Monsignor Georges Lemaître was a Belgian Roman Catholic priest, physicist and astronomer. He is usually credited with the first definitive formulation of the idea of an expanding universe and what was to become known as the Big Bang theory of the origin of the universe, which Lemaître himself called his “hypothesis of the primeval atom” or the “Cosmic Egg”.
Georges Henri Joseph Édouard Lemaître was born on 17 July 1894 at Charleroi, Belgium. After a classical education at a Jesuit secondary school, the Collège du Sacré-Coeur in Charleroi, he began studying civil engineering at the Catholic University of Leuven (Louvain) at the age of 17. In 1914, he interrupted his studies to serve as an artillery officer in the Belgian army for the duration of World War I, at the end of which he received the Military Cross with palms.
After the war, Lemaître studied physics and mathematics, and simultaneously began to prepare for priesthood. He obtained his doctorate in 1920 and was ordained a priest in 1923. That same year, he became a graduate student in astronomy at the University of Cambridge in England, working with Arthur Eddington, who initiated him into modern cosmology, stellar astronomy and numerical analysis. He spent 1924 at Harvard College Observatory in Massachusetts, U.S.A., and at the Massachusetts Institute of Technology. In 1925, he returned to Belgium and became a part-time lecturer (and later a full-time professor) at the Catholic University of Leuven, where he remained for the rest of his career.
In 1927, he discovered a family of solutions to Einstein's field equations of relativity that described not a static universe, but an expanding universe (as, independently, had the Russian Alexander Friedmann in 1922). The report which would eventually bring him international fame, entitled “A homogeneous universe of constant mass and growing radius accounting for the radial velocity of extragalactic nebulae” in translation, was published later in 1927 in the little known journal “Annales de la Société Scientifique de Bruxelles”. In this report, he presented his new idea of an expanding universe, and also derived the first statement of what would later become known as Hubble’s Law (that the outward speed of distant objects in the universe is proportional to their distance from us), and provided the first observational estimation of the Hubble constant.
In 1929, after nearly a decade of observations, Edwin Hubble published his definitive report that the redshift in light coming from distant galaxies is proportional to their distance, effectively confirming Lemaître’s prediction of an expanding universe. However, Lemaître's model of the universe received little notice until it was publicized by the prominent English astronomer Arthur Eddington, who described it as a "brilliant solution" to the outstanding problems of cosmology, and arranged for Lemaître’s theory to be translated and reprinted in the “Monthly Notices of the Royal Astronomical Society” in 1931.
Later in 1931, at a meeting of the British Association in London to discuss the relationship between the physical universe and spirituality, Lemaître first voiced his proposal that the universe had expanded from an initial point, which he called the "primeval atom" or "the Cosmic Egg, exploding at the moment of the creation", a theme he developed further in a report published in the journal “Nature” later that year.
Lemaître argued that, if matter is everywhere receding, it would seem natural to suppose that in the distant past it was closer together, and that, if we go far enough back, we reach a time at which the entire universe was in an extremely compact and compressed state. He spoke, rather vaguely, of some instability being produced by radioactive decay of the primal atom that was sufficient to cause an immense explosion that initiated the expansion of the universe. The theory later became much better known as the "Big Bang" theory after a sarcastic remark of the English astronomer Fred Hoyle in 1949, and its importance today is arguably due more to the revival and revision it received at the hands of George Gamow in 1946.
Lemaître’s proposal initially met with skepticism from his fellow scientists at the time, and even the supportive Eddington found Lemaître’s notion “repugnant”. Einstein was initially unwilling to accept Lemaître's idea of an expanding universe, although he did appreciate Lemaître's argument that the static-Einsteinian model of the universe could not be sustained indefinitely into the past, commenting "Your math is correct, but your physics is abominable".
However, by 1933, the theory had become more widely accepted and newspapers around the world began calling him a famous Belgian scientist and describing him as the leader of the new cosmological physics. Some claim that Einstein’s 1933 comment that “this is the most beautiful and satisfactory explanation of creation to which I have ever listened” was in direct reference to Lemaître’s theory, although others dispute this.
Lemaître received the highest Belgian scientific distinction, the Francqui Prize, in 1934 (proposed by Albert Einstein, among others). He was elected a member of the Pontifical Academy of Sciences in 1936, and remained an active member until his death, accepting the position of president in 1960. In 1941, he was elected member of the Royal Academy of Sciences and Arts of Belgium, and he received the very first Eddington Medal awarded by the Royal Astronomical Society in 1953.
During the 1950s, he gradually gave up part of his teaching workload at Leuven, and he retired completely in 1964, devoting his time to numerical calculation, as well as keeping up his strong interest in the development of computers and in the problems of language and programming.
He died on 20 June 1966, shortly after having learned of the discovery of cosmic microwave background radiation, which provided further evidence for his own intuitions about the birth of the universe.