How as an individual can I know if the Earth is a sphere or a flat disc? What experiment can I do that doesn't involve trusting information from a 3rd party that would prove what the geometry really is?
http://i.imgur.com/O8IpMmi.jpgTry sending a rocket vertically and see what pulls it down and tilts its trajectory! To get out of earth's atmosphere, our rocket has to travel in a concentric circular path, implying the spherical (elliptical?) shape!
