nhabz OP t1_iycyvc7 wrote on November 30, 2022 at 2:08 PM

Reply to comment by WinBarr86 in ELI5: How is that space is “flat” yet we are able to look around the universe (up, down, left, right, etc.,) as if it were not flat? by nhabz

So the universe is actually 3D but we call it 2D to make certain concepts easier to understand?

ialsoagree t1_iyd0byk wrote on November 30, 2022 at 2:20 PM

No no, we call it flat - but flat doesn't mean 2D.

We call paper flat, but paper isn't 2D, it's 3D.

WinBarr86 t1_iyd0ohk wrote on November 30, 2022 at 2:23 PM

We don't call it 2d we call it flat.

Flat is a concept. That concept is easier to explain using a 2d method.

Flat does not mean 2d. Flat means, in this case, the "thickness" of the universe is so small in relation to the width and length. Like a piece of paper. Paper has a "thickness" like 2mil or .07mil. Some paper is super thin, like tracing paper, and some a bit thicker, like construction paper but its all flat and 3d.

Edits for clarity.

urzu_seven t1_iyd39se wrote on November 30, 2022 at 2:42 PM

That is not at all why the geometry of the universe is described as flat. It has nothing to do with “thickness”

WinBarr86 t1_iyd5s0i wrote on November 30, 2022 at 3:01 PM

I'm trying to keep it simple. But plz do explain. Without explaining like your talking to a scientist who knows alot of the concepts of space/time.

Edit.

But we both know space isn't flat.

Spacetime is not flat. It can't be: Einstein's general theory of relativity says that matter and energy curve spacetime, and there are enough matter and energy lying around to provide for curvature.

WinBarr86 t1_iydcvxm wrote on November 30, 2022 at 3:50 PM

Trying to explain the concept of flat as to curved without using mathematical terms is hard. Flat is a concept, just means non curved. To explain in detail requires a fair bit of knowledge of things like diffent types of geometry and understanding fundamentals of curvatures and Euclidean geometry. Best way to explain flat is paper.