Milne, (Edward) Arthur

(1896-1950), astrophysicist and cosmologist

by G. J. Whitrow

© Oxford University Press 2004 All rights reserved

Milne, (Edward) Arthur (1896-1950), astrophysicist and cosmologist, was born in Hull on 14 February 1896, the eldest of three sons of Sidney Arthur Milne (1867-1921), a headmaster in Hull, and Edith Cockcroft (1870-1957), a teacher. Both of his brothers became scientists. Arthur Milne gained his education through a series of scholarships at Hymers College, Hull, which he attended from 1908 to 1913, and Trinity College, Cambridge, which he entered in 1914. Taught by S. Chapman and G. H. Hardy, he gained a first in part one of the mathematics tripos in 1915. A. V. Hill invited him to abandon his studies to analyse the behaviour of shells in the upper atmosphere. Commissioned into the Royal Naval Volunteer Reserve in 1916, by theory and experiment Milne's team refined binaural listening trumpets and produced a standard model for sound ranging. His outstanding mathematics for these projects relating to the earth's atmosphere led to a fellowship at Trinity College in 1919.

Slight in stature, modest and shy, yet quick of speech, Milne exuded vitality. He thrived on the cut and thrust of debate. He liked to build up a subject from a few basic premises, yet the fruitful stimulation he inspired, and his deductive methods were, eventually, of greater scientific value than the originality of his ideas. In 1919 he founded the Trinity Mathematical Society, and was prominent in other science clubs where he enjoyed the friendship of leading figures.

In 1920 H. F. Newall appointed him assistant director of the solar physics observatory. From 1925 to 1928 he was professor of applied mathematics in the University of Manchester. There Milne championed the use of vectors. Much as he enjoyed the informality and culture, he kept in close touch with Cambridge associates. Through constant journeys to the Royal Astronomical Society (he was a council member for nineteen years), and to his beloved Trinity, where he was always about the place, his work benefited from the scrutiny of C. G. Darwin, Newall, and R. H. Fowler, who restrained Milne's more outrageous suggestions. In January 1929, at the age of thirty-two, he took office as the first Rouse Ball professor of mathematics at Oxford and fellow of Wadham College, posts he held for the rest of his life.

It is by his original contributions that Milne's reputation may be judged. These fall into three stages. From 1920 to 1929 his researches centred on problems of radiative equilibrium and the theory of stellar atmospheres, from 1929 to 1935 on the theory of stellar structure, and from 1932 onward with relativity and cosmology. Milne's interest in stellar atmospheres was first aroused by Newall, who sensed his ability to work on theoretical problems concerning the outermost layers of stars, particularly those that deal with the transfer of radiation through an atmosphere and those relating to ionization of the material. These problems have to be combined and this leads to subtle considerations of the interaction of matter and radiation. Milne laid the foundations of stellar atmosphere theory, a subject in its infancy, by a prodigious output of thirty papers between 1920 and 1929, which brought him election to the Royal Society in 1926. Shortly after Darwin's and Fowler's development of statistical mechanics Fowler and Milne collaborated in developing M. Saha's earlier work, and established a theoretical stellar temperature scale for the Harvard sequence. In his 1929 Bakerian lecture 'The structure and opacity of a stellar atmosphere', Milne explained his method for calculating stellar magnitude from the intensity of a spectral line. Although his proposal for a calcium chromosphere proved incorrect it attracted enormous attention, prompting others to a better theory.

At Oxford in 1929-31 he devoted his main energies to developing a theory of stellar structure based on a constructive mathematical critique of the pioneer researches of Sir Arthur Eddington. With neither nuclear and atomic processes, nor the part played by radiation fully understood, Milne's four equations were inadequately defined. He and Jeans seemed to misinterpret Eddington's deductions, based on a perfect gas, and a famous controversy ensued, yet they remained friends. Although much of Milne's criticism was not generally accepted, by 1932 he had developed powerful analytical methods, but he did not apply them to degenerative cores which were discovered in 1930. His methods led to important developments, notably T. G. Cowling's fundamental study of the stability of gaseous stars and Chandrasekhar's standard theory of white dwarf stars.

In May 1932 Milne turned to cosmology. H. H. Plaskett found him less comfortable with quantum and wave mechanics, and missing the constant contact with Cambridge colleagues. But Milne had criticized applied mathematics as characterized by the abstraction of a problem from its physical surroundings (minutes of the Trinity College Mathematical Society, 22 May 1922). Hence in his inaugural Oxford lecture (1929) he declared his ambition to construct mathematical physics from general principles, and his cosmology, quite unlike that of others, stands alone for its deductive methods. Provoked by Jeans's remark that an explanation for the universe's expansion was 'forever beyond our reach' (The Times, 10 May 1932), which Milne dismissed as scientific pessimism, Milne developed a new analysis of time as the basis of his cosmology, and devised a new deductive approach to dynamics and gravitation, as well as to other areas of his studies. The resulting general cosmological theory was called kinematic relativity. The invention of radar showed that it foreshadowed later developments in metrology, including distance measurement by radio astronomy. From his cosmological hypotheses Milne sought to deduce the fundamental laws of physics such as the law of inertia and the law of gravitation. The three main achievements of his work on cosmology were: the discovery with W. H. McCrea of the Newtonian analogues of the various models of relativistic cosmology, the introduction of the uniformly expanding world model, and the systematic investigation of different uniform time scales which suggested secular variation in the gravitational constant, and gave rise to J. B. S. Haldane's biological inferences. Milne considered building up the laws of nature his life's work, but could not achieve this, and his theory was later abandoned. Nevertheless his ideas on time and the expanding universe became part of 'the cosmologist's toolbox' (Matravers, 17).

At Manchester, Milne had taught, and had completed, work started at Cambridge. At Oxford, free of undergraduate lecturing, he reoriented. Milne and his close friend Plaskett, whose appointment to the Savilian chair of astronomy he had largely brought about, built up a leading centre of astrophysics. Through service on many committees Milne improved facilities and gained rooms for a mathematical institute. Milne's weekly colloquia with speakers such as S. Chandrasekhar, E. Hubble, H. N. Russell and A. Einstein, drew graduates in physics, astronomy, and mathematics. These included R. V. Jones, D. G. Kendall, T. G. Cowling, A. G. Walker, and G. J. Whitrow as well as senior men like Lindemann and Hardy, at a time when DPhil students were usually left much to their own devices. With two studentships available, in the mid-1930s Milne and Plaskett started the first graduate school of astrophysics in Britain.

Milne was married twice, first in 1928 to Margaret (Margot) Scott (1901-1938), a chemistry teacher. She was a daughter of Hugh Fraser Campbell (1857-1948), a Scots advocate, and Jessie Theresa Fiddes (1867-1910), the niece of Edward Fiddes, the pro-vice-chancellor of Manchester University, who brought her up. Margot died on 5 October 1938 leaving two daughters and an infant son. In 1940 Milne married Beatrice Brevoort Renwick (1912-1945), daughter of William W. Renwick (1864-1933), an ecclesiastical architect of New York, and his wife, Ilka Howells (d. 1941). Beatrice died on 28 August 1945 leaving a daughter. Milne weathered the loss of both his wives to suicide, and losing his father in 1921 and a brother in 1942, through his self-discipline and his Christian faith. Despite failing health, due to the after effects of encephalitis lethargica contracted in 1924, he maintained his pace to the end, dying of a heart attack on 21 September 1950 at the Princess Hospital, Dublin, at the age of fifty-four. He had been attending a meeting in Dublin of the Royal Astronomical Society. He was buried at Wolvercote cemetery, Oxford, on 25 September.

A founder of modern theoretical astrophysics, and awarded many honours, McCrea considered Milne a man of the highest genius who had played a 'tremendous role' (McCrea, 428). Oxford's twenty annual Milne lectures 1977-96 were held to honour him.

G. J. WHITROW

Sources  
W. H. McCrea, Obits. FRS, 7 (1950-51), 421-43
personal knowledge (2004)
R. J. Tayler, 'E. A. Milne (1896-1950) and the structure of stellar atmospheres and stellar interiors', Quarterly Journal of the Royal Astronomical Society, 37 (1996), 355-63
G. J. Whitrow, 'Milne, Edward Arthur', DSB
H. H. Plaskett, Monthly Notices of the Royal Astronomical Society, 111 (1951), 170-72
S. Chandrasekhar, 'The 1979 Milne lecture: Edward Arthur Milne, his part in the development of modern astrophysics', Quarterly Journal of the Royal Astronomical Society, 21 (1980), 93-107
D. R. Matravers, 'Of Milne and of mathematics: inaugural lecture', University of Portsmouth, 1993, 1-22
W. McCrea, 'Cambridge physics 1925-1929: diamond jubilee of golden years', Interdisciplinary Science Reviews, 11/3 (1986), 269-84
J. Morrell, Science at Oxford, 1914-1939: transforming an arts university (1997), 315-17
private information (2004)
G. Gale and J. Urani, 'Philosophical midwifery and the birthpangs of modern cosmology', American Journal of Physics, 61 (1993), 66-73
G. Gale and J. Urani, 'E. A. Milne and the origins of modern cosmology', The attraction of gravitation, ed. J. Earman, M. Janssen, and J. D. Norton (1994), 390-419
A. J. Harder, 'E. A. Milne: scientific revolutions and the growth of knowledge', Annals of Science, 31 (1974), 351-63
M. W. Smith, 'E. A. Milne and the creation of air defence: some letters from an unprincipled brigand, 1916-1919', Notes and Records of the Royal Society, 44 (1990), 241-55

Archives  
Bodl. Oxf., corresp. and papers
priv. coll., family letters |  CAC Cam., corresp. with A. V. Hill
Institute of Theoretical Astrophysics, Oslo, Norway, S. Rosseland MSS, letters
Nuffield Oxf., corresp. with Lord Cherwell
Princeton University, New Jersey, H. N. Russell MSS
RS, J. Larmor MSS
Trinity Cam., corresp. with Harold Davenport
UCL, K. Pearson MSS  FILM  American Institute of Physics, One Physics Ellipse, College Park, Maryland, Niels Bohr Library, opening of the McDonald Observatory, Texas

Likenesses  
photograph, c.1930, priv. coll.
S. Chandrasekhar, photograph, 1939, priv. coll.
W. Stoneman, two photographs, 1943-5, NPG
portrait, 1944 (Royal Astronomical Society, presidential)

Wealth at death  
£25,511 17s. 9d.: probate, 18 Dec 1950, CGPLA Eng. & Wales


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