Refuting the Flat-Earth theory

[FlatAssembler]

I am thinking about making a YouTube video refuting the Flat Earth Theory, as a former Flat-Earther. Here are the arguments I am planning to use:

1) The dip of the horizon. Flat-Earthers often claim that the horizon is always at your eye-level, like here:

A fact of basic perspective is that the line of the horizon is always at eye level with the observer.

But that is demonstrably not the case. You can observe that in two ways:
a) You can see the sunset twice if you watch the sunset sitting down and then quickly stand up (the sun stays at your eye level, but the horizon imperceptibly falls).
b) You can measure it directly from an airplane using a device with a camera and a gyroscope (like almost all modern mobile phones):

The formula for the dip of the horizon is easily derived from the Round Earth Theory, as anybody who knows high-school mathematics can confirm:


And here we see how is the Round Earth Theory superior to the Flat Earth Theory: it makes such simple and testable predictions. It seems to me that you can never derive an exact formula for anything from the Flat Earth Theory.

2) Why does the gravitational acceleration (9.8m/s2) decrease measurably when you climb up on a mountain? And how is your answer compatible with the rest of the Flat Earth Theory? You don't get to both claim gravity doesn't exist (and that that's why gravity doesn't cause the Flat Earth to collapse under its own weight) and that stars have a gravitational field.

3) If GPS is land-based, how come are GPS devices capable of telling your location, including your elevation, with just three signals? The simple truth is, when you know distance from three points, you can calculate two points where you might be. Those points will be different, mostly in elevation. If GPS devices receive signals from satellites, they can eliminate the point that's above the satellites as impossible. If they receive signals from land-based emitters, they cannot do that.

4) Polar day and polar night on Antarctica. If time zones work the way you claim they do, they would be impossible.

5) A bit of a soft question: Can you point me to any scientific discovery that was made using anything resembling your methods, by making countless ad-hoc hypotheses and asserting massive conspiracies? Yes, science has been wrong before, but scientists were almost always simply mistaken, not lying. Especially not massively colluding with each other.

Do you think that I should change something or add something?