Passage: The other was his senior thesis, on "Forces in Molecules", based on an idea by John C. Slater, who was sufficiently impressed by the paper to have it published. Today, it is known as the Hellmann–Feynman theorem.In 1939, Feynman received a bachelor's degree, and was named a Putnam Fellow. He attained a perfect score on the graduate school entrance exams to Princeton University in physics—an unprecedented feat—and an outstanding score in mathematics, but did poorly on the history and English portions. The head of the physics department there, Henry D. Smyth, had another concern, writing to Philip M. Morse to ask: "Is Feynman Jewish? We have no definite rule against Jews but have to keep their proportion in our department reasonably small because of the difficulty of placing them." Morse conceded that Feynman was indeed Jewish, but reassured Smyth that Feynman's "physiognomy and manner, however, show no trace of this characteristic".Attendees at Feynman's first seminar, which was on the classical version of the Wheeler-Feynman absorber theory, included Albert Einstein, Wolfgang Pauli, and John von Neumann. Pauli made the prescient comment that the theory would be extremely difficult to quantize, and Einstein said that one might try to apply this method to gravity in general relativity, which Sir Fred Hoyle and Jayant Narlikar did much later as the Hoyle–Narlikar theory of gravity. Feynman received a Ph.D. from Princeton in 1942; his thesis advisor was John Archibald Wheeler. In his doctoral thesis titled "The Principle of Least Action in Quantum Mechanics," Feynman applied the principle of stationary action to problems of quantum mechanics, inspired by a desire to quantize the Wheeler–Feynman absorber theory of electrodynamics, and laid the groundwork for the path integral formulation and Feynman diagrams. A key insight was that positrons behaved like electrons moving backwards in time. James Gleick wrote:

Question: what is the title of Feynman Phd thesis?
The Principle of Least Action in Quantum Mechanics