McCrea, William Hunter
MCCREA, WILLIAM HUNTER
(b. Dublin, Ireland, 13 December 1904; d. Lewes, Sussex, United Kingdom, 25 April 1999),
astronomy, astrophysics, cosmology, physics, mathematics.
Sir William McCrea was a tall, gentle man who talked very slowly. But his impish wit clearly showed he was a quick thinker. From the time he began his PhD studies in 1926 under Ralph H. Fowler until nearly the time of his death, McCrea made contributions to mathematics, physics, and almost every area of astronomy, including planetary physics, astrophysics, comets, interstellar hydrogen chemistry, Newtonian cosmology, relativistic cosmology, and steady state cosmology. McCrea’s achievements began early: In a series of papers culminating in 1929–1930, McCrea, following up on work originally begun by Cecilia Payne, demonstrated that hydrogen dominated the solar atmosphere, laying down the basis for what became the accepted view that the ratio of hydrogen to helium is about 3:1.
Although he moved to Derbyshire when he was two, McCrea was always proud of his Irish heritage, and maintained close ties to his homeland throughout his life and work. His later connection to Armagh Observatory, and especially its director Eric Lindsay, did much to sustain that venerable institution during some of its darkest days, just preceding Lindsay’s appointment in 1937. Then, beginning with a mysterious 1940 phone call from the Irish mathematician (and Taoiseach, or prime minister of Ireland) Éamon de Valera, McCrea was intimately involved in the establishment and initial running of Ireland’s justifiably well regarded School for Theoretical Physics. Later, when Ireland’s pulling out of the British Commonwealth led Irish scientists to fear isolation, McCrea was responsible for siting the Royal Astronomical Society’s third summer meeting in Dublin (1950)—its first convening outside the United Kingdom. Similarly, in 1957 he helped to persuade the British Association for the Advancement of Science to hold its annual meeting in Dublin. Throughout all this, and nearly to the end of his life, McCrea also had special interest, not to mention success, in encouraging young Irish scientists and students to work in United Kingdom labs, his own included.
Born in Dublin on 13 December 1904, he died after several years of declining health in Lewes, Sussex, on 25 April 1999, leaving behind his three children Isabel, Sheila, and Roderick. Marian, his wife of many years, had died four years earlier. McCrea’s death marked the end of an era in British astronomy. Indeed, that era’s very existence owed much to McCrea’s own contributions. McCrea attended Chesterfield Grammar School, and went up to Cambridge in 1923 with an entrance scholarship to Trinity. While at Cambridge, he was awarded a Rayleigh Prize in Mathematics, and became a Rouse Ball Senior Student at Trinity. As if this were not enough, McCrea concurrently earned a first-class BSc honors degree in mathematics from the University of London.
In 1928–1929 McCrea was a visiting research student in Göttingen. At that time Göttingen functioned as a finishing school for mathematical physicists drawn from all over the world—McCrea just missed America’s Howard P. Robertson, and studied alongside the Canadian and future Nobel Prize–winner Gerhard Herzberg. At Göttingen he found himself in a hotbed of mathematical physics, both pure and applied: Harald Bohr lectured on periodic functions, and Lev Landau on number theory, while David Hilbert and John von Neuman were the stars of the new mathematics of relativity and quantum mechanics. McCrea was to apply his Göttingen studies immediately in his work on solar atmospheric composition, and shortly thereafter in general relativity and cosmology.
Career Path . After returning from Göttingen, McCrea took an appointment as lecturer in mathematics in Edinburgh; two years later he moved to Imperial College as reader in mathematics, where he stayed until 1936. At that time he moved back to Ireland, to the chair in mathematics at Queen’s University, Belfast. Taking war leave from Queen’s in 1943, he went to work for Patrick M. S. Blackett in the Admiralty in London. He did not leave London for the next twenty-three years: from 1944 until 1966 he served as professor of mathematics and head of department at the University of London’s Royal Holloway College. McCrea’s final move was to the Astronomy Center in Sussex, an institution whose fraught history and birth he had been intimately involved in. Interestingly, it was his first and only official appointment in an astronomy institution!
During his career McCrea accumulated many honors. He became a Fellow of the Royal Society in 1952; served as president of the Royal Astronomical Society (RAS) from 1961 to 1963; was an RAS Gold Medallist in 1976; and was knighted in 1985. He was also a member or fellow of the London Mathematical Society, Royal Irish Academy, and the Royal Society of Edinburgh. In addition to visiting at many universities, McCrea received honorary degrees from five of them. In 1988 he was made a Freeman of the City of London.
Cosmological Research . McCrea is perhaps best known for his work in modern relativistic cosmology. He was in on it from the start. In late September 1931, the British Association for the Advancement of Science held a special session devoted to the evolution of the universe, a topic of considerable interest following Edwin Powell Hubble’s measurements of what appeared to be galactic velocity red-shifts, which soon came to be associated with the expanding cosmological models that Alexander Fried-mann and Georges Lemaître had developed from general relativity theory. Participants in this session, which by its nature constituted the quasi-official origin of modern relativistic cosmology, included all the leading senior workers in the field, for example, Arthur S. Eddington, Willem de Sitter, Edward Arthur Milne, and Herbert Dingle among others. McCrea arrived at the session in a rush, accompanied by the equally young and new astronomer George Cunliffe McVittie, whom he had befriended in Edinburgh. “We got there late,” McCrea was to say later, “and there was a huge overflow crowd. They opened up another room, and set up a loudspeaker, and that’s how we attended the meeting” (Smith interview, 1978). From that point on, McCrea and McVittie were each going to be a lot closer to the action.
The two collaborated on a problem Eddington had set, namely seeing whether a Friedmann-Lemaître expansion, leading to a de Sitter end-state, could be generated from an Einstein beginning state. They did not make much progress; the mathematics, they noted, were formidable. But this introduction to expanding universe models marked the beginning of a lifetime of work in the field for both men.
McCrea’s next project achieved very real success in reducing cosmology’s mathematical formidability. A 1933 paper coauthored with Oxford’s Milne demonstrated the possibility of a Newtonian cosmology, something that no one before, including Isaac Newton himself, had believed could be done. Their results provided a generally available, much simpler model of the universe than relativistic cosmology’s model. Using their model, one could very easily show many results relevantly similar to relativistic results without resorting to the intricate complexities of the general theory of relativity. Of all McCrea’s accomplishments, this one earned him the greatest measure of gratitude from the world’s astronomy students!
His relationship with Milne demonstrates what a deep and loyal friend McCrea could be. Milne was a brilliant, moody person, original yet sometimes arcane in his thinking, and his evident role was to play philosophical gadfly, confronting more conservative sorts such as McVittie and, especially, Dingle. Milne was a controversial figure, and it cost him emotionally. It is hard to imagine Milne soldiering on without the quiet support of McCrea. In one letter, written shortly after the tragic death of his first wife, a horribly depressed Milne thanks McCrea for his “generous encouragement.” The two men stayed close until Milne’s untimely death in 1950; McCrea kept their correspondence throughout most of his life.
During the 1930s and up until the war, McCrea worked on a multitude of problems in astronomy and astrophysics. One area that interested him considerably was the problem of confronting relativistic cosmology with observations; his 1935 paper on the subject laid the foundations for decades of subsequent work.
Once the war started, McCrea withdrew—on his own choosing—from the cosmological fray, and, under Blackett, focused on operational research. After the war, it was back to astrophysics, astronomy, and cosmology. In this last field his influence was once again, and soon, of monumental significance.
Steady State Controversy . In addition to having been one of only two persons to hold the four RAS offices of president, secretary, treasurer, and foreign correspondent, McCrea also served as editor of both leading RAS publications, Observatory and Monthly Notices. It was during service on the latter that he single-handedly initiated one of the more exciting phases of modern cosmology, the controversy over the steady state theory of the universe.
In this theory, Hermann Bondi and his co-author Thomas Gold proposed that, contrary to the then-orthodox relativistic expanding universe theory, the universe did not have an origin in time, but rather had always been as it is now, expanding due to a continuous creation of matter, thereby achieving, as its name indicated, a steady-state. How the original article introducing the theory got accepted for publication is classic McCrea.
During summer 1948, McCrea was serving the RAS as secretary, whose job it was to delegate referees for submitted manuscripts. “I was alone at the time, I think it must have been at the Long Vac. When manuscripts came in, I was supposed to appoint a reviewer, so when Bondi’s manuscript came in, as I was alone, I appointed myself to be reviewer, reviewed the manuscript, and then, as Secretary, accepted it for publication” (Smith interview, 1978, p. 24).
McCrea told this story with a twinkle in his eye. As nearly everyone interested or active in the fields of astronomy, physics, and cosmology knows steady state theory was enormously controversial throughout its lifetime, with passionate devotees and equally passionate haters always set against one another, frequently in print, and sometimes even in public. RAS meetings during the controversy were often fraught with tension among the members. Without McCrea’s intervention it is doubtful that the theory would have seen light of day, let alone such an illustrious venue as Monthly Notices for its introduction.
McCrea was attracted to the steady-state theory from the beginning, for several reasons. First, of course, was the simple fact of his role in its initial publication. Secondly, although the theory’s invoking of a continuous creation of matter—rather than having all matter created in one instant at to —offended many physicists, McCrea was not one of them. Indeed, over the next several years he worked to discover a method to integrate continuous creation into the relativistic field equations. His success was announced in a May 1951 paper “Relativity Theory and the Creation of Matter,” which once and for all settled the question whether the steady-state theory was compatible with general relativity.
Yet, although these reasons were strong ones, there was a third set of reasons that strongly inclined McCrea to pursue the steady-state theory rather than orthodox relativistic expanding theories. It would not be unfair to characterize these reasons as “philosophical.” From the very beginning of his work in the field, McCrea had sought to confront cosmological theory with observation, in part simply to restrain excursions of theorists’ imaginations, and in part to provide evidence for choosing between competing models. As the 1930s became 1940s, it became evident to him and other workers that observational tests for cosmological theory were not thick on the ground. While McCrea put aside his research during the war, he did not stop thinking about this central problem. When the Bondi-Gold theory came along, it offered distinct advantages over relativistic expanding universe theory in this regard. As McCrea would later note, “The simple steady-state model was unique. On conceptual grounds this was … a high recommendation. On observational grounds, it rendered the model as vulnerable as possible to observational test” (McCrea 1968, p. 1296). Bondi and Gold had argued that their theory predicted several specific observations—H-He ratios, galactic density counts, etc.—which, if they failed, would contradict the theory. McCrea liked both the specificity of the predictions, and their logic. As he argued, correctly, predictions that are verified can only provide support for a theory, they cannot verify the theory itself. Contradictions, by contrast, rule out a theory tout court. Bondi, following Karl Popper, emphasized that steady-state was more scientific than relativistic expanding universe theory because it was specifically and directly falsifiable. McCrea appreciated this point about steady-state theory.
Yet, even though he was instrumental in the presentation and development of the steady state theory, when evidence accumulated against it, McCrea gave it up. In review articles in 1968, 1970, and 1984 he specifically addressed the basic cosmological models and evaluated their performance against the available physical evidence, indicating specifically where the steady-state theory had been falsified by observational evidence.
By his later years at Sussex’s Astronomy Center, McCrea had become somewhat skeptical of the cosmological enterprise in general, and Big Bang cosmology in particular. In the end, it seemed that he was disappointed in all cosmological models, perhaps because they failed the high standards he held for both the nature of evidential support and our physical understanding of astronomical processes.
One of McCrea’s more satisfying affairs was the RAS 160th Anniversary Dinner in early 1980. Having been asked to address the gathering, he responded, “Oh, surely Professor X of such and such other Society would be a better choice,” only to be told that “he would be good but he would go on too long.” McCrea: “So I said ‘What about Professor Y of yet another Society?’ ‘Yes, but he would be serious’ was the answer to that one. So I began to get the message—short and silly is what’s wanted” (McCrea, 1980). In the end, what the listeners got was wit, surely, but coupled with wisdom, a typical McCrea performance.
Later Years . A few years later McCrea reflected on his travels and professional experiences in an attempt to explain some of the dynamics of the preceding fifty years of astronomy. His work revealed an amazing genealogy, a fully developed family tree of astronomy’s researchers, teachers, and students at several of the great world centers of the discipline. This work, along with his masterful chapter in R. J. Tayler’s History of the Royal Astronomical Society, remains excellent testimony to both McCrea’s care for his profession, and his care to get the facts right.
McCrea’s ninetieth birthday in December 1994 was a festive occasion at the RAS, with speeches given, toasts made, and many wishes for long life. Some of the material was published, most happily a tribute in the Irish Astronomical Journal to “Sir William McCrea at 90: A Great Irish Astronomer.”
McCrea believed that astronomy, and especially cosmology, could never be separated from deeper meaning. “Cosmology requires, I venture to assert, the concept of Creator and of personality, and together these mean God” (Yourgrau and Breck, p. 72). Supporting this view was McCrea’s religious faith. As he later told an interviewer: “I’m a practicing Christian, and Anglican, and I can claim a real faith. I know there are many problems and puzzles, but one is conscious, at the very least, that there must be a purpose in one’s existence” (Smith Interview, 1978, p. 36).
A similar sentiment appears at the end of his RAS 160th anniversary talk. It is worth quoting at length: After 160 years, the Universe around us that we contemplate as astronomers and geophysicists, is as mysterious as when the Society was founded. We know a great deal more than our founders did about the structure of the Universe. Who would say that we have learned any more about its meaning and purpose? In raising our glasses to the health of our sciences let us hope that in the coming years they will bring us not only still further knowledge of the structure and operation of the Universe, but also some spark of light upon these profounder mysteries.
WORKS BY MCCREA
With Edward A. Milne. “Newtonian Universes and the Curvature of Space.” Quarterly Journal of Mathematics 5 (1934): 73–80.
“Observable Relations in Relativistic Cosmology.” Zeitschrift für Astrophysik 9 (1935): 290–314.
“E. A. Milne.” Monthly Notices of the Royal Astronomical Society 111 (1951): 160–170.
“Relativity Theory and the Creation of Matter.” Proceedings of the Royal Society of London, ser. A, 206 (1951): 562–575.
“Cosmology.” Reports on Progress in Physics 16 (1953): 321–363.
“Cosmology—A Brief Review.” Quarterly Journal of the Royal Astronomical Society 4 (1963): 185–202.
“Cosmology after Half a Century.” Science NS 160 (21 June 1968): 12951–11299.
“A Philosophy for Big-Bang Cosmology.” Nature 228 (1970): 21–24.
“Models, Laws, and the Universe.” In Cosmology, History, and Theology, edited by Wolfgang Yourgrau and Allen D. Breck. New York: Plenum, 1977.
Interview with Robert W. Smith, 22 September 1978. College Park, MD: Niels Bohr Library, American Institute of Physics,
“Address by Professor W. H. McCrea, FRS, at the RAS 160th Anniversary Dinner.” Quarterly Journal of the Royal Astronomical Society 21 (1980): 220–223.
“Physics and Cosmology: Some Interactions.” In The Big Bang and Georges Lemaître: Proceedings of a Symposium in Honour of G. Lemaître Fifty Years after his Initiation of Big-Bang Cosmology, Louvain-la-Neuve, Belgium, 10–13 October 1983, edited by A. Berger. Dordrecht, The Netherlands: Reidel, 1984.
“Cambridge Physics 1925–1929: Diamond Jubilee of Golden Years.” Interdisciplinary Science Reviews 11 (1986): 269–284.
“Clustering of Astronomers.” Annual Review of Astronomy and Astrophysics 25 (1987): 1–22.
“The Decade 1931–1940.” In History of the Royal Astronomical Society, vol. 2, edited by Roger J. Tayler. Palo Alto, CA: Blackwell Scientific, 1987.
Interview with George Gale, 12 October 1988.
Kragh, Helge. Cosmology and Controversy: The Historical Development of Two Theories of the Universe. Princeton, NJ: Princeton University Press, 1996.
McNally, D. “Sir William McCrea at 90: A Great Irish Astronomer.” Irish Astronomical Journal 24 (1997): 49–54.
North, John David. The Norton History of Astronomy and Cosmology. New York: Norton, 1994.