If the universe appears locally flat, what must be true about its radius of curvature if it is curved?

Answer

Its radius must be vastly larger than the region we can observe

If the universe is curved but appears flat locally, it means we are standing on a structure (like a giant sphere) so large that our local vantage point cannot detect the curvature; its radius of curvature must be much larger than the observable universe.

If the universe appears locally flat, what must be true about its radius of curvature if it is curved?
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