The hard problem

[Nyarlathotep]

@Kevin_Levites

So, does measuring the angles of a very large triangle tell us if space is flat or curved, and–if curved–how large the Universe actually is?

That is exactly how it is done. The last time I looked it up the measurements were still showing no curvature; indicated that if the universe was indeed curved, it must be at least 20x the observable volume to hide this fact from the best experiments at the time.