document: By the early 1970s, and following the ‘golden age’ of general relativity that took place in the 1960s, there was a wide array of candidate theories of gravity in existence that could rival Einstein’s. A formalism was needed to deal with this great abundance of possibilities, and this was provided in the form of the Parameterised Post-Newtonian (PPN) formalism by Kenneth Nordtvedt, Kip Thorne and Clifford Will. The PPN formalism was built on the earlier work of Eddington and Dicke, and allowed for the numerous theories available at the time to be compared to cutting edge astrophysical observations such as lunar laser ranging, radio echo, and, in 1974, the Hulse–Taylor binary pulsar. The PPN formalism provided a clear structure within which one could compare and assess various theories, and has been the benchmark for how theories of gravity should be evaluated ever since. We will give an outline of the PPN formalism, and the constraints available within it today, in Section 2.
doc_bio_tags: O O O O O O O O O O B I O O O O O O O O O O O O O B I I O O O O O O O O O O O O O O O O O O O O O O O O O O O O O B O O O O O O O O O O B O O O O O O O O O O O O O O O O O O O O O O O O O B I I I O O B I I B I O O O O B I I O B O O O O O O O O O B I I O O O O O O B I I I I I I I I O O O O O O O O O B O O O O O O O O O O O
extractive_keyphrases: benchmark for how theories of gravity should be evaluated compare and assess cutting edge astrophysical observations general relativity hulse–taylor binary pulsar lunar laser ranging ppn radio echo theories of gravity
abstractive_keyphrases: parameterised post-newtonian ppn formalism