how can scientists say the universe is flat, when it seems to go in all directions?

Question

how can scientists say the universe is flat, when it seems to go in all directions?

In: 2

Answer 1

When they say the universe is “flat” they mean in a geometric sense.

There’s 3 possible geometries for universe: Closed Curve, Flat and Open Curve. They all possible solutions of Einstein’s field equations. I know this is probably getting too complicated, lets get back to the main topic.

In a “flat” geometry, 2 straight parallel lines will never diverge or intersect, they will be parallel to infinity.

In an “closed” geometry, 2 straight parallel lines will will eventually converge, imagine it drawing parallel lines on a basketball. Though, to be clear not all possible closed geometries are like a sphere.

Now, an “open” geometry is visualized like a saddle shape, 2 straight parallel lines will eventually diverge and never intersect while slowing getting further apart.

Hope that kinda helps…