Kenneth Leon Nordtvedt (born 1939) is a professor emeritus in the Physics Department at Montana State University and a senior researcher specializing in relativistic theories of gravity. He was born on April 16, 1939, in Chicago, Illinois. Nordtvedt graduated from the Massachusetts Institute of Technology (1960) and Stanford University (Ph.D., 1964). In the mid-1960s he showed how lunar laser ranging could be used to test a cornerstone of general relativity known as the equivalence principle. He was a board member and scientific advisor overseeing the joint NASA-ESA Space Test of Equivalence Principle mission. He was appointed by then President Ronald Reagan to the National Science Board. He was one of only two academic scientists serving on the board. He served three terms in the Montana state legislature for a six-year period in the early eighties, and there he wrote one of the first inflation indexing reforms of income tax law in the nation. He had support from NASA during the 1970s for his research. His research was the subject of a Wall Street Journal article featured on the front page.
He is also an active genetic genealogist by interests. He has done his own research into genetic haplogroups, particularly the Y DNA group I, to which he belongs. He advises on haplotypes for a population genetics group at FamilyTreeDNA. Nordtvedt has proposed a new most recent common ancestor calculation method.