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.
In: 229
The universe is expanding in all directions, but “flat” in this context is about geometry, not shape. So you’re mixing up the term “flat” as it’s used in everyday life with how cosmologists use it.
When cosmologists talk about the universe being “flat,” they’re talking about its large-scale geometry. Imagine a 2D analogy: If you draw a triangle on a flat piece of paper, the angles add up to 180 degrees, right? But if you draw a triangle on a curved surface, like a sphere, the angles add up to more than 180 degrees. Same deal with the universe. The geometry dictates how parallel lines behave, how shapes form, and whatnot. In a flat universe, general relativity plays out in a way that parallel lines will remain parallel forever, and the angles in a large-scale triangle will add up to 180 degrees. If the universe were “closed” or spherical, parallel lines would eventually converge.
Regarding dimensions, yeah, we live in a 3D world, but when we talk about the shape of the universe, it’s easier to simplify things by using 2D analogies. Our universe is indeed 3D (or even 4D, if you count time), but its “flatness” is a property of its geometry, not its dimensionality.
So, the universe is expanding in all directions, not just “one plane,” but its geometry appears to be flat based on our best measurements. It’s not about how the universe is expanding, but how space-time itself is curved (or not curved, as it appears to be). It’s actually amazing when you think about it.
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