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Originally Posted by d*d
That renders the ballon analogy useless
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How so?
Take a balloon. Make it larger and larger.
Notice how the surface gets more and more flat. You can see this yourself by drawing larger and larger circles, then looking at a small piece of the edge -- as the circle gets larger, 1 cm of the circle's edge gets flatter and flatter.
After you make it really large and nearly flat at any one point, you can still expand it. And, if you are standing on the balloon, the expansion just makes things move away from each other -- it gets to the point where you can't tell the balloon is curved, and all you can see is a locally flat area 'expanding'.
Now imagine it was so flat, it extended off to infinity in all directions. Perfectly flat, not just 'close to flat'. Locally, a really really big balloon and a infinitely flat plane look identical, so locally everything looks the same.
A flat plane is the surface of a balloon grown to infinite size. =)
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The problem with this analogy is that there is a centre to the expansion described, this is not the case with the universe.
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There is a center? Well, there is where you are looking at the plane.
If you are at a point, you see the grid expanding away from you. So you think "oh, I must be at the centre".
Now, lets say you move somewhere else. Surprisingly, you see
exactly the same thing -- everything moves twice as far away from you, and it looks like you are at the centre!
No matter where you are on the infinite plane, when it expands by a factor of two, it looks like you are at the centre of the plane.
This is just like how the universe looks like to us. When we look out into space, we see everything expanding away from
us. In reality, everything is just moving away from everything, so there is no centre. The same thing happens on the infinite plane with a grid drawn on it.
There is no frame of reference other than the grid. All perception is anchored at a point on this grid -- as far as someone can tell, wherever they are on the grid looks stationary, everything else is what is moving.