Flat Earth proponents fail to take into account simple things like the propagation of radio waves, the presence of orbiting satellites, and airline flight paths, all which are real and proven and which are predicated on the gravitational pull and curvature of a sphere. The whole of physics breaks down under the flat earth theory.
The concept of physics breaking down is sort of the point of those who genuinely believe the earth is flat, or at least not the sphere theorized in Copernicus 500 years ago. They believe the heliocentric solar system is an intellectual concept, and that other concepts also account for the same physical phenomena we can see and touch. They base their beliefs upon observing things like the picture of Chicago taken from a distance of 60 miles, which is impossible according to the laws of physics.
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When was the last time you observed satellites orbiting earth from an observation point in space?
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If you answer you've never been in space, that you trust photos taken by NASA, you've proven their point. Our belief that the earth is a sphere circling a star is based on the schooling we received when we were young, and on our willingness to trust authorities and evidence they may present; evidence we were not present to observe for ourselves.
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Here's another one if you feel curious: Go on-line and try to get a reservation for a flight from South Africa to Australia. Measure the distance between South Africa and Australia on a map. Are you able to book a flight non-stop? How many mileage points would you accumulate if you actually took the flight you were able to book?