All the countries have unilaterally agreed to the Antarctica treaty despite claims they are mortal enemies. If that's feasible, it's feasible they have other arrangements to. These things are proof of anything.

The fact is curvature is repeatedly debunked with long distance observations and radio waves. Indisputably so, that's why the topic always shifts to "but what about .... explain that."

Once you get into the physics then it really starts to go downhill. Did you know there were pages that emerged which were removed from the end of Newton's Principia? Want to guess what was in them? Why would they hide those?