
If You Traveled Far Enough Through Space, Would You Return to Your Start Point? - rising-sky
https://www.forbes.com/sites/startswithabang/2018/10/12/if-you-traveled-far-enough-through-space-would-you-return-to-your-starting-point/
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scottmsul
In cosmology, there's a parameter called "curvature". If the curvature were
slightly less than 1, the topology would be "closed", meaning it would be
finite, and traveling in a straight line ends back where you started. This is
like the surface of the Earth, but in 3 dimensions instead of 2. Triangle
angles add up to greater than 180 degrees. If the curvature were equal to 1,
the universe would be "flat", meaning it would be infinite and triangles would
add up to 180. If the curvature were greater than 1, it would be "hyperbolic",
meaning it would be infinite and triangles would add up to less than 180.

If I recall correctly, currently the best measurement of the curvature is 1
+/\- .02, so it's probably flat. What's interesting is if the shape was flat
and the universe were truly infinite, there would be an infinite number of
perfect copies of Earth, the closest of which would be within 10^10^23 meters,
as noted by Max Tegmark (source:
[http://space.mit.edu/home/tegmark/crazy.html](http://space.mit.edu/home/tegmark/crazy.html))

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317070
Think about a torus-chess-board [0]. While it is locally flat, it is finite,
unbounded and you would travel back where you started. Curvature cannot give a
sound argument as to whether the universe is finite or infinite.

[0]
[https://en.wikipedia.org/wiki/Cylinder_chess#Horizontal_Cyli...](https://en.wikipedia.org/wiki/Cylinder_chess#Horizontal_Cylinder_chess_and_Toroidal_chess)

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badosu
The better term related to curvature would be if it's bounded or unbounded.

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joh6nn
Per Brock et al, 2000, yes: the universe is shaped exactly like the Earth. If
you go straight long enough, you'll end up where you were.

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317070
Do you have a link? I cannot find your reference.

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libertymcateer
[https://www.youtube.com/watch?v=yGxSExvJ2L0](https://www.youtube.com/watch?v=yGxSExvJ2L0)

"The Universe is shaped exactly like the Earth, if you go straight long
enough, you'll end up where you were."

Isaac Brock is the lead singer of Modest Mouse.

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IIAOPSW
No.

If you could there would be a few galaxies which would be about equidistant
from us along both paths. Therefore we would notice a few double copies of the
same galaxies. It would be similar to standing in the middle of two mirrors.
IIRC scientists have already ruled out a universe with a "radius" less than
some ridiculous number (like billions of light years).

There. Just saved you a click. This is old and well know. Why is Forbes
writing about it now?

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heavenlyblue
Nope. Our visible universe is bounded by the expansion of space that happens
at the speed of light. That means we can only see a subset of the universe at
any time.

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ikeboy
But if you travel at less than the speed of light you'd never pass that anyway

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PopeDotNinja
If you traveled at the speed of light, you'd still never make it to the edge
of the universe. The edge of the observable universe is moving away from us
faster than the speed of light. [1]

[1]
[https://en.wikipedia.org/wiki/Observable_universe](https://en.wikipedia.org/wiki/Observable_universe)

