Georges Lemaître

Georges Henri Joseph Édouard Lemaître (/ləˈmɛtrə/ lə-MET-rə; French: [ʒɔʁʒ ləmɛːtʁ] ^ⓘ; 17 July 1894 – 20 June 1966) was a Belgian Catholic priest, theoretical physicist, and mathematician who made major contributions to cosmology and astrophysics. He was the first to argue that the recession of galaxies is evidence of an expanding universe and to connect the observational Hubble–Lemaître law with the solution to the Einstein field equations in the general theory of relativity for a homogenous and isotropic universe. That work led Lemaître to propose what he called the "hypothesis of the primeval atom", now regarded as the first formulation of the Big Bang theory of the origin of the universe.

Lemaître studied engineering, mathematics, physics, and philosophy at the Catholic University of Louvain and was ordained as a priest of the Archdiocese of Mechelen in 1923. His ecclesiastical superior and mentor, Cardinal Désiré-Joseph Mercier, encouraged and supported his scientific work, allowing Lemaître to travel to England, where he worked with the astrophysicist Arthur Eddington at the University of Cambridge in 1923–1924, and to the United States, where he worked with Harlow Shapley at the Harvard College Observatory and at the Massachusetts Institute of Technology (MIT) in 1924–1925.

Lemaître was a professor of physics at Louvain from 1927 until his retirement in 1964. A pioneer in the use of computers in physics research, in the 1930s he showed, with Manuel Sandoval Vallarta of MIT, that cosmic rays are deflected by the Earth's magnetic field and must therefore carry electric charge. Lemaître also argued in favor of including a positive cosmological constant in the Einstein field equations, both for conceptual reasons and to help reconcile the age of the universe inferred from the Hubble–Lemaître law with the ages of the oldest stars and the abundances of radionuclides.

Father Lemaître remained until his death a secular priest of the Archdiocese of Mechelen (after 1961, the "Archdiocese of Mechelen-Brussels"). In 1935, he was made an honorary canon of St. Rumbold's Cathedral. In 1960, Pope John XXIII appointed him as Domestic Prelate, entitling him to be addressed as "Monsignor". In that same year he was appointed as president of the Pontifical Academy of Sciences, a post that he occupied until his death. Among other awards, Lemaître received the first Eddington Medal of the Royal Astronomical Society in 1953, "for his work on the expansion of the universe".