only THE SURFACE of the balloon is meant to be considered in the balloon analogy. This surface is a 2-dimensional space. Indeed, when we imagine it, we think of it as a 2-dimensional surface of a 3-dimensional object, namely a sphere, which of course has a geometric center in 3-dimensional space. But really, we're talking ONLY about the 2-dimensional surface, precisely because in a mathematical sense, it is not necessary to refer to the full 3-dimensional sphere to talk about its surface -- the surface exists as a geometrical object quite in its own right. The full sphere is merely a convenience introduced by us (3-d human beings) to visualize the situation.

You are equating the thing we are talking about, space, the universe and the stuff in it as a 2 dimensionsl surface of a sphere...which we don't need to consider since two dimensions are quite enough. This seems to be the cart before the horse problem. ie. Let's not consider the three dimensional sphere since we only need two to explain the theory that dismisses the third dimension in the first place!

Are you saying that space can be thought of as the surface of a sphere? I have seen countless examples of the dots on the balloon analogy where the three dimensions are given as layers on an onion. Each dot on each layer getting farther away from each other per layer and the dots getting father away on different layers...every dot in the onion getting farther away. There is no need for a surface analogy for the dots on the onion analogy to work.

I think because space as a curved 2 dimensional surface is the favorite theory and that dots on a balloon works with that, that a simple 3 dimensional space is thrown out. Remember, these are all theories so no one is known for sure...even the big bang.

Here is a simple question. Prove, simply, that the universe is something other than what it seems to be...a big 3 dimensional bread loaf. If one cant, then there is the possibility of a center.

The whole point of this is this...wouldnt it be amazing to figure out that the center of all expansion, the center of the big bang was somewhere in the neighborhood of Beetlegeus or some other place, even our sun.

tex

 

[marcus]

No one can lay claim to the center, of course.

This does not address whether THERE IS a center to lay claim to.

My point is that, at least intuitively (and I see nothing to refute the intuitive inference) that there must be a center from which everything is expanding. Here are my reasons...

1. At the moment of the explosion (and it certainly was balistic in the sense that everything imminated from that singularity outward) everything began moving outward directly away from it according to all explanations I have heard. This is supported by the fact that everytime I hear an explanation of the expansion I see it defended by showing animations and graphs of an explosion-like event. ...

Tex, the important question here is DO YOU WANT TO UNDERSTAND the picture that astronomers have of the expanding universe? Do you want to learn a bit about the "standard cosmology model"?

There is a generally accepted model. It does not resemble an explosion (that is what is fed the public on TV but not the real story). It is a pretty nice model that fits the data remarkably well. The model also fits the accepted law of gravity (Einstein equation) which has been tested to very high precision.

The Forum here provides a kind of common middle ground where some professionals and some general lay public mingle. New people often arrive with this "explosion" picture in their heads and it is very hard for some of them to get it out of their heads.

The crucial question is do you want to think about the expanding universe in a way that is more like the standard professional model cosmos? Or do you want to cling to the "explosion at some point in space" picture that the general public is fed via popular tv and magazines?

I hope you will reply. I'm curious to know. Welcome to PF cosmo forum, by the way. Have fun, whichever path you choose.

Oh, you might like the "charley" link in that block of links at the end of the post.

 

[Nabeshin]

Are you saying that space can be thought of as the surface of a sphere? I have seen countless examples of the dots on the balloon analogy where the three dimensions are given as layers on an onion. Each dot on each layer getting farther away from each other per layer and the dots getting father away on different layers...every dot in the onion getting farther away. There is no need for a surface analogy for the dots on the onion analogy to work.

These are, in my opinion, a dangerous set of analogies to begin to make. It leads to even more misconceptions than the original balloon analogy! What's trying to be done here, is that people are trying to equate the third dimension in the onion example with time. I.e. the two-dimensional spheres (described by two angular coordinates), and then the radial direction is time. As time increases, the radius of the two dimensional spheres too increase. I personally don't find this very helpful in understanding anything, and think it causes more confusion than good. You have to know the limitations of your analogy before you try to push it very far at all.

Here is a simple question. Prove, simply, that the universe is something other than what it seems to be...a big 3 dimensional bread loaf. If one cant, then there is the possibility of a center.

Look, if you're going to argue 'you can't prove that X isn't true', then you can leave this forum right now. We're scientists, that's not the way science works. We construct models, which give good predictions, and we have faith in these models because they work. The big bang (complete with no center and all!) is one of these. We can never 'prove' it is true. We do not aim to. But there is an incredible amount of predictive power in the big bang model, and has so far been in accordance with every observation we have made. This is why we put so much stock in the theory, and describe it as if it were 'true'. But you have to understand that it's just a model, like all other physical theories.

You're welcome to come up with a full mathematical model describing a universe with a center or whatever you like, include unicorns if it pleases you. Show that it matches observational data, and publish in a peer reviewed physical journal. Then maybe we can talk about it. Until that time, we'll stick to the theory which has made countless verified predictions.

 

[thetexan]

The simple answer is yes, I want to understand whatever makes sense scientifically without doing violence to common sense. I am not the expert to determine which is which so I rely on you guys. I am sure it must be frustrating for you with people like me. I am sorry.

I don't mean an explosion in the sense of a violent release of energy sending everything out in all directions. I mean that something, whatever it is, expansion, gunpowder or otherwise sent everything out in all directions. In that sense it resembles an explosion (to my thinking) in that everything, space, objects, whatever, was sent outward from the previous location which was a small point. I understand that space itself expanded and in doing so gives takes everything with it. I don't understand why what ever you call it, doesn't result in the same thing...that is...lots of stuff out there...where...it used to be all bunched up here in this little point. What ever you call all of that you have the beginning condition, that of everything in a little point followed by all of that stuff spread out everywhere. That must mean it went from here to there which implies at least the idea of a trajectory as seen from a far off vantage point.

I know the idea of a out of system vantage point make seem non-sensical but it helps me to visuallize what happened, if indeed, this is all close to true.

There are two points that I can't grasp, the idea of space being a surface of something and why the big loaf of bread idea is not correct. Are you saying that the universe is not 'containable' in a big box as a finite object?

Yes, I want to understand.

tex

 

[marcus]

... I mean that something, whatever it is, expansion, gunpowder or otherwise sent everything out in all directions. In that sense it resembles an explosion (to my thinking) in that everything, space, objects, whatever, was sent outward from the previous location which was a small point...

I'm trying to think where to begin. Other people may jump in (as some have earlier) and that would be fine. I'll think of something---perhaps not the best.

You know the problem with the "explosion" image is that it occurs at a point in space. that's the basic reason the image is so bad and causes newcomers such confusion.

The universe is ALL SPACE so how could it be concentrated in some "location" located in some other space? There is no other space.

I'm always going to talk about the simplest most standard cosmo model---there are more elaborate fancy models with extra dimensions and crazy extra universes but 9 out of 10 cosmologists never bother with them. The simple standard model is what is used to calculate times/distances with and to compare with observational data.

So the universe at this moment is 3D and it is all space. There is no surrounding space and no edge or boundary to it. It is all space and all existence. That's how the standard model treats it, and it works. Simplest that way.

WE DON'T KNOW whether the volume, at this moment, is finite or infinite. We are getting closer to finding out, but it could still go either way. This confessed ignorance is probably another obstacle to communicating at popular level. Probably TV producers don't want to have a scientist come on the program and say we don't know something as simple as that. So the popularizers fudge or gloss over.

Because it isn't known for sure that the universe is finite, cosmologists of necessity must keep updating both versions. Sometimes showing work in duplicate. They use both the finite version of the standard model and the infinite volume version. More often the infinite version but not so exclusively that it represents a onesided commitment.

In the finite volume case the full universe would in any case be many times larger than the observable portion--- so effectively, for all practical purposes, it gives the same numbers, looks about the same as the infinite case, and fits the data more or less equally well. Better instruments should eventually decide which version to use.

In a 2D analogy there would be two cases: an infinite flat plane or else the surface of a very large balloon so large that it seems flat to the 2D creatures living on it. For them it might as well be an infinite flat plane.
And keep in mind when thinking of any 2D analogy that whichever it is, it is ALL OF SPACE. All existence is concentrated there, there is no above or below the flat plane or inside or outside of the balloon surface.

It takes some care and concentration to think about those 2D analogies.
==========================

Let me know if there are any urgent questions about this so far. I will get back to it. But I'll take a break now.

 

[Drakkith]

Thetexan, imagine this.

Take ALL of the observable universe, about 40 billion light years in radius and cram it into a cube that is 1 meter in diameter to represent the very early universe. Next to this cube is another cube of the same size that contains all of the universe between 40 billion and 120 billion light years from us in our current time. (Each cube is 80 billion light years across in our time) Do this on each side of this cube. Now make more cubes that contain everything from 120-200 billion light years from us. Now continue to do this. Forever. This is what the very very early universe is thought to have been like. A very very dense state, but still infinite in size.

So, now we have a infinite amount of 1 meter cubes everywhere. Now start time up and watch what happens. Each cube expands. From the point of view of ANY particular cube every other cube is being pushed away from it. The further away a particular cube is from your frame of reference cube, the faster it recedes from you, as every cube in between yours and that one is expanding, causing the recession velocity to add up per cube. AKA a cube that is 10 cubes away will recede twice as fast as one 5 cubes away. A cube 100 cubes away will recede 10 times faster than the number 10 cube.

So, there is no center, no explosion, nothing like that.

 

[marcus]

Drakkith, I think part of the trouble is that Discovery Channel viewers are apt to misunderstand the word "singularity" because it sounds like "single point".

So they think the cosmologists are telling them that the universe expanded from a single point.

As you know if the universe now has an infinite volume of space then it always did. It began expanding from an already infinite volume. As in your image, with your many boxes.

One of the original meanings of "singularity" is ODDITY. [Sherlock Holmes might say "Watson, do you not find it singular (i.e. odd, abnormal) that the watchdog did not bark on the night of the alleged robbery?"]

In physics, a singularity means a breakdown of a manmade model, anywhere it stops giving meaningful numbers. This does not have to happen only at a single point. A singularity can occur simultaneously throughout a large region.

But when people hear the word "singularity" they think of the universe expanding outward from a single point located somewhere in space. It reinforces the "explosion" mistake.

 

[alexg]

The simple answer is yes, I want to understand whatever makes sense scientifically without doing violence to common sense.

Then I am sorry for you, because the universe does not really respect 'common sense'. Common sense are those things you've learned will happen in a medium small, low-gravity, slow moving realm of the universe. When you get into the very small, and/or high gravity, and/or relativistically moving universe, 'common sense' no longer applies.

So to understand scientifically what's happening in the universe, you have to suspend common sense. It still works fine in it's realm of application, but it doesn't apply very far.

 

[marcus]

So to understand scientifically what's happening in the universe, you have to suspend common sense...

well, it's really off topic for me to argue with you about this. Tex's thread is not really about common sense, that's a side issue.

But I think it's a matter of degree. And people's common sense differs from person to person.

So their common sense restricts people different amounts.

I feel very comfortable with a 3D space that has no edge or boundary, and has a finite volume. I find that commonsensical.

I don't try to imagine it from the outside (it has no surface or surrounding space) I like to imagine it from the inside. Living in such a space, circumnavigating it, shining beams of light in it.

It is commonsense notion for me because the 2D analog is so familiar. The surface of the earth, which is finite area (as the other is finite volume) and has no edge. "Great circle" routes being the "straight lines" because the shortest distance,etc. etc.

But some people's common sense is more restrictive in that department of imagination, more of an impediment. On the other hand there are places where my common sense is undeveloped and handicaps me, where another person might find something intuitive that I don't.

So people differ.

There may be a lot here that Tex eventually will find commonsensical. And of course because it is a mathematical science based on fitting math models to data, there will be plenty more that he will not. But that's to be expected. Just a question of degree.

 

[Fuzzy Logic]

It's a hard concept to understand and visualize let alone convey.

I like to think of the balloon analogy, but instead of all of the cosmos spread across the entire balloon, our universe is a single dot (not a point) on the surface.

Now blow up the balloon a billion times.

We can't see any curvature from our tiny perspective because the balloon is just too big, however our dot of a universe still stretches along with the balloon. From the perspective of our universe it will seem to expand from all directions.

The balloon analogy would suggest that there could be an inside and an outside, which is not true. At least, we don't know of it. If there is, it would be a 5th dimension.

<edit>
It would also suggest that the space-time would not be expanding uniformly. Which is not what we observe. It appears to be uniform expansion everywhere we look.
Being uniform, there's no way for use to tell what direction the expansion is, if there is, so as far as we know there is no center. Any place you go in our universe, it appears to be the center.
</edit>

To help clarify, some people refer to the raisin bread analogy, where the raisins represent matter and the rising bread is space-time, but it still leaves the same implication because I think most people visualize as if they were looking down upon it from the outside. Instead it's better to think of actually being a raisin in that bread. From your perspective, you can't see the boundaries. For all intents and purposes, there is no boundary because as fast as you try to move through the bread, the bread is expanding even faster.

Still, there is another question. If space-time is expanding and we extrapolate back to the beginning the result is that all of matter was extremely dense at one time. This makes one wonder what the universe is in, because if it was once smaller and more dense, then it suggests that the universe is suspended in something. Well it is, it's suspended in space-time!

 

[thetexan]

Well, I don't want to get folks mad or in an argument. I think I still cling to what seems to me to be logical explanations. Clearly, it's gone well beyond intuitive. What I need is a good book that takes a layman and brings into the current theory with something I can understand. I don't think I am illiterate since I have taught college advanced computer programming and and am an air traffic control instructor as well as a former commercial pilot.

So I guess I need help understanding. And I do want to learn this stuff. So thanks for your all's help in advance.

tex

 

[TallyNole]

First, guys this is my first post. I have been reading on here for awhile and the pure amount of information on this website has blown me away. Thank you to all of you for teaching me so much already.

I have a question or two that goes along with Tex's questions so I hope you don't mind me jumping in here.

So I understand the 2D balloon analogy is just a comparison to the universe and not a theory to explain the universe. But I heard on this forum that some study was done (I don't remember the acronym) that showed that the universe was either nearly flat or exactly flat.

If the universe is not flat and had some curve does that mean if you traveled in one direction would you eventually end up in the same place? For example the surface of the balloon can kinda be considered infinite because if you start in one direction you will continue on forever. Even though you will pass over your starting point many times. Is this how an infinite universe can be considered? Or am I way off base here?

If there is no curve to the universe and what I said above is not true (which I suspect it's not) I have a hard time understanding how there can be an infinite universe without a boundary.

Also, could someone try to explain the difference between a positive curve and a negative curve? I've seen that referenced a couple of times but I have no idea what the difference is. Thank you.

 

[marcus]

But I heard on this forum that some study was done (I don't remember the acronym) that showed that the universe was either nearly flat or exactly flat.

If the universe is not flat and had some curve does that mean if you traveled in one direction would you eventually end up in the same place?...

Also, could someone try to explain the difference between a positive curve and a negative curve? I've seen that referenced a couple of times but I have no idea what the difference is...

Thinking in 2D analogy, the surface of a sphere has positive and a saddle surface has negative. The way you measure is draw a triangle (with great circle segments, as if lightrays would follow the surface---shortest distance "geodesics" for the sides of the triangle)

If the angles add up to more than 180 degrees it is positive, like the sphere.
If the angles add up to less, then it is negative curvature, like the saddle. If angles add to exactly 180 then it is zero curvature, i.e. flat. It might for example be an infinite flat plane.

As a pilot, Tex will have no trouble imagining this triangle that adds to 270 instead of 180. Fly east along equator to longitude 0, (I.e. greenwich meridian) then turn left 90 and fly up the longitude line to the north pole then turn left 90 and follow the 90W longitude line back to the equator, finally turn left 90 again and follow equator back to where you started. You have made a triangle and you only turned a total of 270 degrees (three right angles).

On an ideal flat plane going around a triangle involves a total turning of 360 degrees. So another way to express positive curvature is to say there is a DEFICIT ANGLE. It is roughly proportional to the size of the triangle or other figure that you are going around. The larger the triangle (within reason) the larger the deficit. Little triangles have almost no turning deficit because they think they are flat or nearly.

The study you heard about was probably WMAP and they combined a lot of data and got an ERROR BAR around zero for the curvature. Future studies will narrow it further. So far all we know is it could be a little positive or a little bit negative, or exactly zero. But it certainly is nearly zero in any case.

If it turns out to be positive then the most natural model is the 3D analog of a sphere,and the answer to your question is YES you could circumnavigate such a thing as long as it was not expanding. Expansion, if too fast, would defeat your attempt to circumnavigate.

A 3D sphere is sometimes called a 'hypersphere" or a "3-sphere" or "S³". Dont worry about the jargon, it is just the 3D analog of the 2D surface of the Earth or of a balloon. It is considered FINITE volume. It has no boundary.

A finite thing can either have a boundary or not have a boundary.

A finite thing does not have to be immersed in any larger something. It might exist entirely on its own.

The geometry of a thing does not have to be seen from the outside, it can be explored and probed and measured and experienced from the inside by the creatures that live there. This is good because there may not be any outside vantage point. So a lot of geometry is done from an intrinsic perspective. Like going around triangles and other loops and seeing how much you turned.

 

[marcus]

Tex, you have impressive qualifications. Commercial pilot---traffic-control instructor. It makes sense to me that you would not have a hard time learning some modern differential geometry (the geometry of curved surfaces and 3D spaces often as experienced from within by sort of calculus methods.)
I can't say anything for sure but it would not surprise me if you lucked out, found a decent textbook suitable to your needs, and showed up in a few months knowing some differential geometry.

That is the math basis of General Relativity (ask in the Relativity forum what they think is a good entrylevel diff. geom. text. get it from the library, don't buy, in case it is not right for you)

General Relativity is the math basis of cosmology. Except that cosmology is much much simpler because we have approximately evenly distributed matter so that the curvature is approximately uniform, and we have the almost uniform ancient light (called CMB) which is like a kind of navigation aid because it tells you when the universe thinks you are at rest, sitting still with zero Doppler hotspot in your sky, at rest relative to ancient light.

So conceptually cosmology is way easier than GR. However GR is the math basis. cosmology is a simplified special case with extra tools.

I would suggest you start a thread in Relativity forum that just says what is a good entrylevel GR book? Get a moderator's attention. they like to be helpful. Ask if you need some prerequisite diff. geom. or if the GR text is selfcontained. What can you lose? You don't HAVE to take their suggestions but at least you can scope it out that way.

But if you DONT find a book that is right for you, you can still learn quite a lot just by talking with people here in an informal motley un-academic way.

 

[D H]

The simple answer is yes, I want to understand whatever makes sense scientifically without doing violence to common sense.

You have to let go of that common sense to understand quantum mechanics, relativity, or cosmology. Your common sense is a result of repeated experiences in one very, very narrow spectrum of physical interactions. Most people's common sense is markedly Aristotelean. Even Newtonian physics goes against common sense to some extent. The quantum world, the relativistic world, and the universe as a whole are far removed from the experiences that formed the basis for your common sense. Your common sense doesn't apply. It's one of the first things a young physicist has to learn.

You yourself have already had to learn to let go of your common sense. You mentioned that you are a pilot. Flying is anything but intuitive, at least to most people. That's why so much training is needed. There are some situations in flying that completely defy common sense.

In quantum mechanics, relativity, and cosmology, almost everything completely defies your common sense. That doesn't mean it's wrong. It is your common sense that is out of whack. Your common sense is orders of magnitude outside of its range of applicability.

 

[marcus]

Tex,
here is a free 9 page article by a world-class academic James Hartle:
http://arxiv.org/abs/gr-qc/0506075
click on PDF

He gives his thoughts about teaching Gen Rel to undergraduates. How to motivate it, make it real, not abstract.
He lists a bunch of APPLICATIONS of GR that will make it interesting to undergrads. And other people I think.

Hartle has a textbook called "Gravity" that sells for $70. It would be at a local college library in the math or physics section. I'm getting curious. Does he use his own philosophy about applications to make his textbook interesting?

Another essay by a reputable guy that i personally find less interesting, Robert Wald, giving his thoughts about teaching Gen Rel:http://arxiv.org/abs/gr-qc/0511073
He lists and evaluates the available textbooks and gives high marks to Geroch, General Relativity from A to B. This is only $9.50 and has no math. I didn't like what I saw of it. But Wald is a reputable guy and said it is an excellent introduction. He could be right and I wrong. Wald himself also has a GR textbook.

Personally I think Hartle is more creative and has more interesting ideas about how to motivate and explain. I would say forget the Wald article, and forget his Geroch recommendation and I would read the Hartle article and I'm actually tempted (not to buy but) to track down his textbook at some library. I'm curious. Just my personal attitude.

There is a free online textbook by Sean Carroll that some people I've talked to like. I'll get a link.
http://relativity.livingreviews.org/Articles/lrr-2001-1/
This is a short clearly written online COSMOLOGY text. It was written 2001 but has been updated until around 2008, a lot of simple math formulas. Mathy but nothing terribly hard. And anyway its free. You can read it online in HTML or download it PDF. No pictures.
Here is a "no nonsense" short intro to GR and cosmology in 24 pages by Carroll:
http://preposterousuniverse.com/grnotes/grtinypdf.pdf
Here is a 230 page set of lecture notes by Carroll written in 1997
http://arxiv.org/abs/gr-qc/9712019
basically a free GR textbook! He is a talented communicator.

But my mind keeps going back to that 9 page article by Hartle

 

[Chronos]

We have reached the point where it appears new physics is required to answer the remaining 'big questions', IMO. Scientists have never widely accepted the idea that existing knowledge is a 'horizon' on our ability to understand the universe, AFAIK. To paraphrase Sherlock Holmes - the mission of science is to eliminate the impossible. Whatever remains, however improbable, includes the truth - The universe is a cruel, yet irresistable mistress.

 

[Flatland]

If our universe has to have a center it would exist in a higher dimension and not in our 3d space.

Well, I don't want to get folks mad or in an argument. I think I still cling to what seems to me to be logical explanations. Clearly, it's gone well beyond intuitive. What I need is a good book that takes a layman and brings into the current theory with something I can understand. I don't think I am illiterate since I have taught college advanced computer programming and and am an air traffic control instructor as well as a former commercial pilot.

So I guess I need help understanding. And I do want to learn this stuff. So thanks for your all's help in advance.

tex

What exactly are you having trouble understanding?

First, guys this is my first post. I have been reading on here for awhile and the pure amount of information on this website has blown me away. Thank you to all of you for teaching me so much already.

I have a question or two that goes along with Tex's questions so I hope you don't mind me jumping in here.

So I understand the 2D balloon analogy is just a comparison to the universe and not a theory to explain the universe. But I heard on this forum that some study was done (I don't remember the acronym) that showed that the universe was either nearly flat or exactly flat.

If the universe is not flat and had some curve does that mean if you traveled in one direction would you eventually end up in the same place? For example the surface of the balloon can kinda be considered infinite because if you start in one direction you will continue on forever. Even though you will pass over your starting point many times. Is this how an infinite universe can be considered? Or am I way off base here?

If there is no curve to the universe and what I said above is not true (which I suspect it's not) I have a hard time understanding how there can be an infinite universe without a boundary.

Also, could someone try to explain the difference between a positive curve and a negative curve? I've seen that referenced a couple of times but I have no idea what the difference is. Thank you.

Positive curvature would be like the outside surface of a sphere and negative curvature would be like the inside. The angles of a triangle would add up to more than 180º under positive curvature and less than 180º under negative curvature.

 

[marcus]

Positive curvature would be like the outside surface of a sphere and negative curvature would be like the inside. The angles of a triangle would add up to more than 180º under positive curvature and less than 180º under negative curvature.

The bolded thing is not quite right.
The blue thing is right.

 

[Flustered]

I feel like you cannot compare the expansion of the universe to ants on a balloon. Ants can only move across the surface of the balloon. While we can move in 3D in our universe, now if ants could go inside the balloon and travel to the other side (surface). This analogy would fit perfectly. If you blow a balloon up and tie a knot. The center of the balloon will be inside where all the air is. So the balloon analogy doesn't work at all. If there is a center to the balloon that is expanding, there has to be a center to the universe?

Is there any kind of model or video that shows the big bang in very slow motion. Showing how it expanded? If not, why not?
Why can't scientist make a video showing how space doubled in size so many times in so little time?

How can so many people be convinced that nothing existed before the universe? There is absolutely no proof of this at all, but yet so many followers..

 

[Chalnoth]

Positive curvature would be like the outside surface of a sphere and negative curvature would be like the inside. The angles of a triangle would add up to more than 180º under positive curvature and less than 180º under negative curvature.

Just to clarify Marcus' statement, the inside of a sphere has the exact same curvature as the outside. Negative curvature has a different shape entirely: it's more like a saddle.

 

[Chalnoth]

I feel like you cannot compare the expansion of the universe to ants on a balloon. Ants can only move across the surface of the balloon.

Yes, and we can only move in our three dimensions of space.

Anyway, the main point here is that a center is a point of symmetry. It's a unique point in the space where stuff is the same in basically every direction from it. The Sun, for example, is a reasonable center for our solar system because if we choose it as our center, the rest of the solar system moves around it. If you're near the Earth, then the center of the Earth makes for a good center for most things. If you're talking about our galaxy, well, that's got a center too: Sagittarius A*.

What makes all of these important is they are points of symmetry: the galaxy, or the solar system, or the Earth all look very similar if you rotate those respective systems around those centers. The universe as a whole has no such unique point of symmetry. Instead, you can rotate the entire universe all you like around any point and it will, more or less, look the same. There simply isn't any unique point of symmetry for the whole universe.

 

[Flustered]

Yes, and we can only move in our three dimensions of space.

Anyway, the main point here is that a center is a point of symmetry. It's a unique point in the space where stuff is the same in basically every direction from it. The Sun, for example, is a reasonable center for our solar system because if we choose it as our center, the rest of the solar system moves around it. If you're near the Earth, then the center of the Earth makes for a good center for most things. If you're talking about our galaxy, well, that's got a center too: Sagittarius A*.

What makes all of these important is they are points of symmetry: the galaxy, or the solar system, or the Earth all look very similar if you rotate those respective systems around those centers. The universe as a whole has no such unique point of symmetry. Instead, you can rotate the entire universe all you like around any point and it will, more or less, look the same. There simply isn't any unique point of symmetry for the whole universe.

Yes we can move in 3d, a balloon is 3d. Ants are moving 2d on a 3d object. How does that correspond to our 3d universe? Unless you are implying that our 3d is on a face of a 4d object. I'm not talking about time.

 

[minio]

But our universe is at least 4d object. And I am talking about time.

 

[Chalnoth]

Yes we can move in 3d, a balloon is 3d. Ants are moving 2d on a 3d object. How does that correspond to our 3d universe? Unless you are implying that our 3d is on a face of a 4d object. I'm not talking about time.

Obviously the analogy isn't perfect. No analogy is. That's why they're called analogies. But it works if you note that the ants are moving in two dimensions on a two dimensional surface. It's a two-dimensional analogy for a three-dimensional phenomenon. If you try to talk about the third dimension in the balloon analogy, you're focusing in on the point where the analogy breaks down: it only works if you only consider it as a two-dimensional analogy and nothing more than that, with the third dimension only there for visualization purposes.

 

[Flatland]

Yes we can move in 3d, a balloon is 3d. Ants are moving 2d on a 3d object. How does that correspond to our 3d universe? Unless you are implying that our 3d is on a face of a 4d object. I'm not talking about time.

You can think of our universe as the 3d "surface" of a 4d sphere. That's what the balloon analogy is trying to convey.

 

[DaveC426913]

You can think of our universe as the 3d "surface" of a 4d sphere. That's what the balloon analogy is trying to convey.

It is important to recognize though that it is just an analogy. It does not require the existence of a 4th dimension in order for the 3D universe to have this curvature. i.e. the curvature we see is not evidence of the existence of a 4th dimension.

 

[thetexan]

It seems that my sticking point is going from the 'common sense' idea of the universe being a big loaf of baked bread to only a surface of a sphere or a flat or near flat surface. If I just accept the surface idea then I have no problem understanding the other points. Maybe someone can help me to understand that model. Or better stated, at one point decades ago the big 3 dimensional loaf of bread idea must have been the popular idea. Then, at some point, scientists said 'no, even though that seems common sensical, here is some evidence that points to the idea that the universe is curved...or flat...or whatever' and then that seemed correct. Please help me understand that transition and maybe it will help me see all of this.

tex

 

[marcus]

In cosmology when people say "flat" they mean zero curvature. This can be with 3D space as well as the more familier 2D examples.
What would be an example of UN-flat in the 3D case? Well you would know that you were living in an Un-flat region of 3D space if when you measured the angles of a triangle you kept getting different from 180 degrees.

In a NON-flat 3D region, the bigger the triangle the more noticeable the discrepancy.The bread analogy came into use as a picture of expansion. Popular science writers would talk about RAISIN BREAD DOUGH RISING. The raisins were the galaxies and they were getting farther apart.

An important part of that picture was that the dough was infinitely big. The loaf had no boundary. If you didn't get that detail then you missed an important part of the story.

The rising unbaked bread-dough analogy is still used in popular accounts. We sometimes use it here. You seem to have gotten the notion that things have changed because you used to hear the bread dough analogy and now you hear the word "flat". That doesn't represent a change---the messages are consistent.

The raisin bread-dough analogy actually depicts the case we call "flat". That is infinite volume 3D space with zero curvature where, for example, the angles of a triangle always add up to 180.

 

[voxilla]

If a 2D balloon surface makes sense for a 3D thing, wouldn't make an explosion make even more sense ?

 

[Chalnoth]

If a 2D balloon surface makes sense for a 3D thing, wouldn't make an explosion make even more sense ?

The problem is that explosions are messy. Really messy. Here's some cool high-speed videos of some explosions:


By contrast, the early universe was extraordinarily smooth and uniform, only becoming more clumpy much later on due to the gravitational attraction of matter.

 

[voxilla]

No need to tell me about explosions see my site

 

[Flustered]

Can someone post a picture of a geometric shape that they believe the universe most likely resembles. I heard some cosmologist say that they think the universe is like a soccer ball, and it's looped in on its self.

 

[Chalnoth]

Can someone post a picture of a geometric shape that they believe the universe most likely resembles. I heard some cosmologist say that they think the universe is like a soccer ball, and it's looped in on its self.

Unfortunately, there really isn't any way to say.

Imagine the soccer ball, for example. If our universe happens to be of that shape, then the part of it that we can see is only a teeny tiny fraction of one of the little sections of the ball. So even if the overall shape is rather like a soccer ball, the fact that we can only see this itsy bitsy bit of it means that it would be extremely hard, if not impossible, to ever actually show that it genuinely is that shape.

Our best bet of finding the overall shape, if it is possible at all, is to demonstrate that the start of our universe had to happen in a certain way. It may be (but it is absolutely not guaranteed!) that this kind of start tends to occur with a particular shape. So we may be able to indirectly deduce that our universe is probably of that shape, though we're not anywhere close to that kind of indirect deduction yet. Even then, finding direct evidence will always be hard if not impossible.

 

[Flustered]

Unfortunately, there really isn't any way to say.

Imagine the soccer ball, for example. If our universe happens to be of that shape, then the part of it that we can see is only a teeny tiny fraction of one of the little sections of the ball. So even if the overall shape is rather like a soccer ball, the fact that we can only see this itsy bitsy bit of it means that it would be extremely hard, if not impossible, to ever actually show that it genuinely is that shape.

Our best bet of finding the overall shape, if it is possible at all, is to demonstrate that the start of our universe had to happen in a certain way. It may be (but it is absolutely not guaranteed!) that this kind of start tends to occur with a particular shape. So we may be able to indirectly deduce that our universe is probably of that shape, though we're not anywhere close to that kind of indirect deduction yet. Even then, finding direct evidence will always be hard if not impossible.

Why is it a forgone conclusion that the universe has no edge to it, when we cannot see outside our own observable section? To say there is no edge is absurd in my opinion because our vision it limited.