What does it mean: “The Universe is most probably flat”?
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A piece of paper is a flat 2D thing. If you were a 2D creature living on the paper, you would be able to move left/right and up/down, but you’d be stuck on the piece of paper.
A ball is a 3D thing. The *surface* of the ball, however, is a 2D surface that has been *curved* through 3D space. If you were a 2D creature living on the surface of the ball, you’d be able to move left/right and up/down, but you’d be stuck on the surface of the ball. If that ball was really really big, it would be really hard for you to tell whether you were on a flat piece of paper or on the surface of a ball.
It’s the same for the universe, but one dimension higher. Our 3D space might be “curved” in 4 dimensions, it might not. Our best measurements suggest that it isn’t curved, but if the “ball” of the universe is really really big, then it would be really really hard for us to measure that curvature, so the possibility is there.
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