A few years ago, a documentary on flat-earthers featured a trained geologist who has become convinced that the earth is flat. To test it, being a trained scientist, he designed a good experiment to measure the altitude of a laser beam at a distance from its emitter. He calculated the predicted measurement if Earth is flat and the measurement if Earth is spherical. When he ran the experiment, he got exactly the value he had predicted for a spherical Earth.

The rest of the documentary was him trying to find the error in his instruments and measurements since he knew for a fact that Earth is flat.

It was sad.