Georges Lemaître

Georges Lemaître was born in Charleroi, Belgium, the eldest of four children of Joseph Lemaître, a prosperous industrialist who owned a glassworks factory, and Marguerite née Lannoy, who was the daughter of a brewer. Georges was educated at the , a grammar school in Charleroi run by the Jesuits. In 1910, after a fire destroyed the glassworks, the family moved to Brussels, where Joseph had found a new position as manager for the French bank Société Générale. Georges then became a pupil at another Jesuit school, St. Michael's College. Although he had expressed his interest in pursuing a religious vocation, his father convinced him to attend university first and to train as a mining engineer. University studies and military service In 1911, Lemaître began to study engineering at the Catholic University of Louvain. In 1914, after the outbreak of World War I, Lemaître interrupted his studies to volunteer for the Belgian army. He participated in the Battle of the Yser, in which the Belgians succeeded in halting the German advance. When the army transferred him from the infantry to artillery, Lemaître was sent to complete a course on ballistics. His prospects of promotion to officer rank were dashed after he was marked down for insubordination as a result of pointing out to the instructor a mathematical error in the official artillery manual. However, at the end of hostilities he received the Belgian War Cross with bronze palm, one of only five rank-and-file troops to receive that award from the hands of King Albert I. Lemaître was an admirer of the French Catholic writer Léon Bloy. During a leave from his military service in World War I, Lemaître visited Bloy in Bourg-la-Reine, near Paris, where Bloy was living in a house that had belonged to his late friend and fellow writer Charles Péguy. On that occasion, Lemaître shared with Bloy an essay entitled Les trois premières paroles de Dieu ("The First Three Words of God"), in which he attempted to reconcile the Genesis creation narrative with modern science. Bloy, however, was unimpressed and advised Lemaître to grow more familiar with the works of the Church Fathers. This experience may have contributed to Lemaître's abandonment of the "concordist" effort to reconcile theological and scientific knowledge at a common intellectual level. Years later, Einstein questioned Lemaître on the idea of concordism. Lemaître opposed the idea that faith and science are opposed, but also acknowledged that concordism was invalid. He argued, "Should a priest reject relativity because it contains no authoritative exposition on the doctrine of the Trinity? Once you realize that the Bible does not purport to be a textbook of science, the old controversy between religion and science vanishes" After the war, Lemaître abandoned engineering for the study of physics and mathematics. In 1919 he also completed the course taught at the Higher Institute of Philosophy, established by Cardinal Désiré-Joseph Mercier to promote neo-Thomism. Lemaître obtained his doctorate in science in 1920 with a thesis titled ("The approximation of functions of several real variables"), written under the direction of mathematician Charles de la Vallée-Poussin. Religious training Lemaître had considered joining the Jesuits or the Benedictines, but finally decided to prepare instead for the diocesan priesthood. Between 1920 and 1923 he was a student at the , the seminary for "late vocations" (i.e., mature students for the priesthood) of the Archdiocese of Mechelen. It was during his spare time at the seminary that Lemaître learned the general theory of relativity. He was ordained as a priest on 22 September 1923 by Cardinal Mercier. As a diocesan priest in French-speaking Belgium, he was known as "Abbé Lemaître". At the seminary, Lemaître joined the ("Priestly fraternity of the Friends of Jesus"), which had been created by Cardinal Mercier to promote the spiritual life of select diocesan priests and which was established canonically by his successor, Cardinal Jozef-Ernest van Roey. As a member of the fraternity, Lemaître took vows of chastity, poverty, and obedience, as well as special ("vow of immolation") promising complete submission to the person of Christ. In the spirit of the fraternity, Lemaître did not discuss his involvement with the Amis de Jésus outside of the group, but he regularly made silent retreats in a house called ("Queen of Peace") in Schilde, near Antwerp, and also undertook translations of the mystical works of John of Ruusbroec. Voyage to Britain and the US In 1922, Lemaître applied to the Belgian Ministry of Sciences and Arts for a travel bursary. As part of that application, he submitted a thesis on the astronomical implications of general relativity that included a demonstration that the most general form of the Einstein field equations included a cosmological constant term. The jury awarded Lemaître a prize of 8,000 Belgian francs. Cardinal Mercier supported Lemaître's scientific work and helped him to obtain further financial support for a two-year visit to Great Britain and the United States. Only ten days after his ordination, Lemaître left Belgium to take up residence at St Edmund's House, then a community of Catholic priests studying for degrees at the University of Cambridge and which would later become St Edmund's College. At Cambridge, Lemaître was a research associate in astronomy and worked with the eminent astrophysicist Arthur Eddington, who introduced Lemaître to modern cosmology, stellar astronomy, and numerical analysis. Lemaître then spent the following year at the Harvard College Observatory, in Cambridge, Massachusetts, working with Harlow Shapley, a leading expert in the study of what were then called "spiral nebulae" (now identified as spiral galaxies). Lemaître also registered at that time in the doctoral program in science at the Massachusetts Institute of Technology (MIT), with the Belgian engineer Paul Heymans as his official advisor. == Work on cosmology ==

On his return to Belgium in 1925, Lemaître became a part-time lecturer at the Catholic University of Louvain and began working on a report that was finally published in 1927 in the ("Annals of the Scientific Society of Brussels"), under the title ("A homogeneous Universe of constant mass and growing radius accounting for the radial velocity of extragalactic nebulae"). There he developed (independently of the earlier work of Alexander Friedmann) the argument that the equations of Albert Einstein's general theory of relativity implied that the Universe is not static (see Friedmann equations). Lemaître connected this prediction to what he argued was a simple relation of proportionality between the average recessional velocity of galaxies and their distance to the Earth. This 1927 paper had little impact because the were not widely read by astronomers or physicists outside of Belgium. Moreover, in this 1927 paper Lemaître assumed a universe with a positive cosmological constant, but at this time, Einstein insisted that only a universe in which the cosmological constant had the precise value to make it static was physically acceptable. Lemaître later recalled Einstein saying to him: "" ("your calculations are correct, but your physics is abominable"). Also in 1927, Lemaître returned to MIT to defend his doctoral dissertation on The gravitational field in a fluid sphere of uniform invariant density according to the theory of relativity. Upon obtaining that second doctorate, Lemaître's was appointed ordinary professor at the Catholic University of Louvain. Hubble-Lemaître law , the universe emerged from an extremely dense and hot state (singularity). Space itself has been expanding ever since, carrying galaxies with it, like raisins in a rising loaf of bread. The graphic scheme above is an artist's conception illustrating the expansion of a portion of a flat universe. In 1929, the US astronomer Edwin Hubble published a paper in the Proceedings of the National Academy of Sciences of the United States of America showing, based on better and more abundant data than what Lemaître had had at his disposal in 1927, that, in the average, galaxies recede at a velocity proportional to their distance from the observer. Although Hubble himself did not interpret that result in terms of an expanding Universe, his work attracted widespread attention and soon convinced many experts, including Einstein, that the Universe is not static. The proportionality between distance and recessional velocity for galaxies has since been commonly known as "Hubble's law", but in 2018 the International Astronomical Union (IAU) adopted a resolution recommending that it be referred to as the "Hubble-Lemaître law". Hoyle remained throughout his life an opponent of such "Big Bang" theories, advocating instead a steady-state model of an eternal Universe. In 1948, theoreticians Ralph Alpher, Robert Herman, and George Gamow predicted a different form of "fossil radiation" based on the Big Bang model, now known as the cosmic microwave background (CMB). The CMB was produced when the contents of the expanding Universe cooled sufficiently that they became transparent to electromagnetic radiation. In 1965, shortly before his death, Lemaître learned from his assistant Odon Godart of the recent discovery of the CMB by radio astronomers Arno Penzias and Robert Wilson. That discovery convinced most experts of the scientific validity of the Big Bang. Cosmological constant Lemaître maintained throughout his career that the Einstein field equations should incorporate a positive cosmological constant (\Lambda) term. His reasoning was based on both theoretical and empirical considerations. Lemaître argued in 1958 that "if some extension of relativity towards a broader field, such as quantum theory, has to be achieved the superfluous \Lambda term shall be very much welcomed". He also held that the accelerating expansion of the universe induced by \Lambda could help to reconcile the age of the universe deduced from the Hubble-Lemaître law with the ages of the oldest stars and the observed abundances of radionuclides. Lemaître argued for a positive cosmological constant both in print and in correspondence with Einstein, who was skeptical about the reality of such a term after abandoning his model of a static universe in the early 1930s. The Nobel Prize in Physics for 2011 was awarded to Saul Perlmutter, Brian P. Schmidt, and Adam G. Riess for establishing the reality of the universe's accelerating expansion, based on extensive surveys of Type Ia supernovae used as astronomical "standard candles". In the scientific background for that prize, the Royal Swedish Academy of Sciences credited Lemaître with the idea that such an acceleration is driven by vacuum energy, also modernly called in this context dark energy. Views on relation between science and faith in discussion while sailing back from the 6th General Assembly of the International Astronomical Union, held in Stockholm in 1938 Initially, Lemaître supported concordism. In 1917, he attempted to prove the creation story of Genesis 1, specifically the idea of ex nihilo nihil fit (out of nothing, nothing comes). He reasoned:It is impossible for any body to subsist without emanating light, as all bodies at a certain temperature emit radiation of all wavelengths (theory of black bodies). In a physical sense, absolute darkness is nothingness.… Before the Fiat lux, there was absolutely no light and therefore absolutely nothing existed.Eventually, he abandoned his studies on light, and focused instead on studying relativity. In a 1933 New York Times article, he asserted, "There is no conflict between religion and science to reconcile." He was always anxious that his work on cosmology should be judged on purely scientific criteria; he feared that combining the two (concordism) would both hinder scientific acceptance and misrepresent the faith. In 1951, Pope Pius XII gave an address to the Pontifical Academy of Sciences, with Lemaître in the audience, in which he drew a parallel between the new Big Bang cosmology and the Christian doctrine of creatio ex nihilo: Lemaître was reportedly horrified by that intervention and was later able, with the assistance of Father Daniel O'Connell, the director of the Vatican Observatory, to convince the Pope not make any further public statements on religious or philosophical interpretations of matters concerning physical cosmology. According to the theoretical physicist and Nobel laureate Paul Dirac, == Other scientific work ==

With Manuel Sandoval Vallarta, whom he had met at MIT, Lemaître showed that the intensity of cosmic rays varies with latitude because they are composed of charged particles and therefore are deflected by the Earth's magnetic field. In their calculations, Lemaître and Vallarta made use of MIT's new differential analyzer computer, developed by Vannevar Bush. That work disproved the view, advocated among others by the Nobel laureate Robert Millikan, that cosmic rays were composed of high-energy photons. Lemaître and Vallarta also worked on a theory of primary cosmic radiation and applied it to their investigations of the Sun's magnetic field and the effects of the galaxy's rotation. In 1933, Lemaître found an important inhomogeneous solution of Einstein's field equations describing a spherical dust cloud, the Lemaître–Tolman metric. He became increasingly interested in problems of numerical computation and in the 1930s began to use the most powerful calculator available at the time, the mechanical Mercedes-Euklid. In his only work in physical chemistry, Lemaître collaborated in the numerical calculation of the energy levels of monodeuteroethyelene (a molecule of ethylene with one of its hydrogen atoms replaced by deuterium). In 1948 Lemaître published a mathematical essay titled ("Quaternions and elliptic space"). William Kingdon Clifford had introduced the concept of elliptic space in 1873. Lemaître developed the theory of quaternions from first principles, in the spirit of the Erlangen program. Lemaître also worked on the three-body problem, introducing a new method of regularization to avoid singularities associated with the collisions of two bodies. In the 1950s he worked out an early version of the fast Fourier transform, later developed independently by James Cooley and John Tukey. He introduced the Burroughs E101 electromechanical computer to his university in the late 1950s. In his later years he collaborated with his nephew Gilbert Lemaître on a new programming language called "Velocode", a precursor of BASIC. == Final years ==

During the 1950s, Lemaître gradually gave up part of his teaching workload, ending it completely when he took emeritus status in 1964. In 1960 he was named domestic prelate (with the treatment of "Monsignor") by Pope John XXIII. Lemaître was strongly opposed to the ("Flemish Leuven") movement that sought to make instruction at the Catholic University of Leuven monolingual in Dutch. With the historian Gérard Garitte, in 1962 Lemaître established the (ACAPSUL, "Association of the faculty and scientific personnel of the University of Louvain") to advocate for the continued use of the French language in that institution. After Lemaître's death, the university was separated into a Dutch-speaking institution, KU Leuven, and a French-speaking institution, UCLouvain, based in the planned town of Louvain-la-Neuve ("New Leuven") that was built for that purpose just across the language border in Walloon Brabant. == Honours and recognition ==

On 27 July 1935 Lemaître was appointed as an honorary canon of St. Rumbold's Cathedral by Cardinal Jozef-Ernest van Roey. He was elected a member of the Pontifical Academy of Sciences in 1936, and took an active role there, serving as its president from March 1960 until his death. His proposers were Albert Einstein, Charles de la Vallée-Poussin and Alexandre de Hemptinne. The members of the international jury were Eddington, Langevin, Théophile de Donder and Marcel Dehalu. The same year he received the Mendel Medal of the Villanova University. In 1936, Lemaître received the Prix Jules Janssen, the highest award of the Société astronomique de France, the French astronomical society. Another distinction that the Belgian government reserves for exceptional scientists was allotted to him in 1950: the decennial prize for applied sciences for the period 1933–1942. In 1953, he was given the inaugural Eddington Medal by the Royal Astronomical Society. In 2005, Lemaître was voted to the 61st place of ("The Greatest Belgian"), a Flemish television program on the VRT. In the same year he was voted to the 78th place by the audience of the ("The Greatest Belgians"), a television show of the RTBF. Later, in December 2022, VRT recovered in its archives a lost 20-minute interview with Georges Lemaître in 1964, "a gem", says cosmologist Thomas Hertog. On 17 July 2018, Google Doodle celebrated Georges Lemaître's 124th birthday. On 26 October 2018, an electronic vote among all members of the International Astronomical Union voted 78% to recommend changing the name of the Hubble law to the Hubble–Lemaître law. Namesakes • The lunar crater Lemaître • Friedmann–Lemaître–Robertson–Walker metric • Lemaître coordinates • Lemaître–Tolman metric • Hubble–Lemaître law • Minor planet 1565 Lemaître • The fifth Automated Transfer Vehicle, Georges Lemaître ATV • Norwegian indie electronic band Lemaitre • The is the main building of the UCLouvain's Charleroi campus, adjacent to Lemaître's birthplace == Bibliography ==