Why would it only expand in one plane not every direction like you’d expect?
Also how is a flat universe even possible? Surely since we live in 3 dimensions the universe needs to be a 3 dimensional shape.
Im probably misunderstanding what physicists are trying to say but that’s why im here.
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It’s flat vs spherical in a 3D sense not in a 2D sense. So if it’s spherical, then it’s not a “ball” like the way you would imagine a soccer ball (that’s a 2D ball in a 3D world), but rather a 3D ball in a 4D world.
Basically, if the universe were spherical (in that definition), it means you can go from one point, travel in a straight line and after a long time get back to where you were but from the opposite direction. No you’re not going to run into a “wall” (the edge of the universe) because there’s no such thing. That’s the over-simplification, because of course “straight” line itself is a tricky thing when you have gravity around you (remember gravity bends spacetime itself so your straight line actually is affected by galaxies and blackholes). Also how do you know you get back to the same point, because by that time the Earth will have moved around to a different place.
Anyways that’s the gist, you can travel to one direction and get back from the other direction, that’s what “spherical” means.
If it’s flat, then you can travel to one direction and go forever and keep seeing “new stuff”
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