Georges Lemaître

Georges Lemaître
File:Prelate Father Lemaitre University.jpg Monsignor Georges Lemaître, priest and scientist
Born	July 17, 1894
Died	June 20, 1966
Nationality	Belgian
Known for	Big Bang
Scientific career
Fields	Astronomer, Astrophysicist
Institutions	Université catholique de Louvain

Georges Henri Joseph Éduard Lemaître (July 17, 1894 – June 20, 1966) was a Belgian Roman Catholic priest, honorary prelate, professor of physics and astronomer at the Université catholique de Louvain. He sometimes used the title Abbé or Monsignor.

Lemaître proposed what became known as the Big Bang theory of the origin of the Universe, which he called his 'hypothesis of the primeval atom'.

Work

Lemaitre was a pioneer in applying Einstein's theory of general relativity to cosmology. He suggested a precursor of Hubble's law in 1927. In 1931, he published his primeval atom theory in Nature. At the time, Einstein believed in a static universe and had expressed skepticism about Lemaître's 1927 paper. A similar solution to Einstein's equations, implying a changing radius of the universe, had been proposed in 1922 by Alexander Friedman, as Einstein told Lemaître when he approached him with the theory at the 1927 Solvay Conference. (Einstein had also criticized Friedman's theory.) But it is Lemaître's theory that changed the course of science, for the following reasons:

• Friedman was a mathematician who neither worked with astronomical data nor cared whether his theory was a description of physical reality.
• Friedman died in 1925, soon after first proposing his theory.
• Lemaître worked with astronomers and designed his theory to have testable implications, and to be in accord with observations of the time.
• Arthur Eddington made sure that Lemaître got a hearing in the scientific community.

Lemaître proposed his theory at an opportune time, since Edwin Hubble would soon publish his velocity-distance relation that strongly supported an expanding universe and, consequently, the Big Bang theory. In fact, Lemaître's 1927 paper derived what became known as Hubble's Law, two years before Hubble did so. Because Lemaître spent his entire career in Europe, his contributions are not as well known as those of Hubble or Einstein, men well known in America by virtue of residing there.

Both Friedman and Lemaître concluded that the universe must be expanding. Lemaître further concluded that an initial "creation-like" event must have occurred. This is the Big Bang theory as we know it today, and why he is credited with its discovery.

Einstein at first dismissed Friedman and then (privately) Lemaître out of hand, saying that not all mathematics leads to correct theories. After Hubble's discovery was published, Einstein quickly and publicly endorsed Lemaître's theory, helping both the theory and its proposer get fast recognition.

In 1933, Lemaître found an important inhomogeneous solution of Einstein's field equations describing a spherical dust cloud, the Lemaitre-Tolman metric.

Biography

According to the Big Bang theory, the universe emerged from an extremely dense and hot state (singularity). Space itself has been expanding ever since, carrying galaxies with it.

After a classical education at a Jesuit secondary school (Collège du Sacré-Coeur, Charleroi), Lemaître began studying civil engineering at the Catholic University of Leuven 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 hostilities, he received the Military Cross with palms.

After the war, he studied physics and mathematics, and began to prepare for priesthood. He obtained his doctorate in 1920 with a thesis entitled l'Approximation des fonctions de plusieurs variables réelles (Approximation of functions of several real variables), written under the direction of Charles de la Vallée-Poussin. He was ordained a priest in 1923.

In 1923, he became a graduate student in astronomy at the University of Cambridge, spending a year at St Edmund's House (now St Edmund's College, Cambridge). He worked with Arthur Eddington who initiated him into modern cosmology, stellar astronomy, and numerical analysis. He spent the following year at Harvard College Observatory in Cambridge, Massachusetts with Harlow Shapley, who had just gained a name for his work on nebulae, and at the Massachusetts Institute of Technology, where he registered for the doctorate in sciences.

In 1925, on his return to Belgium, he became a part-time lecturer at the Catholic University of Leuven. He then began the report which would bring him international fame, published in 1927 in the Annales de la Société Scientifique de Bruxelles (Annals of the Scientific Society of Brussels), under the title "Un Univers homogène de masse constante et de rayon croissant rendant compte de la vitesse radiale des nébuleuses extragalactiques" ("A homogeneous Universe of constant mass and growing radius accounting for the radial velocity of extragalactic nebulae"). In this report, he presented his new idea of an expanding Universe, but not yet that of the primeval atom. Instead, the initial state was taken as Einstein's own finite-size static universe model. Unfortunately, the paper had little impact because the journal in which it was published was not widely read by astronomers outside of Belgium.

At this time, Einstein, while not taking exception to the mathematics of Lemaître's theory, refused to accept the idea of an expanding universe; Lemaître recalled him commenting "Vos calculs sont corrects, mais votre physique est abominable" ("Your math is correct, but your physics is abominable.") The same year, Lemaître returned to MIT to present his doctoral thesis on The gravitational field in a fluid sphere of uniform invariant density according to the theory of relativity. Upon obtaining the PhD, he was named ordinary Professor at the Catholic University of Leuven.

In 1930, Eddington published in the Monthly Notices of the Royal Astronomical Society a long commentary on Lemaître's 1927 article, in which he described the latter as a "brilliant solution" to the outstanding problems of cosmology. The original paper was published in an abbreviated English translation in 1931, along with a sequel by Lemaître responding to Eddington's comments. Lemaître was then invited to London in order to take part in a meeting of the British Association on the relation between the physical Universe and spirituality. There he proposed that the Universe expanded from an initial singularity, which he called the "Primeval Atom" and developed in a report published in Nature. Lemaître himself also described his theory as "the Cosmic Egg exploding at the moment of the creation"; it became better known as the "Big Bang theory," the term having originally been a sarcastic remark of Fred Hoyle's.

This proposal met skepticism from his fellow scientists at the time. Eddington found Lemaître's notion unpleasant. Einstein found it suspect because too strongly reminiscent of the Christian dogma of creation. Moreover, he deemed it unjustifiable from a physical point of view. On the other hand, Einstein encouraged Lemaître to look into the possibility of models of non-isotropic expansion, so it's clear he was not altogether dismissive of the concept. He also appreciated Lemaître's argument that a static-Einstein model of the universe could not be sustained indefinitely into the past.

In January 1933, Lemaître and Einstein, who had met on several occasions - in 1927 in Brussels, at the time of a Solvay Conference, in 1932 in Belgium, at the time of a cycle of conferences in Brussels and lastly in 1935 at Princeton - traveled together to California for a series of seminars. After the Belgian detailed his theory, Einstein stood up, applauded, and is supposed to have said, "This is the most beautiful and satisfactory explanation of creation to which I have ever listened." However there is disagreement over the reporting of this quote in the newspapers of the time, and it may be that Einstein was not actually referring to the theory as a whole but to Lemaître's proposal that cosmic rays may in fact be the left over artifacts of the initial "explosion." Later research on cosmic rays by Robert Millikan would undercut this proposal, however.

In 1933, when he resumed his theory of the expanding Universe and published a more detailed version in the Annals of the Scientific Society of Brussels, Lemaître would achieve his greatest glory. Newspapers around the world called him a famous Belgian scientist and described him as the leader of the new cosmological physics.

On March 17, 1934, Lemaître received the Francqui Prize, the highest Belgian scientific distinction, from King Léopold III. His proposers were Albert Einstein, Charles de la Vallée-Poussin and Alexandre de Hemptinne. The members of the international jury were Eddington, Langevin and Théophile de Donder. 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 1936, he was elected member of the Pontifical Academy of Sciences. He took an active role there, became the president in March 1960 and remaining so until his death. At the outset of the Second Vatican Council, he was bemused to find himself appointed by the Pope to sit on a commission investigating the subject of birth control. However, as he could not travel to Rome because of his health (he had suffered a heart attack in December 1964), he demurred, expressing his surprise that he was even chosen, at the time telling a Dominican colleague, P. Henri de Riedmatten, that he thought it was dangerous for a mathematician to venture outside of his specialty. He was also named prelate (Monsignor) in 1960 by Pope John XXIII.

In 1941, he was elected member of the Royal Academy of Sciences and Arts of Belgium.

In 1946, he published his book on L'Hypothèse de l'Atome Primitif (The Primeval Atom Hypothesis). It would be translated into Spanish in the same year and into English in 1950.

In 1953 he was given the very first Eddington Medal awarded by the Royal Astronomical Society.

During the 1950s, he gradually gave up part of his teaching workload, ending it completely with his éméritat in 1964.

At the end of his life, he was devoted more and more to numerical calculation. He was in fact a remarkable algebraicist and arithmetical calculator. Since 1930, he used the most powerful calculating machines of the time like the Mercedes. In 1958, he introduced at the University a Burroughs E 101, the University's first electronic computer. Lemaître kept a strong interest in the development of computers and, even more, in the problems of language and programming. This interest grew with age until it absorbed him almost completely.

He died on June 20 1966, shortly after having learned of the discovery of cosmic microwave background radiation, proof of his intuitions about the birth of the Universe.

Namesakes

• The Lemaître crater, a lunar impact crater
• The Friedmann-Lemaître-Robertson-Walker metric

Trivia

• In 2005 Lemaître was voted to the 61st place of [De Grootste Belg] Error: {{Lang}}: text has italic markup (help) (Dutch for "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 [Le plus grand belge] Error: {{Lang}}: text has italic markup (help) (French for the "The Greatest Belgian"), a Walloon television show of the RTBF.

External links

• 'A Day Without Yesterday': Georges Lemaitre & the Big Bang
• Biography: The Day Without Yesterday: Lemaitre, Einstein and the Birth of Modern Cosmology.
• Dec, 1932 article in Modern Mechanics explaining the Big Bang theory of Abbe George Lemaitre, Belgian mathematician.