How do you arbitrate truth? What if someone starts spreading the idea that gravity does not exist and that the reason you are stuck to the earth is that the g

How do you arbitrate truth? What if someone starts spreading the idea that gravity does not exist and that the reason you are stuck to the earth is that the ground is accelerating upward towards you at 9.8 m/s^2? Who gets to decide whether lies or truth is being spread here? I don't think anyone is qualified to make that call.