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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We live in a three dimensional space.
The question is whether the universe has curvature in a higher dimension.
Think of it like Earth. From our casual perspective, the ground appears “flat” (more or less). But of course, we know we actually live on a sphere and that if you walked long enough in one direction, you’d end up back where you started. So the ground is like a 2D object curving in 3D space.
The question is whether the entire universe has a similar characteristic, a 3D volume curving in a 4D space.
Don’t try to actually imagine what this would look like, our brains aren’t built to process the concept, but mathematically it’s a possibility.
One way we test for this is essentially by measuring the behavior of parallel lines, or the angles between very large hypothetical triangles. On a 2D object a triangle is composed of angles adding up to 180 degrees. But if you draw a 2D triangle on a curved 3D object, those angles can be different. You can build a triangle out of multiple right angles, for example.
As far as we can tell, our universe is flat (this is actually unexpected for mathy reasons). But it’s possible we just aren’t measuring the change over a big enough distance yet (like how you wouldn’t notice a small triangle you draw with chalk on the ground is actually off).
Google “non-euclidean geometry.”
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