the Cosmological Principle

[brianok]

"The Cosmological Principle states that at any instant, over large enough dis-tances, the universe is both isotropic (the same in every direction) and homogeneous (the same at every location)."
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So if I look at a quasar 10 billion light years away, someone living now near that quasar can look opposite from my direction and see a quasar 10 billion light years away, and so on and so on.

Something is wrong here--or is this where the curvature of the universe come into play?

[HenrikOlsen]

The principle is about large scale similarities, ie. same density of stars, same distribution of types of stars, not about local variations.
Whether a quasar is in a specific spot is a matter of local variation, but if you meant to say that if we look 10 billion lightyears away and see about 1 quasar every million cubic light years, then the people there can look here and see the same distribution, then you'd be right.

BTW, my numbers are made up for the purpose of this exercise and is not likely to have any resemblence to any known universe.

[mantiss]

"The Cosmological Principle states that at any instant, over large enough dis-tances, the universe is both isotropic (the same in every direction) and homogeneous (the same at every location)."
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So if I look at a quasar 10 billion light years away, someone living now near that quasar can look opposite from my direction and see a quasar 10 billion light years away, and so on and so on.

Something is wrong here--or is this where the curvature of the universe come into play?

I don't see anything wrong once you consider the timelines, that quasar 10 billion ly away is as it was 10 billion years ago. From it's viewpoint "Today" our part of the universe is just also 10 billion years old.

[brianok]

I am talking about looking in the opposite direction from us and seeing a quasar 10 billion light years away, and someone on that quasar looking in the same direction and seeing one---ad infinitum

[alainprice]

Observable universe and actual size are 2 different things. Look back 13.7 billion years and you will see the primordial universe.

Assuming inflation was faster than light, it becomes a question of how much faster and for how long?

[Blob]

Hum,
it would be quite strange if we were to look out from the bigbang and see our earth...er...

[Ken G]

I am talking about looking in the opposite direction from us and seeing a quasar 10 billion light years away, and someone on that quasar looking in the same direction and seeing one---ad infinitum

Why is there something wrong with this ad infinitum situation? I would rather be more bothered by a significant deviation from that situation. Note that if the universe is spatially infinite, then there's no paradox, and if it is finite, then it is believed to have to wrap around on itself, so eventually you'd come back to where you started and would just be repeating the same steps over and over. Perhaps your issue is what is happening with time. Remember that the cosmological principle only applies at a given age of the universe, so each time you take one of your steps, you have to reset the clock to the current age of 13.7 billion years old. Thus there is never still any quasars at the points where your observers are, as mantiss was saying.