A Note on the Feynman Lectures on Gravitation

Following Feynman's lectures on gravitation, we consider the theory of the gravitational (massless spin-2) field in flat spacetime and present the third- and fourth-order Lagrangian densities for the gravitational field. In particular, we present detailed calculations for the third-order Lagrangian density. We point out that the expression for the third-order Lagrangian density which Feynman provided is not a solution of Feynman's condition that the third-order Lagrangian density must satisfy. However, Feynman's third-order Lagrangian density gives the correct perihelion shift.