Feynman Lectures On Gravitation Direct

: Detailed discussions on planetary motion (including the perihelion shift of Mercury), gravitational waves, and the behavior of light in gravitational fields.

Because these were postgraduate lectures given in the afternoons (while the more famous undergraduate Lectures on Physics were given in the mornings), they require a high level of mathematical maturity. Feynman Lectures on Gravitation - IOPscience Feynman Lectures on Gravitation

: The principle of equivalence, the necessity of a tensor field, and the iterative derivation of field equations. : Detailed discussions on planetary motion (including the

: Explorations of "superstars" (early precursors to quasars), wormholes, black holes, and the large-scale structure of the universe (cosmology). the necessity of a tensor field

: He posits the existence of a massless particle with spin 2 and derives the consistency requirements that lead directly to the non-linear Einstein field equations.