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I'm not sure if this is the correct stackexchange site for this question.

I've been reading this article on Vice Motherboard There’s Growing Evidence That the Universe Is Connected by Giant Structures which while admittedly simplified for simpler folk like me put me wondering:

Is it at all possible that when we look out in to the distant universe in one direction, we are seeing the same galaxies and stars at a different point in time than if we look out in another direction? Could this occur if the distant body is moving laterally at a fast enough velocity relative to our position, or if the shape of the universe itself loops around?

Or is this not a proper interpretation of current theories of cosmology?

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  • $\begingroup$ I would not recommend using Vice as a source of any authentic science. $\endgroup$ – Carl Witthoft Nov 12 '19 at 18:44
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    $\begingroup$ Not suggesting it is! Just put me thinking about my question is all. They don't posit that in the article $\endgroup$ – beirtipol Nov 12 '19 at 20:58
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Could this occur if the distant body is moving laterally at a fast enough velocity relative to our position

Nope. I mean if the universe is flat it doesnt matter how fast the object goes you cannot see it twice in the sky.

or if the shape of the universe itself loops around?

Yes. If the universe has a positive curvature. When we look at the sky, we can see the same object in two opposite directions.

In our universe this is not possible since if the universe is positively curved then the radius of curvature is much larger then the size of the observable universe. So its highly unlikely that we will see the same object in two different positions in the sky.

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In principle, the universe could be geometrically flat (as the evidence indicates) and still "wrap around" as you describe. In the old game Asteroids, when you went off one edge of the screen, you came back in the opposite edge. That is the topology of a torus, but geometrically the screen is flat. There is no mathematical reason the universe could not be like this in its three spatial dimensions. The book The Shape of Space by Jeffrey Weeks discusses this possibility.

I think most cosmologists consider this so unlikely that it's not worth investigating, but I believe some people have reviewed existing data to see if there are statistical patterns in galaxy distribution that would indicate this kind of "closed manifold" structure. They didn't find anything.

So it looks like the answer is No - all the galaxies we see are different.

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