Arthur Eddington
Arthur Stanley Eddington | |
|---|---|
| Born | 28 December 1882 Kendal, Westmorland, England |
| Died | 22 November 1944 (aged 61) Cambridge, England |
| Nationality | British |
| Known for | 1919 eclipse expedition, stellar structure, the Eddington limit, Fundamental Theory |
| Scientific career | |
| Fields | Astronomy, Astrophysics, Relativity |
| Institutions | Royal Observatory, Greenwich; University of Cambridge |
Arthur Stanley Eddington (28 December 1882 – 22 November 1944) was a British astrophysicist, Plumian Professor of Astronomy at Cambridge from 1913 and director of the Cambridge Observatory from 1914. He did more than anyone else to establish general relativity in the English-speaking world, founded the theory of stellar interiors, and spent his last fifteen years on a numerological unification of physics that his colleagues could not follow.
Eddington's astrophysics is uncontested and permanent. In The Internal Constitution of the Stars (1926) he treated a star as a gas sphere in radiative equilibrium, derived the mass–luminosity relation, and established the Eddington limit — the luminosity at which radiation pressure on the outer layers balances gravity, above which a star cannot be stable. He also showed that stellar energy output could not be gravitational contraction and had to be subatomic in origin, before the fusion mechanism was known.
He was a Quaker and a conscientious objector during the First World War, and his advocacy of the theory of a German physicist to a British audience in 1919 was in part a deliberate act of scientific internationalism.
The 1919 eclipse
On 29 May 1919 two British expeditions photographed the star field around the eclipsed Sun: Eddington on Príncipe, and a second party at Sobral in Brazil. General relativity predicted a deflection of starlight at the solar limb of about 1.75 arcseconds — twice the value obtained from a Newtonian corpuscular calculation. Three data sets resulted. The Sobral 4-inch telescope gave about 1.98″, Príncipe about 1.61″, and the Sobral astrographic gave about 0.93″. Eddington and Dyson set the astrographic result aside on the grounds that the mirror had gone out of focus, and announced confirmation of Einstein's value.
The announcement made Einstein world-famous overnight. It has also been argued ever since that the error bars were too large to discriminate, and that discarding the discrepant plate was a decision made with the answer already in view. Later re-examinations of the original plates have on the whole supported the focus diagnosis, and the deflection itself is now confirmed to far higher precision by radio interferometry and by gravitational lensing — but the 1919 measurement, taken by itself, was not decisive, and this is not a fringe position.
Fundamental Theory
From the late 1920s Eddington attempted to derive the constants of nature from pure reasoning. He argued that the fine-structure constant must be exactly 1/136, and when measurement moved against him, 1/137. He calculated the number of protons in the universe as about 1.57×1079 — the Eddington number — and connected it to the ratio of electrical to gravitational force between proton and electron, roughly 1040, an approach that fed into Dirac's large-numbers hypothesis. Fundamental Theory was published posthumously in 1946 and has never been assimilated into mainstream physics.
On this wiki
Eddington appears here in three roles.
As the man who certified relativity. Paul Marmet's "The Deficient Observations of Light Deflection Near the Sun" (2000) is the sharpest statement: Marmet examines the instrument used at Príncipe, argues that displacements of the order claimed were below its theoretical resolution under daytime conditions, and concludes that the deflection has not been reliably observed near the Sun even now. Charles Lane Poor, a Columbia celestial mechanician contemporary with the expedition, made related objections at the time. Ian McCausland's "The Einstein Mystique" (Journal of Scientific Exploration, 2003) and Peter Rowlands's "A Revolution Too Far: The Establishment of General Relativity" (1994) treat the 1919 result as a case study in how a theory becomes unquestionable. Herbert Dingle, who knew Eddington, is the wiki's central figure for the later relativity dispute.
As a cosmologist. Eddington's expanding-universe advocacy and the cosmological constant are argued against throughout Category:Big Bang and Category:Cosmology; see Glenn Borchardt's "The Top 30 Problems with the Big Bang". Andre K T Assis and Marcos C D Neves, in "History of the 2.7 K Temperature Prior to Penzias and Wilson" (Apeiron, 1995), note Eddington among those who estimated a background temperature of interstellar space from starlight long before the microwave background was found — a prediction they argue fits a non-expanding universe at least as well.
As a numerologist — approvingly. Because Fundamental Theory tried to derive constants rather than measure them, it is treated far more sympathetically here than in the mainstream. See "Eddington, Ether and Number" (2008) on the role of the ether in his later work, and Robert J Heaston's "Number Crunching the Large and Small Magnitudes of Physics" (2006).