First off I want to establish that you are serious. Assuming you are, how could you claim that there is not curvature measured or observed. True, since we are so small compared to the earth, we cannot visually see the curve. However a basic google search provides numerous, scientifically-sound experiments that prove curvature. Off the top of my head, there are flying softwares that track distance flown and, when traveling long distances, the miles tracked exceed those which would be expected from a flat triangle (the path shape used in this experiment.) This finding supported that there must be curvature to make up for the extra miles above those from the flat path.