I was quite confused by force description by second derivative versus force generation, where in Klein-Gorden equation, there is also second derivative terms, but no interaction, force is generated as the equation is Linear. Hence dig deep to clarify the two.

In General Relativity, this idea is taken even further:

• Gravity is curvature of spacetime.
• Particles follow geodesics — the “straightest possible paths” — but those geodesics look curved in space and time due to mass-energy.
• There, acceleration caused by gravity is understood as motion along curved spacetime paths.

This confusion is valid, as Gravity is special: the “field” is spacetime itself, so propagation of geometry directly becomes motion of particles.