After the success of quantum electrodynamics, Feynman turned to quantum gravity. By analogy with the photon, which has spin 1, he investigated the consequences of a free massless spin 2 field, and derived the Einstein field equation of general relativity, but little more. The computational device that Feynman discovered then for gravity, "ghosts", which are "particles" in the interior of his diagrams that have the "wrong" connection between spin and statistics, have proved invaluable in explaining the quantum particle behavior of the Yang–Mills theories, for example, QCD and the electro-weak theory. COUNT 5
QSN1 Where did  Feynman find success before moving to quantum gravity ANS1 quantum electrodynamics QSN2 What did Feynman investigate while working on quantum gravity? ANS2 consequences of a free massless spin 2 field QSN3 What equation did Feyman derive? ANS3 Einstein field equation of general relativity QSN4 Which parts of the Yang-Mills theories did Feynman help explain? ANS4 QCD and the electro-weak theory QSN5 What did Feynman's discoveries help explain? ANS5 Yang–Mills theories