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

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

__________________
I'm tired of being enclosed here. I'm wearying to escape into that glorious world, and to be always there: not seeing it dimly through tears: but really with it, and in it. I shall be incomparably beyond and above you all.

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?

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?

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.

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.

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.

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.

__________________
Lighten up! This is a stellar board! Author: duh.

"The Sun, with all the planets revolving around it, and depending on it, can still ripen a bunch of grapes as though it had nothing else in the universe to do..." Author: Galileo supposedly.

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.

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.

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.

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

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.

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.

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.

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.

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.

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.

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.