Harlow Shapley

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Harlow_Shapley 

 

Harlow Shapley
Born	November 2, 1885 Nashville, Missouri, U.S.
Died	October 20, 1972 (aged 86) Boulder, Colorado, U.S.
Nationality	American
Alma mater	University of Missouri, Princeton University
Known for	Determining correct position of Sun within Milky Way Galaxy; head of Harvard College Observatory (1921–1952)
Children	5, including Mildred Shapley Matthews (b. 1915) Willis Shapley (b. 1917) Lloyd Shapley (b. 1923)
Awards	Henry Draper Medal (1926) Gold Medal of the Royal Astronomical Society (1934) Rittenhouse Medal (1935) Bruce Medal (1939)
Scientific career
Fields	Astronomy
Doctoral advisor	Henry Norris Russell
Doctoral students	Cecilia Payne-Gaposchkin, Carl Seyfert
Other notable students	Georges Lemaître

Harlow Shapley (November 2, 1885 – October 20, 1972) was an American scientist, head of the Harvard College Observatory (1921–1952), and political activist during the latter New Deal and Fair Deal.

Shapley used Cepheid variable stars to estimate the size of the Milky Way Galaxy and the Sun's position within it by using parallax. In 1953 he proposed his "liquid water belt" theory, now known as the concept of a habitable zone.

Background

Shapley (first standing from the right) at a Science Service board meeting in 1941

 

Members of the Independent Voters Committee of the Arts and Sciences for Roosevelt visit FDR at the White House (October 1944). From left: Van Wyck Brooks, Hannah Dorner, Jo Davidson, Jan Kiepura, Joseph Cotten, Dorothy Gish, Dr. Harlow Shapley

 

Progressive Citizens of America members, 1947. From left, seated, Henry A. Wallace, Elliott Roosevelt; standing, Dr. Harlow Shapley, Jo Davidson

Shapley was born on a farm five miles outside Nashville, Missouri, to Willis and Sarah (née Stowell) Shapley. He went to school in Jasper, Missouri, but not beyond elementary school. He worked as a journalist after studying at home and covering crime stories as a newspaper reporter for the Daily Sun in Chanute, Kansas, and intermittently for the Times of Joplin, Missouri. In Chanute, he found a Carnegie library and started reading and studying on his own. Shapley returned to complete a six-year high school program in 1.5 years, graduating as class valedictorian.

In 1907, Shapley went to the University of Missouri to study journalism. When he learned that the opening of the School of Journalism had been postponed for a year, he decided to study the first subject he came across in the course directory. Rejecting Archaeology, which Shapley later claimed he could not pronounce, he chose the next subject, Astronomy.

Career

Early years

After graduation, Shapley received a fellowship to Princeton University for graduate work, where he studied under Henry Norris Russell and used the period-luminosity relation for Cepheid variable stars (discovered by Henrietta Swan Leavitt) to determine distances to globular clusters. He was instrumental in moving astronomy away from the idea that Cepheids were spectroscopic binaries, and toward the concept that they were pulsators.

He realized that the Milky Way Galaxy was far larger than previously believed, and that the Sun's place in the galaxy was in a nondescript location. This discovery supports the Copernican principle, according to which the Earth is not at the center of our Solar System, our galaxy, nor our Universe.

The Great Debate of 1920

Shapley participated in the "Great Debate" with Heber D. Curtis on the nature of nebulae and galaxies and the size of the Universe. The debate took place on April 26, 1920, in the hall of the United States National Academy of Sciences in Washington DC. Shapley took the side that spiral nebulae (what are now called galaxies) are inside our Milky Way, while Curtis took the side that the spiral nebulae are 'island universes' far outside our own Milky Way and comparable in size and nature to our own Milky Way. This issue and debate are the start of extragalactic astronomy, while the detailed arguments and data, often with ambiguities, appeared together in 1921.

Characteristic issues were whether Adriaan van Maanen had measured rotation in a spiral nebula, the nature and luminosity of the exploding novae and supernovae seen in spiral galaxies, and the size of our own Milky Way. However, Shapley's actual talk and argument given during the Great Debate were completely different from the published paper. Historian Michael Hoskin says "His decision was to treat the National Academy of Sciences to an address so elementary that much of it was necessarily uncontroversial.", with Shapley's motivation being only to impress a delegation from Harvard who were interviewing him for a possible offer as the next Director of Harvard College Observatory. With the default by Shapley, Curtis won the debate. The astronomical issues were soon resolved in favor of Curtis' position when Edwin Hubble discovered Cepheid variable stars in the Andromeda Galaxy.

At the time of the debate, Shapley was working at the Mount Wilson Observatory, where he had been hired by George Ellery Hale. After the debate, however, he was hired to replace the recently deceased Edward Charles Pickering as director of the Harvard College Observatory (HCO).

Conversion to Hubble's ideas

He is also known to have incorrectly opposed Edwin Hubble's observations that there are additional galaxies in the universe other than the Milky Way. Shapley fiercely critiqued Hubble and regarded his work as junk science. However, after he received a letter from Hubble showing Hubble's observed light curve of V1, he withdrew his criticism. He reportedly told a colleague, "Here is the letter that destroyed my universe." He also encouraged Hubble to write a paper for a joint meeting of the American Astronomical Society and American Association for the Advancement of Science. Hubble's findings went on to fundamentally reshape the scientific view of the universe.

Despite having earlier argued strongly against the idea of galaxies other than our Milky Way, Shapley went on to make significant progress in the research of the distribution of galaxies, working between 1925 and 1932. In this time period, with the Harvard College Observatory, he worked to map 76,000 galaxies. One of the first astronomers to believe in the existence of galaxy superclusters, Shapley later discovered a large and distant example, which was later named the Shapley Supercluster. He estimated the distance to this supercluster at 231 Mpc, which is within 15% of the currently accepted value.

Harvard College Observatory

He served as director of the HCO from 1921–1952. During this time, he hired Cecilia Payne, who, in 1925, became the first person to earn a doctorate at Radcliffe College in the field of astronomy, for work done at Harvard College Observatory.

From 1941 he was on the original standing committee of the Foundation for the Study of Cycles. He also served on the board of trustees of Science Service, now known as Society for Science & the Public, from 1935–1971.

Activism

In the 1940s, Shapley helped found government funded scientific associations, including the National Science Foundation. He shares credit with British biochemist Joseph Needham for the addition of the "S" in UNESCO (United Nations Educational, Scientific and Cultural Organization).

On November 14, 1946, Shapley appeared under subpoena by the House Un-American Activities Committee (HUAC) in his role as member of the Independent Citizens Committee of the Arts, Sciences and Professions (ICCASP), which HUAC described as a "major political arm of the Russophile left". It had opposed re-election of U.S. Representative Joseph William Martin Jr. during mid-term elections that year and was asked to answer questions about the ICCASP's Massachusetts' chapter. HUAC committee chairman John E. Rankin commented about Shapley's attitude, "I have never seen a witness treat a committee with more contempt" and considered contempt of Congress charges. Shapley accused HUAC of "Gestapo methods" and advocated for its abolition, saying that it had made "civic cowards of many citizens" by pursuing the "bogey of political radicalism."

A few weeks later, in early 1947, Shapley became President of the American Association for the Advancement of Science (AAAS). At the time, the AAAS's choice appeared to be a "rebuke" of HUAC and a positive championing of scientists. In his inaugural address, Shapley referred to the danger of the "genius maniac" and proposed the elimination of "all primates that show any evidence or signs of genius or even talent". Other global threats he listed were: drugs that suppressed the desire for sex; boredom; world war with weapons of mass destruction; a plague epidemic.

In March 1949, Shapley chaired the Cultural and Scientific Conference for World Peace at the Waldorf-Astoria in New York. It was sponsored by the National Council of Arts, Sciences and Professions. Arch-conservative William F. Buckley, Jr., authored a 1951 book, God and Man at Yale: The Superstitions of "Academic Freedom," wherein, in the eve of McCarthyism, he attacked liberalism (Buckley's adopted perception of liberalism) at Yale and academia in general. In the book, Buckley cited Shapley's participation and averred that event was "Communist-inspired" and "Russian-dominated."

In 1950, Shapley was instrumental in organizing a campaign in academia against Worlds in Collision by Russian expatriate psychiatrist Immanuel Velikovsky. Scientists generally considered this controversial US bestseller to be pseudoscience.

Personal life

Shapley married Martha Betz (1890–1981) in April 1914, whom he had met in Missouri. She assisted her husband in astronomical research both at Mount Wilson and at Harvard Observatory. She wrote numerous articles on eclipsing stars and other astronomical objects.

They had one daughter, editor and writer Mildred Shapley Matthews; and four sons. These included Lloyd Shapley, a mathematician and economist who won a Nobel Memorial Prize in Economics in 2012, and Willis Shapley, who became a Senior Executive Service leader at NASA.

Although Shapley was an agnostic, he was greatly interested in religion.

Shapley died in a nursing home in Boulder, Colorado on October 20, 1972, shortly before his 87th birthday.

Awards

• Henry Draper Medal of the National Academy of Sciences (1926)
• Prix Jules Janssen of the Société astronomique de France (French Astronomical Society) (1933)
• Rumford Prize of the American Academy of Arts and Sciences (1933) 
• Gold Medal of the Royal Astronomical Society (1934)
• Bruce Medal of the Astronomical Society of the Pacific (1939)
• Janssen Medal from the French Academy of Sciences (1940)
• Pius XI Medal (1941) 
• Franklin Medal (1945)
• Henry Norris Russell Lectureship of the American Astronomical Society (1950)

Legacy

Shapley Supercluster map

Named after him are:

• The crater Shapley on the Moon
• Asteroid 1123 Shapleya
• Shapley Supercluster
• Harlow Shapley Visiting Lectureships In Astronomy, American Astronomical Society

Before the anti-communist phrase "Better Dead Than Red" became popular during McCarthyism in the 1950s, Dr. Shapley said in a 1947 speech entitled "Peace or Pieces" that "A slave world is not worth preserving. Better be lifeless like the cold moon, or primitively vegetal like desolate Mars, than be a planet populated by social robots."

Works

Shapley wrote many books on astronomy and the sciences. Among these was Source Book in Astronomy (New York: McGraw–Hill, 1929, co-written with Helen E. Howarth, also on the staff of the Harvard College Observatory), the first of the publisher's series of source books in the history of the sciences.

In 1953, he wrote the "Liquid Water Belt" which gave scientific credence to the ecosphere theory of Hubertus Strughold.

In his 1957 book "Of Stars and Men", Shapley proposed the term Metagalaxies for what are now called superclusters.

Shapley attended Institute on Religion in an Age of Science conferences at Star Island and was the editor of the book Science Ponders Religion (1960).

• Shapley, Harlow (1972). Galaxies. The Harvard books on astronomy. Harvard University Press. ISBN 978-0674340510.
• Shapley, Harlow (1969). Through Rugged Ways to the Stars. Scribner.
• Shapley, Harlow (1967). Beyond the Observatory. Scribner.
• Shapley, Harlow (1964). The View from a Distant Star: Man's Future in the Universe. Dell Publishing, Co.
• Shapley, Harlow (1960). Source book in astronomy, 1900–1950. Source books in the history of the sciences. Harvard University Press.
• Shapley, Harlow (1958). Of Stars and Men: The Human Response to an Expanding Universe. Beacon Press.
• Shapley, Harlow (1958). A Census of Northern Galaxies in an Area of 3600 Square Degrees. Harvard College Observatory. Annals, v. 88, no. 7. Beacon Press.
• Shapley, Harlow (1953). Climatic Change. Harvard University Press.
• Shapley, Harlow (1948). Galactic and Extragalactic Studies, XVIII. Volume 36. National Academy of Sciences.
• Shapley, Harlow (1936). Time and Its Mysteries. Series 1:Lectures given on the James Arthur Foundation, New York University. New York University Press.
• Shapley, Harlow (1934). The Angular Diameters of Bright Galaxies. The Observatory.
• Shapley, Harlow (1930). Flights from Chaos: A Survey of Material Systems from Atoms to Galaxies, Adapted from Lectures at the College of the City of New York, Class of 1872 Foundation. Whittlesey House, McGraw–Hill Book Company, Inc. Bibcode:1930fcsm.book.....S.
• Shapley, Harlow (1926). Starlight. George H. Doran Co.
• Shapley, Harlow (1924). Descriptions and Positions of 2,829 New Nebulae ... Harvard College Observatory. Annals, v. 85, no. 6. The Observatory.

Georges Lemaître

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Georges_Lema%C3%AEtre

 

The Reverend Monsignor Georges Lemaître RAS Associate
Lemaître in the 1930s
Born	Georges Henri Joseph Édouard Lemaître 17 July 1894 Charleroi, Belgium
Died	20 June 1966 (aged 71) Leuven, Belgium
Nationality	Belgian
Alma mater	Catholic University of Louvain St Edmund's House, Cambridge Massachusetts Institute of Technology
Known for	Theory of the expansion of the universe Big Bang theory Hubble–Lemaître law Lemaître–Tolman metric Lemaître coordinates Friedmann–Lemaître–Robertson–Walker metric
Awards	Francqui Prize (1934) Eddington Medal (1953)
Scientific career
Fields	Cosmology Astrophysics Mathematics
Institutions	Catholic University of Leuven Catholic University of America
Doctoral advisor	Charles Jean de la Vallée-Poussin (Leuven)
Other academic advisors	Arthur Eddington (Cambridge) Harlow Shapley (MIT)
Ecclesiastical career
Religion	Christianity
Church	Catholic Church
Ordained	22 September 1923 by Désiré-Joseph Mercier
Signature

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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, mathematician, astronomer, and professor of physics at the Catholic University of Louvain. He was the first to theorize that the recession of nearby galaxies can be explained by an expanding universe, which was observationally confirmed soon afterwards by Edwin Hubble. He first derived "Hubble's law", now called the Hubble–Lemaître law by the IAU, and published the first estimation of the Hubble constant in 1927, two years before Hubble's article. Lemaître also proposed a version of the "Big Bang theory" of the origin of the universe, calling it the "hypothesis of the primeval atom", and later calling it "the beginning of the world".

Early life

After a classical education at a Jesuit secondary school, the Collège du Sacré-Coeur, in Charleroi, in Belgium, 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 Cardinal Désiré-Joseph Mercier.

In 1923, he became a research associate in astronomy at the University of Cambridge, 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

Millikan, Lemaître and Einstein after Lemaître's lecture at the California Institute of Technology in January 1933.

 

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.

On his return to Belgium in 1925, he became a part-time lecturer at the Catholic University of Louvain and began the report that 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"), that was later to bring him international fame. In this report, he presented the new idea that the universe is expanding, which he derived from General Relativity. This later became known as Hubble's law, even though Lemaître was the first to provide an observational estimate 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 those paragraphs himself when translating the paper for the Royal Astronomical Society, in favour of reports of newer work on the subject, since by that time Hubble's calculations had already improved on Lemaître's 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 PhD, 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, which Eddington described 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. Lemaître'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 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, Lemaître 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 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. Also in 1933, Lemaître served as a visiting professor at The Catholic University of America.

On July 27, 1935, he was named an honorary canon of the Malines cathedral by Cardinal Josef 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.

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.

In relation to Catholic teaching on the origin of the Universe, Lemaître viewed his theory as neutral with neither a connection or a contradiction of the Faith; as a devoted Catholic priest, Lemaître was opposed to 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 domestic 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 was also the first to estimate the numerical value of the Hubble constant.

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 1931, Lemaître 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 1933, Lemaître found an important inhomogeneous solution of Einstein's field equations describing a spherical dust cloud, the Lemaître–Tolman metric.

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.

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.

Honours

On 17 March 1934, Lemaître received the Francqui Prize, the highest Belgian scientific distinction, from King Leopold 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.

In popular culture

In 2019, he was the subject of a survey question: "Should schools in America teach the creation theory of Catholic priest Georges Lemaitre as part of their science curriculum?" 53% of respondents said "No", presumably confusing his theory with Creationism.

Namesakes

• The lunar crater Lemaître
• Lemaître coordinates
• Hubble–Lemaître law
• Lemaître observers in the Schwarzschild vacuum frame fields in general relativity
• Minor planet 1565 Lemaître
• The fifth Automated Transfer Vehicle, Georges Lemaître ATV
• Norwegian indie electronic band Lemaitre
• The Maison Georges Lemaître is the main building of the University of Louvain's UCLouvain Charleroi campus, adjacent to Lemaître's birthplace

Magic number (physics)

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Magic_number_(physics) 

 

A graph of isotope stability, with some of the magic numbers.

In nuclear physics, a magic number is a number of nucleons (either protons or neutrons, separately) such that they are arranged into complete shells within the atomic nucleus. As a result, atomic nuclei with a 'magic' number of protons or neutrons are much more stable than other nuclei. The seven most widely recognized magic numbers as of 2019 are 2, 8, 20, 28, 50, 82, and 126 (sequence A018226 in the OEIS).

For protons, this corresponds to the elements helium, oxygen, calcium, nickel, tin, lead and the hypothetical unbihexium, although 126 is so far only known to be a magic number for neutrons. Atomic nuclei consisting of such a magic number of nucleons have a higher average binding energy per nucleon than one would expect based upon predictions such as the semi-empirical mass formula and are hence more stable against nuclear decay.

The unusual stability of isotopes having magic numbers means that transuranium elements could theoretically be created with extremely large nuclei and yet not be subject to the extremely rapid radioactive decay normally associated with high atomic numbers. Large isotopes with magic numbers of nucleons are said to exist in an island of stability. Unlike the magic numbers 2–126, which are realized in spherical nuclei, theoretical calculations predict that nuclei in the island of stability are deformed.

Before this was realized, higher magic numbers, such as 184, 258, 350, and 462 (sequence A033547 in the OEIS), were predicted based on simple calculations that assumed spherical shapes: these are generated by the formula ${\displaystyle 2({\tbinom {n}{1}}+{\tbinom {n}{2}}+{\tbinom {n}{3}})}$ (see Binomial coefficient). It is now believed that the sequence of spherical magic numbers cannot be extended in this way. Further predicted magic numbers are 114, 122, 124, and 164 for protons as well as 184, 196, 236, and 318 for neutrons. However, more modern calculations predict 228 and 308 for neutrons, along with 184 and 196.

History and etymology

Maria Goeppert Mayer

Upon working on the Manhattan Project, the German physicist Maria Goeppert Mayer became interested in the properties of nuclear fission products, such as decay energies and half-lives. In 1948, she published a body of experimental evidence for the occurrence of closed nuclear shells for nuclei with 50 or 82 protons or 50, 82, and 126 neutrons.

It had already been known earlier that nuclei with 20 protons or neutrons were stable: that was evidenced by calculations by Hungarian-American physicist Eugene Wigner, one of her colleagues in the Manhattan Project. Two years later, in 1950, a new publication followed in which she attributed the shell closures at the magic numbers to spin-orbit coupling.

According to Steven Moszkowski (a student of Maria Goeppert Mayer), the term "magic number" was coined by Wigner: "Wigner too believed in the liquid drop model, but he recognized, from the work of Maria Mayer, the very strong evidence for the closed shells. It seemed a little like magic to him, and that is how the words 'Magic Numbers' were coined."

These magic numbers were the bedrock of the nuclear shell model, which Mayer developed in the following years together with Hans Jensen and culminated in their shared 1963 Nobel Prize in Physics.

Doubly magic

Nuclei which have neutron number and proton (atomic) numbers each equal to one of the magic numbers are called "doubly magic", and are especially stable against decay. The known doubly magic isotopes are helium-4, helium-10, oxygen-16, calcium-40, calcium-48, nickel-48, nickel-56, nickel-78, tin-100, tin-132, and lead-208. However, only the first, third, fourth, and last of these doubly magic nuclides are completely stable, although calcium-48 is extremely long-lived and therefore naturally occurring, disintegrating only by a very inefficient double beta minus decay process.

Doubly-magic effects may allow existence of stable isotopes which otherwise would not have been expected. An example is calcium-40, with 20 neutrons and 20 protons, which is the heaviest stable isotope made of the same number of protons and neutrons. Both calcium-48 and nickel-48 are doubly magic because calcium-48 has 20 protons and 28 neutrons while nickel-48 has 28 protons and 20 neutrons. Calcium-48 is very neutron-rich for such a light element, but like calcium-40, it is stabilized by being doubly magic.

Magic number shell effects are seen in ordinary abundances of elements: helium-4 is among the most abundant (and stable) nuclei in the universe and lead-208 is the heaviest stable nuclide.

Magic effects can keep unstable nuclides from decaying as rapidly as would otherwise be expected. For example, the nuclides tin-100 and tin-132 are examples of doubly magic isotopes of tin that are unstable, and represent endpoints beyond which stability drops off rapidly. Nickel-48, discovered in 1999, is the most proton-rich doubly magic nuclide known. At the other extreme, nickel-78 is also doubly magic, with 28 protons and 50 neutrons, a ratio observed only in much heavier elements, apart from tritium with one proton and two neutrons (⁷⁸Ni: 28/50 = 0.56; ²³⁸U: 92/146 = 0.63).

In December 2006, hassium-270, with 108 protons and 162 neutrons, was discovered by an international team of scientists led by the Technical University of Munich, having a half-life of 9 seconds. Hassium-270 evidently forms part of an island of stability, and may even be doubly magic due to the deformed (American football- or rugby ball-like) shape of this nucleus.

Although Z = 92 and N = 164 are not magic numbers, the undiscovered neutron-rich nucleus uranium-256 may be doubly magic and spherical due to the difference in size between low- and high-angular momentum orbitals, which alters the shape of the nuclear potential.

Derivation

Magic numbers are typically obtained by empirical studies; if the form of the nuclear potential is known, then the Schrödinger equation can be solved for the motion of nucleons and energy levels determined. Nuclear shells are said to occur when the separation between energy levels is significantly greater than the local mean separation.

In the shell model for the nucleus, magic numbers are the numbers of nucleons at which a shell is filled. For instance, the magic number 8 occurs when the 1s_1/2, 1p_3/2, 1p_1/2 energy levels are filled, as there is a large energy gap between the 1p_1/2 and the next highest 1d_5/2 energy levels.

The atomic analog to nuclear magic numbers are those numbers of electrons leading to discontinuities in the ionization energy. These occur for the noble gases helium, neon, argon, krypton, xenon, radon and oganesson. Hence, the "atomic magic numbers" are 2, 10, 18, 36, 54, 86 and 118. As with the nuclear magic numbers, these are expected to be changed in the superheavy region due to spin–orbit coupling effects affecting subshell energy levels. Hence copernicium (112) and flerovium (114) are expected to be more inert than oganesson (118), and the next noble gas after these is expected to occur at element 172 rather than 168 (which would continue the pattern).

In 2010, an alternative explanation of magic numbers was given in terms of symmetry considerations. Based on the fractional extension of the standard rotation group, the ground state properties (including the magic numbers) for metallic clusters and nuclei were simultaneously determined analytically. A specific potential term is not necessary in this model.