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Sunday, February 3, 2019

Arthur Eddington

From Wikipedia, the free encyclopedia
 
Sir Arthur Eddington
Arthur Stanley Eddington.jpg
Arthur Stanley Eddington (1882–1944)
Born
Arthur Stanley Eddington

28 December 1882
Kendal, Westmorland, England, United Kingdom
Died22 November 1944 (aged 61)
Cambridge, Cambridgeshire, England, United Kingdom
ResidenceEngland
NationalityEnglish
CitizenshipBritish
Alma materUniversity of Manchester
Trinity College, Cambridge
Known forEddington limit
Eddington number
Eddington–Dirac number
Eddington–Finkelstein coordinates
AwardsRoyal SocietyRoyal Medal (1928) Smith's Prize (1907) RAS Gold Medal (1924)
Henry Draper Medal (1924)
Bruce Medal (1924)
Knights Bachelor (1930)
Order of Merit (1938)
Scientific career
FieldsAstrophysics
InstitutionsTrinity College, Cambridge
Academic advisorsRobert Alfred Herman
Doctoral studentsSubrahmanyan Chandrasekhar
Leslie Comrie
Gerald Merton
G. L. Clark
Cecilia Payne-Gaposchkin
Hermann Bondi
InfluencesHorace Lamb
Arthur Schuster
John William Graham

Sir Arthur Stanley Eddington OM FRS (28 December 1882 – 22 November 1944) was an English astronomer, physicist, and mathematician of the early 20th century who did his greatest work in astrophysics. He was also a philosopher of science and a popularizer of science. The Eddington limit, the natural limit to the luminosity of stars, or the radiation generated by accretion onto a compact object, is named in his honor.

Around 1920, he anticipated the discovery and mechanism of nuclear fusion processes in stars, in his paper "The Internal Constitution of the Stars". At that time, the source of stellar energy was a complete mystery; Eddington was the first to correctly speculate that the source was fusion of hydrogen into helium.

He is famous for his work concerning the theory of relativity. Eddington wrote a number of articles that announced and explained Einstein's theory of general relativity to the English-speaking world. World War I severed many lines of scientific communication and new developments in German science were not well known in England. He also conducted an expedition to observe the solar eclipse of 29 May 1919 that provided one of the earliest confirmations of general relativity, and he became known for his popular expositions and interpretations of the theory.

Early years

Eddington was born 28 December 1882 in Kendal, Westmorland (now Cumbria), England, the son of Quaker parents, Arthur Henry Eddington, headmaster of the Quaker School, and Sarah Ann Shout.

His father taught at a Quaker training college in Lancashire before moving to Kendal to become headmaster of Stramongate School. He died in the typhoid epidemic which swept England in 1884. His mother was left to bring up her two children with relatively little income. The family moved to Weston-super-Mare where at first Stanley (as his mother and sister always called Eddington) was educated at home before spending three years at a preparatory school. The family lived at a house called Varzin, 42 Walliscote Road, Weston-super-Mare. There is a commemorative plaque on the building explaining Sir Arthur's contribution to science.

In 1893 Eddington entered Brynmelyn School. He proved to be a most capable scholar, particularly in mathematics and English literature. His performance earned him a scholarship to Owens College, Manchester (what was later to become the University of Manchester) in 1898, which he was able to attend, having turned 16 that year. He spent the first year in a general course, but turned to physics for the next three years. Eddington was greatly influenced by his physics and mathematics teachers, Arthur Schuster and Horace Lamb. At Manchester, Eddington lived at Dalton Hall, where he came under the lasting influence of the Quaker mathematician J. W. Graham. His progress was rapid, winning him several scholarships and he graduated with a B.Sc. in physics with First Class Honours in 1902. 

Based on his performance at Owens College, he was awarded a scholarship to Trinity College, Cambridge in 1902. His tutor at Cambridge was Robert Alfred Herman and in 1904 Eddington became the first ever second-year student to be placed as Senior Wrangler. After receiving his M.A. in 1905, he began research on thermionic emission in the Cavendish Laboratory. This did not go well, and meanwhile he spent time teaching mathematics to first year engineering students. This hiatus was brief. Through a recommendation by E. T. Whittaker, his senior colleague at Trinity College, he secured a position at the Royal Observatory in Greenwich where he was to embark on his career in astronomy, a career whose seeds had been sown even as a young child when he would often "try to count the stars".

Plaque at 42 Walliscote Road, Weston-super-Mare

Astronomy

In January 1906, Eddington was nominated to the post of chief assistant to the Astronomer Royal at the Royal Greenwich Observatory. He left Cambridge for Greenwich the following month. He was put to work on a detailed analysis of the parallax of 433 Eros on photographic plates that had started in 1900. He developed a new statistical method based on the apparent drift of two background stars, winning him the Smith's Prize in 1907. The prize won him a Fellowship of Trinity College, Cambridge. In December 1912 George Darwin, son of Charles Darwin, died suddenly and Eddington was promoted to his chair as the Plumian Professor of Astronomy and Experimental Philosophy in early 1913. Later that year, Robert Ball, holder of the theoretical Lowndean chair also died, and Eddington was named the director of the entire Cambridge Observatory the next year. In May 1914 he was elected a Fellow of the Royal Society: he was awarded the Royal Medal in 1928 and delivered the Bakerian Lecture in 1926.

Eddington also investigated the interior of stars through theory, and developed the first true understanding of stellar processes. He began this in 1916 with investigations of possible physical explanations for Cepheid variable stars. He began by extending Karl Schwarzschild's earlier work on radiation pressure in Emden polytropic models. These models treated a star as a sphere of gas held up against gravity by internal thermal pressure, and one of Eddington's chief additions was to show that radiation pressure was necessary to prevent collapse of the sphere. He developed his model despite knowingly lacking firm foundations for understanding opacity and energy generation in the stellar interior. However, his results allowed for calculation of temperature, density and pressure at all points inside a star, and Eddington argued that his theory was so useful for further astrophysical investigation that it should be retained despite not being based on completely accepted physics. James Jeans contributed the important suggestion that stellar matter would certainly be ionized, but that was the end of any collaboration between the pair, who became famous for their lively debates. 

Eddington defended his method by pointing to the utility of his results, particularly his important mass-luminosity relation. This had the unexpected result of showing that virtually all stars, including giants and dwarfs, behaved as ideal gases. In the process of developing his stellar models, he sought to overturn current thinking about the sources of stellar energy. Jeans and others defended the Kelvin–Helmholtz mechanism, which was based on classical mechanics, while Eddington speculated broadly about the qualitative and quantitative consequences of possible proton-electron annihilation and nuclear fusion processes. 

Around 1920, he anticipated the discovery and mechanism of nuclear fusion processes in stars, in his paper The Internal Constitution of the Stars. At that time, the source of stellar energy was a complete mystery; Eddington correctly speculated that the source was fusion of hydrogen into helium, liberating enormous energy according to Einstein's equation E = mc2. This was a particularly remarkable development since at that time fusion and thermonuclear energy, and even the fact that stars are largely composed of hydrogen, had not yet been discovered. Eddington's paper, based on knowledge at the time, reasoned that:
  • The leading theory of stellar energy, the contraction hypothesis, should cause stars' rotation to visibly speed up due to conservation of angular momentum. But observations of Cepheid variable stars showed this was not happening.
  • The only other known plausible source of energy was conversion of matter to energy; Einstein had shown some years earlier that a small amount of matter was equivalent to a large amount of energy.
  • Francis Aston had also recently shown that the mass of a helium atom was about 0.8% less than the mass of the four hydrogen atoms which would, combined, form a helium atom, suggesting that if such a combination could happen, it would release considerable energy as a byproduct.
  • If a star contained just 5% of fusible hydrogen, it would suffice to explain how stars got their energy. (We now know that most 'ordinary' stars contain far more than 5% hydrogen)
  • Further elements might also be fused, and other scientists had speculated that stars were the "crucible" in which light elements combined to create heavy elements, but without more accurate measurements of their atomic masses nothing more could be said at the time.
All of these speculations were proven correct in the following decades. 

With these assumptions, he demonstrated that the interior temperature of stars must be millions of degrees. In 1924, he discovered the mass-luminosity relation for stars. Despite some disagreement, Eddington's models were eventually accepted as a powerful tool for further investigation, particularly in issues of stellar evolution. The confirmation of his estimated stellar diameters by Michelson in 1920 proved crucial in convincing astronomers unused to Eddington's intuitive, exploratory style. Eddington's theory appeared in mature form in 1926 as The Internal Constitution of the Stars, which became an important text for training an entire generation of astrophysicists.

Eddington's work in astrophysics in the late 1920s and the 1930s continued his work in stellar structure, and precipitated further clashes with Jeans and Edward Arthur Milne. An important topic was the extension of his models to take advantage of developments in quantum physics, including the use of degeneracy physics in describing dwarf stars.

Dispute with Chandrasekhar on existence of black holes

The topic of extension of his models precipitated his famous dispute with Subrahmanyan Chandrasekhar, who was then a student at Cambridge. Chandrasekhar's work presaged the discovery of black holes, which at the time seemed so absurdly non-physical that Eddington refused to believe that Chandrasekhar's purely mathematical derivation had consequences for the real world. History clearly proved Eddington wrong, but his motivation remains a matter of some controversy. Chandrasekhar's narrative of this incident, in which his work is harshly rejected, portrays Eddington as rather cruel, dogmatic, and racist. Eddington's criticism seems to have been based on a suspicion that a purely mathematical derivation from relativity theory was not enough to explain away the seemingly daunting physical paradoxes that were inherent to degenerate stars.

Relativity

During World War I, Eddington was Secretary of the Royal Astronomical Society, which meant he was the first to receive a series of letters and papers from Willem de Sitter regarding Einstein's theory of general relativity. Eddington was fortunate in being not only one of the few astronomers with the mathematical skills to understand general relativity, but owing to his internationalist and pacifist views inspired by his Quaker religious beliefs, one of the few at the time who was still interested in pursuing a theory developed by a German physicist. He quickly became the chief supporter and expositor of relativity in Britain. He and Astronomer Royal Frank Watson Dyson organized two expeditions to observe a solar eclipse in 1919 to make the first empirical test of Einstein's theory: the measurement of the deflection of light by the sun's gravitational field. In fact, Dyson's argument for the indispensability of Eddington's expertise in this test was what prevented Eddington from eventually having to enter military service.

When conscription was introduced in Britain on 2 March 1916, Eddington intended to apply for an exemption as a conscientious objector. Cambridge University authorities instead requested and were granted an exemption on the ground of Eddington's work being of national interest. In 1918, this was appealed against by the Ministry of National Service. Before the appeal tribunal in June, Eddington claimed conscientious objector status, which was not recognized and would have ended his exemption in August 1918. A further two hearings took place in June and July, respectively. Eddington's personal statement at the June hearing about his objection to war based on religious grounds is on record. Astronomer Royal, Sir Frank Dyson, supported Eddington at the July hearing with a written statement, emphasising Eddington's essential role in the solar eclipse expedition to Principe in May 1919. Eddington made clear his willingness to serve in the Friends' Ambulance Unit, under the jurisdiction of the British Red Cross, or as a harvest labourer. However, the tribunal's decision to grant a further twelve months exemption from military service was on condition of Eddington continuing his astronomy work, in particular in preparation for the Principe expedition. The war ended before the end of his exemption.

One of Eddington's photographs of the total solar eclipse of 29 May 1919, presented in his 1920 paper announcing its success, confirming Einstein's theory that light "bends"
 
After the war, Eddington travelled to the island of Príncipe off the west coast of Africa to watch the solar eclipse of 29 May 1919. During the eclipse, he took pictures of the stars (several stars in the Hyades cluster include Kappa Tauri of the constellation Taurus) in the region around the Sun. According to the theory of general relativity, stars with light rays that passed near the Sun would appear to have been slightly shifted because their light had been curved by its gravitational field. This effect is noticeable only during eclipses, since otherwise the Sun's brightness obscures the affected stars. Eddington showed that Newtonian gravitation could be interpreted to predict half the shift predicted by Einstein. 

Eddington's observations published the next year confirmed Einstein's theory, and were hailed at the time as evidence of general relativity over the Newtonian model. The news was reported in newspapers all over the world as a major story. Afterward, Eddington embarked on a campaign to popularize relativity and the expedition as landmarks both in scientific development and international scientific relations. 

It has been claimed that Eddington's observations were of poor quality, and he had unjustly discounted simultaneous observations at Sobral, Brazil, which appeared closer to the Newtonian model, but a 1979 re-analysis with modern measuring equipment and contemporary software validated Eddington's results and conclusions. The quality of the 1919 results was indeed poor compared to later observations, but was sufficient to persuade contemporary astronomers. The rejection of the results from the Brazil expedition was due to a defect in the telescopes used which, again, was completely accepted and well understood by contemporary astronomers.

Throughout this period, Eddington lectured on relativity, and was particularly well known for his ability to explain the concepts in lay terms as well as scientific. He collected many of these into the Mathematical Theory of Relativity in 1923, which Albert Einstein suggested was "the finest presentation of the subject in any language." He was an early advocate of Einstein's General Relativity, and an interesting anecdote well illustrates his humour and personal intellectual investment: Ludwik Silberstein, a physicist who thought of himself as an expert on relativity, approached Eddington at the Royal Society's (6 November) 1919 meeting where he had defended Einstein's Relativity with his Brazil-Principe Solar Eclipse calculations with some degree of skepticism, and ruefully charged Arthur as one who claimed to be one of three men who actually understood the theory (Silberstein, of course, was including himself and Einstein as the other). When Eddington refrained from replying, he insisted Arthur not be "so shy", whereupon Eddington replied, "Oh, no! I was wondering who the third one might be!"

Cosmology

Eddington was also heavily involved with the development of the first generation of general relativistic cosmological models. He had been investigating the instability of the Einstein universe when he learned of both Lemaître's 1927 paper postulating an expanding or contracting universe and Hubble's work on the recession of the spiral nebulae. He felt the cosmological constant must have played the crucial role in the universe's evolution from an Einsteinian steady state to its current expanding state, and most of his cosmological investigations focused on the constant's significance and characteristics. In The Mathematical Theory of Relativity, Eddington interpreted the cosmological constant to mean that the universe is "self-gauging".

Fundamental theory and the Eddington number

During the 1920s until his death, Eddington increasingly concentrated on what he called "fundamental theory" which was intended to be a unification of quantum theory, relativity, cosmology, and gravitation. At first he progressed along "traditional" lines, but turned increasingly to an almost numerological analysis of the dimensionless ratios of fundamental constants. 

His basic approach was to combine several fundamental constants in order to produce a dimensionless number. In many cases these would result in numbers close to 1040, its square, or its square root. He was convinced that the mass of the proton and the charge of the electron were a natural and complete specification for constructing a Universe and that their values were not accidental. One of the discoverers of quantum mechanics, Paul Dirac, also pursued this line of investigation, which has become known as the Dirac large numbers hypothesis, and some scientists even today believe it has something to it.

A somewhat damaging statement in his defence of these concepts involved the fine structure constant, α. At the time it was measured to be very close to 1/136, and he argued that the value should in fact be exactly 1/136 for epistemological reasons. Later measurements placed the value much closer to 1/137, at which point he switched his line of reasoning to argue that one more should be added to the degrees of freedom, so that the value should in fact be exactly 1/137, the Eddington number. Wags at the time started calling him "Arthur Adding-one". This change of stance detracted from Eddington's credibility in the physics community. The current measured value is estimated at 1/137.035 999 074(44). 

Eddington believed he had identified an algebraic basis for fundamental physics, which he termed "E-numbers" (representing a certain group – a Clifford algebra). These in effect incorporated spacetime into a higher-dimensional structure. While his theory has long been neglected by the general physics community, similar algebraic notions underlie many modern attempts at a grand unified theory. Moreover, Eddington's emphasis on the values of the fundamental constants, and specifically upon dimensionless numbers derived from them, is nowadays a central concern of physics. In particular, he predicted a number of hydrogen atoms in the Universe 136 × 2256, or equivalently the half of the total number of particles protons + electrons. When equalized with the non-dark energy equivalent number of hydrogen atoms (3/10) × Rc2/GmH, this corresponds to a Universe radius R = 13.8 Giga light year, a value predicted for years from universal constants using an atomic-cosmic symmetry, and compatible with c times the so-called age of the Universe, 13.80(4) Gyr, as determined by the Planck mission in March 2003.

He did not complete this line of research before his death in 1944; his book Fundamental Theory was published posthumously in 1948.

Eddington number for cycling

Eddington is credited with devising a measure of a cyclist's long-distance riding achievements. The Eddington number in the context of cycling is defined as the maximum number E such that the cyclist has cycled E miles on E days. For example, an Eddington number of 70 would imply that the cyclist has cycled at least 70 miles in a day on 70 occasions. Achieving a high Eddington number is difficult since moving from, say, 70 to 75 will probably require more than five new long distance rides since any rides shorter than 75 miles will no longer be included in the reckoning. Eddington's own E-number was 84.

The Eddington number for cycling is analogous to the h-index that quantifies both the actual scientific productivity and the apparent scientific impact of a scientist.

The Eddington Number for cycling has units (indeed applying it to any physical property will result in E having units). For example, an E of 62 miles means a cyclist has covered 62 or more miles on 62 or more days. However, in units of kilometers the 62 miles becomes 100 km. It is possible that the cyclist, while having covered 100 km on 62 days or more, may not have covered 100 km on 100 days or more. Thus the order of bicyclists may change depending on units used. Using the original miles, one cyclist may have an Eddington number of 60 – 60 miles (97 km) in 60 days, another of 50 (corresponding to 80 km). However, the latter may be a regular on a distance like this and get a km-Eddington of 80, while the former only had those 60 days riding, and thus stays at a km-Eddington of 60.

Philosophy

Idealism

Eddington wrote in his book The Nature of the Physical World that "The stuff of the world is mind-stuff."
The mind-stuff of the world is, of course, something more general than our individual conscious minds ... The mind-stuff is not spread in space and time; these are part of the cyclic scheme ultimately derived out of it ... It is necessary to keep reminding ourselves that all knowledge of our environment from which the world of physics is constructed, has entered in the form of messages transmitted along the nerves to the seat of consciousness ... Consciousness is not sharply defined, but fades into subconsciousness; and beyond that we must postulate something indefinite but yet continuous with our mental nature ... It is difficult for the matter-of-fact physicist to accept the view that the substratum of everything is of mental character. But no one can deny that mind is the first and most direct thing in our experience, and all else is remote inference.
— Eddington, The Nature of the Physical World, 276–81.
The idealist conclusion was not integral to his epistemology but was based on two main arguments.
The first derives directly from current physical theory. Briefly, mechanical theories of the ether and of the behaviour of fundamental particles have been discarded in both relativity and quantum physics. From this, Eddington inferred that a materialistic metaphysics was outmoded and that, in consequence, since the disjunction of materialism or idealism are assumed to be exhaustive, an idealistic metaphysics is required. The second, and more interesting argument, was based on Eddington's epistemology, and may be regarded as consisting of two parts. First, all we know of the objective world is its structure, and the structure of the objective world is precisely mirrored in our own consciousness. We therefore have no reason to doubt that the objective world too is "mind-stuff". Dualistic metaphysics, then, cannot be evidentially supported.

But, second, not only can we not know that the objective world is nonmentalistic, we also cannot intelligibly suppose that it could be material. To conceive of a dualism entails attributing material properties to the objective world. However, this presupposes that we could observe that the objective world has material properties. But this is absurd, for whatever is observed must ultimately be the content of our own consciousness, and consequently, nonmaterial. 

Ian Barbour, in his book Issues in Science and Religion (1966), p. 133, cites Eddington's The Nature of the Physical World (1928) for a text that argues the Heisenberg Uncertainty Principles provides a scientific basis for "the defense of the idea of human freedom" and his Science and the Unseen World (1929) for support of philosophical idealism "the thesis that reality is basically mental".

Charles De Koninck points out that Eddington believed in objective reality existing apart from our minds, but was using the phrase "mind-stuff" to highlight the inherent intelligibility of the world: that our minds and the physical world are made of the same "stuff" and that our minds are the inescapable connection to the world. As De Koninck quotes Eddington,
There is a doctrine well known to philosophers that the moon ceases to exist when no one is looking at it. I will not discuss the doctrine since I have not the least idea what is the meaning of the word existence when used in this connection. At any rate the science of astronomy has not been based on this spasmodic kind of moon. In the scientific world (which has to fulfill functions less vague than merely existing) there is a moon which appeared on the scene before the astronomer; it reflects sunlight when no one sees it; it has mass when no one is measuring the mass; it is distant 240,000 miles from the earth when no one is surveying the distance; and it will eclipse the sun in 1999 even if the human race has succeeded in killing itself off before that date.
— Eddington, The Nature of the Physical World, 226

Indeterminism

Against Albert Einstein and others who advocated determinism, indeterminism—championed by Eddington—says that a physical object has an ontologically undetermined component that is not due to the epistemological limitations of physicists' understanding. The uncertainty principle in quantum mechanics, then, would not necessarily be due to hidden variables but to an indeterminism in nature itself.

Popular and philosophical writings

Eddington wrote a clever parody of The Rubaiyat of Omar Khayyam, recounting his 1919 solar eclipse experiment. It contained the following quatrain:
Oh leave the Wise our measures to collate
           One thing at least is certain, LIGHT has WEIGHT,
One thing is certain, and the rest debate—
Light-rays, when near the Sun, DO NOT GO STRAIGHT.

During the 1920s and 30s, Eddington gave numerous lectures, interviews, and radio broadcasts on relativity, in addition to his textbook The Mathematical Theory of Relativity, and later, quantum mechanics. Many of these were gathered into books, including The Nature of the Physical World and New Pathways in Science. His skillful use of literary allusions and humor helped make these famously difficult subjects quite accessible.

Eddington's books and lectures were immensely popular with the public, not only because of Eddington's clear and entertaining exposition, but also for his willingness to discuss the philosophical and religious implications of the new physics. He argued for a deeply rooted philosophical harmony between scientific investigation and religious mysticism, and also that the positivist nature of modern physics (i.e., relativity and quantum physics) provided new room for personal religious experience and free will. Unlike many other spiritual scientists, he rejected the idea that science could provide proof of religious propositions.

He is sometimes misunderstood as having promoted the infinite monkey theorem in his 1928 book The Nature of the Physical World, with the phrase "If an army of monkeys were strumming on typewriters, they might write all the books in the British Museum". It is clear from the context that Eddington is not suggesting that the probability of this happening is worthy of serious consideration. On the contrary, it was a rhetorical illustration of the fact that below certain levels of probability, the term improbable is functionally equivalent to impossible.

His popular writings made him a household name in Great Britain between the world wars.

Death

Eddington died of cancer in the Evelyn Nursing Home, Cambridge, on 22 November 1944. He was unmarried. His body was cremated at Cambridge Crematorium (Cambridgeshire) on 27 November 1944; the cremated remains were buried in the grave of his mother in the Ascension Parish Burial Ground in Cambridge.

Cambridge University's North West Cambridge Development has been named "Eddington" in his honor.

Obituaries

Honors

Awards

Named after him

Service

In popular culture

Publications

Georges Lemaître

From Wikipedia, the free encyclopedia


Georges Lemaître
Portrait Georges Lemaitre.jpg
Portrait of Lemaître
Born17 July 1894
Charleroi, Belgium
Died20 June 1966 (aged 71)
Leuven, Belgium
NationalityBelgian
Alma materCatholic University of Louvain
St Edmund's House, Cambridge
Massachusetts Institute of Technology
Known forTheory of the expansion of the universe
Big Bang theory
Lemaître coordinates
AwardsFrancqui Prize (1934)
Eddington Medal (1953)
Scientific career
FieldsCosmology
Astrophysics
Mathematics
InstitutionsCatholic University of Leuven
Doctoral advisorCharles Jean de la Vallée-Poussin (Leuven)
Arthur Eddington (Cambridge)
Harlow Shapley (MIT)
Doctoral studentsLouis Philippe Bouckaert, Rene van der Borght
Signature
Georges Lemaitre signature.jpg

Georges Henri Joseph Édouard Lemaître, RAS Associate; 17 July 1894 – 20 June 1966) was a Belgian Roman Catholic priest, mathematician, astronomer, and professor of physics at the Catholic University of Louvain. He proposed on theoretical grounds that the universe is expanding, which was observationally confirmed soon afterwards by Edwin Hubble. He was the first to derive what is now known as Hubble's law, or the Hubble-Lemaître law, and made the first estimation of what is now called the Hubble constant, which he published in 1927, two years before Hubble's article. Lemaître also proposed what became known as the "Big Bang theory" of the creation of the universe, originally calling it the "hypothesis of the primeval atom".

Early life

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

After the war, he studied physics and mathematics, and began to prepare for the diocesan priesthood, not for the Jesuits. 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 on 22 September 1923 by the Cardinal Mercier.

In 1923, he became a research associate in astronomy at Cambridge UK, spending a year at St Edmund's House (now St Edmund's College, University of Cambridge). He worked with Arthur Eddington, who introduced him to modern cosmology, stellar astronomy, and numerical analysis. He spent the next year at Harvard College Observatory in Cambridge, Massachusetts, with Harlow Shapley, who had just gained renown for his work on nebulae, and at the Massachusetts Institute of Technology (MIT), where he registered for the doctoral program in sciences.

Career

On his return to Belgium in 1925, he became a part-time lecturer at the Catholic University of Louvain. He began the report which brought him international fame when it was 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 that the universe is expanding, which he derived from General Relativity; this later became known as Hubble's law, but Lemaître provided the first observational estimation of the Hubble constant. The initial state he proposed was taken to be Einstein's own model of a finitely sized static universe. The paper had little impact because the journal in which it was published was not widely read by astronomers outside Belgium; Arthur Eddington reportedly helped translate the article into English in 1931, but the part of it pertaining to the estimation of the "Hubble constant" was not included in the translation for reasons that remained unknown for a long time. This issue was clarified in 2011 by Mario Livio; Lemaître omitted the paragraphs when himself initially translating the paper for the Royal Astronomical Society, in favor of reports of new work on the subject, since by that time Hubble's calculations had already improved on his earlier ones.

At this time, Einstein, while not taking exception to the mathematics of Lemaître's theory, refused to accept that the universe was expanding; Lemaître recalled his commenting "Vos calculs sont corrects, mais votre physique est abominable" ("Your calculations are correct, but your physics is atrocious"). In 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 his Ph.D., he was named ordinary professor at the Catholic University of Louvain. 

In 1931, Arthur 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 later on in 1931, along with a sequel by Lemaître responding to Eddington's comments. Lemaître was then invited to London to participate 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 point, which he called the "Primeval Atom". He developed this idea in a report published in Nature. Lemaitre's theory appeared for the first time in an article for the general reader on science and technology subjects in the December 1932 issue of Popular Science. Lemaître's theory became better known as the "Big Bang theory," a picturesque term playfully coined during a 1949 BBC radio broadcast by the astronomer Fred Hoyle, who was then still a proponent of the steady state universe and remained so until his death in 2001.

Lemaître's proposal met with skepticism from his fellow scientists. Eddington found Lemaître's notion unpleasant. Einstein thought it unjustifiable from a physical point of view, although he encouraged Lemaître to look into the possibility of models of non-isotropic expansion, so it is clear he was not altogether dismissive of the concept. Einstein also appreciated Lemaître's argument that Einstein's model of a static universe could not be sustained into the infinite past.

With Manuel Sandoval Vallarta, Lemaitre discovered that the intensity of cosmic rays varied with latitude because these charged particles are interacting with the Earth's magnetic field. In their calculations, Lemaître and Vallarta made use of the MIT’s differential -analyzer computer developed by Vannevar Bush. They 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.

Lemaître and Einstein met on four 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; in California in January 1933; and in 1935 at Princeton. In 1933 at the California Institute of Technology, after Lemaître 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 referring to the theory as a whole, but only to Lemaître's proposal that cosmic rays may be the leftover artifacts of the initial "explosion". 

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 achieved his greatest public recognition. Newspapers around the world called him a famous Belgian scientist and described him as the leader of the new cosmological physics.

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.

In 1941, he was elected a 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 was translated into Spanish in the same year and into English in 1950.

By 1951, Pope Pius XII declared that Lemaître's theory provided a scientific validation for Catholicism. However, Lemaître resented the Pope's proclamation, stating that the theory was neutral and there was neither a connection nor a contradiction between his religion and his theory. Lemaître and Daniel O'Connell, the Pope's scientific advisor, persuaded the Pope not to mention Creationism publicly, and to stop making proclamations about cosmology. While a devout Roman Catholic, he opposed mixing science with religion, although he held that the two fields were not in conflict.

During the 1950s, he gradually gave up part of his teaching workload, ending it completely when he took emeritus status in 1964. In 1962, strongly opposed to the expulsion of French speakers from the Catholic University of Louvain, he created the ACAPSUL movement together with Gérard Garitte to fight against the split.

During the Second Vatican Council of 1962–65 he was asked by Pope John XXIII to serve on the 4th session of the Pontifical Commission on Birth Control. However, since his health made it impossible for him to travel to Rome – he suffered a heart attack in December 1964 – Lemaître demurred, expressing surprise that he was chosen. He told a Dominican colleague, Père Henri de Riedmatten, that he thought it was dangerous for a mathematician to venture outside of his area of expertise. He was also named Dometisc prelate (Monsignor) in 1960 by Pope John XXIII.

At the end of his life, he was increasingly devoted to problems of numerical calculation. He was a remarkable algebraicist and arithmetical calculator. Since 1930, he had used the most powerful calculating machines of the time, the Mercedes-Euklid. In 1958 he was introduced to the University's Burroughs E 101, its first electronic computer. Lemaître maintained a strong interest in the development of computers and, even more, in the problems of language and computer 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 proposal about the birth of the universe.

Work

Lemaître was a pioneer in applying Albert Einstein's theory of general relativity to cosmology. In a 1927 article, which preceded Edwin Hubble's landmark article by two years, Lemaître derived what became known as Hubble's law and proposed it as a generic phenomenon in relativistic cosmology. Lemaître also estimated the numerical value of the Hubble constant. However, the data used by Lemaître did not allow him to prove that there was an actual linear relation, which Hubble did two years later.

Einstein was skeptical of this paper. When Lemaître approached Einstein at the 1927 Solvay Conference, the latter pointed out that Alexander Friedmann had proposed a similar solution to Einstein's equations in 1922, implying that the radius of the universe increased over time. (Einstein had also criticized Friedmann's calculations, but withdrew his comments.) In 1931, his annus mirabilis, Lemaître published an article in Nature setting out his theory of the "primeval atom."

Friedmann was handicapped by living and working in the USSR, and died in 1925, soon after inventing the Friedmann–Lemaître–Robertson–Walker metric. Because Lemaître spent his entire career in Europe, his scientific work is not as well known in the United States as that of Hubble or Einstein, both well known in the U.S. by virtue of residing there. Nevertheless, Lemaître's theory changed the course of cosmology. This was because Lemaître:
  • Was well acquainted with the work of astronomers, and designed his theory to have testable implications and to be in accord with observations of the time, in particular to explain the observed redshift of galaxies and the linear relation between distances and velocities;
  • 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, Lemaître's Big Bang theory;
  • Had studied under Arthur Eddington, who made sure that Lemaître got a hearing in the scientific community.
Both Friedmann and Lemaître proposed relativistic cosmologies featuring an expanding universe. However, Lemaître was the first to propose that the expansion explains the redshift of galaxies. He further concluded that an initial "creation-like" event must have occurred. In the 1980s, Alan Guth and Andrei Linde modified this theory by adding to it a period of inflation.

Einstein at first dismissed Friedmann, and then (privately) Lemaître, out of hand, saying that not all mathematics lead 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.

Lemaître was also an early adopter of computers for cosmological calculations. He introduced the first computer to his university (a Burroughs E 101) in 1958 and was one of the inventors of the Fast Fourier transform algorithm.

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

In 1931, Lemaitre was the first scientist to propose the expansion of the universe was actually accelerating which was confirmed observationally in the 1990s through observations of very distant Type IA supernova with the Hubble Space Telescope which led to the 2011 Nobel Prize in Physics.

In 1948 Lemaître published a polished mathematical essay "Quaternions et espace elliptique" which clarified an obscure space. William Kingdon Clifford had cryptically described elliptic space in 1873 at a time when versors were too common to mention. Lemaître developed the theory of quaternions from first principles so that his essay can stand on its own, but he recalled the Erlangen program in geometry while developing the metric geometry of elliptic space. H. S. M. Coxeter, another contributor to elliptic geometry, summarized Lemaître's work for Mathematical Reviews

Lemaître was the first theoretical cosmologist ever nominated in 1954 for the Nobel Prize in physics for his prediction of the expanding universe. Remarkably, he was also nominated for the 1956 Nobel prize in chemistry for his primeval-atom theory.

Honors

On 17 March 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, 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 awarded by the Royal Astronomical Society.

In 2005, Lemaître was voted to the 61st place of De Grootste Belg ("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 Les plus grands Belges ("The Greatest Belgians"), a television show of the RTBF.

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

Bibliography

  • G. Lemaître, Discussion sur l'évolution de l'univers, 1927
  • G. Lemaître, L'Hypothèse de l'atome primitif, 1931
  • G. Lemaître, The Primeval Atom – an Essay on Cosmogony, D. Van Nostrand Co, 1946.
  • Lemaître, G. (1931). "The Evolution of the Universe: Discussion". Nature. 128 (3234): 699–701. Bibcode:1931Natur.128..704L. doi:10.1038/128704a0.
  • Lemaître, G. (1927). "Un univers homogène de masse constante et de rayon croissant rendant compte de la vitesse radiale des nébuleuses extragalactiques". Annals of the Scientific Society of Brussels (in French). 47A: 41.
(Translated in: Lemaître, G (1931). "A Homogeneous Universe of Constant Mass and Growing Radius Accounting for the Radial Velocity of Extragalactic Nebulae". Monthly Notices of the Royal Astronomical Society. 91 (5): 483–490. Bibcode:1931MNRAS..91..483L. doi:10.1093/mnras/91.5.483.)

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