- ’Conceive of a universe forever empty of life?' ‘Of course not', a philosopher of old might have said, contemptuously dismissing the question, and adding, over his shoulder, as he walked away, ‘It has no sense to talk about a universe unless there is somebody there to talk about it'.
- That quick dismissal of the idea of a universe without life was not so easy after Copernicus. He dethroned man from a central place in the scheme of things. His model of the motions of the planets and the Earth taught us to look at the world as machine. Out of that beginning has grown a science which at first sight seems to have no special platform for man, mind, or meaning. Man? Pure biochemistry! Mind? Memory model-able by electronic circuitry! Meaning? Why ask after that puzzling and intangible commodity? ‘Sire', some today might rephrase Laplace's famous reply to Napoleon, ‘I have no need of that concept'.
- What is man that the universe should be mindful of him? Telescopes bring light from distant quasi-stellar sources that lived billions of years before life on Earth, before there even was an Earth. Creation's still warm ashes we call ‘natural radioactivity'. A thermometer and the relative abundance of the lighter elements today tell us the correlation between temperature and density in the first three minutes of the universe. Conditions still earlier and still more extreme we read out of particle physics. In the perspective of these violences of matter and field, of these ranges of heat and pressure, of these reaches of space and time, is not man an unimportant bit of dust on an unimportant planet in an unimportant galaxy in an unimportant region somewhere in the vastness of space?
- No! The philosopher of old was right! Meaning is important, is even central. It is not only that man is adapted to the universe. The universe is adapted to man. Imagine a universe in which one or another of the fundamental dimensionless constants of physics is altered by a few percent one way or the other? Man could never come into being in such a universe. That is the central point of the anthropic principle. According to this principle, a life-giving factor lies at the centre of the whole machinery and design of the world.
- What is the status of the anthropic principle? Is it a theorem? No. Is it a mere tautology, equivalent to the trivial statement, ‘The universe has to be such as to admit life, somewhere, at some point in its history, because we are here'? No. Is it a proposition testable by its predictions? Perhaps. Then what is the status of the anthropic principle? That is the issue on which every reader of this fascinating book will want to make his own judgement.
- Nowhere better than in the present account can the reader see new thinking, new ideas, new concepts in the making. The struggles of old to sort sense from nonsense in the domain of heat, phlogiston, and energy by now have almost passed into the limbo of the unappreciated. The belief of many in the early part of this century that ‘Chemical forces are chemical forces, and electrical forces are electrical forces, and never the twain shall meet' has long ago been shattered. Our own time has made enormous headway in sniffing out the sophisticated relations between entropy, information, randomness, and computability. But on a proper assessment of the anthropic principle we are still in the dark. Here above all we see how out of date that old view is, ‘First define your terms, then proceed with your reasoning'. Instead, we know, theory, concepts, and methods of measurement are born into the world, by a single creative act, in inseparable union.
- In advancing a new domain of investigation to the point where it can become an established part of science, it is often more difficult to ask the right questions than to find the right answers, and nowhere more so than in dealing with the anthropic principle. Good judgement, above all, is required, judgement in the sense of George Graves, ‘an awareness of all the factors in the situation, and an appreciation of their relative importance'.
- To the task of history, exposition, and judgement of the anthropic principle the authors of this book bring a unique combination of skills. John Barrow has to his credit a long list of distinguished contributions in the field of astrophysics generally and cosmology in particular. Frank Tipler is widely known for important concepts and theorems in general relativity and gravitation physics.
- It would be difficult to discover a single aspect of the anthropic principle to which the authors do not bring a combination of the best thinking of past and present and new analysis of their own.
- Philosophical considerations connected with the anthropic principle? Of the considerations on this topic contained in Chapters 2 and 3 perhaps half are new contributions of the authors.
- Why, except in the physics of elementary particles at the very smallest scale of lengths, does nature limit itself to three dimensions of space and one of time? Considerations out of past times and present physics on this topic give Chapter 4 a special flavour. In Chapter 6 the authors provide one of the best short reviews of cosmology ever published. In Chapter 8 Barrow and Tipler not only recall the arguments of L. J. Henderson's famous 1913 book, The fitness of the environment. They also spell out George Wald's more recent emphasis on the unique properties of water, carbon dioxide, and nitrogen. They add new arguments to Wald's rating of chlorophyll, an unparalleled agent, as the most effective photosynthetic molecule that anyone could invent. Taking account of biological considerations and modern statistical methods, Barrow and Tipler derive with new clarity Brandon Carter's striking anthropic-principle inequality. It states that the length of time from now, on into the future, for which the earth will continue to be an inhabitable planet will be only a fraction of the time, 4.6 billion years, that it has required for evolution1 on earth to produce man. The Carter inequality, as thus derived, is still more quantitative, still more limiting, still more striking. It states that the fraction of these 4.6 billion years yet to come is smaller than 1/8th, 1/9th, 1/10th, … or less, according as the number of critical or improbable or gateway steps in the past evolution2 of man was 7, 8, 9, ... or more. This amazing prediction looks like being some day testable and therefore would seem to count as ‘falsifiable' in the sense of Karl Popper.
- Chapter 9, outlining a space-travel argument against the existence of extra-terrestrial intelligent life, is almost entirely new. So is the final Chapter 10. It rivals in thought-provoking power any of the others. It discusses the idea that intelligent life will some day spread itself so thoroughly throughout all space that it will ‘begin to transform and continue to transform the universe on a cosmological scale', thus making it possible to transmit ‘the values of humankind... to an arbitrarily distant futurity... an Omega Point... [at which] life will have gained control of all matter and forces...'.
- In the mind of every thinking person there is set aside a special room, a museum of wonders. Every time we enter that museum we find our attention gripped by marvel number one, this strange universe, in which we live and move and have our being. Like a strange botanic specimen newly arrived from a far corner of the earth, it appears at first sight so carefully cleaned of clues that we do not know which are the branches and which are the roots. Which end is up and which is down? Which part is nutrient-giving and which is nutrient-receiving? Man? Or machinery?
- Everyone who finds himself pondering this question from time to time will want to have Barrow and Tipler with him on his voyages of thought. They bring along with them, now and then to speak to us in their own words, a delightful company of rapscallions and wise men, of wits and discoverers. Travelling with the authors and their friends of past and present we find ourselves coming again and again upon issues that are live, current, important.
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