Arthur Eddington


Arthur Eddington : biography

28 December 1882 – 22 November 1944

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 variables. 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.

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 (see Lecchini in #External links and references ). 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.

During World War I Eddington became embroiled in controversy within the British astronomical and scientific communities. Many astronomers, chief among them H.H. Turner, argued that scientific relations with all of the Central Powers should be permanently ended due to their conduct in the war. Eddington, a Quaker pacifist, struggled to keep wartime bitterness out of astronomy. He repeatedly called for British scientists to preserve their pre-war friendships and collegiality with German scientists. Eddington’s pacifism caused severe difficulties during the war, especially when he was called up for conscription in 1918. He claimed conscientious objector status, a position recognized by the law, if somewhat despised by the public. In 1918 the government sought to revoke this deferment, and only the timely intervention of the Astronomer Royal and other high profile figures kept Eddington out of prison.

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. Chandrasekhar’s narrative of this incident, in which his work is harshly rejected, portrays Eddington as rather cruel, dogmatic and racist. This is at variance with Eddington’s character as described by other contemporaries. Eddington’s criticism seems to have been based on a suspicion that a purely mathematical derivation from quantum theory was not enough to explain away the seemingly daunting physical paradoxes that were inherent to degenerate stars.