Below are a few topics on Einstein that relate to flat earthers and other science deniers.
Einstein’s field equations reduce to Newtonian gravity.
- Robert M Wald, “General Relativity” (First Edition 1984), p76 gives the Newtonian limit.
- Hawking and Ellis, “Large scale Structure of Space-time” (1973), p71
- Misner, Thorne and Wheeler, “Gravitation” (1973) p412.
- Sean M Carroll, “Spacetime and Geometry: An introduction to General Relativity“, Section 4.2
Einstein did not “debunk” or “replace” Newtonian gravity. He refined Newtonian gravity.
There are not two forms of gravity. There is one. When the velocity of the objects is not significant and when not near a large gravitational body, use the basic formula: f=GMm/r^2
When the velocity is significant or near a large gravitational mass use Einstein’s field equations.
If you want to use Einstein’s field equations for low velocity and not near a large gravitational mass, you can. The answer will be the same.