Arthur Stanley Eddington

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One of Sir Arthur Stanley Eddington's papers announced Einstein's theory of general relativity to the English-speaking world.

Sir Arthur Stanley Eddington (December 28, 1882November 22, 1944) was arguably the most important astrophysicist from the early 20th century. The Eddington limit, the natural limit to the luminosity that can be radiated by accretion onto a compact object, is named in his honour.

He is famous for his work regarding the Theory of Relativity. Eddington wrote an article, Report on the relativity theory of gravitation, which announced Einstein's theory of general relativity to the English-speaking world. Because of World War I, new developments in German science were not well known in England.

In 1924 he won the Bruce Medal, the Henry Draper Medal and the Gold Medal of the Royal Astronomical Society. He won the Royal Medal of the Royal Society in 1928. He was knighted in 1930, and received the Order of Merit in 1938.

The Eddington Crater on the Moon is named after him, as are the asteroid 2761 Eddington and the Royal Astronomical Society's Eddington Medal.

Contents

Biography

Early years

Eddington was born in Kendal, England, son of Quaker parents. His father, Arthur Henry Eddington, 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, Sarah Ann Stout, came from Darlington and was also from a Quaker family. When his father died, she was left to bring up Arthur and his older sister with relatively little income. The family moved to Weston-super-Mare where at first Arthur was educated at home before spending three years at a preparatory school.

In 1893 Arthur entered Brymelyn School. He proved to be a brilliant scholar and excelled in mathematics and English literature. His records won him a 60 pounds scholarship in 1898, and was able to attend Owens College in Manchester once he turned 16 later 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 one of his mathematics teachers, Horace Lamb. His progress continued to be rapid, winning him several additional scholarships and allowing him to graduate with a B.Sc. with First Class Honours in 1902.

Based on his performance at Owens, he was awarded a 75 pound scholarship at Trinity College, Cambridge, which he entered in 1903. He graduated with a masters in 1905, and entered the Cavendish Laboratory researching thermionic emission. This did not go well so he returned to mathematics, but appeared to not enjoy this very much.

Astronomy

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Eddington helped to experimentally verify the theory of general relativity by observing the appearance of stars around the region of a solar eclipse.

After leaving university later in 1905, Eddington's first full-time position was as the chief assistant to the Astronomer Royal at the Royal Greenwich Observatory. He was put to work on the detailed analysis parallax of 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 Trinity College Fellowship. 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. He was elected a Fellow of the Royal Society shortly thereafter.

During World War I, Eddington was called up for military service. Being a Quaker and a pacifist, he refused to serve in the army as a conscientious objector, and wanted to be allowed to do alternative service instead. Scientific friends of his solved the problem by successfully arguing to relieve him from military duty because of his importance for science.

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One of Eddington's photographs of the 1919 eclipse, presented in his 1920 paper announcing its success.

After the war, Eddington travelled to the island of Principe near Africa to watch the solar eclipse of May 29 1919. During the eclipse, he took pictures of the stars in the region around the Sun. According to the general theory of relativity, stars 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 an eclipse, since otherwise the Sun's brightness obscures the stars. Newtonian gravitation predicted half the shift of general relativity. Reportedly, Eddington's proof of general relativity contained a manipulated set of data that excluded items that did not fit Einstein's theory (John Waller, Einstein's Luck).

The expedition was a major factor in and ultimately helped to discriminate between the two theories. This relativistic shift was indeed found, and was a major science story around the world. It is also the source of the urban rumor that only three people understand relativity; when asked by a reporter who suggested this, Eddington jokingly replied "Oh, who's the third?"

Eddington also investigated the interior of stars through theory, and developed the first true understanding of stellar processes. He modelled stars as gas in radiative equilibrium; the star was stabilized by gravity pulling in, and gas pressure (temperature) and radiation pressure pushing out. Noting that the temperatures meant that the atoms in stars would be almost entirely ionized, he theorized that they would behave as almost-ideal gases, thereby making the mathematics much more tractable.

With these assumptions, he demonstrated that the interior temperature of stars must be millions of degrees. He discovered the mass-luminosity relationship for stars, he calculated the abundance of hydrogen and he produced a theory to explain the pulsation of Cepheid variable stars.

In 1920, Eddington, on the basis of the precise measurements of atomic weights by F. W. Aston, was the first to suggest that stars obtained their energy from nuclear fusion of hydrogen to helium. This was the first suggestion that stars obtained their energy from nuclear fusion, over which he had a long running argument with James Jeans. Later, in 1938 and 1939, Hans Bethe introduced the theory for the fusion, which made the process seem rather "natural" and the debate generally ended.

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.

Fundamental theory

During 1920s until his death, he increasingly concentrated on what he called "fundamental theory" which was intended to be a unification of quantum theory, relativity 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 work was increasingly seen as "crankish", and he became something of a science pariah in his later years.

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 cube 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.

A particularly 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 various reasons. Later measurements placed the value much closer to 1/137, at which point he switched his line of reasoning and claimed that the value should in fact be exactly 1/137, the Eddington number. At this point most other researchers stopped taking his concepts very seriously. The current measured value is estimated at 1/137.035 999 76(50).

He did not complete this line of research before his death in 1944, and his book entitled Fundamental Theory was published posthumously in 1946. Eddington died in Cambridge, England.

Writer

Eddington was a superb populariser of science, writing many books aimed at the layman. He is also attributed with introducing the Infinite Monkey Theorem with the 1929 phrase "If an army of monkeys were strumming on typewriters, they might write all the books in the British Museum".

Publications

  • Eddington, Arthur S., "Stars and Atoms (http://www.bibliomania.com/NonFiction/Eddington/Stars/index.html)". British Association, Oxford. August 1926.
  • Eddington, Arthur S., "The internal Constitution of Stars". Cambridge University Press, Cambridge. 1926. ISBN 0521337089
  • Eddington, Arthur S., "Fundamental Theory" Cambridge University Press, London. 1928.
  • Eddington, Arthur S., "Science and the Unseen World". New York: Macmillan, 1929. ISBN 0849514266
  • Eddington, Arthur S., "Expanding Universe: Astronomy's 'Great Debate', 1900-1931". Cambridge University Press. ISBN 0521349761
  • Eddington, Arthur S., "The Nature of the Physical World". The MacMillan Company. November 1928. ASIN 0841438854
  • Eddington, Arthur S., "New Pathways in Science". Cambridge University Press, Cambridge. 1935.
  • Eddington, Arthur S., "Space, Time and Gravitation: An Outline of the General Relativity Theory". Cambridge University Press. ISBN 0521337097
  • Eddington, Arthur S., "Philosophy of Physical Science". Textbook Publishers. ISBN 0758120540
  • Eddington, Arthur S., "The Domain of Physical Science".

See also

External links and references

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Obituaries

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