Why does the sun appear to go below the horizon on a flat Earth?

I'm trying to understand so bare with me, please provide a full explanation for this phenomenon. If light refraction is to be the case, then there should be an experiment to test this hypothesis, if you found any please inform me. thx

come on...

I'm trying to understand so bare with me, please provide a full explanation for this phenomenon. If light refraction is to be the case, then there should be an experiment to test this hypothesis, if you found any please inform me. thx

I believe the answer you are looking for is that the Earth isn't flat, therefore the sun does go below the horizon.  However, please be prepared for completely unverifiable, unsubstantiated, and absolutely baseless claims concerning "atmoplanic lensing" and other plucked from air excuses to defend the pancake planet!