Comment by tialaramex
8 hours ago
If your planet is tiny, it's very easy to figure out that it's a ball, a child can see it with their bare eyes. The planets in "Outer Wilds" are like that.
Because this planet is larger, smart people trying to figure out how it works used simple tools and measurements to conclude that it's a ball, we know that Greeks and Romans figured this out, I'm sure other civilisations did too.
Greg Egan's "Incandescence" has people who live somewhere where you can discover, in this same way, General Relativity. There's a small but noticeable difference between the simple linear results we'd see for Newtonian physics in rudimentary experiments and what they can observe and they figure out why. Since they have no context for what it means to observe this and have (to their memory) always lived somewhere this happens, they aren't terrified by this discovery any more than we were terrified to discover how our Sun must work - so much hydrogen in one place that it undergoes spontaneous nuclear fusion which releases so much energy that we can easily see by it even after it is no longer directly visible, OK cool, I still need groceries.
It’s easy to see that the surface of the earth is a ball - or at least a curved surface - simply by going to the seaside and watching ships dip below the horizon before they fully disappear.
The ancient Greeks proved it was a ball and measured the dimensions of it using mathematics, but the concept of a curved earth was known to seafarers long before that.