Universe Expansion

[earthman2110]

I cant seem to understand how we can look to the edges of our universe and see things that happened billions of years ago. I understand that the universe is expanding at an increasing rate, and that nothing can travel faster than light. If everything is expanding away from a fixed point, wouldnt we (our galaxy) have to be traveling as fast as light to be able to look back toward that point and see what happened? In other words, wouldnt the light traveling from the beginning of our universe have already passed us? Any response will help. Thanks

[§rv]

that's always been something I never understood myself......

[rwald]

I tried to answer this question, and then I realized that I didn't entirely know the answer myself. I've got a related question, though: When we say that a given galaxy/quasar/whatever is X meters away from us, is that how far away it is now, or how far away it was when it emitted the light that we now see? Or do such distinctions not make sense in a relativistic universe?

[earthman2110]

rwald, that is a great question. it makes no sense to me either, but i suppose that it must measure the distance from us that the source of light was when it gave off the light. right?

[rwald]

My guess is that the question "How far away is such-and-such galaxy now?" doesn't really have meaning, because for all we know such-and-such galaxy was swallowed by a black hole centuries ago. All we can really tell is what was happening when it last emitted light that we now see.

However, that makes me even more uncomfortable about your question: If we see a quasar (or whatever) 10 billion light-years away, does that mean that 10 billion years ago (only 3.7 billion years after the Big Bang), the universe was already 10 billion light-years across? One possible resolution to this would be if the universe were infinte spacially, but I'm not sure if that's the right answer.

[Ian Goddard]

If everything is expanding away from a fixed point [...]

But that "if" is not the case in the prevailing Big Bang model known as the Inflation Theory. According to Inflation there is no center of expansion. Imagine a checker board, or metric, spread across all space with every box therein expanding, or inflating -- there is no center of the expansion since the expansion is happening everywhere. Everything is expanding away from every point, not from one central point.

[Sam5]

Imagine a checker board, or metric, spread across all space with every box therein expanding, or inflating -- there is no center of the expansion since the expansion is happening everywhere.

The center of the expansion is the center of the checker board.

[Ian Goddard]

Imagine a checker board, or metric, spread across all space with every box therein expanding, or inflating -- there is no center of the expansion since the expansion is happening everywhere.

The center of the expansion is the center of the checker board.

No it isn't. If a set of points placed at the intersections on a square grid around a central point expand uniquely from that central point n distance per unit of time, the grid structure initially defined by those points will not be maintained (get some graph paper and see). On the other hand, what I described is the case where the points expand apart and the grid structure is maintained, and in that case there is no center of expansion; the expansion behavior favors no point.

[George]

Well, if we are going to talk about the center, maybe we should talk about the edge. I wouldn't want to be only half confussed.

Would it be kinda like going to the edge of Earth? Not possible. However, I have talked to some in West Texas who claim they can see it from out there.

[Sam5]

No it isn't. If a set of points placed at the intersections on a square grid around a central point expand uniquely from that central point n distance per unit of time, the grid structure initially defined by those points will not be maintained (get some graph paper and see). On the other hand, what I described is the case where the points expand apart and the grid structure is maintained, and in that case there is no center of expansion; the expansion behavior favors no point.

What you are talking about is a big flat expanding Euclidean plane. What you’ve described still has a center.

If you turn it into 3-D, you’ve got a big expanding cube, with sharp edges on the outside and eight corner points. Even an expanding cube has a center.

If you use polar graph paper, the graph paper still has a center.

[rwald]

If I'm not mistaken, the more popular theory is that the universe in infinite in size. If that were the case, then there would be no edge, and no conceptual problem. The alternative, that the universe is finite in size, would be resolved in almost the same way that flat-Earth theory was: the left edge would wrap around to the right edge, and the top edge would wrap around to the bottom edge (making a torus, not a sphere, but you get the idea). Actually, the shape of the universe wouldn't necessarily need to be a torus (especially because it's got an extra dimension), but that's probably the easiest to visualize.

[Ian Goddard]

If a set of points placed at the intersections on a square grid around a central point expand uniquely from that central point n distance per unit of time, the grid structure initially defined by those points will not be maintained (get some graph paper and see). On the other hand, what I described is the case where the points expand apart and the grid structure is maintained, and in that case there is no center of expansion; the expansion behavior favors no point.

What you are talking about is a big flat expanding Euclidean plane. What you’ve described still has a center.

If you turn it into 3-D, you’ve got a big expanding cube, with sharp edges on the outside and eight corner points. Even an expanding cube has a center.

If you use polar graph paper, the graph paper still has a center.

Actually only you've stipulated known edges. And you've switched your counter from saying an expanding finite space must have a "center of expansion" to the irrefutable "it must have a center" -- as if that counters something I said. I believe my last reply provides an actual definition for your initial counter about a center of expansion that differentiates such from no center of expansion.

[Sam5]

Actually only you've stipulated known edges. And you've switched your counter from saying an expanding finite space must have a "center of expansion" to the irrefutable "it must have a center" -- as if that counters something I said. I believe my last reply provides an actual definition for your initial counter about a center of expansion that differentiates such from no center of expansion.

Your counter merely has a circular expansion on a checkerboard of squares or on a sheet of Euclidean-square graph paper. In either of those cases, the expansion has a center.

You stipulated the edges by referring to a “checkerboard”. I don’t know if the universe has edges or not.

[Sam5]

If I'm not mistaken, the more popular theory is that the universe in infinite in size. If that were the case, then there would be no edge, and no conceptual problem. The alternative, that the universe is finite in size, would be resolved in almost the same way that flat-Earth theory was: the left edge would wrap around to the right edge, and the top edge would wrap around to the bottom edge (making a torus, not a sphere, but you get the idea). Actually, the shape of the universe wouldn't necessarily need to be a torus (especially because it's got an extra dimension), but that's probably the easiest to visualize.

Hey, your guess is just as good as mine, and in fact it is just as good as anyone else's.

[Normandy6644]

As far as the whole "center" argument is concerned, if you have expansion in infinite direction, then every point becomes the center. This appears to be more or less what is observed.

Also, it is useful to think of distant objects not as far away in just distance or just time, but rather both. This is where spacetime comes in. It is difficult to grasp conceptually since our minds can only conceive of certain sizes. In the end we're just measuring from our own frame of reference, and so spacetime looks as though it's centered on us, when in fact it's centered on everything.

[Ian Goddard]

Actually only you've stipulated known edges. And you've switched your counter from saying an expanding finite space must have a "center of expansion" to the irrefutable "it must have a center" -- as if that counters something I said. I believe my last reply provides an actual definition for your initial counter about a center of expansion that differentiates such from no center of expansion.

Your counter merely has a circular expansion on a checkerboard of squares or on a sheet of Euclidean-square graph paper. In either of those cases, the expansion has a center.

I disagree and believe only one of the two expansion models I've defined above comports to a "center of expansion." Just because an object has a center does not mean it can only exapand from its center.

You stipulated the edges by referring to a “checkerboard”. I don’t know if the universe has edges or not.

Not really, I said: "Imagine a checker board, or metric, spread across all space..." That onto which the checker-board metric is being mapped is "all space," and the edges of all space are unknown.

[russ_watters]

"Imagine a checker board, or metric, spread across all space..." That onto which the checker-board metric is being mapped is "all space," and the edges of all space are unknown.

This is why I prefer the expanding balloon analogy. The checkerboard analogy requires an infinite space: the expanding balloon is finite.

If you're on the surface of an expanding balloon (2d surface expanding in 3d), as it expands, objects move away faster the further they are away from you. You appear to be the center, but every other point on the balloon can say the same thing. It also makes it possible to travel around the balloon and get back where you started - an interesting possibility for 3d space.

So, regardless of whether the universe is finite or infinite, there still isn't a center.

[Ian Goddard]

"Imagine a checker board, or metric, spread across all space..." That onto which the checker-board metric is being mapped is "all space," and the edges of all space are unknown.

This is why I prefer the expanding balloon analogy. The checkerboard analogy requires an infinite space: the expanding balloon is finite.

Yes, that's a common analogy, and so is showing an inflating grid metric. And even in the case of a grid with known edges (such as a checker board) there can be noncentral expansion. In short, there are two things at hand: (1) a center of an area and (2) a center of an expansion. If there is 1 and expansion is occurring, there is not necessarily 2. If a whole object uniformly inflates where each subregion inflates to the same degree as all others, the inflation has no center, ie, no point on the object around which or from which the inflation is uniquely radiating -- the inflation is originating from everywhere in the object.

Such noncentral expansion of a finite object is differentiable from central expansion, which defines a unique center point around and from which expansion radiates. I defined such above in this statement: "If a set of points placed at the intersections on a square grid around a central point expand uniquely from that central point n distance per unit of time, the grid structure initially defined by those points will not be maintained (get some graph paper and see)." On the other hand, noncentral expansion is the case where the grid structure is maintained, in which case there is no unique point in the object that can be defined as the center of the expansion even as the object has a center.

[Sam5]

I disagree and believe only one of the two expansion models I've defined above comports to a "center of expansion." Just because an object has a center does not mean it can only exapand from its center.
snip

Not really, I said: "Imagine a checker board, or metric, spread across all space..." That onto which the checker-board metric is being mapped is "all space," and the edges of all space are unknown.

Yes, but the edges of a checker board are known, and they are straight. The center of a checker board is also known, and it is at an equal distance from all 4 corners.

Even if you try to expand the edges of a checker board so large we can’t see the edges, your defining it as a “checker board” tells us what its edges look like. Trying to hide the edges by putting them at a great distance does not do away with the "checker board's" center.

[Sam5]

This is why I prefer the expanding balloon analogy. The checkerboard analogy requires an infinite space: the expanding balloon is finite.

If you're on the surface of an expanding balloon (2d surface expanding in 3d), as it expands, objects move away faster the further they are away from you. You appear to be the center, but every other point on the balloon can say the same thing. It also makes it possible to travel around the balloon and get back where you started - an interesting possibility for 3d space.

So, regardless of whether the universe is finite or infinite, there still isn't a center.

You don't know if there is a center or not.

We do not live on the surface of a balloon. We do not live on the “surface” of our universe. Our universe is 3-D plus time and seems to be expanding outwards. If this is a Euclidean expansion, and if you run the expansion backward, that will show you where the center is.

[Ian Goddard]

Not really, I said: "Imagine a checker board, or metric, spread across all space..." That onto which the checker-board metric is being mapped is "all space," and the edges of all space are unknown.

Yes, but the edges of a checker board are known, and they are straight. The center of a checker board is also known, and it is at an equal distance from all 4 corners.

Even if you try to expand the edges of a checker board so large we can’t see the edges, your defining it as a “checker board” tells us what its edges look like. Trying to hide the edges by putting them at a great distance does not do away with the "checker board's" center.

It should be obvious that the purpose of saying "checker board" was not to talk about a checker board but to transmit a mental picture of space marked off with a square-grid metric. The statement, "Imagine a checker board, or metric, spread across all space" designates the metric, or square-grid pattern, as the issue. The use of "or" in this fashion is not exclusive but means "in other words" as a standard. The fact that I could meaningfully say "Imagine a checker-board metric across an infinite space," shows that edges are not necessarily indicated, especially if something without known edges like "all space" has been indicated as the topic of focus.

But this of course is totally superfluous. The counter you initially raised against my response to the poster was that any expanding finite region has a center of expansion because it has a center, which I believe I debunked.

[russ_watters]

And even in the case of a grid with known edges (such as a checker board) there can be noncentral expansion. In short, there are two things at hand: (1) a center of an area and (2) a center of an expansion. If there is 1 and expansion is occurring, there is not necessarily 2. If a whole object uniformly inflates where each subregion inflates to the same degree as all others, the inflation has no center, ie, no point on the object around which or from which the inflation is uniquely radiating -- the inflation is originating from everywhere in the object.

Good point. I hadn't thought of that (then again, it was 3am).

[Sam5]

Good point. I hadn't thought of that (then again, it was 3am).

Hey, are you going to tell us how “the expansion of space” works?

Does “old space” stretch, or is “new space” added to the old space? Tell us how that works.

[Sam5]

The counter you initially raised against my response to the poster was that any expanding finite region has a center of expansion because it has a center, which I believe I debunked.

You haven’t debunked anything, and neither you nor I know what’s beyond our visible limits or whether the universe has a “center” or not. If it is infinite, it most likely doesn’t have a center. But if it’s finite, it most likely does.

This is the very same question that confronted Newton 350 years ago, and nobody knows the answer to it.

[Ian Goddard]

The counter you initially raised against my response to the poster was that any expanding finite region has a center of expansion because it has a center, which I believe I debunked.

You haven’t debunked anything, and neither you nor I know what’s beyond our visible limits or whether the universe has a “center” or not. If it is infinite, it most likely doesn’t have a center. But if it’s finite, it most likely does.

This is the very same question that confronted Newton 350 years ago, and nobody knows the answer to it.

Once again you've switched the issue, this time from "Can a finite expanding object with known edges expand without a center of expansion?" to "Does the universe have a center?" I claimed to debunk your view on the former, not any view on the latter. So you counter a straw man.

[ZaphodBeeblebrox]

Good point. I hadn't thought of that (then again, it was 3am).

Hey, are you going to tell us how “the expansion of space” works?

Does “old space” stretch, or is “new space” added to the old space? Tell us how that works.

Perhaps a Graphic will work.

*=*=*
| | |
*=*=*
| | |
*=*=*

Now, I shall expand it, first just Exponentially from the Center Point:

*====       ====*
|               |
 |      *      |
  |     |     |
   |    |    |
   *==  *  ==*
   |    |    |
  |     |     |
 |      *      |
|               |
*====       ====*

Notice how our nifty little Metric, broke down.

Now, for a Uniform Expansion, from each and every one of the Grid Points:

*=*=*
| | |
*=*=*
| | |
*=*=*

*==*==*
|  |  |
|  |  |
*==*==*
|  |  |
|  |  |
*==*==*

*====*====*
|    |    |
|    |    |
|    |    |
|    |    |
*====*====*
|    |    |
|    |    |
|    |    |
|    |    |
*====*====*

A Truly Beautiful Grid, huh?

And all because of Universal Expansion.

[Ian Goddard]

Thanks Zaphod! That's the point I was trying to get across. Noncentral expansion can occur even over a finite region with a known center.

[ZaphodBeeblebrox]

Thanks Zaphod! That's the point I was trying to get across. Noncentral expansion can occur even over a finite region with a known center.

No Problem!

It was Fun!

And doesn't the Exploded Metric like kind of like an Hour Glass, or maybe even a Butterfly, what an Effect to See!

[Sam5]

Good point. I hadn't thought of that (then again, it was 3am).

Hey, are you going to tell us how “the expansion of space” works?

Does “old space” stretch, or is “new space” added to the old space? Tell us how that works.

Perhaps a Graphic will work.

You haven’t “expanded space”. Your last white background page is just as wide as your first one. My computer screen didn’t “expand”. All you did was add some extra = = = characters with your keyboard. What do you think we in the “general public” are, a bunch of idiots?

Stop conning us and give us a FULL SCIENTIFIC explanation of how “space expands”.

[Sam5]

Thanks Zaphod! That's the point I was trying to get across. Noncentral expansion can occur even over a finite region with a known center.

Hey, all he did was add a few of these: = = = with his keyboard. Do you think I fell off the turnip truck just last week?