MacTutor
Fred Hoyle
Fellow and President of the RAS, Plumian Professor of Astronomy, and Director of the Institute of Astronomy, Cambridge, RAS Gold Medallist, Royal Society Royal Medallist; astrophysicist, cosmologist and prolific writer.
Fred Hoyle was the astrophysicist par excellence and much else. He wrote technical papers on an astonishingly wide range of astronomical topics, his most important work permanently widening our vistas and influencing strongly the direction of future research. As a popularizer of science, he inherited the mantle of James Jeans and Arthur Eddington. His 1950 radio lectures on The Nature of the Universe, given long before television became the principal medium, carned him the unofficial title, the "radio cosmologist". Their published version and his later volume Frontiers of Astronomy were read avidly by old and young, and many who later achieved scientific distinction have acknowledged that his books led them to make astronomy their vocation. His restless mind led him to write forcefully and often provocatively on important issues in areas a long way from his own exper tise. He wrote also some very readable books of science fiction, including The Black Cloud, Ossim's Ride, October the First is Too Late and Rockets in Ursa Major, the last in collaboration with his son Geoffrey; and for relaxation, he produced a farce, a pantomime and an opera libretto. His autobiography Home is Where the Wind Blows appeared in 1994.
Fred was born in the Yorkshire dales, the son of a wool merchant descended from Huguenot refugees. From Bingley Grammar School he went up to Emmanuel College, Cambridge in 1933 to read mathematics. In 1936 he won the Tripos Part III Mayhew Prize. As Paul Dirac's research student, in 1938 he was awarded the first Smith's Prize for an essay on B-decay, and in 1939 he was elected to a fellowship of St John's for a thesis on quantum electrodynamics. While always retaining his interest in fundamental physics, his subsequent research was primarily in astronomy and cosmology, stimulated to some extent by interaction with Ray Lyttleton. The War took him away from Cambridge to work for the Admiralty on radar and other technical projects. The after-hours discussions with his fellow workers Hermann Bondi and Thomas Gold bore fruit when all three returned to Cambridge after the War.
Fred was a controversial figure all his life, but in at least two major areas stellar and cosmological nucleosynthesis, and stellar structure and evolution – it is universally agreed that his contributions are outstanding. His 1946 paper "The synthesis of the elements from hydrogen" gave a detailed account of the production of the "iron peak" elements through the equilibrium or e-process. The paper was written when little was known of the variation of composition from star to star and when it was still believed that all the elements might have been produced in one event. The fusion of hydrogen to form helium – the energy source for main sequence stars – had been elucidated in the late 30s by Hans A Bethe and Carl-Friedrich von Weizsäcker. A major difficulty facing nucleosynthesis was how to build up elements beyond helium, since Be formed from two helium nuclei is very unstable. A key proposal was made by Edwin E Salpeter, who showed that in high temperature-density regions deep inside an evolved star, a third helium nucleus could occasionally approach the Be before it dissociates and react to form C. But as Ed himself pointed out, this "triple-a" process seemed to lead to a new embarrassment: once a carbon nucleus had been formed, it would rapidly fuse with another helium nucleus to produce oxygen, and again possibly to produce Ne. Fred's conviction that the observed element ratios, in particular the C:O ratio, are not adventitions factors in our universe but should emerge from nuclear astrophysical theory, led him to predict that there must be an energy level in the carbon nucleus some 7 MeV above its ground state, making the triple-a process resonant and so much more rapid than Salpeter's rate. This dramatic prediction was subsequently confirmed at CalTech by William A Fowler ("Willy") and colleagues. It can be seen as an early example of the predictive potential of what we now call the Anthropic Principle: carbon is crucial for the origin of life and so for the existence of physicists capable of studying the universe, so there must be a way that carbon can be produced. No wonder the late Richard Feynman commented in his New York accent: "We are at last beginning to understand 'Univoise.' "
Fred went on to a collaboration with Willy Fowler, E. Margaret Burbidge and Geoffrey R Burbidge that led to their epoch-making article "Synthesis of the elements in stars" (referred to always as "BFH"), which provides a theory for the production of all nuclei upwards from C. (Similar ideas were put forward in the same year by A G W Cameron.) This monumental work has stood the test of time, modified in detail but not in principle. Later, he and Willy pioneered investigation of the approach to a supernova explosion, which is the main mechanism by which highly-processed material is returned to the interstellar medium.
However, the hypothesis that all the elements had been built up from hydrogen during normal stellar evolution was confronted with the "helium problem" - the observation of an apparently universal helium content in even the oldest objects, far higher than could be produced during main sequence evolution. The short Nature paper with Roger Tayler entitled "The mystery of the cosmic helium abundance", though to some extent duplicating earlier work by C Hayashi and later by R A Alpher, J W Follin and R C Herman, is nevertheless another landmark. In spite of Fred's strong predilections in favour of a steady-state universe, the paper agreed that the helium could have been produced in the early phases of a hot "big-bang" universe (the term that he had invented, intending it to be pejorative, but which is now accepted as merely descriptive). The paper drew attention to the importance of the number of neutrino types, and noted also that similar physical conditions would be present in collapsed massive objects. (It seems that although in the first draft of the paper there was a reference to an expected cosmical background radiation, it did not appear in the published version.) The topic was elaborated in a later paper written with Willy and Robert V Wagoner.
It remains a mystery why Fred's name was not bracketed with Willy Fowler's in the 1983 Nobel Prize award. And although the names of Hoyle and Salpeter were subsequently submitted to the Nobel Committee, recognition of the oustanding importance of their solution of the carbon problem had to await the award to them jointly by the Royal Swedish Academy of Sciences of the 1997 Crafoord Prize.
Parallel to this, Fred made many very important contributions to our understanding of stellar evolution. His early papers (with Lyttleton and Bondi) on accretion now appear as pioneering the study of the two-way interaction between stars and the interstellar medium. Together with Lyttleton, he applied the recently published studies on energy liberation by thermonuclear helium synthesis to reformulate Eddington's classical work on homogeneous stellar models, rediscovering the Cowling point-convective model as the paradigm for early-type stars. Two further papers confirmed that stellar models with an inhomogeneous structure could explain the large radii of red giant stars (a conclusion already reached independently by E J Õpik in an inaccessible journal). At about the same time, Fred argued convincingly for a high rather than a moderate hydrogen/helium content in stars. The landmark paper entitled "The evolution of Type II stars", written jointly with Martin Schwarzschild, gave the first complete discussion of the evolution of a low-mass star from the main sequence to the top of the red-giant branch. (As in the later paper by C Hayashi on pre-main sequence stars, E A Milne's contention that the photospheric boundary condition would affect strongly the predicted luminosity, though indeed irrelevant for the stars that he and Eddington were studying, turned out to be valid on the giant branch.) And together with Brian Haselgrove, he used the red giant theory to increase the estimated galactic age to about 10 billion years, similar to the value obtained by Hoyle and Fowler from cosmochronology in the following year. In 1994, Hoyle and Schwarzschild were awarded jointly the Balzan Prize for their work on the evolution of the stars.
Fred's ongoing publications on cosmology began in 1948 with his version of the steady-state theory, parallel to that by Hermann Bondi and Tommy Gold. From the start he preferred to formulate the theory by writing down appropriate modifications of the field equations of general relativity. Of the series of arguments from observation raised over the years against the theory, he was justly sceptical of the overstated claims made for the early 2C radio source survey. It was the evidence for a universal high helium abundance that he took really seriously, leading to the paper with Roger Tayler already cited. Together with Geoffrey Burbidge and Jayant V Narlikar, he continued the search for a variant of steady-state cosmology that would nevertheless account for all the observations the radio source counts, the quasar red-shifts, the microwave background and the abundances of helium and light isotopes, summarized in their 1999 book A different approach to cosmology. To most other workers in cosmology, it may appear as a labour of love. I would myself say that at a time when - as a consequence of accumulating observational evidence standard big-bang theory has acquired the explicit or tacit support of most of the astronomical community, it has been good for the health of the cosmological enterprise that an intellect as powerful as Fred's should ensure that possible alternatives do not go by default.
I recall going to the ADC theatre in Cambridge in 1950 to see Barbara Hoyle's production of A Midsummer Night's Dream, with Fred in the part of Bottom the weaver. It was a magnificent performance, especially in the scene where Bottom wants to be considered for all the parts in the play within the play. It reminded both me and my late friend Dennis Sciama of how in addition to his major areas of research, outlined above, Fred had a finger in most other pies on the astrophysical menu. Reading through his bibliography, one is reminded of his ideas on the solar corona and solar flares; his picture of hierarchical star formation; the series of papers with Chandra Wickramasinghe on dust grains; his papers on high-energy astrophysics, including those with Willy Fowler on extremely massive stars; and the many papers with Jayant Narlikar on gravitation and on electrodynamics and cosmology. One should remember also his organizational efforts. He finally persuaded Cambridge to set up the Institute of (Theoretical) Astronomy, taking a leading part in the detailed planning and costing. (The main building is now known appropriately as the Hoyle Building.) He also did excellent work for the Anglo-Australian Telescope, first as a member of the Science Research Council, and later as Chairman of the AAT board. When by 1972 he felt unable to continue working in Cambridge, he had built up a centre which under a series of eminent directors has retained its world-class sta-tus, while he continued writing, first from the Lake District and latterly from Bournemouth.
For most of us, the feeling that we are taking a significant step towards the ultimate resolution of an important astrophysical problem is sufficient motivation. But for Fred, I suspect that this was not enough: he needed to feel that in whatever he was working on at the moment, he was producing at least a close approximation to the definitive answer. He gave such a hostage to fortune when he concluded his 1950 radio lectures - before the discovery of quasars, pulsars, X-ray sources, putative black holes and the background microwave radiation - with the optimistic statement that the picture of the universe that he had presented was unlikely to change. But equally, he was usually self-critical enough to recognize when observational evidence and theoretical work required abandonment of a cherished model, replacing it sometimes by one that he had earlier rather too hastily dismissed. One admired both his flexibility of mind and fecundity of ideas; but I would have preferred, earlier and later, a more cautious presentation of his currently favoured picture, e.g. on the origin of the solar system.
It must be admitted that at times his style was unnecessarily polemical and could be embarrassing to his friends and admirers, e.g. in his interactions with the Cambridge radio astronomers (where indeed there was provocation), and even more so in his forays into other areas, especially when commenting on what he thought was facile theorizing. He was particularly critical of the standard Darwinian picture of evolution, which he claimed violated elementary laws of probability. Though a life-long unbeliever, in this area he seemed latterly to be incorporating a teleological strand into his thought. He did not accept the "Primordial Soup Theory" for the origin of life on Earth, arguing rather for his version of "Panspermia", in which viable cells were (and are still being) transported earthwards from space on comets. He went further in arguing that epidemics originated outside Earth's atmosphere, predictably arousing fierce hostility. Much earlier, a book in which he predicted economic disaster for the UK unless there was a drastic reduction of the population by mass emigration, provoked a review with the title "A cobbler a long way from his last". Confronted every day with evidence that professionally-trained economists have so little success in their often mutually contradictory predictions, one can only look on with awed respect at Fred's willingness to stick his neck out.
But maybe one should not jib at his willingness to court controversy. One hears it said that academic institutions in which there is no internal rivalry are also significantly less productive, tending to degenerate into mutual admiration societies. And I recall the worldly-wise rabbinical gloss on a bland, almost tautological verse in Ecclesiasticus: not "The wisdom of the scribes..." but "The envy of the scribes increases wisdom".
He was a towering figure; in Martin Rees's words, in his golden years he "injected more good ideas into the field of astronomy and cosmology than anyone else". His legacy to all working astronomers and indeed to the informed laity is manifest. I count myself fortunate to have begun my research career as a student of the one and only Fred Hoyle.
Leon Mestel.
Fred was born in the Yorkshire dales, the son of a wool merchant descended from Huguenot refugees. From Bingley Grammar School he went up to Emmanuel College, Cambridge in 1933 to read mathematics. In 1936 he won the Tripos Part III Mayhew Prize. As Paul Dirac's research student, in 1938 he was awarded the first Smith's Prize for an essay on B-decay, and in 1939 he was elected to a fellowship of St John's for a thesis on quantum electrodynamics. While always retaining his interest in fundamental physics, his subsequent research was primarily in astronomy and cosmology, stimulated to some extent by interaction with Ray Lyttleton. The War took him away from Cambridge to work for the Admiralty on radar and other technical projects. The after-hours discussions with his fellow workers Hermann Bondi and Thomas Gold bore fruit when all three returned to Cambridge after the War.
Fred was a controversial figure all his life, but in at least two major areas stellar and cosmological nucleosynthesis, and stellar structure and evolution – it is universally agreed that his contributions are outstanding. His 1946 paper "The synthesis of the elements from hydrogen" gave a detailed account of the production of the "iron peak" elements through the equilibrium or e-process. The paper was written when little was known of the variation of composition from star to star and when it was still believed that all the elements might have been produced in one event. The fusion of hydrogen to form helium – the energy source for main sequence stars – had been elucidated in the late 30s by Hans A Bethe and Carl-Friedrich von Weizsäcker. A major difficulty facing nucleosynthesis was how to build up elements beyond helium, since Be formed from two helium nuclei is very unstable. A key proposal was made by Edwin E Salpeter, who showed that in high temperature-density regions deep inside an evolved star, a third helium nucleus could occasionally approach the Be before it dissociates and react to form C. But as Ed himself pointed out, this "triple-a" process seemed to lead to a new embarrassment: once a carbon nucleus had been formed, it would rapidly fuse with another helium nucleus to produce oxygen, and again possibly to produce Ne. Fred's conviction that the observed element ratios, in particular the C:O ratio, are not adventitions factors in our universe but should emerge from nuclear astrophysical theory, led him to predict that there must be an energy level in the carbon nucleus some 7 MeV above its ground state, making the triple-a process resonant and so much more rapid than Salpeter's rate. This dramatic prediction was subsequently confirmed at CalTech by William A Fowler ("Willy") and colleagues. It can be seen as an early example of the predictive potential of what we now call the Anthropic Principle: carbon is crucial for the origin of life and so for the existence of physicists capable of studying the universe, so there must be a way that carbon can be produced. No wonder the late Richard Feynman commented in his New York accent: "We are at last beginning to understand 'Univoise.' "
Fred went on to a collaboration with Willy Fowler, E. Margaret Burbidge and Geoffrey R Burbidge that led to their epoch-making article "Synthesis of the elements in stars" (referred to always as "BFH"), which provides a theory for the production of all nuclei upwards from C. (Similar ideas were put forward in the same year by A G W Cameron.) This monumental work has stood the test of time, modified in detail but not in principle. Later, he and Willy pioneered investigation of the approach to a supernova explosion, which is the main mechanism by which highly-processed material is returned to the interstellar medium.
However, the hypothesis that all the elements had been built up from hydrogen during normal stellar evolution was confronted with the "helium problem" - the observation of an apparently universal helium content in even the oldest objects, far higher than could be produced during main sequence evolution. The short Nature paper with Roger Tayler entitled "The mystery of the cosmic helium abundance", though to some extent duplicating earlier work by C Hayashi and later by R A Alpher, J W Follin and R C Herman, is nevertheless another landmark. In spite of Fred's strong predilections in favour of a steady-state universe, the paper agreed that the helium could have been produced in the early phases of a hot "big-bang" universe (the term that he had invented, intending it to be pejorative, but which is now accepted as merely descriptive). The paper drew attention to the importance of the number of neutrino types, and noted also that similar physical conditions would be present in collapsed massive objects. (It seems that although in the first draft of the paper there was a reference to an expected cosmical background radiation, it did not appear in the published version.) The topic was elaborated in a later paper written with Willy and Robert V Wagoner.
It remains a mystery why Fred's name was not bracketed with Willy Fowler's in the 1983 Nobel Prize award. And although the names of Hoyle and Salpeter were subsequently submitted to the Nobel Committee, recognition of the oustanding importance of their solution of the carbon problem had to await the award to them jointly by the Royal Swedish Academy of Sciences of the 1997 Crafoord Prize.
Parallel to this, Fred made many very important contributions to our understanding of stellar evolution. His early papers (with Lyttleton and Bondi) on accretion now appear as pioneering the study of the two-way interaction between stars and the interstellar medium. Together with Lyttleton, he applied the recently published studies on energy liberation by thermonuclear helium synthesis to reformulate Eddington's classical work on homogeneous stellar models, rediscovering the Cowling point-convective model as the paradigm for early-type stars. Two further papers confirmed that stellar models with an inhomogeneous structure could explain the large radii of red giant stars (a conclusion already reached independently by E J Õpik in an inaccessible journal). At about the same time, Fred argued convincingly for a high rather than a moderate hydrogen/helium content in stars. The landmark paper entitled "The evolution of Type II stars", written jointly with Martin Schwarzschild, gave the first complete discussion of the evolution of a low-mass star from the main sequence to the top of the red-giant branch. (As in the later paper by C Hayashi on pre-main sequence stars, E A Milne's contention that the photospheric boundary condition would affect strongly the predicted luminosity, though indeed irrelevant for the stars that he and Eddington were studying, turned out to be valid on the giant branch.) And together with Brian Haselgrove, he used the red giant theory to increase the estimated galactic age to about 10 billion years, similar to the value obtained by Hoyle and Fowler from cosmochronology in the following year. In 1994, Hoyle and Schwarzschild were awarded jointly the Balzan Prize for their work on the evolution of the stars.
Fred's ongoing publications on cosmology began in 1948 with his version of the steady-state theory, parallel to that by Hermann Bondi and Tommy Gold. From the start he preferred to formulate the theory by writing down appropriate modifications of the field equations of general relativity. Of the series of arguments from observation raised over the years against the theory, he was justly sceptical of the overstated claims made for the early 2C radio source survey. It was the evidence for a universal high helium abundance that he took really seriously, leading to the paper with Roger Tayler already cited. Together with Geoffrey Burbidge and Jayant V Narlikar, he continued the search for a variant of steady-state cosmology that would nevertheless account for all the observations the radio source counts, the quasar red-shifts, the microwave background and the abundances of helium and light isotopes, summarized in their 1999 book A different approach to cosmology. To most other workers in cosmology, it may appear as a labour of love. I would myself say that at a time when - as a consequence of accumulating observational evidence standard big-bang theory has acquired the explicit or tacit support of most of the astronomical community, it has been good for the health of the cosmological enterprise that an intellect as powerful as Fred's should ensure that possible alternatives do not go by default.
I recall going to the ADC theatre in Cambridge in 1950 to see Barbara Hoyle's production of A Midsummer Night's Dream, with Fred in the part of Bottom the weaver. It was a magnificent performance, especially in the scene where Bottom wants to be considered for all the parts in the play within the play. It reminded both me and my late friend Dennis Sciama of how in addition to his major areas of research, outlined above, Fred had a finger in most other pies on the astrophysical menu. Reading through his bibliography, one is reminded of his ideas on the solar corona and solar flares; his picture of hierarchical star formation; the series of papers with Chandra Wickramasinghe on dust grains; his papers on high-energy astrophysics, including those with Willy Fowler on extremely massive stars; and the many papers with Jayant Narlikar on gravitation and on electrodynamics and cosmology. One should remember also his organizational efforts. He finally persuaded Cambridge to set up the Institute of (Theoretical) Astronomy, taking a leading part in the detailed planning and costing. (The main building is now known appropriately as the Hoyle Building.) He also did excellent work for the Anglo-Australian Telescope, first as a member of the Science Research Council, and later as Chairman of the AAT board. When by 1972 he felt unable to continue working in Cambridge, he had built up a centre which under a series of eminent directors has retained its world-class sta-tus, while he continued writing, first from the Lake District and latterly from Bournemouth.
For most of us, the feeling that we are taking a significant step towards the ultimate resolution of an important astrophysical problem is sufficient motivation. But for Fred, I suspect that this was not enough: he needed to feel that in whatever he was working on at the moment, he was producing at least a close approximation to the definitive answer. He gave such a hostage to fortune when he concluded his 1950 radio lectures - before the discovery of quasars, pulsars, X-ray sources, putative black holes and the background microwave radiation - with the optimistic statement that the picture of the universe that he had presented was unlikely to change. But equally, he was usually self-critical enough to recognize when observational evidence and theoretical work required abandonment of a cherished model, replacing it sometimes by one that he had earlier rather too hastily dismissed. One admired both his flexibility of mind and fecundity of ideas; but I would have preferred, earlier and later, a more cautious presentation of his currently favoured picture, e.g. on the origin of the solar system.
It must be admitted that at times his style was unnecessarily polemical and could be embarrassing to his friends and admirers, e.g. in his interactions with the Cambridge radio astronomers (where indeed there was provocation), and even more so in his forays into other areas, especially when commenting on what he thought was facile theorizing. He was particularly critical of the standard Darwinian picture of evolution, which he claimed violated elementary laws of probability. Though a life-long unbeliever, in this area he seemed latterly to be incorporating a teleological strand into his thought. He did not accept the "Primordial Soup Theory" for the origin of life on Earth, arguing rather for his version of "Panspermia", in which viable cells were (and are still being) transported earthwards from space on comets. He went further in arguing that epidemics originated outside Earth's atmosphere, predictably arousing fierce hostility. Much earlier, a book in which he predicted economic disaster for the UK unless there was a drastic reduction of the population by mass emigration, provoked a review with the title "A cobbler a long way from his last". Confronted every day with evidence that professionally-trained economists have so little success in their often mutually contradictory predictions, one can only look on with awed respect at Fred's willingness to stick his neck out.
But maybe one should not jib at his willingness to court controversy. One hears it said that academic institutions in which there is no internal rivalry are also significantly less productive, tending to degenerate into mutual admiration societies. And I recall the worldly-wise rabbinical gloss on a bland, almost tautological verse in Ecclesiasticus: not "The wisdom of the scribes..." but "The envy of the scribes increases wisdom".
He was a towering figure; in Martin Rees's words, in his golden years he "injected more good ideas into the field of astronomy and cosmology than anyone else". His legacy to all working astronomers and indeed to the informed laity is manifest. I count myself fortunate to have begun my research career as a student of the one and only Fred Hoyle.
Leon Mestel.
Fred Hoyle's obituary appeared in Journal of the Royal Astronomical Society 42.5 (2001), 23-24.