[Arp220]

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we are at the center of the *observable* universe.

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Okay, keep helping me through this conceptual block I'm having.

Posit an observer way out there, say 200 BLY from our universe neighborhood. And let's ignore the complication that it takes awhile for our light to reach the observer.

The observer looks, and sees odd happenings over there -- an expanding bunch of hot specks.

From a god's eye point of view, isn't our observable universe an expanding globe? What am I missing?


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Youre not necessarily missing anything [img]/images/graemlins/wink.gif[/img]

We, unfortunately, do not have a 'gods eye' point of view. If we did we might see many things.

Heres an example:

One way to visualize the expansion of the universe is to take a balloon, paint lots of tiny specks on the balloon, and then gradually blow it up. If you, as 'god', look at the balloon, you see all the points expanding away from each other. You see a 3 dimensional object (the balloon) expanding into a 3 dimensional space (the room youre in).

Ok, now lets change our point of view. The surface of the balloon, with all the galaxies on it, is effectively a two dimensional object (lets ignore the thickness of the balloon for now) that is 'curved' in a three dimensional space. So, now imagine you are a TWO dimensional resident of one of those little dots on the balloons surface. You look at all the other dots, expanding away from you in all directions. From your point of view, you are at the center of the observable universe, but you cannot identify an 'absolute' point from which everything is expanding away. Because, if you went and lived in another dot, you'd see everything expanding away from that dot.

Many people see this example and conclude that the expansion is simple - we are three dimensional, but the universe is expanding 'into' a fourth spatial dimension. This is however not accurate. If this was the case we would see some very clear indicators from particle physics, but we do not.

So, the ultimate answer to your question is that nobody really understands the fundamentals behind the expansion of the universe. We see that it is expanding. We see that it is not expanding into a bigger volume. We have evidence that the expansion is not due to a simple increase in the number of spatial dimensions.

So we're still trying to find out what exactly is going on.