If you draw a triangle between the north pole and two points on the equator, measure the inside angles, and add them up, it will add up to more than 180^o, which demonstrates the surface of the Earth to be curved. And of course that's just the extreme, and you can do it on a smaller scale. It isn't something you can easily demonstrate by yourself, but you are pointing to an actual scientific experiment that could be done. Every physicist will confirm this, so it becomes up to the kook (CIA asset) to refute all of established physics. Just a random thought.