Actually Einstein got more than what happens to mass in a gravitational field, but it also includes massless particles as well. Note that even photons obey the Einstein field equations. It would seem that you are still relying on \(\displaystyle E = mc^2\), That's pretty common. This is really what Einstein came up with:"Okay, I pretty much understand what you are talking about when you say "projections." It's pretty standard in Linear Algebra and stuff."
What render space scale in projective geometry? Human/math?
Einstein got the physical meaning for affine geometry. It's the existence of mass.
This semi-tramp got the physical meaning for projective geometry. It's the matter states.
That dragon loves in playing standard math game.
See here for more information."...And I am beginning to suspect that we aren't talking about the same thing when you say projective geometry."
Absolute misconcept. There is only one projective geometry created by human. What different is the organization of contents or details shown are different in different books published.