Working with this question but with more of a fantasy bent, I was wondering how long it would take a civilization to learn/realize that they lived on the inside of a Dyson sphere (or hollow earth or something similar) under the following circumstances:
- Light is provided by a central source that emits directional light somewhat akin a lighthouse.
GravitySome force that may or may not be gravity but approximates gravity regardless pulls in a uniform manner towards the shell without the shell rotating.
- A 3 AU sphere as described in the original question.
Barring magical methods (divination magic, praying and asking deities, etc.), could a civilization living on the inside of such a Dyson sphere determine that they A) didn't live on a flat plane and/or B) lived inside of a sphere and when (at what real-world technological level) could they accomplish it?