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Modern cosmology in retrospect
138
Physics of the Earth and Planetary Interiors, 69 (1991) 138-147 Elsevier Science Publishers B.V., Amsterdam
Book Reviews Modern Cosmology in Retrospect. B. Bertotti, R. Balbinot, S. Bergia and A. Messina (Editors), Cambridge University Press, Cambridge, 1990, 426 pp., £40.00 (US$69.50) hardback, ISBN: 0 521 37213 5. The Big Bang has been with us for so long that it is sometimes hard to remember that it was once just a somewhat pejorative term invented by Hoyle for one cosmological model among many. Modern Cosmology in Retrospect forms the proceedings of a meeting held in Bologna in 1988 to trace the roots of the current cosmological paradigm from the early years of this century up to the serendipitous discovery of the cosmic microwave background in 1965, and the gradual refinement of the calculations of the primodial abundances of the elements in the post-war years. There are contributions from many of the major protagonists in this story: Alpher and Hermann, Hoyle and Bondi, Wilson, and collaborators of Ryle among others, and also more historical works which put in context much of the received wisdom of cosmology today. One point that emerges is the importance and far-sightedness of the body of Georges Lema~tre's work, sometimes neglected in the English-speaking world. Indeed, with the publication of his 1931 paper " T h e Beginning of the World from the Point of View of the Quantum Theory" he might be regarded as the founder of the stillembryonic discipline of quantum cosmology. Modern Cosmology could not exist without General Relativity, but when Einstein constructed his theory it was generally presumed that the Universe was static, and the interpretation of the spiral nebulae as other star systems like our Milky Way was still controversial. Thus Einstein searched for a static solution to his equations, and indeed found one at the cost of introducing the famous cosmological term (which he later regarded as a mistake). Such was the predisposition towards static solutions that little attention was paid to Friedmann and Lema~tre when they proposed ex-
panding models, even though redshift data had been published steadily by Hubble and many others all through the twenties. Ellis, in this volume, presents the transition from a static to an evolving universe as a Kuhnian paradigm shift: it occurred around 1930 under the accumulated weight of evidence, and perhaps the last straw was Eddington's proof that the Einstein universe was unstable. Together with Osterbrock's piece on the genesis of observational cosmology in these years, and Seitter and Duerbeck on the German astronomer Carl Wilhelm Wirtz, these articles fill in some fascinating details on the discovery of one of the few hard facts in cosmology. In a sense, another observation of fundamental importance to cosmology had been made centuries earlier by Ch6seaux, and possibly even by Halley, " t h e night sky is dark". Today we speak of Olbers' paradox, "every line of sight in an infinite and unbounded universe must eventually cross the surface of a star, and therefore the night sky should be as bright as the sun". An article by Edward Harrison makes clear how the resolution of this historical paradox rests on the notion of an expanding or evolving universe, " t h e Steady State universe uses its exponentially increasing redshift to hide distant stars, while in the Big Bang model the night sky is dark because the universe has finite age". In fact, in the Big Bang, every line of sight does cross a surface as hot as the sun's, the cosmic photosphere, where the photons of the cosmic microwave background last interacted with the rapidly cooling primordial plasma. It is expansion of the universe which dilutes and cools the photons to their current apparent temperature of 2.735K. Wilson's account of the discovery of this radiation by him and Penzias forms another part of the success of the Big Bang. Although it had been predicted well before 1965 by G a m o w and others, it seems not to have been taken very seriously and Penzias and Wilson wrote up their paper very modestly, calling it " A Measurement
139 of Excess Antenna Temperature". But it was the CMB that finished off the already ailing Steady State model, leaving the field clear for a Big Bang, which had already been shown to do significantly better in predicting the abundances of the light elements. The contribution by Alpher and Hermann makes clear the evolution of the calculation from Gamow's paper in !946, where elements were synthesised by neutron capture reactions in a cold univers, radiation density was originally ignored. But perversely enough, what made many astronomers abandon the Steady State, philosophically appealing as it is, was a piece of work later shown to be seriously flawed, the 2nd Cambridge catalogue of radio sources. The articles on this subject are a little frustating, for underlying the confrontation of theory and observation was the confrontation of two personalities, those of Hoyle and Ryle. Why was Ryle so confident in his assertion that the data contradicted the Steady State theory? And does the fierceness of the resulting controversy have any bearing on Hoyle's continuing support of the Steady State to this day? It is often said that science is impersonal, but in this episode there are signs of something more, which we can only glimpse by reading between the lines. M. H I N D M A R S H (Newcastle upon Tyne, UK)
The New Solar System. J. Kelly Beatty and A. Chaikin (Editors), 3rd Edn., Cambridge University Press, Cambridge, 1990, 326 pp., £13.95, paperback, ISBN: 0-521-36965-7. The first edition of this book, published in 1981, provided an excellent introduction to our knowledge of the solar system. The new third edition is, if anything, better than previous editions and has substantial changes and additions bringing it as up-to-date as one might expect in such a fast moving field of exploration. The New Solar System has several important characteristics. Firstly, it is wide-ranging in its scope involving astronomy, physics, geology,
meteorology and all the other disciplines which can be applied to the study of the solar system. Because of this, the book is a valuable source of information even for professional planetary scientists to broaden their knowledge. Secondly, it is an authoritative book. The editors have carefully chosen authors for each of the individual chapters who are research leaders in their subject. Lastly, it is superbly illustrated and a joy to browse through for the illustrations alone. Following an introduction by Carl Sagan, the one time Associate Deputy Administrator at NASA, Noel Hinners, describes the history of solar system exploration by space craft and the philosophy behind it, as well as the future in space. This is a frank chapter which draws together all aspects, including budgets and politics. At the hub of the solar system is a star, our Sun. Robert Noyes, in Chapter 2, gives a clear description of the physics and chemistry of the Sun, its structure and the way it has evolved and will continue to evolve with time. As well as light and heat, the Sun also sheds ionised gases which spread out through the solar system as the solar wind and which interact with other bodies in the solar system. The way in which this happens is discussed by James van Allen in the third chapter, entitled "Magnetospheres, cosmic rays and the interplanetary medium". Both the Moon and Mars are given their own chapters; Paul Spudis describes the Moon, drawing together information from photogeology, sample analysis and geophysics. This chapter also discusses the origin of the Moon and future exploration of our satellite. The 'red planet' is described by Michael Carr, leader of the Viking Orbiter Imaging Team. As might be expected, this discussion concentrates on surface processes interpreted from Viking images. The Earth is the topic of Chapter 6. In this chapter, Don Anderson takes us through the origin, composition and structure of the Earth and plate tectonics. Two chapters compare the surfaces and atmospheres of the terrestrial planets. James Head deals with surface processes and history of the Earth and other so-called Earth-like planets, whilst James Pollack discusses composition, structure, origin and evolution of the atmospheres of those terrestrial planets that have one.
Physics of the Earth and Planetary Interiors, 69 (1991) 138-147 Elsevier Science Publishers B.V., Amsterdam
Book Reviews Modern Cosmology in Retrospect. B. Bertotti, R. Balbinot, S. Bergia and A. Messina (Editors), Cambridge University Press, Cambridge, 1990, 426 pp., £40.00 (US$69.50) hardback, ISBN: 0 521 37213 5. The Big Bang has been with us for so long that it is sometimes hard to remember that it was once just a somewhat pejorative term invented by Hoyle for one cosmological model among many. Modern Cosmology in Retrospect forms the proceedings of a meeting held in Bologna in 1988 to trace the roots of the current cosmological paradigm from the early years of this century up to the serendipitous discovery of the cosmic microwave background in 1965, and the gradual refinement of the calculations of the primodial abundances of the elements in the post-war years. There are contributions from many of the major protagonists in this story: Alpher and Hermann, Hoyle and Bondi, Wilson, and collaborators of Ryle among others, and also more historical works which put in context much of the received wisdom of cosmology today. One point that emerges is the importance and far-sightedness of the body of Georges Lema~tre's work, sometimes neglected in the English-speaking world. Indeed, with the publication of his 1931 paper " T h e Beginning of the World from the Point of View of the Quantum Theory" he might be regarded as the founder of the stillembryonic discipline of quantum cosmology. Modern Cosmology could not exist without General Relativity, but when Einstein constructed his theory it was generally presumed that the Universe was static, and the interpretation of the spiral nebulae as other star systems like our Milky Way was still controversial. Thus Einstein searched for a static solution to his equations, and indeed found one at the cost of introducing the famous cosmological term (which he later regarded as a mistake). Such was the predisposition towards static solutions that little attention was paid to Friedmann and Lema~tre when they proposed ex-
panding models, even though redshift data had been published steadily by Hubble and many others all through the twenties. Ellis, in this volume, presents the transition from a static to an evolving universe as a Kuhnian paradigm shift: it occurred around 1930 under the accumulated weight of evidence, and perhaps the last straw was Eddington's proof that the Einstein universe was unstable. Together with Osterbrock's piece on the genesis of observational cosmology in these years, and Seitter and Duerbeck on the German astronomer Carl Wilhelm Wirtz, these articles fill in some fascinating details on the discovery of one of the few hard facts in cosmology. In a sense, another observation of fundamental importance to cosmology had been made centuries earlier by Ch6seaux, and possibly even by Halley, " t h e night sky is dark". Today we speak of Olbers' paradox, "every line of sight in an infinite and unbounded universe must eventually cross the surface of a star, and therefore the night sky should be as bright as the sun". An article by Edward Harrison makes clear how the resolution of this historical paradox rests on the notion of an expanding or evolving universe, " t h e Steady State universe uses its exponentially increasing redshift to hide distant stars, while in the Big Bang model the night sky is dark because the universe has finite age". In fact, in the Big Bang, every line of sight does cross a surface as hot as the sun's, the cosmic photosphere, where the photons of the cosmic microwave background last interacted with the rapidly cooling primordial plasma. It is expansion of the universe which dilutes and cools the photons to their current apparent temperature of 2.735K. Wilson's account of the discovery of this radiation by him and Penzias forms another part of the success of the Big Bang. Although it had been predicted well before 1965 by G a m o w and others, it seems not to have been taken very seriously and Penzias and Wilson wrote up their paper very modestly, calling it " A Measurement
139 of Excess Antenna Temperature". But it was the CMB that finished off the already ailing Steady State model, leaving the field clear for a Big Bang, which had already been shown to do significantly better in predicting the abundances of the light elements. The contribution by Alpher and Hermann makes clear the evolution of the calculation from Gamow's paper in !946, where elements were synthesised by neutron capture reactions in a cold univers, radiation density was originally ignored. But perversely enough, what made many astronomers abandon the Steady State, philosophically appealing as it is, was a piece of work later shown to be seriously flawed, the 2nd Cambridge catalogue of radio sources. The articles on this subject are a little frustating, for underlying the confrontation of theory and observation was the confrontation of two personalities, those of Hoyle and Ryle. Why was Ryle so confident in his assertion that the data contradicted the Steady State theory? And does the fierceness of the resulting controversy have any bearing on Hoyle's continuing support of the Steady State to this day? It is often said that science is impersonal, but in this episode there are signs of something more, which we can only glimpse by reading between the lines. M. H I N D M A R S H (Newcastle upon Tyne, UK)
The New Solar System. J. Kelly Beatty and A. Chaikin (Editors), 3rd Edn., Cambridge University Press, Cambridge, 1990, 326 pp., £13.95, paperback, ISBN: 0-521-36965-7. The first edition of this book, published in 1981, provided an excellent introduction to our knowledge of the solar system. The new third edition is, if anything, better than previous editions and has substantial changes and additions bringing it as up-to-date as one might expect in such a fast moving field of exploration. The New Solar System has several important characteristics. Firstly, it is wide-ranging in its scope involving astronomy, physics, geology,
meteorology and all the other disciplines which can be applied to the study of the solar system. Because of this, the book is a valuable source of information even for professional planetary scientists to broaden their knowledge. Secondly, it is an authoritative book. The editors have carefully chosen authors for each of the individual chapters who are research leaders in their subject. Lastly, it is superbly illustrated and a joy to browse through for the illustrations alone. Following an introduction by Carl Sagan, the one time Associate Deputy Administrator at NASA, Noel Hinners, describes the history of solar system exploration by space craft and the philosophy behind it, as well as the future in space. This is a frank chapter which draws together all aspects, including budgets and politics. At the hub of the solar system is a star, our Sun. Robert Noyes, in Chapter 2, gives a clear description of the physics and chemistry of the Sun, its structure and the way it has evolved and will continue to evolve with time. As well as light and heat, the Sun also sheds ionised gases which spread out through the solar system as the solar wind and which interact with other bodies in the solar system. The way in which this happens is discussed by James van Allen in the third chapter, entitled "Magnetospheres, cosmic rays and the interplanetary medium". Both the Moon and Mars are given their own chapters; Paul Spudis describes the Moon, drawing together information from photogeology, sample analysis and geophysics. This chapter also discusses the origin of the Moon and future exploration of our satellite. The 'red planet' is described by Michael Carr, leader of the Viking Orbiter Imaging Team. As might be expected, this discussion concentrates on surface processes interpreted from Viking images. The Earth is the topic of Chapter 6. In this chapter, Don Anderson takes us through the origin, composition and structure of the Earth and plate tectonics. Two chapters compare the surfaces and atmospheres of the terrestrial planets. James Head deals with surface processes and history of the Earth and other so-called Earth-like planets, whilst James Pollack discusses composition, structure, origin and evolution of the atmospheres of those terrestrial planets that have one.