Quote: DirkDiggler "So why when you set off from say point A in a plane (providing you've got enough fuel and the jet streams don't blow you off course) do you end up back at point A.'"
Don't encourage it.
It doesn't matter what you say or provide evidence of, they always have some convoluted way of dismissing it. Why face the sheer wall of facts and evidence when you can invent and peddle some ridiculous alternative.
I'd hazard a guess that he/she is of the religious literalism type, that takes everything in their holy book literally. Searching for evidence to fit their 'facts', rather than let the evidence dictate the fact. If it isn't religious belief driving the delusion, then they don't really have an excuse.