It’s very easy to prove the Earth is curved with geometry (unless geometry is fake?), but people like to be stupid or controversial - or both. Example from 240 BCE.

The “Two Sticks” Shadow Experiment (Eratosthenes’ Proof)

Around 240 BCE, a Greek scholar named Eratosthenes proved the Earth is round using nothing more than: two sticks, sunlight, and geometry.

What he observed, at noon on the same day: In Syene (modern Aswan) a vertical stick cast no shadow (Sun directly overhead). In Alexandria (~800 km north) ? a vertical stick did cast a shadow at about 7.2°

If Earth were flat, Sunlight would hit both sticks at the same angle. Both sticks should cast identical shadows. But they don’t. The only way sunlight can hit two vertical objects at different angles at the same time
is if the surface between them is curved.

Proof!
No space agencies
No trust in institutions
No satellites
No aircraft
No “photos could be fake” arguments

Just:
Same Sun
Same time
Different angles
= Curved surface

From that single angle difference, Eratosthenes even calculated Earth’s circumference — landing remarkably close to the modern value of about 40,075 km. Flat Earth literally cannot produce that geometry.
#flatearth