Dear Readers,
Could I just draw your attention to an important figure in the history of philosophy - Descartes. Yes, he was the man who said "I think, therefore I am" (Je pense, donc, je suis). However, he did someting much more important than coin a phrase. His philosophy began with "First, doubt everything".
What did this mean? It meant that not only could you not trust the perceptions of others, but you could not trust your own senses - sight, touch and so on. The only thing one can trust, he thought, was cold reason (something many people often lack).
Descartes maintained that there was nothing to determine that the world in which we were living was 'real' in any sense - how can you tell that you're not simply living in a particularly consistent dream?
So, how does this relate to the "Flat Earth" belief? For all you or I know, we may be living on a flat earth that we perceive to be spherical, or vice versa, simply because our senses if they exist (and afterwards, our brain, if it too exists) translate the signals they receive in a certain way.
Of course, there may be no such thing as a physical or material world, and the perception of a reality is simply a creation of the subconcious mind. To me, none of you may really exist. But any of those options can neither be disproven or proven (rather like the existence of God).