Do we 100% know what the geometry of the Universe is?

[Nugatory]

All stars/planets in universe lay at same plane as earth? How thick is this plane?

You are misunderstanding what “spatially flat” means. Intuitively it means that the Euclidean geometry works everywhere - the Pythagorean theorem is valid, parallel lines never intersect, the interior angles of a triangle add to 180 degrees, and so forth. The opposite of “flat” is “curved”.

It’s easy to visualize a three-dimensional flat space - we live in one, it’s the only three-dimension space we’ve ever known. It’s not so easy to visualize a three-dimensional curved space so we have to fall back on a two-dimensional analogy: the surface of a sheet of paper is two-dimensional and flat so Euclidean geometry works; the two-dimensional surface of the earth is not flat and Euclidean geometry doesn’t work (lines of longitude, initially parallel at the equator intersect at the poles, the interior angles of a triangle with two vertices on the equator and the third at a pole add to more than 180 degrees, and so forth).

 

[Drakkith]

But how can this be physically possible?
Example with fluid, if you decrease distance between each molecule of air, shouldn't it come to one point?

No, not if the fluid extends infinitely in all directions. In such a situation, as the distance between the molecules decreases, the density of the fluid approaches infinity everywhere while at the same time the volume always remains infinite.

 

[PeterDonis]

Thread closed for moderation.

 

[PeterDonis]

After moderator review, the thread will remain closed. Thanks to all who participated.