How do they know it to be true if they've never done the experiments? 
For crying out loud, Tom. Why are you so fixated on "experiments?", when Rowbothems "experiments" are worthless. This biggest mistake you have made over the years is to put
all your "faith" in FE experiments, ignoring or misinterpreting the observational evidence which is freely available and far more compelling.
When the observation evidence (for example position and the movement of the heavens) does not agree with the results of your experiments (the window/the water), then you are left with no option but to distort the entire cosmos using unprecedented fields and forces, which do not agree with existing models.
For example the movement of Celestial Gears, the sun, the moon, the planets, is simply put down to the "vast cornucopia of stars, swirling around". That's it. When scrutinised, this throws up even more fundamental questions that you stared with (like why exactly do the sun, moon and planets constantly change their orbit), and so it goes on.
I think you yourself, deep down, have your doubts. Why are you not busly research and analysing these Celestial Gears? Afraid of Failure? ... Of course! you don't need to worry because Zetetics excuses you from any of that dangerous "evidence gathering" stuff. Why let the truth get in the way of a good theory?