|Born||December 28, 1882
|Died||November 22, 1944
|Institutions||University of Cambridge|
|Alma mater||University of Cambridge|
|Academic advisor||Horace Lamb|
|Notable students||Leslie Comrie|
|Known for||Eddington limit
|Notable prizes||Royal Society Royal Medal (1928)|
|Eddington received an MA in 1915 and did not have a doctorate or doctoral advisor. However, Horace Lamb was a major academic influence and can be considered an equivalent mentor.|
Sir Arthur Stanley Eddington, OM (December 28, 1882 – November 22, 1944) was an astrophysicist of 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 in 1919, 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.
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 he 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 not to enjoy this very much.
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 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 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 but because he was a member of the Religious Society of Friends (Quakers) and a pacifist, he refused to serve in the army. As a conscientious objector he requested 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.
After the war, Eddington travelled to the island of Príncipe 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 theory of general 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.
Eddington's observations published next year (Dyson, F.W., Eddington, A.S., & Davidson, C.R. 1920 A Determination of the Deflection of Light by the Sun's Gravitational Field, from Observations Made at the Total Eclipse of May 29, 1919 Mem. R. Astron. Soc., 220, 291-333) confirmed Einstein's theory, and were hailed at the time as a conclusive proof of general relativity over the Newtonian model; the news was reported in newspapers all over the world as a major story. It is also the source of the urban legend that only three people understand relativity; when asked by a reporter who suggested this, Eddington jokingly replied "Oh, who's the third?"
However, recent historical examinations of the case have shown that the raw data were inconclusive, and that Eddington was arbitrarily selective in choosing which results to use. For a detailed account, see predictive power.
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.
The first suggestion that stars obtained their energy from nuclear fusion of hydrogen to helium is commonly attributed to Eddington, but was in fact made earlier by the French Nobel Prize winner Jean Baptiste Perrin. Eddington was one of the most vocal champions of this theory, and he had a long-running argument with James Jeans over it. 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.
He strongly opposed the budding scientist Subrahmanyan Chandrasekhar about his theory on the maximum mass of stars known as white dwarfs, the mass above which the star collapses and becomes a neutron star, quark star or black hole. Chandrasekhar was subsequently proven to be right, and went on to win the Nobel Prize in Physics in 1983.
During the 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 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. One of the discoverers of quantum mechanics, P. A. M. 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 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 1/137.03599911.
Eddington believed he had discovered an algebraic basis for fundamental physics, which he termed "E-frames" (representing a particular group). While his theory has long been abandoned by the general physics community, similar algebraic notions underlie many modern attempts at a grand unified theory.
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.
Named after him
Eddington was a superb populariser of science, writing many books aimed at the layman. He 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".