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The universe could possibly wrap back onto itself, or it could be in infinite flat space. Imagine the difference between being on an infinite plane, or on the surface of a large sphere. In both o...
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#2: Post edited
by
Olin Lathrop
·
2021-08-08T12:54:21Z (over 2 years ago)
- The universe could possibly wrap back onto itself, or it could be in infinite <i>flat</i> space.
Imagine the difference between being on an infinite plane, or on the surface of a large sphere. In both of these 2D worlds, the universe would appear to extend infinitely in all directions. Yes, in the sphere case you would eventually see yourself. But we assume the sphere is so large that this is either impractical, or light hasn't had time to go all the way around yet.- Now imagine this happening on the surface of a 4D sphere. That "surface" would be a 3D space, not the 2D space on a 3D sphere as above. The astronomers looking in all directions can't tell whether they are stuck on the surface of a 4D sphere, or in a <i>flat</i> (not wrapped) 3D space. There are other possible topologies too. At present, we just don't know which case we are in.
- The universe could possibly wrap back onto itself, or it could be in infinite <i>flat</i> space.
- Imagine the difference between being on an infinite plane, or on the surface of a large sphere. In both of these 2D worlds, the universe would appear to extend infinitely in all directions. Yes, in the sphere case you would eventually see yourself. But we assume the sphere is so large that this is either impractical, unrecognizable, or light hasn't had time to go all the way around yet.
- Now imagine this happening on the surface of a 4D sphere. That "surface" would be a 3D space, not the 2D space on a 3D sphere as above. The astronomers looking in all directions can't tell whether they are stuck on the surface of a 4D sphere, or in a <i>flat</i> (not wrapped) 3D space. There are other possible topologies too. At present, we just don't know which case we are in.
#1: Initial revision
by
Olin Lathrop
·
2021-08-08T12:53:14Z (over 2 years ago)
The universe could possibly wrap back onto itself, or it could be in infinite <i>flat</i> space. Imagine the difference between being on an infinite plane, or on the surface of a large sphere. In both of these 2D worlds, the universe would appear to extend infinitely in all directions. Yes, in the sphere case you would eventually see yourself. But we assume the sphere is so large that this is either impractical, or light hasn't had time to go all the way around yet. Now imagine this happening on the surface of a 4D sphere. That "surface" would be a 3D space, not the 2D space on a 3D sphere as above. The astronomers looking in all directions can't tell whether they are stuck on the surface of a 4D sphere, or in a <i>flat</i> (not wrapped) 3D space. There are other possible topologies too. At present, we just don't know which case we are in.